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diff --git a/gcc-4.8.1/gcc/doc/invoke.texi b/gcc-4.8.1/gcc/doc/invoke.texi deleted file mode 100644 index a3e2ee0f3..000000000 --- a/gcc-4.8.1/gcc/doc/invoke.texi +++ /dev/null @@ -1,20995 +0,0 @@ -@c Copyright (C) 1988-2013 Free Software Foundation, Inc. -@c This is part of the GCC manual. -@c For copying conditions, see the file gcc.texi. - -@ignore -@c man begin INCLUDE -@include gcc-vers.texi -@c man end - -@c man begin COPYRIGHT -Copyright @copyright{} 1988-2013 Free Software Foundation, Inc. - -Permission is granted to copy, distribute and/or modify this document -under the terms of the GNU Free Documentation License, Version 1.3 or -any later version published by the Free Software Foundation; with the -Invariant Sections being ``GNU General Public License'' and ``Funding -Free Software'', the Front-Cover texts being (a) (see below), and with -the Back-Cover Texts being (b) (see below). A copy of the license is -included in the gfdl(7) man page. - -(a) The FSF's Front-Cover Text is: - - A GNU Manual - -(b) The FSF's Back-Cover Text is: - - You have freedom to copy and modify this GNU Manual, like GNU - software. Copies published by the Free Software Foundation raise - funds for GNU development. -@c man end -@c Set file name and title for the man page. -@setfilename gcc -@settitle GNU project C and C++ compiler -@c man begin SYNOPSIS -gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] - [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] - [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] - [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] - [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] - [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] - [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} - -Only the most useful options are listed here; see below for the -remainder. @samp{g++} accepts mostly the same options as @samp{gcc}. -@c man end -@c man begin SEEALSO -gpl(7), gfdl(7), fsf-funding(7), -cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) -and the Info entries for @file{gcc}, @file{cpp}, @file{as}, -@file{ld}, @file{binutils} and @file{gdb}. -@c man end -@c man begin BUGS -For instructions on reporting bugs, see -@w{@value{BUGURL}}. -@c man end -@c man begin AUTHOR -See the Info entry for @command{gcc}, or -@w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, -for contributors to GCC@. -@c man end -@end ignore - -@node Invoking GCC -@chapter GCC Command Options -@cindex GCC command options -@cindex command options -@cindex options, GCC command - -@c man begin DESCRIPTION -When you invoke GCC, it normally does preprocessing, compilation, -assembly and linking. The ``overall options'' allow you to stop this -process at an intermediate stage. For example, the @option{-c} option -says not to run the linker. Then the output consists of object files -output by the assembler. - -Other options are passed on to one stage of processing. Some options -control the preprocessor and others the compiler itself. Yet other -options control the assembler and linker; most of these are not -documented here, since you rarely need to use any of them. - -@cindex C compilation options -Most of the command-line options that you can use with GCC are useful -for C programs; when an option is only useful with another language -(usually C++), the explanation says so explicitly. If the description -for a particular option does not mention a source language, you can use -that option with all supported languages. - -@cindex C++ compilation options -@xref{Invoking G++,,Compiling C++ Programs}, for a summary of special -options for compiling C++ programs. - -@cindex grouping options -@cindex options, grouping -The @command{gcc} program accepts options and file names as operands. Many -options have multi-letter names; therefore multiple single-letter options -may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d --v}}. - -@cindex order of options -@cindex options, order -You can mix options and other arguments. For the most part, the order -you use doesn't matter. Order does matter when you use several -options of the same kind; for example, if you specify @option{-L} more -than once, the directories are searched in the order specified. Also, -the placement of the @option{-l} option is significant. - -Many options have long names starting with @samp{-f} or with -@samp{-W}---for example, -@option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of -these have both positive and negative forms; the negative form of -@option{-ffoo} is @option{-fno-foo}. This manual documents -only one of these two forms, whichever one is not the default. - -@c man end - -@xref{Option Index}, for an index to GCC's options. - -@menu -* Option Summary:: Brief list of all options, without explanations. -* Overall Options:: Controlling the kind of output: - an executable, object files, assembler files, - or preprocessed source. -* Invoking G++:: Compiling C++ programs. -* C Dialect Options:: Controlling the variant of C language compiled. -* C++ Dialect Options:: Variations on C++. -* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C - and Objective-C++. -* Language Independent Options:: Controlling how diagnostics should be - formatted. -* Warning Options:: How picky should the compiler be? -* Debugging Options:: Symbol tables, measurements, and debugging dumps. -* Optimize Options:: How much optimization? -* Preprocessor Options:: Controlling header files and macro definitions. - Also, getting dependency information for Make. -* Assembler Options:: Passing options to the assembler. -* Link Options:: Specifying libraries and so on. -* Directory Options:: Where to find header files and libraries. - Where to find the compiler executable files. -* Spec Files:: How to pass switches to sub-processes. -* Target Options:: Running a cross-compiler, or an old version of GCC. -* Submodel Options:: Specifying minor hardware or convention variations, - such as 68010 vs 68020. -* Code Gen Options:: Specifying conventions for function calls, data layout - and register usage. -* Environment Variables:: Env vars that affect GCC. -* Precompiled Headers:: Compiling a header once, and using it many times. -@end menu - -@c man begin OPTIONS - -@node Option Summary -@section Option Summary - -Here is a summary of all the options, grouped by type. Explanations are -in the following sections. - -@table @emph -@item Overall Options -@xref{Overall Options,,Options Controlling the Kind of Output}. -@gccoptlist{-c -S -E -o @var{file} -no-canonical-prefixes @gol --pipe -pass-exit-codes @gol --x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol ---version -wrapper @@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol --fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{arg} -fdump-go-spec=@var{file}} - -@item C Language Options -@xref{C Dialect Options,,Options Controlling C Dialect}. -@gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol --aux-info @var{filename} -fallow-parameterless-variadic-functions @gol --fno-asm -fno-builtin -fno-builtin-@var{function} @gol --fhosted -ffreestanding -fopenmp -fms-extensions -fplan9-extensions @gol --trigraphs -traditional -traditional-cpp @gol --fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol --fsigned-bitfields -fsigned-char @gol --funsigned-bitfields -funsigned-char} - -@item C++ Language Options -@xref{C++ Dialect Options,,Options Controlling C++ Dialect}. -@gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol --fconstexpr-depth=@var{n} -ffriend-injection @gol --fno-elide-constructors @gol --fno-enforce-eh-specs @gol --ffor-scope -fno-for-scope -fno-gnu-keywords @gol --fno-implicit-templates @gol --fno-implicit-inline-templates @gol --fno-implement-inlines -fms-extensions @gol --fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol --fno-optional-diags -fpermissive @gol --fno-pretty-templates @gol --frepo -fno-rtti -fstats -ftemplate-backtrace-limit=@var{n} @gol --ftemplate-depth=@var{n} @gol --fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol --fno-default-inline -fvisibility-inlines-hidden @gol --fvisibility-ms-compat @gol --fext-numeric-literals @gol --Wabi -Wconversion-null -Wctor-dtor-privacy @gol --Wdelete-non-virtual-dtor -Wliteral-suffix -Wnarrowing @gol --Wnoexcept -Wnon-virtual-dtor -Wreorder @gol --Weffc++ -Wstrict-null-sentinel @gol --Wno-non-template-friend -Wold-style-cast @gol --Woverloaded-virtual -Wno-pmf-conversions @gol --Wsign-promo} - -@item Objective-C and Objective-C++ Language Options -@xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling -Objective-C and Objective-C++ Dialects}. -@gccoptlist{-fconstant-string-class=@var{class-name} @gol --fgnu-runtime -fnext-runtime @gol --fno-nil-receivers @gol --fobjc-abi-version=@var{n} @gol --fobjc-call-cxx-cdtors @gol --fobjc-direct-dispatch @gol --fobjc-exceptions @gol --fobjc-gc @gol --fobjc-nilcheck @gol --fobjc-std=objc1 @gol --freplace-objc-classes @gol --fzero-link @gol --gen-decls @gol --Wassign-intercept @gol --Wno-protocol -Wselector @gol --Wstrict-selector-match @gol --Wundeclared-selector} - -@item Language Independent Options -@xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}. -@gccoptlist{-fmessage-length=@var{n} @gol --fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol --fno-diagnostics-show-option -fno-diagnostics-show-caret} - -@item Warning Options -@xref{Warning Options,,Options to Request or Suppress Warnings}. -@gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol --pedantic-errors @gol --w -Wextra -Wall -Waddress -Waggregate-return @gol --Waggressive-loop-optimizations -Warray-bounds @gol --Wno-attributes -Wno-builtin-macro-redefined @gol --Wc++-compat -Wc++11-compat -Wcast-align -Wcast-qual @gol --Wchar-subscripts -Wclobbered -Wcomment @gol --Wconversion -Wcoverage-mismatch -Wno-cpp -Wno-deprecated @gol --Wno-deprecated-declarations -Wdisabled-optimization @gol --Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare @gol --Wno-endif-labels -Werror -Werror=* @gol --Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol --Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol --Wformat-security -Wformat-y2k @gol --Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol --Wignored-qualifiers @gol --Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol --Winit-self -Winline -Wmaybe-uninitialized @gol --Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol --Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol --Wlogical-op -Wlong-long @gol --Wmain -Wmaybe-uninitialized -Wmissing-braces -Wmissing-field-initializers @gol --Wmissing-include-dirs @gol --Wno-mudflap @gol --Wno-multichar -Wnonnull -Wno-overflow @gol --Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol --Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol --Wpointer-arith -Wno-pointer-to-int-cast @gol --Wredundant-decls -Wno-return-local-addr @gol --Wreturn-type -Wsequence-point -Wshadow @gol --Wsign-compare -Wsign-conversion -Wsizeof-pointer-memaccess @gol --Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol --Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol --Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol --Wmissing-format-attribute @gol --Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol --Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef @gol --Wuninitialized -Wunknown-pragmas -Wno-pragmas @gol --Wunsuffixed-float-constants -Wunused -Wunused-function @gol --Wunused-label -Wunused-local-typedefs -Wunused-parameter @gol --Wno-unused-result -Wunused-value @gol -Wunused-variable @gol --Wunused-but-set-parameter -Wunused-but-set-variable @gol --Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol --Wvla -Wvolatile-register-var -Wwrite-strings -Wzero-as-null-pointer-constant} - -@item C and Objective-C-only Warning Options -@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol --Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol --Wold-style-declaration -Wold-style-definition @gol --Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol --Wdeclaration-after-statement -Wpointer-sign} - -@item Debugging Options -@xref{Debugging Options,,Options for Debugging Your Program or GCC}. -@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol --fsanitize=@var{style} @gol --fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol --fdisable-ipa-@var{pass_name} @gol --fdisable-rtl-@var{pass_name} @gol --fdisable-rtl-@var{pass-name}=@var{range-list} @gol --fdisable-tree-@var{pass_name} @gol --fdisable-tree-@var{pass-name}=@var{range-list} @gol --fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol --fdump-translation-unit@r{[}-@var{n}@r{]} @gol --fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol --fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol --fdump-passes @gol --fdump-statistics @gol --fdump-tree-all @gol --fdump-tree-original@r{[}-@var{n}@r{]} @gol --fdump-tree-optimized@r{[}-@var{n}@r{]} @gol --fdump-tree-cfg -fdump-tree-alias @gol --fdump-tree-ch @gol --fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol --fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol --fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol --fdump-tree-dom@r{[}-@var{n}@r{]} @gol --fdump-tree-dse@r{[}-@var{n}@r{]} @gol --fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol --fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol --fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol --fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol --fdump-tree-nrv -fdump-tree-vect @gol --fdump-tree-sink @gol --fdump-tree-sra@r{[}-@var{n}@r{]} @gol --fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol --fdump-tree-fre@r{[}-@var{n}@r{]} @gol --fdump-tree-vrp@r{[}-@var{n}@r{]} @gol --ftree-vectorizer-verbose=@var{n} @gol --fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol --fdump-final-insns=@var{file} @gol --fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol --feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol --feliminate-unused-debug-symbols -femit-class-debug-always @gol --fenable-@var{kind}-@var{pass} @gol --fenable-@var{kind}-@var{pass}=@var{range-list} @gol --fdebug-types-section -fmem-report-wpa @gol --fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol --fopt-info @gol --fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol --frandom-seed=@var{string} -fsched-verbose=@var{n} @gol --fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol --fstack-usage -ftest-coverage -ftime-report -fvar-tracking @gol --fvar-tracking-assignments -fvar-tracking-assignments-toggle @gol --g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol --ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol --gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol --gvms -gxcoff -gxcoff+ @gol --fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol --fdebug-prefix-map=@var{old}=@var{new} @gol --femit-struct-debug-baseonly -femit-struct-debug-reduced @gol --femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol --p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol --print-multi-directory -print-multi-lib -print-multi-os-directory @gol --print-prog-name=@var{program} -print-search-dirs -Q @gol --print-sysroot -print-sysroot-headers-suffix @gol --save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}} - -@item Optimization Options -@xref{Optimize Options,,Options that Control Optimization}. -@gccoptlist{-faggressive-loop-optimizations -falign-functions[=@var{n}] @gol --falign-jumps[=@var{n}] @gol --falign-labels[=@var{n}] -falign-loops[=@var{n}] @gol --fassociative-math -fauto-inc-dec -fbranch-probabilities @gol --fbranch-target-load-optimize -fbranch-target-load-optimize2 @gol --fbtr-bb-exclusive -fcaller-saves @gol --fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack @gol --fcompare-elim -fcprop-registers -fcrossjumping @gol --fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol --fcx-limited-range @gol --fdata-sections -fdce -fdelayed-branch @gol --fdelete-null-pointer-checks -fdevirtualize -fdse @gol --fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol --ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol --fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol --fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol --fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol --fif-conversion2 -findirect-inlining @gol --finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol --finline-small-functions -fipa-cp -fipa-cp-clone @gol --fipa-pta -fipa-profile -fipa-pure-const -fipa-reference @gol --fira-algorithm=@var{algorithm} @gol --fira-region=@var{region} -fira-hoist-pressure @gol --fira-loop-pressure -fno-ira-share-save-slots @gol --fno-ira-share-spill-slots -fira-verbose=@var{n} @gol --fivopts -fkeep-inline-functions -fkeep-static-consts @gol --floop-block -floop-interchange -floop-strip-mine -floop-nest-optimize @gol --floop-parallelize-all -flto -flto-compression-level @gol --flto-partition=@var{alg} -flto-report -fmerge-all-constants @gol --fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol --fmove-loop-invariants fmudflap -fmudflapir -fmudflapth -fno-branch-count-reg @gol --fno-default-inline @gol --fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol --fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol --fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol --fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol --fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol --fpartial-inlining -fpeel-loops -fpredictive-commoning @gol --fprefetch-loop-arrays -fprofile-report @gol --fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol --fprofile-generate=@var{path} @gol --fprofile-use -fprofile-use=@var{path} -fprofile-values @gol --freciprocal-math -free -fregmove -frename-registers -freorder-blocks @gol --freorder-blocks-and-partition -freorder-functions @gol --frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol --frounding-math -fsched2-use-superblocks -fsched-pressure @gol --fsched-spec-load -fsched-spec-load-dangerous @gol --fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol --fsched-group-heuristic -fsched-critical-path-heuristic @gol --fsched-spec-insn-heuristic -fsched-rank-heuristic @gol --fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol --fschedule-insns -fschedule-insns2 -fsection-anchors @gol --fselective-scheduling -fselective-scheduling2 @gol --fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol --fshrink-wrap -fsignaling-nans -fsingle-precision-constant @gol --fsplit-ivs-in-unroller -fsplit-wide-types -fstack-protector @gol --fstack-protector-all -fstrict-aliasing -fstrict-overflow @gol --fthread-jumps -ftracer -ftree-bit-ccp @gol --ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol --ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop @gol --ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse @gol --ftree-forwprop -ftree-fre -ftree-loop-if-convert @gol --ftree-loop-if-convert-stores -ftree-loop-im @gol --ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol --ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol --ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol --ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol --ftree-switch-conversion -ftree-tail-merge @gol --ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol --funit-at-a-time -funroll-all-loops -funroll-loops @gol --funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol --fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol --fwhole-program -fwpa -fuse-ld=@var{linker} -fuse-linker-plugin @gol ---param @var{name}=@var{value} --O -O0 -O1 -O2 -O3 -Os -Ofast -Og} - -@item Preprocessor Options -@xref{Preprocessor Options,,Options Controlling the Preprocessor}. -@gccoptlist{-A@var{question}=@var{answer} @gol --A-@var{question}@r{[}=@var{answer}@r{]} @gol --C -dD -dI -dM -dN @gol --D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol --idirafter @var{dir} @gol --include @var{file} -imacros @var{file} @gol --iprefix @var{file} -iwithprefix @var{dir} @gol --iwithprefixbefore @var{dir} -isystem @var{dir} @gol --imultilib @var{dir} -isysroot @var{dir} @gol --M -MM -MF -MG -MP -MQ -MT -nostdinc @gol --P -fdebug-cpp -ftrack-macro-expansion -fworking-directory @gol --remap -trigraphs -undef -U@var{macro} @gol --Wp,@var{option} -Xpreprocessor @var{option} -no-integrated-cpp} - -@item Assembler Option -@xref{Assembler Options,,Passing Options to the Assembler}. -@gccoptlist{-Wa,@var{option} -Xassembler @var{option}} - -@item Linker Options -@xref{Link Options,,Options for Linking}. -@gccoptlist{@var{object-file-name} -l@var{library} @gol --nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol --s -static -static-libgcc -static-libstdc++ @gol --static-libasan -static-libtsan @gol --shared -shared-libgcc -symbolic @gol --T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol --u @var{symbol}} - -@item Directory Options -@xref{Directory Options,,Options for Directory Search}. -@gccoptlist{-B@var{prefix} -I@var{dir} -iplugindir=@var{dir} @gol --iquote@var{dir} -L@var{dir} -specs=@var{file} -I- @gol ---sysroot=@var{dir} --no-sysroot-suffix} - -@item Machine Dependent Options -@xref{Submodel Options,,Hardware Models and Configurations}. -@c This list is ordered alphanumerically by subsection name. -@c Try and put the significant identifier (CPU or system) first, -@c so users have a clue at guessing where the ones they want will be. - -@emph{AArch64 Options} -@gccoptlist{-mbig-endian -mlittle-endian @gol --mgeneral-regs-only @gol --mcmodel=tiny -mcmodel=small -mcmodel=large @gol --mstrict-align @gol --momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol --mtls-dialect=desc -mtls-dialect=traditional @gol --march=@var{name} -mcpu=@var{name} -mtune=@var{name}} - -@emph{Adapteva Epiphany Options} -@gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol --mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol --msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol --mround-nearest -mlong-calls -mshort-calls -msmall16 @gol --mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol --msplit-vecmove-early -m1reg-@var{reg}} - -@emph{ARM Options} -@gccoptlist{-mapcs-frame -mno-apcs-frame @gol --mabi=@var{name} @gol --mapcs-stack-check -mno-apcs-stack-check @gol --mapcs-float -mno-apcs-float @gol --mapcs-reentrant -mno-apcs-reentrant @gol --msched-prolog -mno-sched-prolog @gol --mlittle-endian -mbig-endian -mwords-little-endian @gol --mfloat-abi=@var{name} @gol --mfp16-format=@var{name} --mthumb-interwork -mno-thumb-interwork @gol --mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol --mstructure-size-boundary=@var{n} @gol --mabort-on-noreturn @gol --mlong-calls -mno-long-calls @gol --msingle-pic-base -mno-single-pic-base @gol --mpic-register=@var{reg} @gol --mnop-fun-dllimport @gol --mpoke-function-name @gol --mthumb -marm @gol --mtpcs-frame -mtpcs-leaf-frame @gol --mcaller-super-interworking -mcallee-super-interworking @gol --mtp=@var{name} -mtls-dialect=@var{dialect} @gol --mword-relocations @gol --mfix-cortex-m3-ldrd @gol --munaligned-access} - -@emph{AVR Options} -@gccoptlist{-mmcu=@var{mcu} -maccumulate-args -mbranch-cost=@var{cost} @gol --mcall-prologues -mint8 -mno-interrupts -mrelax @gol --mstrict-X -mtiny-stack -Waddr-space-convert} - -@emph{Blackfin Options} -@gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol --msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol --mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol --mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol --mno-id-shared-library -mshared-library-id=@var{n} @gol --mleaf-id-shared-library -mno-leaf-id-shared-library @gol --msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol --mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol --micplb} - -@emph{C6X Options} -@gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol --msim -msdata=@var{sdata-type}} - -@emph{CRIS Options} -@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol --mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol --metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol --mstack-align -mdata-align -mconst-align @gol --m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol --melf -maout -melinux -mlinux -sim -sim2 @gol --mmul-bug-workaround -mno-mul-bug-workaround} - -@emph{CR16 Options} -@gccoptlist{-mmac @gol --mcr16cplus -mcr16c @gol --msim -mint32 -mbit-ops --mdata-model=@var{model}} - -@emph{Darwin Options} -@gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol --arch_only -bind_at_load -bundle -bundle_loader @gol --client_name -compatibility_version -current_version @gol --dead_strip @gol --dependency-file -dylib_file -dylinker_install_name @gol --dynamic -dynamiclib -exported_symbols_list @gol --filelist -flat_namespace -force_cpusubtype_ALL @gol --force_flat_namespace -headerpad_max_install_names @gol --iframework @gol --image_base -init -install_name -keep_private_externs @gol --multi_module -multiply_defined -multiply_defined_unused @gol --noall_load -no_dead_strip_inits_and_terms @gol --nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol --pagezero_size -prebind -prebind_all_twolevel_modules @gol --private_bundle -read_only_relocs -sectalign @gol --sectobjectsymbols -whyload -seg1addr @gol --sectcreate -sectobjectsymbols -sectorder @gol --segaddr -segs_read_only_addr -segs_read_write_addr @gol --seg_addr_table -seg_addr_table_filename -seglinkedit @gol --segprot -segs_read_only_addr -segs_read_write_addr @gol --single_module -static -sub_library -sub_umbrella @gol --twolevel_namespace -umbrella -undefined @gol --unexported_symbols_list -weak_reference_mismatches @gol --whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol --mkernel -mone-byte-bool} - -@emph{DEC Alpha Options} -@gccoptlist{-mno-fp-regs -msoft-float @gol --mieee -mieee-with-inexact -mieee-conformant @gol --mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol --mtrap-precision=@var{mode} -mbuild-constants @gol --mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol --mbwx -mmax -mfix -mcix @gol --mfloat-vax -mfloat-ieee @gol --mexplicit-relocs -msmall-data -mlarge-data @gol --msmall-text -mlarge-text @gol --mmemory-latency=@var{time}} - -@emph{FR30 Options} -@gccoptlist{-msmall-model -mno-lsim} - -@emph{FRV Options} -@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol --mhard-float -msoft-float @gol --malloc-cc -mfixed-cc -mdword -mno-dword @gol --mdouble -mno-double @gol --mmedia -mno-media -mmuladd -mno-muladd @gol --mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol --mlinked-fp -mlong-calls -malign-labels @gol --mlibrary-pic -macc-4 -macc-8 @gol --mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol --moptimize-membar -mno-optimize-membar @gol --mscc -mno-scc -mcond-exec -mno-cond-exec @gol --mvliw-branch -mno-vliw-branch @gol --mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol --mno-nested-cond-exec -mtomcat-stats @gol --mTLS -mtls @gol --mcpu=@var{cpu}} - -@emph{GNU/Linux Options} -@gccoptlist{-mglibc -muclibc -mbionic -mandroid @gol --tno-android-cc -tno-android-ld} - -@emph{H8/300 Options} -@gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300} - -@emph{HPPA Options} -@gccoptlist{-march=@var{architecture-type} @gol --mbig-switch -mdisable-fpregs -mdisable-indexing @gol --mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol --mfixed-range=@var{register-range} @gol --mjump-in-delay -mlinker-opt -mlong-calls @gol --mlong-load-store -mno-big-switch -mno-disable-fpregs @gol --mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol --mno-jump-in-delay -mno-long-load-store @gol --mno-portable-runtime -mno-soft-float @gol --mno-space-regs -msoft-float -mpa-risc-1-0 @gol --mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol --mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol --munix=@var{unix-std} -nolibdld -static -threads} - -@emph{i386 and x86-64 Options} -@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol --mfpmath=@var{unit} @gol --masm=@var{dialect} -mno-fancy-math-387 @gol --mno-fp-ret-in-387 -msoft-float @gol --mno-wide-multiply -mrtd -malign-double @gol --mpreferred-stack-boundary=@var{num} @gol --mincoming-stack-boundary=@var{num} @gol --mcld -mcx16 -msahf -mmovbe -mcrc32 @gol --mrecip -mrecip=@var{opt} @gol --mvzeroupper -mprefer-avx128 @gol --mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol --mavx2 -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma @gol --msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt @gol --mbmi2 -mrtm -mlwp -mthreads @gol --mno-align-stringops -minline-all-stringops @gol --minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol --mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol --m96bit-long-double -mlong-double-64 -mlong-double-80 @gol --mregparm=@var{num} -msseregparm @gol --mveclibabi=@var{type} -mvect8-ret-in-mem @gol --mpc32 -mpc64 -mpc80 -mstackrealign @gol --momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol --mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol --m32 -m64 -mx32 -mlarge-data-threshold=@var{num} @gol --msse2avx -mfentry -m8bit-idiv @gol --mavx256-split-unaligned-load -mavx256-split-unaligned-store} - -@emph{i386 and x86-64 Windows Options} -@gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol --mnop-fun-dllimport -mthread @gol --municode -mwin32 -mwindows -fno-set-stack-executable} - -@emph{IA-64 Options} -@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol --mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol --mconstant-gp -mauto-pic -mfused-madd @gol --minline-float-divide-min-latency @gol --minline-float-divide-max-throughput @gol --mno-inline-float-divide @gol --minline-int-divide-min-latency @gol --minline-int-divide-max-throughput @gol --mno-inline-int-divide @gol --minline-sqrt-min-latency -minline-sqrt-max-throughput @gol --mno-inline-sqrt @gol --mdwarf2-asm -mearly-stop-bits @gol --mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol --mtune=@var{cpu-type} -milp32 -mlp64 @gol --msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol --msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol --msched-spec-ldc -msched-spec-control-ldc @gol --msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol --msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol --msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol --msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}} - -@emph{LM32 Options} -@gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol --msign-extend-enabled -muser-enabled} - -@emph{M32R/D Options} -@gccoptlist{-m32r2 -m32rx -m32r @gol --mdebug @gol --malign-loops -mno-align-loops @gol --missue-rate=@var{number} @gol --mbranch-cost=@var{number} @gol --mmodel=@var{code-size-model-type} @gol --msdata=@var{sdata-type} @gol --mno-flush-func -mflush-func=@var{name} @gol --mno-flush-trap -mflush-trap=@var{number} @gol --G @var{num}} - -@emph{M32C Options} -@gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} - -@emph{M680x0 Options} -@gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} --m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol --m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol --mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol --mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol --mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol --malign-int -mstrict-align -msep-data -mno-sep-data @gol --mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol --mxgot -mno-xgot} - -@emph{MCore Options} -@gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol --mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol --m4byte-functions -mno-4byte-functions -mcallgraph-data @gol --mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol --mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} - -@emph{MeP Options} -@gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol --mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol --mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol --mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol --mtiny=@var{n}} - -@emph{MicroBlaze Options} -@gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol --mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol --mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol --mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol --mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model}} - -@emph{MIPS Options} -@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol --mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol --mips64 -mips64r2 @gol --mips16 -mno-mips16 -mflip-mips16 @gol --minterlink-mips16 -mno-interlink-mips16 @gol --mabi=@var{abi} -mabicalls -mno-abicalls @gol --mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol --mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol --mno-float -msingle-float -mdouble-float @gol --mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol --mmcu -mmno-mcu @gol --mfpu=@var{fpu-type} @gol --msmartmips -mno-smartmips @gol --mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol --mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol --mlong64 -mlong32 -msym32 -mno-sym32 @gol --G@var{num} -mlocal-sdata -mno-local-sdata @gol --mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol --membedded-data -mno-embedded-data @gol --muninit-const-in-rodata -mno-uninit-const-in-rodata @gol --mcode-readable=@var{setting} @gol --msplit-addresses -mno-split-addresses @gol --mexplicit-relocs -mno-explicit-relocs @gol --mcheck-zero-division -mno-check-zero-division @gol --mdivide-traps -mdivide-breaks @gol --mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol --mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol --mfix-24k -mno-fix-24k @gol --mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol --mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 @gol --mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol --mflush-func=@var{func} -mno-flush-func @gol --mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol --mfp-exceptions -mno-fp-exceptions @gol --mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol --mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address} - -@emph{MMIX Options} -@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol --mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol --melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol --mno-base-addresses -msingle-exit -mno-single-exit} - -@emph{MN10300 Options} -@gccoptlist{-mmult-bug -mno-mult-bug @gol --mno-am33 -mam33 -mam33-2 -mam34 @gol --mtune=@var{cpu-type} @gol --mreturn-pointer-on-d0 @gol --mno-crt0 -mrelax -mliw -msetlb} - -@emph{Moxie Options} -@gccoptlist{-meb -mel -mno-crt0} - -@emph{PDP-11 Options} -@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol --mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol --mint16 -mno-int32 -mfloat32 -mno-float64 @gol --mfloat64 -mno-float32 -mabshi -mno-abshi @gol --mbranch-expensive -mbranch-cheap @gol --munix-asm -mdec-asm} - -@emph{picoChip Options} -@gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol --msymbol-as-address -mno-inefficient-warnings} - -@emph{PowerPC Options} -See RS/6000 and PowerPC Options. - -@emph{RL78 Options} -@gccoptlist{-msim -mmul=none -mmul=g13 -mmul=rl78} - -@emph{RS/6000 and PowerPC Options} -@gccoptlist{-mcpu=@var{cpu-type} @gol --mtune=@var{cpu-type} @gol --mcmodel=@var{code-model} @gol --mpowerpc64 @gol --maltivec -mno-altivec @gol --mpowerpc-gpopt -mno-powerpc-gpopt @gol --mpowerpc-gfxopt -mno-powerpc-gfxopt @gol --mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol --mfprnd -mno-fprnd @gol --mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol --mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol --m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol --malign-power -malign-natural @gol --msoft-float -mhard-float -mmultiple -mno-multiple @gol --msingle-float -mdouble-float -msimple-fpu @gol --mstring -mno-string -mupdate -mno-update @gol --mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol --mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol --mstrict-align -mno-strict-align -mrelocatable @gol --mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol --mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol --mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol --mprioritize-restricted-insns=@var{priority} @gol --msched-costly-dep=@var{dependence_type} @gol --minsert-sched-nops=@var{scheme} @gol --mcall-sysv -mcall-netbsd @gol --maix-struct-return -msvr4-struct-return @gol --mabi=@var{abi-type} -msecure-plt -mbss-plt @gol --mblock-move-inline-limit=@var{num} @gol --misel -mno-isel @gol --misel=yes -misel=no @gol --mspe -mno-spe @gol --mspe=yes -mspe=no @gol --mpaired @gol --mgen-cell-microcode -mwarn-cell-microcode @gol --mvrsave -mno-vrsave @gol --mmulhw -mno-mulhw @gol --mdlmzb -mno-dlmzb @gol --mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol --mprototype -mno-prototype @gol --msim -mmvme -mads -myellowknife -memb -msdata @gol --msdata=@var{opt} -mvxworks -G @var{num} -pthread @gol --mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol --mno-recip-precision @gol --mveclibabi=@var{type} -mfriz -mno-friz @gol --mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol --msave-toc-indirect -mno-save-toc-indirect} - -@emph{RX Options} -@gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol --mcpu=@gol --mbig-endian-data -mlittle-endian-data @gol --msmall-data @gol --msim -mno-sim@gol --mas100-syntax -mno-as100-syntax@gol --mrelax@gol --mmax-constant-size=@gol --mint-register=@gol --mpid@gol --mno-warn-multiple-fast-interrupts@gol --msave-acc-in-interrupts} - -@emph{S/390 and zSeries Options} -@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol --mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol --mlong-double-64 -mlong-double-128 @gol --mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol --msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol --m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol --mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol --mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard} - -@emph{Score Options} -@gccoptlist{-meb -mel @gol --mnhwloop @gol --muls @gol --mmac @gol --mscore5 -mscore5u -mscore7 -mscore7d} - -@emph{SH Options} -@gccoptlist{-m1 -m2 -m2e @gol --m2a-nofpu -m2a-single-only -m2a-single -m2a @gol --m3 -m3e @gol --m4-nofpu -m4-single-only -m4-single -m4 @gol --m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol --m5-64media -m5-64media-nofpu @gol --m5-32media -m5-32media-nofpu @gol --m5-compact -m5-compact-nofpu @gol --mb -ml -mdalign -mrelax @gol --mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol --mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol --mspace -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol --mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol --mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol --maccumulate-outgoing-args -minvalid-symbols @gol --matomic-model=@var{atomic-model} @gol --mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch -mcbranchdi -mcmpeqdi @gol --mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol --mpretend-cmove -mtas} - -@emph{Solaris 2 Options} -@gccoptlist{-mimpure-text -mno-impure-text @gol --pthreads -pthread} - -@emph{SPARC Options} -@gccoptlist{-mcpu=@var{cpu-type} @gol --mtune=@var{cpu-type} @gol --mcmodel=@var{code-model} @gol --mmemory-model=@var{mem-model} @gol --m32 -m64 -mapp-regs -mno-app-regs @gol --mfaster-structs -mno-faster-structs -mflat -mno-flat @gol --mfpu -mno-fpu -mhard-float -msoft-float @gol --mhard-quad-float -msoft-quad-float @gol --mstack-bias -mno-stack-bias @gol --munaligned-doubles -mno-unaligned-doubles @gol --mv8plus -mno-v8plus -mvis -mno-vis @gol --mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol --mcbcond -mno-cbcond @gol --mfmaf -mno-fmaf -mpopc -mno-popc @gol --mfix-at697f} - -@emph{SPU Options} -@gccoptlist{-mwarn-reloc -merror-reloc @gol --msafe-dma -munsafe-dma @gol --mbranch-hints @gol --msmall-mem -mlarge-mem -mstdmain @gol --mfixed-range=@var{register-range} @gol --mea32 -mea64 @gol --maddress-space-conversion -mno-address-space-conversion @gol --mcache-size=@var{cache-size} @gol --matomic-updates -mno-atomic-updates} - -@emph{System V Options} -@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} - -@emph{TILE-Gx Options} -@gccoptlist{-mcpu=@var{cpu} -m32 -m64 -mcmodel=@var{code-model}} - -@emph{TILEPro Options} -@gccoptlist{-mcpu=@var{cpu} -m32} - -@emph{V850 Options} -@gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol --mprolog-function -mno-prolog-function -mspace @gol --mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol --mapp-regs -mno-app-regs @gol --mdisable-callt -mno-disable-callt @gol --mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol --mv850e -mv850 -mv850e3v5 @gol --mloop @gol --mrelax @gol --mlong-jumps @gol --msoft-float @gol --mhard-float @gol --mgcc-abi @gol --mrh850-abi @gol --mbig-switch} - -@emph{VAX Options} -@gccoptlist{-mg -mgnu -munix} - -@emph{VMS Options} -@gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol --mpointer-size=@var{size}} - -@emph{VxWorks Options} -@gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol --Xbind-lazy -Xbind-now} - -@emph{x86-64 Options} -See i386 and x86-64 Options. - -@emph{Xstormy16 Options} -@gccoptlist{-msim} - -@emph{Xtensa Options} -@gccoptlist{-mconst16 -mno-const16 @gol --mfused-madd -mno-fused-madd @gol --mforce-no-pic @gol --mserialize-volatile -mno-serialize-volatile @gol --mtext-section-literals -mno-text-section-literals @gol --mtarget-align -mno-target-align @gol --mlongcalls -mno-longcalls} - -@emph{zSeries Options} -See S/390 and zSeries Options. - -@item Code Generation Options -@xref{Code Gen Options,,Options for Code Generation Conventions}. -@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol --ffixed-@var{reg} -fexceptions @gol --fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol --fasynchronous-unwind-tables @gol --finhibit-size-directive -finstrument-functions @gol --finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol --finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol --fno-common -fno-ident @gol --fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol --fno-jump-tables @gol --frecord-gcc-switches @gol --freg-struct-return -fshort-enums @gol --fshort-double -fshort-wchar @gol --fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol --fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol --fno-stack-limit -fsplit-stack @gol --fleading-underscore -ftls-model=@var{model} @gol --fstack-reuse=@var{reuse_level} @gol --ftrapv -fwrapv -fbounds-check @gol --fvisibility -fstrict-volatile-bitfields -fsync-libcalls} -@end table - -@menu -* Overall Options:: Controlling the kind of output: - an executable, object files, assembler files, - or preprocessed source. -* C Dialect Options:: Controlling the variant of C language compiled. -* C++ Dialect Options:: Variations on C++. -* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C - and Objective-C++. -* Language Independent Options:: Controlling how diagnostics should be - formatted. -* Warning Options:: How picky should the compiler be? -* Debugging Options:: Symbol tables, measurements, and debugging dumps. -* Optimize Options:: How much optimization? -* Preprocessor Options:: Controlling header files and macro definitions. - Also, getting dependency information for Make. -* Assembler Options:: Passing options to the assembler. -* Link Options:: Specifying libraries and so on. -* Directory Options:: Where to find header files and libraries. - Where to find the compiler executable files. -* Spec Files:: How to pass switches to sub-processes. -* Target Options:: Running a cross-compiler, or an old version of GCC. -@end menu - -@node Overall Options -@section Options Controlling the Kind of Output - -Compilation can involve up to four stages: preprocessing, compilation -proper, assembly and linking, always in that order. GCC is capable of -preprocessing and compiling several files either into several -assembler input files, or into one assembler input file; then each -assembler input file produces an object file, and linking combines all -the object files (those newly compiled, and those specified as input) -into an executable file. - -@cindex file name suffix -For any given input file, the file name suffix determines what kind of -compilation is done: - -@table @gcctabopt -@item @var{file}.c -C source code that must be preprocessed. - -@item @var{file}.i -C source code that should not be preprocessed. - -@item @var{file}.ii -C++ source code that should not be preprocessed. - -@item @var{file}.m -Objective-C source code. Note that you must link with the @file{libobjc} -library to make an Objective-C program work. - -@item @var{file}.mi -Objective-C source code that should not be preprocessed. - -@item @var{file}.mm -@itemx @var{file}.M -Objective-C++ source code. Note that you must link with the @file{libobjc} -library to make an Objective-C++ program work. Note that @samp{.M} refers -to a literal capital M@. - -@item @var{file}.mii -Objective-C++ source code that should not be preprocessed. - -@item @var{file}.h -C, C++, Objective-C or Objective-C++ header file to be turned into a -precompiled header (default), or C, C++ header file to be turned into an -Ada spec (via the @option{-fdump-ada-spec} switch). - -@item @var{file}.cc -@itemx @var{file}.cp -@itemx @var{file}.cxx -@itemx @var{file}.cpp -@itemx @var{file}.CPP -@itemx @var{file}.c++ -@itemx @var{file}.C -C++ source code that must be preprocessed. Note that in @samp{.cxx}, -the last two letters must both be literally @samp{x}. Likewise, -@samp{.C} refers to a literal capital C@. - -@item @var{file}.mm -@itemx @var{file}.M -Objective-C++ source code that must be preprocessed. - -@item @var{file}.mii -Objective-C++ source code that should not be preprocessed. - -@item @var{file}.hh -@itemx @var{file}.H -@itemx @var{file}.hp -@itemx @var{file}.hxx -@itemx @var{file}.hpp -@itemx @var{file}.HPP -@itemx @var{file}.h++ -@itemx @var{file}.tcc -C++ header file to be turned into a precompiled header or Ada spec. - -@item @var{file}.f -@itemx @var{file}.for -@itemx @var{file}.ftn -Fixed form Fortran source code that should not be preprocessed. - -@item @var{file}.F -@itemx @var{file}.FOR -@itemx @var{file}.fpp -@itemx @var{file}.FPP -@itemx @var{file}.FTN -Fixed form Fortran source code that must be preprocessed (with the traditional -preprocessor). - -@item @var{file}.f90 -@itemx @var{file}.f95 -@itemx @var{file}.f03 -@itemx @var{file}.f08 -Free form Fortran source code that should not be preprocessed. - -@item @var{file}.F90 -@itemx @var{file}.F95 -@itemx @var{file}.F03 -@itemx @var{file}.F08 -Free form Fortran source code that must be preprocessed (with the -traditional preprocessor). - -@item @var{file}.go -Go source code. - -@c FIXME: Descriptions of Java file types. -@c @var{file}.java -@c @var{file}.class -@c @var{file}.zip -@c @var{file}.jar - -@item @var{file}.ads -Ada source code file that contains a library unit declaration (a -declaration of a package, subprogram, or generic, or a generic -instantiation), or a library unit renaming declaration (a package, -generic, or subprogram renaming declaration). Such files are also -called @dfn{specs}. - -@item @var{file}.adb -Ada source code file containing a library unit body (a subprogram or -package body). Such files are also called @dfn{bodies}. - -@c GCC also knows about some suffixes for languages not yet included: -@c Pascal: -@c @var{file}.p -@c @var{file}.pas -@c Ratfor: -@c @var{file}.r - -@item @var{file}.s -Assembler code. - -@item @var{file}.S -@itemx @var{file}.sx -Assembler code that must be preprocessed. - -@item @var{other} -An object file to be fed straight into linking. -Any file name with no recognized suffix is treated this way. -@end table - -@opindex x -You can specify the input language explicitly with the @option{-x} option: - -@table @gcctabopt -@item -x @var{language} -Specify explicitly the @var{language} for the following input files -(rather than letting the compiler choose a default based on the file -name suffix). This option applies to all following input files until -the next @option{-x} option. Possible values for @var{language} are: -@smallexample -c c-header cpp-output -c++ c++-header c++-cpp-output -objective-c objective-c-header objective-c-cpp-output -objective-c++ objective-c++-header objective-c++-cpp-output -assembler assembler-with-cpp -ada -f77 f77-cpp-input f95 f95-cpp-input -go -java -@end smallexample - -@item -x none -Turn off any specification of a language, so that subsequent files are -handled according to their file name suffixes (as they are if @option{-x} -has not been used at all). - -@item -pass-exit-codes -@opindex pass-exit-codes -Normally the @command{gcc} program exits with the code of 1 if any -phase of the compiler returns a non-success return code. If you specify -@option{-pass-exit-codes}, the @command{gcc} program instead returns with -the numerically highest error produced by any phase returning an error -indication. The C, C++, and Fortran front ends return 4 if an internal -compiler error is encountered. -@end table - -If you only want some of the stages of compilation, you can use -@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and -one of the options @option{-c}, @option{-S}, or @option{-E} to say where -@command{gcc} is to stop. Note that some combinations (for example, -@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. - -@table @gcctabopt -@item -c -@opindex c -Compile or assemble the source files, but do not link. The linking -stage simply is not done. The ultimate output is in the form of an -object file for each source file. - -By default, the object file name for a source file is made by replacing -the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. - -Unrecognized input files, not requiring compilation or assembly, are -ignored. - -@item -S -@opindex S -Stop after the stage of compilation proper; do not assemble. The output -is in the form of an assembler code file for each non-assembler input -file specified. - -By default, the assembler file name for a source file is made by -replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. - -Input files that don't require compilation are ignored. - -@item -E -@opindex E -Stop after the preprocessing stage; do not run the compiler proper. The -output is in the form of preprocessed source code, which is sent to the -standard output. - -Input files that don't require preprocessing are ignored. - -@cindex output file option -@item -o @var{file} -@opindex o -Place output in file @var{file}. This applies to whatever -sort of output is being produced, whether it be an executable file, -an object file, an assembler file or preprocessed C code. - -If @option{-o} is not specified, the default is to put an executable -file in @file{a.out}, the object file for -@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its -assembler file in @file{@var{source}.s}, a precompiled header file in -@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on -standard output. - -@item -v -@opindex v -Print (on standard error output) the commands executed to run the stages -of compilation. Also print the version number of the compiler driver -program and of the preprocessor and the compiler proper. - -@item -### -@opindex ### -Like @option{-v} except the commands are not executed and arguments -are quoted unless they contain only alphanumeric characters or @code{./-_}. -This is useful for shell scripts to capture the driver-generated command lines. - -@item -pipe -@opindex pipe -Use pipes rather than temporary files for communication between the -various stages of compilation. This fails to work on some systems where -the assembler is unable to read from a pipe; but the GNU assembler has -no trouble. - -@item --help -@opindex help -Print (on the standard output) a description of the command-line options -understood by @command{gcc}. If the @option{-v} option is also specified -then @option{--help} is also passed on to the various processes -invoked by @command{gcc}, so that they can display the command-line options -they accept. If the @option{-Wextra} option has also been specified -(prior to the @option{--help} option), then command-line options that -have no documentation associated with them are also displayed. - -@item --target-help -@opindex target-help -Print (on the standard output) a description of target-specific command-line -options for each tool. For some targets extra target-specific -information may also be printed. - -@item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]} -Print (on the standard output) a description of the command-line -options understood by the compiler that fit into all specified classes -and qualifiers. These are the supported classes: - -@table @asis -@item @samp{optimizers} -Display all of the optimization options supported by the -compiler. - -@item @samp{warnings} -Display all of the options controlling warning messages -produced by the compiler. - -@item @samp{target} -Display target-specific options. Unlike the -@option{--target-help} option however, target-specific options of the -linker and assembler are not displayed. This is because those -tools do not currently support the extended @option{--help=} syntax. - -@item @samp{params} -Display the values recognized by the @option{--param} -option. - -@item @var{language} -Display the options supported for @var{language}, where -@var{language} is the name of one of the languages supported in this -version of GCC@. - -@item @samp{common} -Display the options that are common to all languages. -@end table - -These are the supported qualifiers: - -@table @asis -@item @samp{undocumented} -Display only those options that are undocumented. - -@item @samp{joined} -Display options taking an argument that appears after an equal -sign in the same continuous piece of text, such as: -@samp{--help=target}. - -@item @samp{separate} -Display options taking an argument that appears as a separate word -following the original option, such as: @samp{-o output-file}. -@end table - -Thus for example to display all the undocumented target-specific -switches supported by the compiler, use: - -@smallexample ---help=target,undocumented -@end smallexample - -The sense of a qualifier can be inverted by prefixing it with the -@samp{^} character, so for example to display all binary warning -options (i.e., ones that are either on or off and that do not take an -argument) that have a description, use: - -@smallexample ---help=warnings,^joined,^undocumented -@end smallexample - -The argument to @option{--help=} should not consist solely of inverted -qualifiers. - -Combining several classes is possible, although this usually -restricts the output so much that there is nothing to display. One -case where it does work, however, is when one of the classes is -@var{target}. For example, to display all the target-specific -optimization options, use: - -@smallexample ---help=target,optimizers -@end smallexample - -The @option{--help=} option can be repeated on the command line. Each -successive use displays its requested class of options, skipping -those that have already been displayed. - -If the @option{-Q} option appears on the command line before the -@option{--help=} option, then the descriptive text displayed by -@option{--help=} is changed. Instead of describing the displayed -options, an indication is given as to whether the option is enabled, -disabled or set to a specific value (assuming that the compiler -knows this at the point where the @option{--help=} option is used). - -Here is a truncated example from the ARM port of @command{gcc}: - -@smallexample - % gcc -Q -mabi=2 --help=target -c - The following options are target specific: - -mabi= 2 - -mabort-on-noreturn [disabled] - -mapcs [disabled] -@end smallexample - -The output is sensitive to the effects of previous command-line -options, so for example it is possible to find out which optimizations -are enabled at @option{-O2} by using: - -@smallexample --Q -O2 --help=optimizers -@end smallexample - -Alternatively you can discover which binary optimizations are enabled -by @option{-O3} by using: - -@smallexample -gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts -gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts -diff /tmp/O2-opts /tmp/O3-opts | grep enabled -@end smallexample - -@item -no-canonical-prefixes -@opindex no-canonical-prefixes -Do not expand any symbolic links, resolve references to @samp{/../} -or @samp{/./}, or make the path absolute when generating a relative -prefix. - -@item --version -@opindex version -Display the version number and copyrights of the invoked GCC@. - -@item -wrapper -@opindex wrapper -Invoke all subcommands under a wrapper program. The name of the -wrapper program and its parameters are passed as a comma separated -list. - -@smallexample -gcc -c t.c -wrapper gdb,--args -@end smallexample - -@noindent -This invokes all subprograms of @command{gcc} under -@samp{gdb --args}, thus the invocation of @command{cc1} is -@samp{gdb --args cc1 @dots{}}. - -@item -fplugin=@var{name}.so -Load the plugin code in file @var{name}.so, assumed to be a -shared object to be dlopen'd by the compiler. The base name of -the shared object file is used to identify the plugin for the -purposes of argument parsing (See -@option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below). -Each plugin should define the callback functions specified in the -Plugins API. - -@item -fplugin-arg-@var{name}-@var{key}=@var{value} -Define an argument called @var{key} with a value of @var{value} -for the plugin called @var{name}. - -@item -fdump-ada-spec@r{[}-slim@r{]} -For C and C++ source and include files, generate corresponding Ada -specs. @xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn, -GNAT User's Guide}, which provides detailed documentation on this feature. - -@item -fdump-go-spec=@var{file} -For input files in any language, generate corresponding Go -declarations in @var{file}. This generates Go @code{const}, -@code{type}, @code{var}, and @code{func} declarations which may be a -useful way to start writing a Go interface to code written in some -other language. - -@include @value{srcdir}/../libiberty/at-file.texi -@end table - -@node Invoking G++ -@section Compiling C++ Programs - -@cindex suffixes for C++ source -@cindex C++ source file suffixes -C++ source files conventionally use one of the suffixes @samp{.C}, -@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or -@samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp}, -@samp{.H}, or (for shared template code) @samp{.tcc}; and -preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes -files with these names and compiles them as C++ programs even if you -call the compiler the same way as for compiling C programs (usually -with the name @command{gcc}). - -@findex g++ -@findex c++ -However, the use of @command{gcc} does not add the C++ library. -@command{g++} is a program that calls GCC and automatically specifies linking -against the C++ library. It treats @samp{.c}, -@samp{.h} and @samp{.i} files as C++ source files instead of C source -files unless @option{-x} is used. This program is also useful when -precompiling a C header file with a @samp{.h} extension for use in C++ -compilations. On many systems, @command{g++} is also installed with -the name @command{c++}. - -@cindex invoking @command{g++} -When you compile C++ programs, you may specify many of the same -command-line options that you use for compiling programs in any -language; or command-line options meaningful for C and related -languages; or options that are meaningful only for C++ programs. -@xref{C Dialect Options,,Options Controlling C Dialect}, for -explanations of options for languages related to C@. -@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for -explanations of options that are meaningful only for C++ programs. - -@node C Dialect Options -@section Options Controlling C Dialect -@cindex dialect options -@cindex language dialect options -@cindex options, dialect - -The following options control the dialect of C (or languages derived -from C, such as C++, Objective-C and Objective-C++) that the compiler -accepts: - -@table @gcctabopt -@cindex ANSI support -@cindex ISO support -@item -ansi -@opindex ansi -In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is -equivalent to @option{-std=c++98}. - -This turns off certain features of GCC that are incompatible with ISO -C90 (when compiling C code), or of standard C++ (when compiling C++ code), -such as the @code{asm} and @code{typeof} keywords, and -predefined macros such as @code{unix} and @code{vax} that identify the -type of system you are using. It also enables the undesirable and -rarely used ISO trigraph feature. For the C compiler, -it disables recognition of C++ style @samp{//} comments as well as -the @code{inline} keyword. - -The alternate keywords @code{__asm__}, @code{__extension__}, -@code{__inline__} and @code{__typeof__} continue to work despite -@option{-ansi}. You would not want to use them in an ISO C program, of -course, but it is useful to put them in header files that might be included -in compilations done with @option{-ansi}. Alternate predefined macros -such as @code{__unix__} and @code{__vax__} are also available, with or -without @option{-ansi}. - -The @option{-ansi} option does not cause non-ISO programs to be -rejected gratuitously. For that, @option{-Wpedantic} is required in -addition to @option{-ansi}. @xref{Warning Options}. - -The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} -option is used. Some header files may notice this macro and refrain -from declaring certain functions or defining certain macros that the -ISO standard doesn't call for; this is to avoid interfering with any -programs that might use these names for other things. - -Functions that are normally built in but do not have semantics -defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in -functions when @option{-ansi} is used. @xref{Other Builtins,,Other -built-in functions provided by GCC}, for details of the functions -affected. - -@item -std= -@opindex std -Determine the language standard. @xref{Standards,,Language Standards -Supported by GCC}, for details of these standard versions. This option -is currently only supported when compiling C or C++. - -The compiler can accept several base standards, such as @samp{c90} or -@samp{c++98}, and GNU dialects of those standards, such as -@samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the -compiler accepts all programs following that standard plus those -using GNU extensions that do not contradict it. For example, -@option{-std=c90} turns off certain features of GCC that are -incompatible with ISO C90, such as the @code{asm} and @code{typeof} -keywords, but not other GNU extensions that do not have a meaning in -ISO C90, such as omitting the middle term of a @code{?:} -expression. On the other hand, when a GNU dialect of a standard is -specified, all features supported by the compiler are enabled, even when -those features change the meaning of the base standard. As a result, some -strict-conforming programs may be rejected. The particular standard -is used by @option{-Wpedantic} to identify which features are GNU -extensions given that version of the standard. For example -@option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//} -comments, while @option{-std=gnu99 -Wpedantic} does not. - -A value for this option must be provided; possible values are - -@table @samp -@item c90 -@itemx c89 -@itemx iso9899:1990 -Support all ISO C90 programs (certain GNU extensions that conflict -with ISO C90 are disabled). Same as @option{-ansi} for C code. - -@item iso9899:199409 -ISO C90 as modified in amendment 1. - -@item c99 -@itemx c9x -@itemx iso9899:1999 -@itemx iso9899:199x -ISO C99. Note that this standard is not yet fully supported; see -@w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The -names @samp{c9x} and @samp{iso9899:199x} are deprecated. - -@item c11 -@itemx c1x -@itemx iso9899:2011 -ISO C11, the 2011 revision of the ISO C standard. -Support is incomplete and experimental. The name @samp{c1x} is -deprecated. - -@item gnu90 -@itemx gnu89 -GNU dialect of ISO C90 (including some C99 features). This -is the default for C code. - -@item gnu99 -@itemx gnu9x -GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC, -this will become the default. The name @samp{gnu9x} is deprecated. - -@item gnu11 -@itemx gnu1x -GNU dialect of ISO C11. Support is incomplete and experimental. The -name @samp{gnu1x} is deprecated. - -@item c++98 -@itemx c++03 -The 1998 ISO C++ standard plus the 2003 technical corrigendum and some -additional defect reports. Same as @option{-ansi} for C++ code. - -@item gnu++98 -@itemx gnu++03 -GNU dialect of @option{-std=c++98}. This is the default for -C++ code. - -@item c++11 -@itemx c++0x -The 2011 ISO C++ standard plus amendments. Support for C++11 is still -experimental, and may change in incompatible ways in future releases. -The name @samp{c++0x} is deprecated. - -@item gnu++11 -@itemx gnu++0x -GNU dialect of @option{-std=c++11}. Support for C++11 is still -experimental, and may change in incompatible ways in future releases. -The name @samp{gnu++0x} is deprecated. - -@item c++1y -The next revision of the ISO C++ standard, tentatively planned for -2017. Support is highly experimental, and will almost certainly -change in incompatible ways in future releases. - -@item gnu++1y -GNU dialect of @option{-std=c++1y}. Support is highly experimental, -and will almost certainly change in incompatible ways in future -releases. -@end table - -@item -fgnu89-inline -@opindex fgnu89-inline -The option @option{-fgnu89-inline} tells GCC to use the traditional -GNU semantics for @code{inline} functions when in C99 mode. -@xref{Inline,,An Inline Function is As Fast As a Macro}. This option -is accepted and ignored by GCC versions 4.1.3 up to but not including -4.3. In GCC versions 4.3 and later it changes the behavior of GCC in -C99 mode. Using this option is roughly equivalent to adding the -@code{gnu_inline} function attribute to all inline functions -(@pxref{Function Attributes}). - -The option @option{-fno-gnu89-inline} explicitly tells GCC to use the -C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it -specifies the default behavior). This option was first supported in -GCC 4.3. This option is not supported in @option{-std=c90} or -@option{-std=gnu90} mode. - -The preprocessor macros @code{__GNUC_GNU_INLINE__} and -@code{__GNUC_STDC_INLINE__} may be used to check which semantics are -in effect for @code{inline} functions. @xref{Common Predefined -Macros,,,cpp,The C Preprocessor}. - -@item -aux-info @var{filename} -@opindex aux-info -Output to the given filename prototyped declarations for all functions -declared and/or defined in a translation unit, including those in header -files. This option is silently ignored in any language other than C@. - -Besides declarations, the file indicates, in comments, the origin of -each declaration (source file and line), whether the declaration was -implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or -@samp{O} for old, respectively, in the first character after the line -number and the colon), and whether it came from a declaration or a -definition (@samp{C} or @samp{F}, respectively, in the following -character). In the case of function definitions, a K&R-style list of -arguments followed by their declarations is also provided, inside -comments, after the declaration. - -@item -fallow-parameterless-variadic-functions -Accept variadic functions without named parameters. - -Although it is possible to define such a function, this is not very -useful as it is not possible to read the arguments. This is only -supported for C as this construct is allowed by C++. - -@item -fno-asm -@opindex fno-asm -Do not recognize @code{asm}, @code{inline} or @code{typeof} as a -keyword, so that code can use these words as identifiers. You can use -the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} -instead. @option{-ansi} implies @option{-fno-asm}. - -In C++, this switch only affects the @code{typeof} keyword, since -@code{asm} and @code{inline} are standard keywords. You may want to -use the @option{-fno-gnu-keywords} flag instead, which has the same -effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this -switch only affects the @code{asm} and @code{typeof} keywords, since -@code{inline} is a standard keyword in ISO C99. - -@item -fno-builtin -@itemx -fno-builtin-@var{function} -@opindex fno-builtin -@cindex built-in functions -Don't recognize built-in functions that do not begin with -@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in -functions provided by GCC}, for details of the functions affected, -including those which are not built-in functions when @option{-ansi} or -@option{-std} options for strict ISO C conformance are used because they -do not have an ISO standard meaning. - -GCC normally generates special code to handle certain built-in functions -more efficiently; for instance, calls to @code{alloca} may become single -instructions which adjust the stack directly, and calls to @code{memcpy} -may become inline copy loops. The resulting code is often both smaller -and faster, but since the function calls no longer appear as such, you -cannot set a breakpoint on those calls, nor can you change the behavior -of the functions by linking with a different library. In addition, -when a function is recognized as a built-in function, GCC may use -information about that function to warn about problems with calls to -that function, or to generate more efficient code, even if the -resulting code still contains calls to that function. For example, -warnings are given with @option{-Wformat} for bad calls to -@code{printf} when @code{printf} is built in and @code{strlen} is -known not to modify global memory. - -With the @option{-fno-builtin-@var{function}} option -only the built-in function @var{function} is -disabled. @var{function} must not begin with @samp{__builtin_}. If a -function is named that is not built-in in this version of GCC, this -option is ignored. There is no corresponding -@option{-fbuiltin-@var{function}} option; if you wish to enable -built-in functions selectively when using @option{-fno-builtin} or -@option{-ffreestanding}, you may define macros such as: - -@smallexample -#define abs(n) __builtin_abs ((n)) -#define strcpy(d, s) __builtin_strcpy ((d), (s)) -@end smallexample - -@item -fhosted -@opindex fhosted -@cindex hosted environment - -Assert that compilation targets a hosted environment. This implies -@option{-fbuiltin}. A hosted environment is one in which the -entire standard library is available, and in which @code{main} has a return -type of @code{int}. Examples are nearly everything except a kernel. -This is equivalent to @option{-fno-freestanding}. - -@item -ffreestanding -@opindex ffreestanding -@cindex hosted environment - -Assert that compilation targets a freestanding environment. This -implies @option{-fno-builtin}. A freestanding environment -is one in which the standard library may not exist, and program startup may -not necessarily be at @code{main}. The most obvious example is an OS kernel. -This is equivalent to @option{-fno-hosted}. - -@xref{Standards,,Language Standards Supported by GCC}, for details of -freestanding and hosted environments. - -@item -fopenmp -@opindex fopenmp -@cindex OpenMP parallel -Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and -@code{!$omp} in Fortran. When @option{-fopenmp} is specified, the -compiler generates parallel code according to the OpenMP Application -Program Interface v3.0 @w{@uref{http://www.openmp.org/}}. This option -implies @option{-pthread}, and thus is only supported on targets that -have support for @option{-pthread}. - -@item -fgnu-tm -@opindex fgnu-tm -When the option @option{-fgnu-tm} is specified, the compiler -generates code for the Linux variant of Intel's current Transactional -Memory ABI specification document (Revision 1.1, May 6 2009). This is -an experimental feature whose interface may change in future versions -of GCC, as the official specification changes. Please note that not -all architectures are supported for this feature. - -For more information on GCC's support for transactional memory, -@xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU -Transactional Memory Library}. - -Note that the transactional memory feature is not supported with -non-call exceptions (@option{-fnon-call-exceptions}). - -@item -fms-extensions -@opindex fms-extensions -Accept some non-standard constructs used in Microsoft header files. - -In C++ code, this allows member names in structures to be similar -to previous types declarations. - -@smallexample -typedef int UOW; -struct ABC @{ - UOW UOW; -@}; -@end smallexample - -Some cases of unnamed fields in structures and unions are only -accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union -fields within structs/unions}, for details. - -@item -fplan9-extensions -Accept some non-standard constructs used in Plan 9 code. - -This enables @option{-fms-extensions}, permits passing pointers to -structures with anonymous fields to functions that expect pointers to -elements of the type of the field, and permits referring to anonymous -fields declared using a typedef. @xref{Unnamed Fields,,Unnamed -struct/union fields within structs/unions}, for details. This is only -supported for C, not C++. - -@item -trigraphs -@opindex trigraphs -Support ISO C trigraphs. The @option{-ansi} option (and @option{-std} -options for strict ISO C conformance) implies @option{-trigraphs}. - -@cindex traditional C language -@cindex C language, traditional -@item -traditional -@itemx -traditional-cpp -@opindex traditional-cpp -@opindex traditional -Formerly, these options caused GCC to attempt to emulate a pre-standard -C compiler. They are now only supported with the @option{-E} switch. -The preprocessor continues to support a pre-standard mode. See the GNU -CPP manual for details. - -@item -fcond-mismatch -@opindex fcond-mismatch -Allow conditional expressions with mismatched types in the second and -third arguments. The value of such an expression is void. This option -is not supported for C++. - -@item -flax-vector-conversions -@opindex flax-vector-conversions -Allow implicit conversions between vectors with differing numbers of -elements and/or incompatible element types. This option should not be -used for new code. - -@item -funsigned-char -@opindex funsigned-char -Let the type @code{char} be unsigned, like @code{unsigned char}. - -Each kind of machine has a default for what @code{char} should -be. It is either like @code{unsigned char} by default or like -@code{signed char} by default. - -Ideally, a portable program should always use @code{signed char} or -@code{unsigned char} when it depends on the signedness of an object. -But many programs have been written to use plain @code{char} and -expect it to be signed, or expect it to be unsigned, depending on the -machines they were written for. This option, and its inverse, let you -make such a program work with the opposite default. - -The type @code{char} is always a distinct type from each of -@code{signed char} or @code{unsigned char}, even though its behavior -is always just like one of those two. - -@item -fsigned-char -@opindex fsigned-char -Let the type @code{char} be signed, like @code{signed char}. - -Note that this is equivalent to @option{-fno-unsigned-char}, which is -the negative form of @option{-funsigned-char}. Likewise, the option -@option{-fno-signed-char} is equivalent to @option{-funsigned-char}. - -@item -fsigned-bitfields -@itemx -funsigned-bitfields -@itemx -fno-signed-bitfields -@itemx -fno-unsigned-bitfields -@opindex fsigned-bitfields -@opindex funsigned-bitfields -@opindex fno-signed-bitfields -@opindex fno-unsigned-bitfields -These options control whether a bit-field is signed or unsigned, when the -declaration does not use either @code{signed} or @code{unsigned}. By -default, such a bit-field is signed, because this is consistent: the -basic integer types such as @code{int} are signed types. -@end table - -@node C++ Dialect Options -@section Options Controlling C++ Dialect - -@cindex compiler options, C++ -@cindex C++ options, command-line -@cindex options, C++ -This section describes the command-line options that are only meaningful -for C++ programs. You can also use most of the GNU compiler options -regardless of what language your program is in. For example, you -might compile a file @code{firstClass.C} like this: - -@smallexample -g++ -g -frepo -O -c firstClass.C -@end smallexample - -@noindent -In this example, only @option{-frepo} is an option meant -only for C++ programs; you can use the other options with any -language supported by GCC@. - -Here is a list of options that are @emph{only} for compiling C++ programs: - -@table @gcctabopt - -@item -fabi-version=@var{n} -@opindex fabi-version -Use version @var{n} of the C++ ABI@. The default is version 2. - -Version 0 refers to the version conforming most closely to -the C++ ABI specification. Therefore, the ABI obtained using version 0 -will change in different versions of G++ as ABI bugs are fixed. - -Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. - -Version 2 is the version of the C++ ABI that first appeared in G++ 3.4. - -Version 3 corrects an error in mangling a constant address as a -template argument. - -Version 4, which first appeared in G++ 4.5, implements a standard -mangling for vector types. - -Version 5, which first appeared in G++ 4.6, corrects the mangling of -attribute const/volatile on function pointer types, decltype of a -plain decl, and use of a function parameter in the declaration of -another parameter. - -Version 6, which first appeared in G++ 4.7, corrects the promotion -behavior of C++11 scoped enums and the mangling of template argument -packs, const/static_cast, prefix ++ and --, and a class scope function -used as a template argument. - -See also @option{-Wabi}. - -@item -fno-access-control -@opindex fno-access-control -Turn off all access checking. This switch is mainly useful for working -around bugs in the access control code. - -@item -fcheck-new -@opindex fcheck-new -Check that the pointer returned by @code{operator new} is non-null -before attempting to modify the storage allocated. This check is -normally unnecessary because the C++ standard specifies that -@code{operator new} only returns @code{0} if it is declared -@samp{throw()}, in which case the compiler always checks the -return value even without this option. In all other cases, when -@code{operator new} has a non-empty exception specification, memory -exhaustion is signalled by throwing @code{std::bad_alloc}. See also -@samp{new (nothrow)}. - -@item -fconstexpr-depth=@var{n} -@opindex fconstexpr-depth -Set the maximum nested evaluation depth for C++11 constexpr functions -to @var{n}. A limit is needed to detect endless recursion during -constant expression evaluation. The minimum specified by the standard -is 512. - -@item -fdeduce-init-list -@opindex fdeduce-init-list -Enable deduction of a template type parameter as -@code{std::initializer_list} from a brace-enclosed initializer list, i.e.@: - -@smallexample -template <class T> auto forward(T t) -> decltype (realfn (t)) -@{ - return realfn (t); -@} - -void f() -@{ - forward(@{1,2@}); // call forward<std::initializer_list<int>> -@} -@end smallexample - -This deduction was implemented as a possible extension to the -originally proposed semantics for the C++11 standard, but was not part -of the final standard, so it is disabled by default. This option is -deprecated, and may be removed in a future version of G++. - -@item -ffriend-injection -@opindex ffriend-injection -Inject friend functions into the enclosing namespace, so that they are -visible outside the scope of the class in which they are declared. -Friend functions were documented to work this way in the old Annotated -C++ Reference Manual, and versions of G++ before 4.1 always worked -that way. However, in ISO C++ a friend function that is not declared -in an enclosing scope can only be found using argument dependent -lookup. This option causes friends to be injected as they were in -earlier releases. - -This option is for compatibility, and may be removed in a future -release of G++. - -@item -fno-elide-constructors -@opindex fno-elide-constructors -The C++ standard allows an implementation to omit creating a temporary -that is only used to initialize another object of the same type. -Specifying this option disables that optimization, and forces G++ to -call the copy constructor in all cases. - -@item -fno-enforce-eh-specs -@opindex fno-enforce-eh-specs -Don't generate code to check for violation of exception specifications -at run time. This option violates the C++ standard, but may be useful -for reducing code size in production builds, much like defining -@samp{NDEBUG}. This does not give user code permission to throw -exceptions in violation of the exception specifications; the compiler -still optimizes based on the specifications, so throwing an -unexpected exception results in undefined behavior at run time. - -@item -fextern-tls-init -@itemx -fno-extern-tls-init -@opindex fextern-tls-init -@opindex fno-extern-tls-init -The C++11 and OpenMP standards allow @samp{thread_local} and -@samp{threadprivate} variables to have dynamic (runtime) -initialization. To support this, any use of such a variable goes -through a wrapper function that performs any necessary initialization. -When the use and definition of the variable are in the same -translation unit, this overhead can be optimized away, but when the -use is in a different translation unit there is significant overhead -even if the variable doesn't actually need dynamic initialization. If -the programmer can be sure that no use of the variable in a -non-defining TU needs to trigger dynamic initialization (either -because the variable is statically initialized, or a use of the -variable in the defining TU will be executed before any uses in -another TU), they can avoid this overhead with the -@option{-fno-extern-tls-init} option. - -On targets that support symbol aliases, the default is -@option{-fextern-tls-init}. On targets that do not support symbol -aliases, the default is @option{-fno-extern-tls-init}. - -@item -ffor-scope -@itemx -fno-for-scope -@opindex ffor-scope -@opindex fno-for-scope -If @option{-ffor-scope} is specified, the scope of variables declared in -a @i{for-init-statement} is limited to the @samp{for} loop itself, -as specified by the C++ standard. -If @option{-fno-for-scope} is specified, the scope of variables declared in -a @i{for-init-statement} extends to the end of the enclosing scope, -as was the case in old versions of G++, and other (traditional) -implementations of C++. - -If neither flag is given, the default is to follow the standard, -but to allow and give a warning for old-style code that would -otherwise be invalid, or have different behavior. - -@item -fno-gnu-keywords -@opindex fno-gnu-keywords -Do not recognize @code{typeof} as a keyword, so that code can use this -word as an identifier. You can use the keyword @code{__typeof__} instead. -@option{-ansi} implies @option{-fno-gnu-keywords}. - -@item -fno-implicit-templates -@opindex fno-implicit-templates -Never emit code for non-inline templates that are instantiated -implicitly (i.e.@: by use); only emit code for explicit instantiations. -@xref{Template Instantiation}, for more information. - -@item -fno-implicit-inline-templates -@opindex fno-implicit-inline-templates -Don't emit code for implicit instantiations of inline templates, either. -The default is to handle inlines differently so that compiles with and -without optimization need the same set of explicit instantiations. - -@item -fno-implement-inlines -@opindex fno-implement-inlines -To save space, do not emit out-of-line copies of inline functions -controlled by @samp{#pragma implementation}. This causes linker -errors if these functions are not inlined everywhere they are called. - -@item -fms-extensions -@opindex fms-extensions -Disable Wpedantic warnings about constructs used in MFC, such as implicit -int and getting a pointer to member function via non-standard syntax. - -@item -fno-nonansi-builtins -@opindex fno-nonansi-builtins -Disable built-in declarations of functions that are not mandated by -ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, -@code{index}, @code{bzero}, @code{conjf}, and other related functions. - -@item -fnothrow-opt -@opindex fnothrow-opt -Treat a @code{throw()} exception specification as if it were a -@code{noexcept} specification to reduce or eliminate the text size -overhead relative to a function with no exception specification. If -the function has local variables of types with non-trivial -destructors, the exception specification actually makes the -function smaller because the EH cleanups for those variables can be -optimized away. The semantic effect is that an exception thrown out of -a function with such an exception specification results in a call -to @code{terminate} rather than @code{unexpected}. - -@item -fno-operator-names -@opindex fno-operator-names -Do not treat the operator name keywords @code{and}, @code{bitand}, -@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as -synonyms as keywords. - -@item -fno-optional-diags -@opindex fno-optional-diags -Disable diagnostics that the standard says a compiler does not need to -issue. Currently, the only such diagnostic issued by G++ is the one for -a name having multiple meanings within a class. - -@item -fpermissive -@opindex fpermissive -Downgrade some diagnostics about nonconformant code from errors to -warnings. Thus, using @option{-fpermissive} allows some -nonconforming code to compile. - -@item -fno-pretty-templates -@opindex fno-pretty-templates -When an error message refers to a specialization of a function -template, the compiler normally prints the signature of the -template followed by the template arguments and any typedefs or -typenames in the signature (e.g. @code{void f(T) [with T = int]} -rather than @code{void f(int)}) so that it's clear which template is -involved. When an error message refers to a specialization of a class -template, the compiler omits any template arguments that match -the default template arguments for that template. If either of these -behaviors make it harder to understand the error message rather than -easier, you can use @option{-fno-pretty-templates} to disable them. - -@item -frepo -@opindex frepo -Enable automatic template instantiation at link time. This option also -implies @option{-fno-implicit-templates}. @xref{Template -Instantiation}, for more information. - -@item -fno-rtti -@opindex fno-rtti -Disable generation of information about every class with virtual -functions for use by the C++ run-time type identification features -(@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts -of the language, you can save some space by using this flag. Note that -exception handling uses the same information, but G++ generates it as -needed. The @samp{dynamic_cast} operator can still be used for casts that -do not require run-time type information, i.e.@: casts to @code{void *} or to -unambiguous base classes. - -@item -fstats -@opindex fstats -Emit statistics about front-end processing at the end of the compilation. -This information is generally only useful to the G++ development team. - -@item -fstrict-enums -@opindex fstrict-enums -Allow the compiler to optimize using the assumption that a value of -enumerated type can only be one of the values of the enumeration (as -defined in the C++ standard; basically, a value that can be -represented in the minimum number of bits needed to represent all the -enumerators). This assumption may not be valid if the program uses a -cast to convert an arbitrary integer value to the enumerated type. - -@item -ftemplate-backtrace-limit=@var{n} -@opindex ftemplate-backtrace-limit -Set the maximum number of template instantiation notes for a single -warning or error to @var{n}. The default value is 10. - -@item -ftemplate-depth=@var{n} -@opindex ftemplate-depth -Set the maximum instantiation depth for template classes to @var{n}. -A limit on the template instantiation depth is needed to detect -endless recursions during template class instantiation. ANSI/ISO C++ -conforming programs must not rely on a maximum depth greater than 17 -(changed to 1024 in C++11). The default value is 900, as the compiler -can run out of stack space before hitting 1024 in some situations. - -@item -fno-threadsafe-statics -@opindex fno-threadsafe-statics -Do not emit the extra code to use the routines specified in the C++ -ABI for thread-safe initialization of local statics. You can use this -option to reduce code size slightly in code that doesn't need to be -thread-safe. - -@item -fuse-cxa-atexit -@opindex fuse-cxa-atexit -Register destructors for objects with static storage duration with the -@code{__cxa_atexit} function rather than the @code{atexit} function. -This option is required for fully standards-compliant handling of static -destructors, but only works if your C library supports -@code{__cxa_atexit}. - -@item -fno-use-cxa-get-exception-ptr -@opindex fno-use-cxa-get-exception-ptr -Don't use the @code{__cxa_get_exception_ptr} runtime routine. This -causes @code{std::uncaught_exception} to be incorrect, but is necessary -if the runtime routine is not available. - -@item -fvisibility-inlines-hidden -@opindex fvisibility-inlines-hidden -This switch declares that the user does not attempt to compare -pointers to inline functions or methods where the addresses of the two functions -are taken in different shared objects. - -The effect of this is that GCC may, effectively, mark inline methods with -@code{__attribute__ ((visibility ("hidden")))} so that they do not -appear in the export table of a DSO and do not require a PLT indirection -when used within the DSO@. Enabling this option can have a dramatic effect -on load and link times of a DSO as it massively reduces the size of the -dynamic export table when the library makes heavy use of templates. - -The behavior of this switch is not quite the same as marking the -methods as hidden directly, because it does not affect static variables -local to the function or cause the compiler to deduce that -the function is defined in only one shared object. - -You may mark a method as having a visibility explicitly to negate the -effect of the switch for that method. For example, if you do want to -compare pointers to a particular inline method, you might mark it as -having default visibility. Marking the enclosing class with explicit -visibility has no effect. - -Explicitly instantiated inline methods are unaffected by this option -as their linkage might otherwise cross a shared library boundary. -@xref{Template Instantiation}. - -@item -fvisibility-ms-compat -@opindex fvisibility-ms-compat -This flag attempts to use visibility settings to make GCC's C++ -linkage model compatible with that of Microsoft Visual Studio. - -The flag makes these changes to GCC's linkage model: - -@enumerate -@item -It sets the default visibility to @code{hidden}, like -@option{-fvisibility=hidden}. - -@item -Types, but not their members, are not hidden by default. - -@item -The One Definition Rule is relaxed for types without explicit -visibility specifications that are defined in more than one -shared object: those declarations are permitted if they are -permitted when this option is not used. -@end enumerate - -In new code it is better to use @option{-fvisibility=hidden} and -export those classes that are intended to be externally visible. -Unfortunately it is possible for code to rely, perhaps accidentally, -on the Visual Studio behavior. - -Among the consequences of these changes are that static data members -of the same type with the same name but defined in different shared -objects are different, so changing one does not change the other; -and that pointers to function members defined in different shared -objects may not compare equal. When this flag is given, it is a -violation of the ODR to define types with the same name differently. - -@item -fno-weak -@opindex fno-weak -Do not use weak symbol support, even if it is provided by the linker. -By default, G++ uses weak symbols if they are available. This -option exists only for testing, and should not be used by end-users; -it results in inferior code and has no benefits. This option may -be removed in a future release of G++. - -@item -nostdinc++ -@opindex nostdinc++ -Do not search for header files in the standard directories specific to -C++, but do still search the other standard directories. (This option -is used when building the C++ library.) -@end table - -In addition, these optimization, warning, and code generation options -have meanings only for C++ programs: - -@table @gcctabopt -@item -fno-default-inline -@opindex fno-default-inline -Do not assume @samp{inline} for functions defined inside a class scope. -@xref{Optimize Options,,Options That Control Optimization}. Note that these -functions have linkage like inline functions; they just aren't -inlined by default. - -@item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)} -@opindex Wabi -@opindex Wno-abi -Warn when G++ generates code that is probably not compatible with the -vendor-neutral C++ ABI@. Although an effort has been made to warn about -all such cases, there are probably some cases that are not warned about, -even though G++ is generating incompatible code. There may also be -cases where warnings are emitted even though the code that is generated -is compatible. - -You should rewrite your code to avoid these warnings if you are -concerned about the fact that code generated by G++ may not be binary -compatible with code generated by other compilers. - -The known incompatibilities in @option{-fabi-version=2} (the default) include: - -@itemize @bullet - -@item -A template with a non-type template parameter of reference type is -mangled incorrectly: -@smallexample -extern int N; -template <int &> struct S @{@}; -void n (S<N>) @{2@} -@end smallexample - -This is fixed in @option{-fabi-version=3}. - -@item -SIMD vector types declared using @code{__attribute ((vector_size))} are -mangled in a non-standard way that does not allow for overloading of -functions taking vectors of different sizes. - -The mangling is changed in @option{-fabi-version=4}. -@end itemize - -The known incompatibilities in @option{-fabi-version=1} include: - -@itemize @bullet - -@item -Incorrect handling of tail-padding for bit-fields. G++ may attempt to -pack data into the same byte as a base class. For example: - -@smallexample -struct A @{ virtual void f(); int f1 : 1; @}; -struct B : public A @{ int f2 : 1; @}; -@end smallexample - -@noindent -In this case, G++ places @code{B::f2} into the same byte -as @code{A::f1}; other compilers do not. You can avoid this problem -by explicitly padding @code{A} so that its size is a multiple of the -byte size on your platform; that causes G++ and other compilers to -lay out @code{B} identically. - -@item -Incorrect handling of tail-padding for virtual bases. G++ does not use -tail padding when laying out virtual bases. For example: - -@smallexample -struct A @{ virtual void f(); char c1; @}; -struct B @{ B(); char c2; @}; -struct C : public A, public virtual B @{@}; -@end smallexample - -@noindent -In this case, G++ does not place @code{B} into the tail-padding for -@code{A}; other compilers do. You can avoid this problem by -explicitly padding @code{A} so that its size is a multiple of its -alignment (ignoring virtual base classes); that causes G++ and other -compilers to lay out @code{C} identically. - -@item -Incorrect handling of bit-fields with declared widths greater than that -of their underlying types, when the bit-fields appear in a union. For -example: - -@smallexample -union U @{ int i : 4096; @}; -@end smallexample - -@noindent -Assuming that an @code{int} does not have 4096 bits, G++ makes the -union too small by the number of bits in an @code{int}. - -@item -Empty classes can be placed at incorrect offsets. For example: - -@smallexample -struct A @{@}; - -struct B @{ - A a; - virtual void f (); -@}; - -struct C : public B, public A @{@}; -@end smallexample - -@noindent -G++ places the @code{A} base class of @code{C} at a nonzero offset; -it should be placed at offset zero. G++ mistakenly believes that the -@code{A} data member of @code{B} is already at offset zero. - -@item -Names of template functions whose types involve @code{typename} or -template template parameters can be mangled incorrectly. - -@smallexample -template <typename Q> -void f(typename Q::X) @{@} - -template <template <typename> class Q> -void f(typename Q<int>::X) @{@} -@end smallexample - -@noindent -Instantiations of these templates may be mangled incorrectly. - -@end itemize - -It also warns about psABI-related changes. The known psABI changes at this -point include: - -@itemize @bullet - -@item -For SysV/x86-64, unions with @code{long double} members are -passed in memory as specified in psABI. For example: - -@smallexample -union U @{ - long double ld; - int i; -@}; -@end smallexample - -@noindent -@code{union U} is always passed in memory. - -@end itemize - -@item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)} -@opindex Wctor-dtor-privacy -@opindex Wno-ctor-dtor-privacy -Warn when a class seems unusable because all the constructors or -destructors in that class are private, and it has neither friends nor -public static member functions. Also warn if there are no non-private -methods, and there's at least one private member function that isn't -a constructor or destructor. - -@item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)} -@opindex Wdelete-non-virtual-dtor -@opindex Wno-delete-non-virtual-dtor -Warn when @samp{delete} is used to destroy an instance of a class that -has virtual functions and non-virtual destructor. It is unsafe to delete -an instance of a derived class through a pointer to a base class if the -base class does not have a virtual destructor. This warning is enabled -by @option{-Wall}. - -@item -Wliteral-suffix @r{(C++ and Objective-C++ only)} -@opindex Wliteral-suffix -@opindex Wno-literal-suffix -Warn when a string or character literal is followed by a ud-suffix which does -not begin with an underscore. As a conforming extension, GCC treats such -suffixes as separate preprocessing tokens in order to maintain backwards -compatibility with code that uses formatting macros from @code{<inttypes.h>}. -For example: - -@smallexample -#define __STDC_FORMAT_MACROS -#include <inttypes.h> -#include <stdio.h> - -int main() @{ - int64_t i64 = 123; - printf("My int64: %"PRId64"\n", i64); -@} -@end smallexample - -In this case, @code{PRId64} is treated as a separate preprocessing token. - -This warning is enabled by default. - -@item -Wnarrowing @r{(C++ and Objective-C++ only)} -@opindex Wnarrowing -@opindex Wno-narrowing -Warn when a narrowing conversion prohibited by C++11 occurs within -@samp{@{ @}}, e.g. - -@smallexample -int i = @{ 2.2 @}; // error: narrowing from double to int -@end smallexample - -This flag is included in @option{-Wall} and @option{-Wc++11-compat}. - -With @option{-std=c++11}, @option{-Wno-narrowing} suppresses the diagnostic -required by the standard. Note that this does not affect the meaning -of well-formed code; narrowing conversions are still considered -ill-formed in SFINAE context. - -@item -Wnoexcept @r{(C++ and Objective-C++ only)} -@opindex Wnoexcept -@opindex Wno-noexcept -Warn when a noexcept-expression evaluates to false because of a call -to a function that does not have a non-throwing exception -specification (i.e. @samp{throw()} or @samp{noexcept}) but is known by -the compiler to never throw an exception. - -@item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)} -@opindex Wnon-virtual-dtor -@opindex Wno-non-virtual-dtor -Warn when a class has virtual functions and an accessible non-virtual -destructor, in which case it is possible but unsafe to delete -an instance of a derived class through a pointer to the base class. -This warning is also enabled if @option{-Weffc++} is specified. - -@item -Wreorder @r{(C++ and Objective-C++ only)} -@opindex Wreorder -@opindex Wno-reorder -@cindex reordering, warning -@cindex warning for reordering of member initializers -Warn when the order of member initializers given in the code does not -match the order in which they must be executed. For instance: - -@smallexample -struct A @{ - int i; - int j; - A(): j (0), i (1) @{ @} -@}; -@end smallexample - -@noindent -The compiler rearranges the member initializers for @samp{i} -and @samp{j} to match the declaration order of the members, emitting -a warning to that effect. This warning is enabled by @option{-Wall}. - -@item -fext-numeric-literals @r{(C++ and Objective-C++ only)} -@opindex fext-numeric-literals -@opindex fno-ext-numeric-literals -Accept imaginary, fixed-point, or machine-defined -literal number suffixes as GNU extensions. -When this option is turned off these suffixes are treated -as C++11 user-defined literal numeric suffixes. -This is on by default for all pre-C++11 dialects and all GNU dialects: -@option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11}, -@option{-std=gnu++1y}. -This option is off by default -for ISO C++11 onwards (@option{-std=c++11}, ...). -@end table - -The following @option{-W@dots{}} options are not affected by @option{-Wall}. - -@table @gcctabopt -@item -Weffc++ @r{(C++ and Objective-C++ only)} -@opindex Weffc++ -@opindex Wno-effc++ -Warn about violations of the following style guidelines from Scott Meyers' -@cite{Effective C++, Second Edition} book: - -@itemize @bullet -@item -Item 11: Define a copy constructor and an assignment operator for classes -with dynamically-allocated memory. - -@item -Item 12: Prefer initialization to assignment in constructors. - -@item -Item 14: Make destructors virtual in base classes. - -@item -Item 15: Have @code{operator=} return a reference to @code{*this}. - -@item -Item 23: Don't try to return a reference when you must return an object. - -@end itemize - -Also warn about violations of the following style guidelines from -Scott Meyers' @cite{More Effective C++} book: - -@itemize @bullet -@item -Item 6: Distinguish between prefix and postfix forms of increment and -decrement operators. - -@item -Item 7: Never overload @code{&&}, @code{||}, or @code{,}. - -@end itemize - -When selecting this option, be aware that the standard library -headers do not obey all of these guidelines; use @samp{grep -v} -to filter out those warnings. - -@item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)} -@opindex Wstrict-null-sentinel -@opindex Wno-strict-null-sentinel -Warn about the use of an uncasted @code{NULL} as sentinel. When -compiling only with GCC this is a valid sentinel, as @code{NULL} is defined -to @code{__null}. Although it is a null pointer constant rather than a -null pointer, it is guaranteed to be of the same size as a pointer. -But this use is not portable across different compilers. - -@item -Wno-non-template-friend @r{(C++ and Objective-C++ only)} -@opindex Wno-non-template-friend -@opindex Wnon-template-friend -Disable warnings when non-templatized friend functions are declared -within a template. Since the advent of explicit template specification -support in G++, if the name of the friend is an unqualified-id (i.e., -@samp{friend foo(int)}), the C++ language specification demands that the -friend declare or define an ordinary, nontemplate function. (Section -14.5.3). Before G++ implemented explicit specification, unqualified-ids -could be interpreted as a particular specialization of a templatized -function. Because this non-conforming behavior is no longer the default -behavior for G++, @option{-Wnon-template-friend} allows the compiler to -check existing code for potential trouble spots and is on by default. -This new compiler behavior can be turned off with -@option{-Wno-non-template-friend}, which keeps the conformant compiler code -but disables the helpful warning. - -@item -Wold-style-cast @r{(C++ and Objective-C++ only)} -@opindex Wold-style-cast -@opindex Wno-old-style-cast -Warn if an old-style (C-style) cast to a non-void type is used within -a C++ program. The new-style casts (@samp{dynamic_cast}, -@samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are -less vulnerable to unintended effects and much easier to search for. - -@item -Woverloaded-virtual @r{(C++ and Objective-C++ only)} -@opindex Woverloaded-virtual -@opindex Wno-overloaded-virtual -@cindex overloaded virtual function, warning -@cindex warning for overloaded virtual function -Warn when a function declaration hides virtual functions from a -base class. For example, in: - -@smallexample -struct A @{ - virtual void f(); -@}; - -struct B: public A @{ - void f(int); -@}; -@end smallexample - -the @code{A} class version of @code{f} is hidden in @code{B}, and code -like: - -@smallexample -B* b; -b->f(); -@end smallexample - -@noindent -fails to compile. - -@item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)} -@opindex Wno-pmf-conversions -@opindex Wpmf-conversions -Disable the diagnostic for converting a bound pointer to member function -to a plain pointer. - -@item -Wsign-promo @r{(C++ and Objective-C++ only)} -@opindex Wsign-promo -@opindex Wno-sign-promo -Warn when overload resolution chooses a promotion from unsigned or -enumerated type to a signed type, over a conversion to an unsigned type of -the same size. Previous versions of G++ tried to preserve -unsignedness, but the standard mandates the current behavior. -@end table - -@node Objective-C and Objective-C++ Dialect Options -@section Options Controlling Objective-C and Objective-C++ Dialects - -@cindex compiler options, Objective-C and Objective-C++ -@cindex Objective-C and Objective-C++ options, command-line -@cindex options, Objective-C and Objective-C++ -(NOTE: This manual does not describe the Objective-C and Objective-C++ -languages themselves. @xref{Standards,,Language Standards -Supported by GCC}, for references.) - -This section describes the command-line options that are only meaningful -for Objective-C and Objective-C++ programs. You can also use most of -the language-independent GNU compiler options. -For example, you might compile a file @code{some_class.m} like this: - -@smallexample -gcc -g -fgnu-runtime -O -c some_class.m -@end smallexample - -@noindent -In this example, @option{-fgnu-runtime} is an option meant only for -Objective-C and Objective-C++ programs; you can use the other options with -any language supported by GCC@. - -Note that since Objective-C is an extension of the C language, Objective-C -compilations may also use options specific to the C front-end (e.g., -@option{-Wtraditional}). Similarly, Objective-C++ compilations may use -C++-specific options (e.g., @option{-Wabi}). - -Here is a list of options that are @emph{only} for compiling Objective-C -and Objective-C++ programs: - -@table @gcctabopt -@item -fconstant-string-class=@var{class-name} -@opindex fconstant-string-class -Use @var{class-name} as the name of the class to instantiate for each -literal string specified with the syntax @code{@@"@dots{}"}. The default -class name is @code{NXConstantString} if the GNU runtime is being used, and -@code{NSConstantString} if the NeXT runtime is being used (see below). The -@option{-fconstant-cfstrings} option, if also present, overrides the -@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals -to be laid out as constant CoreFoundation strings. - -@item -fgnu-runtime -@opindex fgnu-runtime -Generate object code compatible with the standard GNU Objective-C -runtime. This is the default for most types of systems. - -@item -fnext-runtime -@opindex fnext-runtime -Generate output compatible with the NeXT runtime. This is the default -for NeXT-based systems, including Darwin and Mac OS X@. The macro -@code{__NEXT_RUNTIME__} is predefined if (and only if) this option is -used. - -@item -fno-nil-receivers -@opindex fno-nil-receivers -Assume that all Objective-C message dispatches (@code{[receiver -message:arg]}) in this translation unit ensure that the receiver is -not @code{nil}. This allows for more efficient entry points in the -runtime to be used. This option is only available in conjunction with -the NeXT runtime and ABI version 0 or 1. - -@item -fobjc-abi-version=@var{n} -@opindex fobjc-abi-version -Use version @var{n} of the Objective-C ABI for the selected runtime. -This option is currently supported only for the NeXT runtime. In that -case, Version 0 is the traditional (32-bit) ABI without support for -properties and other Objective-C 2.0 additions. Version 1 is the -traditional (32-bit) ABI with support for properties and other -Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If -nothing is specified, the default is Version 0 on 32-bit target -machines, and Version 2 on 64-bit target machines. - -@item -fobjc-call-cxx-cdtors -@opindex fobjc-call-cxx-cdtors -For each Objective-C class, check if any of its instance variables is a -C++ object with a non-trivial default constructor. If so, synthesize a -special @code{- (id) .cxx_construct} instance method which runs -non-trivial default constructors on any such instance variables, in order, -and then return @code{self}. Similarly, check if any instance variable -is a C++ object with a non-trivial destructor, and if so, synthesize a -special @code{- (void) .cxx_destruct} method which runs -all such default destructors, in reverse order. - -The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} -methods thusly generated only operate on instance variables -declared in the current Objective-C class, and not those inherited -from superclasses. It is the responsibility of the Objective-C -runtime to invoke all such methods in an object's inheritance -hierarchy. The @code{- (id) .cxx_construct} methods are invoked -by the runtime immediately after a new object instance is allocated; -the @code{- (void) .cxx_destruct} methods are invoked immediately -before the runtime deallocates an object instance. - -As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has -support for invoking the @code{- (id) .cxx_construct} and -@code{- (void) .cxx_destruct} methods. - -@item -fobjc-direct-dispatch -@opindex fobjc-direct-dispatch -Allow fast jumps to the message dispatcher. On Darwin this is -accomplished via the comm page. - -@item -fobjc-exceptions -@opindex fobjc-exceptions -Enable syntactic support for structured exception handling in -Objective-C, similar to what is offered by C++ and Java. This option -is required to use the Objective-C keywords @code{@@try}, -@code{@@throw}, @code{@@catch}, @code{@@finally} and -@code{@@synchronized}. This option is available with both the GNU -runtime and the NeXT runtime (but not available in conjunction with -the NeXT runtime on Mac OS X 10.2 and earlier). - -@item -fobjc-gc -@opindex fobjc-gc -Enable garbage collection (GC) in Objective-C and Objective-C++ -programs. This option is only available with the NeXT runtime; the -GNU runtime has a different garbage collection implementation that -does not require special compiler flags. - -@item -fobjc-nilcheck -@opindex fobjc-nilcheck -For the NeXT runtime with version 2 of the ABI, check for a nil -receiver in method invocations before doing the actual method call. -This is the default and can be disabled using -@option{-fno-objc-nilcheck}. Class methods and super calls are never -checked for nil in this way no matter what this flag is set to. -Currently this flag does nothing when the GNU runtime, or an older -version of the NeXT runtime ABI, is used. - -@item -fobjc-std=objc1 -@opindex fobjc-std -Conform to the language syntax of Objective-C 1.0, the language -recognized by GCC 4.0. This only affects the Objective-C additions to -the C/C++ language; it does not affect conformance to C/C++ standards, -which is controlled by the separate C/C++ dialect option flags. When -this option is used with the Objective-C or Objective-C++ compiler, -any Objective-C syntax that is not recognized by GCC 4.0 is rejected. -This is useful if you need to make sure that your Objective-C code can -be compiled with older versions of GCC@. - -@item -freplace-objc-classes -@opindex freplace-objc-classes -Emit a special marker instructing @command{ld(1)} not to statically link in -the resulting object file, and allow @command{dyld(1)} to load it in at -run time instead. This is used in conjunction with the Fix-and-Continue -debugging mode, where the object file in question may be recompiled and -dynamically reloaded in the course of program execution, without the need -to restart the program itself. Currently, Fix-and-Continue functionality -is only available in conjunction with the NeXT runtime on Mac OS X 10.3 -and later. - -@item -fzero-link -@opindex fzero-link -When compiling for the NeXT runtime, the compiler ordinarily replaces calls -to @code{objc_getClass("@dots{}")} (when the name of the class is known at -compile time) with static class references that get initialized at load time, -which improves run-time performance. Specifying the @option{-fzero-link} flag -suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} -to be retained. This is useful in Zero-Link debugging mode, since it allows -for individual class implementations to be modified during program execution. -The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")} -regardless of command-line options. - -@item -gen-decls -@opindex gen-decls -Dump interface declarations for all classes seen in the source file to a -file named @file{@var{sourcename}.decl}. - -@item -Wassign-intercept @r{(Objective-C and Objective-C++ only)} -@opindex Wassign-intercept -@opindex Wno-assign-intercept -Warn whenever an Objective-C assignment is being intercepted by the -garbage collector. - -@item -Wno-protocol @r{(Objective-C and Objective-C++ only)} -@opindex Wno-protocol -@opindex Wprotocol -If a class is declared to implement a protocol, a warning is issued for -every method in the protocol that is not implemented by the class. The -default behavior is to issue a warning for every method not explicitly -implemented in the class, even if a method implementation is inherited -from the superclass. If you use the @option{-Wno-protocol} option, then -methods inherited from the superclass are considered to be implemented, -and no warning is issued for them. - -@item -Wselector @r{(Objective-C and Objective-C++ only)} -@opindex Wselector -@opindex Wno-selector -Warn if multiple methods of different types for the same selector are -found during compilation. The check is performed on the list of methods -in the final stage of compilation. Additionally, a check is performed -for each selector appearing in a @code{@@selector(@dots{})} -expression, and a corresponding method for that selector has been found -during compilation. Because these checks scan the method table only at -the end of compilation, these warnings are not produced if the final -stage of compilation is not reached, for example because an error is -found during compilation, or because the @option{-fsyntax-only} option is -being used. - -@item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)} -@opindex Wstrict-selector-match -@opindex Wno-strict-selector-match -Warn if multiple methods with differing argument and/or return types are -found for a given selector when attempting to send a message using this -selector to a receiver of type @code{id} or @code{Class}. When this flag -is off (which is the default behavior), the compiler omits such warnings -if any differences found are confined to types that share the same size -and alignment. - -@item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)} -@opindex Wundeclared-selector -@opindex Wno-undeclared-selector -Warn if a @code{@@selector(@dots{})} expression referring to an -undeclared selector is found. A selector is considered undeclared if no -method with that name has been declared before the -@code{@@selector(@dots{})} expression, either explicitly in an -@code{@@interface} or @code{@@protocol} declaration, or implicitly in -an @code{@@implementation} section. This option always performs its -checks as soon as a @code{@@selector(@dots{})} expression is found, -while @option{-Wselector} only performs its checks in the final stage of -compilation. This also enforces the coding style convention -that methods and selectors must be declared before being used. - -@item -print-objc-runtime-info -@opindex print-objc-runtime-info -Generate C header describing the largest structure that is passed by -value, if any. - -@end table - -@node Language Independent Options -@section Options to Control Diagnostic Messages Formatting -@cindex options to control diagnostics formatting -@cindex diagnostic messages -@cindex message formatting - -Traditionally, diagnostic messages have been formatted irrespective of -the output device's aspect (e.g.@: its width, @dots{}). You can use the -options described below -to control the formatting algorithm for diagnostic messages, -e.g.@: how many characters per line, how often source location -information should be reported. Note that some language front ends may not -honor these options. - -@table @gcctabopt -@item -fmessage-length=@var{n} -@opindex fmessage-length -Try to format error messages so that they fit on lines of about @var{n} -characters. The default is 72 characters for @command{g++} and 0 for the rest of -the front ends supported by GCC@. If @var{n} is zero, then no -line-wrapping is done; each error message appears on a single -line. - -@item -fdiagnostics-show-location=once -@opindex fdiagnostics-show-location -Only meaningful in line-wrapping mode. Instructs the diagnostic messages -reporter to emit source location information @emph{once}; that is, in -case the message is too long to fit on a single physical line and has to -be wrapped, the source location won't be emitted (as prefix) again, -over and over, in subsequent continuation lines. This is the default -behavior. - -@item -fdiagnostics-show-location=every-line -Only meaningful in line-wrapping mode. Instructs the diagnostic -messages reporter to emit the same source location information (as -prefix) for physical lines that result from the process of breaking -a message which is too long to fit on a single line. - -@item -fno-diagnostics-show-option -@opindex fno-diagnostics-show-option -@opindex fdiagnostics-show-option -By default, each diagnostic emitted includes text indicating the -command-line option that directly controls the diagnostic (if such an -option is known to the diagnostic machinery). Specifying the -@option{-fno-diagnostics-show-option} flag suppresses that behavior. - -@item -fno-diagnostics-show-caret -@opindex fno-diagnostics-show-caret -@opindex fdiagnostics-show-caret -By default, each diagnostic emitted includes the original source line -and a caret '^' indicating the column. This option suppresses this -information. - -@end table - -@node Warning Options -@section Options to Request or Suppress Warnings -@cindex options to control warnings -@cindex warning messages -@cindex messages, warning -@cindex suppressing warnings - -Warnings are diagnostic messages that report constructions that -are not inherently erroneous but that are risky or suggest there -may have been an error. - -The following language-independent options do not enable specific -warnings but control the kinds of diagnostics produced by GCC@. - -@table @gcctabopt -@cindex syntax checking -@item -fsyntax-only -@opindex fsyntax-only -Check the code for syntax errors, but don't do anything beyond that. - -@item -fmax-errors=@var{n} -@opindex fmax-errors -Limits the maximum number of error messages to @var{n}, at which point -GCC bails out rather than attempting to continue processing the source -code. If @var{n} is 0 (the default), there is no limit on the number -of error messages produced. If @option{-Wfatal-errors} is also -specified, then @option{-Wfatal-errors} takes precedence over this -option. - -@item -w -@opindex w -Inhibit all warning messages. - -@item -Werror -@opindex Werror -@opindex Wno-error -Make all warnings into errors. - -@item -Werror= -@opindex Werror= -@opindex Wno-error= -Make the specified warning into an error. The specifier for a warning -is appended; for example @option{-Werror=switch} turns the warnings -controlled by @option{-Wswitch} into errors. This switch takes a -negative form, to be used to negate @option{-Werror} for specific -warnings; for example @option{-Wno-error=switch} makes -@option{-Wswitch} warnings not be errors, even when @option{-Werror} -is in effect. - -The warning message for each controllable warning includes the -option that controls the warning. That option can then be used with -@option{-Werror=} and @option{-Wno-error=} as described above. -(Printing of the option in the warning message can be disabled using the -@option{-fno-diagnostics-show-option} flag.) - -Note that specifying @option{-Werror=}@var{foo} automatically implies -@option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not -imply anything. - -@item -Wfatal-errors -@opindex Wfatal-errors -@opindex Wno-fatal-errors -This option causes the compiler to abort compilation on the first error -occurred rather than trying to keep going and printing further error -messages. - -@end table - -You can request many specific warnings with options beginning with -@samp{-W}, for example @option{-Wimplicit} to request warnings on -implicit declarations. Each of these specific warning options also -has a negative form beginning @samp{-Wno-} to turn off warnings; for -example, @option{-Wno-implicit}. This manual lists only one of the -two forms, whichever is not the default. For further -language-specific options also refer to @ref{C++ Dialect Options} and -@ref{Objective-C and Objective-C++ Dialect Options}. - -When an unrecognized warning option is requested (e.g., -@option{-Wunknown-warning}), GCC emits a diagnostic stating -that the option is not recognized. However, if the @option{-Wno-} form -is used, the behavior is slightly different: no diagnostic is -produced for @option{-Wno-unknown-warning} unless other diagnostics -are being produced. This allows the use of new @option{-Wno-} options -with old compilers, but if something goes wrong, the compiler -warns that an unrecognized option is present. - -@table @gcctabopt -@item -Wpedantic -@itemx -pedantic -@opindex pedantic -@opindex Wpedantic -Issue all the warnings demanded by strict ISO C and ISO C++; -reject all programs that use forbidden extensions, and some other -programs that do not follow ISO C and ISO C++. For ISO C, follows the -version of the ISO C standard specified by any @option{-std} option used. - -Valid ISO C and ISO C++ programs should compile properly with or without -this option (though a rare few require @option{-ansi} or a -@option{-std} option specifying the required version of ISO C)@. However, -without this option, certain GNU extensions and traditional C and C++ -features are supported as well. With this option, they are rejected. - -@option{-Wpedantic} does not cause warning messages for use of the -alternate keywords whose names begin and end with @samp{__}. Pedantic -warnings are also disabled in the expression that follows -@code{__extension__}. However, only system header files should use -these escape routes; application programs should avoid them. -@xref{Alternate Keywords}. - -Some users try to use @option{-Wpedantic} to check programs for strict ISO -C conformance. They soon find that it does not do quite what they want: -it finds some non-ISO practices, but not all---only those for which -ISO C @emph{requires} a diagnostic, and some others for which -diagnostics have been added. - -A feature to report any failure to conform to ISO C might be useful in -some instances, but would require considerable additional work and would -be quite different from @option{-Wpedantic}. We don't have plans to -support such a feature in the near future. - -Where the standard specified with @option{-std} represents a GNU -extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a -corresponding @dfn{base standard}, the version of ISO C on which the GNU -extended dialect is based. Warnings from @option{-Wpedantic} are given -where they are required by the base standard. (It does not make sense -for such warnings to be given only for features not in the specified GNU -C dialect, since by definition the GNU dialects of C include all -features the compiler supports with the given option, and there would be -nothing to warn about.) - -@item -pedantic-errors -@opindex pedantic-errors -Like @option{-Wpedantic}, except that errors are produced rather than -warnings. - -@item -Wall -@opindex Wall -@opindex Wno-all -This enables all the warnings about constructions that some users -consider questionable, and that are easy to avoid (or modify to -prevent the warning), even in conjunction with macros. This also -enables some language-specific warnings described in @ref{C++ Dialect -Options} and @ref{Objective-C and Objective-C++ Dialect Options}. - -@option{-Wall} turns on the following warning flags: - -@gccoptlist{-Waddress @gol --Warray-bounds @r{(only with} @option{-O2}@r{)} @gol --Wc++11-compat @gol --Wchar-subscripts @gol --Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol --Wimplicit-int @r{(C and Objective-C only)} @gol --Wimplicit-function-declaration @r{(C and Objective-C only)} @gol --Wcomment @gol --Wformat @gol --Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol --Wmaybe-uninitialized @gol --Wmissing-braces @r{(only for C/ObjC)} @gol --Wnonnull @gol --Wparentheses @gol --Wpointer-sign @gol --Wreorder @gol --Wreturn-type @gol --Wsequence-point @gol --Wsign-compare @r{(only in C++)} @gol --Wstrict-aliasing @gol --Wstrict-overflow=1 @gol --Wswitch @gol --Wtrigraphs @gol --Wuninitialized @gol --Wunknown-pragmas @gol --Wunused-function @gol --Wunused-label @gol --Wunused-value @gol --Wunused-variable @gol --Wvolatile-register-var @gol -} - -Note that some warning flags are not implied by @option{-Wall}. Some of -them warn about constructions that users generally do not consider -questionable, but which occasionally you might wish to check for; -others warn about constructions that are necessary or hard to avoid in -some cases, and there is no simple way to modify the code to suppress -the warning. Some of them are enabled by @option{-Wextra} but many of -them must be enabled individually. - -@item -Wextra -@opindex W -@opindex Wextra -@opindex Wno-extra -This enables some extra warning flags that are not enabled by -@option{-Wall}. (This option used to be called @option{-W}. The older -name is still supported, but the newer name is more descriptive.) - -@gccoptlist{-Wclobbered @gol --Wempty-body @gol --Wignored-qualifiers @gol --Wmissing-field-initializers @gol --Wmissing-parameter-type @r{(C only)} @gol --Wold-style-declaration @r{(C only)} @gol --Woverride-init @gol --Wsign-compare @gol --Wtype-limits @gol --Wuninitialized @gol --Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol --Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol -} - -The option @option{-Wextra} also prints warning messages for the -following cases: - -@itemize @bullet - -@item -A pointer is compared against integer zero with @samp{<}, @samp{<=}, -@samp{>}, or @samp{>=}. - -@item -(C++ only) An enumerator and a non-enumerator both appear in a -conditional expression. - -@item -(C++ only) Ambiguous virtual bases. - -@item -(C++ only) Subscripting an array that has been declared @samp{register}. - -@item -(C++ only) Taking the address of a variable that has been declared -@samp{register}. - -@item -(C++ only) A base class is not initialized in a derived class's copy -constructor. - -@end itemize - -@item -Wchar-subscripts -@opindex Wchar-subscripts -@opindex Wno-char-subscripts -Warn if an array subscript has type @code{char}. This is a common cause -of error, as programmers often forget that this type is signed on some -machines. -This warning is enabled by @option{-Wall}. - -@item -Wcomment -@opindex Wcomment -@opindex Wno-comment -Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} -comment, or whenever a Backslash-Newline appears in a @samp{//} comment. -This warning is enabled by @option{-Wall}. - -@item -Wno-coverage-mismatch -@opindex Wno-coverage-mismatch -Warn if feedback profiles do not match when using the -@option{-fprofile-use} option. -If a source file is changed between compiling with @option{-fprofile-gen} and -with @option{-fprofile-use}, the files with the profile feedback can fail -to match the source file and GCC cannot use the profile feedback -information. By default, this warning is enabled and is treated as an -error. @option{-Wno-coverage-mismatch} can be used to disable the -warning or @option{-Wno-error=coverage-mismatch} can be used to -disable the error. Disabling the error for this warning can result in -poorly optimized code and is useful only in the -case of very minor changes such as bug fixes to an existing code-base. -Completely disabling the warning is not recommended. - -@item -Wno-cpp -@r{(C, Objective-C, C++, Objective-C++ and Fortran only)} - -Suppress warning messages emitted by @code{#warning} directives. - -@item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)} -@opindex Wdouble-promotion -@opindex Wno-double-promotion -Give a warning when a value of type @code{float} is implicitly -promoted to @code{double}. CPUs with a 32-bit ``single-precision'' -floating-point unit implement @code{float} in hardware, but emulate -@code{double} in software. On such a machine, doing computations -using @code{double} values is much more expensive because of the -overhead required for software emulation. - -It is easy to accidentally do computations with @code{double} because -floating-point literals are implicitly of type @code{double}. For -example, in: -@smallexample -@group -float area(float radius) -@{ - return 3.14159 * radius * radius; -@} -@end group -@end smallexample -the compiler performs the entire computation with @code{double} -because the floating-point literal is a @code{double}. - -@item -Wformat -@itemx -Wformat=@var{n} -@opindex Wformat -@opindex Wno-format -@opindex ffreestanding -@opindex fno-builtin -@opindex Wformat= -Check calls to @code{printf} and @code{scanf}, etc., to make sure that -the arguments supplied have types appropriate to the format string -specified, and that the conversions specified in the format string make -sense. This includes standard functions, and others specified by format -attributes (@pxref{Function Attributes}), in the @code{printf}, -@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, -not in the C standard) families (or other target-specific families). -Which functions are checked without format attributes having been -specified depends on the standard version selected, and such checks of -functions without the attribute specified are disabled by -@option{-ffreestanding} or @option{-fno-builtin}. - -The formats are checked against the format features supported by GNU -libc version 2.2. These include all ISO C90 and C99 features, as well -as features from the Single Unix Specification and some BSD and GNU -extensions. Other library implementations may not support all these -features; GCC does not support warning about features that go beyond a -particular library's limitations. However, if @option{-Wpedantic} is used -with @option{-Wformat}, warnings are given about format features not -in the selected standard version (but not for @code{strfmon} formats, -since those are not in any version of the C standard). @xref{C Dialect -Options,,Options Controlling C Dialect}. - -@table @gcctabopt -@item -Wformat=1 -@itemx -Wformat -Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and -@option{-Wno-format} is equivalent to @option{-Wformat=0}. Since -@option{-Wformat} also checks for null format arguments for several -functions, @option{-Wformat} also implies @option{-Wnonnull}. Some -aspects of this level of format checking can be disabled by the -options: @option{-Wno-format-contains-nul}, -@option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}. -@option{-Wformat} is enabled by @option{-Wall}. - -@item -Wno-format-contains-nul -@opindex Wno-format-contains-nul -@opindex Wformat-contains-nul -If @option{-Wformat} is specified, do not warn about format strings that -contain NUL bytes. - -@item -Wno-format-extra-args -@opindex Wno-format-extra-args -@opindex Wformat-extra-args -If @option{-Wformat} is specified, do not warn about excess arguments to a -@code{printf} or @code{scanf} format function. The C standard specifies -that such arguments are ignored. - -Where the unused arguments lie between used arguments that are -specified with @samp{$} operand number specifications, normally -warnings are still given, since the implementation could not know what -type to pass to @code{va_arg} to skip the unused arguments. However, -in the case of @code{scanf} formats, this option suppresses the -warning if the unused arguments are all pointers, since the Single -Unix Specification says that such unused arguments are allowed. - -@item -Wno-format-zero-length -@opindex Wno-format-zero-length -@opindex Wformat-zero-length -If @option{-Wformat} is specified, do not warn about zero-length formats. -The C standard specifies that zero-length formats are allowed. - - -@item -Wformat=2 -Enable @option{-Wformat} plus additional format checks. Currently -equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security --Wformat-y2k}. - -@item -Wformat-nonliteral -@opindex Wformat-nonliteral -@opindex Wno-format-nonliteral -If @option{-Wformat} is specified, also warn if the format string is not a -string literal and so cannot be checked, unless the format function -takes its format arguments as a @code{va_list}. - -@item -Wformat-security -@opindex Wformat-security -@opindex Wno-format-security -If @option{-Wformat} is specified, also warn about uses of format -functions that represent possible security problems. At present, this -warns about calls to @code{printf} and @code{scanf} functions where the -format string is not a string literal and there are no format arguments, -as in @code{printf (foo);}. This may be a security hole if the format -string came from untrusted input and contains @samp{%n}. (This is -currently a subset of what @option{-Wformat-nonliteral} warns about, but -in future warnings may be added to @option{-Wformat-security} that are not -included in @option{-Wformat-nonliteral}.) - -@item -Wformat-y2k -@opindex Wformat-y2k -@opindex Wno-format-y2k -If @option{-Wformat} is specified, also warn about @code{strftime} -formats that may yield only a two-digit year. -@end table - -@item -Wnonnull -@opindex Wnonnull -@opindex Wno-nonnull -Warn about passing a null pointer for arguments marked as -requiring a non-null value by the @code{nonnull} function attribute. - -@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It -can be disabled with the @option{-Wno-nonnull} option. - -@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)} -@opindex Winit-self -@opindex Wno-init-self -Warn about uninitialized variables that are initialized with themselves. -Note this option can only be used with the @option{-Wuninitialized} option. - -For example, GCC warns about @code{i} being uninitialized in the -following snippet only when @option{-Winit-self} has been specified: -@smallexample -@group -int f() -@{ - int i = i; - return i; -@} -@end group -@end smallexample - -This warning is enabled by @option{-Wall} in C++. - -@item -Wimplicit-int @r{(C and Objective-C only)} -@opindex Wimplicit-int -@opindex Wno-implicit-int -Warn when a declaration does not specify a type. -This warning is enabled by @option{-Wall}. - -@item -Wimplicit-function-declaration @r{(C and Objective-C only)} -@opindex Wimplicit-function-declaration -@opindex Wno-implicit-function-declaration -Give a warning whenever a function is used before being declared. In -C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is -enabled by default and it is made into an error by -@option{-pedantic-errors}. This warning is also enabled by -@option{-Wall}. - -@item -Wimplicit @r{(C and Objective-C only)} -@opindex Wimplicit -@opindex Wno-implicit -Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. -This warning is enabled by @option{-Wall}. - -@item -Wignored-qualifiers @r{(C and C++ only)} -@opindex Wignored-qualifiers -@opindex Wno-ignored-qualifiers -Warn if the return type of a function has a type qualifier -such as @code{const}. For ISO C such a type qualifier has no effect, -since the value returned by a function is not an lvalue. -For C++, the warning is only emitted for scalar types or @code{void}. -ISO C prohibits qualified @code{void} return types on function -definitions, so such return types always receive a warning -even without this option. - -This warning is also enabled by @option{-Wextra}. - -@item -Wmain -@opindex Wmain -@opindex Wno-main -Warn if the type of @samp{main} is suspicious. @samp{main} should be -a function with external linkage, returning int, taking either zero -arguments, two, or three arguments of appropriate types. This warning -is enabled by default in C++ and is enabled by either @option{-Wall} -or @option{-Wpedantic}. - -@item -Wmissing-braces -@opindex Wmissing-braces -@opindex Wno-missing-braces -Warn if an aggregate or union initializer is not fully bracketed. In -the following example, the initializer for @samp{a} is not fully -bracketed, but that for @samp{b} is fully bracketed. This warning is -enabled by @option{-Wall} in C. - -@smallexample -int a[2][2] = @{ 0, 1, 2, 3 @}; -int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; -@end smallexample - -This warning is enabled by @option{-Wall}. - -@item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)} -@opindex Wmissing-include-dirs -@opindex Wno-missing-include-dirs -Warn if a user-supplied include directory does not exist. - -@item -Wparentheses -@opindex Wparentheses -@opindex Wno-parentheses -Warn if parentheses are omitted in certain contexts, such -as when there is an assignment in a context where a truth value -is expected, or when operators are nested whose precedence people -often get confused about. - -Also warn if a comparison like @samp{x<=y<=z} appears; this is -equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different -interpretation from that of ordinary mathematical notation. - -Also warn about constructions where there may be confusion to which -@code{if} statement an @code{else} branch belongs. Here is an example of -such a case: - -@smallexample -@group -@{ - if (a) - if (b) - foo (); - else - bar (); -@} -@end group -@end smallexample - -In C/C++, every @code{else} branch belongs to the innermost possible -@code{if} statement, which in this example is @code{if (b)}. This is -often not what the programmer expected, as illustrated in the above -example by indentation the programmer chose. When there is the -potential for this confusion, GCC issues a warning when this flag -is specified. To eliminate the warning, add explicit braces around -the innermost @code{if} statement so there is no way the @code{else} -can belong to the enclosing @code{if}. The resulting code -looks like this: - -@smallexample -@group -@{ - if (a) - @{ - if (b) - foo (); - else - bar (); - @} -@} -@end group -@end smallexample - -Also warn for dangerous uses of the GNU extension to -@code{?:} with omitted middle operand. When the condition -in the @code{?}: operator is a boolean expression, the omitted value is -always 1. Often programmers expect it to be a value computed -inside the conditional expression instead. - -This warning is enabled by @option{-Wall}. - -@item -Wsequence-point -@opindex Wsequence-point -@opindex Wno-sequence-point -Warn about code that may have undefined semantics because of violations -of sequence point rules in the C and C++ standards. - -The C and C++ standards define the order in which expressions in a C/C++ -program are evaluated in terms of @dfn{sequence points}, which represent -a partial ordering between the execution of parts of the program: those -executed before the sequence point, and those executed after it. These -occur after the evaluation of a full expression (one which is not part -of a larger expression), after the evaluation of the first operand of a -@code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a -function is called (but after the evaluation of its arguments and the -expression denoting the called function), and in certain other places. -Other than as expressed by the sequence point rules, the order of -evaluation of subexpressions of an expression is not specified. All -these rules describe only a partial order rather than a total order, -since, for example, if two functions are called within one expression -with no sequence point between them, the order in which the functions -are called is not specified. However, the standards committee have -ruled that function calls do not overlap. - -It is not specified when between sequence points modifications to the -values of objects take effect. Programs whose behavior depends on this -have undefined behavior; the C and C++ standards specify that ``Between -the previous and next sequence point an object shall have its stored -value modified at most once by the evaluation of an expression. -Furthermore, the prior value shall be read only to determine the value -to be stored.''. If a program breaks these rules, the results on any -particular implementation are entirely unpredictable. - -Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] -= b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not -diagnosed by this option, and it may give an occasional false positive -result, but in general it has been found fairly effective at detecting -this sort of problem in programs. - -The standard is worded confusingly, therefore there is some debate -over the precise meaning of the sequence point rules in subtle cases. -Links to discussions of the problem, including proposed formal -definitions, may be found on the GCC readings page, at -@uref{http://gcc.gnu.org/@/readings.html}. - -This warning is enabled by @option{-Wall} for C and C++. - -@item -Wno-return-local-addr -@opindex Wno-return-local-addr -@opindex Wreturn-local-addr -Do not warn about returning a pointer (or in C++, a reference) to a -variable that goes out of scope after the function returns. - -@item -Wreturn-type -@opindex Wreturn-type -@opindex Wno-return-type -Warn whenever a function is defined with a return type that defaults -to @code{int}. Also warn about any @code{return} statement with no -return value in a function whose return type is not @code{void} -(falling off the end of the function body is considered returning -without a value), and about a @code{return} statement with an -expression in a function whose return type is @code{void}. - -For C++, a function without return type always produces a diagnostic -message, even when @option{-Wno-return-type} is specified. The only -exceptions are @samp{main} and functions defined in system headers. - -This warning is enabled by @option{-Wall}. - -@item -Wswitch -@opindex Wswitch -@opindex Wno-switch -Warn whenever a @code{switch} statement has an index of enumerated type -and lacks a @code{case} for one or more of the named codes of that -enumeration. (The presence of a @code{default} label prevents this -warning.) @code{case} labels outside the enumeration range also -provoke warnings when this option is used (even if there is a -@code{default} label). -This warning is enabled by @option{-Wall}. - -@item -Wswitch-default -@opindex Wswitch-default -@opindex Wno-switch-default -Warn whenever a @code{switch} statement does not have a @code{default} -case. - -@item -Wswitch-enum -@opindex Wswitch-enum -@opindex Wno-switch-enum -Warn whenever a @code{switch} statement has an index of enumerated type -and lacks a @code{case} for one or more of the named codes of that -enumeration. @code{case} labels outside the enumeration range also -provoke warnings when this option is used. The only difference -between @option{-Wswitch} and this option is that this option gives a -warning about an omitted enumeration code even if there is a -@code{default} label. - -@item -Wsync-nand @r{(C and C++ only)} -@opindex Wsync-nand -@opindex Wno-sync-nand -Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch} -built-in functions are used. These functions changed semantics in GCC 4.4. - -@item -Wtrigraphs -@opindex Wtrigraphs -@opindex Wno-trigraphs -Warn if any trigraphs are encountered that might change the meaning of -the program (trigraphs within comments are not warned about). -This warning is enabled by @option{-Wall}. - -@item -Wunused-but-set-parameter -@opindex Wunused-but-set-parameter -@opindex Wno-unused-but-set-parameter -Warn whenever a function parameter is assigned to, but otherwise unused -(aside from its declaration). - -To suppress this warning use the @samp{unused} attribute -(@pxref{Variable Attributes}). - -This warning is also enabled by @option{-Wunused} together with -@option{-Wextra}. - -@item -Wunused-but-set-variable -@opindex Wunused-but-set-variable -@opindex Wno-unused-but-set-variable -Warn whenever a local variable is assigned to, but otherwise unused -(aside from its declaration). -This warning is enabled by @option{-Wall}. - -To suppress this warning use the @samp{unused} attribute -(@pxref{Variable Attributes}). - -This warning is also enabled by @option{-Wunused}, which is enabled -by @option{-Wall}. - -@item -Wunused-function -@opindex Wunused-function -@opindex Wno-unused-function -Warn whenever a static function is declared but not defined or a -non-inline static function is unused. -This warning is enabled by @option{-Wall}. - -@item -Wunused-label -@opindex Wunused-label -@opindex Wno-unused-label -Warn whenever a label is declared but not used. -This warning is enabled by @option{-Wall}. - -To suppress this warning use the @samp{unused} attribute -(@pxref{Variable Attributes}). - -@item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)} -@opindex Wunused-local-typedefs -Warn when a typedef locally defined in a function is not used. -This warning is enabled by @option{-Wall}. - -@item -Wunused-parameter -@opindex Wunused-parameter -@opindex Wno-unused-parameter -Warn whenever a function parameter is unused aside from its declaration. - -To suppress this warning use the @samp{unused} attribute -(@pxref{Variable Attributes}). - -@item -Wno-unused-result -@opindex Wunused-result -@opindex Wno-unused-result -Do not warn if a caller of a function marked with attribute -@code{warn_unused_result} (@pxref{Function Attributes}) does not use -its return value. The default is @option{-Wunused-result}. - -@item -Wunused-variable -@opindex Wunused-variable -@opindex Wno-unused-variable -Warn whenever a local variable or non-constant static variable is unused -aside from its declaration. -This warning is enabled by @option{-Wall}. - -To suppress this warning use the @samp{unused} attribute -(@pxref{Variable Attributes}). - -@item -Wunused-value -@opindex Wunused-value -@opindex Wno-unused-value -Warn whenever a statement computes a result that is explicitly not -used. To suppress this warning cast the unused expression to -@samp{void}. This includes an expression-statement or the left-hand -side of a comma expression that contains no side effects. For example, -an expression such as @samp{x[i,j]} causes a warning, while -@samp{x[(void)i,j]} does not. - -This warning is enabled by @option{-Wall}. - -@item -Wunused -@opindex Wunused -@opindex Wno-unused -All the above @option{-Wunused} options combined. - -In order to get a warning about an unused function parameter, you must -either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies -@option{-Wunused}), or separately specify @option{-Wunused-parameter}. - -@item -Wuninitialized -@opindex Wuninitialized -@opindex Wno-uninitialized -Warn if an automatic variable is used without first being initialized -or if a variable may be clobbered by a @code{setjmp} call. In C++, -warn if a non-static reference or non-static @samp{const} member -appears in a class without constructors. - -If you want to warn about code that uses the uninitialized value of the -variable in its own initializer, use the @option{-Winit-self} option. - -These warnings occur for individual uninitialized or clobbered -elements of structure, union or array variables as well as for -variables that are uninitialized or clobbered as a whole. They do -not occur for variables or elements declared @code{volatile}. Because -these warnings depend on optimization, the exact variables or elements -for which there are warnings depends on the precise optimization -options and version of GCC used. - -Note that there may be no warning about a variable that is used only -to compute a value that itself is never used, because such -computations may be deleted by data flow analysis before the warnings -are printed. - -@item -Wmaybe-uninitialized -@opindex Wmaybe-uninitialized -@opindex Wno-maybe-uninitialized -For an automatic variable, if there exists a path from the function -entry to a use of the variable that is initialized, but there exist -some other paths for which the variable is not initialized, the compiler -emits a warning if it cannot prove the uninitialized paths are not -executed at run time. These warnings are made optional because GCC is -not smart enough to see all the reasons why the code might be correct -in spite of appearing to have an error. Here is one example of how -this can happen: - -@smallexample -@group -@{ - int x; - switch (y) - @{ - case 1: x = 1; - break; - case 2: x = 4; - break; - case 3: x = 5; - @} - foo (x); -@} -@end group -@end smallexample - -@noindent -If the value of @code{y} is always 1, 2 or 3, then @code{x} is -always initialized, but GCC doesn't know this. To suppress the -warning, you need to provide a default case with assert(0) or -similar code. - -@cindex @code{longjmp} warnings -This option also warns when a non-volatile automatic variable might be -changed by a call to @code{longjmp}. These warnings as well are possible -only in optimizing compilation. - -The compiler sees only the calls to @code{setjmp}. It cannot know -where @code{longjmp} will be called; in fact, a signal handler could -call it at any point in the code. As a result, you may get a warning -even when there is in fact no problem because @code{longjmp} cannot -in fact be called at the place that would cause a problem. - -Some spurious warnings can be avoided if you declare all the functions -you use that never return as @code{noreturn}. @xref{Function -Attributes}. - -This warning is enabled by @option{-Wall} or @option{-Wextra}. - -@item -Wunknown-pragmas -@opindex Wunknown-pragmas -@opindex Wno-unknown-pragmas -@cindex warning for unknown pragmas -@cindex unknown pragmas, warning -@cindex pragmas, warning of unknown -Warn when a @code{#pragma} directive is encountered that is not understood by -GCC@. If this command-line option is used, warnings are even issued -for unknown pragmas in system header files. This is not the case if -the warnings are only enabled by the @option{-Wall} command-line option. - -@item -Wno-pragmas -@opindex Wno-pragmas -@opindex Wpragmas -Do not warn about misuses of pragmas, such as incorrect parameters, -invalid syntax, or conflicts between pragmas. See also -@option{-Wunknown-pragmas}. - -@item -Wstrict-aliasing -@opindex Wstrict-aliasing -@opindex Wno-strict-aliasing -This option is only active when @option{-fstrict-aliasing} is active. -It warns about code that might break the strict aliasing rules that the -compiler is using for optimization. The warning does not catch all -cases, but does attempt to catch the more common pitfalls. It is -included in @option{-Wall}. -It is equivalent to @option{-Wstrict-aliasing=3} - -@item -Wstrict-aliasing=n -@opindex Wstrict-aliasing=n -This option is only active when @option{-fstrict-aliasing} is active. -It warns about code that might break the strict aliasing rules that the -compiler is using for optimization. -Higher levels correspond to higher accuracy (fewer false positives). -Higher levels also correspond to more effort, similar to the way @option{-O} -works. -@option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}. - -Level 1: Most aggressive, quick, least accurate. -Possibly useful when higher levels -do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few -false negatives. However, it has many false positives. -Warns for all pointer conversions between possibly incompatible types, -even if never dereferenced. Runs in the front end only. - -Level 2: Aggressive, quick, not too precise. -May still have many false positives (not as many as level 1 though), -and few false negatives (but possibly more than level 1). -Unlike level 1, it only warns when an address is taken. Warns about -incomplete types. Runs in the front end only. - -Level 3 (default for @option{-Wstrict-aliasing}): -Should have very few false positives and few false -negatives. Slightly slower than levels 1 or 2 when optimization is enabled. -Takes care of the common pun+dereference pattern in the front end: -@code{*(int*)&some_float}. -If optimization is enabled, it also runs in the back end, where it deals -with multiple statement cases using flow-sensitive points-to information. -Only warns when the converted pointer is dereferenced. -Does not warn about incomplete types. - -@item -Wstrict-overflow -@itemx -Wstrict-overflow=@var{n} -@opindex Wstrict-overflow -@opindex Wno-strict-overflow -This option is only active when @option{-fstrict-overflow} is active. -It warns about cases where the compiler optimizes based on the -assumption that signed overflow does not occur. Note that it does not -warn about all cases where the code might overflow: it only warns -about cases where the compiler implements some optimization. Thus -this warning depends on the optimization level. - -An optimization that assumes that signed overflow does not occur is -perfectly safe if the values of the variables involved are such that -overflow never does, in fact, occur. Therefore this warning can -easily give a false positive: a warning about code that is not -actually a problem. To help focus on important issues, several -warning levels are defined. No warnings are issued for the use of -undefined signed overflow when estimating how many iterations a loop -requires, in particular when determining whether a loop will be -executed at all. - -@table @gcctabopt -@item -Wstrict-overflow=1 -Warn about cases that are both questionable and easy to avoid. For -example, with @option{-fstrict-overflow}, the compiler simplifies -@code{x + 1 > x} to @code{1}. This level of -@option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels -are not, and must be explicitly requested. - -@item -Wstrict-overflow=2 -Also warn about other cases where a comparison is simplified to a -constant. For example: @code{abs (x) >= 0}. This can only be -simplified when @option{-fstrict-overflow} is in effect, because -@code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than -zero. @option{-Wstrict-overflow} (with no level) is the same as -@option{-Wstrict-overflow=2}. - -@item -Wstrict-overflow=3 -Also warn about other cases where a comparison is simplified. For -example: @code{x + 1 > 1} is simplified to @code{x > 0}. - -@item -Wstrict-overflow=4 -Also warn about other simplifications not covered by the above cases. -For example: @code{(x * 10) / 5} is simplified to @code{x * 2}. - -@item -Wstrict-overflow=5 -Also warn about cases where the compiler reduces the magnitude of a -constant involved in a comparison. For example: @code{x + 2 > y} is -simplified to @code{x + 1 >= y}. This is reported only at the -highest warning level because this simplification applies to many -comparisons, so this warning level gives a very large number of -false positives. -@end table - -@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} -@opindex Wsuggest-attribute= -@opindex Wno-suggest-attribute= -Warn for cases where adding an attribute may be beneficial. The -attributes currently supported are listed below. - -@table @gcctabopt -@item -Wsuggest-attribute=pure -@itemx -Wsuggest-attribute=const -@itemx -Wsuggest-attribute=noreturn -@opindex Wsuggest-attribute=pure -@opindex Wno-suggest-attribute=pure -@opindex Wsuggest-attribute=const -@opindex Wno-suggest-attribute=const -@opindex Wsuggest-attribute=noreturn -@opindex Wno-suggest-attribute=noreturn - -Warn about functions that might be candidates for attributes -@code{pure}, @code{const} or @code{noreturn}. The compiler only warns for -functions visible in other compilation units or (in the case of @code{pure} and -@code{const}) if it cannot prove that the function returns normally. A function -returns normally if it doesn't contain an infinite loop or return abnormally -by throwing, calling @code{abort()} or trapping. This analysis requires option -@option{-fipa-pure-const}, which is enabled by default at @option{-O} and -higher. Higher optimization levels improve the accuracy of the analysis. - -@item -Wsuggest-attribute=format -@itemx -Wmissing-format-attribute -@opindex Wsuggest-attribute=format -@opindex Wmissing-format-attribute -@opindex Wno-suggest-attribute=format -@opindex Wno-missing-format-attribute -@opindex Wformat -@opindex Wno-format - -Warn about function pointers that might be candidates for @code{format} -attributes. Note these are only possible candidates, not absolute ones. -GCC guesses that function pointers with @code{format} attributes that -are used in assignment, initialization, parameter passing or return -statements should have a corresponding @code{format} attribute in the -resulting type. I.e.@: the left-hand side of the assignment or -initialization, the type of the parameter variable, or the return type -of the containing function respectively should also have a @code{format} -attribute to avoid the warning. - -GCC also warns about function definitions that might be -candidates for @code{format} attributes. Again, these are only -possible candidates. GCC guesses that @code{format} attributes -might be appropriate for any function that calls a function like -@code{vprintf} or @code{vscanf}, but this might not always be the -case, and some functions for which @code{format} attributes are -appropriate may not be detected. -@end table - -@item -Warray-bounds -@opindex Wno-array-bounds -@opindex Warray-bounds -This option is only active when @option{-ftree-vrp} is active -(default for @option{-O2} and above). It warns about subscripts to arrays -that are always out of bounds. This warning is enabled by @option{-Wall}. - -@item -Wno-div-by-zero -@opindex Wno-div-by-zero -@opindex Wdiv-by-zero -Do not warn about compile-time integer division by zero. Floating-point -division by zero is not warned about, as it can be a legitimate way of -obtaining infinities and NaNs. - -@item -Wsystem-headers -@opindex Wsystem-headers -@opindex Wno-system-headers -@cindex warnings from system headers -@cindex system headers, warnings from -Print warning messages for constructs found in system header files. -Warnings from system headers are normally suppressed, on the assumption -that they usually do not indicate real problems and would only make the -compiler output harder to read. Using this command-line option tells -GCC to emit warnings from system headers as if they occurred in user -code. However, note that using @option{-Wall} in conjunction with this -option does @emph{not} warn about unknown pragmas in system -headers---for that, @option{-Wunknown-pragmas} must also be used. - -@item -Wtrampolines -@opindex Wtrampolines -@opindex Wno-trampolines - Warn about trampolines generated for pointers to nested functions. - - A trampoline is a small piece of data or code that is created at run - time on the stack when the address of a nested function is taken, and - is used to call the nested function indirectly. For some targets, it - is made up of data only and thus requires no special treatment. But, - for most targets, it is made up of code and thus requires the stack - to be made executable in order for the program to work properly. - -@item -Wfloat-equal -@opindex Wfloat-equal -@opindex Wno-float-equal -Warn if floating-point values are used in equality comparisons. - -The idea behind this is that sometimes it is convenient (for the -programmer) to consider floating-point values as approximations to -infinitely precise real numbers. If you are doing this, then you need -to compute (by analyzing the code, or in some other way) the maximum or -likely maximum error that the computation introduces, and allow for it -when performing comparisons (and when producing output, but that's a -different problem). In particular, instead of testing for equality, you -should check to see whether the two values have ranges that overlap; and -this is done with the relational operators, so equality comparisons are -probably mistaken. - -@item -Wtraditional @r{(C and Objective-C only)} -@opindex Wtraditional -@opindex Wno-traditional -Warn about certain constructs that behave differently in traditional and -ISO C@. Also warn about ISO C constructs that have no traditional C -equivalent, and/or problematic constructs that should be avoided. - -@itemize @bullet -@item -Macro parameters that appear within string literals in the macro body. -In traditional C macro replacement takes place within string literals, -but in ISO C it does not. - -@item -In traditional C, some preprocessor directives did not exist. -Traditional preprocessors only considered a line to be a directive -if the @samp{#} appeared in column 1 on the line. Therefore -@option{-Wtraditional} warns about directives that traditional C -understands but ignores because the @samp{#} does not appear as the -first character on the line. It also suggests you hide directives like -@samp{#pragma} not understood by traditional C by indenting them. Some -traditional implementations do not recognize @samp{#elif}, so this option -suggests avoiding it altogether. - -@item -A function-like macro that appears without arguments. - -@item -The unary plus operator. - -@item -The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point -constant suffixes. (Traditional C does support the @samp{L} suffix on integer -constants.) Note, these suffixes appear in macros defined in the system -headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}. -Use of these macros in user code might normally lead to spurious -warnings, however GCC's integrated preprocessor has enough context to -avoid warning in these cases. - -@item -A function declared external in one block and then used after the end of -the block. - -@item -A @code{switch} statement has an operand of type @code{long}. - -@item -A non-@code{static} function declaration follows a @code{static} one. -This construct is not accepted by some traditional C compilers. - -@item -The ISO type of an integer constant has a different width or -signedness from its traditional type. This warning is only issued if -the base of the constant is ten. I.e.@: hexadecimal or octal values, which -typically represent bit patterns, are not warned about. - -@item -Usage of ISO string concatenation is detected. - -@item -Initialization of automatic aggregates. - -@item -Identifier conflicts with labels. Traditional C lacks a separate -namespace for labels. - -@item -Initialization of unions. If the initializer is zero, the warning is -omitted. This is done under the assumption that the zero initializer in -user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing -initializer warnings and relies on default initialization to zero in the -traditional C case. - -@item -Conversions by prototypes between fixed/floating-point values and vice -versa. The absence of these prototypes when compiling with traditional -C causes serious problems. This is a subset of the possible -conversion warnings; for the full set use @option{-Wtraditional-conversion}. - -@item -Use of ISO C style function definitions. This warning intentionally is -@emph{not} issued for prototype declarations or variadic functions -because these ISO C features appear in your code when using -libiberty's traditional C compatibility macros, @code{PARAMS} and -@code{VPARAMS}. This warning is also bypassed for nested functions -because that feature is already a GCC extension and thus not relevant to -traditional C compatibility. -@end itemize - -@item -Wtraditional-conversion @r{(C and Objective-C only)} -@opindex Wtraditional-conversion -@opindex Wno-traditional-conversion -Warn if a prototype causes a type conversion that is different from what -would happen to the same argument in the absence of a prototype. This -includes conversions of fixed point to floating and vice versa, and -conversions changing the width or signedness of a fixed-point argument -except when the same as the default promotion. - -@item -Wdeclaration-after-statement @r{(C and Objective-C only)} -@opindex Wdeclaration-after-statement -@opindex Wno-declaration-after-statement -Warn when a declaration is found after a statement in a block. This -construct, known from C++, was introduced with ISO C99 and is by default -allowed in GCC@. It is not supported by ISO C90 and was not supported by -GCC versions before GCC 3.0. @xref{Mixed Declarations}. - -@item -Wundef -@opindex Wundef -@opindex Wno-undef -Warn if an undefined identifier is evaluated in an @samp{#if} directive. - -@item -Wno-endif-labels -@opindex Wno-endif-labels -@opindex Wendif-labels -Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text. - -@item -Wshadow -@opindex Wshadow -@opindex Wno-shadow -Warn whenever a local variable or type declaration shadows another variable, -parameter, type, or class member (in C++), or whenever a built-in function -is shadowed. Note that in C++, the compiler warns if a local variable -shadows an explicit typedef, but not if it shadows a struct/class/enum. - -@item -Wlarger-than=@var{len} -@opindex Wlarger-than=@var{len} -@opindex Wlarger-than-@var{len} -Warn whenever an object of larger than @var{len} bytes is defined. - -@item -Wframe-larger-than=@var{len} -@opindex Wframe-larger-than -Warn if the size of a function frame is larger than @var{len} bytes. -The computation done to determine the stack frame size is approximate -and not conservative. -The actual requirements may be somewhat greater than @var{len} -even if you do not get a warning. In addition, any space allocated -via @code{alloca}, variable-length arrays, or related constructs -is not included by the compiler when determining -whether or not to issue a warning. - -@item -Wno-free-nonheap-object -@opindex Wno-free-nonheap-object -@opindex Wfree-nonheap-object -Do not warn when attempting to free an object that was not allocated -on the heap. - -@item -Wstack-usage=@var{len} -@opindex Wstack-usage -Warn if the stack usage of a function might be larger than @var{len} bytes. -The computation done to determine the stack usage is conservative. -Any space allocated via @code{alloca}, variable-length arrays, or related -constructs is included by the compiler when determining whether or not to -issue a warning. - -The message is in keeping with the output of @option{-fstack-usage}. - -@itemize -@item -If the stack usage is fully static but exceeds the specified amount, it's: - -@smallexample - warning: stack usage is 1120 bytes -@end smallexample -@item -If the stack usage is (partly) dynamic but bounded, it's: - -@smallexample - warning: stack usage might be 1648 bytes -@end smallexample -@item -If the stack usage is (partly) dynamic and not bounded, it's: - -@smallexample - warning: stack usage might be unbounded -@end smallexample -@end itemize - -@item -Wunsafe-loop-optimizations -@opindex Wunsafe-loop-optimizations -@opindex Wno-unsafe-loop-optimizations -Warn if the loop cannot be optimized because the compiler cannot -assume anything on the bounds of the loop indices. With -@option{-funsafe-loop-optimizations} warn if the compiler makes -such assumptions. - -@item -Wno-pedantic-ms-format @r{(MinGW targets only)} -@opindex Wno-pedantic-ms-format -@opindex Wpedantic-ms-format -When used in combination with @option{-Wformat} -and @option{-pedantic} without GNU extensions, this option -disables the warnings about non-ISO @code{printf} / @code{scanf} format -width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets, -which depend on the MS runtime. - -@item -Wpointer-arith -@opindex Wpointer-arith -@opindex Wno-pointer-arith -Warn about anything that depends on the ``size of'' a function type or -of @code{void}. GNU C assigns these types a size of 1, for -convenience in calculations with @code{void *} pointers and pointers -to functions. In C++, warn also when an arithmetic operation involves -@code{NULL}. This warning is also enabled by @option{-Wpedantic}. - -@item -Wtype-limits -@opindex Wtype-limits -@opindex Wno-type-limits -Warn if a comparison is always true or always false due to the limited -range of the data type, but do not warn for constant expressions. For -example, warn if an unsigned variable is compared against zero with -@samp{<} or @samp{>=}. This warning is also enabled by -@option{-Wextra}. - -@item -Wbad-function-cast @r{(C and Objective-C only)} -@opindex Wbad-function-cast -@opindex Wno-bad-function-cast -Warn whenever a function call is cast to a non-matching type. -For example, warn if @code{int malloc()} is cast to @code{anything *}. - -@item -Wc++-compat @r{(C and Objective-C only)} -Warn about ISO C constructs that are outside of the common subset of -ISO C and ISO C++, e.g.@: request for implicit conversion from -@code{void *} to a pointer to non-@code{void} type. - -@item -Wc++11-compat @r{(C++ and Objective-C++ only)} -Warn about C++ constructs whose meaning differs between ISO C++ 1998 -and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords -in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is -enabled by @option{-Wall}. - -@item -Wcast-qual -@opindex Wcast-qual -@opindex Wno-cast-qual -Warn whenever a pointer is cast so as to remove a type qualifier from -the target type. For example, warn if a @code{const char *} is cast -to an ordinary @code{char *}. - -Also warn when making a cast that introduces a type qualifier in an -unsafe way. For example, casting @code{char **} to @code{const char **} -is unsafe, as in this example: - -@smallexample - /* p is char ** value. */ - const char **q = (const char **) p; - /* Assignment of readonly string to const char * is OK. */ - *q = "string"; - /* Now char** pointer points to read-only memory. */ - **p = 'b'; -@end smallexample - -@item -Wcast-align -@opindex Wcast-align -@opindex Wno-cast-align -Warn whenever a pointer is cast such that the required alignment of the -target is increased. For example, warn if a @code{char *} is cast to -an @code{int *} on machines where integers can only be accessed at -two- or four-byte boundaries. - -@item -Wwrite-strings -@opindex Wwrite-strings -@opindex Wno-write-strings -When compiling C, give string constants the type @code{const -char[@var{length}]} so that copying the address of one into a -non-@code{const} @code{char *} pointer produces a warning. These -warnings help you find at compile time code that can try to write -into a string constant, but only if you have been very careful about -using @code{const} in declarations and prototypes. Otherwise, it is -just a nuisance. This is why we did not make @option{-Wall} request -these warnings. - -When compiling C++, warn about the deprecated conversion from string -literals to @code{char *}. This warning is enabled by default for C++ -programs. - -@item -Wclobbered -@opindex Wclobbered -@opindex Wno-clobbered -Warn for variables that might be changed by @samp{longjmp} or -@samp{vfork}. This warning is also enabled by @option{-Wextra}. - -@item -Wconversion -@opindex Wconversion -@opindex Wno-conversion -Warn for implicit conversions that may alter a value. This includes -conversions between real and integer, like @code{abs (x)} when -@code{x} is @code{double}; conversions between signed and unsigned, -like @code{unsigned ui = -1}; and conversions to smaller types, like -@code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs -((int) x)} and @code{ui = (unsigned) -1}, or if the value is not -changed by the conversion like in @code{abs (2.0)}. Warnings about -conversions between signed and unsigned integers can be disabled by -using @option{-Wno-sign-conversion}. - -For C++, also warn for confusing overload resolution for user-defined -conversions; and conversions that never use a type conversion -operator: conversions to @code{void}, the same type, a base class or a -reference to them. Warnings about conversions between signed and -unsigned integers are disabled by default in C++ unless -@option{-Wsign-conversion} is explicitly enabled. - -@item -Wno-conversion-null @r{(C++ and Objective-C++ only)} -@opindex Wconversion-null -@opindex Wno-conversion-null -Do not warn for conversions between @code{NULL} and non-pointer -types. @option{-Wconversion-null} is enabled by default. - -@item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)} -@opindex Wzero-as-null-pointer-constant -@opindex Wno-zero-as-null-pointer-constant -Warn when a literal '0' is used as null pointer constant. This can -be useful to facilitate the conversion to @code{nullptr} in C++11. - -@item -Wuseless-cast @r{(C++ and Objective-C++ only)} -@opindex Wuseless-cast -@opindex Wno-useless-cast -Warn when an expression is casted to its own type. - -@item -Wempty-body -@opindex Wempty-body -@opindex Wno-empty-body -Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do -while} statement. This warning is also enabled by @option{-Wextra}. - -@item -Wenum-compare -@opindex Wenum-compare -@opindex Wno-enum-compare -Warn about a comparison between values of different enumerated types. -In C++ enumeral mismatches in conditional expressions are also -diagnosed and the warning is enabled by default. In C this warning is -enabled by @option{-Wall}. - -@item -Wjump-misses-init @r{(C, Objective-C only)} -@opindex Wjump-misses-init -@opindex Wno-jump-misses-init -Warn if a @code{goto} statement or a @code{switch} statement jumps -forward across the initialization of a variable, or jumps backward to a -label after the variable has been initialized. This only warns about -variables that are initialized when they are declared. This warning is -only supported for C and Objective-C; in C++ this sort of branch is an -error in any case. - -@option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It -can be disabled with the @option{-Wno-jump-misses-init} option. - -@item -Wsign-compare -@opindex Wsign-compare -@opindex Wno-sign-compare -@cindex warning for comparison of signed and unsigned values -@cindex comparison of signed and unsigned values, warning -@cindex signed and unsigned values, comparison warning -Warn when a comparison between signed and unsigned values could produce -an incorrect result when the signed value is converted to unsigned. -This warning is also enabled by @option{-Wextra}; to get the other warnings -of @option{-Wextra} without this warning, use @option{-Wextra -Wno-sign-compare}. - -@item -Wsign-conversion -@opindex Wsign-conversion -@opindex Wno-sign-conversion -Warn for implicit conversions that may change the sign of an integer -value, like assigning a signed integer expression to an unsigned -integer variable. An explicit cast silences the warning. In C, this -option is enabled also by @option{-Wconversion}. - -@item -Wsizeof-pointer-memaccess -@opindex Wsizeof-pointer-memaccess -@opindex Wno-sizeof-pointer-memaccess -Warn for suspicious length parameters to certain string and memory built-in -functions if the argument uses @code{sizeof}. This warning warns e.g.@: -about @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not an array, -but a pointer, and suggests a possible fix, or about -@code{memcpy (&foo, ptr, sizeof (&foo));}. This warning is enabled by -@option{-Wall}. - -@item -Waddress -@opindex Waddress -@opindex Wno-address -Warn about suspicious uses of memory addresses. These include using -the address of a function in a conditional expression, such as -@code{void func(void); if (func)}, and comparisons against the memory -address of a string literal, such as @code{if (x == "abc")}. Such -uses typically indicate a programmer error: the address of a function -always evaluates to true, so their use in a conditional usually -indicate that the programmer forgot the parentheses in a function -call; and comparisons against string literals result in unspecified -behavior and are not portable in C, so they usually indicate that the -programmer intended to use @code{strcmp}. This warning is enabled by -@option{-Wall}. - -@item -Wlogical-op -@opindex Wlogical-op -@opindex Wno-logical-op -Warn about suspicious uses of logical operators in expressions. -This includes using logical operators in contexts where a -bit-wise operator is likely to be expected. - -@item -Waggregate-return -@opindex Waggregate-return -@opindex Wno-aggregate-return -Warn if any functions that return structures or unions are defined or -called. (In languages where you can return an array, this also elicits -a warning.) - -@item -Wno-aggressive-loop-optimizations -@opindex Wno-aggressive-loop-optimizations -@opindex Waggressive-loop-optimizations -Warn if in a loop with constant number of iterations the compiler detects -undefined behavior in some statement during one or more of the iterations. - -@item -Wno-attributes -@opindex Wno-attributes -@opindex Wattributes -Do not warn if an unexpected @code{__attribute__} is used, such as -unrecognized attributes, function attributes applied to variables, -etc. This does not stop errors for incorrect use of supported -attributes. - -@item -Wno-builtin-macro-redefined -@opindex Wno-builtin-macro-redefined -@opindex Wbuiltin-macro-redefined -Do not warn if certain built-in macros are redefined. This suppresses -warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__}, -@code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}. - -@item -Wstrict-prototypes @r{(C and Objective-C only)} -@opindex Wstrict-prototypes -@opindex Wno-strict-prototypes -Warn if a function is declared or defined without specifying the -argument types. (An old-style function definition is permitted without -a warning if preceded by a declaration that specifies the argument -types.) - -@item -Wold-style-declaration @r{(C and Objective-C only)} -@opindex Wold-style-declaration -@opindex Wno-old-style-declaration -Warn for obsolescent usages, according to the C Standard, in a -declaration. For example, warn if storage-class specifiers like -@code{static} are not the first things in a declaration. This warning -is also enabled by @option{-Wextra}. - -@item -Wold-style-definition @r{(C and Objective-C only)} -@opindex Wold-style-definition -@opindex Wno-old-style-definition -Warn if an old-style function definition is used. A warning is given -even if there is a previous prototype. - -@item -Wmissing-parameter-type @r{(C and Objective-C only)} -@opindex Wmissing-parameter-type -@opindex Wno-missing-parameter-type -A function parameter is declared without a type specifier in K&R-style -functions: - -@smallexample -void foo(bar) @{ @} -@end smallexample - -This warning is also enabled by @option{-Wextra}. - -@item -Wmissing-prototypes @r{(C and Objective-C only)} -@opindex Wmissing-prototypes -@opindex Wno-missing-prototypes -Warn if a global function is defined without a previous prototype -declaration. This warning is issued even if the definition itself -provides a prototype. Use this option to detect global functions -that do not have a matching prototype declaration in a header file. -This option is not valid for C++ because all function declarations -provide prototypes and a non-matching declaration will declare an -overload rather than conflict with an earlier declaration. -Use @option{-Wmissing-declarations} to detect missing declarations in C++. - -@item -Wmissing-declarations -@opindex Wmissing-declarations -@opindex Wno-missing-declarations -Warn if a global function is defined without a previous declaration. -Do so even if the definition itself provides a prototype. -Use this option to detect global functions that are not declared in -header files. In C, no warnings are issued for functions with previous -non-prototype declarations; use @option{-Wmissing-prototype} to detect -missing prototypes. In C++, no warnings are issued for function templates, -or for inline functions, or for functions in anonymous namespaces. - -@item -Wmissing-field-initializers -@opindex Wmissing-field-initializers -@opindex Wno-missing-field-initializers -@opindex W -@opindex Wextra -@opindex Wno-extra -Warn if a structure's initializer has some fields missing. For -example, the following code causes such a warning, because -@code{x.h} is implicitly zero: - -@smallexample -struct s @{ int f, g, h; @}; -struct s x = @{ 3, 4 @}; -@end smallexample - -This option does not warn about designated initializers, so the following -modification does not trigger a warning: - -@smallexample -struct s @{ int f, g, h; @}; -struct s x = @{ .f = 3, .g = 4 @}; -@end smallexample - -This warning is included in @option{-Wextra}. To get other @option{-Wextra} -warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}. - -@item -Wno-multichar -@opindex Wno-multichar -@opindex Wmultichar -Do not warn if a multicharacter constant (@samp{'FOOF'}) is used. -Usually they indicate a typo in the user's code, as they have -implementation-defined values, and should not be used in portable code. - -@item -Wnormalized=<none|id|nfc|nfkc> -@opindex Wnormalized= -@cindex NFC -@cindex NFKC -@cindex character set, input normalization -In ISO C and ISO C++, two identifiers are different if they are -different sequences of characters. However, sometimes when characters -outside the basic ASCII character set are used, you can have two -different character sequences that look the same. To avoid confusion, -the ISO 10646 standard sets out some @dfn{normalization rules} which -when applied ensure that two sequences that look the same are turned into -the same sequence. GCC can warn you if you are using identifiers that -have not been normalized; this option controls that warning. - -There are four levels of warning supported by GCC@. The default is -@option{-Wnormalized=nfc}, which warns about any identifier that is -not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the -recommended form for most uses. - -Unfortunately, there are some characters allowed in identifiers by -ISO C and ISO C++ that, when turned into NFC, are not allowed in -identifiers. That is, there's no way to use these symbols in portable -ISO C or C++ and have all your identifiers in NFC@. -@option{-Wnormalized=id} suppresses the warning for these characters. -It is hoped that future versions of the standards involved will correct -this, which is why this option is not the default. - -You can switch the warning off for all characters by writing -@option{-Wnormalized=none}. You should only do this if you -are using some other normalization scheme (like ``D''), because -otherwise you can easily create bugs that are literally impossible to see. - -Some characters in ISO 10646 have distinct meanings but look identical -in some fonts or display methodologies, especially once formatting has -been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL -LETTER N'', displays just like a regular @code{n} that has been -placed in a superscript. ISO 10646 defines the @dfn{NFKC} -normalization scheme to convert all these into a standard form as -well, and GCC warns if your code is not in NFKC if you use -@option{-Wnormalized=nfkc}. This warning is comparable to warning -about every identifier that contains the letter O because it might be -confused with the digit 0, and so is not the default, but may be -useful as a local coding convention if the programming environment -cannot be fixed to display these characters distinctly. - -@item -Wno-deprecated -@opindex Wno-deprecated -@opindex Wdeprecated -Do not warn about usage of deprecated features. @xref{Deprecated Features}. - -@item -Wno-deprecated-declarations -@opindex Wno-deprecated-declarations -@opindex Wdeprecated-declarations -Do not warn about uses of functions (@pxref{Function Attributes}), -variables (@pxref{Variable Attributes}), and types (@pxref{Type -Attributes}) marked as deprecated by using the @code{deprecated} -attribute. - -@item -Wno-overflow -@opindex Wno-overflow -@opindex Woverflow -Do not warn about compile-time overflow in constant expressions. - -@item -Woverride-init @r{(C and Objective-C only)} -@opindex Woverride-init -@opindex Wno-override-init -@opindex W -@opindex Wextra -@opindex Wno-extra -Warn if an initialized field without side effects is overridden when -using designated initializers (@pxref{Designated Inits, , Designated -Initializers}). - -This warning is included in @option{-Wextra}. To get other -@option{-Wextra} warnings without this one, use @option{-Wextra --Wno-override-init}. - -@item -Wpacked -@opindex Wpacked -@opindex Wno-packed -Warn if a structure is given the packed attribute, but the packed -attribute has no effect on the layout or size of the structure. -Such structures may be mis-aligned for little benefit. For -instance, in this code, the variable @code{f.x} in @code{struct bar} -is misaligned even though @code{struct bar} does not itself -have the packed attribute: - -@smallexample -@group -struct foo @{ - int x; - char a, b, c, d; -@} __attribute__((packed)); -struct bar @{ - char z; - struct foo f; -@}; -@end group -@end smallexample - -@item -Wpacked-bitfield-compat -@opindex Wpacked-bitfield-compat -@opindex Wno-packed-bitfield-compat -The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute -on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but -the change can lead to differences in the structure layout. GCC -informs you when the offset of such a field has changed in GCC 4.4. -For example there is no longer a 4-bit padding between field @code{a} -and @code{b} in this structure: - -@smallexample -struct foo -@{ - char a:4; - char b:8; -@} __attribute__ ((packed)); -@end smallexample - -This warning is enabled by default. Use -@option{-Wno-packed-bitfield-compat} to disable this warning. - -@item -Wpadded -@opindex Wpadded -@opindex Wno-padded -Warn if padding is included in a structure, either to align an element -of the structure or to align the whole structure. Sometimes when this -happens it is possible to rearrange the fields of the structure to -reduce the padding and so make the structure smaller. - -@item -Wredundant-decls -@opindex Wredundant-decls -@opindex Wno-redundant-decls -Warn if anything is declared more than once in the same scope, even in -cases where multiple declaration is valid and changes nothing. - -@item -Wnested-externs @r{(C and Objective-C only)} -@opindex Wnested-externs -@opindex Wno-nested-externs -Warn if an @code{extern} declaration is encountered within a function. - -@item -Wno-inherited-variadic-ctor -@opindex Winherited-variadic-ctor -@opindex Wno-inherited-variadic-ctor -Suppress warnings about use of C++11 inheriting constructors when the -base class inherited from has a C variadic constructor; the warning is -on by default because the ellipsis is not inherited. - -@item -Winline -@opindex Winline -@opindex Wno-inline -Warn if a function that is declared as inline cannot be inlined. -Even with this option, the compiler does not warn about failures to -inline functions declared in system headers. - -The compiler uses a variety of heuristics to determine whether or not -to inline a function. For example, the compiler takes into account -the size of the function being inlined and the amount of inlining -that has already been done in the current function. Therefore, -seemingly insignificant changes in the source program can cause the -warnings produced by @option{-Winline} to appear or disappear. - -@item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)} -@opindex Wno-invalid-offsetof -@opindex Winvalid-offsetof -Suppress warnings from applying the @samp{offsetof} macro to a non-POD -type. According to the 1998 ISO C++ standard, applying @samp{offsetof} -to a non-POD type is undefined. In existing C++ implementations, -however, @samp{offsetof} typically gives meaningful results even when -applied to certain kinds of non-POD types (such as a simple -@samp{struct} that fails to be a POD type only by virtue of having a -constructor). This flag is for users who are aware that they are -writing nonportable code and who have deliberately chosen to ignore the -warning about it. - -The restrictions on @samp{offsetof} may be relaxed in a future version -of the C++ standard. - -@item -Wno-int-to-pointer-cast -@opindex Wno-int-to-pointer-cast -@opindex Wint-to-pointer-cast -Suppress warnings from casts to pointer type of an integer of a -different size. In C++, casting to a pointer type of smaller size is -an error. @option{Wint-to-pointer-cast} is enabled by default. - - -@item -Wno-pointer-to-int-cast @r{(C and Objective-C only)} -@opindex Wno-pointer-to-int-cast -@opindex Wpointer-to-int-cast -Suppress warnings from casts from a pointer to an integer type of a -different size. - -@item -Winvalid-pch -@opindex Winvalid-pch -@opindex Wno-invalid-pch -Warn if a precompiled header (@pxref{Precompiled Headers}) is found in -the search path but can't be used. - -@item -Wlong-long -@opindex Wlong-long -@opindex Wno-long-long -Warn if @samp{long long} type is used. This is enabled by either -@option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98 -modes. To inhibit the warning messages, use @option{-Wno-long-long}. - -@item -Wvariadic-macros -@opindex Wvariadic-macros -@opindex Wno-variadic-macros -Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU -alternate syntax when in pedantic ISO C99 mode. This is default. -To inhibit the warning messages, use @option{-Wno-variadic-macros}. - -@item -Wvarargs -@opindex Wvarargs -@opindex Wno-varargs -Warn upon questionable usage of the macros used to handle variable -arguments like @samp{va_start}. This is default. To inhibit the -warning messages, use @option{-Wno-varargs}. - -@item -Wvector-operation-performance -@opindex Wvector-operation-performance -@opindex Wno-vector-operation-performance -Warn if vector operation is not implemented via SIMD capabilities of the -architecture. Mainly useful for the performance tuning. -Vector operation can be implemented @code{piecewise}, which means that the -scalar operation is performed on every vector element; -@code{in parallel}, which means that the vector operation is implemented -using scalars of wider type, which normally is more performance efficient; -and @code{as a single scalar}, which means that vector fits into a -scalar type. - -@item -Wno-virtual-move-assign -@opindex Wvirtual-move-assign -@opindex Wno-virtual-move-assign -Suppress warnings about inheriting from a virtual base with a -non-trivial C++11 move assignment operator. This is dangerous because -if the virtual base is reachable along more than one path, it will be -moved multiple times, which can mean both objects end up in the -moved-from state. If the move assignment operator is written to avoid -moving from a moved-from object, this warning can be disabled. - -@item -Wvla -@opindex Wvla -@opindex Wno-vla -Warn if variable length array is used in the code. -@option{-Wno-vla} prevents the @option{-Wpedantic} warning of -the variable length array. - -@item -Wvolatile-register-var -@opindex Wvolatile-register-var -@opindex Wno-volatile-register-var -Warn if a register variable is declared volatile. The volatile -modifier does not inhibit all optimizations that may eliminate reads -and/or writes to register variables. This warning is enabled by -@option{-Wall}. - -@item -Wdisabled-optimization -@opindex Wdisabled-optimization -@opindex Wno-disabled-optimization -Warn if a requested optimization pass is disabled. This warning does -not generally indicate that there is anything wrong with your code; it -merely indicates that GCC's optimizers are unable to handle the code -effectively. Often, the problem is that your code is too big or too -complex; GCC refuses to optimize programs when the optimization -itself is likely to take inordinate amounts of time. - -@item -Wpointer-sign @r{(C and Objective-C only)} -@opindex Wpointer-sign -@opindex Wno-pointer-sign -Warn for pointer argument passing or assignment with different signedness. -This option is only supported for C and Objective-C@. It is implied by -@option{-Wall} and by @option{-Wpedantic}, which can be disabled with -@option{-Wno-pointer-sign}. - -@item -Wstack-protector -@opindex Wstack-protector -@opindex Wno-stack-protector -This option is only active when @option{-fstack-protector} is active. It -warns about functions that are not protected against stack smashing. - -@item -Wno-mudflap -@opindex Wno-mudflap -Suppress warnings about constructs that cannot be instrumented by -@option{-fmudflap}. - -@item -Woverlength-strings -@opindex Woverlength-strings -@opindex Wno-overlength-strings -Warn about string constants that are longer than the ``minimum -maximum'' length specified in the C standard. Modern compilers -generally allow string constants that are much longer than the -standard's minimum limit, but very portable programs should avoid -using longer strings. - -The limit applies @emph{after} string constant concatenation, and does -not count the trailing NUL@. In C90, the limit was 509 characters; in -C99, it was raised to 4095. C++98 does not specify a normative -minimum maximum, so we do not diagnose overlength strings in C++@. - -This option is implied by @option{-Wpedantic}, and can be disabled with -@option{-Wno-overlength-strings}. - -@item -Wunsuffixed-float-constants @r{(C and Objective-C only)} -@opindex Wunsuffixed-float-constants - -Issue a warning for any floating constant that does not have -a suffix. When used together with @option{-Wsystem-headers} it -warns about such constants in system header files. This can be useful -when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma -from the decimal floating-point extension to C99. -@end table - -@node Debugging Options -@section Options for Debugging Your Program or GCC -@cindex options, debugging -@cindex debugging information options - -GCC has various special options that are used for debugging -either your program or GCC: - -@table @gcctabopt -@item -g -@opindex g -Produce debugging information in the operating system's native format -(stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging -information. - -On most systems that use stabs format, @option{-g} enables use of extra -debugging information that only GDB can use; this extra information -makes debugging work better in GDB but probably makes other debuggers -crash or -refuse to read the program. If you want to control for certain whether -to generate the extra information, use @option{-gstabs+}, @option{-gstabs}, -@option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below). - -GCC allows you to use @option{-g} with -@option{-O}. The shortcuts taken by optimized code may occasionally -produce surprising results: some variables you declared may not exist -at all; flow of control may briefly move where you did not expect it; -some statements may not be executed because they compute constant -results or their values are already at hand; some statements may -execute in different places because they have been moved out of loops. - -Nevertheless it proves possible to debug optimized output. This makes -it reasonable to use the optimizer for programs that might have bugs. - -The following options are useful when GCC is generated with the -capability for more than one debugging format. - -@item -gsplit-dwarf -@opindex gsplit-dwarf -Separate as much dwarf debugging information as possible into a -separate output file with the extension .dwo. This option allows -the build system to avoid linking files with debug information. To -be useful, this option requires a debugger capable of reading .dwo -files. - -@item -ggdb -@opindex ggdb -Produce debugging information for use by GDB@. This means to use the -most expressive format available (DWARF 2, stabs, or the native format -if neither of those are supported), including GDB extensions if at all -possible. - -@item -gpubnames -@opindex gpubnames -Generate dwarf .debug_pubnames and .debug_pubtypes sections. - -@item -gstabs -@opindex gstabs -Produce debugging information in stabs format (if that is supported), -without GDB extensions. This is the format used by DBX on most BSD -systems. On MIPS, Alpha and System V Release 4 systems this option -produces stabs debugging output that is not understood by DBX or SDB@. -On System V Release 4 systems this option requires the GNU assembler. - -@item -feliminate-unused-debug-symbols -@opindex feliminate-unused-debug-symbols -Produce debugging information in stabs format (if that is supported), -for only symbols that are actually used. - -@item -femit-class-debug-always -Instead of emitting debugging information for a C++ class in only one -object file, emit it in all object files using the class. This option -should be used only with debuggers that are unable to handle the way GCC -normally emits debugging information for classes because using this -option increases the size of debugging information by as much as a -factor of two. - -@item -fdebug-types-section -@opindex fdebug-types-section -@opindex fno-debug-types-section -When using DWARF Version 4 or higher, type DIEs can be put into -their own @code{.debug_types} section instead of making them part of the -@code{.debug_info} section. It is more efficient to put them in a separate -comdat sections since the linker can then remove duplicates. -But not all DWARF consumers support @code{.debug_types} sections yet -and on some objects @code{.debug_types} produces larger instead of smaller -debugging information. - -@item -gstabs+ -@opindex gstabs+ -Produce debugging information in stabs format (if that is supported), -using GNU extensions understood only by the GNU debugger (GDB)@. The -use of these extensions is likely to make other debuggers crash or -refuse to read the program. - -@item -gcoff -@opindex gcoff -Produce debugging information in COFF format (if that is supported). -This is the format used by SDB on most System V systems prior to -System V Release 4. - -@item -gxcoff -@opindex gxcoff -Produce debugging information in XCOFF format (if that is supported). -This is the format used by the DBX debugger on IBM RS/6000 systems. - -@item -gxcoff+ -@opindex gxcoff+ -Produce debugging information in XCOFF format (if that is supported), -using GNU extensions understood only by the GNU debugger (GDB)@. The -use of these extensions is likely to make other debuggers crash or -refuse to read the program, and may cause assemblers other than the GNU -assembler (GAS) to fail with an error. - -@item -gdwarf-@var{version} -@opindex gdwarf-@var{version} -Produce debugging information in DWARF format (if that is supported). -The value of @var{version} may be either 2, 3 or 4; the default version -for most targets is 4. - -Note that with DWARF Version 2, some ports require and always -use some non-conflicting DWARF 3 extensions in the unwind tables. - -Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments} -for maximum benefit. - -@item -grecord-gcc-switches -@opindex grecord-gcc-switches -This switch causes the command-line options used to invoke the -compiler that may affect code generation to be appended to the -DW_AT_producer attribute in DWARF debugging information. The options -are concatenated with spaces separating them from each other and from -the compiler version. See also @option{-frecord-gcc-switches} for another -way of storing compiler options into the object file. This is the default. - -@item -gno-record-gcc-switches -@opindex gno-record-gcc-switches -Disallow appending command-line options to the DW_AT_producer attribute -in DWARF debugging information. - -@item -gstrict-dwarf -@opindex gstrict-dwarf -Disallow using extensions of later DWARF standard version than selected -with @option{-gdwarf-@var{version}}. On most targets using non-conflicting -DWARF extensions from later standard versions is allowed. - -@item -gno-strict-dwarf -@opindex gno-strict-dwarf -Allow using extensions of later DWARF standard version than selected with -@option{-gdwarf-@var{version}}. - -@item -gvms -@opindex gvms -Produce debugging information in Alpha/VMS debug format (if that is -supported). This is the format used by DEBUG on Alpha/VMS systems. - -@item -g@var{level} -@itemx -ggdb@var{level} -@itemx -gstabs@var{level} -@itemx -gcoff@var{level} -@itemx -gxcoff@var{level} -@itemx -gvms@var{level} -Request debugging information and also use @var{level} to specify how -much information. The default level is 2. - -Level 0 produces no debug information at all. Thus, @option{-g0} negates -@option{-g}. - -Level 1 produces minimal information, enough for making backtraces in -parts of the program that you don't plan to debug. This includes -descriptions of functions and external variables, but no information -about local variables and no line numbers. - -Level 3 includes extra information, such as all the macro definitions -present in the program. Some debuggers support macro expansion when -you use @option{-g3}. - -@option{-gdwarf-2} does not accept a concatenated debug level, because -GCC used to support an option @option{-gdwarf} that meant to generate -debug information in version 1 of the DWARF format (which is very -different from version 2), and it would have been too confusing. That -debug format is long obsolete, but the option cannot be changed now. -Instead use an additional @option{-g@var{level}} option to change the -debug level for DWARF. - -@item -gtoggle -@opindex gtoggle -Turn off generation of debug info, if leaving out this option -generates it, or turn it on at level 2 otherwise. The position of this -argument in the command line does not matter; it takes effect after all -other options are processed, and it does so only once, no matter how -many times it is given. This is mainly intended to be used with -@option{-fcompare-debug}. - -@item -fsanitize=address -Enable AddressSanitizer, a fast memory error detector. -Memory access instructions will be instrumented to detect -out-of-bounds and use-after-free bugs. -See @uref{http://code.google.com/p/address-sanitizer/} for more details. - -@item -fsanitize=thread -Enable ThreadSanitizer, a fast data race detector. -Memory access instructions will be instrumented to detect -data race bugs. -See @uref{http://code.google.com/p/data-race-test/wiki/ThreadSanitizer} for more details. - -@item -fdump-final-insns@r{[}=@var{file}@r{]} -@opindex fdump-final-insns -Dump the final internal representation (RTL) to @var{file}. If the -optional argument is omitted (or if @var{file} is @code{.}), the name -of the dump file is determined by appending @code{.gkd} to the -compilation output file name. - -@item -fcompare-debug@r{[}=@var{opts}@r{]} -@opindex fcompare-debug -@opindex fno-compare-debug -If no error occurs during compilation, run the compiler a second time, -adding @var{opts} and @option{-fcompare-debug-second} to the arguments -passed to the second compilation. Dump the final internal -representation in both compilations, and print an error if they differ. - -If the equal sign is omitted, the default @option{-gtoggle} is used. - -The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty -and nonzero, implicitly enables @option{-fcompare-debug}. If -@env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash, -then it is used for @var{opts}, otherwise the default @option{-gtoggle} -is used. - -@option{-fcompare-debug=}, with the equal sign but without @var{opts}, -is equivalent to @option{-fno-compare-debug}, which disables the dumping -of the final representation and the second compilation, preventing even -@env{GCC_COMPARE_DEBUG} from taking effect. - -To verify full coverage during @option{-fcompare-debug} testing, set -@env{GCC_COMPARE_DEBUG} to say @samp{-fcompare-debug-not-overridden}, -which GCC rejects as an invalid option in any actual compilation -(rather than preprocessing, assembly or linking). To get just a -warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug -not overridden} will do. - -@item -fcompare-debug-second -@opindex fcompare-debug-second -This option is implicitly passed to the compiler for the second -compilation requested by @option{-fcompare-debug}, along with options to -silence warnings, and omitting other options that would cause -side-effect compiler outputs to files or to the standard output. Dump -files and preserved temporary files are renamed so as to contain the -@code{.gk} additional extension during the second compilation, to avoid -overwriting those generated by the first. - -When this option is passed to the compiler driver, it causes the -@emph{first} compilation to be skipped, which makes it useful for little -other than debugging the compiler proper. - -@item -feliminate-dwarf2-dups -@opindex feliminate-dwarf2-dups -Compress DWARF 2 debugging information by eliminating duplicated -information about each symbol. This option only makes sense when -generating DWARF 2 debugging information with @option{-gdwarf-2}. - -@item -femit-struct-debug-baseonly -Emit debug information for struct-like types -only when the base name of the compilation source file -matches the base name of file in which the struct is defined. - -This option substantially reduces the size of debugging information, -but at significant potential loss in type information to the debugger. -See @option{-femit-struct-debug-reduced} for a less aggressive option. -See @option{-femit-struct-debug-detailed} for more detailed control. - -This option works only with DWARF 2. - -@item -femit-struct-debug-reduced -Emit debug information for struct-like types -only when the base name of the compilation source file -matches the base name of file in which the type is defined, -unless the struct is a template or defined in a system header. - -This option significantly reduces the size of debugging information, -with some potential loss in type information to the debugger. -See @option{-femit-struct-debug-baseonly} for a more aggressive option. -See @option{-femit-struct-debug-detailed} for more detailed control. - -This option works only with DWARF 2. - -@item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} -Specify the struct-like types -for which the compiler generates debug information. -The intent is to reduce duplicate struct debug information -between different object files within the same program. - -This option is a detailed version of -@option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly}, -which serves for most needs. - -A specification has the syntax@* -[@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none}) - -The optional first word limits the specification to -structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}). -A struct type is used directly when it is the type of a variable, member. -Indirect uses arise through pointers to structs. -That is, when use of an incomplete struct is valid, the use is indirect. -An example is -@samp{struct one direct; struct two * indirect;}. - -The optional second word limits the specification to -ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}). -Generic structs are a bit complicated to explain. -For C++, these are non-explicit specializations of template classes, -or non-template classes within the above. -Other programming languages have generics, -but @option{-femit-struct-debug-detailed} does not yet implement them. - -The third word specifies the source files for those -structs for which the compiler should emit debug information. -The values @samp{none} and @samp{any} have the normal meaning. -The value @samp{base} means that -the base of name of the file in which the type declaration appears -must match the base of the name of the main compilation file. -In practice, this means that when compiling @file{foo.c}, debug information -is generated for types declared in that file and @file{foo.h}, -but not other header files. -The value @samp{sys} means those types satisfying @samp{base} -or declared in system or compiler headers. - -You may need to experiment to determine the best settings for your application. - -The default is @option{-femit-struct-debug-detailed=all}. - -This option works only with DWARF 2. - -@item -fno-merge-debug-strings -@opindex fmerge-debug-strings -@opindex fno-merge-debug-strings -Direct the linker to not merge together strings in the debugging -information that are identical in different object files. Merging is -not supported by all assemblers or linkers. Merging decreases the size -of the debug information in the output file at the cost of increasing -link processing time. Merging is enabled by default. - -@item -fdebug-prefix-map=@var{old}=@var{new} -@opindex fdebug-prefix-map -When compiling files in directory @file{@var{old}}, record debugging -information describing them as in @file{@var{new}} instead. - -@item -fno-dwarf2-cfi-asm -@opindex fdwarf2-cfi-asm -@opindex fno-dwarf2-cfi-asm -Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section -instead of using GAS @code{.cfi_*} directives. - -@cindex @command{prof} -@item -p -@opindex p -Generate extra code to write profile information suitable for the -analysis program @command{prof}. You must use this option when compiling -the source files you want data about, and you must also use it when -linking. - -@cindex @command{gprof} -@item -pg -@opindex pg -Generate extra code to write profile information suitable for the -analysis program @command{gprof}. You must use this option when compiling -the source files you want data about, and you must also use it when -linking. - -@item -Q -@opindex Q -Makes the compiler print out each function name as it is compiled, and -print some statistics about each pass when it finishes. - -@item -ftime-report -@opindex ftime-report -Makes the compiler print some statistics about the time consumed by each -pass when it finishes. - -@item -fmem-report -@opindex fmem-report -Makes the compiler print some statistics about permanent memory -allocation when it finishes. - -@item -fmem-report-wpa -@opindex fmem-report-wpa -Makes the compiler print some statistics about permanent memory -allocation for the WPA phase only. - -@item -fpre-ipa-mem-report -@opindex fpre-ipa-mem-report -@item -fpost-ipa-mem-report -@opindex fpost-ipa-mem-report -Makes the compiler print some statistics about permanent memory -allocation before or after interprocedural optimization. - -@item -fprofile-report -@opindex fprofile-report -Makes the compiler print some statistics about consistency of the -(estimated) profile and effect of individual passes. - -@item -fstack-usage -@opindex fstack-usage -Makes the compiler output stack usage information for the program, on a -per-function basis. The filename for the dump is made by appending -@file{.su} to the @var{auxname}. @var{auxname} is generated from the name of -the output file, if explicitly specified and it is not an executable, -otherwise it is the basename of the source file. An entry is made up -of three fields: - -@itemize -@item -The name of the function. -@item -A number of bytes. -@item -One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}. -@end itemize - -The qualifier @code{static} means that the function manipulates the stack -statically: a fixed number of bytes are allocated for the frame on function -entry and released on function exit; no stack adjustments are otherwise made -in the function. The second field is this fixed number of bytes. - -The qualifier @code{dynamic} means that the function manipulates the stack -dynamically: in addition to the static allocation described above, stack -adjustments are made in the body of the function, for example to push/pop -arguments around function calls. If the qualifier @code{bounded} is also -present, the amount of these adjustments is bounded at compile time and -the second field is an upper bound of the total amount of stack used by -the function. If it is not present, the amount of these adjustments is -not bounded at compile time and the second field only represents the -bounded part. - -@item -fprofile-arcs -@opindex fprofile-arcs -Add code so that program flow @dfn{arcs} are instrumented. During -execution the program records how many times each branch and call is -executed and how many times it is taken or returns. When the compiled -program exits it saves this data to a file called -@file{@var{auxname}.gcda} for each source file. The data may be used for -profile-directed optimizations (@option{-fbranch-probabilities}), or for -test coverage analysis (@option{-ftest-coverage}). Each object file's -@var{auxname} is generated from the name of the output file, if -explicitly specified and it is not the final executable, otherwise it is -the basename of the source file. In both cases any suffix is removed -(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or -@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}). -@xref{Cross-profiling}. - -@cindex @command{gcov} -@item --coverage -@opindex coverage - -This option is used to compile and link code instrumented for coverage -analysis. The option is a synonym for @option{-fprofile-arcs} -@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when -linking). See the documentation for those options for more details. - -@itemize - -@item -Compile the source files with @option{-fprofile-arcs} plus optimization -and code generation options. For test coverage analysis, use the -additional @option{-ftest-coverage} option. You do not need to profile -every source file in a program. - -@item -Link your object files with @option{-lgcov} or @option{-fprofile-arcs} -(the latter implies the former). - -@item -Run the program on a representative workload to generate the arc profile -information. This may be repeated any number of times. You can run -concurrent instances of your program, and provided that the file system -supports locking, the data files will be correctly updated. Also -@code{fork} calls are detected and correctly handled (double counting -will not happen). - -@item -For profile-directed optimizations, compile the source files again with -the same optimization and code generation options plus -@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that -Control Optimization}). - -@item -For test coverage analysis, use @command{gcov} to produce human readable -information from the @file{.gcno} and @file{.gcda} files. Refer to the -@command{gcov} documentation for further information. - -@end itemize - -With @option{-fprofile-arcs}, for each function of your program GCC -creates a program flow graph, then finds a spanning tree for the graph. -Only arcs that are not on the spanning tree have to be instrumented: the -compiler adds code to count the number of times that these arcs are -executed. When an arc is the only exit or only entrance to a block, the -instrumentation code can be added to the block; otherwise, a new basic -block must be created to hold the instrumentation code. - -@need 2000 -@item -ftest-coverage -@opindex ftest-coverage -Produce a notes file that the @command{gcov} code-coverage utility -(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to -show program coverage. Each source file's note file is called -@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option -above for a description of @var{auxname} and instructions on how to -generate test coverage data. Coverage data matches the source files -more closely if you do not optimize. - -@item -fdbg-cnt-list -@opindex fdbg-cnt-list -Print the name and the counter upper bound for all debug counters. - - -@item -fdbg-cnt=@var{counter-value-list} -@opindex fdbg-cnt -Set the internal debug counter upper bound. @var{counter-value-list} -is a comma-separated list of @var{name}:@var{value} pairs -which sets the upper bound of each debug counter @var{name} to @var{value}. -All debug counters have the initial upper bound of @code{UINT_MAX}; -thus @code{dbg_cnt()} returns true always unless the upper bound -is set by this option. -For example, with @option{-fdbg-cnt=dce:10,tail_call:0}, -@code{dbg_cnt(dce)} returns true only for first 10 invocations. - -@item -fenable-@var{kind}-@var{pass} -@itemx -fdisable-@var{kind}-@var{pass}=@var{range-list} -@opindex fdisable- -@opindex fenable- - -This is a set of options that are used to explicitly disable/enable -optimization passes. These options are intended for use for debugging GCC. -Compiler users should use regular options for enabling/disabling -passes instead. - -@table @gcctabopt - -@item -fdisable-ipa-@var{pass} -Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is -statically invoked in the compiler multiple times, the pass name should be -appended with a sequential number starting from 1. - -@item -fdisable-rtl-@var{pass} -@itemx -fdisable-rtl-@var{pass}=@var{range-list} -Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is -statically invoked in the compiler multiple times, the pass name should be -appended with a sequential number starting from 1. @var{range-list} is a -comma-separated list of function ranges or assembler names. Each range is a number -pair separated by a colon. The range is inclusive in both ends. If the range -is trivial, the number pair can be simplified as a single number. If the -function's call graph node's @var{uid} falls within one of the specified ranges, -the @var{pass} is disabled for that function. The @var{uid} is shown in the -function header of a dump file, and the pass names can be dumped by using -option @option{-fdump-passes}. - -@item -fdisable-tree-@var{pass} -@itemx -fdisable-tree-@var{pass}=@var{range-list} -Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of -option arguments. - -@item -fenable-ipa-@var{pass} -Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is -statically invoked in the compiler multiple times, the pass name should be -appended with a sequential number starting from 1. - -@item -fenable-rtl-@var{pass} -@itemx -fenable-rtl-@var{pass}=@var{range-list} -Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument -description and examples. - -@item -fenable-tree-@var{pass} -@itemx -fenable-tree-@var{pass}=@var{range-list} -Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description -of option arguments. - -@end table - -Here are some examples showing uses of these options. - -@smallexample - -# disable ccp1 for all functions - -fdisable-tree-ccp1 -# disable complete unroll for function whose cgraph node uid is 1 - -fenable-tree-cunroll=1 -# disable gcse2 for functions at the following ranges [1,1], -# [300,400], and [400,1000] -# disable gcse2 for functions foo and foo2 - -fdisable-rtl-gcse2=foo,foo2 -# disable early inlining - -fdisable-tree-einline -# disable ipa inlining - -fdisable-ipa-inline -# enable tree full unroll - -fenable-tree-unroll - -@end smallexample - -@item -d@var{letters} -@itemx -fdump-rtl-@var{pass} -@itemx -fdump-rtl-@var{pass}=@var{filename} -@opindex d -Says to make debugging dumps during compilation at times specified by -@var{letters}. This is used for debugging the RTL-based passes of the -compiler. The file names for most of the dumps are made by appending -a pass number and a word to the @var{dumpname}, and the files are -created in the directory of the output file. In case of -@option{=@var{filename}} option, the dump is output on the given file -instead of the pass numbered dump files. Note that the pass number is -computed statically as passes get registered into the pass manager. -Thus the numbering is not related to the dynamic order of execution of -passes. In particular, a pass installed by a plugin could have a -number over 200 even if it executed quite early. @var{dumpname} is -generated from the name of the output file, if explicitly specified -and it is not an executable, otherwise it is the basename of the -source file. These switches may have different effects when -@option{-E} is used for preprocessing. - -Debug dumps can be enabled with a @option{-fdump-rtl} switch or some -@option{-d} option @var{letters}. Here are the possible -letters for use in @var{pass} and @var{letters}, and their meanings: - -@table @gcctabopt - -@item -fdump-rtl-alignments -@opindex fdump-rtl-alignments -Dump after branch alignments have been computed. - -@item -fdump-rtl-asmcons -@opindex fdump-rtl-asmcons -Dump after fixing rtl statements that have unsatisfied in/out constraints. - -@item -fdump-rtl-auto_inc_dec -@opindex fdump-rtl-auto_inc_dec -Dump after auto-inc-dec discovery. This pass is only run on -architectures that have auto inc or auto dec instructions. - -@item -fdump-rtl-barriers -@opindex fdump-rtl-barriers -Dump after cleaning up the barrier instructions. - -@item -fdump-rtl-bbpart -@opindex fdump-rtl-bbpart -Dump after partitioning hot and cold basic blocks. - -@item -fdump-rtl-bbro -@opindex fdump-rtl-bbro -Dump after block reordering. - -@item -fdump-rtl-btl1 -@itemx -fdump-rtl-btl2 -@opindex fdump-rtl-btl2 -@opindex fdump-rtl-btl2 -@option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping -after the two branch -target load optimization passes. - -@item -fdump-rtl-bypass -@opindex fdump-rtl-bypass -Dump after jump bypassing and control flow optimizations. - -@item -fdump-rtl-combine -@opindex fdump-rtl-combine -Dump after the RTL instruction combination pass. - -@item -fdump-rtl-compgotos -@opindex fdump-rtl-compgotos -Dump after duplicating the computed gotos. - -@item -fdump-rtl-ce1 -@itemx -fdump-rtl-ce2 -@itemx -fdump-rtl-ce3 -@opindex fdump-rtl-ce1 -@opindex fdump-rtl-ce2 -@opindex fdump-rtl-ce3 -@option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and -@option{-fdump-rtl-ce3} enable dumping after the three -if conversion passes. - -@item -fdump-rtl-cprop_hardreg -@opindex fdump-rtl-cprop_hardreg -Dump after hard register copy propagation. - -@item -fdump-rtl-csa -@opindex fdump-rtl-csa -Dump after combining stack adjustments. - -@item -fdump-rtl-cse1 -@itemx -fdump-rtl-cse2 -@opindex fdump-rtl-cse1 -@opindex fdump-rtl-cse2 -@option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after -the two common subexpression elimination passes. - -@item -fdump-rtl-dce -@opindex fdump-rtl-dce -Dump after the standalone dead code elimination passes. - -@item -fdump-rtl-dbr -@opindex fdump-rtl-dbr -Dump after delayed branch scheduling. - -@item -fdump-rtl-dce1 -@itemx -fdump-rtl-dce2 -@opindex fdump-rtl-dce1 -@opindex fdump-rtl-dce2 -@option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after -the two dead store elimination passes. - -@item -fdump-rtl-eh -@opindex fdump-rtl-eh -Dump after finalization of EH handling code. - -@item -fdump-rtl-eh_ranges -@opindex fdump-rtl-eh_ranges -Dump after conversion of EH handling range regions. - -@item -fdump-rtl-expand -@opindex fdump-rtl-expand -Dump after RTL generation. - -@item -fdump-rtl-fwprop1 -@itemx -fdump-rtl-fwprop2 -@opindex fdump-rtl-fwprop1 -@opindex fdump-rtl-fwprop2 -@option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable -dumping after the two forward propagation passes. - -@item -fdump-rtl-gcse1 -@itemx -fdump-rtl-gcse2 -@opindex fdump-rtl-gcse1 -@opindex fdump-rtl-gcse2 -@option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping -after global common subexpression elimination. - -@item -fdump-rtl-init-regs -@opindex fdump-rtl-init-regs -Dump after the initialization of the registers. - -@item -fdump-rtl-initvals -@opindex fdump-rtl-initvals -Dump after the computation of the initial value sets. - -@item -fdump-rtl-into_cfglayout -@opindex fdump-rtl-into_cfglayout -Dump after converting to cfglayout mode. - -@item -fdump-rtl-ira -@opindex fdump-rtl-ira -Dump after iterated register allocation. - -@item -fdump-rtl-jump -@opindex fdump-rtl-jump -Dump after the second jump optimization. - -@item -fdump-rtl-loop2 -@opindex fdump-rtl-loop2 -@option{-fdump-rtl-loop2} enables dumping after the rtl -loop optimization passes. - -@item -fdump-rtl-mach -@opindex fdump-rtl-mach -Dump after performing the machine dependent reorganization pass, if that -pass exists. - -@item -fdump-rtl-mode_sw -@opindex fdump-rtl-mode_sw -Dump after removing redundant mode switches. - -@item -fdump-rtl-rnreg -@opindex fdump-rtl-rnreg -Dump after register renumbering. - -@item -fdump-rtl-outof_cfglayout -@opindex fdump-rtl-outof_cfglayout -Dump after converting from cfglayout mode. - -@item -fdump-rtl-peephole2 -@opindex fdump-rtl-peephole2 -Dump after the peephole pass. - -@item -fdump-rtl-postreload -@opindex fdump-rtl-postreload -Dump after post-reload optimizations. - -@item -fdump-rtl-pro_and_epilogue -@opindex fdump-rtl-pro_and_epilogue -Dump after generating the function prologues and epilogues. - -@item -fdump-rtl-regmove -@opindex fdump-rtl-regmove -Dump after the register move pass. - -@item -fdump-rtl-sched1 -@itemx -fdump-rtl-sched2 -@opindex fdump-rtl-sched1 -@opindex fdump-rtl-sched2 -@option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping -after the basic block scheduling passes. - -@item -fdump-rtl-see -@opindex fdump-rtl-see -Dump after sign extension elimination. - -@item -fdump-rtl-seqabstr -@opindex fdump-rtl-seqabstr -Dump after common sequence discovery. - -@item -fdump-rtl-shorten -@opindex fdump-rtl-shorten -Dump after shortening branches. - -@item -fdump-rtl-sibling -@opindex fdump-rtl-sibling -Dump after sibling call optimizations. - -@item -fdump-rtl-split1 -@itemx -fdump-rtl-split2 -@itemx -fdump-rtl-split3 -@itemx -fdump-rtl-split4 -@itemx -fdump-rtl-split5 -@opindex fdump-rtl-split1 -@opindex fdump-rtl-split2 -@opindex fdump-rtl-split3 -@opindex fdump-rtl-split4 -@opindex fdump-rtl-split5 -@option{-fdump-rtl-split1}, @option{-fdump-rtl-split2}, -@option{-fdump-rtl-split3}, @option{-fdump-rtl-split4} and -@option{-fdump-rtl-split5} enable dumping after five rounds of -instruction splitting. - -@item -fdump-rtl-sms -@opindex fdump-rtl-sms -Dump after modulo scheduling. This pass is only run on some -architectures. - -@item -fdump-rtl-stack -@opindex fdump-rtl-stack -Dump after conversion from GCC's ``flat register file'' registers to the -x87's stack-like registers. This pass is only run on x86 variants. - -@item -fdump-rtl-subreg1 -@itemx -fdump-rtl-subreg2 -@opindex fdump-rtl-subreg1 -@opindex fdump-rtl-subreg2 -@option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after -the two subreg expansion passes. - -@item -fdump-rtl-unshare -@opindex fdump-rtl-unshare -Dump after all rtl has been unshared. - -@item -fdump-rtl-vartrack -@opindex fdump-rtl-vartrack -Dump after variable tracking. - -@item -fdump-rtl-vregs -@opindex fdump-rtl-vregs -Dump after converting virtual registers to hard registers. - -@item -fdump-rtl-web -@opindex fdump-rtl-web -Dump after live range splitting. - -@item -fdump-rtl-regclass -@itemx -fdump-rtl-subregs_of_mode_init -@itemx -fdump-rtl-subregs_of_mode_finish -@itemx -fdump-rtl-dfinit -@itemx -fdump-rtl-dfinish -@opindex fdump-rtl-regclass -@opindex fdump-rtl-subregs_of_mode_init -@opindex fdump-rtl-subregs_of_mode_finish -@opindex fdump-rtl-dfinit -@opindex fdump-rtl-dfinish -These dumps are defined but always produce empty files. - -@item -da -@itemx -fdump-rtl-all -@opindex da -@opindex fdump-rtl-all -Produce all the dumps listed above. - -@item -dA -@opindex dA -Annotate the assembler output with miscellaneous debugging information. - -@item -dD -@opindex dD -Dump all macro definitions, at the end of preprocessing, in addition to -normal output. - -@item -dH -@opindex dH -Produce a core dump whenever an error occurs. - -@item -dp -@opindex dp -Annotate the assembler output with a comment indicating which -pattern and alternative is used. The length of each instruction is -also printed. - -@item -dP -@opindex dP -Dump the RTL in the assembler output as a comment before each instruction. -Also turns on @option{-dp} annotation. - -@item -dx -@opindex dx -Just generate RTL for a function instead of compiling it. Usually used -with @option{-fdump-rtl-expand}. -@end table - -@item -fdump-noaddr -@opindex fdump-noaddr -When doing debugging dumps, suppress address output. This makes it more -feasible to use diff on debugging dumps for compiler invocations with -different compiler binaries and/or different -text / bss / data / heap / stack / dso start locations. - -@item -fdump-unnumbered -@opindex fdump-unnumbered -When doing debugging dumps, suppress instruction numbers and address output. -This makes it more feasible to use diff on debugging dumps for compiler -invocations with different options, in particular with and without -@option{-g}. - -@item -fdump-unnumbered-links -@opindex fdump-unnumbered-links -When doing debugging dumps (see @option{-d} option above), suppress -instruction numbers for the links to the previous and next instructions -in a sequence. - -@item -fdump-translation-unit @r{(C++ only)} -@itemx -fdump-translation-unit-@var{options} @r{(C++ only)} -@opindex fdump-translation-unit -Dump a representation of the tree structure for the entire translation -unit to a file. The file name is made by appending @file{.tu} to the -source file name, and the file is created in the same directory as the -output file. If the @samp{-@var{options}} form is used, @var{options} -controls the details of the dump as described for the -@option{-fdump-tree} options. - -@item -fdump-class-hierarchy @r{(C++ only)} -@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)} -@opindex fdump-class-hierarchy -Dump a representation of each class's hierarchy and virtual function -table layout to a file. The file name is made by appending -@file{.class} to the source file name, and the file is created in the -same directory as the output file. If the @samp{-@var{options}} form -is used, @var{options} controls the details of the dump as described -for the @option{-fdump-tree} options. - -@item -fdump-ipa-@var{switch} -@opindex fdump-ipa -Control the dumping at various stages of inter-procedural analysis -language tree to a file. The file name is generated by appending a -switch specific suffix to the source file name, and the file is created -in the same directory as the output file. The following dumps are -possible: - -@table @samp -@item all -Enables all inter-procedural analysis dumps. - -@item cgraph -Dumps information about call-graph optimization, unused function removal, -and inlining decisions. - -@item inline -Dump after function inlining. - -@end table - -@item -fdump-passes -@opindex fdump-passes -Dump the list of optimization passes that are turned on and off by -the current command-line options. - -@item -fdump-statistics-@var{option} -@opindex fdump-statistics -Enable and control dumping of pass statistics in a separate file. The -file name is generated by appending a suffix ending in -@samp{.statistics} to the source file name, and the file is created in -the same directory as the output file. If the @samp{-@var{option}} -form is used, @samp{-stats} causes counters to be summed over the -whole compilation unit while @samp{-details} dumps every event as -the passes generate them. The default with no option is to sum -counters for each function compiled. - -@item -fdump-tree-@var{switch} -@itemx -fdump-tree-@var{switch}-@var{options} -@itemx -fdump-tree-@var{switch}-@var{options}=@var{filename} -@opindex fdump-tree -Control the dumping at various stages of processing the intermediate -language tree to a file. The file name is generated by appending a -switch-specific suffix to the source file name, and the file is -created in the same directory as the output file. In case of -@option{=@var{filename}} option, the dump is output on the given file -instead of the auto named dump files. If the @samp{-@var{options}} -form is used, @var{options} is a list of @samp{-} separated options -which control the details of the dump. Not all options are applicable -to all dumps; those that are not meaningful are ignored. The -following options are available - -@table @samp -@item address -Print the address of each node. Usually this is not meaningful as it -changes according to the environment and source file. Its primary use -is for tying up a dump file with a debug environment. -@item asmname -If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that -in the dump instead of @code{DECL_NAME}. Its primary use is ease of -use working backward from mangled names in the assembly file. -@item slim -When dumping front-end intermediate representations, inhibit dumping -of members of a scope or body of a function merely because that scope -has been reached. Only dump such items when they are directly reachable -by some other path. - -When dumping pretty-printed trees, this option inhibits dumping the -bodies of control structures. - -When dumping RTL, print the RTL in slim (condensed) form instead of -the default LISP-like representation. -@item raw -Print a raw representation of the tree. By default, trees are -pretty-printed into a C-like representation. -@item details -Enable more detailed dumps (not honored by every dump option). Also -include information from the optimization passes. -@item stats -Enable dumping various statistics about the pass (not honored by every dump -option). -@item blocks -Enable showing basic block boundaries (disabled in raw dumps). -@item graph -For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}), -dump a representation of the control flow graph suitable for viewing with -GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in -the file is pretty-printed as a subgraph, so that GraphViz can render them -all in a single plot. - -This option currently only works for RTL dumps, and the RTL is always -dumped in slim form. -@item vops -Enable showing virtual operands for every statement. -@item lineno -Enable showing line numbers for statements. -@item uid -Enable showing the unique ID (@code{DECL_UID}) for each variable. -@item verbose -Enable showing the tree dump for each statement. -@item eh -Enable showing the EH region number holding each statement. -@item scev -Enable showing scalar evolution analysis details. -@item optimized -Enable showing optimization information (only available in certain -passes). -@item missed -Enable showing missed optimization information (only available in certain -passes). -@item notes -Enable other detailed optimization information (only available in -certain passes). -@item =@var{filename} -Instead of an auto named dump file, output into the given file -name. The file names @file{stdout} and @file{stderr} are treated -specially and are considered already open standard streams. For -example, - -@smallexample -gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump - -fdump-tree-pre=stderr file.c -@end smallexample - -outputs vectorizer dump into @file{foo.dump}, while the PRE dump is -output on to @file{stderr}. If two conflicting dump filenames are -given for the same pass, then the latter option overrides the earlier -one. - -@item all -Turn on all options, except @option{raw}, @option{slim}, @option{verbose} -and @option{lineno}. - -@item optall -Turn on all optimization options, i.e., @option{optimized}, -@option{missed}, and @option{note}. -@end table - -The following tree dumps are possible: -@table @samp - -@item original -@opindex fdump-tree-original -Dump before any tree based optimization, to @file{@var{file}.original}. - -@item optimized -@opindex fdump-tree-optimized -Dump after all tree based optimization, to @file{@var{file}.optimized}. - -@item gimple -@opindex fdump-tree-gimple -Dump each function before and after the gimplification pass to a file. The -file name is made by appending @file{.gimple} to the source file name. - -@item cfg -@opindex fdump-tree-cfg -Dump the control flow graph of each function to a file. The file name is -made by appending @file{.cfg} to the source file name. - -@item ch -@opindex fdump-tree-ch -Dump each function after copying loop headers. The file name is made by -appending @file{.ch} to the source file name. - -@item ssa -@opindex fdump-tree-ssa -Dump SSA related information to a file. The file name is made by appending -@file{.ssa} to the source file name. - -@item alias -@opindex fdump-tree-alias -Dump aliasing information for each function. The file name is made by -appending @file{.alias} to the source file name. - -@item ccp -@opindex fdump-tree-ccp -Dump each function after CCP@. The file name is made by appending -@file{.ccp} to the source file name. - -@item storeccp -@opindex fdump-tree-storeccp -Dump each function after STORE-CCP@. The file name is made by appending -@file{.storeccp} to the source file name. - -@item pre -@opindex fdump-tree-pre -Dump trees after partial redundancy elimination. The file name is made -by appending @file{.pre} to the source file name. - -@item fre -@opindex fdump-tree-fre -Dump trees after full redundancy elimination. The file name is made -by appending @file{.fre} to the source file name. - -@item copyprop -@opindex fdump-tree-copyprop -Dump trees after copy propagation. The file name is made -by appending @file{.copyprop} to the source file name. - -@item store_copyprop -@opindex fdump-tree-store_copyprop -Dump trees after store copy-propagation. The file name is made -by appending @file{.store_copyprop} to the source file name. - -@item dce -@opindex fdump-tree-dce -Dump each function after dead code elimination. The file name is made by -appending @file{.dce} to the source file name. - -@item mudflap -@opindex fdump-tree-mudflap -Dump each function after adding mudflap instrumentation. The file name is -made by appending @file{.mudflap} to the source file name. - -@item sra -@opindex fdump-tree-sra -Dump each function after performing scalar replacement of aggregates. The -file name is made by appending @file{.sra} to the source file name. - -@item sink -@opindex fdump-tree-sink -Dump each function after performing code sinking. The file name is made -by appending @file{.sink} to the source file name. - -@item dom -@opindex fdump-tree-dom -Dump each function after applying dominator tree optimizations. The file -name is made by appending @file{.dom} to the source file name. - -@item dse -@opindex fdump-tree-dse -Dump each function after applying dead store elimination. The file -name is made by appending @file{.dse} to the source file name. - -@item phiopt -@opindex fdump-tree-phiopt -Dump each function after optimizing PHI nodes into straightline code. The file -name is made by appending @file{.phiopt} to the source file name. - -@item forwprop -@opindex fdump-tree-forwprop -Dump each function after forward propagating single use variables. The file -name is made by appending @file{.forwprop} to the source file name. - -@item copyrename -@opindex fdump-tree-copyrename -Dump each function after applying the copy rename optimization. The file -name is made by appending @file{.copyrename} to the source file name. - -@item nrv -@opindex fdump-tree-nrv -Dump each function after applying the named return value optimization on -generic trees. The file name is made by appending @file{.nrv} to the source -file name. - -@item vect -@opindex fdump-tree-vect -Dump each function after applying vectorization of loops. The file name is -made by appending @file{.vect} to the source file name. - -@item slp -@opindex fdump-tree-slp -Dump each function after applying vectorization of basic blocks. The file name -is made by appending @file{.slp} to the source file name. - -@item vrp -@opindex fdump-tree-vrp -Dump each function after Value Range Propagation (VRP). The file name -is made by appending @file{.vrp} to the source file name. - -@item all -@opindex fdump-tree-all -Enable all the available tree dumps with the flags provided in this option. -@end table - -@item -fopt-info -@itemx -fopt-info-@var{options} -@itemx -fopt-info-@var{options}=@var{filename} -@opindex fopt-info -Controls optimization dumps from various optimization passes. If the -@samp{-@var{options}} form is used, @var{options} is a list of -@samp{-} separated options to select the dump details and -optimizations. If @var{options} is not specified, it defaults to -@option{all} for details and @option{optall} for optimization -groups. If the @var{filename} is not specified, it defaults to -@file{stderr}. Note that the output @var{filename} will be overwritten -in case of multiple translation units. If a combined output from -multiple translation units is desired, @file{stderr} should be used -instead. - -The options can be divided into two groups, 1) options describing the -verbosity of the dump, and 2) options describing which optimizations -should be included. The options from both the groups can be freely -mixed as they are non-overlapping. However, in case of any conflicts, -the latter options override the earlier options on the command -line. Though multiple -fopt-info options are accepted, only one of -them can have @option{=filename}. If other filenames are provided then -all but the first one are ignored. - -The dump verbosity has the following options - -@table @samp -@item optimized -Print information when an optimization is successfully applied. It is -up to a pass to decide which information is relevant. For example, the -vectorizer passes print the source location of loops which got -successfully vectorized. -@item missed -Print information about missed optimizations. Individual passes -control which information to include in the output. For example, - -@smallexample -gcc -O2 -ftree-vectorize -fopt-info-vec-missed -@end smallexample - -will print information about missed optimization opportunities from -vectorization passes on stderr. -@item note -Print verbose information about optimizations, such as certain -transformations, more detailed messages about decisions etc. -@item all -Print detailed optimization information. This includes -@var{optimized}, @var{missed}, and @var{note}. -@end table - -The second set of options describes a group of optimizations and may -include one or more of the following. - -@table @samp -@item ipa -Enable dumps from all interprocedural optimizations. -@item loop -Enable dumps from all loop optimizations. -@item inline -Enable dumps from all inlining optimizations. -@item vec -Enable dumps from all vectorization optimizations. -@end table - -For example, -@smallexample -gcc -O3 -fopt-info-missed=missed.all -@end smallexample - -outputs missed optimization report from all the passes into -@file{missed.all}. - -As another example, -@smallexample -gcc -O3 -fopt-info-inline-optimized-missed=inline.txt -@end smallexample - -will output information about missed optimizations as well as -optimized locations from all the inlining passes into -@file{inline.txt}. - -If the @var{filename} is provided, then the dumps from all the -applicable optimizations are concatenated into the @file{filename}. -Otherwise the dump is output onto @file{stderr}. If @var{options} is -omitted, it defaults to @option{all-optall}, which means dump all -available optimization info from all the passes. In the following -example, all optimization info is output on to @file{stderr}. - -@smallexample -gcc -O3 -fopt-info -@end smallexample - -Note that @option{-fopt-info-vec-missed} behaves the same as -@option{-fopt-info-missed-vec}. - -As another example, consider - -@smallexample -gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt -@end smallexample - -Here the two output filenames @file{vec.miss} and @file{loop.opt} are -in conflict since only one output file is allowed. In this case, only -the first option takes effect and the subsequent options are -ignored. Thus only the @file{vec.miss} is produced which cotaints -dumps from the vectorizer about missed opportunities. - -@item -ftree-vectorizer-verbose=@var{n} -@opindex ftree-vectorizer-verbose -This option is deprecated and is implemented in terms of -@option{-fopt-info}. Please use @option{-fopt-info-@var{kind}} form -instead, where @var{kind} is one of the valid opt-info options. It -prints additional optimization information. For @var{n}=0 no -diagnostic information is reported. If @var{n}=1 the vectorizer -reports each loop that got vectorized, and the total number of loops -that got vectorized. If @var{n}=2 the vectorizer reports locations -which could not be vectorized and the reasons for those. For any -higher verbosity levels all the analysis and transformation -information from the vectorizer is reported. - -Note that the information output by @option{-ftree-vectorizer-verbose} -option is sent to @file{stderr}. If the equivalent form -@option{-fopt-info-@var{options}=@var{filename}} is used then the -output is sent into @var{filename} instead. - -@item -frandom-seed=@var{string} -@opindex frandom-seed -This option provides a seed that GCC uses in place of -random numbers in generating certain symbol names -that have to be different in every compiled file. It is also used to -place unique stamps in coverage data files and the object files that -produce them. You can use the @option{-frandom-seed} option to produce -reproducibly identical object files. - -The @var{string} should be different for every file you compile. - -@item -fsched-verbose=@var{n} -@opindex fsched-verbose -On targets that use instruction scheduling, this option controls the -amount of debugging output the scheduler prints. This information is -written to standard error, unless @option{-fdump-rtl-sched1} or -@option{-fdump-rtl-sched2} is specified, in which case it is output -to the usual dump listing file, @file{.sched1} or @file{.sched2} -respectively. However for @var{n} greater than nine, the output is -always printed to standard error. - -For @var{n} greater than zero, @option{-fsched-verbose} outputs the -same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}. -For @var{n} greater than one, it also output basic block probabilities, -detailed ready list information and unit/insn info. For @var{n} greater -than two, it includes RTL at abort point, control-flow and regions info. -And for @var{n} over four, @option{-fsched-verbose} also includes -dependence info. - -@item -save-temps -@itemx -save-temps=cwd -@opindex save-temps -Store the usual ``temporary'' intermediate files permanently; place them -in the current directory and name them based on the source file. Thus, -compiling @file{foo.c} with @option{-c -save-temps} produces files -@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a -preprocessed @file{foo.i} output file even though the compiler now -normally uses an integrated preprocessor. - -When used in combination with the @option{-x} command-line option, -@option{-save-temps} is sensible enough to avoid over writing an -input source file with the same extension as an intermediate file. -The corresponding intermediate file may be obtained by renaming the -source file before using @option{-save-temps}. - -If you invoke GCC in parallel, compiling several different source -files that share a common base name in different subdirectories or the -same source file compiled for multiple output destinations, it is -likely that the different parallel compilers will interfere with each -other, and overwrite the temporary files. For instance: - -@smallexample -gcc -save-temps -o outdir1/foo.o indir1/foo.c& -gcc -save-temps -o outdir2/foo.o indir2/foo.c& -@end smallexample - -may result in @file{foo.i} and @file{foo.o} being written to -simultaneously by both compilers. - -@item -save-temps=obj -@opindex save-temps=obj -Store the usual ``temporary'' intermediate files permanently. If the -@option{-o} option is used, the temporary files are based on the -object file. If the @option{-o} option is not used, the -@option{-save-temps=obj} switch behaves like @option{-save-temps}. - -For example: - -@smallexample -gcc -save-temps=obj -c foo.c -gcc -save-temps=obj -c bar.c -o dir/xbar.o -gcc -save-temps=obj foobar.c -o dir2/yfoobar -@end smallexample - -@noindent -creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i}, -@file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and -@file{dir2/yfoobar.o}. - -@item -time@r{[}=@var{file}@r{]} -@opindex time -Report the CPU time taken by each subprocess in the compilation -sequence. For C source files, this is the compiler proper and assembler -(plus the linker if linking is done). - -Without the specification of an output file, the output looks like this: - -@smallexample -# cc1 0.12 0.01 -# as 0.00 0.01 -@end smallexample - -The first number on each line is the ``user time'', that is time spent -executing the program itself. The second number is ``system time'', -time spent executing operating system routines on behalf of the program. -Both numbers are in seconds. - -With the specification of an output file, the output is appended to the -named file, and it looks like this: - -@smallexample -0.12 0.01 cc1 @var{options} -0.00 0.01 as @var{options} -@end smallexample - -The ``user time'' and the ``system time'' are moved before the program -name, and the options passed to the program are displayed, so that one -can later tell what file was being compiled, and with which options. - -@item -fvar-tracking -@opindex fvar-tracking -Run variable tracking pass. It computes where variables are stored at each -position in code. Better debugging information is then generated -(if the debugging information format supports this information). - -It is enabled by default when compiling with optimization (@option{-Os}, -@option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and -the debug info format supports it. - -@item -fvar-tracking-assignments -@opindex fvar-tracking-assignments -@opindex fno-var-tracking-assignments -Annotate assignments to user variables early in the compilation and -attempt to carry the annotations over throughout the compilation all the -way to the end, in an attempt to improve debug information while -optimizing. Use of @option{-gdwarf-4} is recommended along with it. - -It can be enabled even if var-tracking is disabled, in which case -annotations are created and maintained, but discarded at the end. - -@item -fvar-tracking-assignments-toggle -@opindex fvar-tracking-assignments-toggle -@opindex fno-var-tracking-assignments-toggle -Toggle @option{-fvar-tracking-assignments}, in the same way that -@option{-gtoggle} toggles @option{-g}. - -@item -print-file-name=@var{library} -@opindex print-file-name -Print the full absolute name of the library file @var{library} that -would be used when linking---and don't do anything else. With this -option, GCC does not compile or link anything; it just prints the -file name. - -@item -print-multi-directory -@opindex print-multi-directory -Print the directory name corresponding to the multilib selected by any -other switches present in the command line. This directory is supposed -to exist in @env{GCC_EXEC_PREFIX}. - -@item -print-multi-lib -@opindex print-multi-lib -Print the mapping from multilib directory names to compiler switches -that enable them. The directory name is separated from the switches by -@samp{;}, and each switch starts with an @samp{@@} instead of the -@samp{-}, without spaces between multiple switches. This is supposed to -ease shell processing. - -@item -print-multi-os-directory -@opindex print-multi-os-directory -Print the path to OS libraries for the selected -multilib, relative to some @file{lib} subdirectory. If OS libraries are -present in the @file{lib} subdirectory and no multilibs are used, this is -usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}} -sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or -@file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}} -subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}. - -@item -print-multiarch -@opindex print-multiarch -Print the path to OS libraries for the selected multiarch, -relative to some @file{lib} subdirectory. - -@item -print-prog-name=@var{program} -@opindex print-prog-name -Like @option{-print-file-name}, but searches for a program such as @samp{cpp}. - -@item -print-libgcc-file-name -@opindex print-libgcc-file-name -Same as @option{-print-file-name=libgcc.a}. - -This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} -but you do want to link with @file{libgcc.a}. You can do: - -@smallexample -gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` -@end smallexample - -@item -print-search-dirs -@opindex print-search-dirs -Print the name of the configured installation directory and a list of -program and library directories @command{gcc} searches---and don't do anything else. - -This is useful when @command{gcc} prints the error message -@samp{installation problem, cannot exec cpp0: No such file or directory}. -To resolve this you either need to put @file{cpp0} and the other compiler -components where @command{gcc} expects to find them, or you can set the environment -variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. -Don't forget the trailing @samp{/}. -@xref{Environment Variables}. - -@item -print-sysroot -@opindex print-sysroot -Print the target sysroot directory that is used during -compilation. This is the target sysroot specified either at configure -time or using the @option{--sysroot} option, possibly with an extra -suffix that depends on compilation options. If no target sysroot is -specified, the option prints nothing. - -@item -print-sysroot-headers-suffix -@opindex print-sysroot-headers-suffix -Print the suffix added to the target sysroot when searching for -headers, or give an error if the compiler is not configured with such -a suffix---and don't do anything else. - -@item -dumpmachine -@opindex dumpmachine -Print the compiler's target machine (for example, -@samp{i686-pc-linux-gnu})---and don't do anything else. - -@item -dumpversion -@opindex dumpversion -Print the compiler version (for example, @samp{3.0})---and don't do -anything else. - -@item -dumpspecs -@opindex dumpspecs -Print the compiler's built-in specs---and don't do anything else. (This -is used when GCC itself is being built.) @xref{Spec Files}. - -@item -fno-eliminate-unused-debug-types -@opindex feliminate-unused-debug-types -@opindex fno-eliminate-unused-debug-types -Normally, when producing DWARF 2 output, GCC avoids producing debug symbol -output for types that are nowhere used in the source file being compiled. -Sometimes it is useful to have GCC emit debugging -information for all types declared in a compilation -unit, regardless of whether or not they are actually used -in that compilation unit, for example -if, in the debugger, you want to cast a value to a type that is -not actually used in your program (but is declared). More often, -however, this results in a significant amount of wasted space. -@end table - -@node Optimize Options -@section Options That Control Optimization -@cindex optimize options -@cindex options, optimization - -These options control various sorts of optimizations. - -Without any optimization option, the compiler's goal is to reduce the -cost of compilation and to make debugging produce the expected -results. Statements are independent: if you stop the program with a -breakpoint between statements, you can then assign a new value to any -variable or change the program counter to any other statement in the -function and get exactly the results you expect from the source -code. - -Turning on optimization flags makes the compiler attempt to improve -the performance and/or code size at the expense of compilation time -and possibly the ability to debug the program. - -The compiler performs optimization based on the knowledge it has of the -program. Compiling multiple files at once to a single output file mode allows -the compiler to use information gained from all of the files when compiling -each of them. - -Not all optimizations are controlled directly by a flag. Only -optimizations that have a flag are listed in this section. - -Most optimizations are only enabled if an @option{-O} level is set on -the command line. Otherwise they are disabled, even if individual -optimization flags are specified. - -Depending on the target and how GCC was configured, a slightly different -set of optimizations may be enabled at each @option{-O} level than -those listed here. You can invoke GCC with @option{-Q --help=optimizers} -to find out the exact set of optimizations that are enabled at each level. -@xref{Overall Options}, for examples. - -@table @gcctabopt -@item -O -@itemx -O1 -@opindex O -@opindex O1 -Optimize. Optimizing compilation takes somewhat more time, and a lot -more memory for a large function. - -With @option{-O}, the compiler tries to reduce code size and execution -time, without performing any optimizations that take a great deal of -compilation time. - -@option{-O} turns on the following optimization flags: -@gccoptlist{ --fauto-inc-dec @gol --fcompare-elim @gol --fcprop-registers @gol --fdce @gol --fdefer-pop @gol --fdelayed-branch @gol --fdse @gol --fguess-branch-probability @gol --fif-conversion2 @gol --fif-conversion @gol --fipa-pure-const @gol --fipa-profile @gol --fipa-reference @gol --fmerge-constants --fsplit-wide-types @gol --ftree-bit-ccp @gol --ftree-builtin-call-dce @gol --ftree-ccp @gol --ftree-ch @gol --ftree-copyrename @gol --ftree-dce @gol --ftree-dominator-opts @gol --ftree-dse @gol --ftree-forwprop @gol --ftree-fre @gol --ftree-phiprop @gol --ftree-slsr @gol --ftree-sra @gol --ftree-pta @gol --ftree-ter @gol --funit-at-a-time} - -@option{-O} also turns on @option{-fomit-frame-pointer} on machines -where doing so does not interfere with debugging. - -@item -O2 -@opindex O2 -Optimize even more. GCC performs nearly all supported optimizations -that do not involve a space-speed tradeoff. -As compared to @option{-O}, this option increases both compilation time -and the performance of the generated code. - -@option{-O2} turns on all optimization flags specified by @option{-O}. It -also turns on the following optimization flags: -@gccoptlist{-fthread-jumps @gol --falign-functions -falign-jumps @gol --falign-loops -falign-labels @gol --fcaller-saves @gol --fcrossjumping @gol --fcse-follow-jumps -fcse-skip-blocks @gol --fdelete-null-pointer-checks @gol --fdevirtualize @gol --fexpensive-optimizations @gol --fgcse -fgcse-lm @gol --fhoist-adjacent-loads @gol --finline-small-functions @gol --findirect-inlining @gol --fipa-sra @gol --foptimize-sibling-calls @gol --fpartial-inlining @gol --fpeephole2 @gol --fregmove @gol --freorder-blocks -freorder-functions @gol --frerun-cse-after-loop @gol --fsched-interblock -fsched-spec @gol --fschedule-insns -fschedule-insns2 @gol --fstrict-aliasing -fstrict-overflow @gol --ftree-switch-conversion -ftree-tail-merge @gol --ftree-pre @gol --ftree-vrp} - -Please note the warning under @option{-fgcse} about -invoking @option{-O2} on programs that use computed gotos. - -@item -O3 -@opindex O3 -Optimize yet more. @option{-O3} turns on all optimizations specified -by @option{-O2} and also turns on the @option{-finline-functions}, -@option{-funswitch-loops}, @option{-fpredictive-commoning}, -@option{-fgcse-after-reload}, @option{-ftree-vectorize}, -@option{-fvect-cost-model}, -@option{-ftree-partial-pre} and @option{-fipa-cp-clone} options. - -@item -O0 -@opindex O0 -Reduce compilation time and make debugging produce the expected -results. This is the default. - -@item -Os -@opindex Os -Optimize for size. @option{-Os} enables all @option{-O2} optimizations that -do not typically increase code size. It also performs further -optimizations designed to reduce code size. - -@option{-Os} disables the following optimization flags: -@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol --falign-labels -freorder-blocks -freorder-blocks-and-partition @gol --fprefetch-loop-arrays -ftree-vect-loop-version} - -@item -Ofast -@opindex Ofast -Disregard strict standards compliance. @option{-Ofast} enables all -@option{-O3} optimizations. It also enables optimizations that are not -valid for all standard-compliant programs. -It turns on @option{-ffast-math} and the Fortran-specific -@option{-fno-protect-parens} and @option{-fstack-arrays}. - -@item -Og -@opindex Og -Optimize debugging experience. @option{-Og} enables optimizations -that do not interfere with debugging. It should be the optimization -level of choice for the standard edit-compile-debug cycle, offering -a reasonable level of optimization while maintaining fast compilation -and a good debugging experience. - -If you use multiple @option{-O} options, with or without level numbers, -the last such option is the one that is effective. -@end table - -Options of the form @option{-f@var{flag}} specify machine-independent -flags. Most flags have both positive and negative forms; the negative -form of @option{-ffoo} is @option{-fno-foo}. In the table -below, only one of the forms is listed---the one you typically -use. You can figure out the other form by either removing @samp{no-} -or adding it. - -The following options control specific optimizations. They are either -activated by @option{-O} options or are related to ones that are. You -can use the following flags in the rare cases when ``fine-tuning'' of -optimizations to be performed is desired. - -@table @gcctabopt -@item -fno-default-inline -@opindex fno-default-inline -Do not make member functions inline by default merely because they are -defined inside the class scope (C++ only). Otherwise, when you specify -@w{@option{-O}}, member functions defined inside class scope are compiled -inline by default; i.e., you don't need to add @samp{inline} in front of -the member function name. - -@item -fno-defer-pop -@opindex fno-defer-pop -Always pop the arguments to each function call as soon as that function -returns. For machines that must pop arguments after a function call, -the compiler normally lets arguments accumulate on the stack for several -function calls and pops them all at once. - -Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fforward-propagate -@opindex fforward-propagate -Perform a forward propagation pass on RTL@. The pass tries to combine two -instructions and checks if the result can be simplified. If loop unrolling -is active, two passes are performed and the second is scheduled after -loop unrolling. - -This option is enabled by default at optimization levels @option{-O}, -@option{-O2}, @option{-O3}, @option{-Os}. - -@item -ffp-contract=@var{style} -@opindex ffp-contract -@option{-ffp-contract=off} disables floating-point expression contraction. -@option{-ffp-contract=fast} enables floating-point expression contraction -such as forming of fused multiply-add operations if the target has -native support for them. -@option{-ffp-contract=on} enables floating-point expression contraction -if allowed by the language standard. This is currently not implemented -and treated equal to @option{-ffp-contract=off}. - -The default is @option{-ffp-contract=fast}. - -@item -fomit-frame-pointer -@opindex fomit-frame-pointer -Don't keep the frame pointer in a register for functions that -don't need one. This avoids the instructions to save, set up and -restore frame pointers; it also makes an extra register available -in many functions. @strong{It also makes debugging impossible on -some machines.} - -On some machines, such as the VAX, this flag has no effect, because -the standard calling sequence automatically handles the frame pointer -and nothing is saved by pretending it doesn't exist. The -machine-description macro @code{FRAME_POINTER_REQUIRED} controls -whether a target machine supports this flag. @xref{Registers,,Register -Usage, gccint, GNU Compiler Collection (GCC) Internals}. - -Starting with GCC version 4.6, the default setting (when not optimizing for -size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets has been changed to -@option{-fomit-frame-pointer}. The default can be reverted to -@option{-fno-omit-frame-pointer} by configuring GCC with the -@option{--enable-frame-pointer} configure option. - -Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -foptimize-sibling-calls -@opindex foptimize-sibling-calls -Optimize sibling and tail recursive calls. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fno-inline -@opindex fno-inline -Do not expand any functions inline apart from those marked with -the @code{always_inline} attribute. This is the default when not -optimizing. - -Single functions can be exempted from inlining by marking them -with the @code{noinline} attribute. - -@item -finline-small-functions -@opindex finline-small-functions -Integrate functions into their callers when their body is smaller than expected -function call code (so overall size of program gets smaller). The compiler -heuristically decides which functions are simple enough to be worth integrating -in this way. This inlining applies to all functions, even those not declared -inline. - -Enabled at level @option{-O2}. - -@item -findirect-inlining -@opindex findirect-inlining -Inline also indirect calls that are discovered to be known at compile -time thanks to previous inlining. This option has any effect only -when inlining itself is turned on by the @option{-finline-functions} -or @option{-finline-small-functions} options. - -Enabled at level @option{-O2}. - -@item -finline-functions -@opindex finline-functions -Consider all functions for inlining, even if they are not declared inline. -The compiler heuristically decides which functions are worth integrating -in this way. - -If all calls to a given function are integrated, and the function is -declared @code{static}, then the function is normally not output as -assembler code in its own right. - -Enabled at level @option{-O3}. - -@item -finline-functions-called-once -@opindex finline-functions-called-once -Consider all @code{static} functions called once for inlining into their -caller even if they are not marked @code{inline}. If a call to a given -function is integrated, then the function is not output as assembler code -in its own right. - -Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}. - -@item -fearly-inlining -@opindex fearly-inlining -Inline functions marked by @code{always_inline} and functions whose body seems -smaller than the function call overhead early before doing -@option{-fprofile-generate} instrumentation and real inlining pass. Doing so -makes profiling significantly cheaper and usually inlining faster on programs -having large chains of nested wrapper functions. - -Enabled by default. - -@item -fipa-sra -@opindex fipa-sra -Perform interprocedural scalar replacement of aggregates, removal of -unused parameters and replacement of parameters passed by reference -by parameters passed by value. - -Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}. - -@item -finline-limit=@var{n} -@opindex finline-limit -By default, GCC limits the size of functions that can be inlined. This flag -allows coarse control of this limit. @var{n} is the size of functions that -can be inlined in number of pseudo instructions. - -Inlining is actually controlled by a number of parameters, which may be -specified individually by using @option{--param @var{name}=@var{value}}. -The @option{-finline-limit=@var{n}} option sets some of these parameters -as follows: - -@table @gcctabopt -@item max-inline-insns-single -is set to @var{n}/2. -@item max-inline-insns-auto -is set to @var{n}/2. -@end table - -See below for a documentation of the individual -parameters controlling inlining and for the defaults of these parameters. - -@emph{Note:} there may be no value to @option{-finline-limit} that results -in default behavior. - -@emph{Note:} pseudo instruction represents, in this particular context, an -abstract measurement of function's size. In no way does it represent a count -of assembly instructions and as such its exact meaning might change from one -release to an another. - -@item -fno-keep-inline-dllexport -@opindex -fno-keep-inline-dllexport -This is a more fine-grained version of @option{-fkeep-inline-functions}, -which applies only to functions that are declared using the @code{dllexport} -attribute or declspec (@xref{Function Attributes,,Declaring Attributes of -Functions}.) - -@item -fkeep-inline-functions -@opindex fkeep-inline-functions -In C, emit @code{static} functions that are declared @code{inline} -into the object file, even if the function has been inlined into all -of its callers. This switch does not affect functions using the -@code{extern inline} extension in GNU C90@. In C++, emit any and all -inline functions into the object file. - -@item -fkeep-static-consts -@opindex fkeep-static-consts -Emit variables declared @code{static const} when optimization isn't turned -on, even if the variables aren't referenced. - -GCC enables this option by default. If you want to force the compiler to -check if a variable is referenced, regardless of whether or not -optimization is turned on, use the @option{-fno-keep-static-consts} option. - -@item -fmerge-constants -@opindex fmerge-constants -Attempt to merge identical constants (string constants and floating-point -constants) across compilation units. - -This option is the default for optimized compilation if the assembler and -linker support it. Use @option{-fno-merge-constants} to inhibit this -behavior. - -Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fmerge-all-constants -@opindex fmerge-all-constants -Attempt to merge identical constants and identical variables. - -This option implies @option{-fmerge-constants}. In addition to -@option{-fmerge-constants} this considers e.g.@: even constant initialized -arrays or initialized constant variables with integral or floating-point -types. Languages like C or C++ require each variable, including multiple -instances of the same variable in recursive calls, to have distinct locations, -so using this option results in non-conforming -behavior. - -@item -fmodulo-sched -@opindex fmodulo-sched -Perform swing modulo scheduling immediately before the first scheduling -pass. This pass looks at innermost loops and reorders their -instructions by overlapping different iterations. - -@item -fmodulo-sched-allow-regmoves -@opindex fmodulo-sched-allow-regmoves -Perform more aggressive SMS-based modulo scheduling with register moves -allowed. By setting this flag certain anti-dependences edges are -deleted, which triggers the generation of reg-moves based on the -life-range analysis. This option is effective only with -@option{-fmodulo-sched} enabled. - -@item -fno-branch-count-reg -@opindex fno-branch-count-reg -Do not use ``decrement and branch'' instructions on a count register, -but instead generate a sequence of instructions that decrement a -register, compare it against zero, then branch based upon the result. -This option is only meaningful on architectures that support such -instructions, which include x86, PowerPC, IA-64 and S/390. - -The default is @option{-fbranch-count-reg}. - -@item -fno-function-cse -@opindex fno-function-cse -Do not put function addresses in registers; make each instruction that -calls a constant function contain the function's address explicitly. - -This option results in less efficient code, but some strange hacks -that alter the assembler output may be confused by the optimizations -performed when this option is not used. - -The default is @option{-ffunction-cse} - -@item -fno-zero-initialized-in-bss -@opindex fno-zero-initialized-in-bss -If the target supports a BSS section, GCC by default puts variables that -are initialized to zero into BSS@. This can save space in the resulting -code. - -This option turns off this behavior because some programs explicitly -rely on variables going to the data section---e.g., so that the -resulting executable can find the beginning of that section and/or make -assumptions based on that. - -The default is @option{-fzero-initialized-in-bss}. - -@item -fmudflap -fmudflapth -fmudflapir -@opindex fmudflap -@opindex fmudflapth -@opindex fmudflapir -@cindex bounds checking -@cindex mudflap -For front-ends that support it (C and C++), instrument all risky -pointer/array dereferencing operations, some standard library -string/heap functions, and some other associated constructs with -range/validity tests. Modules so instrumented should be immune to -buffer overflows, invalid heap use, and some other classes of C/C++ -programming errors. The instrumentation relies on a separate runtime -library (@file{libmudflap}), which is linked into a program if -@option{-fmudflap} is given at link time. Run-time behavior of the -instrumented program is controlled by the @env{MUDFLAP_OPTIONS} -environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out} -for its options. - -Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to -link if your program is multi-threaded. Use @option{-fmudflapir}, in -addition to @option{-fmudflap} or @option{-fmudflapth}, if -instrumentation should ignore pointer reads. This produces less -instrumentation (and therefore faster execution) and still provides -some protection against outright memory corrupting writes, but allows -erroneously read data to propagate within a program. - -@item -fthread-jumps -@opindex fthread-jumps -Perform optimizations that check to see if a jump branches to a -location where another comparison subsumed by the first is found. If -so, the first branch is redirected to either the destination of the -second branch or a point immediately following it, depending on whether -the condition is known to be true or false. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fsplit-wide-types -@opindex fsplit-wide-types -When using a type that occupies multiple registers, such as @code{long -long} on a 32-bit system, split the registers apart and allocate them -independently. This normally generates better code for those types, -but may make debugging more difficult. - -Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, -@option{-Os}. - -@item -fcse-follow-jumps -@opindex fcse-follow-jumps -In common subexpression elimination (CSE), scan through jump instructions -when the target of the jump is not reached by any other path. For -example, when CSE encounters an @code{if} statement with an -@code{else} clause, CSE follows the jump when the condition -tested is false. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fcse-skip-blocks -@opindex fcse-skip-blocks -This is similar to @option{-fcse-follow-jumps}, but causes CSE to -follow jumps that conditionally skip over blocks. When CSE -encounters a simple @code{if} statement with no else clause, -@option{-fcse-skip-blocks} causes CSE to follow the jump around the -body of the @code{if}. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -frerun-cse-after-loop -@opindex frerun-cse-after-loop -Re-run common subexpression elimination after loop optimizations are -performed. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fgcse -@opindex fgcse -Perform a global common subexpression elimination pass. -This pass also performs global constant and copy propagation. - -@emph{Note:} When compiling a program using computed gotos, a GCC -extension, you may get better run-time performance if you disable -the global common subexpression elimination pass by adding -@option{-fno-gcse} to the command line. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fgcse-lm -@opindex fgcse-lm -When @option{-fgcse-lm} is enabled, global common subexpression elimination -attempts to move loads that are only killed by stores into themselves. This -allows a loop containing a load/store sequence to be changed to a load outside -the loop, and a copy/store within the loop. - -Enabled by default when @option{-fgcse} is enabled. - -@item -fgcse-sm -@opindex fgcse-sm -When @option{-fgcse-sm} is enabled, a store motion pass is run after -global common subexpression elimination. This pass attempts to move -stores out of loops. When used in conjunction with @option{-fgcse-lm}, -loops containing a load/store sequence can be changed to a load before -the loop and a store after the loop. - -Not enabled at any optimization level. - -@item -fgcse-las -@opindex fgcse-las -When @option{-fgcse-las} is enabled, the global common subexpression -elimination pass eliminates redundant loads that come after stores to the -same memory location (both partial and full redundancies). - -Not enabled at any optimization level. - -@item -fgcse-after-reload -@opindex fgcse-after-reload -When @option{-fgcse-after-reload} is enabled, a redundant load elimination -pass is performed after reload. The purpose of this pass is to clean up -redundant spilling. - -@item -faggressive-loop-optimizations -@opindex faggressive-loop-optimizations -This option tells the loop optimizer to use language constraints to -derive bounds for the number of iterations of a loop. This assumes that -loop code does not invoke undefined behavior by for example causing signed -integer overflows or out-of-bound array accesses. The bounds for the -number of iterations of a loop are used to guide loop unrolling and peeling -and loop exit test optimizations. -This option is enabled by default. - -@item -funsafe-loop-optimizations -@opindex funsafe-loop-optimizations -This option tells the loop optimizer to assume that loop indices do not -overflow, and that loops with nontrivial exit condition are not -infinite. This enables a wider range of loop optimizations even if -the loop optimizer itself cannot prove that these assumptions are valid. -If you use @option{-Wunsafe-loop-optimizations}, the compiler warns you -if it finds this kind of loop. - -@item -fcrossjumping -@opindex fcrossjumping -Perform cross-jumping transformation. -This transformation unifies equivalent code and saves code size. The -resulting code may or may not perform better than without cross-jumping. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fauto-inc-dec -@opindex fauto-inc-dec -Combine increments or decrements of addresses with memory accesses. -This pass is always skipped on architectures that do not have -instructions to support this. Enabled by default at @option{-O} and -higher on architectures that support this. - -@item -fdce -@opindex fdce -Perform dead code elimination (DCE) on RTL@. -Enabled by default at @option{-O} and higher. - -@item -fdse -@opindex fdse -Perform dead store elimination (DSE) on RTL@. -Enabled by default at @option{-O} and higher. - -@item -fif-conversion -@opindex fif-conversion -Attempt to transform conditional jumps into branch-less equivalents. This -includes use of conditional moves, min, max, set flags and abs instructions, and -some tricks doable by standard arithmetics. The use of conditional execution -on chips where it is available is controlled by @code{if-conversion2}. - -Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fif-conversion2 -@opindex fif-conversion2 -Use conditional execution (where available) to transform conditional jumps into -branch-less equivalents. - -Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fdelete-null-pointer-checks -@opindex fdelete-null-pointer-checks -Assume that programs cannot safely dereference null pointers, and that -no code or data element resides there. This enables simple constant -folding optimizations at all optimization levels. In addition, other -optimization passes in GCC use this flag to control global dataflow -analyses that eliminate useless checks for null pointers; these assume -that if a pointer is checked after it has already been dereferenced, -it cannot be null. - -Note however that in some environments this assumption is not true. -Use @option{-fno-delete-null-pointer-checks} to disable this optimization -for programs that depend on that behavior. - -Some targets, especially embedded ones, disable this option at all levels. -Otherwise it is enabled at all levels: @option{-O0}, @option{-O1}, -@option{-O2}, @option{-O3}, @option{-Os}. Passes that use the information -are enabled independently at different optimization levels. - -@item -fdevirtualize -@opindex fdevirtualize -Attempt to convert calls to virtual functions to direct calls. This -is done both within a procedure and interprocedurally as part of -indirect inlining (@code{-findirect-inlining}) and interprocedural constant -propagation (@option{-fipa-cp}). -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fexpensive-optimizations -@opindex fexpensive-optimizations -Perform a number of minor optimizations that are relatively expensive. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -free -@opindex free -Attempt to remove redundant extension instructions. This is especially -helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit -registers after writing to their lower 32-bit half. - -Enabled for x86 at levels @option{-O2}, @option{-O3}. - -@item -foptimize-register-move -@itemx -fregmove -@opindex foptimize-register-move -@opindex fregmove -Attempt to reassign register numbers in move instructions and as -operands of other simple instructions in order to maximize the amount of -register tying. This is especially helpful on machines with two-operand -instructions. - -Note @option{-fregmove} and @option{-foptimize-register-move} are the same -optimization. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fira-algorithm=@var{algorithm} -Use the specified coloring algorithm for the integrated register -allocator. The @var{algorithm} argument can be @samp{priority}, which -specifies Chow's priority coloring, or @samp{CB}, which specifies -Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented -for all architectures, but for those targets that do support it, it is -the default because it generates better code. - -@item -fira-region=@var{region} -Use specified regions for the integrated register allocator. The -@var{region} argument should be one of the following: - -@table @samp - -@item all -Use all loops as register allocation regions. -This can give the best results for machines with a small and/or -irregular register set. - -@item mixed -Use all loops except for loops with small register pressure -as the regions. This value usually gives -the best results in most cases and for most architectures, -and is enabled by default when compiling with optimization for speed -(@option{-O}, @option{-O2}, @dots{}). - -@item one -Use all functions as a single region. -This typically results in the smallest code size, and is enabled by default for -@option{-Os} or @option{-O0}. - -@end table - -@item -fira-hoist-pressure -@opindex fira-hoist-pressure -Use IRA to evaluate register pressure in the code hoisting pass for -decisions to hoist expressions. This option usually results in smaller -code, but it can slow the compiler down. - -This option is enabled at level @option{-Os} for all targets. - -@item -fira-loop-pressure -@opindex fira-loop-pressure -Use IRA to evaluate register pressure in loops for decisions to move -loop invariants. This option usually results in generation -of faster and smaller code on machines with large register files (>= 32 -registers), but it can slow the compiler down. - -This option is enabled at level @option{-O3} for some targets. - -@item -fno-ira-share-save-slots -@opindex fno-ira-share-save-slots -Disable sharing of stack slots used for saving call-used hard -registers living through a call. Each hard register gets a -separate stack slot, and as a result function stack frames are -larger. - -@item -fno-ira-share-spill-slots -@opindex fno-ira-share-spill-slots -Disable sharing of stack slots allocated for pseudo-registers. Each -pseudo-register that does not get a hard register gets a separate -stack slot, and as a result function stack frames are larger. - -@item -fira-verbose=@var{n} -@opindex fira-verbose -Control the verbosity of the dump file for the integrated register allocator. -The default value is 5. If the value @var{n} is greater or equal to 10, -the dump output is sent to stderr using the same format as @var{n} minus 10. - -@item -fdelayed-branch -@opindex fdelayed-branch -If supported for the target machine, attempt to reorder instructions -to exploit instruction slots available after delayed branch -instructions. - -Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fschedule-insns -@opindex fschedule-insns -If supported for the target machine, attempt to reorder instructions to -eliminate execution stalls due to required data being unavailable. This -helps machines that have slow floating point or memory load instructions -by allowing other instructions to be issued until the result of the load -or floating-point instruction is required. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -fschedule-insns2 -@opindex fschedule-insns2 -Similar to @option{-fschedule-insns}, but requests an additional pass of -instruction scheduling after register allocation has been done. This is -especially useful on machines with a relatively small number of -registers and where memory load instructions take more than one cycle. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fno-sched-interblock -@opindex fno-sched-interblock -Don't schedule instructions across basic blocks. This is normally -enabled by default when scheduling before register allocation, i.e.@: -with @option{-fschedule-insns} or at @option{-O2} or higher. - -@item -fno-sched-spec -@opindex fno-sched-spec -Don't allow speculative motion of non-load instructions. This is normally -enabled by default when scheduling before register allocation, i.e.@: -with @option{-fschedule-insns} or at @option{-O2} or higher. - -@item -fsched-pressure -@opindex fsched-pressure -Enable register pressure sensitive insn scheduling before register -allocation. This only makes sense when scheduling before register -allocation is enabled, i.e.@: with @option{-fschedule-insns} or at -@option{-O2} or higher. Usage of this option can improve the -generated code and decrease its size by preventing register pressure -increase above the number of available hard registers and subsequent -spills in register allocation. - -@item -fsched-spec-load -@opindex fsched-spec-load -Allow speculative motion of some load instructions. This only makes -sense when scheduling before register allocation, i.e.@: with -@option{-fschedule-insns} or at @option{-O2} or higher. - -@item -fsched-spec-load-dangerous -@opindex fsched-spec-load-dangerous -Allow speculative motion of more load instructions. This only makes -sense when scheduling before register allocation, i.e.@: with -@option{-fschedule-insns} or at @option{-O2} or higher. - -@item -fsched-stalled-insns -@itemx -fsched-stalled-insns=@var{n} -@opindex fsched-stalled-insns -Define how many insns (if any) can be moved prematurely from the queue -of stalled insns into the ready list during the second scheduling pass. -@option{-fno-sched-stalled-insns} means that no insns are moved -prematurely, @option{-fsched-stalled-insns=0} means there is no limit -on how many queued insns can be moved prematurely. -@option{-fsched-stalled-insns} without a value is equivalent to -@option{-fsched-stalled-insns=1}. - -@item -fsched-stalled-insns-dep -@itemx -fsched-stalled-insns-dep=@var{n} -@opindex fsched-stalled-insns-dep -Define how many insn groups (cycles) are examined for a dependency -on a stalled insn that is a candidate for premature removal from the queue -of stalled insns. This has an effect only during the second scheduling pass, -and only if @option{-fsched-stalled-insns} is used. -@option{-fno-sched-stalled-insns-dep} is equivalent to -@option{-fsched-stalled-insns-dep=0}. -@option{-fsched-stalled-insns-dep} without a value is equivalent to -@option{-fsched-stalled-insns-dep=1}. - -@item -fsched2-use-superblocks -@opindex fsched2-use-superblocks -When scheduling after register allocation, use superblock scheduling. -This allows motion across basic block boundaries, -resulting in faster schedules. This option is experimental, as not all machine -descriptions used by GCC model the CPU closely enough to avoid unreliable -results from the algorithm. - -This only makes sense when scheduling after register allocation, i.e.@: with -@option{-fschedule-insns2} or at @option{-O2} or higher. - -@item -fsched-group-heuristic -@opindex fsched-group-heuristic -Enable the group heuristic in the scheduler. This heuristic favors -the instruction that belongs to a schedule group. This is enabled -by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} -or @option{-fschedule-insns2} or at @option{-O2} or higher. - -@item -fsched-critical-path-heuristic -@opindex fsched-critical-path-heuristic -Enable the critical-path heuristic in the scheduler. This heuristic favors -instructions on the critical path. This is enabled by default when -scheduling is enabled, i.e.@: with @option{-fschedule-insns} -or @option{-fschedule-insns2} or at @option{-O2} or higher. - -@item -fsched-spec-insn-heuristic -@opindex fsched-spec-insn-heuristic -Enable the speculative instruction heuristic in the scheduler. This -heuristic favors speculative instructions with greater dependency weakness. -This is enabled by default when scheduling is enabled, i.e.@: -with @option{-fschedule-insns} or @option{-fschedule-insns2} -or at @option{-O2} or higher. - -@item -fsched-rank-heuristic -@opindex fsched-rank-heuristic -Enable the rank heuristic in the scheduler. This heuristic favors -the instruction belonging to a basic block with greater size or frequency. -This is enabled by default when scheduling is enabled, i.e.@: -with @option{-fschedule-insns} or @option{-fschedule-insns2} or -at @option{-O2} or higher. - -@item -fsched-last-insn-heuristic -@opindex fsched-last-insn-heuristic -Enable the last-instruction heuristic in the scheduler. This heuristic -favors the instruction that is less dependent on the last instruction -scheduled. This is enabled by default when scheduling is enabled, -i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or -at @option{-O2} or higher. - -@item -fsched-dep-count-heuristic -@opindex fsched-dep-count-heuristic -Enable the dependent-count heuristic in the scheduler. This heuristic -favors the instruction that has more instructions depending on it. -This is enabled by default when scheduling is enabled, i.e.@: -with @option{-fschedule-insns} or @option{-fschedule-insns2} or -at @option{-O2} or higher. - -@item -freschedule-modulo-scheduled-loops -@opindex freschedule-modulo-scheduled-loops -Modulo scheduling is performed before traditional scheduling. If a loop -is modulo scheduled, later scheduling passes may change its schedule. -Use this option to control that behavior. - -@item -fselective-scheduling -@opindex fselective-scheduling -Schedule instructions using selective scheduling algorithm. Selective -scheduling runs instead of the first scheduler pass. - -@item -fselective-scheduling2 -@opindex fselective-scheduling2 -Schedule instructions using selective scheduling algorithm. Selective -scheduling runs instead of the second scheduler pass. - -@item -fsel-sched-pipelining -@opindex fsel-sched-pipelining -Enable software pipelining of innermost loops during selective scheduling. -This option has no effect unless one of @option{-fselective-scheduling} or -@option{-fselective-scheduling2} is turned on. - -@item -fsel-sched-pipelining-outer-loops -@opindex fsel-sched-pipelining-outer-loops -When pipelining loops during selective scheduling, also pipeline outer loops. -This option has no effect unless @option{-fsel-sched-pipelining} is turned on. - -@item -fshrink-wrap -@opindex fshrink-wrap -Emit function prologues only before parts of the function that need it, -rather than at the top of the function. This flag is enabled by default at -@option{-O} and higher. - -@item -fcaller-saves -@opindex fcaller-saves -Enable allocation of values to registers that are clobbered by -function calls, by emitting extra instructions to save and restore the -registers around such calls. Such allocation is done only when it -seems to result in better code. - -This option is always enabled by default on certain machines, usually -those which have no call-preserved registers to use instead. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fcombine-stack-adjustments -@opindex fcombine-stack-adjustments -Tracks stack adjustments (pushes and pops) and stack memory references -and then tries to find ways to combine them. - -Enabled by default at @option{-O1} and higher. - -@item -fconserve-stack -@opindex fconserve-stack -Attempt to minimize stack usage. The compiler attempts to use less -stack space, even if that makes the program slower. This option -implies setting the @option{large-stack-frame} parameter to 100 -and the @option{large-stack-frame-growth} parameter to 400. - -@item -ftree-reassoc -@opindex ftree-reassoc -Perform reassociation on trees. This flag is enabled by default -at @option{-O} and higher. - -@item -ftree-pre -@opindex ftree-pre -Perform partial redundancy elimination (PRE) on trees. This flag is -enabled by default at @option{-O2} and @option{-O3}. - -@item -ftree-partial-pre -@opindex ftree-partial-pre -Make partial redundancy elimination (PRE) more aggressive. This flag is -enabled by default at @option{-O3}. - -@item -ftree-forwprop -@opindex ftree-forwprop -Perform forward propagation on trees. This flag is enabled by default -at @option{-O} and higher. - -@item -ftree-fre -@opindex ftree-fre -Perform full redundancy elimination (FRE) on trees. The difference -between FRE and PRE is that FRE only considers expressions -that are computed on all paths leading to the redundant computation. -This analysis is faster than PRE, though it exposes fewer redundancies. -This flag is enabled by default at @option{-O} and higher. - -@item -ftree-phiprop -@opindex ftree-phiprop -Perform hoisting of loads from conditional pointers on trees. This -pass is enabled by default at @option{-O} and higher. - -@item -fhoist-adjacent-loads -@opindex hoist-adjacent-loads -Speculatively hoist loads from both branches of an if-then-else if the -loads are from adjacent locations in the same structure and the target -architecture has a conditional move instruction. This flag is enabled -by default at @option{-O2} and higher. - -@item -ftree-copy-prop -@opindex ftree-copy-prop -Perform copy propagation on trees. This pass eliminates unnecessary -copy operations. This flag is enabled by default at @option{-O} and -higher. - -@item -fipa-pure-const -@opindex fipa-pure-const -Discover which functions are pure or constant. -Enabled by default at @option{-O} and higher. - -@item -fipa-reference -@opindex fipa-reference -Discover which static variables do not escape the -compilation unit. -Enabled by default at @option{-O} and higher. - -@item -fipa-pta -@opindex fipa-pta -Perform interprocedural pointer analysis and interprocedural modification -and reference analysis. This option can cause excessive memory and -compile-time usage on large compilation units. It is not enabled by -default at any optimization level. - -@item -fipa-profile -@opindex fipa-profile -Perform interprocedural profile propagation. The functions called only from -cold functions are marked as cold. Also functions executed once (such as -@code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold -functions and loop less parts of functions executed once are then optimized for -size. -Enabled by default at @option{-O} and higher. - -@item -fipa-cp -@opindex fipa-cp -Perform interprocedural constant propagation. -This optimization analyzes the program to determine when values passed -to functions are constants and then optimizes accordingly. -This optimization can substantially increase performance -if the application has constants passed to functions. -This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}. - -@item -fipa-cp-clone -@opindex fipa-cp-clone -Perform function cloning to make interprocedural constant propagation stronger. -When enabled, interprocedural constant propagation performs function cloning -when externally visible function can be called with constant arguments. -Because this optimization can create multiple copies of functions, -it may significantly increase code size -(see @option{--param ipcp-unit-growth=@var{value}}). -This flag is enabled by default at @option{-O3}. - -@item -ftree-sink -@opindex ftree-sink -Perform forward store motion on trees. This flag is -enabled by default at @option{-O} and higher. - -@item -ftree-bit-ccp -@opindex ftree-bit-ccp -Perform sparse conditional bit constant propagation on trees and propagate -pointer alignment information. -This pass only operates on local scalar variables and is enabled by default -at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled. - -@item -ftree-ccp -@opindex ftree-ccp -Perform sparse conditional constant propagation (CCP) on trees. This -pass only operates on local scalar variables and is enabled by default -at @option{-O} and higher. - -@item -ftree-switch-conversion -Perform conversion of simple initializations in a switch to -initializations from a scalar array. This flag is enabled by default -at @option{-O2} and higher. - -@item -ftree-tail-merge -Look for identical code sequences. When found, replace one with a jump to the -other. This optimization is known as tail merging or cross jumping. This flag -is enabled by default at @option{-O2} and higher. The compilation time -in this pass can -be limited using @option{max-tail-merge-comparisons} parameter and -@option{max-tail-merge-iterations} parameter. - -@item -ftree-dce -@opindex ftree-dce -Perform dead code elimination (DCE) on trees. This flag is enabled by -default at @option{-O} and higher. - -@item -ftree-builtin-call-dce -@opindex ftree-builtin-call-dce -Perform conditional dead code elimination (DCE) for calls to built-in functions -that may set @code{errno} but are otherwise side-effect free. This flag is -enabled by default at @option{-O2} and higher if @option{-Os} is not also -specified. - -@item -ftree-dominator-opts -@opindex ftree-dominator-opts -Perform a variety of simple scalar cleanups (constant/copy -propagation, redundancy elimination, range propagation and expression -simplification) based on a dominator tree traversal. This also -performs jump threading (to reduce jumps to jumps). This flag is -enabled by default at @option{-O} and higher. - -@item -ftree-dse -@opindex ftree-dse -Perform dead store elimination (DSE) on trees. A dead store is a store into -a memory location that is later overwritten by another store without -any intervening loads. In this case the earlier store can be deleted. This -flag is enabled by default at @option{-O} and higher. - -@item -ftree-ch -@opindex ftree-ch -Perform loop header copying on trees. This is beneficial since it increases -effectiveness of code motion optimizations. It also saves one jump. This flag -is enabled by default at @option{-O} and higher. It is not enabled -for @option{-Os}, since it usually increases code size. - -@item -ftree-loop-optimize -@opindex ftree-loop-optimize -Perform loop optimizations on trees. This flag is enabled by default -at @option{-O} and higher. - -@item -ftree-loop-linear -@opindex ftree-loop-linear -Perform loop interchange transformations on tree. Same as -@option{-floop-interchange}. To use this code transformation, GCC has -to be configured with @option{--with-ppl} and @option{--with-cloog} to -enable the Graphite loop transformation infrastructure. - -@item -floop-interchange -@opindex floop-interchange -Perform loop interchange transformations on loops. Interchanging two -nested loops switches the inner and outer loops. For example, given a -loop like: -@smallexample -DO J = 1, M - DO I = 1, N - A(J, I) = A(J, I) * C - ENDDO -ENDDO -@end smallexample -loop interchange transforms the loop as if it were written: -@smallexample -DO I = 1, N - DO J = 1, M - A(J, I) = A(J, I) * C - ENDDO -ENDDO -@end smallexample -which can be beneficial when @code{N} is larger than the caches, -because in Fortran, the elements of an array are stored in memory -contiguously by column, and the original loop iterates over rows, -potentially creating at each access a cache miss. This optimization -applies to all the languages supported by GCC and is not limited to -Fortran. To use this code transformation, GCC has to be configured -with @option{--with-ppl} and @option{--with-cloog} to enable the -Graphite loop transformation infrastructure. - -@item -floop-strip-mine -@opindex floop-strip-mine -Perform loop strip mining transformations on loops. Strip mining -splits a loop into two nested loops. The outer loop has strides -equal to the strip size and the inner loop has strides of the -original loop within a strip. The strip length can be changed -using the @option{loop-block-tile-size} parameter. For example, -given a loop like: -@smallexample -DO I = 1, N - A(I) = A(I) + C -ENDDO -@end smallexample -loop strip mining transforms the loop as if it were written: -@smallexample -DO II = 1, N, 51 - DO I = II, min (II + 50, N) - A(I) = A(I) + C - ENDDO -ENDDO -@end smallexample -This optimization applies to all the languages supported by GCC and is -not limited to Fortran. To use this code transformation, GCC has to -be configured with @option{--with-ppl} and @option{--with-cloog} to -enable the Graphite loop transformation infrastructure. - -@item -floop-block -@opindex floop-block -Perform loop blocking transformations on loops. Blocking strip mines -each loop in the loop nest such that the memory accesses of the -element loops fit inside caches. The strip length can be changed -using the @option{loop-block-tile-size} parameter. For example, given -a loop like: -@smallexample -DO I = 1, N - DO J = 1, M - A(J, I) = B(I) + C(J) - ENDDO -ENDDO -@end smallexample -loop blocking transforms the loop as if it were written: -@smallexample -DO II = 1, N, 51 - DO JJ = 1, M, 51 - DO I = II, min (II + 50, N) - DO J = JJ, min (JJ + 50, M) - A(J, I) = B(I) + C(J) - ENDDO - ENDDO - ENDDO -ENDDO -@end smallexample -which can be beneficial when @code{M} is larger than the caches, -because the innermost loop iterates over a smaller amount of data -which can be kept in the caches. This optimization applies to all the -languages supported by GCC and is not limited to Fortran. To use this -code transformation, GCC has to be configured with @option{--with-ppl} -and @option{--with-cloog} to enable the Graphite loop transformation -infrastructure. - -@item -fgraphite-identity -@opindex fgraphite-identity -Enable the identity transformation for graphite. For every SCoP we generate -the polyhedral representation and transform it back to gimple. Using -@option{-fgraphite-identity} we can check the costs or benefits of the -GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations -are also performed by the code generator CLooG, like index splitting and -dead code elimination in loops. - -@item -floop-nest-optimize -@opindex floop-nest-optimize -Enable the ISL based loop nest optimizer. This is a generic loop nest -optimizer based on the Pluto optimization algorithms. It calculates a loop -structure optimized for data-locality and parallelism. This option -is experimental. - -@item -floop-parallelize-all -@opindex floop-parallelize-all -Use the Graphite data dependence analysis to identify loops that can -be parallelized. Parallelize all the loops that can be analyzed to -not contain loop carried dependences without checking that it is -profitable to parallelize the loops. - -@item -fcheck-data-deps -@opindex fcheck-data-deps -Compare the results of several data dependence analyzers. This option -is used for debugging the data dependence analyzers. - -@item -ftree-loop-if-convert -Attempt to transform conditional jumps in the innermost loops to -branch-less equivalents. The intent is to remove control-flow from -the innermost loops in order to improve the ability of the -vectorization pass to handle these loops. This is enabled by default -if vectorization is enabled. - -@item -ftree-loop-if-convert-stores -Attempt to also if-convert conditional jumps containing memory writes. -This transformation can be unsafe for multi-threaded programs as it -transforms conditional memory writes into unconditional memory writes. -For example, -@smallexample -for (i = 0; i < N; i++) - if (cond) - A[i] = expr; -@end smallexample -is transformed to -@smallexample -for (i = 0; i < N; i++) - A[i] = cond ? expr : A[i]; -@end smallexample -potentially producing data races. - -@item -ftree-loop-distribution -Perform loop distribution. This flag can improve cache performance on -big loop bodies and allow further loop optimizations, like -parallelization or vectorization, to take place. For example, the loop -@smallexample -DO I = 1, N - A(I) = B(I) + C - D(I) = E(I) * F -ENDDO -@end smallexample -is transformed to -@smallexample -DO I = 1, N - A(I) = B(I) + C -ENDDO -DO I = 1, N - D(I) = E(I) * F -ENDDO -@end smallexample - -@item -ftree-loop-distribute-patterns -Perform loop distribution of patterns that can be code generated with -calls to a library. This flag is enabled by default at @option{-O3}. - -This pass distributes the initialization loops and generates a call to -memset zero. For example, the loop -@smallexample -DO I = 1, N - A(I) = 0 - B(I) = A(I) + I -ENDDO -@end smallexample -is transformed to -@smallexample -DO I = 1, N - A(I) = 0 -ENDDO -DO I = 1, N - B(I) = A(I) + I -ENDDO -@end smallexample -and the initialization loop is transformed into a call to memset zero. - -@item -ftree-loop-im -@opindex ftree-loop-im -Perform loop invariant motion on trees. This pass moves only invariants that -are hard to handle at RTL level (function calls, operations that expand to -nontrivial sequences of insns). With @option{-funswitch-loops} it also moves -operands of conditions that are invariant out of the loop, so that we can use -just trivial invariantness analysis in loop unswitching. The pass also includes -store motion. - -@item -ftree-loop-ivcanon -@opindex ftree-loop-ivcanon -Create a canonical counter for number of iterations in loops for which -determining number of iterations requires complicated analysis. Later -optimizations then may determine the number easily. Useful especially -in connection with unrolling. - -@item -fivopts -@opindex fivopts -Perform induction variable optimizations (strength reduction, induction -variable merging and induction variable elimination) on trees. - -@item -ftree-parallelize-loops=n -@opindex ftree-parallelize-loops -Parallelize loops, i.e., split their iteration space to run in n threads. -This is only possible for loops whose iterations are independent -and can be arbitrarily reordered. The optimization is only -profitable on multiprocessor machines, for loops that are CPU-intensive, -rather than constrained e.g.@: by memory bandwidth. This option -implies @option{-pthread}, and thus is only supported on targets -that have support for @option{-pthread}. - -@item -ftree-pta -@opindex ftree-pta -Perform function-local points-to analysis on trees. This flag is -enabled by default at @option{-O} and higher. - -@item -ftree-sra -@opindex ftree-sra -Perform scalar replacement of aggregates. This pass replaces structure -references with scalars to prevent committing structures to memory too -early. This flag is enabled by default at @option{-O} and higher. - -@item -ftree-copyrename -@opindex ftree-copyrename -Perform copy renaming on trees. This pass attempts to rename compiler -temporaries to other variables at copy locations, usually resulting in -variable names which more closely resemble the original variables. This flag -is enabled by default at @option{-O} and higher. - -@item -ftree-coalesce-inlined-vars -Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to -combine small user-defined variables too, but only if they were inlined -from other functions. It is a more limited form of -@option{-ftree-coalesce-vars}. This may harm debug information of such -inlined variables, but it will keep variables of the inlined-into -function apart from each other, such that they are more likely to -contain the expected values in a debugging session. This was the -default in GCC versions older than 4.7. - -@item -ftree-coalesce-vars -Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to -combine small user-defined variables too, instead of just compiler -temporaries. This may severely limit the ability to debug an optimized -program compiled with @option{-fno-var-tracking-assignments}. In the -negated form, this flag prevents SSA coalescing of user variables, -including inlined ones. This option is enabled by default. - -@item -ftree-ter -@opindex ftree-ter -Perform temporary expression replacement during the SSA->normal phase. Single -use/single def temporaries are replaced at their use location with their -defining expression. This results in non-GIMPLE code, but gives the expanders -much more complex trees to work on resulting in better RTL generation. This is -enabled by default at @option{-O} and higher. - -@item -ftree-slsr -@opindex ftree-slsr -Perform straight-line strength reduction on trees. This recognizes related -expressions involving multiplications and replaces them by less expensive -calculations when possible. This is enabled by default at @option{-O} and -higher. - -@item -ftree-vectorize -@opindex ftree-vectorize -Perform loop vectorization on trees. This flag is enabled by default at -@option{-O3}. - -@item -ftree-slp-vectorize -@opindex ftree-slp-vectorize -Perform basic block vectorization on trees. This flag is enabled by default at -@option{-O3} and when @option{-ftree-vectorize} is enabled. - -@item -ftree-vect-loop-version -@opindex ftree-vect-loop-version -Perform loop versioning when doing loop vectorization on trees. When a loop -appears to be vectorizable except that data alignment or data dependence cannot -be determined at compile time, then vectorized and non-vectorized versions of -the loop are generated along with run-time checks for alignment or dependence -to control which version is executed. This option is enabled by default -except at level @option{-Os} where it is disabled. - -@item -fvect-cost-model -@opindex fvect-cost-model -Enable cost model for vectorization. This option is enabled by default at -@option{-O3}. - -@item -ftree-vrp -@opindex ftree-vrp -Perform Value Range Propagation on trees. This is similar to the -constant propagation pass, but instead of values, ranges of values are -propagated. This allows the optimizers to remove unnecessary range -checks like array bound checks and null pointer checks. This is -enabled by default at @option{-O2} and higher. Null pointer check -elimination is only done if @option{-fdelete-null-pointer-checks} is -enabled. - -@item -ftracer -@opindex ftracer -Perform tail duplication to enlarge superblock size. This transformation -simplifies the control flow of the function allowing other optimizations to do -a better job. - -@item -funroll-loops -@opindex funroll-loops -Unroll loops whose number of iterations can be determined at compile -time or upon entry to the loop. @option{-funroll-loops} implies -@option{-frerun-cse-after-loop}. This option makes code larger, -and may or may not make it run faster. - -@item -funroll-all-loops -@opindex funroll-all-loops -Unroll all loops, even if their number of iterations is uncertain when -the loop is entered. This usually makes programs run more slowly. -@option{-funroll-all-loops} implies the same options as -@option{-funroll-loops}, - -@item -fsplit-ivs-in-unroller -@opindex fsplit-ivs-in-unroller -Enables expression of values of induction variables in later iterations -of the unrolled loop using the value in the first iteration. This breaks -long dependency chains, thus improving efficiency of the scheduling passes. - -A combination of @option{-fweb} and CSE is often sufficient to obtain the -same effect. However, that is not reliable in cases where the loop body -is more complicated than a single basic block. It also does not work at all -on some architectures due to restrictions in the CSE pass. - -This optimization is enabled by default. - -@item -fvariable-expansion-in-unroller -@opindex fvariable-expansion-in-unroller -With this option, the compiler creates multiple copies of some -local variables when unrolling a loop, which can result in superior code. - -@item -fpartial-inlining -@opindex fpartial-inlining -Inline parts of functions. This option has any effect only -when inlining itself is turned on by the @option{-finline-functions} -or @option{-finline-small-functions} options. - -Enabled at level @option{-O2}. - -@item -fpredictive-commoning -@opindex fpredictive-commoning -Perform predictive commoning optimization, i.e., reusing computations -(especially memory loads and stores) performed in previous -iterations of loops. - -This option is enabled at level @option{-O3}. - -@item -fprefetch-loop-arrays -@opindex fprefetch-loop-arrays -If supported by the target machine, generate instructions to prefetch -memory to improve the performance of loops that access large arrays. - -This option may generate better or worse code; results are highly -dependent on the structure of loops within the source code. - -Disabled at level @option{-Os}. - -@item -fno-peephole -@itemx -fno-peephole2 -@opindex fno-peephole -@opindex fno-peephole2 -Disable any machine-specific peephole optimizations. The difference -between @option{-fno-peephole} and @option{-fno-peephole2} is in how they -are implemented in the compiler; some targets use one, some use the -other, a few use both. - -@option{-fpeephole} is enabled by default. -@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fno-guess-branch-probability -@opindex fno-guess-branch-probability -Do not guess branch probabilities using heuristics. - -GCC uses heuristics to guess branch probabilities if they are -not provided by profiling feedback (@option{-fprofile-arcs}). These -heuristics are based on the control flow graph. If some branch probabilities -are specified by @samp{__builtin_expect}, then the heuristics are -used to guess branch probabilities for the rest of the control flow graph, -taking the @samp{__builtin_expect} info into account. The interactions -between the heuristics and @samp{__builtin_expect} can be complex, and in -some cases, it may be useful to disable the heuristics so that the effects -of @samp{__builtin_expect} are easier to understand. - -The default is @option{-fguess-branch-probability} at levels -@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -freorder-blocks -@opindex freorder-blocks -Reorder basic blocks in the compiled function in order to reduce number of -taken branches and improve code locality. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -freorder-blocks-and-partition -@opindex freorder-blocks-and-partition -In addition to reordering basic blocks in the compiled function, in order -to reduce number of taken branches, partitions hot and cold basic blocks -into separate sections of the assembly and .o files, to improve -paging and cache locality performance. - -This optimization is automatically turned off in the presence of -exception handling, for linkonce sections, for functions with a user-defined -section attribute and on any architecture that does not support named -sections. - -@item -freorder-functions -@opindex freorder-functions -Reorder functions in the object file in order to -improve code locality. This is implemented by using special -subsections @code{.text.hot} for most frequently executed functions and -@code{.text.unlikely} for unlikely executed functions. Reordering is done by -the linker so object file format must support named sections and linker must -place them in a reasonable way. - -Also profile feedback must be available to make this option effective. See -@option{-fprofile-arcs} for details. - -Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fstrict-aliasing -@opindex fstrict-aliasing -Allow the compiler to assume the strictest aliasing rules applicable to -the language being compiled. For C (and C++), this activates -optimizations based on the type of expressions. In particular, an -object of one type is assumed never to reside at the same address as an -object of a different type, unless the types are almost the same. For -example, an @code{unsigned int} can alias an @code{int}, but not a -@code{void*} or a @code{double}. A character type may alias any other -type. - -@anchor{Type-punning}Pay special attention to code like this: -@smallexample -union a_union @{ - int i; - double d; -@}; - -int f() @{ - union a_union t; - t.d = 3.0; - return t.i; -@} -@end smallexample -The practice of reading from a different union member than the one most -recently written to (called ``type-punning'') is common. Even with -@option{-fstrict-aliasing}, type-punning is allowed, provided the memory -is accessed through the union type. So, the code above works as -expected. @xref{Structures unions enumerations and bit-fields -implementation}. However, this code might not: -@smallexample -int f() @{ - union a_union t; - int* ip; - t.d = 3.0; - ip = &t.i; - return *ip; -@} -@end smallexample - -Similarly, access by taking the address, casting the resulting pointer -and dereferencing the result has undefined behavior, even if the cast -uses a union type, e.g.: -@smallexample -int f() @{ - double d = 3.0; - return ((union a_union *) &d)->i; -@} -@end smallexample - -The @option{-fstrict-aliasing} option is enabled at levels -@option{-O2}, @option{-O3}, @option{-Os}. - -@item -fstrict-overflow -@opindex fstrict-overflow -Allow the compiler to assume strict signed overflow rules, depending -on the language being compiled. For C (and C++) this means that -overflow when doing arithmetic with signed numbers is undefined, which -means that the compiler may assume that it does not happen. This -permits various optimizations. For example, the compiler assumes -that an expression like @code{i + 10 > i} is always true for -signed @code{i}. This assumption is only valid if signed overflow is -undefined, as the expression is false if @code{i + 10} overflows when -using twos complement arithmetic. When this option is in effect any -attempt to determine whether an operation on signed numbers -overflows must be written carefully to not actually involve overflow. - -This option also allows the compiler to assume strict pointer -semantics: given a pointer to an object, if adding an offset to that -pointer does not produce a pointer to the same object, the addition is -undefined. This permits the compiler to conclude that @code{p + u > -p} is always true for a pointer @code{p} and unsigned integer -@code{u}. This assumption is only valid because pointer wraparound is -undefined, as the expression is false if @code{p + u} overflows using -twos complement arithmetic. - -See also the @option{-fwrapv} option. Using @option{-fwrapv} means -that integer signed overflow is fully defined: it wraps. When -@option{-fwrapv} is used, there is no difference between -@option{-fstrict-overflow} and @option{-fno-strict-overflow} for -integers. With @option{-fwrapv} certain types of overflow are -permitted. For example, if the compiler gets an overflow when doing -arithmetic on constants, the overflowed value can still be used with -@option{-fwrapv}, but not otherwise. - -The @option{-fstrict-overflow} option is enabled at levels -@option{-O2}, @option{-O3}, @option{-Os}. - -@item -falign-functions -@itemx -falign-functions=@var{n} -@opindex falign-functions -Align the start of functions to the next power-of-two greater than -@var{n}, skipping up to @var{n} bytes. For instance, -@option{-falign-functions=32} aligns functions to the next 32-byte -boundary, but @option{-falign-functions=24} aligns to the next -32-byte boundary only if this can be done by skipping 23 bytes or less. - -@option{-fno-align-functions} and @option{-falign-functions=1} are -equivalent and mean that functions are not aligned. - -Some assemblers only support this flag when @var{n} is a power of two; -in that case, it is rounded up. - -If @var{n} is not specified or is zero, use a machine-dependent default. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -falign-labels -@itemx -falign-labels=@var{n} -@opindex falign-labels -Align all branch targets to a power-of-two boundary, skipping up to -@var{n} bytes like @option{-falign-functions}. This option can easily -make code slower, because it must insert dummy operations for when the -branch target is reached in the usual flow of the code. - -@option{-fno-align-labels} and @option{-falign-labels=1} are -equivalent and mean that labels are not aligned. - -If @option{-falign-loops} or @option{-falign-jumps} are applicable and -are greater than this value, then their values are used instead. - -If @var{n} is not specified or is zero, use a machine-dependent default -which is very likely to be @samp{1}, meaning no alignment. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -falign-loops -@itemx -falign-loops=@var{n} -@opindex falign-loops -Align loops to a power-of-two boundary, skipping up to @var{n} bytes -like @option{-falign-functions}. If the loops are -executed many times, this makes up for any execution of the dummy -operations. - -@option{-fno-align-loops} and @option{-falign-loops=1} are -equivalent and mean that loops are not aligned. - -If @var{n} is not specified or is zero, use a machine-dependent default. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -falign-jumps -@itemx -falign-jumps=@var{n} -@opindex falign-jumps -Align branch targets to a power-of-two boundary, for branch targets -where the targets can only be reached by jumping, skipping up to @var{n} -bytes like @option{-falign-functions}. In this case, no dummy operations -need be executed. - -@option{-fno-align-jumps} and @option{-falign-jumps=1} are -equivalent and mean that loops are not aligned. - -If @var{n} is not specified or is zero, use a machine-dependent default. - -Enabled at levels @option{-O2}, @option{-O3}. - -@item -funit-at-a-time -@opindex funit-at-a-time -This option is left for compatibility reasons. @option{-funit-at-a-time} -has no effect, while @option{-fno-unit-at-a-time} implies -@option{-fno-toplevel-reorder} and @option{-fno-section-anchors}. - -Enabled by default. - -@item -fno-toplevel-reorder -@opindex fno-toplevel-reorder -Do not reorder top-level functions, variables, and @code{asm} -statements. Output them in the same order that they appear in the -input file. When this option is used, unreferenced static variables -are not removed. This option is intended to support existing code -that relies on a particular ordering. For new code, it is better to -use attributes. - -Enabled at level @option{-O0}. When disabled explicitly, it also implies -@option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some -targets. - -@item -fweb -@opindex fweb -Constructs webs as commonly used for register allocation purposes and assign -each web individual pseudo register. This allows the register allocation pass -to operate on pseudos directly, but also strengthens several other optimization -passes, such as CSE, loop optimizer and trivial dead code remover. It can, -however, make debugging impossible, since variables no longer stay in a -``home register''. - -Enabled by default with @option{-funroll-loops}. - -@item -fwhole-program -@opindex fwhole-program -Assume that the current compilation unit represents the whole program being -compiled. All public functions and variables with the exception of @code{main} -and those merged by attribute @code{externally_visible} become static functions -and in effect are optimized more aggressively by interprocedural optimizers. - -This option should not be used in combination with @code{-flto}. -Instead relying on a linker plugin should provide safer and more precise -information. - -@item -flto[=@var{n}] -@opindex flto -This option runs the standard link-time optimizer. When invoked -with source code, it generates GIMPLE (one of GCC's internal -representations) and writes it to special ELF sections in the object -file. When the object files are linked together, all the function -bodies are read from these ELF sections and instantiated as if they -had been part of the same translation unit. - -To use the link-time optimizer, @option{-flto} needs to be specified at -compile time and during the final link. For example: - -@smallexample -gcc -c -O2 -flto foo.c -gcc -c -O2 -flto bar.c -gcc -o myprog -flto -O2 foo.o bar.o -@end smallexample - -The first two invocations to GCC save a bytecode representation -of GIMPLE into special ELF sections inside @file{foo.o} and -@file{bar.o}. The final invocation reads the GIMPLE bytecode from -@file{foo.o} and @file{bar.o}, merges the two files into a single -internal image, and compiles the result as usual. Since both -@file{foo.o} and @file{bar.o} are merged into a single image, this -causes all the interprocedural analyses and optimizations in GCC to -work across the two files as if they were a single one. This means, -for example, that the inliner is able to inline functions in -@file{bar.o} into functions in @file{foo.o} and vice-versa. - -Another (simpler) way to enable link-time optimization is: - -@smallexample -gcc -o myprog -flto -O2 foo.c bar.c -@end smallexample - -The above generates bytecode for @file{foo.c} and @file{bar.c}, -merges them together into a single GIMPLE representation and optimizes -them as usual to produce @file{myprog}. - -The only important thing to keep in mind is that to enable link-time -optimizations the @option{-flto} flag needs to be passed to both the -compile and the link commands. - -To make whole program optimization effective, it is necessary to make -certain whole program assumptions. The compiler needs to know -what functions and variables can be accessed by libraries and runtime -outside of the link-time optimized unit. When supported by the linker, -the linker plugin (see @option{-fuse-linker-plugin}) passes information -to the compiler about used and externally visible symbols. When -the linker plugin is not available, @option{-fwhole-program} should be -used to allow the compiler to make these assumptions, which leads -to more aggressive optimization decisions. - -Note that when a file is compiled with @option{-flto}, the generated -object file is larger than a regular object file because it -contains GIMPLE bytecodes and the usual final code. This means that -object files with LTO information can be linked as normal object -files; if @option{-flto} is not passed to the linker, no -interprocedural optimizations are applied. - -Additionally, the optimization flags used to compile individual files -are not necessarily related to those used at link time. For instance, - -@smallexample -gcc -c -O0 -flto foo.c -gcc -c -O0 -flto bar.c -gcc -o myprog -flto -O3 foo.o bar.o -@end smallexample - -This produces individual object files with unoptimized assembler -code, but the resulting binary @file{myprog} is optimized at -@option{-O3}. If, instead, the final binary is generated without -@option{-flto}, then @file{myprog} is not optimized. - -When producing the final binary with @option{-flto}, GCC only -applies link-time optimizations to those files that contain bytecode. -Therefore, you can mix and match object files and libraries with -GIMPLE bytecodes and final object code. GCC automatically selects -which files to optimize in LTO mode and which files to link without -further processing. - -There are some code generation flags preserved by GCC when -generating bytecodes, as they need to be used during the final link -stage. Currently, the following options are saved into the GIMPLE -bytecode files: @option{-fPIC}, @option{-fcommon} and all the -@option{-m} target flags. - -At link time, these options are read in and reapplied. Note that the -current implementation makes no attempt to recognize conflicting -values for these options. If different files have conflicting option -values (e.g., one file is compiled with @option{-fPIC} and another -isn't), the compiler simply uses the last value read from the -bytecode files. It is recommended, then, that you compile all the files -participating in the same link with the same options. - -If LTO encounters objects with C linkage declared with incompatible -types in separate translation units to be linked together (undefined -behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be -issued. The behavior is still undefined at run time. - -Another feature of LTO is that it is possible to apply interprocedural -optimizations on files written in different languages. This requires -support in the language front end. Currently, the C, C++ and -Fortran front ends are capable of emitting GIMPLE bytecodes, so -something like this should work: - -@smallexample -gcc -c -flto foo.c -g++ -c -flto bar.cc -gfortran -c -flto baz.f90 -g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran -@end smallexample - -Notice that the final link is done with @command{g++} to get the C++ -runtime libraries and @option{-lgfortran} is added to get the Fortran -runtime libraries. In general, when mixing languages in LTO mode, you -should use the same link command options as when mixing languages in a -regular (non-LTO) compilation; all you need to add is @option{-flto} to -all the compile and link commands. - -If object files containing GIMPLE bytecode are stored in a library archive, say -@file{libfoo.a}, it is possible to extract and use them in an LTO link if you -are using a linker with plugin support. To enable this feature, use -the flag @option{-fuse-linker-plugin} at link time: - -@smallexample -gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo -@end smallexample - -With the linker plugin enabled, the linker extracts the needed -GIMPLE files from @file{libfoo.a} and passes them on to the running GCC -to make them part of the aggregated GIMPLE image to be optimized. - -If you are not using a linker with plugin support and/or do not -enable the linker plugin, then the objects inside @file{libfoo.a} -are extracted and linked as usual, but they do not participate -in the LTO optimization process. - -Link-time optimizations do not require the presence of the whole program to -operate. If the program does not require any symbols to be exported, it is -possible to combine @option{-flto} and @option{-fwhole-program} to allow -the interprocedural optimizers to use more aggressive assumptions which may -lead to improved optimization opportunities. -Use of @option{-fwhole-program} is not needed when linker plugin is -active (see @option{-fuse-linker-plugin}). - -The current implementation of LTO makes no -attempt to generate bytecode that is portable between different -types of hosts. The bytecode files are versioned and there is a -strict version check, so bytecode files generated in one version of -GCC will not work with an older/newer version of GCC@. - -Link-time optimization does not work well with generation of debugging -information. Combining @option{-flto} with -@option{-g} is currently experimental and expected to produce wrong -results. - -If you specify the optional @var{n}, the optimization and code -generation done at link time is executed in parallel using @var{n} -parallel jobs by utilizing an installed @command{make} program. The -environment variable @env{MAKE} may be used to override the program -used. The default value for @var{n} is 1. - -You can also specify @option{-flto=jobserver} to use GNU make's -job server mode to determine the number of parallel jobs. This -is useful when the Makefile calling GCC is already executing in parallel. -You must prepend a @samp{+} to the command recipe in the parent Makefile -for this to work. This option likely only works if @env{MAKE} is -GNU make. - -This option is disabled by default. - -@item -flto-partition=@var{alg} -@opindex flto-partition -Specify the partitioning algorithm used by the link-time optimizer. -The value is either @code{1to1} to specify a partitioning mirroring -the original source files or @code{balanced} to specify partitioning -into equally sized chunks (whenever possible) or @code{max} to create -new partition for every symbol where possible. Specifying @code{none} -as an algorithm disables partitioning and streaming completely. -The default value is @code{balanced}. While @code{1to1} can be used -as an workaround for various code ordering issues, the @code{max} -partitioning is intended for internal testing only. - -@item -flto-compression-level=@var{n} -This option specifies the level of compression used for intermediate -language written to LTO object files, and is only meaningful in -conjunction with LTO mode (@option{-flto}). Valid -values are 0 (no compression) to 9 (maximum compression). Values -outside this range are clamped to either 0 or 9. If the option is not -given, a default balanced compression setting is used. - -@item -flto-report -Prints a report with internal details on the workings of the link-time -optimizer. The contents of this report vary from version to version. -It is meant to be useful to GCC developers when processing object -files in LTO mode (via @option{-flto}). - -Disabled by default. - -@item -fuse-linker-plugin -Enables the use of a linker plugin during link-time optimization. This -option relies on plugin support in the linker, which is available in gold -or in GNU ld 2.21 or newer. - -This option enables the extraction of object files with GIMPLE bytecode out -of library archives. This improves the quality of optimization by exposing -more code to the link-time optimizer. This information specifies what -symbols can be accessed externally (by non-LTO object or during dynamic -linking). Resulting code quality improvements on binaries (and shared -libraries that use hidden visibility) are similar to @code{-fwhole-program}. -See @option{-flto} for a description of the effect of this flag and how to -use it. - -This option is enabled by default when LTO support in GCC is enabled -and GCC was configured for use with -a linker supporting plugins (GNU ld 2.21 or newer or gold). - -@item -ffat-lto-objects -@opindex ffat-lto-objects -Fat LTO objects are object files that contain both the intermediate language -and the object code. This makes them usable for both LTO linking and normal -linking. This option is effective only when compiling with @option{-flto} -and is ignored at link time. - -@option{-fno-fat-lto-objects} improves compilation time over plain LTO, but -requires the complete toolchain to be aware of LTO. It requires a linker with -linker plugin support for basic functionality. Additionally, -@command{nm}, @command{ar} and @command{ranlib} -need to support linker plugins to allow a full-featured build environment -(capable of building static libraries etc). GCC provides the @command{gcc-ar}, -@command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options -to these tools. With non fat LTO makefiles need to be modified to use them. - -The default is @option{-ffat-lto-objects} but this default is intended to -change in future releases when linker plugin enabled environments become more -common. - -@item -fcompare-elim -@opindex fcompare-elim -After register allocation and post-register allocation instruction splitting, -identify arithmetic instructions that compute processor flags similar to a -comparison operation based on that arithmetic. If possible, eliminate the -explicit comparison operation. - -This pass only applies to certain targets that cannot explicitly represent -the comparison operation before register allocation is complete. - -Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fuse-ld=bfd -Use the @command{bfd} linker instead of the default linker. - -@item -fuse-ld=gold -Use the @command{gold} linker instead of the default linker. - -@item -fcprop-registers -@opindex fcprop-registers -After register allocation and post-register allocation instruction splitting, -perform a copy-propagation pass to try to reduce scheduling dependencies -and occasionally eliminate the copy. - -Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. - -@item -fprofile-correction -@opindex fprofile-correction -Profiles collected using an instrumented binary for multi-threaded programs may -be inconsistent due to missed counter updates. When this option is specified, -GCC uses heuristics to correct or smooth out such inconsistencies. By -default, GCC emits an error message when an inconsistent profile is detected. - -@item -fprofile-dir=@var{path} -@opindex fprofile-dir - -Set the directory to search for the profile data files in to @var{path}. -This option affects only the profile data generated by -@option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs} -and used by @option{-fprofile-use} and @option{-fbranch-probabilities} -and its related options. Both absolute and relative paths can be used. -By default, GCC uses the current directory as @var{path}, thus the -profile data file appears in the same directory as the object file. - -@item -fprofile-generate -@itemx -fprofile-generate=@var{path} -@opindex fprofile-generate - -Enable options usually used for instrumenting application to produce -profile useful for later recompilation with profile feedback based -optimization. You must use @option{-fprofile-generate} both when -compiling and when linking your program. - -The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}. - -If @var{path} is specified, GCC looks at the @var{path} to find -the profile feedback data files. See @option{-fprofile-dir}. - -@item -fprofile-use -@itemx -fprofile-use=@var{path} -@opindex fprofile-use -Enable profile feedback directed optimizations, and optimizations -generally profitable only with profile feedback available. - -The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt}, -@code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}, @code{-ftree-vectorize}, -@code{ftree-loop-distribute-patterns} - -By default, GCC emits an error message if the feedback profiles do not -match the source code. This error can be turned into a warning by using -@option{-Wcoverage-mismatch}. Note this may result in poorly optimized -code. - -If @var{path} is specified, GCC looks at the @var{path} to find -the profile feedback data files. See @option{-fprofile-dir}. -@end table - -The following options control compiler behavior regarding floating-point -arithmetic. These options trade off between speed and -correctness. All must be specifically enabled. - -@table @gcctabopt -@item -ffloat-store -@opindex ffloat-store -Do not store floating-point variables in registers, and inhibit other -options that might change whether a floating-point value is taken from a -register or memory. - -@cindex floating-point precision -This option prevents undesirable excess precision on machines such as -the 68000 where the floating registers (of the 68881) keep more -precision than a @code{double} is supposed to have. Similarly for the -x86 architecture. For most programs, the excess precision does only -good, but a few programs rely on the precise definition of IEEE floating -point. Use @option{-ffloat-store} for such programs, after modifying -them to store all pertinent intermediate computations into variables. - -@item -fexcess-precision=@var{style} -@opindex fexcess-precision -This option allows further control over excess precision on machines -where floating-point registers have more precision than the IEEE -@code{float} and @code{double} types and the processor does not -support operations rounding to those types. By default, -@option{-fexcess-precision=fast} is in effect; this means that -operations are carried out in the precision of the registers and that -it is unpredictable when rounding to the types specified in the source -code takes place. When compiling C, if -@option{-fexcess-precision=standard} is specified then excess -precision follows the rules specified in ISO C99; in particular, -both casts and assignments cause values to be rounded to their -semantic types (whereas @option{-ffloat-store} only affects -assignments). This option is enabled by default for C if a strict -conformance option such as @option{-std=c99} is used. - -@opindex mfpmath -@option{-fexcess-precision=standard} is not implemented for languages -other than C, and has no effect if -@option{-funsafe-math-optimizations} or @option{-ffast-math} is -specified. On the x86, it also has no effect if @option{-mfpmath=sse} -or @option{-mfpmath=sse+387} is specified; in the former case, IEEE -semantics apply without excess precision, and in the latter, rounding -is unpredictable. - -@item -ffast-math -@opindex ffast-math -Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, -@option{-ffinite-math-only}, @option{-fno-rounding-math}, -@option{-fno-signaling-nans} and @option{-fcx-limited-range}. - -This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. - -This option is not turned on by any @option{-O} option besides -@option{-Ofast} since it can result in incorrect output for programs -that depend on an exact implementation of IEEE or ISO rules/specifications -for math functions. It may, however, yield faster code for programs -that do not require the guarantees of these specifications. - -@item -fno-math-errno -@opindex fno-math-errno -Do not set @code{errno} after calling math functions that are executed -with a single instruction, e.g., @code{sqrt}. A program that relies on -IEEE exceptions for math error handling may want to use this flag -for speed while maintaining IEEE arithmetic compatibility. - -This option is not turned on by any @option{-O} option since -it can result in incorrect output for programs that depend on -an exact implementation of IEEE or ISO rules/specifications for -math functions. It may, however, yield faster code for programs -that do not require the guarantees of these specifications. - -The default is @option{-fmath-errno}. - -On Darwin systems, the math library never sets @code{errno}. There is -therefore no reason for the compiler to consider the possibility that -it might, and @option{-fno-math-errno} is the default. - -@item -funsafe-math-optimizations -@opindex funsafe-math-optimizations - -Allow optimizations for floating-point arithmetic that (a) assume -that arguments and results are valid and (b) may violate IEEE or -ANSI standards. When used at link-time, it may include libraries -or startup files that change the default FPU control word or other -similar optimizations. - -This option is not turned on by any @option{-O} option since -it can result in incorrect output for programs that depend on -an exact implementation of IEEE or ISO rules/specifications for -math functions. It may, however, yield faster code for programs -that do not require the guarantees of these specifications. -Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math}, -@option{-fassociative-math} and @option{-freciprocal-math}. - -The default is @option{-fno-unsafe-math-optimizations}. - -@item -fassociative-math -@opindex fassociative-math - -Allow re-association of operands in series of floating-point operations. -This violates the ISO C and C++ language standard by possibly changing -computation result. NOTE: re-ordering may change the sign of zero as -well as ignore NaNs and inhibit or create underflow or overflow (and -thus cannot be used on code that relies on rounding behavior like -@code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons -and thus may not be used when ordered comparisons are required. -This option requires that both @option{-fno-signed-zeros} and -@option{-fno-trapping-math} be in effect. Moreover, it doesn't make -much sense with @option{-frounding-math}. For Fortran the option -is automatically enabled when both @option{-fno-signed-zeros} and -@option{-fno-trapping-math} are in effect. - -The default is @option{-fno-associative-math}. - -@item -freciprocal-math -@opindex freciprocal-math - -Allow the reciprocal of a value to be used instead of dividing by -the value if this enables optimizations. For example @code{x / y} -can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)} -is subject to common subexpression elimination. Note that this loses -precision and increases the number of flops operating on the value. - -The default is @option{-fno-reciprocal-math}. - -@item -ffinite-math-only -@opindex ffinite-math-only -Allow optimizations for floating-point arithmetic that assume -that arguments and results are not NaNs or +-Infs. - -This option is not turned on by any @option{-O} option since -it can result in incorrect output for programs that depend on -an exact implementation of IEEE or ISO rules/specifications for -math functions. It may, however, yield faster code for programs -that do not require the guarantees of these specifications. - -The default is @option{-fno-finite-math-only}. - -@item -fno-signed-zeros -@opindex fno-signed-zeros -Allow optimizations for floating-point arithmetic that ignore the -signedness of zero. IEEE arithmetic specifies the behavior of -distinct +0.0 and @minus{}0.0 values, which then prohibits simplification -of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}). -This option implies that the sign of a zero result isn't significant. - -The default is @option{-fsigned-zeros}. - -@item -fno-trapping-math -@opindex fno-trapping-math -Compile code assuming that floating-point operations cannot generate -user-visible traps. These traps include division by zero, overflow, -underflow, inexact result and invalid operation. This option requires -that @option{-fno-signaling-nans} be in effect. Setting this option may -allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example. - -This option should never be turned on by any @option{-O} option since -it can result in incorrect output for programs that depend on -an exact implementation of IEEE or ISO rules/specifications for -math functions. - -The default is @option{-ftrapping-math}. - -@item -frounding-math -@opindex frounding-math -Disable transformations and optimizations that assume default floating-point -rounding behavior. This is round-to-zero for all floating point -to integer conversions, and round-to-nearest for all other arithmetic -truncations. This option should be specified for programs that change -the FP rounding mode dynamically, or that may be executed with a -non-default rounding mode. This option disables constant folding of -floating-point expressions at compile time (which may be affected by -rounding mode) and arithmetic transformations that are unsafe in the -presence of sign-dependent rounding modes. - -The default is @option{-fno-rounding-math}. - -This option is experimental and does not currently guarantee to -disable all GCC optimizations that are affected by rounding mode. -Future versions of GCC may provide finer control of this setting -using C99's @code{FENV_ACCESS} pragma. This command-line option -will be used to specify the default state for @code{FENV_ACCESS}. - -@item -fsignaling-nans -@opindex fsignaling-nans -Compile code assuming that IEEE signaling NaNs may generate user-visible -traps during floating-point operations. Setting this option disables -optimizations that may change the number of exceptions visible with -signaling NaNs. This option implies @option{-ftrapping-math}. - -This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to -be defined. - -The default is @option{-fno-signaling-nans}. - -This option is experimental and does not currently guarantee to -disable all GCC optimizations that affect signaling NaN behavior. - -@item -fsingle-precision-constant -@opindex fsingle-precision-constant -Treat floating-point constants as single precision instead of -implicitly converting them to double-precision constants. - -@item -fcx-limited-range -@opindex fcx-limited-range -When enabled, this option states that a range reduction step is not -needed when performing complex division. Also, there is no checking -whether the result of a complex multiplication or division is @code{NaN -+ I*NaN}, with an attempt to rescue the situation in that case. The -default is @option{-fno-cx-limited-range}, but is enabled by -@option{-ffast-math}. - -This option controls the default setting of the ISO C99 -@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to -all languages. - -@item -fcx-fortran-rules -@opindex fcx-fortran-rules -Complex multiplication and division follow Fortran rules. Range -reduction is done as part of complex division, but there is no checking -whether the result of a complex multiplication or division is @code{NaN -+ I*NaN}, with an attempt to rescue the situation in that case. - -The default is @option{-fno-cx-fortran-rules}. - -@end table - -The following options control optimizations that may improve -performance, but are not enabled by any @option{-O} options. This -section includes experimental options that may produce broken code. - -@table @gcctabopt -@item -fbranch-probabilities -@opindex fbranch-probabilities -After running a program compiled with @option{-fprofile-arcs} -(@pxref{Debugging Options,, Options for Debugging Your Program or -@command{gcc}}), you can compile it a second time using -@option{-fbranch-probabilities}, to improve optimizations based on -the number of times each branch was taken. When a program -compiled with @option{-fprofile-arcs} exits, it saves arc execution -counts to a file called @file{@var{sourcename}.gcda} for each source -file. The information in this data file is very dependent on the -structure of the generated code, so you must use the same source code -and the same optimization options for both compilations. - -With @option{-fbranch-probabilities}, GCC puts a -@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. -These can be used to improve optimization. Currently, they are only -used in one place: in @file{reorg.c}, instead of guessing which path a -branch is most likely to take, the @samp{REG_BR_PROB} values are used to -exactly determine which path is taken more often. - -@item -fprofile-values -@opindex fprofile-values -If combined with @option{-fprofile-arcs}, it adds code so that some -data about values of expressions in the program is gathered. - -With @option{-fbranch-probabilities}, it reads back the data gathered -from profiling values of expressions for usage in optimizations. - -Enabled with @option{-fprofile-generate} and @option{-fprofile-use}. - -@item -fvpt -@opindex fvpt -If combined with @option{-fprofile-arcs}, this option instructs the compiler -to add code to gather information about values of expressions. - -With @option{-fbranch-probabilities}, it reads back the data gathered -and actually performs the optimizations based on them. -Currently the optimizations include specialization of division operations -using the knowledge about the value of the denominator. - -@item -frename-registers -@opindex frename-registers -Attempt to avoid false dependencies in scheduled code by making use -of registers left over after register allocation. This optimization -most benefits processors with lots of registers. Depending on the -debug information format adopted by the target, however, it can -make debugging impossible, since variables no longer stay in -a ``home register''. - -Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}. - -@item -ftracer -@opindex ftracer -Perform tail duplication to enlarge superblock size. This transformation -simplifies the control flow of the function allowing other optimizations to do -a better job. - -Enabled with @option{-fprofile-use}. - -@item -funroll-loops -@opindex funroll-loops -Unroll loops whose number of iterations can be determined at compile time or -upon entry to the loop. @option{-funroll-loops} implies -@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}. -It also turns on complete loop peeling (i.e.@: complete removal of loops with -a small constant number of iterations). This option makes code larger, and may -or may not make it run faster. - -Enabled with @option{-fprofile-use}. - -@item -funroll-all-loops -@opindex funroll-all-loops -Unroll all loops, even if their number of iterations is uncertain when -the loop is entered. This usually makes programs run more slowly. -@option{-funroll-all-loops} implies the same options as -@option{-funroll-loops}. - -@item -fpeel-loops -@opindex fpeel-loops -Peels loops for which there is enough information that they do not -roll much (from profile feedback). It also turns on complete loop peeling -(i.e.@: complete removal of loops with small constant number of iterations). - -Enabled with @option{-fprofile-use}. - -@item -fmove-loop-invariants -@opindex fmove-loop-invariants -Enables the loop invariant motion pass in the RTL loop optimizer. Enabled -at level @option{-O1} - -@item -funswitch-loops -@opindex funswitch-loops -Move branches with loop invariant conditions out of the loop, with duplicates -of the loop on both branches (modified according to result of the condition). - -@item -ffunction-sections -@itemx -fdata-sections -@opindex ffunction-sections -@opindex fdata-sections -Place each function or data item into its own section in the output -file if the target supports arbitrary sections. The name of the -function or the name of the data item determines the section's name -in the output file. - -Use these options on systems where the linker can perform optimizations -to improve locality of reference in the instruction space. Most systems -using the ELF object format and SPARC processors running Solaris 2 have -linkers with such optimizations. AIX may have these optimizations in -the future. - -Only use these options when there are significant benefits from doing -so. When you specify these options, the assembler and linker -create larger object and executable files and are also slower. -You cannot use @code{gprof} on all systems if you -specify this option, and you may have problems with debugging if -you specify both this option and @option{-g}. - -@item -fbranch-target-load-optimize -@opindex fbranch-target-load-optimize -Perform branch target register load optimization before prologue / epilogue -threading. -The use of target registers can typically be exposed only during reload, -thus hoisting loads out of loops and doing inter-block scheduling needs -a separate optimization pass. - -@item -fbranch-target-load-optimize2 -@opindex fbranch-target-load-optimize2 -Perform branch target register load optimization after prologue / epilogue -threading. - -@item -fbtr-bb-exclusive -@opindex fbtr-bb-exclusive -When performing branch target register load optimization, don't reuse -branch target registers within any basic block. - -@item -fstack-protector -@opindex fstack-protector -Emit extra code to check for buffer overflows, such as stack smashing -attacks. This is done by adding a guard variable to functions with -vulnerable objects. This includes functions that call @code{alloca}, and -functions with buffers larger than 8 bytes. The guards are initialized -when a function is entered and then checked when the function exits. -If a guard check fails, an error message is printed and the program exits. - -@item -fstack-protector-all -@opindex fstack-protector-all -Like @option{-fstack-protector} except that all functions are protected. - -@item -fsection-anchors -@opindex fsection-anchors -Try to reduce the number of symbolic address calculations by using -shared ``anchor'' symbols to address nearby objects. This transformation -can help to reduce the number of GOT entries and GOT accesses on some -targets. - -For example, the implementation of the following function @code{foo}: - -@smallexample -static int a, b, c; -int foo (void) @{ return a + b + c; @} -@end smallexample - -@noindent -usually calculates the addresses of all three variables, but if you -compile it with @option{-fsection-anchors}, it accesses the variables -from a common anchor point instead. The effect is similar to the -following pseudocode (which isn't valid C): - -@smallexample -int foo (void) -@{ - register int *xr = &x; - return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; -@} -@end smallexample - -Not all targets support this option. - -@item --param @var{name}=@var{value} -@opindex param -In some places, GCC uses various constants to control the amount of -optimization that is done. For example, GCC does not inline functions -that contain more than a certain number of instructions. You can -control some of these constants on the command line using the -@option{--param} option. - -The names of specific parameters, and the meaning of the values, are -tied to the internals of the compiler, and are subject to change -without notice in future releases. - -In each case, the @var{value} is an integer. The allowable choices for -@var{name} are: - -@table @gcctabopt -@item predictable-branch-outcome -When branch is predicted to be taken with probability lower than this threshold -(in percent), then it is considered well predictable. The default is 10. - -@item max-crossjump-edges -The maximum number of incoming edges to consider for cross-jumping. -The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in -the number of edges incoming to each block. Increasing values mean -more aggressive optimization, making the compilation time increase with -probably small improvement in executable size. - -@item min-crossjump-insns -The minimum number of instructions that must be matched at the end -of two blocks before cross-jumping is performed on them. This -value is ignored in the case where all instructions in the block being -cross-jumped from are matched. The default value is 5. - -@item max-grow-copy-bb-insns -The maximum code size expansion factor when copying basic blocks -instead of jumping. The expansion is relative to a jump instruction. -The default value is 8. - -@item max-goto-duplication-insns -The maximum number of instructions to duplicate to a block that jumps -to a computed goto. To avoid @math{O(N^2)} behavior in a number of -passes, GCC factors computed gotos early in the compilation process, -and unfactors them as late as possible. Only computed jumps at the -end of a basic blocks with no more than max-goto-duplication-insns are -unfactored. The default value is 8. - -@item max-delay-slot-insn-search -The maximum number of instructions to consider when looking for an -instruction to fill a delay slot. If more than this arbitrary number of -instructions are searched, the time savings from filling the delay slot -are minimal, so stop searching. Increasing values mean more -aggressive optimization, making the compilation time increase with probably -small improvement in execution time. - -@item max-delay-slot-live-search -When trying to fill delay slots, the maximum number of instructions to -consider when searching for a block with valid live register -information. Increasing this arbitrarily chosen value means more -aggressive optimization, increasing the compilation time. This parameter -should be removed when the delay slot code is rewritten to maintain the -control-flow graph. - -@item max-gcse-memory -The approximate maximum amount of memory that can be allocated in -order to perform the global common subexpression elimination -optimization. If more memory than specified is required, the -optimization is not done. - -@item max-gcse-insertion-ratio -If the ratio of expression insertions to deletions is larger than this value -for any expression, then RTL PRE inserts or removes the expression and thus -leaves partially redundant computations in the instruction stream. The default value is 20. - -@item max-pending-list-length -The maximum number of pending dependencies scheduling allows -before flushing the current state and starting over. Large functions -with few branches or calls can create excessively large lists which -needlessly consume memory and resources. - -@item max-modulo-backtrack-attempts -The maximum number of backtrack attempts the scheduler should make -when modulo scheduling a loop. Larger values can exponentially increase -compilation time. - -@item max-inline-insns-single -Several parameters control the tree inliner used in GCC@. -This number sets the maximum number of instructions (counted in GCC's -internal representation) in a single function that the tree inliner -considers for inlining. This only affects functions declared -inline and methods implemented in a class declaration (C++). -The default value is 400. - -@item max-inline-insns-auto -When you use @option{-finline-functions} (included in @option{-O3}), -a lot of functions that would otherwise not be considered for inlining -by the compiler are investigated. To those functions, a different -(more restrictive) limit compared to functions declared inline can -be applied. -The default value is 40. - -@item inline-min-speedup -When estimated performance improvement of caller + callee runtime exceeds this -threshold (in precent), the function can be inlined regardless the limit on -@option{--param max-inline-insns-single} and @option{--param -max-inline-insns-auto}. - -@item large-function-insns -The limit specifying really large functions. For functions larger than this -limit after inlining, inlining is constrained by -@option{--param large-function-growth}. This parameter is useful primarily -to avoid extreme compilation time caused by non-linear algorithms used by the -back end. -The default value is 2700. - -@item large-function-growth -Specifies maximal growth of large function caused by inlining in percents. -The default value is 100 which limits large function growth to 2.0 times -the original size. - -@item large-unit-insns -The limit specifying large translation unit. Growth caused by inlining of -units larger than this limit is limited by @option{--param inline-unit-growth}. -For small units this might be too tight. -For example, consider a unit consisting of function A -that is inline and B that just calls A three times. If B is small relative to -A, the growth of unit is 300\% and yet such inlining is very sane. For very -large units consisting of small inlineable functions, however, the overall unit -growth limit is needed to avoid exponential explosion of code size. Thus for -smaller units, the size is increased to @option{--param large-unit-insns} -before applying @option{--param inline-unit-growth}. The default is 10000. - -@item inline-unit-growth -Specifies maximal overall growth of the compilation unit caused by inlining. -The default value is 30 which limits unit growth to 1.3 times the original -size. - -@item ipcp-unit-growth -Specifies maximal overall growth of the compilation unit caused by -interprocedural constant propagation. The default value is 10 which limits -unit growth to 1.1 times the original size. - -@item large-stack-frame -The limit specifying large stack frames. While inlining the algorithm is trying -to not grow past this limit too much. The default value is 256 bytes. - -@item large-stack-frame-growth -Specifies maximal growth of large stack frames caused by inlining in percents. -The default value is 1000 which limits large stack frame growth to 11 times -the original size. - -@item max-inline-insns-recursive -@itemx max-inline-insns-recursive-auto -Specifies the maximum number of instructions an out-of-line copy of a -self-recursive inline -function can grow into by performing recursive inlining. - -For functions declared inline, @option{--param max-inline-insns-recursive} is -taken into account. For functions not declared inline, recursive inlining -happens only when @option{-finline-functions} (included in @option{-O3}) is -enabled and @option{--param max-inline-insns-recursive-auto} is used. The -default value is 450. - -@item max-inline-recursive-depth -@itemx max-inline-recursive-depth-auto -Specifies the maximum recursion depth used for recursive inlining. - -For functions declared inline, @option{--param max-inline-recursive-depth} is -taken into account. For functions not declared inline, recursive inlining -happens only when @option{-finline-functions} (included in @option{-O3}) is -enabled and @option{--param max-inline-recursive-depth-auto} is used. The -default value is 8. - -@item min-inline-recursive-probability -Recursive inlining is profitable only for function having deep recursion -in average and can hurt for function having little recursion depth by -increasing the prologue size or complexity of function body to other -optimizers. - -When profile feedback is available (see @option{-fprofile-generate}) the actual -recursion depth can be guessed from probability that function recurses via a -given call expression. This parameter limits inlining only to call expressions -whose probability exceeds the given threshold (in percents). -The default value is 10. - -@item early-inlining-insns -Specify growth that the early inliner can make. In effect it increases -the amount of inlining for code having a large abstraction penalty. -The default value is 10. - -@item max-early-inliner-iterations -@itemx max-early-inliner-iterations -Limit of iterations of the early inliner. This basically bounds -the number of nested indirect calls the early inliner can resolve. -Deeper chains are still handled by late inlining. - -@item comdat-sharing-probability -@itemx comdat-sharing-probability -Probability (in percent) that C++ inline function with comdat visibility -are shared across multiple compilation units. The default value is 20. - -@item min-vect-loop-bound -The minimum number of iterations under which loops are not vectorized -when @option{-ftree-vectorize} is used. The number of iterations after -vectorization needs to be greater than the value specified by this option -to allow vectorization. The default value is 0. - -@item gcse-cost-distance-ratio -Scaling factor in calculation of maximum distance an expression -can be moved by GCSE optimizations. This is currently supported only in the -code hoisting pass. The bigger the ratio, the more aggressive code hoisting -is with simple expressions, i.e., the expressions that have cost -less than @option{gcse-unrestricted-cost}. Specifying 0 disables -hoisting of simple expressions. The default value is 10. - -@item gcse-unrestricted-cost -Cost, roughly measured as the cost of a single typical machine -instruction, at which GCSE optimizations do not constrain -the distance an expression can travel. This is currently -supported only in the code hoisting pass. The lesser the cost, -the more aggressive code hoisting is. Specifying 0 -allows all expressions to travel unrestricted distances. -The default value is 3. - -@item max-hoist-depth -The depth of search in the dominator tree for expressions to hoist. -This is used to avoid quadratic behavior in hoisting algorithm. -The value of 0 does not limit on the search, but may slow down compilation -of huge functions. The default value is 30. - -@item max-tail-merge-comparisons -The maximum amount of similar bbs to compare a bb with. This is used to -avoid quadratic behavior in tree tail merging. The default value is 10. - -@item max-tail-merge-iterations -The maximum amount of iterations of the pass over the function. This is used to -limit compilation time in tree tail merging. The default value is 2. - -@item max-unrolled-insns -The maximum number of instructions that a loop may have to be unrolled. -If a loop is unrolled, this parameter also determines how many times -the loop code is unrolled. - -@item max-average-unrolled-insns -The maximum number of instructions biased by probabilities of their execution -that a loop may have to be unrolled. If a loop is unrolled, -this parameter also determines how many times the loop code is unrolled. - -@item max-unroll-times -The maximum number of unrollings of a single loop. - -@item max-peeled-insns -The maximum number of instructions that a loop may have to be peeled. -If a loop is peeled, this parameter also determines how many times -the loop code is peeled. - -@item max-peel-times -The maximum number of peelings of a single loop. - -@item max-peel-branches -The maximum number of branches on the hot path through the peeled sequence. - -@item max-completely-peeled-insns -The maximum number of insns of a completely peeled loop. - -@item max-completely-peel-times -The maximum number of iterations of a loop to be suitable for complete peeling. - -@item max-completely-peel-loop-nest-depth -The maximum depth of a loop nest suitable for complete peeling. - -@item max-unswitch-insns -The maximum number of insns of an unswitched loop. - -@item max-unswitch-level -The maximum number of branches unswitched in a single loop. - -@item lim-expensive -The minimum cost of an expensive expression in the loop invariant motion. - -@item iv-consider-all-candidates-bound -Bound on number of candidates for induction variables, below which -all candidates are considered for each use in induction variable -optimizations. If there are more candidates than this, -only the most relevant ones are considered to avoid quadratic time complexity. - -@item iv-max-considered-uses -The induction variable optimizations give up on loops that contain more -induction variable uses. - -@item iv-always-prune-cand-set-bound -If the number of candidates in the set is smaller than this value, -always try to remove unnecessary ivs from the set -when adding a new one. - -@item scev-max-expr-size -Bound on size of expressions used in the scalar evolutions analyzer. -Large expressions slow the analyzer. - -@item scev-max-expr-complexity -Bound on the complexity of the expressions in the scalar evolutions analyzer. -Complex expressions slow the analyzer. - -@item omega-max-vars -The maximum number of variables in an Omega constraint system. -The default value is 128. - -@item omega-max-geqs -The maximum number of inequalities in an Omega constraint system. -The default value is 256. - -@item omega-max-eqs -The maximum number of equalities in an Omega constraint system. -The default value is 128. - -@item omega-max-wild-cards -The maximum number of wildcard variables that the Omega solver is -able to insert. The default value is 18. - -@item omega-hash-table-size -The size of the hash table in the Omega solver. The default value is -550. - -@item omega-max-keys -The maximal number of keys used by the Omega solver. The default -value is 500. - -@item omega-eliminate-redundant-constraints -When set to 1, use expensive methods to eliminate all redundant -constraints. The default value is 0. - -@item vect-max-version-for-alignment-checks -The maximum number of run-time checks that can be performed when -doing loop versioning for alignment in the vectorizer. See option -@option{-ftree-vect-loop-version} for more information. - -@item vect-max-version-for-alias-checks -The maximum number of run-time checks that can be performed when -doing loop versioning for alias in the vectorizer. See option -@option{-ftree-vect-loop-version} for more information. - -@item max-iterations-to-track -The maximum number of iterations of a loop the brute-force algorithm -for analysis of the number of iterations of the loop tries to evaluate. - -@item hot-bb-count-ws-permille -A basic block profile count is considered hot if it contributes to -the given permillage (i.e. 0...1000) of the entire profiled execution. - -@item hot-bb-frequency-fraction -Select fraction of the entry block frequency of executions of basic block in -function given basic block needs to have to be considered hot. - -@item max-predicted-iterations -The maximum number of loop iterations we predict statically. This is useful -in cases where a function contains a single loop with known bound and -another loop with unknown bound. -The known number of iterations is predicted correctly, while -the unknown number of iterations average to roughly 10. This means that the -loop without bounds appears artificially cold relative to the other one. - -@item align-threshold - -Select fraction of the maximal frequency of executions of a basic block in -a function to align the basic block. - -@item align-loop-iterations - -A loop expected to iterate at least the selected number of iterations is -aligned. - -@item tracer-dynamic-coverage -@itemx tracer-dynamic-coverage-feedback - -This value is used to limit superblock formation once the given percentage of -executed instructions is covered. This limits unnecessary code size -expansion. - -The @option{tracer-dynamic-coverage-feedback} is used only when profile -feedback is available. The real profiles (as opposed to statically estimated -ones) are much less balanced allowing the threshold to be larger value. - -@item tracer-max-code-growth -Stop tail duplication once code growth has reached given percentage. This is -a rather artificial limit, as most of the duplicates are eliminated later in -cross jumping, so it may be set to much higher values than is the desired code -growth. - -@item tracer-min-branch-ratio - -Stop reverse growth when the reverse probability of best edge is less than this -threshold (in percent). - -@item tracer-min-branch-ratio -@itemx tracer-min-branch-ratio-feedback - -Stop forward growth if the best edge has probability lower than this -threshold. - -Similarly to @option{tracer-dynamic-coverage} two values are present, one for -compilation for profile feedback and one for compilation without. The value -for compilation with profile feedback needs to be more conservative (higher) in -order to make tracer effective. - -@item max-cse-path-length - -The maximum number of basic blocks on path that CSE considers. -The default is 10. - -@item max-cse-insns -The maximum number of instructions CSE processes before flushing. -The default is 1000. - -@item ggc-min-expand - -GCC uses a garbage collector to manage its own memory allocation. This -parameter specifies the minimum percentage by which the garbage -collector's heap should be allowed to expand between collections. -Tuning this may improve compilation speed; it has no effect on code -generation. - -The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when -RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is -the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If -GCC is not able to calculate RAM on a particular platform, the lower -bound of 30% is used. Setting this parameter and -@option{ggc-min-heapsize} to zero causes a full collection to occur at -every opportunity. This is extremely slow, but can be useful for -debugging. - -@item ggc-min-heapsize - -Minimum size of the garbage collector's heap before it begins bothering -to collect garbage. The first collection occurs after the heap expands -by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again, -tuning this may improve compilation speed, and has no effect on code -generation. - -The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that -tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but -with a lower bound of 4096 (four megabytes) and an upper bound of -131072 (128 megabytes). If GCC is not able to calculate RAM on a -particular platform, the lower bound is used. Setting this parameter -very large effectively disables garbage collection. Setting this -parameter and @option{ggc-min-expand} to zero causes a full collection -to occur at every opportunity. - -@item max-reload-search-insns -The maximum number of instruction reload should look backward for equivalent -register. Increasing values mean more aggressive optimization, making the -compilation time increase with probably slightly better performance. -The default value is 100. - -@item max-cselib-memory-locations -The maximum number of memory locations cselib should take into account. -Increasing values mean more aggressive optimization, making the compilation time -increase with probably slightly better performance. The default value is 500. - -@item reorder-blocks-duplicate -@itemx reorder-blocks-duplicate-feedback - -Used by the basic block reordering pass to decide whether to use unconditional -branch or duplicate the code on its destination. Code is duplicated when its -estimated size is smaller than this value multiplied by the estimated size of -unconditional jump in the hot spots of the program. - -The @option{reorder-block-duplicate-feedback} is used only when profile -feedback is available. It may be set to higher values than -@option{reorder-block-duplicate} since information about the hot spots is more -accurate. - -@item max-sched-ready-insns -The maximum number of instructions ready to be issued the scheduler should -consider at any given time during the first scheduling pass. Increasing -values mean more thorough searches, making the compilation time increase -with probably little benefit. The default value is 100. - -@item max-sched-region-blocks -The maximum number of blocks in a region to be considered for -interblock scheduling. The default value is 10. - -@item max-pipeline-region-blocks -The maximum number of blocks in a region to be considered for -pipelining in the selective scheduler. The default value is 15. - -@item max-sched-region-insns -The maximum number of insns in a region to be considered for -interblock scheduling. The default value is 100. - -@item max-pipeline-region-insns -The maximum number of insns in a region to be considered for -pipelining in the selective scheduler. The default value is 200. - -@item min-spec-prob -The minimum probability (in percents) of reaching a source block -for interblock speculative scheduling. The default value is 40. - -@item max-sched-extend-regions-iters -The maximum number of iterations through CFG to extend regions. -A value of 0 (the default) disables region extensions. - -@item max-sched-insn-conflict-delay -The maximum conflict delay for an insn to be considered for speculative motion. -The default value is 3. - -@item sched-spec-prob-cutoff -The minimal probability of speculation success (in percents), so that -speculative insns are scheduled. -The default value is 40. - -@item sched-spec-state-edge-prob-cutoff -The minimum probability an edge must have for the scheduler to save its -state across it. -The default value is 10. - -@item sched-mem-true-dep-cost -Minimal distance (in CPU cycles) between store and load targeting same -memory locations. The default value is 1. - -@item selsched-max-lookahead -The maximum size of the lookahead window of selective scheduling. It is a -depth of search for available instructions. -The default value is 50. - -@item selsched-max-sched-times -The maximum number of times that an instruction is scheduled during -selective scheduling. This is the limit on the number of iterations -through which the instruction may be pipelined. The default value is 2. - -@item selsched-max-insns-to-rename -The maximum number of best instructions in the ready list that are considered -for renaming in the selective scheduler. The default value is 2. - -@item sms-min-sc -The minimum value of stage count that swing modulo scheduler -generates. The default value is 2. - -@item max-last-value-rtl -The maximum size measured as number of RTLs that can be recorded in an expression -in combiner for a pseudo register as last known value of that register. The default -is 10000. - -@item integer-share-limit -Small integer constants can use a shared data structure, reducing the -compiler's memory usage and increasing its speed. This sets the maximum -value of a shared integer constant. The default value is 256. - -@item ssp-buffer-size -The minimum size of buffers (i.e.@: arrays) that receive stack smashing -protection when @option{-fstack-protection} is used. - -@item max-jump-thread-duplication-stmts -Maximum number of statements allowed in a block that needs to be -duplicated when threading jumps. - -@item max-fields-for-field-sensitive -Maximum number of fields in a structure treated in -a field sensitive manner during pointer analysis. The default is zero -for @option{-O0} and @option{-O1}, -and 100 for @option{-Os}, @option{-O2}, and @option{-O3}. - -@item prefetch-latency -Estimate on average number of instructions that are executed before -prefetch finishes. The distance prefetched ahead is proportional -to this constant. Increasing this number may also lead to less -streams being prefetched (see @option{simultaneous-prefetches}). - -@item simultaneous-prefetches -Maximum number of prefetches that can run at the same time. - -@item l1-cache-line-size -The size of cache line in L1 cache, in bytes. - -@item l1-cache-size -The size of L1 cache, in kilobytes. - -@item l2-cache-size -The size of L2 cache, in kilobytes. - -@item min-insn-to-prefetch-ratio -The minimum ratio between the number of instructions and the -number of prefetches to enable prefetching in a loop. - -@item prefetch-min-insn-to-mem-ratio -The minimum ratio between the number of instructions and the -number of memory references to enable prefetching in a loop. - -@item use-canonical-types -Whether the compiler should use the ``canonical'' type system. By -default, this should always be 1, which uses a more efficient internal -mechanism for comparing types in C++ and Objective-C++. However, if -bugs in the canonical type system are causing compilation failures, -set this value to 0 to disable canonical types. - -@item switch-conversion-max-branch-ratio -Switch initialization conversion refuses to create arrays that are -bigger than @option{switch-conversion-max-branch-ratio} times the number of -branches in the switch. - -@item max-partial-antic-length -Maximum length of the partial antic set computed during the tree -partial redundancy elimination optimization (@option{-ftree-pre}) when -optimizing at @option{-O3} and above. For some sorts of source code -the enhanced partial redundancy elimination optimization can run away, -consuming all of the memory available on the host machine. This -parameter sets a limit on the length of the sets that are computed, -which prevents the runaway behavior. Setting a value of 0 for -this parameter allows an unlimited set length. - -@item sccvn-max-scc-size -Maximum size of a strongly connected component (SCC) during SCCVN -processing. If this limit is hit, SCCVN processing for the whole -function is not done and optimizations depending on it are -disabled. The default maximum SCC size is 10000. - -@item sccvn-max-alias-queries-per-access -Maximum number of alias-oracle queries we perform when looking for -redundancies for loads and stores. If this limit is hit the search -is aborted and the load or store is not considered redundant. The -number of queries is algorithmically limited to the number of -stores on all paths from the load to the function entry. -The default maxmimum number of queries is 1000. - -@item ira-max-loops-num -IRA uses regional register allocation by default. If a function -contains more loops than the number given by this parameter, only at most -the given number of the most frequently-executed loops form regions -for regional register allocation. The default value of the -parameter is 100. - -@item ira-max-conflict-table-size -Although IRA uses a sophisticated algorithm to compress the conflict -table, the table can still require excessive amounts of memory for -huge functions. If the conflict table for a function could be more -than the size in MB given by this parameter, the register allocator -instead uses a faster, simpler, and lower-quality -algorithm that does not require building a pseudo-register conflict table. -The default value of the parameter is 2000. - -@item ira-loop-reserved-regs -IRA can be used to evaluate more accurate register pressure in loops -for decisions to move loop invariants (see @option{-O3}). The number -of available registers reserved for some other purposes is given -by this parameter. The default value of the parameter is 2, which is -the minimal number of registers needed by typical instructions. -This value is the best found from numerous experiments. - -@item loop-invariant-max-bbs-in-loop -Loop invariant motion can be very expensive, both in compilation time and -in amount of needed compile-time memory, with very large loops. Loops -with more basic blocks than this parameter won't have loop invariant -motion optimization performed on them. The default value of the -parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above. - -@item loop-max-datarefs-for-datadeps -Building data dapendencies is expensive for very large loops. This -parameter limits the number of data references in loops that are -considered for data dependence analysis. These large loops are no -handled by the optimizations using loop data dependencies. -The default value is 1000. - -@item max-vartrack-size -Sets a maximum number of hash table slots to use during variable -tracking dataflow analysis of any function. If this limit is exceeded -with variable tracking at assignments enabled, analysis for that -function is retried without it, after removing all debug insns from -the function. If the limit is exceeded even without debug insns, var -tracking analysis is completely disabled for the function. Setting -the parameter to zero makes it unlimited. - -@item max-vartrack-expr-depth -Sets a maximum number of recursion levels when attempting to map -variable names or debug temporaries to value expressions. This trades -compilation time for more complete debug information. If this is set too -low, value expressions that are available and could be represented in -debug information may end up not being used; setting this higher may -enable the compiler to find more complex debug expressions, but compile -time and memory use may grow. The default is 12. - -@item min-nondebug-insn-uid -Use uids starting at this parameter for nondebug insns. The range below -the parameter is reserved exclusively for debug insns created by -@option{-fvar-tracking-assignments}, but debug insns may get -(non-overlapping) uids above it if the reserved range is exhausted. - -@item ipa-sra-ptr-growth-factor -IPA-SRA replaces a pointer to an aggregate with one or more new -parameters only when their cumulative size is less or equal to -@option{ipa-sra-ptr-growth-factor} times the size of the original -pointer parameter. - -@item tm-max-aggregate-size -When making copies of thread-local variables in a transaction, this -parameter specifies the size in bytes after which variables are -saved with the logging functions as opposed to save/restore code -sequence pairs. This option only applies when using -@option{-fgnu-tm}. - -@item graphite-max-nb-scop-params -To avoid exponential effects in the Graphite loop transforms, the -number of parameters in a Static Control Part (SCoP) is bounded. The -default value is 10 parameters. A variable whose value is unknown at -compilation time and defined outside a SCoP is a parameter of the SCoP. - -@item graphite-max-bbs-per-function -To avoid exponential effects in the detection of SCoPs, the size of -the functions analyzed by Graphite is bounded. The default value is -100 basic blocks. - -@item loop-block-tile-size -Loop blocking or strip mining transforms, enabled with -@option{-floop-block} or @option{-floop-strip-mine}, strip mine each -loop in the loop nest by a given number of iterations. The strip -length can be changed using the @option{loop-block-tile-size} -parameter. The default value is 51 iterations. - -@item ipa-cp-value-list-size -IPA-CP attempts to track all possible values and types passed to a function's -parameter in order to propagate them and perform devirtualization. -@option{ipa-cp-value-list-size} is the maximum number of values and types it -stores per one formal parameter of a function. - -@item lto-partitions -Specify desired number of partitions produced during WHOPR compilation. -The number of partitions should exceed the number of CPUs used for compilation. -The default value is 32. - -@item lto-minpartition -Size of minimal partition for WHOPR (in estimated instructions). -This prevents expenses of splitting very small programs into too many -partitions. - -@item cxx-max-namespaces-for-diagnostic-help -The maximum number of namespaces to consult for suggestions when C++ -name lookup fails for an identifier. The default is 1000. - -@item sink-frequency-threshold -The maximum relative execution frequency (in percents) of the target block -relative to a statement's original block to allow statement sinking of a -statement. Larger numbers result in more aggressive statement sinking. -The default value is 75. A small positive adjustment is applied for -statements with memory operands as those are even more profitable so sink. - -@item max-stores-to-sink -The maximum number of conditional stores paires that can be sunk. Set to 0 -if either vectorization (@option{-ftree-vectorize}) or if-conversion -(@option{-ftree-loop-if-convert}) is disabled. The default is 2. - -@item allow-load-data-races -Allow optimizers to introduce new data races on loads. -Set to 1 to allow, otherwise to 0. This option is enabled by default -unless implicitly set by the @option{-fmemory-model=} option. - -@item allow-store-data-races -Allow optimizers to introduce new data races on stores. -Set to 1 to allow, otherwise to 0. This option is enabled by default -unless implicitly set by the @option{-fmemory-model=} option. - -@item allow-packed-load-data-races -Allow optimizers to introduce new data races on packed data loads. -Set to 1 to allow, otherwise to 0. This option is enabled by default -unless implicitly set by the @option{-fmemory-model=} option. - -@item allow-packed-store-data-races -Allow optimizers to introduce new data races on packed data stores. -Set to 1 to allow, otherwise to 0. This option is enabled by default -unless implicitly set by the @option{-fmemory-model=} option. - -@item case-values-threshold -The smallest number of different values for which it is best to use a -jump-table instead of a tree of conditional branches. If the value is -0, use the default for the machine. The default is 0. - -@item tree-reassoc-width -Set the maximum number of instructions executed in parallel in -reassociated tree. This parameter overrides target dependent -heuristics used by default if has non zero value. - -@item sched-pressure-algorithm -Choose between the two available implementations of -@option{-fsched-pressure}. Algorithm 1 is the original implementation -and is the more likely to prevent instructions from being reordered. -Algorithm 2 was designed to be a compromise between the relatively -conservative approach taken by algorithm 1 and the rather aggressive -approach taken by the default scheduler. It relies more heavily on -having a regular register file and accurate register pressure classes. -See @file{haifa-sched.c} in the GCC sources for more details. - -The default choice depends on the target. - -@item max-slsr-cand-scan -Set the maximum number of existing candidates that will be considered when -seeking a basis for a new straight-line strength reduction candidate. - -@end table -@end table - -@node Preprocessor Options -@section Options Controlling the Preprocessor -@cindex preprocessor options -@cindex options, preprocessor - -These options control the C preprocessor, which is run on each C source -file before actual compilation. - -If you use the @option{-E} option, nothing is done except preprocessing. -Some of these options make sense only together with @option{-E} because -they cause the preprocessor output to be unsuitable for actual -compilation. - -@table @gcctabopt -@item -Wp,@var{option} -@opindex Wp -You can use @option{-Wp,@var{option}} to bypass the compiler driver -and pass @var{option} directly through to the preprocessor. If -@var{option} contains commas, it is split into multiple options at the -commas. However, many options are modified, translated or interpreted -by the compiler driver before being passed to the preprocessor, and -@option{-Wp} forcibly bypasses this phase. The preprocessor's direct -interface is undocumented and subject to change, so whenever possible -you should avoid using @option{-Wp} and let the driver handle the -options instead. - -@item -Xpreprocessor @var{option} -@opindex Xpreprocessor -Pass @var{option} as an option to the preprocessor. You can use this to -supply system-specific preprocessor options that GCC does not -recognize. - -If you want to pass an option that takes an argument, you must use -@option{-Xpreprocessor} twice, once for the option and once for the argument. - -@item -no-integrated-cpp -@opindex no-integrated-cpp -Perform preprocessing as a separate pass before compilation. -By default, GCC performs preprocessing as an integrated part of -input tokenization and parsing. -If this option is provided, the appropriate language front end -(@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++, -and Objective-C, respectively) is instead invoked twice, -once for preprocessing only and once for actual compilation -of the preprocessed input. -This option may be useful in conjunction with the @option{-B} or -@option{-wrapper} options to specify an alternate preprocessor or -perform additional processing of the program source between -normal preprocessing and compilation. -@end table - -@include cppopts.texi - -@node Assembler Options -@section Passing Options to the Assembler - -@c prevent bad page break with this line -You can pass options to the assembler. - -@table @gcctabopt -@item -Wa,@var{option} -@opindex Wa -Pass @var{option} as an option to the assembler. If @var{option} -contains commas, it is split into multiple options at the commas. - -@item -Xassembler @var{option} -@opindex Xassembler -Pass @var{option} as an option to the assembler. You can use this to -supply system-specific assembler options that GCC does not -recognize. - -If you want to pass an option that takes an argument, you must use -@option{-Xassembler} twice, once for the option and once for the argument. - -@end table - -@node Link Options -@section Options for Linking -@cindex link options -@cindex options, linking - -These options come into play when the compiler links object files into -an executable output file. They are meaningless if the compiler is -not doing a link step. - -@table @gcctabopt -@cindex file names -@item @var{object-file-name} -A file name that does not end in a special recognized suffix is -considered to name an object file or library. (Object files are -distinguished from libraries by the linker according to the file -contents.) If linking is done, these object files are used as input -to the linker. - -@item -c -@itemx -S -@itemx -E -@opindex c -@opindex S -@opindex E -If any of these options is used, then the linker is not run, and -object file names should not be used as arguments. @xref{Overall -Options}. - -@cindex Libraries -@item -l@var{library} -@itemx -l @var{library} -@opindex l -Search the library named @var{library} when linking. (The second -alternative with the library as a separate argument is only for -POSIX compliance and is not recommended.) - -It makes a difference where in the command you write this option; the -linker searches and processes libraries and object files in the order they -are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} -after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers -to functions in @samp{z}, those functions may not be loaded. - -The linker searches a standard list of directories for the library, -which is actually a file named @file{lib@var{library}.a}. The linker -then uses this file as if it had been specified precisely by name. - -The directories searched include several standard system directories -plus any that you specify with @option{-L}. - -Normally the files found this way are library files---archive files -whose members are object files. The linker handles an archive file by -scanning through it for members which define symbols that have so far -been referenced but not defined. But if the file that is found is an -ordinary object file, it is linked in the usual fashion. The only -difference between using an @option{-l} option and specifying a file name -is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a} -and searches several directories. - -@item -lobjc -@opindex lobjc -You need this special case of the @option{-l} option in order to -link an Objective-C or Objective-C++ program. - -@item -nostartfiles -@opindex nostartfiles -Do not use the standard system startup files when linking. -The standard system libraries are used normally, unless @option{-nostdlib} -or @option{-nodefaultlibs} is used. - -@item -nodefaultlibs -@opindex nodefaultlibs -Do not use the standard system libraries when linking. -Only the libraries you specify are passed to the linker, and options -specifying linkage of the system libraries, such as @code{-static-libgcc} -or @code{-shared-libgcc}, are ignored. -The standard startup files are used normally, unless @option{-nostartfiles} -is used. - -The compiler may generate calls to @code{memcmp}, -@code{memset}, @code{memcpy} and @code{memmove}. -These entries are usually resolved by entries in -libc. These entry points should be supplied through some other -mechanism when this option is specified. - -@item -nostdlib -@opindex nostdlib -Do not use the standard system startup files or libraries when linking. -No startup files and only the libraries you specify are passed to -the linker, and options specifying linkage of the system libraries, such as -@code{-static-libgcc} or @code{-shared-libgcc}, are ignored. - -The compiler may generate calls to @code{memcmp}, @code{memset}, -@code{memcpy} and @code{memmove}. -These entries are usually resolved by entries in -libc. These entry points should be supplied through some other -mechanism when this option is specified. - -@cindex @option{-lgcc}, use with @option{-nostdlib} -@cindex @option{-nostdlib} and unresolved references -@cindex unresolved references and @option{-nostdlib} -@cindex @option{-lgcc}, use with @option{-nodefaultlibs} -@cindex @option{-nodefaultlibs} and unresolved references -@cindex unresolved references and @option{-nodefaultlibs} -One of the standard libraries bypassed by @option{-nostdlib} and -@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines -which GCC uses to overcome shortcomings of particular machines, or special -needs for some languages. -(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler -Collection (GCC) Internals}, -for more discussion of @file{libgcc.a}.) -In most cases, you need @file{libgcc.a} even when you want to avoid -other standard libraries. In other words, when you specify @option{-nostdlib} -or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. -This ensures that you have no unresolved references to internal GCC -library subroutines. -(An example of such an internal subroutine is @samp{__main}, used to ensure C++ -constructors are called; @pxref{Collect2,,@code{collect2}, gccint, -GNU Compiler Collection (GCC) Internals}.) - -@item -pie -@opindex pie -Produce a position independent executable on targets that support it. -For predictable results, you must also specify the same set of options -used for compilation (@option{-fpie}, @option{-fPIE}, -or model suboptions) when you specify this linker option. - -@item -rdynamic -@opindex rdynamic -Pass the flag @option{-export-dynamic} to the ELF linker, on targets -that support it. This instructs the linker to add all symbols, not -only used ones, to the dynamic symbol table. This option is needed -for some uses of @code{dlopen} or to allow obtaining backtraces -from within a program. - -@item -s -@opindex s -Remove all symbol table and relocation information from the executable. - -@item -static -@opindex static -On systems that support dynamic linking, this prevents linking with the shared -libraries. On other systems, this option has no effect. - -@item -shared -@opindex shared -Produce a shared object which can then be linked with other objects to -form an executable. Not all systems support this option. For predictable -results, you must also specify the same set of options used for compilation -(@option{-fpic}, @option{-fPIC}, or model suboptions) when -you specify this linker option.@footnote{On some systems, @samp{gcc -shared} -needs to build supplementary stub code for constructors to work. On -multi-libbed systems, @samp{gcc -shared} must select the correct support -libraries to link against. Failing to supply the correct flags may lead -to subtle defects. Supplying them in cases where they are not necessary -is innocuous.} - -@item -shared-libgcc -@itemx -static-libgcc -@opindex shared-libgcc -@opindex static-libgcc -On systems that provide @file{libgcc} as a shared library, these options -force the use of either the shared or static version, respectively. -If no shared version of @file{libgcc} was built when the compiler was -configured, these options have no effect. - -There are several situations in which an application should use the -shared @file{libgcc} instead of the static version. The most common -of these is when the application wishes to throw and catch exceptions -across different shared libraries. In that case, each of the libraries -as well as the application itself should use the shared @file{libgcc}. - -Therefore, the G++ and GCJ drivers automatically add -@option{-shared-libgcc} whenever you build a shared library or a main -executable, because C++ and Java programs typically use exceptions, so -this is the right thing to do. - -If, instead, you use the GCC driver to create shared libraries, you may -find that they are not always linked with the shared @file{libgcc}. -If GCC finds, at its configuration time, that you have a non-GNU linker -or a GNU linker that does not support option @option{--eh-frame-hdr}, -it links the shared version of @file{libgcc} into shared libraries -by default. Otherwise, it takes advantage of the linker and optimizes -away the linking with the shared version of @file{libgcc}, linking with -the static version of libgcc by default. This allows exceptions to -propagate through such shared libraries, without incurring relocation -costs at library load time. - -However, if a library or main executable is supposed to throw or catch -exceptions, you must link it using the G++ or GCJ driver, as appropriate -for the languages used in the program, or using the option -@option{-shared-libgcc}, such that it is linked with the shared -@file{libgcc}. - -@item -static-libasan -When the @option{-fsanitize=address} option is used to link a program, -the GCC driver automatically links against @option{libasan}. If -@file{libasan} is available as a shared library, and the @option{-static} -option is not used, then this links against the shared version of -@file{libasan}. The @option{-static-libasan} option directs the GCC -driver to link @file{libasan} statically, without necessarily linking -other libraries statically. - -@item -static-libtsan -When the @option{-fsanitize=thread} option is used to link a program, -the GCC driver automatically links against @option{libtsan}. If -@file{libtsan} is available as a shared library, and the @option{-static} -option is not used, then this links against the shared version of -@file{libtsan}. The @option{-static-libtsan} option directs the GCC -driver to link @file{libtsan} statically, without necessarily linking -other libraries statically. - -@item -static-libstdc++ -When the @command{g++} program is used to link a C++ program, it -normally automatically links against @option{libstdc++}. If -@file{libstdc++} is available as a shared library, and the -@option{-static} option is not used, then this links against the -shared version of @file{libstdc++}. That is normally fine. However, it -is sometimes useful to freeze the version of @file{libstdc++} used by -the program without going all the way to a fully static link. The -@option{-static-libstdc++} option directs the @command{g++} driver to -link @file{libstdc++} statically, without necessarily linking other -libraries statically. - -@item -symbolic -@opindex symbolic -Bind references to global symbols when building a shared object. Warn -about any unresolved references (unless overridden by the link editor -option @option{-Xlinker -z -Xlinker defs}). Only a few systems support -this option. - -@item -T @var{script} -@opindex T -@cindex linker script -Use @var{script} as the linker script. This option is supported by most -systems using the GNU linker. On some targets, such as bare-board -targets without an operating system, the @option{-T} option may be required -when linking to avoid references to undefined symbols. - -@item -Xlinker @var{option} -@opindex Xlinker -Pass @var{option} as an option to the linker. You can use this to -supply system-specific linker options that GCC does not recognize. - -If you want to pass an option that takes a separate argument, you must use -@option{-Xlinker} twice, once for the option and once for the argument. -For example, to pass @option{-assert definitions}, you must write -@option{-Xlinker -assert -Xlinker definitions}. It does not work to write -@option{-Xlinker "-assert definitions"}, because this passes the entire -string as a single argument, which is not what the linker expects. - -When using the GNU linker, it is usually more convenient to pass -arguments to linker options using the @option{@var{option}=@var{value}} -syntax than as separate arguments. For example, you can specify -@option{-Xlinker -Map=output.map} rather than -@option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support -this syntax for command-line options. - -@item -Wl,@var{option} -@opindex Wl -Pass @var{option} as an option to the linker. If @var{option} contains -commas, it is split into multiple options at the commas. You can use this -syntax to pass an argument to the option. -For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the -linker. When using the GNU linker, you can also get the same effect with -@option{-Wl,-Map=output.map}. - -@item -u @var{symbol} -@opindex u -Pretend the symbol @var{symbol} is undefined, to force linking of -library modules to define it. You can use @option{-u} multiple times with -different symbols to force loading of additional library modules. -@end table - -@node Directory Options -@section Options for Directory Search -@cindex directory options -@cindex options, directory search -@cindex search path - -These options specify directories to search for header files, for -libraries and for parts of the compiler: - -@table @gcctabopt -@item -I@var{dir} -@opindex I -Add the directory @var{dir} to the head of the list of directories to be -searched for header files. This can be used to override a system header -file, substituting your own version, since these directories are -searched before the system header file directories. However, you should -not use this option to add directories that contain vendor-supplied -system header files (use @option{-isystem} for that). If you use more than -one @option{-I} option, the directories are scanned in left-to-right -order; the standard system directories come after. - -If a standard system include directory, or a directory specified with -@option{-isystem}, is also specified with @option{-I}, the @option{-I} -option is ignored. The directory is still searched but as a -system directory at its normal position in the system include chain. -This is to ensure that GCC's procedure to fix buggy system headers and -the ordering for the @code{include_next} directive are not inadvertently changed. -If you really need to change the search order for system directories, -use the @option{-nostdinc} and/or @option{-isystem} options. - -@item -iplugindir=@var{dir} -Set the directory to search for plugins that are passed -by @option{-fplugin=@var{name}} instead of -@option{-fplugin=@var{path}/@var{name}.so}. This option is not meant -to be used by the user, but only passed by the driver. - -@item -iquote@var{dir} -@opindex iquote -Add the directory @var{dir} to the head of the list of directories to -be searched for header files only for the case of @samp{#include -"@var{file}"}; they are not searched for @samp{#include <@var{file}>}, -otherwise just like @option{-I}. - -@item -L@var{dir} -@opindex L -Add directory @var{dir} to the list of directories to be searched -for @option{-l}. - -@item -B@var{prefix} -@opindex B -This option specifies where to find the executables, libraries, -include files, and data files of the compiler itself. - -The compiler driver program runs one or more of the subprograms -@command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries -@var{prefix} as a prefix for each program it tries to run, both with and -without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). - -For each subprogram to be run, the compiler driver first tries the -@option{-B} prefix, if any. If that name is not found, or if @option{-B} -is not specified, the driver tries two standard prefixes, -@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of -those results in a file name that is found, the unmodified program -name is searched for using the directories specified in your -@env{PATH} environment variable. - -The compiler checks to see if the path provided by the @option{-B} -refers to a directory, and if necessary it adds a directory -separator character at the end of the path. - -@option{-B} prefixes that effectively specify directory names also apply -to libraries in the linker, because the compiler translates these -options into @option{-L} options for the linker. They also apply to -includes files in the preprocessor, because the compiler translates these -options into @option{-isystem} options for the preprocessor. In this case, -the compiler appends @samp{include} to the prefix. - -The runtime support file @file{libgcc.a} can also be searched for using -the @option{-B} prefix, if needed. If it is not found there, the two -standard prefixes above are tried, and that is all. The file is left -out of the link if it is not found by those means. - -Another way to specify a prefix much like the @option{-B} prefix is to use -the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment -Variables}. - -As a special kludge, if the path provided by @option{-B} is -@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to -9, then it is replaced by @file{[dir/]include}. This is to help -with boot-strapping the compiler. - -@item -specs=@var{file} -@opindex specs -Process @var{file} after the compiler reads in the standard @file{specs} -file, in order to override the defaults which the @command{gcc} driver -program uses when determining what switches to pass to @command{cc1}, -@command{cc1plus}, @command{as}, @command{ld}, etc. More than one -@option{-specs=@var{file}} can be specified on the command line, and they -are processed in order, from left to right. - -@item --sysroot=@var{dir} -@opindex sysroot -Use @var{dir} as the logical root directory for headers and libraries. -For example, if the compiler normally searches for headers in -@file{/usr/include} and libraries in @file{/usr/lib}, it instead -searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}. - -If you use both this option and the @option{-isysroot} option, then -the @option{--sysroot} option applies to libraries, but the -@option{-isysroot} option applies to header files. - -The GNU linker (beginning with version 2.16) has the necessary support -for this option. If your linker does not support this option, the -header file aspect of @option{--sysroot} still works, but the -library aspect does not. - -@item --no-sysroot-suffix -@opindex no-sysroot-suffix -For some targets, a suffix is added to the root directory specified -with @option{--sysroot}, depending on the other options used, so that -headers may for example be found in -@file{@var{dir}/@var{suffix}/usr/include} instead of -@file{@var{dir}/usr/include}. This option disables the addition of -such a suffix. - -@item -I- -@opindex I- -This option has been deprecated. Please use @option{-iquote} instead for -@option{-I} directories before the @option{-I-} and remove the @option{-I-}. -Any directories you specify with @option{-I} options before the @option{-I-} -option are searched only for the case of @samp{#include "@var{file}"}; -they are not searched for @samp{#include <@var{file}>}. - -If additional directories are specified with @option{-I} options after -the @option{-I-}, these directories are searched for all @samp{#include} -directives. (Ordinarily @emph{all} @option{-I} directories are used -this way.) - -In addition, the @option{-I-} option inhibits the use of the current -directory (where the current input file came from) as the first search -directory for @samp{#include "@var{file}"}. There is no way to -override this effect of @option{-I-}. With @option{-I.} you can specify -searching the directory that is current when the compiler is -invoked. That is not exactly the same as what the preprocessor does -by default, but it is often satisfactory. - -@option{-I-} does not inhibit the use of the standard system directories -for header files. Thus, @option{-I-} and @option{-nostdinc} are -independent. -@end table - -@c man end - -@node Spec Files -@section Specifying subprocesses and the switches to pass to them -@cindex Spec Files - -@command{gcc} is a driver program. It performs its job by invoking a -sequence of other programs to do the work of compiling, assembling and -linking. GCC interprets its command-line parameters and uses these to -deduce which programs it should invoke, and which command-line options -it ought to place on their command lines. This behavior is controlled -by @dfn{spec strings}. In most cases there is one spec string for each -program that GCC can invoke, but a few programs have multiple spec -strings to control their behavior. The spec strings built into GCC can -be overridden by using the @option{-specs=} command-line switch to specify -a spec file. - -@dfn{Spec files} are plaintext files that are used to construct spec -strings. They consist of a sequence of directives separated by blank -lines. The type of directive is determined by the first non-whitespace -character on the line, which can be one of the following: - -@table @code -@item %@var{command} -Issues a @var{command} to the spec file processor. The commands that can -appear here are: - -@table @code -@item %include <@var{file}> -@cindex @code{%include} -Search for @var{file} and insert its text at the current point in the -specs file. - -@item %include_noerr <@var{file}> -@cindex @code{%include_noerr} -Just like @samp{%include}, but do not generate an error message if the include -file cannot be found. - -@item %rename @var{old_name} @var{new_name} -@cindex @code{%rename} -Rename the spec string @var{old_name} to @var{new_name}. - -@end table - -@item *[@var{spec_name}]: -This tells the compiler to create, override or delete the named spec -string. All lines after this directive up to the next directive or -blank line are considered to be the text for the spec string. If this -results in an empty string then the spec is deleted. (Or, if the -spec did not exist, then nothing happens.) Otherwise, if the spec -does not currently exist a new spec is created. If the spec does -exist then its contents are overridden by the text of this -directive, unless the first character of that text is the @samp{+} -character, in which case the text is appended to the spec. - -@item [@var{suffix}]: -Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive -and up to the next directive or blank line are considered to make up the -spec string for the indicated suffix. When the compiler encounters an -input file with the named suffix, it processes the spec string in -order to work out how to compile that file. For example: - -@smallexample -.ZZ: -z-compile -input %i -@end smallexample - -This says that any input file whose name ends in @samp{.ZZ} should be -passed to the program @samp{z-compile}, which should be invoked with the -command-line switch @option{-input} and with the result of performing the -@samp{%i} substitution. (See below.) - -As an alternative to providing a spec string, the text following a -suffix directive can be one of the following: - -@table @code -@item @@@var{language} -This says that the suffix is an alias for a known @var{language}. This is -similar to using the @option{-x} command-line switch to GCC to specify a -language explicitly. For example: - -@smallexample -.ZZ: -@@c++ -@end smallexample - -Says that .ZZ files are, in fact, C++ source files. - -@item #@var{name} -This causes an error messages saying: - -@smallexample -@var{name} compiler not installed on this system. -@end smallexample -@end table - -GCC already has an extensive list of suffixes built into it. -This directive adds an entry to the end of the list of suffixes, but -since the list is searched from the end backwards, it is effectively -possible to override earlier entries using this technique. - -@end table - -GCC has the following spec strings built into it. Spec files can -override these strings or create their own. Note that individual -targets can also add their own spec strings to this list. - -@smallexample -asm Options to pass to the assembler -asm_final Options to pass to the assembler post-processor -cpp Options to pass to the C preprocessor -cc1 Options to pass to the C compiler -cc1plus Options to pass to the C++ compiler -endfile Object files to include at the end of the link -link Options to pass to the linker -lib Libraries to include on the command line to the linker -libgcc Decides which GCC support library to pass to the linker -linker Sets the name of the linker -predefines Defines to be passed to the C preprocessor -signed_char Defines to pass to CPP to say whether @code{char} is signed - by default -startfile Object files to include at the start of the link -@end smallexample - -Here is a small example of a spec file: - -@smallexample -%rename lib old_lib - -*lib: ---start-group -lgcc -lc -leval1 --end-group %(old_lib) -@end smallexample - -This example renames the spec called @samp{lib} to @samp{old_lib} and -then overrides the previous definition of @samp{lib} with a new one. -The new definition adds in some extra command-line options before -including the text of the old definition. - -@dfn{Spec strings} are a list of command-line options to be passed to their -corresponding program. In addition, the spec strings can contain -@samp{%}-prefixed sequences to substitute variable text or to -conditionally insert text into the command line. Using these constructs -it is possible to generate quite complex command lines. - -Here is a table of all defined @samp{%}-sequences for spec -strings. Note that spaces are not generated automatically around the -results of expanding these sequences. Therefore you can concatenate them -together or combine them with constant text in a single argument. - -@table @code -@item %% -Substitute one @samp{%} into the program name or argument. - -@item %i -Substitute the name of the input file being processed. - -@item %b -Substitute the basename of the input file being processed. -This is the substring up to (and not including) the last period -and not including the directory. - -@item %B -This is the same as @samp{%b}, but include the file suffix (text after -the last period). - -@item %d -Marks the argument containing or following the @samp{%d} as a -temporary file name, so that that file is deleted if GCC exits -successfully. Unlike @samp{%g}, this contributes no text to the -argument. - -@item %g@var{suffix} -Substitute a file name that has suffix @var{suffix} and is chosen -once per compilation, and mark the argument in the same way as -@samp{%d}. To reduce exposure to denial-of-service attacks, the file -name is now chosen in a way that is hard to predict even when previously -chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} -might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches -the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is -treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} -was simply substituted with a file name chosen once per compilation, -without regard to any appended suffix (which was therefore treated -just like ordinary text), making such attacks more likely to succeed. - -@item %u@var{suffix} -Like @samp{%g}, but generates a new temporary file name -each time it appears instead of once per compilation. - -@item %U@var{suffix} -Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a -new one if there is no such last file name. In the absence of any -@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share -the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} -involves the generation of two distinct file names, one -for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was -simply substituted with a file name chosen for the previous @samp{%u}, -without regard to any appended suffix. - -@item %j@var{suffix} -Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is -writable, and if @option{-save-temps} is not used; -otherwise, substitute the name -of a temporary file, just like @samp{%u}. This temporary file is not -meant for communication between processes, but rather as a junk -disposal mechanism. - -@item %|@var{suffix} -@itemx %m@var{suffix} -Like @samp{%g}, except if @option{-pipe} is in effect. In that case -@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at -all. These are the two most common ways to instruct a program that it -should read from standard input or write to standard output. If you -need something more elaborate you can use an @samp{%@{pipe:@code{X}@}} -construct: see for example @file{f/lang-specs.h}. - -@item %.@var{SUFFIX} -Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args -when it is subsequently output with @samp{%*}. @var{SUFFIX} is -terminated by the next space or %. - -@item %w -Marks the argument containing or following the @samp{%w} as the -designated output file of this compilation. This puts the argument -into the sequence of arguments that @samp{%o} substitutes. - -@item %o -Substitutes the names of all the output files, with spaces -automatically placed around them. You should write spaces -around the @samp{%o} as well or the results are undefined. -@samp{%o} is for use in the specs for running the linker. -Input files whose names have no recognized suffix are not compiled -at all, but they are included among the output files, so they are -linked. - -@item %O -Substitutes the suffix for object files. Note that this is -handled specially when it immediately follows @samp{%g, %u, or %U}, -because of the need for those to form complete file names. The -handling is such that @samp{%O} is treated exactly as if it had already -been substituted, except that @samp{%g, %u, and %U} do not currently -support additional @var{suffix} characters following @samp{%O} as they do -following, for example, @samp{.o}. - -@item %p -Substitutes the standard macro predefinitions for the -current target machine. Use this when running @code{cpp}. - -@item %P -Like @samp{%p}, but puts @samp{__} before and after the name of each -predefined macro, except for macros that start with @samp{__} or with -@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO -C@. - -@item %I -Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}), -@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), -@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options) -and @option{-imultilib} as necessary. - -@item %s -Current argument is the name of a library or startup file of some sort. -Search for that file in a standard list of directories and substitute -the full name found. The current working directory is included in the -list of directories scanned. - -@item %T -Current argument is the name of a linker script. Search for that file -in the current list of directories to scan for libraries. If the file -is located insert a @option{--script} option into the command line -followed by the full path name found. If the file is not found then -generate an error message. Note: the current working directory is not -searched. - -@item %e@var{str} -Print @var{str} as an error message. @var{str} is terminated by a newline. -Use this when inconsistent options are detected. - -@item %(@var{name}) -Substitute the contents of spec string @var{name} at this point. - -@item %x@{@var{option}@} -Accumulate an option for @samp{%X}. - -@item %X -Output the accumulated linker options specified by @option{-Wl} or a @samp{%x} -spec string. - -@item %Y -Output the accumulated assembler options specified by @option{-Wa}. - -@item %Z -Output the accumulated preprocessor options specified by @option{-Wp}. - -@item %a -Process the @code{asm} spec. This is used to compute the -switches to be passed to the assembler. - -@item %A -Process the @code{asm_final} spec. This is a spec string for -passing switches to an assembler post-processor, if such a program is -needed. - -@item %l -Process the @code{link} spec. This is the spec for computing the -command line passed to the linker. Typically it makes use of the -@samp{%L %G %S %D and %E} sequences. - -@item %D -Dump out a @option{-L} option for each directory that GCC believes might -contain startup files. If the target supports multilibs then the -current multilib directory is prepended to each of these paths. - -@item %L -Process the @code{lib} spec. This is a spec string for deciding which -libraries are included on the command line to the linker. - -@item %G -Process the @code{libgcc} spec. This is a spec string for deciding -which GCC support library is included on the command line to the linker. - -@item %S -Process the @code{startfile} spec. This is a spec for deciding which -object files are the first ones passed to the linker. Typically -this might be a file named @file{crt0.o}. - -@item %E -Process the @code{endfile} spec. This is a spec string that specifies -the last object files that are passed to the linker. - -@item %C -Process the @code{cpp} spec. This is used to construct the arguments -to be passed to the C preprocessor. - -@item %1 -Process the @code{cc1} spec. This is used to construct the options to be -passed to the actual C compiler (@samp{cc1}). - -@item %2 -Process the @code{cc1plus} spec. This is used to construct the options to be -passed to the actual C++ compiler (@samp{cc1plus}). - -@item %* -Substitute the variable part of a matched option. See below. -Note that each comma in the substituted string is replaced by -a single space. - -@item %<@code{S} -Remove all occurrences of @code{-S} from the command line. Note---this -command is position dependent. @samp{%} commands in the spec string -before this one see @code{-S}, @samp{%} commands in the spec string -after this one do not. - -@item %:@var{function}(@var{args}) -Call the named function @var{function}, passing it @var{args}. -@var{args} is first processed as a nested spec string, then split -into an argument vector in the usual fashion. The function returns -a string which is processed as if it had appeared literally as part -of the current spec. - -The following built-in spec functions are provided: - -@table @code -@item @code{getenv} -The @code{getenv} spec function takes two arguments: an environment -variable name and a string. If the environment variable is not -defined, a fatal error is issued. Otherwise, the return value is the -value of the environment variable concatenated with the string. For -example, if @env{TOPDIR} is defined as @file{/path/to/top}, then: - -@smallexample -%:getenv(TOPDIR /include) -@end smallexample - -expands to @file{/path/to/top/include}. - -@item @code{if-exists} -The @code{if-exists} spec function takes one argument, an absolute -pathname to a file. If the file exists, @code{if-exists} returns the -pathname. Here is a small example of its usage: - -@smallexample -*startfile: -crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s -@end smallexample - -@item @code{if-exists-else} -The @code{if-exists-else} spec function is similar to the @code{if-exists} -spec function, except that it takes two arguments. The first argument is -an absolute pathname to a file. If the file exists, @code{if-exists-else} -returns the pathname. If it does not exist, it returns the second argument. -This way, @code{if-exists-else} can be used to select one file or another, -based on the existence of the first. Here is a small example of its usage: - -@smallexample -*startfile: -crt0%O%s %:if-exists(crti%O%s) \ -%:if-exists-else(crtbeginT%O%s crtbegin%O%s) -@end smallexample - -@item @code{replace-outfile} -The @code{replace-outfile} spec function takes two arguments. It looks for the -first argument in the outfiles array and replaces it with the second argument. Here -is a small example of its usage: - -@smallexample -%@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@} -@end smallexample - -@item @code{remove-outfile} -The @code{remove-outfile} spec function takes one argument. It looks for the -first argument in the outfiles array and removes it. Here is a small example -its usage: - -@smallexample -%:remove-outfile(-lm) -@end smallexample - -@item @code{pass-through-libs} -The @code{pass-through-libs} spec function takes any number of arguments. It -finds any @option{-l} options and any non-options ending in @file{.a} (which it -assumes are the names of linker input library archive files) and returns a -result containing all the found arguments each prepended by -@option{-plugin-opt=-pass-through=} and joined by spaces. This list is -intended to be passed to the LTO linker plugin. - -@smallexample -%:pass-through-libs(%G %L %G) -@end smallexample - -@item @code{print-asm-header} -The @code{print-asm-header} function takes no arguments and simply -prints a banner like: - -@smallexample -Assembler options -================= - -Use "-Wa,OPTION" to pass "OPTION" to the assembler. -@end smallexample - -It is used to separate compiler options from assembler options -in the @option{--target-help} output. -@end table - -@item %@{@code{S}@} -Substitutes the @code{-S} switch, if that switch is given to GCC@. -If that switch is not specified, this substitutes nothing. Note that -the leading dash is omitted when specifying this option, and it is -automatically inserted if the substitution is performed. Thus the spec -string @samp{%@{foo@}} matches the command-line option @option{-foo} -and outputs the command-line option @option{-foo}. - -@item %W@{@code{S}@} -Like %@{@code{S}@} but mark last argument supplied within as a file to be -deleted on failure. - -@item %@{@code{S}*@} -Substitutes all the switches specified to GCC whose names start -with @code{-S}, but which also take an argument. This is used for -switches like @option{-o}, @option{-D}, @option{-I}, etc. -GCC considers @option{-o foo} as being -one switch whose name starts with @samp{o}. %@{o*@} substitutes this -text, including the space. Thus two arguments are generated. - -@item %@{@code{S}*&@code{T}*@} -Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options -(the order of @code{S} and @code{T} in the spec is not significant). -There can be any number of ampersand-separated variables; for each the -wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. - -@item %@{@code{S}:@code{X}@} -Substitutes @code{X}, if the @option{-S} switch is given to GCC@. - -@item %@{!@code{S}:@code{X}@} -Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@. - -@item %@{@code{S}*:@code{X}@} -Substitutes @code{X} if one or more switches whose names start with -@code{-S} are specified to GCC@. Normally @code{X} is substituted only -once, no matter how many such switches appeared. However, if @code{%*} -appears somewhere in @code{X}, then @code{X} is substituted once -for each matching switch, with the @code{%*} replaced by the part of -that switch matching the @code{*}. - -@item %@{.@code{S}:@code{X}@} -Substitutes @code{X}, if processing a file with suffix @code{S}. - -@item %@{!.@code{S}:@code{X}@} -Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}. - -@item %@{,@code{S}:@code{X}@} -Substitutes @code{X}, if processing a file for language @code{S}. - -@item %@{!,@code{S}:@code{X}@} -Substitutes @code{X}, if not processing a file for language @code{S}. - -@item %@{@code{S}|@code{P}:@code{X}@} -Substitutes @code{X} if either @code{-S} or @code{-P} is given to -GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and -@code{*} sequences as well, although they have a stronger binding than -the @samp{|}. If @code{%*} appears in @code{X}, all of the -alternatives must be starred, and only the first matching alternative -is substituted. - -For example, a spec string like this: - -@smallexample -%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} -@end smallexample - -@noindent -outputs the following command-line options from the following input -command-line options: - -@smallexample -fred.c -foo -baz -jim.d -bar -boggle --d fred.c -foo -baz -boggle --d jim.d -bar -baz -boggle -@end smallexample - -@item %@{S:X; T:Y; :D@} - -If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is -given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can -be as many clauses as you need. This may be combined with @code{.}, -@code{,}, @code{!}, @code{|}, and @code{*} as needed. - - -@end table - -The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar -construct may contain other nested @samp{%} constructs or spaces, or -even newlines. They are processed as usual, as described above. -Trailing white space in @code{X} is ignored. White space may also -appear anywhere on the left side of the colon in these constructs, -except between @code{.} or @code{*} and the corresponding word. - -The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are -handled specifically in these constructs. If another value of -@option{-O} or the negated form of a @option{-f}, @option{-m}, or -@option{-W} switch is found later in the command line, the earlier -switch value is ignored, except with @{@code{S}*@} where @code{S} is -just one letter, which passes all matching options. - -The character @samp{|} at the beginning of the predicate text is used to -indicate that a command should be piped to the following command, but -only if @option{-pipe} is specified. - -It is built into GCC which switches take arguments and which do not. -(You might think it would be useful to generalize this to allow each -compiler's spec to say which switches take arguments. But this cannot -be done in a consistent fashion. GCC cannot even decide which input -files have been specified without knowing which switches take arguments, -and it must know which input files to compile in order to tell which -compilers to run). - -GCC also knows implicitly that arguments starting in @option{-l} are to be -treated as compiler output files, and passed to the linker in their -proper position among the other output files. - -@c man begin OPTIONS - -@node Target Options -@section Specifying Target Machine and Compiler Version -@cindex target options -@cindex cross compiling -@cindex specifying machine version -@cindex specifying compiler version and target machine -@cindex compiler version, specifying -@cindex target machine, specifying - -The usual way to run GCC is to run the executable called @command{gcc}, or -@command{@var{machine}-gcc} when cross-compiling, or -@command{@var{machine}-gcc-@var{version}} to run a version other than the -one that was installed last. - -@node Submodel Options -@section Hardware Models and Configurations -@cindex submodel options -@cindex specifying hardware config -@cindex hardware models and configurations, specifying -@cindex machine dependent options - -Each target machine types can have its own -special options, starting with @samp{-m}, to choose among various -hardware models or configurations---for example, 68010 vs 68020, -floating coprocessor or none. A single installed version of the -compiler can compile for any model or configuration, according to the -options specified. - -Some configurations of the compiler also support additional special -options, usually for compatibility with other compilers on the same -platform. - -@c This list is ordered alphanumerically by subsection name. -@c It should be the same order and spelling as these options are listed -@c in Machine Dependent Options - -@menu -* AArch64 Options:: -* Adapteva Epiphany Options:: -* ARM Options:: -* AVR Options:: -* Blackfin Options:: -* C6X Options:: -* CRIS Options:: -* CR16 Options:: -* Darwin Options:: -* DEC Alpha Options:: -* FR30 Options:: -* FRV Options:: -* GNU/Linux Options:: -* H8/300 Options:: -* HPPA Options:: -* i386 and x86-64 Options:: -* i386 and x86-64 Windows Options:: -* IA-64 Options:: -* LM32 Options:: -* M32C Options:: -* M32R/D Options:: -* M680x0 Options:: -* MCore Options:: -* MeP Options:: -* MicroBlaze Options:: -* MIPS Options:: -* MMIX Options:: -* MN10300 Options:: -* Moxie Options:: -* PDP-11 Options:: -* picoChip Options:: -* PowerPC Options:: -* RL78 Options:: -* RS/6000 and PowerPC Options:: -* RX Options:: -* S/390 and zSeries Options:: -* Score Options:: -* SH Options:: -* Solaris 2 Options:: -* SPARC Options:: -* SPU Options:: -* System V Options:: -* TILE-Gx Options:: -* TILEPro Options:: -* V850 Options:: -* VAX Options:: -* VMS Options:: -* VxWorks Options:: -* x86-64 Options:: -* Xstormy16 Options:: -* Xtensa Options:: -* zSeries Options:: -@end menu - -@node AArch64 Options -@subsection AArch64 Options -@cindex AArch64 Options - -These options are defined for AArch64 implementations: - -@table @gcctabopt - -@item -mbig-endian -@opindex mbig-endian -Generate big-endian code. This is the default when GCC is configured for an -@samp{aarch64_be-*-*} target. - -@item -mgeneral-regs-only -@opindex mgeneral-regs-only -Generate code which uses only the general registers. - -@item -mlittle-endian -@opindex mlittle-endian -Generate little-endian code. This is the default when GCC is configured for an -@samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target. - -@item -mcmodel=tiny -@opindex mcmodel=tiny -Generate code for the tiny code model. The program and its statically defined -symbols must be within 1GB of each other. Pointers are 64 bits. Programs can -be statically or dynamically linked. This model is not fully implemented and -mostly treated as @samp{small}. - -@item -mcmodel=small -@opindex mcmodel=small -Generate code for the small code model. The program and its statically defined -symbols must be within 4GB of each other. Pointers are 64 bits. Programs can -be statically or dynamically linked. This is the default code model. - -@item -mcmodel=large -@opindex mcmodel=large -Generate code for the large code model. This makes no assumptions about -addresses and sizes of sections. Pointers are 64 bits. Programs can be -statically linked only. - -@item -mstrict-align -@opindex mstrict-align -Do not assume that unaligned memory references will be handled by the system. - -@item -momit-leaf-frame-pointer -@itemx -mno-omit-leaf-frame-pointer -@opindex momit-leaf-frame-pointer -@opindex mno-omit-leaf-frame-pointer -Omit or keep the frame pointer in leaf functions. The former behaviour is the -default. - -@item -mtls-dialect=desc -@opindex mtls-dialect=desc -Use TLS descriptors as the thread-local storage mechanism for dynamic accesses -of TLS variables. This is the default. - -@item -mtls-dialect=traditional -@opindex mtls-dialect=traditional -Use traditional TLS as the thread-local storage mechanism for dynamic accesses -of TLS variables. - -@item -march=@var{name} -@opindex march -Specify the name of the target architecture, optionally suffixed by one or -more feature modifiers. This option has the form -@option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the -only value for @var{arch} is @samp{armv8-a}. The possible values for -@var{feature} are documented in the sub-section below. - -Where conflicting feature modifiers are specified, the right-most feature is -used. - -GCC uses this name to determine what kind of instructions it can emit when -generating assembly code. This option can be used in conjunction with or -instead of the @option{-mcpu=} option. - -@item -mcpu=@var{name} -@opindex mcpu -Specify the name of the target processor, optionally suffixed by one or more -feature modifiers. This option has the form -@option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the -possible values for @var{cpu} are @samp{generic}, @samp{large}. The -possible values for @var{feature} are documented in the sub-section -below. - -Where conflicting feature modifiers are specified, the right-most feature is -used. - -GCC uses this name to determine what kind of instructions it can emit when -generating assembly code. - -@item -mtune=@var{name} -@opindex mtune -Specify the name of the processor to tune the performance for. The code will -be tuned as if the target processor were of the type specified in this option, -but still using instructions compatible with the target processor specified -by a @option{-mcpu=} option. This option cannot be suffixed by feature -modifiers. - -@end table - -@subsubsection @option{-march} and @option{-mcpu} feature modifiers -@cindex @option{-march} feature modifiers -@cindex @option{-mcpu} feature modifiers -Feature modifiers used with @option{-march} and @option{-mcpu} can be one -the following: - -@table @samp -@item crypto -Enable Crypto extension. This implies Advanced SIMD is enabled. -@item fp -Enable floating-point instructions. -@item simd -Enable Advanced SIMD instructions. This implies floating-point instructions -are enabled. This is the default for all current possible values for options -@option{-march} and @option{-mcpu=}. -@end table - -@node Adapteva Epiphany Options -@subsection Adapteva Epiphany Options - -These @samp{-m} options are defined for Adapteva Epiphany: - -@table @gcctabopt -@item -mhalf-reg-file -@opindex mhalf-reg-file -Don't allocate any register in the range @code{r32}@dots{}@code{r63}. -That allows code to run on hardware variants that lack these registers. - -@item -mprefer-short-insn-regs -@opindex mprefer-short-insn-regs -Preferrentially allocate registers that allow short instruction generation. -This can result in increased instruction count, so this may either reduce or -increase overall code size. - -@item -mbranch-cost=@var{num} -@opindex mbranch-cost -Set the cost of branches to roughly @var{num} ``simple'' instructions. -This cost is only a heuristic and is not guaranteed to produce -consistent results across releases. - -@item -mcmove -@opindex mcmove -Enable the generation of conditional moves. - -@item -mnops=@var{num} -@opindex mnops -Emit @var{num} NOPs before every other generated instruction. - -@item -mno-soft-cmpsf -@opindex mno-soft-cmpsf -For single-precision floating-point comparisons, emit an @code{fsub} instruction -and test the flags. This is faster than a software comparison, but can -get incorrect results in the presence of NaNs, or when two different small -numbers are compared such that their difference is calculated as zero. -The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant, -software comparisons. - -@item -mstack-offset=@var{num} -@opindex mstack-offset -Set the offset between the top of the stack and the stack pointer. -E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7} -can be used by leaf functions without stack allocation. -Values other than @samp{8} or @samp{16} are untested and unlikely to work. -Note also that this option changes the ABI; compiling a program with a -different stack offset than the libraries have been compiled with -generally does not work. -This option can be useful if you want to evaluate if a different stack -offset would give you better code, but to actually use a different stack -offset to build working programs, it is recommended to configure the -toolchain with the appropriate @option{--with-stack-offset=@var{num}} option. - -@item -mno-round-nearest -@opindex mno-round-nearest -Make the scheduler assume that the rounding mode has been set to -truncating. The default is @option{-mround-nearest}. - -@item -mlong-calls -@opindex mlong-calls -If not otherwise specified by an attribute, assume all calls might be beyond -the offset range of the @code{b} / @code{bl} instructions, and therefore load the -function address into a register before performing a (otherwise direct) call. -This is the default. - -@item -mshort-calls -@opindex short-calls -If not otherwise specified by an attribute, assume all direct calls are -in the range of the @code{b} / @code{bl} instructions, so use these instructions -for direct calls. The default is @option{-mlong-calls}. - -@item -msmall16 -@opindex msmall16 -Assume addresses can be loaded as 16-bit unsigned values. This does not -apply to function addresses for which @option{-mlong-calls} semantics -are in effect. - -@item -mfp-mode=@var{mode} -@opindex mfp-mode -Set the prevailing mode of the floating-point unit. -This determines the floating-point mode that is provided and expected -at function call and return time. Making this mode match the mode you -predominantly need at function start can make your programs smaller and -faster by avoiding unnecessary mode switches. - -@var{mode} can be set to one the following values: - -@table @samp -@item caller -Any mode at function entry is valid, and retained or restored when -the function returns, and when it calls other functions. -This mode is useful for compiling libraries or other compilation units -you might want to incorporate into different programs with different -prevailing FPU modes, and the convenience of being able to use a single -object file outweighs the size and speed overhead for any extra -mode switching that might be needed, compared with what would be needed -with a more specific choice of prevailing FPU mode. - -@item truncate -This is the mode used for floating-point calculations with -truncating (i.e.@: round towards zero) rounding mode. That includes -conversion from floating point to integer. - -@item round-nearest -This is the mode used for floating-point calculations with -round-to-nearest-or-even rounding mode. - -@item int -This is the mode used to perform integer calculations in the FPU, e.g.@: -integer multiply, or integer multiply-and-accumulate. -@end table - -The default is @option{-mfp-mode=caller} - -@item -mnosplit-lohi -@itemx -mno-postinc -@itemx -mno-postmodify -@opindex mnosplit-lohi -@opindex mno-postinc -@opindex mno-postmodify -Code generation tweaks that disable, respectively, splitting of 32-bit -loads, generation of post-increment addresses, and generation of -post-modify addresses. The defaults are @option{msplit-lohi}, -@option{-mpost-inc}, and @option{-mpost-modify}. - -@item -mnovect-double -@opindex mno-vect-double -Change the preferred SIMD mode to SImode. The default is -@option{-mvect-double}, which uses DImode as preferred SIMD mode. - -@item -max-vect-align=@var{num} -@opindex max-vect-align -The maximum alignment for SIMD vector mode types. -@var{num} may be 4 or 8. The default is 8. -Note that this is an ABI change, even though many library function -interfaces are unaffected if they don't use SIMD vector modes -in places that affect size and/or alignment of relevant types. - -@item -msplit-vecmove-early -@opindex msplit-vecmove-early -Split vector moves into single word moves before reload. In theory this -can give better register allocation, but so far the reverse seems to be -generally the case. - -@item -m1reg-@var{reg} -@opindex m1reg- -Specify a register to hold the constant @minus{}1, which makes loading small negative -constants and certain bitmasks faster. -Allowable values for @var{reg} are @samp{r43} and @samp{r63}, -which specify use of that register as a fixed register, -and @samp{none}, which means that no register is used for this -purpose. The default is @option{-m1reg-none}. - -@end table - -@node ARM Options -@subsection ARM Options -@cindex ARM options - -These @samp{-m} options are defined for Advanced RISC Machines (ARM) -architectures: - -@table @gcctabopt -@item -mabi=@var{name} -@opindex mabi -Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu}, -@samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}. - -@item -mapcs-frame -@opindex mapcs-frame -Generate a stack frame that is compliant with the ARM Procedure Call -Standard for all functions, even if this is not strictly necessary for -correct execution of the code. Specifying @option{-fomit-frame-pointer} -with this option causes the stack frames not to be generated for -leaf functions. The default is @option{-mno-apcs-frame}. - -@item -mapcs -@opindex mapcs -This is a synonym for @option{-mapcs-frame}. - -@ignore -@c not currently implemented -@item -mapcs-stack-check -@opindex mapcs-stack-check -Generate code to check the amount of stack space available upon entry to -every function (that actually uses some stack space). If there is -insufficient space available then either the function -@samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} is -called, depending upon the amount of stack space required. The runtime -system is required to provide these functions. The default is -@option{-mno-apcs-stack-check}, since this produces smaller code. - -@c not currently implemented -@item -mapcs-float -@opindex mapcs-float -Pass floating-point arguments using the floating-point registers. This is -one of the variants of the APCS@. This option is recommended if the -target hardware has a floating-point unit or if a lot of floating-point -arithmetic is going to be performed by the code. The default is -@option{-mno-apcs-float}, since the size of integer-only code is -slightly increased if @option{-mapcs-float} is used. - -@c not currently implemented -@item -mapcs-reentrant -@opindex mapcs-reentrant -Generate reentrant, position-independent code. The default is -@option{-mno-apcs-reentrant}. -@end ignore - -@item -mthumb-interwork -@opindex mthumb-interwork -Generate code that supports calling between the ARM and Thumb -instruction sets. Without this option, on pre-v5 architectures, the -two instruction sets cannot be reliably used inside one program. The -default is @option{-mno-thumb-interwork}, since slightly larger code -is generated when @option{-mthumb-interwork} is specified. In AAPCS -configurations this option is meaningless. - -@item -mno-sched-prolog -@opindex mno-sched-prolog -Prevent the reordering of instructions in the function prologue, or the -merging of those instruction with the instructions in the function's -body. This means that all functions start with a recognizable set -of instructions (or in fact one of a choice from a small set of -different function prologues), and this information can be used to -locate the start of functions inside an executable piece of code. The -default is @option{-msched-prolog}. - -@item -mfloat-abi=@var{name} -@opindex mfloat-abi -Specifies which floating-point ABI to use. Permissible values -are: @samp{soft}, @samp{softfp} and @samp{hard}. - -Specifying @samp{soft} causes GCC to generate output containing -library calls for floating-point operations. -@samp{softfp} allows the generation of code using hardware floating-point -instructions, but still uses the soft-float calling conventions. -@samp{hard} allows generation of floating-point instructions -and uses FPU-specific calling conventions. - -The default depends on the specific target configuration. Note that -the hard-float and soft-float ABIs are not link-compatible; you must -compile your entire program with the same ABI, and link with a -compatible set of libraries. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a processor running in little-endian mode. This is -the default for all standard configurations. - -@item -mbig-endian -@opindex mbig-endian -Generate code for a processor running in big-endian mode; the default is -to compile code for a little-endian processor. - -@item -mwords-little-endian -@opindex mwords-little-endian -This option only applies when generating code for big-endian processors. -Generate code for a little-endian word order but a big-endian byte -order. That is, a byte order of the form @samp{32107654}. Note: this -option should only be used if you require compatibility with code for -big-endian ARM processors generated by versions of the compiler prior to -2.8. This option is now deprecated. - -@item -mcpu=@var{name} -@opindex mcpu -This specifies the name of the target ARM processor. GCC uses this name -to determine what kind of instructions it can emit when generating -assembly code. Permissible names are: @samp{arm2}, @samp{arm250}, -@samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610}, -@samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm}, -@samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700}, -@samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100}, -@samp{arm720}, -@samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s}, -@samp{arm710t}, @samp{arm720t}, @samp{arm740t}, -@samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100}, -@samp{strongarm1110}, -@samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920}, -@samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s}, -@samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi}, -@samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s}, -@samp{arm10e}, @samp{arm1020e}, @samp{arm1022e}, -@samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp}, -@samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s}, -@samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8}, @samp{cortex-a9}, -@samp{cortex-a15}, @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-r5}, -@samp{cortex-m4}, @samp{cortex-m3}, -@samp{cortex-m1}, -@samp{cortex-m0}, -@samp{cortex-m0plus}, -@samp{marvell-pj4}, -@samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}, -@samp{fa526}, @samp{fa626}, -@samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te}. - - -@option{-mcpu=generic-@var{arch}} is also permissible, and is -equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}. -See @option{-mtune} for more information. - -@option{-mcpu=native} causes the compiler to auto-detect the CPU -of the build computer. At present, this feature is only supported on -Linux, and not all architectures are recognized. If the auto-detect is -unsuccessful the option has no effect. - -@item -mtune=@var{name} -@opindex mtune -This option is very similar to the @option{-mcpu=} option, except that -instead of specifying the actual target processor type, and hence -restricting which instructions can be used, it specifies that GCC should -tune the performance of the code as if the target were of the type -specified in this option, but still choosing the instructions it -generates based on the CPU specified by a @option{-mcpu=} option. -For some ARM implementations better performance can be obtained by using -this option. - -@option{-mtune=generic-@var{arch}} specifies that GCC should tune the -performance for a blend of processors within architecture @var{arch}. -The aim is to generate code that run well on the current most popular -processors, balancing between optimizations that benefit some CPUs in the -range, and avoiding performance pitfalls of other CPUs. The effects of -this option may change in future GCC versions as CPU models come and go. - -@option{-mtune=native} causes the compiler to auto-detect the CPU -of the build computer. At present, this feature is only supported on -Linux, and not all architectures are recognized. If the auto-detect is -unsuccessful the option has no effect. - -@item -march=@var{name} -@opindex march -This specifies the name of the target ARM architecture. GCC uses this -name to determine what kind of instructions it can emit when generating -assembly code. This option can be used in conjunction with or instead -of the @option{-mcpu=} option. Permissible names are: @samp{armv2}, -@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t}, -@samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te}, -@samp{armv6}, @samp{armv6j}, -@samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m}, -@samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m}, -@samp{armv8-a}, -@samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}. - -@option{-march=native} causes the compiler to auto-detect the architecture -of the build computer. At present, this feature is only supported on -Linux, and not all architectures are recognized. If the auto-detect is -unsuccessful the option has no effect. - -@item -mfpu=@var{name} -@opindex mfpu -This specifies what floating-point hardware (or hardware emulation) is -available on the target. Permissible names are: @samp{vfp}, @samp{vfpv3}, -@samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, -@samp{vfpv3xd-fp16}, @samp{neon}, @samp{neon-fp16}, @samp{vfpv4}, -@samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4}, -@samp{fp-armv8}, @samp{neon-fp-armv8}, and @samp{crypto-neon-fp-armv8}. - -If @option{-msoft-float} is specified this specifies the format of -floating-point values. - -If the selected floating-point hardware includes the NEON extension -(e.g. @option{-mfpu}=@samp{neon}), note that floating-point -operations are not generated by GCC's auto-vectorization pass unless -@option{-funsafe-math-optimizations} is also specified. This is -because NEON hardware does not fully implement the IEEE 754 standard for -floating-point arithmetic (in particular denormal values are treated as -zero), so the use of NEON instructions may lead to a loss of precision. - -@item -mfp16-format=@var{name} -@opindex mfp16-format -Specify the format of the @code{__fp16} half-precision floating-point type. -Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative}; -the default is @samp{none}, in which case the @code{__fp16} type is not -defined. @xref{Half-Precision}, for more information. - -@item -mstructure-size-boundary=@var{n} -@opindex mstructure-size-boundary -The sizes of all structures and unions are rounded up to a multiple -of the number of bits set by this option. Permissible values are 8, 32 -and 64. The default value varies for different toolchains. For the COFF -targeted toolchain the default value is 8. A value of 64 is only allowed -if the underlying ABI supports it. - -Specifying a larger number can produce faster, more efficient code, but -can also increase the size of the program. Different values are potentially -incompatible. Code compiled with one value cannot necessarily expect to -work with code or libraries compiled with another value, if they exchange -information using structures or unions. - -@item -mabort-on-noreturn -@opindex mabort-on-noreturn -Generate a call to the function @code{abort} at the end of a -@code{noreturn} function. It is executed if the function tries to -return. - -@item -mlong-calls -@itemx -mno-long-calls -@opindex mlong-calls -@opindex mno-long-calls -Tells the compiler to perform function calls by first loading the -address of the function into a register and then performing a subroutine -call on this register. This switch is needed if the target function -lies outside of the 64-megabyte addressing range of the offset-based -version of subroutine call instruction. - -Even if this switch is enabled, not all function calls are turned -into long calls. The heuristic is that static functions, functions -that have the @samp{short-call} attribute, functions that are inside -the scope of a @samp{#pragma no_long_calls} directive, and functions whose -definitions have already been compiled within the current compilation -unit are not turned into long calls. The exceptions to this rule are -that weak function definitions, functions with the @samp{long-call} -attribute or the @samp{section} attribute, and functions that are within -the scope of a @samp{#pragma long_calls} directive are always -turned into long calls. - -This feature is not enabled by default. Specifying -@option{-mno-long-calls} restores the default behavior, as does -placing the function calls within the scope of a @samp{#pragma -long_calls_off} directive. Note these switches have no effect on how -the compiler generates code to handle function calls via function -pointers. - -@item -msingle-pic-base -@opindex msingle-pic-base -Treat the register used for PIC addressing as read-only, rather than -loading it in the prologue for each function. The runtime system is -responsible for initializing this register with an appropriate value -before execution begins. - -@item -mpic-register=@var{reg} -@opindex mpic-register -Specify the register to be used for PIC addressing. The default is R10 -unless stack-checking is enabled, when R9 is used. - -@item -mpoke-function-name -@opindex mpoke-function-name -Write the name of each function into the text section, directly -preceding the function prologue. The generated code is similar to this: - -@smallexample - t0 - .ascii "arm_poke_function_name", 0 - .align - t1 - .word 0xff000000 + (t1 - t0) - arm_poke_function_name - mov ip, sp - stmfd sp!, @{fp, ip, lr, pc@} - sub fp, ip, #4 -@end smallexample - -When performing a stack backtrace, code can inspect the value of -@code{pc} stored at @code{fp + 0}. If the trace function then looks at -location @code{pc - 12} and the top 8 bits are set, then we know that -there is a function name embedded immediately preceding this location -and has length @code{((pc[-3]) & 0xff000000)}. - -@item -mthumb -@itemx -marm -@opindex marm -@opindex mthumb - -Select between generating code that executes in ARM and Thumb -states. The default for most configurations is to generate code -that executes in ARM state, but the default can be changed by -configuring GCC with the @option{--with-mode=}@var{state} -configure option. - -@item -mtpcs-frame -@opindex mtpcs-frame -Generate a stack frame that is compliant with the Thumb Procedure Call -Standard for all non-leaf functions. (A leaf function is one that does -not call any other functions.) The default is @option{-mno-tpcs-frame}. - -@item -mtpcs-leaf-frame -@opindex mtpcs-leaf-frame -Generate a stack frame that is compliant with the Thumb Procedure Call -Standard for all leaf functions. (A leaf function is one that does -not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. - -@item -mcallee-super-interworking -@opindex mcallee-super-interworking -Gives all externally visible functions in the file being compiled an ARM -instruction set header which switches to Thumb mode before executing the -rest of the function. This allows these functions to be called from -non-interworking code. This option is not valid in AAPCS configurations -because interworking is enabled by default. - -@item -mcaller-super-interworking -@opindex mcaller-super-interworking -Allows calls via function pointers (including virtual functions) to -execute correctly regardless of whether the target code has been -compiled for interworking or not. There is a small overhead in the cost -of executing a function pointer if this option is enabled. This option -is not valid in AAPCS configurations because interworking is enabled -by default. - -@item -mtp=@var{name} -@opindex mtp -Specify the access model for the thread local storage pointer. The valid -models are @option{soft}, which generates calls to @code{__aeabi_read_tp}, -@option{cp15}, which fetches the thread pointer from @code{cp15} directly -(supported in the arm6k architecture), and @option{auto}, which uses the -best available method for the selected processor. The default setting is -@option{auto}. - -@item -mtls-dialect=@var{dialect} -@opindex mtls-dialect -Specify the dialect to use for accessing thread local storage. Two -@var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The -@samp{gnu} dialect selects the original GNU scheme for supporting -local and global dynamic TLS models. The @samp{gnu2} dialect -selects the GNU descriptor scheme, which provides better performance -for shared libraries. The GNU descriptor scheme is compatible with -the original scheme, but does require new assembler, linker and -library support. Initial and local exec TLS models are unaffected by -this option and always use the original scheme. - -@item -mword-relocations -@opindex mword-relocations -Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). -This is enabled by default on targets (uClinux, SymbianOS) where the runtime -loader imposes this restriction, and when @option{-fpic} or @option{-fPIC} -is specified. - -@item -mfix-cortex-m3-ldrd -@opindex mfix-cortex-m3-ldrd -Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions -with overlapping destination and base registers are used. This option avoids -generating these instructions. This option is enabled by default when -@option{-mcpu=cortex-m3} is specified. - -@item -munaligned-access -@itemx -mno-unaligned-access -@opindex munaligned-access -@opindex mno-unaligned-access -Enables (or disables) reading and writing of 16- and 32- bit values -from addresses that are not 16- or 32- bit aligned. By default -unaligned access is disabled for all pre-ARMv6 and all ARMv6-M -architectures, and enabled for all other architectures. If unaligned -access is not enabled then words in packed data structures will be -accessed a byte at a time. - -The ARM attribute @code{Tag_CPU_unaligned_access} will be set in the -generated object file to either true or false, depending upon the -setting of this option. If unaligned access is enabled then the -preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} will also be -defined. - -@end table - -@node AVR Options -@subsection AVR Options -@cindex AVR Options - -These options are defined for AVR implementations: - -@table @gcctabopt -@item -mmcu=@var{mcu} -@opindex mmcu -Specify Atmel AVR instruction set architectures (ISA) or MCU type. - -The default for this option is@tie{}@code{avr2}. - -GCC supports the following AVR devices and ISAs: - -@include avr-mmcu.texi - -@item -maccumulate-args -@opindex maccumulate-args -Accumulate outgoing function arguments and acquire/release the needed -stack space for outgoing function arguments once in function -prologue/epilogue. Without this option, outgoing arguments are pushed -before calling a function and popped afterwards. - -Popping the arguments after the function call can be expensive on -AVR so that accumulating the stack space might lead to smaller -executables because arguments need not to be removed from the -stack after such a function call. - -This option can lead to reduced code size for functions that perform -several calls to functions that get their arguments on the stack like -calls to printf-like functions. - -@item -mbranch-cost=@var{cost} -@opindex mbranch-cost -Set the branch costs for conditional branch instructions to -@var{cost}. Reasonable values for @var{cost} are small, non-negative -integers. The default branch cost is 0. - -@item -mcall-prologues -@opindex mcall-prologues -Functions prologues/epilogues are expanded as calls to appropriate -subroutines. Code size is smaller. - -@item -mint8 -@opindex mint8 -Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a -@code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes, -and @code{long long} is 4 bytes. Please note that this option does not -conform to the C standards, but it results in smaller code -size. - -@item -mno-interrupts -@opindex mno-interrupts -Generated code is not compatible with hardware interrupts. -Code size is smaller. - -@item -mrelax -@opindex mrelax -Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter -@code{RCALL} resp.@: @code{RJMP} instruction if applicable. -Setting @code{-mrelax} just adds the @code{--relax} option to the -linker command line when the linker is called. - -Jump relaxing is performed by the linker because jump offsets are not -known before code is located. Therefore, the assembler code generated by the -compiler is the same, but the instructions in the executable may -differ from instructions in the assembler code. - -Relaxing must be turned on if linker stubs are needed, see the -section on @code{EIND} and linker stubs below. - -@item -msp8 -@opindex msp8 -Treat the stack pointer register as an 8-bit register, -i.e.@: assume the high byte of the stack pointer is zero. -In general, you don't need to set this option by hand. - -This option is used internally by the compiler to select and -build multilibs for architectures @code{avr2} and @code{avr25}. -These architectures mix devices with and without @code{SPH}. -For any setting other than @code{-mmcu=avr2} or @code{-mmcu=avr25} -the compiler driver will add or remove this option from the compiler -proper's command line, because the compiler then knows if the device -or architecture has an 8-bit stack pointer and thus no @code{SPH} -register or not. - -@item -mstrict-X -@opindex mstrict-X -Use address register @code{X} in a way proposed by the hardware. This means -that @code{X} is only used in indirect, post-increment or -pre-decrement addressing. - -Without this option, the @code{X} register may be used in the same way -as @code{Y} or @code{Z} which then is emulated by additional -instructions. -For example, loading a value with @code{X+const} addressing with a -small non-negative @code{const < 64} to a register @var{Rn} is -performed as - -@example -adiw r26, const ; X += const -ld @var{Rn}, X ; @var{Rn} = *X -sbiw r26, const ; X -= const -@end example - -@item -mtiny-stack -@opindex mtiny-stack -Only change the lower 8@tie{}bits of the stack pointer. - -@item -Waddr-space-convert -@opindex Waddr-space-convert -Warn about conversions between address spaces in the case where the -resulting address space is not contained in the incoming address space. -@end table - -@subsubsection @code{EIND} and Devices with more than 128 Ki Bytes of Flash -@cindex @code{EIND} -Pointers in the implementation are 16@tie{}bits wide. -The address of a function or label is represented as word address so -that indirect jumps and calls can target any code address in the -range of 64@tie{}Ki words. - -In order to facilitate indirect jump on devices with more than 128@tie{}Ki -bytes of program memory space, there is a special function register called -@code{EIND} that serves as most significant part of the target address -when @code{EICALL} or @code{EIJMP} instructions are used. - -Indirect jumps and calls on these devices are handled as follows by -the compiler and are subject to some limitations: - -@itemize @bullet - -@item -The compiler never sets @code{EIND}. - -@item -The compiler uses @code{EIND} implicitely in @code{EICALL}/@code{EIJMP} -instructions or might read @code{EIND} directly in order to emulate an -indirect call/jump by means of a @code{RET} instruction. - -@item -The compiler assumes that @code{EIND} never changes during the startup -code or during the application. In particular, @code{EIND} is not -saved/restored in function or interrupt service routine -prologue/epilogue. - -@item -For indirect calls to functions and computed goto, the linker -generates @emph{stubs}. Stubs are jump pads sometimes also called -@emph{trampolines}. Thus, the indirect call/jump jumps to such a stub. -The stub contains a direct jump to the desired address. - -@item -Linker relaxation must be turned on so that the linker will generate -the stubs correctly an all situaltion. See the compiler option -@code{-mrelax} and the linler option @code{--relax}. -There are corner cases where the linker is supposed to generate stubs -but aborts without relaxation and without a helpful error message. - -@item -The default linker script is arranged for code with @code{EIND = 0}. -If code is supposed to work for a setup with @code{EIND != 0}, a custom -linker script has to be used in order to place the sections whose -name start with @code{.trampolines} into the segment where @code{EIND} -points to. - -@item -The startup code from libgcc never sets @code{EIND}. -Notice that startup code is a blend of code from libgcc and AVR-LibC. -For the impact of AVR-LibC on @code{EIND}, see the -@w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC user manual}}. - -@item -It is legitimate for user-specific startup code to set up @code{EIND} -early, for example by means of initialization code located in -section @code{.init3}. Such code runs prior to general startup code -that initializes RAM and calls constructors, but after the bit -of startup code from AVR-LibC that sets @code{EIND} to the segment -where the vector table is located. -@example -#include <avr/io.h> - -static void -__attribute__((section(".init3"),naked,used,no_instrument_function)) -init3_set_eind (void) -@{ - __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" - "out %i0,r24" :: "n" (&EIND) : "r24","memory"); -@} -@end example - -@noindent -The @code{__trampolines_start} symbol is defined in the linker script. - -@item -Stubs are generated automatically by the linker if -the following two conditions are met: -@itemize @minus - -@item The address of a label is taken by means of the @code{gs} modifier -(short for @emph{generate stubs}) like so: -@example -LDI r24, lo8(gs(@var{func})) -LDI r25, hi8(gs(@var{func})) -@end example -@item The final location of that label is in a code segment -@emph{outside} the segment where the stubs are located. -@end itemize - -@item -The compiler emits such @code{gs} modifiers for code labels in the -following situations: -@itemize @minus -@item Taking address of a function or code label. -@item Computed goto. -@item If prologue-save function is used, see @option{-mcall-prologues} -command-line option. -@item Switch/case dispatch tables. If you do not want such dispatch -tables you can specify the @option{-fno-jump-tables} command-line option. -@item C and C++ constructors/destructors called during startup/shutdown. -@item If the tools hit a @code{gs()} modifier explained above. -@end itemize - -@item -Jumping to non-symbolic addresses like so is @emph{not} supported: - -@example -int main (void) -@{ - /* Call function at word address 0x2 */ - return ((int(*)(void)) 0x2)(); -@} -@end example - -Instead, a stub has to be set up, i.e.@: the function has to be called -through a symbol (@code{func_4} in the example): - -@example -int main (void) -@{ - extern int func_4 (void); - - /* Call function at byte address 0x4 */ - return func_4(); -@} -@end example - -and the application be linked with @code{-Wl,--defsym,func_4=0x4}. -Alternatively, @code{func_4} can be defined in the linker script. -@end itemize - -@subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers -@cindex @code{RAMPD} -@cindex @code{RAMPX} -@cindex @code{RAMPY} -@cindex @code{RAMPZ} -Some AVR devices support memories larger than the 64@tie{}KiB range -that can be accessed with 16-bit pointers. To access memory locations -outside this 64@tie{}KiB range, the contentent of a @code{RAMP} -register is used as high part of the address: -The @code{X}, @code{Y}, @code{Z} address register is concatenated -with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function -register, respectively, to get a wide address. Similarly, -@code{RAMPD} is used together with direct addressing. - -@itemize -@item -The startup code initializes the @code{RAMP} special function -registers with zero. - -@item -If a @ref{AVR Named Address Spaces,named address space} other than -generic or @code{__flash} is used, then @code{RAMPZ} is set -as needed before the operation. - -@item -If the device supports RAM larger than 64@tie{KiB} and the compiler -needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ} -is reset to zero after the operation. - -@item -If the device comes with a specific @code{RAMP} register, the ISR -prologue/epilogue saves/restores that SFR and initializes it with -zero in case the ISR code might (implicitly) use it. - -@item -RAM larger than 64@tie{KiB} is not supported by GCC for AVR targets. -If you use inline assembler to read from locations outside the -16-bit address range and change one of the @code{RAMP} registers, -you must reset it to zero after the access. - -@end itemize - -@subsubsection AVR Built-in Macros - -GCC defines several built-in macros so that the user code can test -for the presence or absence of features. Almost any of the following -built-in macros are deduced from device capabilities and thus -triggered by the @code{-mmcu=} command-line option. - -For even more AVR-specific built-in macros see -@ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}. - -@table @code - -@item __AVR_ARCH__ -Build-in macro that resolves to a decimal number that identifies the -architecture and depends on the @code{-mmcu=@var{mcu}} option. -Possible values are: - -@code{2}, @code{25}, @code{3}, @code{31}, @code{35}, -@code{4}, @code{5}, @code{51}, @code{6}, @code{102}, @code{104}, -@code{105}, @code{106}, @code{107} - -for @var{mcu}=@code{avr2}, @code{avr25}, @code{avr3}, -@code{avr31}, @code{avr35}, @code{avr4}, @code{avr5}, @code{avr51}, -@code{avr6}, @code{avrxmega2}, @code{avrxmega4}, @code{avrxmega5}, -@code{avrxmega6}, @code{avrxmega7}, respectively. -If @var{mcu} specifies a device, this built-in macro is set -accordingly. For example, with @code{-mmcu=atmega8} the macro will be -defined to @code{4}. - -@item __AVR_@var{Device}__ -Setting @code{-mmcu=@var{device}} defines this built-in macro which reflects -the device's name. For example, @code{-mmcu=atmega8} defines the -built-in macro @code{__AVR_ATmega8__}, @code{-mmcu=attiny261a} defines -@code{__AVR_ATtiny261A__}, etc. - -The built-in macros' names follow -the scheme @code{__AVR_@var{Device}__} where @var{Device} is -the device name as from the AVR user manual. The difference between -@var{Device} in the built-in macro and @var{device} in -@code{-mmcu=@var{device}} is that the latter is always lowercase. - -If @var{device} is not a device but only a core architecture like -@code{avr51}, this macro will not be defined. - -@item __AVR_XMEGA__ -The device / architecture belongs to the XMEGA family of devices. - -@item __AVR_HAVE_ELPM__ -The device has the the @code{ELPM} instruction. - -@item __AVR_HAVE_ELPMX__ -The device has the @code{ELPM R@var{n},Z} and @code{ELPM -R@var{n},Z+} instructions. - -@item __AVR_HAVE_MOVW__ -The device has the @code{MOVW} instruction to perform 16-bit -register-register moves. - -@item __AVR_HAVE_LPMX__ -The device has the @code{LPM R@var{n},Z} and -@code{LPM R@var{n},Z+} instructions. - -@item __AVR_HAVE_MUL__ -The device has a hardware multiplier. - -@item __AVR_HAVE_JMP_CALL__ -The device has the @code{JMP} and @code{CALL} instructions. -This is the case for devices with at least 16@tie{}KiB of program -memory. - -@item __AVR_HAVE_EIJMP_EICALL__ -@itemx __AVR_3_BYTE_PC__ -The device has the @code{EIJMP} and @code{EICALL} instructions. -This is the case for devices with more than 128@tie{}KiB of program memory. -This also means that the program counter -(PC) is 3@tie{}bytes wide. - -@item __AVR_2_BYTE_PC__ -The program counter (PC) is 2@tie{}bytes wide. This is the case for devices -with up to 128@tie{}KiB of program memory. - -@item __AVR_HAVE_8BIT_SP__ -@itemx __AVR_HAVE_16BIT_SP__ -The stack pointer (SP) register is treated as 8-bit respectively -16-bit register by the compiler. -The definition of these macros is affected by @code{-mtiny-stack}. - -@item __AVR_HAVE_SPH__ -@itemx __AVR_SP8__ -The device has the SPH (high part of stack pointer) special function -register or has an 8-bit stack pointer, respectively. -The definition of these macros is affected by @code{-mmcu=} and -in the cases of @code{-mmcu=avr2} and @code{-mmcu=avr25} also -by @code{-msp8}. - -@item __AVR_HAVE_RAMPD__ -@itemx __AVR_HAVE_RAMPX__ -@itemx __AVR_HAVE_RAMPY__ -@itemx __AVR_HAVE_RAMPZ__ -The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY}, -@code{RAMPZ} special function register, respectively. - -@item __NO_INTERRUPTS__ -This macro reflects the @code{-mno-interrupts} command line option. - -@item __AVR_ERRATA_SKIP__ -@itemx __AVR_ERRATA_SKIP_JMP_CALL__ -Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit -instructions because of a hardware erratum. Skip instructions are -@code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}. -The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also -set. - -@item __AVR_SFR_OFFSET__=@var{offset} -Instructions that can address I/O special function registers directly -like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different -address as if addressed by an instruction to access RAM like @code{LD} -or @code{STS}. This offset depends on the device architecture and has -to be subtracted from the RAM address in order to get the -respective I/O@tie{}address. - -@item __WITH_AVRLIBC__ -The compiler is configured to be used together with AVR-Libc. -See the @code{--with-avrlibc} configure option. - -@end table - -@node Blackfin Options -@subsection Blackfin Options -@cindex Blackfin Options - -@table @gcctabopt -@item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} -@opindex mcpu= -Specifies the name of the target Blackfin processor. Currently, @var{cpu} -can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518}, -@samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526}, -@samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533}, -@samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539}, -@samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549}, -@samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m}, -@samp{bf561}, @samp{bf592}. - -The optional @var{sirevision} specifies the silicon revision of the target -Blackfin processor. Any workarounds available for the targeted silicon revision -are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled. -If @var{sirevision} is @samp{any}, all workarounds for the targeted processor -are enabled. The @code{__SILICON_REVISION__} macro is defined to two -hexadecimal digits representing the major and minor numbers in the silicon -revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__} -is not defined. If @var{sirevision} is @samp{any}, the -@code{__SILICON_REVISION__} is defined to be @code{0xffff}. -If this optional @var{sirevision} is not used, GCC assumes the latest known -silicon revision of the targeted Blackfin processor. - -GCC defines a preprocessor macro for the specified @var{cpu}. -For the @samp{bfin-elf} toolchain, this option causes the hardware BSP -provided by libgloss to be linked in if @option{-msim} is not given. - -Without this option, @samp{bf532} is used as the processor by default. - -Note that support for @samp{bf561} is incomplete. For @samp{bf561}, -only the preprocessor macro is defined. - -@item -msim -@opindex msim -Specifies that the program will be run on the simulator. This causes -the simulator BSP provided by libgloss to be linked in. This option -has effect only for @samp{bfin-elf} toolchain. -Certain other options, such as @option{-mid-shared-library} and -@option{-mfdpic}, imply @option{-msim}. - -@item -momit-leaf-frame-pointer -@opindex momit-leaf-frame-pointer -Don't keep the frame pointer in a register for leaf functions. This -avoids the instructions to save, set up and restore frame pointers and -makes an extra register available in leaf functions. The option -@option{-fomit-frame-pointer} removes the frame pointer for all functions, -which might make debugging harder. - -@item -mspecld-anomaly -@opindex mspecld-anomaly -When enabled, the compiler ensures that the generated code does not -contain speculative loads after jump instructions. If this option is used, -@code{__WORKAROUND_SPECULATIVE_LOADS} is defined. - -@item -mno-specld-anomaly -@opindex mno-specld-anomaly -Don't generate extra code to prevent speculative loads from occurring. - -@item -mcsync-anomaly -@opindex mcsync-anomaly -When enabled, the compiler ensures that the generated code does not -contain CSYNC or SSYNC instructions too soon after conditional branches. -If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined. - -@item -mno-csync-anomaly -@opindex mno-csync-anomaly -Don't generate extra code to prevent CSYNC or SSYNC instructions from -occurring too soon after a conditional branch. - -@item -mlow-64k -@opindex mlow-64k -When enabled, the compiler is free to take advantage of the knowledge that -the entire program fits into the low 64k of memory. - -@item -mno-low-64k -@opindex mno-low-64k -Assume that the program is arbitrarily large. This is the default. - -@item -mstack-check-l1 -@opindex mstack-check-l1 -Do stack checking using information placed into L1 scratchpad memory by the -uClinux kernel. - -@item -mid-shared-library -@opindex mid-shared-library -Generate code that supports shared libraries via the library ID method. -This allows for execute in place and shared libraries in an environment -without virtual memory management. This option implies @option{-fPIC}. -With a @samp{bfin-elf} target, this option implies @option{-msim}. - -@item -mno-id-shared-library -@opindex mno-id-shared-library -Generate code that doesn't assume ID-based shared libraries are being used. -This is the default. - -@item -mleaf-id-shared-library -@opindex mleaf-id-shared-library -Generate code that supports shared libraries via the library ID method, -but assumes that this library or executable won't link against any other -ID shared libraries. That allows the compiler to use faster code for jumps -and calls. - -@item -mno-leaf-id-shared-library -@opindex mno-leaf-id-shared-library -Do not assume that the code being compiled won't link against any ID shared -libraries. Slower code is generated for jump and call insns. - -@item -mshared-library-id=n -@opindex mshared-library-id -Specifies the identification number of the ID-based shared library being -compiled. Specifying a value of 0 generates more compact code; specifying -other values forces the allocation of that number to the current -library but is no more space- or time-efficient than omitting this option. - -@item -msep-data -@opindex msep-data -Generate code that allows the data segment to be located in a different -area of memory from the text segment. This allows for execute in place in -an environment without virtual memory management by eliminating relocations -against the text section. - -@item -mno-sep-data -@opindex mno-sep-data -Generate code that assumes that the data segment follows the text segment. -This is the default. - -@item -mlong-calls -@itemx -mno-long-calls -@opindex mlong-calls -@opindex mno-long-calls -Tells the compiler to perform function calls by first loading the -address of the function into a register and then performing a subroutine -call on this register. This switch is needed if the target function -lies outside of the 24-bit addressing range of the offset-based -version of subroutine call instruction. - -This feature is not enabled by default. Specifying -@option{-mno-long-calls} restores the default behavior. Note these -switches have no effect on how the compiler generates code to handle -function calls via function pointers. - -@item -mfast-fp -@opindex mfast-fp -Link with the fast floating-point library. This library relaxes some of -the IEEE floating-point standard's rules for checking inputs against -Not-a-Number (NAN), in the interest of performance. - -@item -minline-plt -@opindex minline-plt -Enable inlining of PLT entries in function calls to functions that are -not known to bind locally. It has no effect without @option{-mfdpic}. - -@item -mmulticore -@opindex mmulticore -Build a standalone application for multicore Blackfin processors. -This option causes proper start files and link scripts supporting -multicore to be used, and defines the macro @code{__BFIN_MULTICORE}. -It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. - -This option can be used with @option{-mcorea} or @option{-mcoreb}, which -selects the one-application-per-core programming model. Without -@option{-mcorea} or @option{-mcoreb}, the single-application/dual-core -programming model is used. In this model, the main function of Core B -should be named as @code{coreb_main}. - -If this option is not used, the single-core application programming -model is used. - -@item -mcorea -@opindex mcorea -Build a standalone application for Core A of BF561 when using -the one-application-per-core programming model. Proper start files -and link scripts are used to support Core A, and the macro -@code{__BFIN_COREA} is defined. -This option can only be used in conjunction with @option{-mmulticore}. - -@item -mcoreb -@opindex mcoreb -Build a standalone application for Core B of BF561 when using -the one-application-per-core programming model. Proper start files -and link scripts are used to support Core B, and the macro -@code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main} -should be used instead of @code{main}. -This option can only be used in conjunction with @option{-mmulticore}. - -@item -msdram -@opindex msdram -Build a standalone application for SDRAM. Proper start files and -link scripts are used to put the application into SDRAM, and the macro -@code{__BFIN_SDRAM} is defined. -The loader should initialize SDRAM before loading the application. - -@item -micplb -@opindex micplb -Assume that ICPLBs are enabled at run time. This has an effect on certain -anomaly workarounds. For Linux targets, the default is to assume ICPLBs -are enabled; for standalone applications the default is off. -@end table - -@node C6X Options -@subsection C6X Options -@cindex C6X Options - -@table @gcctabopt -@item -march=@var{name} -@opindex march -This specifies the name of the target architecture. GCC uses this -name to determine what kind of instructions it can emit when generating -assembly code. Permissible names are: @samp{c62x}, -@samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}. - -@item -mbig-endian -@opindex mbig-endian -Generate code for a big-endian target. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a little-endian target. This is the default. - -@item -msim -@opindex msim -Choose startup files and linker script suitable for the simulator. - -@item -msdata=default -@opindex msdata=default -Put small global and static data in the @samp{.neardata} section, -which is pointed to by register @code{B14}. Put small uninitialized -global and static data in the @samp{.bss} section, which is adjacent -to the @samp{.neardata} section. Put small read-only data into the -@samp{.rodata} section. The corresponding sections used for large -pieces of data are @samp{.fardata}, @samp{.far} and @samp{.const}. - -@item -msdata=all -@opindex msdata=all -Put all data, not just small objects, into the sections reserved for -small data, and use addressing relative to the @code{B14} register to -access them. - -@item -msdata=none -@opindex msdata=none -Make no use of the sections reserved for small data, and use absolute -addresses to access all data. Put all initialized global and static -data in the @samp{.fardata} section, and all uninitialized data in the -@samp{.far} section. Put all constant data into the @samp{.const} -section. -@end table - -@node CRIS Options -@subsection CRIS Options -@cindex CRIS Options - -These options are defined specifically for the CRIS ports. - -@table @gcctabopt -@item -march=@var{architecture-type} -@itemx -mcpu=@var{architecture-type} -@opindex march -@opindex mcpu -Generate code for the specified architecture. The choices for -@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for -respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@. -Default is @samp{v0} except for cris-axis-linux-gnu, where the default is -@samp{v10}. - -@item -mtune=@var{architecture-type} -@opindex mtune -Tune to @var{architecture-type} everything applicable about the generated -code, except for the ABI and the set of available instructions. The -choices for @var{architecture-type} are the same as for -@option{-march=@var{architecture-type}}. - -@item -mmax-stack-frame=@var{n} -@opindex mmax-stack-frame -Warn when the stack frame of a function exceeds @var{n} bytes. - -@item -metrax4 -@itemx -metrax100 -@opindex metrax4 -@opindex metrax100 -The options @option{-metrax4} and @option{-metrax100} are synonyms for -@option{-march=v3} and @option{-march=v8} respectively. - -@item -mmul-bug-workaround -@itemx -mno-mul-bug-workaround -@opindex mmul-bug-workaround -@opindex mno-mul-bug-workaround -Work around a bug in the @code{muls} and @code{mulu} instructions for CPU -models where it applies. This option is active by default. - -@item -mpdebug -@opindex mpdebug -Enable CRIS-specific verbose debug-related information in the assembly -code. This option also has the effect of turning off the @samp{#NO_APP} -formatted-code indicator to the assembler at the beginning of the -assembly file. - -@item -mcc-init -@opindex mcc-init -Do not use condition-code results from previous instruction; always emit -compare and test instructions before use of condition codes. - -@item -mno-side-effects -@opindex mno-side-effects -Do not emit instructions with side effects in addressing modes other than -post-increment. - -@item -mstack-align -@itemx -mno-stack-align -@itemx -mdata-align -@itemx -mno-data-align -@itemx -mconst-align -@itemx -mno-const-align -@opindex mstack-align -@opindex mno-stack-align -@opindex mdata-align -@opindex mno-data-align -@opindex mconst-align -@opindex mno-const-align -These options (@samp{no-} options) arrange (eliminate arrangements) for the -stack frame, individual data and constants to be aligned for the maximum -single data access size for the chosen CPU model. The default is to -arrange for 32-bit alignment. ABI details such as structure layout are -not affected by these options. - -@item -m32-bit -@itemx -m16-bit -@itemx -m8-bit -@opindex m32-bit -@opindex m16-bit -@opindex m8-bit -Similar to the stack- data- and const-align options above, these options -arrange for stack frame, writable data and constants to all be 32-bit, -16-bit or 8-bit aligned. The default is 32-bit alignment. - -@item -mno-prologue-epilogue -@itemx -mprologue-epilogue -@opindex mno-prologue-epilogue -@opindex mprologue-epilogue -With @option{-mno-prologue-epilogue}, the normal function prologue and -epilogue which set up the stack frame are omitted and no return -instructions or return sequences are generated in the code. Use this -option only together with visual inspection of the compiled code: no -warnings or errors are generated when call-saved registers must be saved, -or storage for local variables needs to be allocated. - -@item -mno-gotplt -@itemx -mgotplt -@opindex mno-gotplt -@opindex mgotplt -With @option{-fpic} and @option{-fPIC}, don't generate (do generate) -instruction sequences that load addresses for functions from the PLT part -of the GOT rather than (traditional on other architectures) calls to the -PLT@. The default is @option{-mgotplt}. - -@item -melf -@opindex melf -Legacy no-op option only recognized with the cris-axis-elf and -cris-axis-linux-gnu targets. - -@item -mlinux -@opindex mlinux -Legacy no-op option only recognized with the cris-axis-linux-gnu target. - -@item -sim -@opindex sim -This option, recognized for the cris-axis-elf, arranges -to link with input-output functions from a simulator library. Code, -initialized data and zero-initialized data are allocated consecutively. - -@item -sim2 -@opindex sim2 -Like @option{-sim}, but pass linker options to locate initialized data at -0x40000000 and zero-initialized data at 0x80000000. -@end table - -@node CR16 Options -@subsection CR16 Options -@cindex CR16 Options - -These options are defined specifically for the CR16 ports. - -@table @gcctabopt - -@item -mmac -@opindex mmac -Enable the use of multiply-accumulate instructions. Disabled by default. - -@item -mcr16cplus -@itemx -mcr16c -@opindex mcr16cplus -@opindex mcr16c -Generate code for CR16C or CR16C+ architecture. CR16C+ architecture -is default. - -@item -msim -@opindex msim -Links the library libsim.a which is in compatible with simulator. Applicable -to ELF compiler only. - -@item -mint32 -@opindex mint32 -Choose integer type as 32-bit wide. - -@item -mbit-ops -@opindex mbit-ops -Generates @code{sbit}/@code{cbit} instructions for bit manipulations. - -@item -mdata-model=@var{model} -@opindex mdata-model -Choose a data model. The choices for @var{model} are @samp{near}, -@samp{far} or @samp{medium}. @samp{medium} is default. -However, @samp{far} is not valid with @option{-mcr16c}, as the -CR16C architecture does not support the far data model. -@end table - -@node Darwin Options -@subsection Darwin Options -@cindex Darwin options - -These options are defined for all architectures running the Darwin operating -system. - -FSF GCC on Darwin does not create ``fat'' object files; it creates -an object file for the single architecture that GCC was built to -target. Apple's GCC on Darwin does create ``fat'' files if multiple -@option{-arch} options are used; it does so by running the compiler or -linker multiple times and joining the results together with -@file{lipo}. - -The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or -@samp{i686}) is determined by the flags that specify the ISA -that GCC is targeting, like @option{-mcpu} or @option{-march}. The -@option{-force_cpusubtype_ALL} option can be used to override this. - -The Darwin tools vary in their behavior when presented with an ISA -mismatch. The assembler, @file{as}, only permits instructions to -be used that are valid for the subtype of the file it is generating, -so you cannot put 64-bit instructions in a @samp{ppc750} object file. -The linker for shared libraries, @file{/usr/bin/libtool}, fails -and prints an error if asked to create a shared library with a less -restrictive subtype than its input files (for instance, trying to put -a @samp{ppc970} object file in a @samp{ppc7400} library). The linker -for executables, @command{ld}, quietly gives the executable the most -restrictive subtype of any of its input files. - -@table @gcctabopt -@item -F@var{dir} -@opindex F -Add the framework directory @var{dir} to the head of the list of -directories to be searched for header files. These directories are -interleaved with those specified by @option{-I} options and are -scanned in a left-to-right order. - -A framework directory is a directory with frameworks in it. A -framework is a directory with a @file{Headers} and/or -@file{PrivateHeaders} directory contained directly in it that ends -in @file{.framework}. The name of a framework is the name of this -directory excluding the @file{.framework}. Headers associated with -the framework are found in one of those two directories, with -@file{Headers} being searched first. A subframework is a framework -directory that is in a framework's @file{Frameworks} directory. -Includes of subframework headers can only appear in a header of a -framework that contains the subframework, or in a sibling subframework -header. Two subframeworks are siblings if they occur in the same -framework. A subframework should not have the same name as a -framework; a warning is issued if this is violated. Currently a -subframework cannot have subframeworks; in the future, the mechanism -may be extended to support this. The standard frameworks can be found -in @file{/System/Library/Frameworks} and -@file{/Library/Frameworks}. An example include looks like -@code{#include <Framework/header.h>}, where @file{Framework} denotes -the name of the framework and @file{header.h} is found in the -@file{PrivateHeaders} or @file{Headers} directory. - -@item -iframework@var{dir} -@opindex iframework -Like @option{-F} except the directory is a treated as a system -directory. The main difference between this @option{-iframework} and -@option{-F} is that with @option{-iframework} the compiler does not -warn about constructs contained within header files found via -@var{dir}. This option is valid only for the C family of languages. - -@item -gused -@opindex gused -Emit debugging information for symbols that are used. For stabs -debugging format, this enables @option{-feliminate-unused-debug-symbols}. -This is by default ON@. - -@item -gfull -@opindex gfull -Emit debugging information for all symbols and types. - -@item -mmacosx-version-min=@var{version} -The earliest version of MacOS X that this executable will run on -is @var{version}. Typical values of @var{version} include @code{10.1}, -@code{10.2}, and @code{10.3.9}. - -If the compiler was built to use the system's headers by default, -then the default for this option is the system version on which the -compiler is running, otherwise the default is to make choices that -are compatible with as many systems and code bases as possible. - -@item -mkernel -@opindex mkernel -Enable kernel development mode. The @option{-mkernel} option sets -@option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit}, -@option{-fno-exceptions}, @option{-fno-non-call-exceptions}, -@option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where -applicable. This mode also sets @option{-mno-altivec}, -@option{-msoft-float}, @option{-fno-builtin} and -@option{-mlong-branch} for PowerPC targets. - -@item -mone-byte-bool -@opindex mone-byte-bool -Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}. -By default @samp{sizeof(bool)} is @samp{4} when compiling for -Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this -option has no effect on x86. - -@strong{Warning:} The @option{-mone-byte-bool} switch causes GCC -to generate code that is not binary compatible with code generated -without that switch. Using this switch may require recompiling all -other modules in a program, including system libraries. Use this -switch to conform to a non-default data model. - -@item -mfix-and-continue -@itemx -ffix-and-continue -@itemx -findirect-data -@opindex mfix-and-continue -@opindex ffix-and-continue -@opindex findirect-data -Generate code suitable for fast turnaround development, such as to -allow GDB to dynamically load @code{.o} files into already-running -programs. @option{-findirect-data} and @option{-ffix-and-continue} -are provided for backwards compatibility. - -@item -all_load -@opindex all_load -Loads all members of static archive libraries. -See man ld(1) for more information. - -@item -arch_errors_fatal -@opindex arch_errors_fatal -Cause the errors having to do with files that have the wrong architecture -to be fatal. - -@item -bind_at_load -@opindex bind_at_load -Causes the output file to be marked such that the dynamic linker will -bind all undefined references when the file is loaded or launched. - -@item -bundle -@opindex bundle -Produce a Mach-o bundle format file. -See man ld(1) for more information. - -@item -bundle_loader @var{executable} -@opindex bundle_loader -This option specifies the @var{executable} that will load the build -output file being linked. See man ld(1) for more information. - -@item -dynamiclib -@opindex dynamiclib -When passed this option, GCC produces a dynamic library instead of -an executable when linking, using the Darwin @file{libtool} command. - -@item -force_cpusubtype_ALL -@opindex force_cpusubtype_ALL -This causes GCC's output file to have the @var{ALL} subtype, instead of -one controlled by the @option{-mcpu} or @option{-march} option. - -@item -allowable_client @var{client_name} -@itemx -client_name -@itemx -compatibility_version -@itemx -current_version -@itemx -dead_strip -@itemx -dependency-file -@itemx -dylib_file -@itemx -dylinker_install_name -@itemx -dynamic -@itemx -exported_symbols_list -@itemx -filelist -@need 800 -@itemx -flat_namespace -@itemx -force_flat_namespace -@itemx -headerpad_max_install_names -@itemx -image_base -@itemx -init -@itemx -install_name -@itemx -keep_private_externs -@itemx -multi_module -@itemx -multiply_defined -@itemx -multiply_defined_unused -@need 800 -@itemx -noall_load -@itemx -no_dead_strip_inits_and_terms -@itemx -nofixprebinding -@itemx -nomultidefs -@itemx -noprebind -@itemx -noseglinkedit -@itemx -pagezero_size -@itemx -prebind -@itemx -prebind_all_twolevel_modules -@itemx -private_bundle -@need 800 -@itemx -read_only_relocs -@itemx -sectalign -@itemx -sectobjectsymbols -@itemx -whyload -@itemx -seg1addr -@itemx -sectcreate -@itemx -sectobjectsymbols -@itemx -sectorder -@itemx -segaddr -@itemx -segs_read_only_addr -@need 800 -@itemx -segs_read_write_addr -@itemx -seg_addr_table -@itemx -seg_addr_table_filename -@itemx -seglinkedit -@itemx -segprot -@itemx -segs_read_only_addr -@itemx -segs_read_write_addr -@itemx -single_module -@itemx -static -@itemx -sub_library -@need 800 -@itemx -sub_umbrella -@itemx -twolevel_namespace -@itemx -umbrella -@itemx -undefined -@itemx -unexported_symbols_list -@itemx -weak_reference_mismatches -@itemx -whatsloaded -@opindex allowable_client -@opindex client_name -@opindex compatibility_version -@opindex current_version -@opindex dead_strip -@opindex dependency-file -@opindex dylib_file -@opindex dylinker_install_name -@opindex dynamic -@opindex exported_symbols_list -@opindex filelist -@opindex flat_namespace -@opindex force_flat_namespace -@opindex headerpad_max_install_names -@opindex image_base -@opindex init -@opindex install_name -@opindex keep_private_externs -@opindex multi_module -@opindex multiply_defined -@opindex multiply_defined_unused -@opindex noall_load -@opindex no_dead_strip_inits_and_terms -@opindex nofixprebinding -@opindex nomultidefs -@opindex noprebind -@opindex noseglinkedit -@opindex pagezero_size -@opindex prebind -@opindex prebind_all_twolevel_modules -@opindex private_bundle -@opindex read_only_relocs -@opindex sectalign -@opindex sectobjectsymbols -@opindex whyload -@opindex seg1addr -@opindex sectcreate -@opindex sectobjectsymbols -@opindex sectorder -@opindex segaddr -@opindex segs_read_only_addr -@opindex segs_read_write_addr -@opindex seg_addr_table -@opindex seg_addr_table_filename -@opindex seglinkedit -@opindex segprot -@opindex segs_read_only_addr -@opindex segs_read_write_addr -@opindex single_module -@opindex static -@opindex sub_library -@opindex sub_umbrella -@opindex twolevel_namespace -@opindex umbrella -@opindex undefined -@opindex unexported_symbols_list -@opindex weak_reference_mismatches -@opindex whatsloaded -These options are passed to the Darwin linker. The Darwin linker man page -describes them in detail. -@end table - -@node DEC Alpha Options -@subsection DEC Alpha Options - -These @samp{-m} options are defined for the DEC Alpha implementations: - -@table @gcctabopt -@item -mno-soft-float -@itemx -msoft-float -@opindex mno-soft-float -@opindex msoft-float -Use (do not use) the hardware floating-point instructions for -floating-point operations. When @option{-msoft-float} is specified, -functions in @file{libgcc.a} are used to perform floating-point -operations. Unless they are replaced by routines that emulate the -floating-point operations, or compiled in such a way as to call such -emulations routines, these routines issue floating-point -operations. If you are compiling for an Alpha without floating-point -operations, you must ensure that the library is built so as not to call -them. - -Note that Alpha implementations without floating-point operations are -required to have floating-point registers. - -@item -mfp-reg -@itemx -mno-fp-regs -@opindex mfp-reg -@opindex mno-fp-regs -Generate code that uses (does not use) the floating-point register set. -@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point -register set is not used, floating-point operands are passed in integer -registers as if they were integers and floating-point results are passed -in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, -so any function with a floating-point argument or return value called by code -compiled with @option{-mno-fp-regs} must also be compiled with that -option. - -A typical use of this option is building a kernel that does not use, -and hence need not save and restore, any floating-point registers. - -@item -mieee -@opindex mieee -The Alpha architecture implements floating-point hardware optimized for -maximum performance. It is mostly compliant with the IEEE floating-point -standard. However, for full compliance, software assistance is -required. This option generates code fully IEEE-compliant code -@emph{except} that the @var{inexact-flag} is not maintained (see below). -If this option is turned on, the preprocessor macro @code{_IEEE_FP} is -defined during compilation. The resulting code is less efficient but is -able to correctly support denormalized numbers and exceptional IEEE -values such as not-a-number and plus/minus infinity. Other Alpha -compilers call this option @option{-ieee_with_no_inexact}. - -@item -mieee-with-inexact -@opindex mieee-with-inexact -This is like @option{-mieee} except the generated code also maintains -the IEEE @var{inexact-flag}. Turning on this option causes the -generated code to implement fully-compliant IEEE math. In addition to -@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor -macro. On some Alpha implementations the resulting code may execute -significantly slower than the code generated by default. Since there is -very little code that depends on the @var{inexact-flag}, you should -normally not specify this option. Other Alpha compilers call this -option @option{-ieee_with_inexact}. - -@item -mfp-trap-mode=@var{trap-mode} -@opindex mfp-trap-mode -This option controls what floating-point related traps are enabled. -Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. -The trap mode can be set to one of four values: - -@table @samp -@item n -This is the default (normal) setting. The only traps that are enabled -are the ones that cannot be disabled in software (e.g., division by zero -trap). - -@item u -In addition to the traps enabled by @samp{n}, underflow traps are enabled -as well. - -@item su -Like @samp{u}, but the instructions are marked to be safe for software -completion (see Alpha architecture manual for details). - -@item sui -Like @samp{su}, but inexact traps are enabled as well. -@end table - -@item -mfp-rounding-mode=@var{rounding-mode} -@opindex mfp-rounding-mode -Selects the IEEE rounding mode. Other Alpha compilers call this option -@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one -of: - -@table @samp -@item n -Normal IEEE rounding mode. Floating-point numbers are rounded towards -the nearest machine number or towards the even machine number in case -of a tie. - -@item m -Round towards minus infinity. - -@item c -Chopped rounding mode. Floating-point numbers are rounded towards zero. - -@item d -Dynamic rounding mode. A field in the floating-point control register -(@var{fpcr}, see Alpha architecture reference manual) controls the -rounding mode in effect. The C library initializes this register for -rounding towards plus infinity. Thus, unless your program modifies the -@var{fpcr}, @samp{d} corresponds to round towards plus infinity. -@end table - -@item -mtrap-precision=@var{trap-precision} -@opindex mtrap-precision -In the Alpha architecture, floating-point traps are imprecise. This -means without software assistance it is impossible to recover from a -floating trap and program execution normally needs to be terminated. -GCC can generate code that can assist operating system trap handlers -in determining the exact location that caused a floating-point trap. -Depending on the requirements of an application, different levels of -precisions can be selected: - -@table @samp -@item p -Program precision. This option is the default and means a trap handler -can only identify which program caused a floating-point exception. - -@item f -Function precision. The trap handler can determine the function that -caused a floating-point exception. - -@item i -Instruction precision. The trap handler can determine the exact -instruction that caused a floating-point exception. -@end table - -Other Alpha compilers provide the equivalent options called -@option{-scope_safe} and @option{-resumption_safe}. - -@item -mieee-conformant -@opindex mieee-conformant -This option marks the generated code as IEEE conformant. You must not -use this option unless you also specify @option{-mtrap-precision=i} and either -@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect -is to emit the line @samp{.eflag 48} in the function prologue of the -generated assembly file. - -@item -mbuild-constants -@opindex mbuild-constants -Normally GCC examines a 32- or 64-bit integer constant to -see if it can construct it from smaller constants in two or three -instructions. If it cannot, it outputs the constant as a literal and -generates code to load it from the data segment at run time. - -Use this option to require GCC to construct @emph{all} integer constants -using code, even if it takes more instructions (the maximum is six). - -You typically use this option to build a shared library dynamic -loader. Itself a shared library, it must relocate itself in memory -before it can find the variables and constants in its own data segment. - -@item -mbwx -@itemx -mno-bwx -@itemx -mcix -@itemx -mno-cix -@itemx -mfix -@itemx -mno-fix -@itemx -mmax -@itemx -mno-max -@opindex mbwx -@opindex mno-bwx -@opindex mcix -@opindex mno-cix -@opindex mfix -@opindex mno-fix -@opindex mmax -@opindex mno-max -Indicate whether GCC should generate code to use the optional BWX, -CIX, FIX and MAX instruction sets. The default is to use the instruction -sets supported by the CPU type specified via @option{-mcpu=} option or that -of the CPU on which GCC was built if none is specified. - -@item -mfloat-vax -@itemx -mfloat-ieee -@opindex mfloat-vax -@opindex mfloat-ieee -Generate code that uses (does not use) VAX F and G floating-point -arithmetic instead of IEEE single and double precision. - -@item -mexplicit-relocs -@itemx -mno-explicit-relocs -@opindex mexplicit-relocs -@opindex mno-explicit-relocs -Older Alpha assemblers provided no way to generate symbol relocations -except via assembler macros. Use of these macros does not allow -optimal instruction scheduling. GNU binutils as of version 2.12 -supports a new syntax that allows the compiler to explicitly mark -which relocations should apply to which instructions. This option -is mostly useful for debugging, as GCC detects the capabilities of -the assembler when it is built and sets the default accordingly. - -@item -msmall-data -@itemx -mlarge-data -@opindex msmall-data -@opindex mlarge-data -When @option{-mexplicit-relocs} is in effect, static data is -accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} -is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} -(the @code{.sdata} and @code{.sbss} sections) and are accessed via -16-bit relocations off of the @code{$gp} register. This limits the -size of the small data area to 64KB, but allows the variables to be -directly accessed via a single instruction. - -The default is @option{-mlarge-data}. With this option the data area -is limited to just below 2GB@. Programs that require more than 2GB of -data must use @code{malloc} or @code{mmap} to allocate the data in the -heap instead of in the program's data segment. - -When generating code for shared libraries, @option{-fpic} implies -@option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. - -@item -msmall-text -@itemx -mlarge-text -@opindex msmall-text -@opindex mlarge-text -When @option{-msmall-text} is used, the compiler assumes that the -code of the entire program (or shared library) fits in 4MB, and is -thus reachable with a branch instruction. When @option{-msmall-data} -is used, the compiler can assume that all local symbols share the -same @code{$gp} value, and thus reduce the number of instructions -required for a function call from 4 to 1. - -The default is @option{-mlarge-text}. - -@item -mcpu=@var{cpu_type} -@opindex mcpu -Set the instruction set and instruction scheduling parameters for -machine type @var{cpu_type}. You can specify either the @samp{EV} -style name or the corresponding chip number. GCC supports scheduling -parameters for the EV4, EV5 and EV6 family of processors and -chooses the default values for the instruction set from the processor -you specify. If you do not specify a processor type, GCC defaults -to the processor on which the compiler was built. - -Supported values for @var{cpu_type} are - -@table @samp -@item ev4 -@itemx ev45 -@itemx 21064 -Schedules as an EV4 and has no instruction set extensions. - -@item ev5 -@itemx 21164 -Schedules as an EV5 and has no instruction set extensions. - -@item ev56 -@itemx 21164a -Schedules as an EV5 and supports the BWX extension. - -@item pca56 -@itemx 21164pc -@itemx 21164PC -Schedules as an EV5 and supports the BWX and MAX extensions. - -@item ev6 -@itemx 21264 -Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. - -@item ev67 -@itemx 21264a -Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. -@end table - -Native toolchains also support the value @samp{native}, -which selects the best architecture option for the host processor. -@option{-mcpu=native} has no effect if GCC does not recognize -the processor. - -@item -mtune=@var{cpu_type} -@opindex mtune -Set only the instruction scheduling parameters for machine type -@var{cpu_type}. The instruction set is not changed. - -Native toolchains also support the value @samp{native}, -which selects the best architecture option for the host processor. -@option{-mtune=native} has no effect if GCC does not recognize -the processor. - -@item -mmemory-latency=@var{time} -@opindex mmemory-latency -Sets the latency the scheduler should assume for typical memory -references as seen by the application. This number is highly -dependent on the memory access patterns used by the application -and the size of the external cache on the machine. - -Valid options for @var{time} are - -@table @samp -@item @var{number} -A decimal number representing clock cycles. - -@item L1 -@itemx L2 -@itemx L3 -@itemx main -The compiler contains estimates of the number of clock cycles for -``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches -(also called Dcache, Scache, and Bcache), as well as to main memory. -Note that L3 is only valid for EV5. - -@end table -@end table - -@node FR30 Options -@subsection FR30 Options -@cindex FR30 Options - -These options are defined specifically for the FR30 port. - -@table @gcctabopt - -@item -msmall-model -@opindex msmall-model -Use the small address space model. This can produce smaller code, but -it does assume that all symbolic values and addresses fit into a -20-bit range. - -@item -mno-lsim -@opindex mno-lsim -Assume that runtime support has been provided and so there is no need -to include the simulator library (@file{libsim.a}) on the linker -command line. - -@end table - -@node FRV Options -@subsection FRV Options -@cindex FRV Options - -@table @gcctabopt -@item -mgpr-32 -@opindex mgpr-32 - -Only use the first 32 general-purpose registers. - -@item -mgpr-64 -@opindex mgpr-64 - -Use all 64 general-purpose registers. - -@item -mfpr-32 -@opindex mfpr-32 - -Use only the first 32 floating-point registers. - -@item -mfpr-64 -@opindex mfpr-64 - -Use all 64 floating-point registers. - -@item -mhard-float -@opindex mhard-float - -Use hardware instructions for floating-point operations. - -@item -msoft-float -@opindex msoft-float - -Use library routines for floating-point operations. - -@item -malloc-cc -@opindex malloc-cc - -Dynamically allocate condition code registers. - -@item -mfixed-cc -@opindex mfixed-cc - -Do not try to dynamically allocate condition code registers, only -use @code{icc0} and @code{fcc0}. - -@item -mdword -@opindex mdword - -Change ABI to use double word insns. - -@item -mno-dword -@opindex mno-dword - -Do not use double word instructions. - -@item -mdouble -@opindex mdouble - -Use floating-point double instructions. - -@item -mno-double -@opindex mno-double - -Do not use floating-point double instructions. - -@item -mmedia -@opindex mmedia - -Use media instructions. - -@item -mno-media -@opindex mno-media - -Do not use media instructions. - -@item -mmuladd -@opindex mmuladd - -Use multiply and add/subtract instructions. - -@item -mno-muladd -@opindex mno-muladd - -Do not use multiply and add/subtract instructions. - -@item -mfdpic -@opindex mfdpic - -Select the FDPIC ABI, which uses function descriptors to represent -pointers to functions. Without any PIC/PIE-related options, it -implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it -assumes GOT entries and small data are within a 12-bit range from the -GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets -are computed with 32 bits. -With a @samp{bfin-elf} target, this option implies @option{-msim}. - -@item -minline-plt -@opindex minline-plt - -Enable inlining of PLT entries in function calls to functions that are -not known to bind locally. It has no effect without @option{-mfdpic}. -It's enabled by default if optimizing for speed and compiling for -shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an -optimization option such as @option{-O3} or above is present in the -command line. - -@item -mTLS -@opindex mTLS - -Assume a large TLS segment when generating thread-local code. - -@item -mtls -@opindex mtls - -Do not assume a large TLS segment when generating thread-local code. - -@item -mgprel-ro -@opindex mgprel-ro - -Enable the use of @code{GPREL} relocations in the FDPIC ABI for data -that is known to be in read-only sections. It's enabled by default, -except for @option{-fpic} or @option{-fpie}: even though it may help -make the global offset table smaller, it trades 1 instruction for 4. -With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4, -one of which may be shared by multiple symbols, and it avoids the need -for a GOT entry for the referenced symbol, so it's more likely to be a -win. If it is not, @option{-mno-gprel-ro} can be used to disable it. - -@item -multilib-library-pic -@opindex multilib-library-pic - -Link with the (library, not FD) pic libraries. It's implied by -@option{-mlibrary-pic}, as well as by @option{-fPIC} and -@option{-fpic} without @option{-mfdpic}. You should never have to use -it explicitly. - -@item -mlinked-fp -@opindex mlinked-fp - -Follow the EABI requirement of always creating a frame pointer whenever -a stack frame is allocated. This option is enabled by default and can -be disabled with @option{-mno-linked-fp}. - -@item -mlong-calls -@opindex mlong-calls - -Use indirect addressing to call functions outside the current -compilation unit. This allows the functions to be placed anywhere -within the 32-bit address space. - -@item -malign-labels -@opindex malign-labels - -Try to align labels to an 8-byte boundary by inserting NOPs into the -previous packet. This option only has an effect when VLIW packing -is enabled. It doesn't create new packets; it merely adds NOPs to -existing ones. - -@item -mlibrary-pic -@opindex mlibrary-pic - -Generate position-independent EABI code. - -@item -macc-4 -@opindex macc-4 - -Use only the first four media accumulator registers. - -@item -macc-8 -@opindex macc-8 - -Use all eight media accumulator registers. - -@item -mpack -@opindex mpack - -Pack VLIW instructions. - -@item -mno-pack -@opindex mno-pack - -Do not pack VLIW instructions. - -@item -mno-eflags -@opindex mno-eflags - -Do not mark ABI switches in e_flags. - -@item -mcond-move -@opindex mcond-move - -Enable the use of conditional-move instructions (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-cond-move -@opindex mno-cond-move - -Disable the use of conditional-move instructions. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mscc -@opindex mscc - -Enable the use of conditional set instructions (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-scc -@opindex mno-scc - -Disable the use of conditional set instructions. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mcond-exec -@opindex mcond-exec - -Enable the use of conditional execution (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-cond-exec -@opindex mno-cond-exec - -Disable the use of conditional execution. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mvliw-branch -@opindex mvliw-branch - -Run a pass to pack branches into VLIW instructions (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-vliw-branch -@opindex mno-vliw-branch - -Do not run a pass to pack branches into VLIW instructions. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mmulti-cond-exec -@opindex mmulti-cond-exec - -Enable optimization of @code{&&} and @code{||} in conditional execution -(default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-multi-cond-exec -@opindex mno-multi-cond-exec - -Disable optimization of @code{&&} and @code{||} in conditional execution. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mnested-cond-exec -@opindex mnested-cond-exec - -Enable nested conditional execution optimizations (default). - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -mno-nested-cond-exec -@opindex mno-nested-cond-exec - -Disable nested conditional execution optimizations. - -This switch is mainly for debugging the compiler and will likely be removed -in a future version. - -@item -moptimize-membar -@opindex moptimize-membar - -This switch removes redundant @code{membar} instructions from the -compiler-generated code. It is enabled by default. - -@item -mno-optimize-membar -@opindex mno-optimize-membar - -This switch disables the automatic removal of redundant @code{membar} -instructions from the generated code. - -@item -mtomcat-stats -@opindex mtomcat-stats - -Cause gas to print out tomcat statistics. - -@item -mcpu=@var{cpu} -@opindex mcpu - -Select the processor type for which to generate code. Possible values are -@samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450}, -@samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}. - -@end table - -@node GNU/Linux Options -@subsection GNU/Linux Options - -These @samp{-m} options are defined for GNU/Linux targets: - -@table @gcctabopt -@item -mglibc -@opindex mglibc -Use the GNU C library. This is the default except -on @samp{*-*-linux-*uclibc*} and @samp{*-*-linux-*android*} targets. - -@item -muclibc -@opindex muclibc -Use uClibc C library. This is the default on -@samp{*-*-linux-*uclibc*} targets. - -@item -mbionic -@opindex mbionic -Use Bionic C library. This is the default on -@samp{*-*-linux-*android*} targets. - -@item -mandroid -@opindex mandroid -Compile code compatible with Android platform. This is the default on -@samp{*-*-linux-*android*} targets. - -When compiling, this option enables @option{-mbionic}, @option{-fPIC}, -@option{-fno-exceptions} and @option{-fno-rtti} by default. When linking, -this option makes the GCC driver pass Android-specific options to the linker. -Finally, this option causes the preprocessor macro @code{__ANDROID__} -to be defined. - -@item -tno-android-cc -@opindex tno-android-cc -Disable compilation effects of @option{-mandroid}, i.e., do not enable -@option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and -@option{-fno-rtti} by default. - -@item -tno-android-ld -@opindex tno-android-ld -Disable linking effects of @option{-mandroid}, i.e., pass standard Linux -linking options to the linker. - -@end table - -@node H8/300 Options -@subsection H8/300 Options - -These @samp{-m} options are defined for the H8/300 implementations: - -@table @gcctabopt -@item -mrelax -@opindex mrelax -Shorten some address references at link time, when possible; uses the -linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, -ld, Using ld}, for a fuller description. - -@item -mh -@opindex mh -Generate code for the H8/300H@. - -@item -ms -@opindex ms -Generate code for the H8S@. - -@item -mn -@opindex mn -Generate code for the H8S and H8/300H in the normal mode. This switch -must be used either with @option{-mh} or @option{-ms}. - -@item -ms2600 -@opindex ms2600 -Generate code for the H8S/2600. This switch must be used with @option{-ms}. - -@item -mexr -@opindex mexr -Extended registers are stored on stack before execution of function -with monitor attribute. Default option is @option{-mexr}. -This option is valid only for H8S targets. - -@item -mno-exr -@opindex mno-exr -Extended registers are not stored on stack before execution of function -with monitor attribute. Default option is @option{-mno-exr}. -This option is valid only for H8S targets. - -@item -mint32 -@opindex mint32 -Make @code{int} data 32 bits by default. - -@item -malign-300 -@opindex malign-300 -On the H8/300H and H8S, use the same alignment rules as for the H8/300. -The default for the H8/300H and H8S is to align longs and floats on -4-byte boundaries. -@option{-malign-300} causes them to be aligned on 2-byte boundaries. -This option has no effect on the H8/300. -@end table - -@node HPPA Options -@subsection HPPA Options -@cindex HPPA Options - -These @samp{-m} options are defined for the HPPA family of computers: - -@table @gcctabopt -@item -march=@var{architecture-type} -@opindex march -Generate code for the specified architecture. The choices for -@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA -1.1, and @samp{2.0} for PA 2.0 processors. Refer to -@file{/usr/lib/sched.models} on an HP-UX system to determine the proper -architecture option for your machine. Code compiled for lower numbered -architectures runs on higher numbered architectures, but not the -other way around. - -@item -mpa-risc-1-0 -@itemx -mpa-risc-1-1 -@itemx -mpa-risc-2-0 -@opindex mpa-risc-1-0 -@opindex mpa-risc-1-1 -@opindex mpa-risc-2-0 -Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. - -@item -mbig-switch -@opindex mbig-switch -Generate code suitable for big switch tables. Use this option only if -the assembler/linker complain about out-of-range branches within a switch -table. - -@item -mjump-in-delay -@opindex mjump-in-delay -Fill delay slots of function calls with unconditional jump instructions -by modifying the return pointer for the function call to be the target -of the conditional jump. - -@item -mdisable-fpregs -@opindex mdisable-fpregs -Prevent floating-point registers from being used in any manner. This is -necessary for compiling kernels that perform lazy context switching of -floating-point registers. If you use this option and attempt to perform -floating-point operations, the compiler aborts. - -@item -mdisable-indexing -@opindex mdisable-indexing -Prevent the compiler from using indexing address modes. This avoids some -rather obscure problems when compiling MIG generated code under MACH@. - -@item -mno-space-regs -@opindex mno-space-regs -Generate code that assumes the target has no space registers. This allows -GCC to generate faster indirect calls and use unscaled index address modes. - -Such code is suitable for level 0 PA systems and kernels. - -@item -mfast-indirect-calls -@opindex mfast-indirect-calls -Generate code that assumes calls never cross space boundaries. This -allows GCC to emit code that performs faster indirect calls. - -This option does not work in the presence of shared libraries or nested -functions. - -@item -mfixed-range=@var{register-range} -@opindex mfixed-range -Generate code treating the given register range as fixed registers. -A fixed register is one that the register allocator cannot use. This is -useful when compiling kernel code. A register range is specified as -two registers separated by a dash. Multiple register ranges can be -specified separated by a comma. - -@item -mlong-load-store -@opindex mlong-load-store -Generate 3-instruction load and store sequences as sometimes required by -the HP-UX 10 linker. This is equivalent to the @samp{+k} option to -the HP compilers. - -@item -mportable-runtime -@opindex mportable-runtime -Use the portable calling conventions proposed by HP for ELF systems. - -@item -mgas -@opindex mgas -Enable the use of assembler directives only GAS understands. - -@item -mschedule=@var{cpu-type} -@opindex mschedule -Schedule code according to the constraints for the machine type -@var{cpu-type}. The choices for @var{cpu-type} are @samp{700} -@samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer -to @file{/usr/lib/sched.models} on an HP-UX system to determine the -proper scheduling option for your machine. The default scheduling is -@samp{8000}. - -@item -mlinker-opt -@opindex mlinker-opt -Enable the optimization pass in the HP-UX linker. Note this makes symbolic -debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 -linkers in which they give bogus error messages when linking some programs. - -@item -msoft-float -@opindex msoft-float -Generate output containing library calls for floating point. -@strong{Warning:} the requisite libraries are not available for all HPPA -targets. Normally the facilities of the machine's usual C compiler are -used, but this cannot be done directly in cross-compilation. You must make -your own arrangements to provide suitable library functions for -cross-compilation. - -@option{-msoft-float} changes the calling convention in the output file; -therefore, it is only useful if you compile @emph{all} of a program with -this option. In particular, you need to compile @file{libgcc.a}, the -library that comes with GCC, with @option{-msoft-float} in order for -this to work. - -@item -msio -@opindex msio -Generate the predefine, @code{_SIO}, for server IO@. The default is -@option{-mwsio}. This generates the predefines, @code{__hp9000s700}, -@code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These -options are available under HP-UX and HI-UX@. - -@item -mgnu-ld -@opindex mgnu-ld -Use options specific to GNU @command{ld}. -This passes @option{-shared} to @command{ld} when -building a shared library. It is the default when GCC is configured, -explicitly or implicitly, with the GNU linker. This option does not -affect which @command{ld} is called; it only changes what parameters -are passed to that @command{ld}. -The @command{ld} that is called is determined by the -@option{--with-ld} configure option, GCC's program search path, and -finally by the user's @env{PATH}. The linker used by GCC can be printed -using @samp{which `gcc -print-prog-name=ld`}. This option is only available -on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. - -@item -mhp-ld -@opindex mhp-ld -Use options specific to HP @command{ld}. -This passes @option{-b} to @command{ld} when building -a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all -links. It is the default when GCC is configured, explicitly or -implicitly, with the HP linker. This option does not affect -which @command{ld} is called; it only changes what parameters are passed to that -@command{ld}. -The @command{ld} that is called is determined by the @option{--with-ld} -configure option, GCC's program search path, and finally by the user's -@env{PATH}. The linker used by GCC can be printed using @samp{which -`gcc -print-prog-name=ld`}. This option is only available on the 64-bit -HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. - -@item -mlong-calls -@opindex mno-long-calls -Generate code that uses long call sequences. This ensures that a call -is always able to reach linker generated stubs. The default is to generate -long calls only when the distance from the call site to the beginning -of the function or translation unit, as the case may be, exceeds a -predefined limit set by the branch type being used. The limits for -normal calls are 7,600,000 and 240,000 bytes, respectively for the -PA 2.0 and PA 1.X architectures. Sibcalls are always limited at -240,000 bytes. - -Distances are measured from the beginning of functions when using the -@option{-ffunction-sections} option, or when using the @option{-mgas} -and @option{-mno-portable-runtime} options together under HP-UX with -the SOM linker. - -It is normally not desirable to use this option as it degrades -performance. However, it may be useful in large applications, -particularly when partial linking is used to build the application. - -The types of long calls used depends on the capabilities of the -assembler and linker, and the type of code being generated. The -impact on systems that support long absolute calls, and long pic -symbol-difference or pc-relative calls should be relatively small. -However, an indirect call is used on 32-bit ELF systems in pic code -and it is quite long. - -@item -munix=@var{unix-std} -@opindex march -Generate compiler predefines and select a startfile for the specified -UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95} -and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95} -is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX -11.11 and later. The default values are @samp{93} for HP-UX 10.00, -@samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11 -and later. - -@option{-munix=93} provides the same predefines as GCC 3.3 and 3.4. -@option{-munix=95} provides additional predefines for @code{XOPEN_UNIX} -and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}. -@option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX}, -@code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and -@code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}. - -It is @emph{important} to note that this option changes the interfaces -for various library routines. It also affects the operational behavior -of the C library. Thus, @emph{extreme} care is needed in using this -option. - -Library code that is intended to operate with more than one UNIX -standard must test, set and restore the variable @var{__xpg4_extended_mask} -as appropriate. Most GNU software doesn't provide this capability. - -@item -nolibdld -@opindex nolibdld -Suppress the generation of link options to search libdld.sl when the -@option{-static} option is specified on HP-UX 10 and later. - -@item -static -@opindex static -The HP-UX implementation of setlocale in libc has a dependency on -libdld.sl. There isn't an archive version of libdld.sl. Thus, -when the @option{-static} option is specified, special link options -are needed to resolve this dependency. - -On HP-UX 10 and later, the GCC driver adds the necessary options to -link with libdld.sl when the @option{-static} option is specified. -This causes the resulting binary to be dynamic. On the 64-bit port, -the linkers generate dynamic binaries by default in any case. The -@option{-nolibdld} option can be used to prevent the GCC driver from -adding these link options. - -@item -threads -@opindex threads -Add support for multithreading with the @dfn{dce thread} library -under HP-UX@. This option sets flags for both the preprocessor and -linker. -@end table - -@node i386 and x86-64 Options -@subsection Intel 386 and AMD x86-64 Options -@cindex i386 Options -@cindex x86-64 Options -@cindex Intel 386 Options -@cindex AMD x86-64 Options - -These @samp{-m} options are defined for the i386 and x86-64 family of -computers: - -@table @gcctabopt - -@item -march=@var{cpu-type} -@opindex march -Generate instructions for the machine type @var{cpu-type}. In contrast to -@option{-mtune=@var{cpu-type}}, which merely tunes the generated code -for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC -to generate code that may not run at all on processors other than the one -indicated. Specifying @option{-march=@var{cpu-type}} implies -@option{-mtune=@var{cpu-type}}. - -The choices for @var{cpu-type} are: - -@table @samp -@item native -This selects the CPU to generate code for at compilation time by determining -the processor type of the compiling machine. Using @option{-march=native} -enables all instruction subsets supported by the local machine (hence -the result might not run on different machines). Using @option{-mtune=native} -produces code optimized for the local machine under the constraints -of the selected instruction set. - -@item i386 -Original Intel i386 CPU@. - -@item i486 -Intel i486 CPU@. (No scheduling is implemented for this chip.) - -@item i586 -@itemx pentium -Intel Pentium CPU with no MMX support. - -@item pentium-mmx -Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. - -@item pentiumpro -Intel Pentium Pro CPU@. - -@item i686 -When used with @option{-march}, the Pentium Pro -instruction set is used, so the code runs on all i686 family chips. -When used with @option{-mtune}, it has the same meaning as @samp{generic}. - -@item pentium2 -Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set -support. - -@item pentium3 -@itemx pentium3m -Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction -set support. - -@item pentium-m -Intel Pentium M; low-power version of Intel Pentium III CPU -with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks. - -@item pentium4 -@itemx pentium4m -Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support. - -@item prescott -Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction -set support. - -@item nocona -Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, -SSE2 and SSE3 instruction set support. - -@item core2 -Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 -instruction set support. - -@item corei7 -Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1 -and SSE4.2 instruction set support. - -@item corei7-avx -Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, AVX, AES and PCLMUL instruction set support. - -@item core-avx-i -Intel Core CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, -SSE4.1, SSE4.2, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C instruction -set support. - -@item atom -Intel Atom CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 -instruction set support. - -@item k6 -AMD K6 CPU with MMX instruction set support. - -@item k6-2 -@itemx k6-3 -Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support. - -@item athlon -@itemx athlon-tbird -AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions -support. - -@item athlon-4 -@itemx athlon-xp -@itemx athlon-mp -Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE -instruction set support. - -@item k8 -@itemx opteron -@itemx athlon64 -@itemx athlon-fx -Processors based on the AMD K8 core with x86-64 instruction set support, -including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. -(This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit -instruction set extensions.) - -@item k8-sse3 -@itemx opteron-sse3 -@itemx athlon64-sse3 -Improved versions of AMD K8 cores with SSE3 instruction set support. - -@item amdfam10 -@itemx barcelona -CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This -supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit -instruction set extensions.) - -@item bdver1 -CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This -supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, -SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) -@item bdver2 -AMD Family 15h core based CPUs with x86-64 instruction set support. (This -supersets BMI, TBM, F16C, FMA, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, -SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set -extensions.) -@item bdver3 -AMD Family 15h core based CPUs with x86-64 instruction set support. (This -supersets BMI, TBM, F16C, FMA, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, -SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set -extensions. - -@item btver1 -CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This -supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit -instruction set extensions.) - -@item btver2 -CPUs based on AMD Family 16h cores with x86-64 instruction set support. This -includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM, -SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions. - -@item winchip-c6 -IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction -set support. - -@item winchip2 -IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@: -instruction set support. - -@item c3 -VIA C3 CPU with MMX and 3DNow!@: instruction set support. (No scheduling is -implemented for this chip.) - -@item c3-2 -VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. -(No scheduling is -implemented for this chip.) - -@item geode -AMD Geode embedded processor with MMX and 3DNow!@: instruction set support. -@end table - -@item -mtune=@var{cpu-type} -@opindex mtune -Tune to @var{cpu-type} everything applicable about the generated code, except -for the ABI and the set of available instructions. -While picking a specific @var{cpu-type} schedules things appropriately -for that particular chip, the compiler does not generate any code that -cannot run on the default machine type unless you use a -@option{-march=@var{cpu-type}} option. -For example, if GCC is configured for i686-pc-linux-gnu -then @option{-mtune=pentium4} generates code that is tuned for Pentium 4 -but still runs on i686 machines. - -The choices for @var{cpu-type} are the same as for @option{-march}. -In addition, @option{-mtune} supports an extra choice for @var{cpu-type}: - -@table @samp -@item generic -Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors. -If you know the CPU on which your code will run, then you should use -the corresponding @option{-mtune} or @option{-march} option instead of -@option{-mtune=generic}. But, if you do not know exactly what CPU users -of your application will have, then you should use this option. - -As new processors are deployed in the marketplace, the behavior of this -option will change. Therefore, if you upgrade to a newer version of -GCC, code generation controlled by this option will change to reflect -the processors -that are most common at the time that version of GCC is released. - -There is no @option{-march=generic} option because @option{-march} -indicates the instruction set the compiler can use, and there is no -generic instruction set applicable to all processors. In contrast, -@option{-mtune} indicates the processor (or, in this case, collection of -processors) for which the code is optimized. -@end table - -@item -mcpu=@var{cpu-type} -@opindex mcpu -A deprecated synonym for @option{-mtune}. - -@item -mfpmath=@var{unit} -@opindex mfpmath -Generate floating-point arithmetic for selected unit @var{unit}. The choices -for @var{unit} are: - -@table @samp -@item 387 -Use the standard 387 floating-point coprocessor present on the majority of chips and -emulated otherwise. Code compiled with this option runs almost everywhere. -The temporary results are computed in 80-bit precision instead of the precision -specified by the type, resulting in slightly different results compared to most -of other chips. See @option{-ffloat-store} for more detailed description. - -This is the default choice for i386 compiler. - -@item sse -Use scalar floating-point instructions present in the SSE instruction set. -This instruction set is supported by Pentium III and newer chips, -and in the AMD line -by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE -instruction set supports only single-precision arithmetic, thus the double and -extended-precision arithmetic are still done using 387. A later version, present -only in Pentium 4 and AMD x86-64 chips, supports double-precision -arithmetic too. - -For the i386 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse} -or @option{-msse2} switches to enable SSE extensions and make this option -effective. For the x86-64 compiler, these extensions are enabled by default. - -The resulting code should be considerably faster in the majority of cases and avoid -the numerical instability problems of 387 code, but may break some existing -code that expects temporaries to be 80 bits. - -This is the default choice for the x86-64 compiler. - -@item sse,387 -@itemx sse+387 -@itemx both -Attempt to utilize both instruction sets at once. This effectively doubles the -amount of available registers, and on chips with separate execution units for -387 and SSE the execution resources too. Use this option with care, as it is -still experimental, because the GCC register allocator does not model separate -functional units well, resulting in unstable performance. -@end table - -@item -masm=@var{dialect} -@opindex masm=@var{dialect} -Output assembly instructions using selected @var{dialect}. Supported -choices are @samp{intel} or @samp{att} (the default). Darwin does -not support @samp{intel}. - -@item -mieee-fp -@itemx -mno-ieee-fp -@opindex mieee-fp -@opindex mno-ieee-fp -Control whether or not the compiler uses IEEE floating-point -comparisons. These correctly handle the case where the result of a -comparison is unordered. - -@item -msoft-float -@opindex msoft-float -Generate output containing library calls for floating point. - -@strong{Warning:} the requisite libraries are not part of GCC@. -Normally the facilities of the machine's usual C compiler are used, but -this can't be done directly in cross-compilation. You must make your -own arrangements to provide suitable library functions for -cross-compilation. - -On machines where a function returns floating-point results in the 80387 -register stack, some floating-point opcodes may be emitted even if -@option{-msoft-float} is used. - -@item -mno-fp-ret-in-387 -@opindex mno-fp-ret-in-387 -Do not use the FPU registers for return values of functions. - -The usual calling convention has functions return values of types -@code{float} and @code{double} in an FPU register, even if there -is no FPU@. The idea is that the operating system should emulate -an FPU@. - -The option @option{-mno-fp-ret-in-387} causes such values to be returned -in ordinary CPU registers instead. - -@item -mno-fancy-math-387 -@opindex mno-fancy-math-387 -Some 387 emulators do not support the @code{sin}, @code{cos} and -@code{sqrt} instructions for the 387. Specify this option to avoid -generating those instructions. This option is the default on FreeBSD, -OpenBSD and NetBSD@. This option is overridden when @option{-march} -indicates that the target CPU always has an FPU and so the -instruction does not need emulation. These -instructions are not generated unless you also use the -@option{-funsafe-math-optimizations} switch. - -@item -malign-double -@itemx -mno-align-double -@opindex malign-double -@opindex mno-align-double -Control whether GCC aligns @code{double}, @code{long double}, and -@code{long long} variables on a two-word boundary or a one-word -boundary. Aligning @code{double} variables on a two-word boundary -produces code that runs somewhat faster on a Pentium at the -expense of more memory. - -On x86-64, @option{-malign-double} is enabled by default. - -@strong{Warning:} if you use the @option{-malign-double} switch, -structures containing the above types are aligned differently than -the published application binary interface specifications for the 386 -and are not binary compatible with structures in code compiled -without that switch. - -@item -m96bit-long-double -@itemx -m128bit-long-double -@opindex m96bit-long-double -@opindex m128bit-long-double -These switches control the size of @code{long double} type. The i386 -application binary interface specifies the size to be 96 bits, -so @option{-m96bit-long-double} is the default in 32-bit mode. - -Modern architectures (Pentium and newer) prefer @code{long double} -to be aligned to an 8- or 16-byte boundary. In arrays or structures -conforming to the ABI, this is not possible. So specifying -@option{-m128bit-long-double} aligns @code{long double} -to a 16-byte boundary by padding the @code{long double} with an additional -32-bit zero. - -In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as -its ABI specifies that @code{long double} is aligned on 16-byte boundary. - -Notice that neither of these options enable any extra precision over the x87 -standard of 80 bits for a @code{long double}. - -@strong{Warning:} if you override the default value for your target ABI, this -changes the size of -structures and arrays containing @code{long double} variables, -as well as modifying the function calling convention for functions taking -@code{long double}. Hence they are not binary-compatible -with code compiled without that switch. - -@item -mlong-double-64 -@itemx -mlong-double-80 -@opindex mlong-double-64 -@opindex mlong-double-80 -These switches control the size of @code{long double} type. A size -of 64 bits makes the @code{long double} type equivalent to the @code{double} -type. This is the default for Bionic C library. - -@strong{Warning:} if you override the default value for your target ABI, this -changes the size of -structures and arrays containing @code{long double} variables, -as well as modifying the function calling convention for functions taking -@code{long double}. Hence they are not binary-compatible -with code compiled without that switch. - -@item -mlarge-data-threshold=@var{threshold} -@opindex mlarge-data-threshold -When @option{-mcmodel=medium} is specified, data objects larger than -@var{threshold} are placed in the large data section. This value must be the -same across all objects linked into the binary, and defaults to 65535. - -@item -mrtd -@opindex mrtd -Use a different function-calling convention, in which functions that -take a fixed number of arguments return with the @code{ret @var{num}} -instruction, which pops their arguments while returning. This saves one -instruction in the caller since there is no need to pop the arguments -there. - -You can specify that an individual function is called with this calling -sequence with the function attribute @samp{stdcall}. You can also -override the @option{-mrtd} option by using the function attribute -@samp{cdecl}. @xref{Function Attributes}. - -@strong{Warning:} this calling convention is incompatible with the one -normally used on Unix, so you cannot use it if you need to call -libraries compiled with the Unix compiler. - -Also, you must provide function prototypes for all functions that -take variable numbers of arguments (including @code{printf}); -otherwise incorrect code is generated for calls to those -functions. - -In addition, seriously incorrect code results if you call a -function with too many arguments. (Normally, extra arguments are -harmlessly ignored.) - -@item -mregparm=@var{num} -@opindex mregparm -Control how many registers are used to pass integer arguments. By -default, no registers are used to pass arguments, and at most 3 -registers can be used. You can control this behavior for a specific -function by using the function attribute @samp{regparm}. -@xref{Function Attributes}. - -@strong{Warning:} if you use this switch, and -@var{num} is nonzero, then you must build all modules with the same -value, including any libraries. This includes the system libraries and -startup modules. - -@item -msseregparm -@opindex msseregparm -Use SSE register passing conventions for float and double arguments -and return values. You can control this behavior for a specific -function by using the function attribute @samp{sseregparm}. -@xref{Function Attributes}. - -@strong{Warning:} if you use this switch then you must build all -modules with the same value, including any libraries. This includes -the system libraries and startup modules. - -@item -mvect8-ret-in-mem -@opindex mvect8-ret-in-mem -Return 8-byte vectors in memory instead of MMX registers. This is the -default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun -Studio compilers until version 12. Later compiler versions (starting -with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which -is the default on Solaris@tie{}10 and later. @emph{Only} use this option if -you need to remain compatible with existing code produced by those -previous compiler versions or older versions of GCC@. - -@item -mpc32 -@itemx -mpc64 -@itemx -mpc80 -@opindex mpc32 -@opindex mpc64 -@opindex mpc80 - -Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32} -is specified, the significands of results of floating-point operations are -rounded to 24 bits (single precision); @option{-mpc64} rounds the -significands of results of floating-point operations to 53 bits (double -precision) and @option{-mpc80} rounds the significands of results of -floating-point operations to 64 bits (extended double precision), which is -the default. When this option is used, floating-point operations in higher -precisions are not available to the programmer without setting the FPU -control word explicitly. - -Setting the rounding of floating-point operations to less than the default -80 bits can speed some programs by 2% or more. Note that some mathematical -libraries assume that extended-precision (80-bit) floating-point operations -are enabled by default; routines in such libraries could suffer significant -loss of accuracy, typically through so-called ``catastrophic cancellation'', -when this option is used to set the precision to less than extended precision. - -@item -mstackrealign -@opindex mstackrealign -Realign the stack at entry. On the Intel x86, the @option{-mstackrealign} -option generates an alternate prologue and epilogue that realigns the -run-time stack if necessary. This supports mixing legacy codes that keep -4-byte stack alignment with modern codes that keep 16-byte stack alignment for -SSE compatibility. See also the attribute @code{force_align_arg_pointer}, -applicable to individual functions. - -@item -mpreferred-stack-boundary=@var{num} -@opindex mpreferred-stack-boundary -Attempt to keep the stack boundary aligned to a 2 raised to @var{num} -byte boundary. If @option{-mpreferred-stack-boundary} is not specified, -the default is 4 (16 bytes or 128 bits). - -@strong{Warning:} When generating code for the x86-64 architecture with -SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be -used to keep the stack boundary aligned to 8 byte boundary. Since -x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and -intended to be used in controlled environment where stack space is -important limitation. This option will lead to wrong code when functions -compiled with 16 byte stack alignment (such as functions from a standard -library) are called with misaligned stack. In this case, SSE -instructions may lead to misaligned memory access traps. In addition, -variable arguments will be handled incorrectly for 16 byte aligned -objects (including x87 long double and __int128), leading to wrong -results. You must build all modules with -@option{-mpreferred-stack-boundary=3}, including any libraries. This -includes the system libraries and startup modules. - -@item -mincoming-stack-boundary=@var{num} -@opindex mincoming-stack-boundary -Assume the incoming stack is aligned to a 2 raised to @var{num} byte -boundary. If @option{-mincoming-stack-boundary} is not specified, -the one specified by @option{-mpreferred-stack-boundary} is used. - -On Pentium and Pentium Pro, @code{double} and @code{long double} values -should be aligned to an 8-byte boundary (see @option{-malign-double}) or -suffer significant run time performance penalties. On Pentium III, the -Streaming SIMD Extension (SSE) data type @code{__m128} may not work -properly if it is not 16-byte aligned. - -To ensure proper alignment of this values on the stack, the stack boundary -must be as aligned as that required by any value stored on the stack. -Further, every function must be generated such that it keeps the stack -aligned. Thus calling a function compiled with a higher preferred -stack boundary from a function compiled with a lower preferred stack -boundary most likely misaligns the stack. It is recommended that -libraries that use callbacks always use the default setting. - -This extra alignment does consume extra stack space, and generally -increases code size. Code that is sensitive to stack space usage, such -as embedded systems and operating system kernels, may want to reduce the -preferred alignment to @option{-mpreferred-stack-boundary=2}. - -@item -mmmx -@itemx -mno-mmx -@itemx -msse -@itemx -mno-sse -@itemx -msse2 -@itemx -mno-sse2 -@itemx -msse3 -@itemx -mno-sse3 -@itemx -mssse3 -@itemx -mno-ssse3 -@itemx -msse4.1 -@need 800 -@itemx -mno-sse4.1 -@itemx -msse4.2 -@itemx -mno-sse4.2 -@itemx -msse4 -@itemx -mno-sse4 -@itemx -mavx -@itemx -mno-avx -@itemx -mavx2 -@itemx -mno-avx2 -@itemx -maes -@itemx -mno-aes -@itemx -mpclmul -@need 800 -@itemx -mno-pclmul -@itemx -mfsgsbase -@itemx -mno-fsgsbase -@itemx -mrdrnd -@itemx -mno-rdrnd -@itemx -mf16c -@itemx -mno-f16c -@itemx -mfma -@itemx -mno-fma -@itemx -msse4a -@itemx -mno-sse4a -@itemx -mfma4 -@need 800 -@itemx -mno-fma4 -@itemx -mxop -@itemx -mno-xop -@itemx -mlwp -@itemx -mno-lwp -@itemx -m3dnow -@itemx -mno-3dnow -@itemx -mpopcnt -@itemx -mno-popcnt -@itemx -mabm -@itemx -mno-abm -@itemx -mbmi -@itemx -mbmi2 -@itemx -mno-bmi -@itemx -mno-bmi2 -@itemx -mlzcnt -@itemx -mno-lzcnt -@itemx -mrtm -@itemx -mtbm -@itemx -mno-tbm -@opindex mmmx -@opindex mno-mmx -@opindex msse -@opindex mno-sse -@opindex m3dnow -@opindex mno-3dnow -These switches enable or disable the use of instructions in the MMX, SSE, -SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, F16C, -FMA, SSE4A, FMA4, XOP, LWP, ABM, BMI, BMI2, LZCNT, RTM or 3DNow!@: -extended instruction sets. -These extensions are also available as built-in functions: see -@ref{X86 Built-in Functions}, for details of the functions enabled and -disabled by these switches. - -To generate SSE/SSE2 instructions automatically from floating-point -code (as opposed to 387 instructions), see @option{-mfpmath=sse}. - -GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it -generates new AVX instructions or AVX equivalence for all SSEx instructions -when needed. - -These options enable GCC to use these extended instructions in -generated code, even without @option{-mfpmath=sse}. Applications that -perform run-time CPU detection must compile separate files for each -supported architecture, using the appropriate flags. In particular, -the file containing the CPU detection code should be compiled without -these options. - -@item -mcld -@opindex mcld -This option instructs GCC to emit a @code{cld} instruction in the prologue -of functions that use string instructions. String instructions depend on -the DF flag to select between autoincrement or autodecrement mode. While the -ABI specifies the DF flag to be cleared on function entry, some operating -systems violate this specification by not clearing the DF flag in their -exception dispatchers. The exception handler can be invoked with the DF flag -set, which leads to wrong direction mode when string instructions are used. -This option can be enabled by default on 32-bit x86 targets by configuring -GCC with the @option{--enable-cld} configure option. Generation of @code{cld} -instructions can be suppressed with the @option{-mno-cld} compiler option -in this case. - -@item -mvzeroupper -@opindex mvzeroupper -This option instructs GCC to emit a @code{vzeroupper} instruction -before a transfer of control flow out of the function to minimize -the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper} -intrinsics. - -@item -mprefer-avx128 -@opindex mprefer-avx128 -This option instructs GCC to use 128-bit AVX instructions instead of -256-bit AVX instructions in the auto-vectorizer. - -@item -mcx16 -@opindex mcx16 -This option enables GCC to generate @code{CMPXCHG16B} instructions. -@code{CMPXCHG16B} allows for atomic operations on 128-bit double quadword -(or oword) data types. -This is useful for high-resolution counters that can be updated -by multiple processors (or cores). This instruction is generated as part of -atomic built-in functions: see @ref{__sync Builtins} or -@ref{__atomic Builtins} for details. - -@item -msahf -@opindex msahf -This option enables generation of @code{SAHF} instructions in 64-bit code. -Early Intel Pentium 4 CPUs with Intel 64 support, -prior to the introduction of Pentium 4 G1 step in December 2005, -lacked the @code{LAHF} and @code{SAHF} instructions -which were supported by AMD64. -These are load and store instructions, respectively, for certain status flags. -In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod}, -@code{drem}, and @code{remainder} built-in functions; -see @ref{Other Builtins} for details. - -@item -mmovbe -@opindex mmovbe -This option enables use of the @code{movbe} instruction to implement -@code{__builtin_bswap32} and @code{__builtin_bswap64}. - -@item -mcrc32 -@opindex mcrc32 -This option enables built-in functions @code{__builtin_ia32_crc32qi}, -@code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and -@code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction. - -@item -mrecip -@opindex mrecip -This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions -(and their vectorized variants @code{RCPPS} and @code{RSQRTPS}) -with an additional Newton-Raphson step -to increase precision instead of @code{DIVSS} and @code{SQRTSS} -(and their vectorized -variants) for single-precision floating-point arguments. These instructions -are generated only when @option{-funsafe-math-optimizations} is enabled -together with @option{-finite-math-only} and @option{-fno-trapping-math}. -Note that while the throughput of the sequence is higher than the throughput -of the non-reciprocal instruction, the precision of the sequence can be -decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994). - -Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS} -(or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option -combination), and doesn't need @option{-mrecip}. - -Also note that GCC emits the above sequence with additional Newton-Raphson step -for vectorized single-float division and vectorized @code{sqrtf(@var{x})} -already with @option{-ffast-math} (or the above option combination), and -doesn't need @option{-mrecip}. - -@item -mrecip=@var{opt} -@opindex mrecip=opt -This option controls which reciprocal estimate instructions -may be used. @var{opt} is a comma-separated list of options, which may -be preceded by a @samp{!} to invert the option: - -@table @samp -@item all -Enable all estimate instructions. - -@item default -Enable the default instructions, equivalent to @option{-mrecip}. - -@item none -Disable all estimate instructions, equivalent to @option{-mno-recip}. - -@item div -Enable the approximation for scalar division. - -@item vec-div -Enable the approximation for vectorized division. - -@item sqrt -Enable the approximation for scalar square root. - -@item vec-sqrt -Enable the approximation for vectorized square root. -@end table - -So, for example, @option{-mrecip=all,!sqrt} enables -all of the reciprocal approximations, except for square root. - -@item -mveclibabi=@var{type} -@opindex mveclibabi -Specifies the ABI type to use for vectorizing intrinsics using an -external library. Supported values for @var{type} are @samp{svml} -for the Intel short -vector math library and @samp{acml} for the AMD math core library. -To use this option, both @option{-ftree-vectorize} and -@option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML -ABI-compatible library must be specified at link time. - -GCC currently emits calls to @code{vmldExp2}, -@code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2}, -@code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2}, -@code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2}, -@code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2}, -@code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104}, -@code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4}, -@code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4}, -@code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4}, -@code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding -function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin}, -@code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2}, -@code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf}, -@code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f}, -@code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type -when @option{-mveclibabi=acml} is used. - -@item -mabi=@var{name} -@opindex mabi -Generate code for the specified calling convention. Permissible values -are @samp{sysv} for the ABI used on GNU/Linux and other systems, and -@samp{ms} for the Microsoft ABI. The default is to use the Microsoft -ABI when targeting Microsoft Windows and the SysV ABI on all other systems. -You can control this behavior for a specific function by -using the function attribute @samp{ms_abi}/@samp{sysv_abi}. -@xref{Function Attributes}. - -@item -mtls-dialect=@var{type} -@opindex mtls-dialect -Generate code to access thread-local storage using the @samp{gnu} or -@samp{gnu2} conventions. @samp{gnu} is the conservative default; -@samp{gnu2} is more efficient, but it may add compile- and run-time -requirements that cannot be satisfied on all systems. - -@item -mpush-args -@itemx -mno-push-args -@opindex mpush-args -@opindex mno-push-args -Use PUSH operations to store outgoing parameters. This method is shorter -and usually equally fast as method using SUB/MOV operations and is enabled -by default. In some cases disabling it may improve performance because of -improved scheduling and reduced dependencies. - -@item -maccumulate-outgoing-args -@opindex maccumulate-outgoing-args -If enabled, the maximum amount of space required for outgoing arguments is -computed in the function prologue. This is faster on most modern CPUs -because of reduced dependencies, improved scheduling and reduced stack usage -when the preferred stack boundary is not equal to 2. The drawback is a notable -increase in code size. This switch implies @option{-mno-push-args}. - -@item -mthreads -@opindex mthreads -Support thread-safe exception handling on MinGW. Programs that rely -on thread-safe exception handling must compile and link all code with the -@option{-mthreads} option. When compiling, @option{-mthreads} defines -@code{-D_MT}; when linking, it links in a special thread helper library -@option{-lmingwthrd} which cleans up per-thread exception-handling data. - -@item -mno-align-stringops -@opindex mno-align-stringops -Do not align the destination of inlined string operations. This switch reduces -code size and improves performance in case the destination is already aligned, -but GCC doesn't know about it. - -@item -minline-all-stringops -@opindex minline-all-stringops -By default GCC inlines string operations only when the destination is -known to be aligned to least a 4-byte boundary. -This enables more inlining and increases code -size, but may improve performance of code that depends on fast -@code{memcpy}, @code{strlen}, -and @code{memset} for short lengths. - -@item -minline-stringops-dynamically -@opindex minline-stringops-dynamically -For string operations of unknown size, use run-time checks with -inline code for small blocks and a library call for large blocks. - -@item -mstringop-strategy=@var{alg} -@opindex mstringop-strategy=@var{alg} -Override the internal decision heuristic for the particular algorithm to use -for inlining string operations. The allowed values for @var{alg} are: - -@table @samp -@item rep_byte -@itemx rep_4byte -@itemx rep_8byte -Expand using i386 @code{rep} prefix of the specified size. - -@item byte_loop -@itemx loop -@itemx unrolled_loop -Expand into an inline loop. - -@item libcall -Always use a library call. -@end table - -@item -momit-leaf-frame-pointer -@opindex momit-leaf-frame-pointer -Don't keep the frame pointer in a register for leaf functions. This -avoids the instructions to save, set up, and restore frame pointers and -makes an extra register available in leaf functions. The option -@option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions, -which might make debugging harder. - -@item -mtls-direct-seg-refs -@itemx -mno-tls-direct-seg-refs -@opindex mtls-direct-seg-refs -Controls whether TLS variables may be accessed with offsets from the -TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit), -or whether the thread base pointer must be added. Whether or not this -is valid depends on the operating system, and whether it maps the -segment to cover the entire TLS area. - -For systems that use the GNU C Library, the default is on. - -@item -msse2avx -@itemx -mno-sse2avx -@opindex msse2avx -Specify that the assembler should encode SSE instructions with VEX -prefix. The option @option{-mavx} turns this on by default. - -@item -mfentry -@itemx -mno-fentry -@opindex mfentry -If profiling is active (@option{-pg}), put the profiling -counter call before the prologue. -Note: On x86 architectures the attribute @code{ms_hook_prologue} -isn't possible at the moment for @option{-mfentry} and @option{-pg}. - -@item -m8bit-idiv -@itemx -mno-8bit-idiv -@opindex 8bit-idiv -On some processors, like Intel Atom, 8-bit unsigned integer divide is -much faster than 32-bit/64-bit integer divide. This option generates a -run-time check. If both dividend and divisor are within range of 0 -to 255, 8-bit unsigned integer divide is used instead of -32-bit/64-bit integer divide. - -@item -mavx256-split-unaligned-load -@itemx -mavx256-split-unaligned-store -@opindex avx256-split-unaligned-load -@opindex avx256-split-unaligned-store -Split 32-byte AVX unaligned load and store. - -@end table - -These @samp{-m} switches are supported in addition to the above -on x86-64 processors in 64-bit environments. - -@table @gcctabopt -@item -m32 -@itemx -m64 -@itemx -mx32 -@opindex m32 -@opindex m64 -@opindex mx32 -Generate code for a 32-bit or 64-bit environment. -The @option{-m32} option sets @code{int}, @code{long}, and pointer types -to 32 bits, and -generates code that runs on any i386 system. - -The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer -types to 64 bits, and generates code for the x86-64 architecture. -For Darwin only the @option{-m64} option also turns off the @option{-fno-pic} -and @option{-mdynamic-no-pic} options. - -The @option{-mx32} option sets @code{int}, @code{long}, and pointer types -to 32 bits, and -generates code for the x86-64 architecture. - -@item -mno-red-zone -@opindex mno-red-zone -Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated -by the x86-64 ABI; it is a 128-byte area beyond the location of the -stack pointer that is not modified by signal or interrupt handlers -and therefore can be used for temporary data without adjusting the stack -pointer. The flag @option{-mno-red-zone} disables this red zone. - -@item -mcmodel=small -@opindex mcmodel=small -Generate code for the small code model: the program and its symbols must -be linked in the lower 2 GB of the address space. Pointers are 64 bits. -Programs can be statically or dynamically linked. This is the default -code model. - -@item -mcmodel=kernel -@opindex mcmodel=kernel -Generate code for the kernel code model. The kernel runs in the -negative 2 GB of the address space. -This model has to be used for Linux kernel code. - -@item -mcmodel=medium -@opindex mcmodel=medium -Generate code for the medium model: the program is linked in the lower 2 -GB of the address space. Small symbols are also placed there. Symbols -with sizes larger than @option{-mlarge-data-threshold} are put into -large data or BSS sections and can be located above 2GB. Programs can -be statically or dynamically linked. - -@item -mcmodel=large -@opindex mcmodel=large -Generate code for the large model. This model makes no assumptions -about addresses and sizes of sections. - -@item -maddress-mode=long -@opindex maddress-mode=long -Generate code for long address mode. This is only supported for 64-bit -and x32 environments. It is the default address mode for 64-bit -environments. - -@item -maddress-mode=short -@opindex maddress-mode=short -Generate code for short address mode. This is only supported for 32-bit -and x32 environments. It is the default address mode for 32-bit and -x32 environments. -@end table - -@node i386 and x86-64 Windows Options -@subsection i386 and x86-64 Windows Options -@cindex i386 and x86-64 Windows Options - -These additional options are available for Microsoft Windows targets: - -@table @gcctabopt -@item -mconsole -@opindex mconsole -This option -specifies that a console application is to be generated, by -instructing the linker to set the PE header subsystem type -required for console applications. -This option is available for Cygwin and MinGW targets and is -enabled by default on those targets. - -@item -mdll -@opindex mdll -This option is available for Cygwin and MinGW targets. It -specifies that a DLL---a dynamic link library---is to be -generated, enabling the selection of the required runtime -startup object and entry point. - -@item -mnop-fun-dllimport -@opindex mnop-fun-dllimport -This option is available for Cygwin and MinGW targets. It -specifies that the @code{dllimport} attribute should be ignored. - -@item -mthread -@opindex mthread -This option is available for MinGW targets. It specifies -that MinGW-specific thread support is to be used. - -@item -municode -@opindex municode -This option is available for MinGW-w64 targets. It causes -the @code{UNICODE} preprocessor macro to be predefined, and -chooses Unicode-capable runtime startup code. - -@item -mwin32 -@opindex mwin32 -This option is available for Cygwin and MinGW targets. It -specifies that the typical Microsoft Windows predefined macros are to -be set in the pre-processor, but does not influence the choice -of runtime library/startup code. - -@item -mwindows -@opindex mwindows -This option is available for Cygwin and MinGW targets. It -specifies that a GUI application is to be generated by -instructing the linker to set the PE header subsystem type -appropriately. - -@item -fno-set-stack-executable -@opindex fno-set-stack-executable -This option is available for MinGW targets. It specifies that -the executable flag for the stack used by nested functions isn't -set. This is necessary for binaries running in kernel mode of -Microsoft Windows, as there the User32 API, which is used to set executable -privileges, isn't available. - -@item -fwritable-relocated-rdata -@opindex fno-writable-relocated-rdata -This option is available for MinGW and Cygwin targets. It specifies -that relocated-data in read-only section is put into .data -section. This is a necessary for older runtimes not supporting -modification of .rdata sections for pseudo-relocation. - -@item -mpe-aligned-commons -@opindex mpe-aligned-commons -This option is available for Cygwin and MinGW targets. It -specifies that the GNU extension to the PE file format that -permits the correct alignment of COMMON variables should be -used when generating code. It is enabled by default if -GCC detects that the target assembler found during configuration -supports the feature. -@end table - -See also under @ref{i386 and x86-64 Options} for standard options. - -@node IA-64 Options -@subsection IA-64 Options -@cindex IA-64 Options - -These are the @samp{-m} options defined for the Intel IA-64 architecture. - -@table @gcctabopt -@item -mbig-endian -@opindex mbig-endian -Generate code for a big-endian target. This is the default for HP-UX@. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a little-endian target. This is the default for AIX5 -and GNU/Linux. - -@item -mgnu-as -@itemx -mno-gnu-as -@opindex mgnu-as -@opindex mno-gnu-as -Generate (or don't) code for the GNU assembler. This is the default. -@c Also, this is the default if the configure option @option{--with-gnu-as} -@c is used. - -@item -mgnu-ld -@itemx -mno-gnu-ld -@opindex mgnu-ld -@opindex mno-gnu-ld -Generate (or don't) code for the GNU linker. This is the default. -@c Also, this is the default if the configure option @option{--with-gnu-ld} -@c is used. - -@item -mno-pic -@opindex mno-pic -Generate code that does not use a global pointer register. The result -is not position independent code, and violates the IA-64 ABI@. - -@item -mvolatile-asm-stop -@itemx -mno-volatile-asm-stop -@opindex mvolatile-asm-stop -@opindex mno-volatile-asm-stop -Generate (or don't) a stop bit immediately before and after volatile asm -statements. - -@item -mregister-names -@itemx -mno-register-names -@opindex mregister-names -@opindex mno-register-names -Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for -the stacked registers. This may make assembler output more readable. - -@item -mno-sdata -@itemx -msdata -@opindex mno-sdata -@opindex msdata -Disable (or enable) optimizations that use the small data section. This may -be useful for working around optimizer bugs. - -@item -mconstant-gp -@opindex mconstant-gp -Generate code that uses a single constant global pointer value. This is -useful when compiling kernel code. - -@item -mauto-pic -@opindex mauto-pic -Generate code that is self-relocatable. This implies @option{-mconstant-gp}. -This is useful when compiling firmware code. - -@item -minline-float-divide-min-latency -@opindex minline-float-divide-min-latency -Generate code for inline divides of floating-point values -using the minimum latency algorithm. - -@item -minline-float-divide-max-throughput -@opindex minline-float-divide-max-throughput -Generate code for inline divides of floating-point values -using the maximum throughput algorithm. - -@item -mno-inline-float-divide -@opindex mno-inline-float-divide -Do not generate inline code for divides of floating-point values. - -@item -minline-int-divide-min-latency -@opindex minline-int-divide-min-latency -Generate code for inline divides of integer values -using the minimum latency algorithm. - -@item -minline-int-divide-max-throughput -@opindex minline-int-divide-max-throughput -Generate code for inline divides of integer values -using the maximum throughput algorithm. - -@item -mno-inline-int-divide -@opindex mno-inline-int-divide -Do not generate inline code for divides of integer values. - -@item -minline-sqrt-min-latency -@opindex minline-sqrt-min-latency -Generate code for inline square roots -using the minimum latency algorithm. - -@item -minline-sqrt-max-throughput -@opindex minline-sqrt-max-throughput -Generate code for inline square roots -using the maximum throughput algorithm. - -@item -mno-inline-sqrt -@opindex mno-inline-sqrt -Do not generate inline code for @code{sqrt}. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Do (don't) generate code that uses the fused multiply/add or multiply/subtract -instructions. The default is to use these instructions. - -@item -mno-dwarf2-asm -@itemx -mdwarf2-asm -@opindex mno-dwarf2-asm -@opindex mdwarf2-asm -Don't (or do) generate assembler code for the DWARF 2 line number debugging -info. This may be useful when not using the GNU assembler. - -@item -mearly-stop-bits -@itemx -mno-early-stop-bits -@opindex mearly-stop-bits -@opindex mno-early-stop-bits -Allow stop bits to be placed earlier than immediately preceding the -instruction that triggered the stop bit. This can improve instruction -scheduling, but does not always do so. - -@item -mfixed-range=@var{register-range} -@opindex mfixed-range -Generate code treating the given register range as fixed registers. -A fixed register is one that the register allocator cannot use. This is -useful when compiling kernel code. A register range is specified as -two registers separated by a dash. Multiple register ranges can be -specified separated by a comma. - -@item -mtls-size=@var{tls-size} -@opindex mtls-size -Specify bit size of immediate TLS offsets. Valid values are 14, 22, and -64. - -@item -mtune=@var{cpu-type} -@opindex mtune -Tune the instruction scheduling for a particular CPU, Valid values are -@samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2}, -and @samp{mckinley}. - -@item -milp32 -@itemx -mlp64 -@opindex milp32 -@opindex mlp64 -Generate code for a 32-bit or 64-bit environment. -The 32-bit environment sets int, long and pointer to 32 bits. -The 64-bit environment sets int to 32 bits and long and pointer -to 64 bits. These are HP-UX specific flags. - -@item -mno-sched-br-data-spec -@itemx -msched-br-data-spec -@opindex mno-sched-br-data-spec -@opindex msched-br-data-spec -(Dis/En)able data speculative scheduling before reload. -This results in generation of @code{ld.a} instructions and -the corresponding check instructions (@code{ld.c} / @code{chk.a}). -The default is 'disable'. - -@item -msched-ar-data-spec -@itemx -mno-sched-ar-data-spec -@opindex msched-ar-data-spec -@opindex mno-sched-ar-data-spec -(En/Dis)able data speculative scheduling after reload. -This results in generation of @code{ld.a} instructions and -the corresponding check instructions (@code{ld.c} / @code{chk.a}). -The default is 'enable'. - -@item -mno-sched-control-spec -@itemx -msched-control-spec -@opindex mno-sched-control-spec -@opindex msched-control-spec -(Dis/En)able control speculative scheduling. This feature is -available only during region scheduling (i.e.@: before reload). -This results in generation of the @code{ld.s} instructions and -the corresponding check instructions @code{chk.s}. -The default is 'disable'. - -@item -msched-br-in-data-spec -@itemx -mno-sched-br-in-data-spec -@opindex msched-br-in-data-spec -@opindex mno-sched-br-in-data-spec -(En/Dis)able speculative scheduling of the instructions that -are dependent on the data speculative loads before reload. -This is effective only with @option{-msched-br-data-spec} enabled. -The default is 'enable'. - -@item -msched-ar-in-data-spec -@itemx -mno-sched-ar-in-data-spec -@opindex msched-ar-in-data-spec -@opindex mno-sched-ar-in-data-spec -(En/Dis)able speculative scheduling of the instructions that -are dependent on the data speculative loads after reload. -This is effective only with @option{-msched-ar-data-spec} enabled. -The default is 'enable'. - -@item -msched-in-control-spec -@itemx -mno-sched-in-control-spec -@opindex msched-in-control-spec -@opindex mno-sched-in-control-spec -(En/Dis)able speculative scheduling of the instructions that -are dependent on the control speculative loads. -This is effective only with @option{-msched-control-spec} enabled. -The default is 'enable'. - -@item -mno-sched-prefer-non-data-spec-insns -@itemx -msched-prefer-non-data-spec-insns -@opindex mno-sched-prefer-non-data-spec-insns -@opindex msched-prefer-non-data-spec-insns -If enabled, data-speculative instructions are chosen for schedule -only if there are no other choices at the moment. This makes -the use of the data speculation much more conservative. -The default is 'disable'. - -@item -mno-sched-prefer-non-control-spec-insns -@itemx -msched-prefer-non-control-spec-insns -@opindex mno-sched-prefer-non-control-spec-insns -@opindex msched-prefer-non-control-spec-insns -If enabled, control-speculative instructions are chosen for schedule -only if there are no other choices at the moment. This makes -the use of the control speculation much more conservative. -The default is 'disable'. - -@item -mno-sched-count-spec-in-critical-path -@itemx -msched-count-spec-in-critical-path -@opindex mno-sched-count-spec-in-critical-path -@opindex msched-count-spec-in-critical-path -If enabled, speculative dependencies are considered during -computation of the instructions priorities. This makes the use of the -speculation a bit more conservative. -The default is 'disable'. - -@item -msched-spec-ldc -@opindex msched-spec-ldc -Use a simple data speculation check. This option is on by default. - -@item -msched-control-spec-ldc -@opindex msched-spec-ldc -Use a simple check for control speculation. This option is on by default. - -@item -msched-stop-bits-after-every-cycle -@opindex msched-stop-bits-after-every-cycle -Place a stop bit after every cycle when scheduling. This option is on -by default. - -@item -msched-fp-mem-deps-zero-cost -@opindex msched-fp-mem-deps-zero-cost -Assume that floating-point stores and loads are not likely to cause a conflict -when placed into the same instruction group. This option is disabled by -default. - -@item -msel-sched-dont-check-control-spec -@opindex msel-sched-dont-check-control-spec -Generate checks for control speculation in selective scheduling. -This flag is disabled by default. - -@item -msched-max-memory-insns=@var{max-insns} -@opindex msched-max-memory-insns -Limit on the number of memory insns per instruction group, giving lower -priority to subsequent memory insns attempting to schedule in the same -instruction group. Frequently useful to prevent cache bank conflicts. -The default value is 1. - -@item -msched-max-memory-insns-hard-limit -@opindex msched-max-memory-insns-hard-limit -Makes the limit specified by @option{msched-max-memory-insns} a hard limit, -disallowing more than that number in an instruction group. -Otherwise, the limit is ``soft'', meaning that non-memory operations -are preferred when the limit is reached, but memory operations may still -be scheduled. - -@end table - -@node LM32 Options -@subsection LM32 Options -@cindex LM32 options - -These @option{-m} options are defined for the LatticeMico32 architecture: - -@table @gcctabopt -@item -mbarrel-shift-enabled -@opindex mbarrel-shift-enabled -Enable barrel-shift instructions. - -@item -mdivide-enabled -@opindex mdivide-enabled -Enable divide and modulus instructions. - -@item -mmultiply-enabled -@opindex multiply-enabled -Enable multiply instructions. - -@item -msign-extend-enabled -@opindex msign-extend-enabled -Enable sign extend instructions. - -@item -muser-enabled -@opindex muser-enabled -Enable user-defined instructions. - -@end table - -@node M32C Options -@subsection M32C Options -@cindex M32C options - -@table @gcctabopt -@item -mcpu=@var{name} -@opindex mcpu= -Select the CPU for which code is generated. @var{name} may be one of -@samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to -/60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for -the M32C/80 series. - -@item -msim -@opindex msim -Specifies that the program will be run on the simulator. This causes -an alternate runtime library to be linked in which supports, for -example, file I/O@. You must not use this option when generating -programs that will run on real hardware; you must provide your own -runtime library for whatever I/O functions are needed. - -@item -memregs=@var{number} -@opindex memregs= -Specifies the number of memory-based pseudo-registers GCC uses -during code generation. These pseudo-registers are used like real -registers, so there is a tradeoff between GCC's ability to fit the -code into available registers, and the performance penalty of using -memory instead of registers. Note that all modules in a program must -be compiled with the same value for this option. Because of that, you -must not use this option with GCC's default runtime libraries. - -@end table - -@node M32R/D Options -@subsection M32R/D Options -@cindex M32R/D options - -These @option{-m} options are defined for Renesas M32R/D architectures: - -@table @gcctabopt -@item -m32r2 -@opindex m32r2 -Generate code for the M32R/2@. - -@item -m32rx -@opindex m32rx -Generate code for the M32R/X@. - -@item -m32r -@opindex m32r -Generate code for the M32R@. This is the default. - -@item -mmodel=small -@opindex mmodel=small -Assume all objects live in the lower 16MB of memory (so that their addresses -can be loaded with the @code{ld24} instruction), and assume all subroutines -are reachable with the @code{bl} instruction. -This is the default. - -The addressability of a particular object can be set with the -@code{model} attribute. - -@item -mmodel=medium -@opindex mmodel=medium -Assume objects may be anywhere in the 32-bit address space (the compiler -generates @code{seth/add3} instructions to load their addresses), and -assume all subroutines are reachable with the @code{bl} instruction. - -@item -mmodel=large -@opindex mmodel=large -Assume objects may be anywhere in the 32-bit address space (the compiler -generates @code{seth/add3} instructions to load their addresses), and -assume subroutines may not be reachable with the @code{bl} instruction -(the compiler generates the much slower @code{seth/add3/jl} -instruction sequence). - -@item -msdata=none -@opindex msdata=none -Disable use of the small data area. Variables are put into -one of @samp{.data}, @samp{.bss}, or @samp{.rodata} (unless the -@code{section} attribute has been specified). -This is the default. - -The small data area consists of sections @samp{.sdata} and @samp{.sbss}. -Objects may be explicitly put in the small data area with the -@code{section} attribute using one of these sections. - -@item -msdata=sdata -@opindex msdata=sdata -Put small global and static data in the small data area, but do not -generate special code to reference them. - -@item -msdata=use -@opindex msdata=use -Put small global and static data in the small data area, and generate -special instructions to reference them. - -@item -G @var{num} -@opindex G -@cindex smaller data references -Put global and static objects less than or equal to @var{num} bytes -into the small data or BSS sections instead of the normal data or BSS -sections. The default value of @var{num} is 8. -The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} -for this option to have any effect. - -All modules should be compiled with the same @option{-G @var{num}} value. -Compiling with different values of @var{num} may or may not work; if it -doesn't the linker gives an error message---incorrect code is not -generated. - -@item -mdebug -@opindex mdebug -Makes the M32R-specific code in the compiler display some statistics -that might help in debugging programs. - -@item -malign-loops -@opindex malign-loops -Align all loops to a 32-byte boundary. - -@item -mno-align-loops -@opindex mno-align-loops -Do not enforce a 32-byte alignment for loops. This is the default. - -@item -missue-rate=@var{number} -@opindex missue-rate=@var{number} -Issue @var{number} instructions per cycle. @var{number} can only be 1 -or 2. - -@item -mbranch-cost=@var{number} -@opindex mbranch-cost=@var{number} -@var{number} can only be 1 or 2. If it is 1 then branches are -preferred over conditional code, if it is 2, then the opposite applies. - -@item -mflush-trap=@var{number} -@opindex mflush-trap=@var{number} -Specifies the trap number to use to flush the cache. The default is -12. Valid numbers are between 0 and 15 inclusive. - -@item -mno-flush-trap -@opindex mno-flush-trap -Specifies that the cache cannot be flushed by using a trap. - -@item -mflush-func=@var{name} -@opindex mflush-func=@var{name} -Specifies the name of the operating system function to call to flush -the cache. The default is @emph{_flush_cache}, but a function call -is only used if a trap is not available. - -@item -mno-flush-func -@opindex mno-flush-func -Indicates that there is no OS function for flushing the cache. - -@end table - -@node M680x0 Options -@subsection M680x0 Options -@cindex M680x0 options - -These are the @samp{-m} options defined for M680x0 and ColdFire processors. -The default settings depend on which architecture was selected when -the compiler was configured; the defaults for the most common choices -are given below. - -@table @gcctabopt -@item -march=@var{arch} -@opindex march -Generate code for a specific M680x0 or ColdFire instruction set -architecture. Permissible values of @var{arch} for M680x0 -architectures are: @samp{68000}, @samp{68010}, @samp{68020}, -@samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire -architectures are selected according to Freescale's ISA classification -and the permissible values are: @samp{isaa}, @samp{isaaplus}, -@samp{isab} and @samp{isac}. - -GCC defines a macro @samp{__mcf@var{arch}__} whenever it is generating -code for a ColdFire target. The @var{arch} in this macro is one of the -@option{-march} arguments given above. - -When used together, @option{-march} and @option{-mtune} select code -that runs on a family of similar processors but that is optimized -for a particular microarchitecture. - -@item -mcpu=@var{cpu} -@opindex mcpu -Generate code for a specific M680x0 or ColdFire processor. -The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020}, -@samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332} -and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table -below, which also classifies the CPUs into families: - -@multitable @columnfractions 0.20 0.80 -@item @strong{Family} @tab @strong{@samp{-mcpu} arguments} -@item @samp{51} @tab @samp{51} @samp{51ac} @samp{51ag} @samp{51cn} @samp{51em} @samp{51je} @samp{51jf} @samp{51jg} @samp{51jm} @samp{51mm} @samp{51qe} @samp{51qm} -@item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206} -@item @samp{5206e} @tab @samp{5206e} -@item @samp{5208} @tab @samp{5207} @samp{5208} -@item @samp{5211a} @tab @samp{5210a} @samp{5211a} -@item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213} -@item @samp{5216} @tab @samp{5214} @samp{5216} -@item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235} -@item @samp{5225} @tab @samp{5224} @samp{5225} -@item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259} -@item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x} -@item @samp{5249} @tab @samp{5249} -@item @samp{5250} @tab @samp{5250} -@item @samp{5271} @tab @samp{5270} @samp{5271} -@item @samp{5272} @tab @samp{5272} -@item @samp{5275} @tab @samp{5274} @samp{5275} -@item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x} -@item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017} -@item @samp{5307} @tab @samp{5307} -@item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x} -@item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x} -@item @samp{5407} @tab @samp{5407} -@item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485} -@end multitable - -@option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if -@var{arch} is compatible with @var{cpu}. Other combinations of -@option{-mcpu} and @option{-march} are rejected. - -GCC defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target -@var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}}, -where the value of @var{family} is given by the table above. - -@item -mtune=@var{tune} -@opindex mtune -Tune the code for a particular microarchitecture within the -constraints set by @option{-march} and @option{-mcpu}. -The M680x0 microarchitectures are: @samp{68000}, @samp{68010}, -@samp{68020}, @samp{68030}, @samp{68040}, @samp{68060} -and @samp{cpu32}. The ColdFire microarchitectures -are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}. - -You can also use @option{-mtune=68020-40} for code that needs -to run relatively well on 68020, 68030 and 68040 targets. -@option{-mtune=68020-60} is similar but includes 68060 targets -as well. These two options select the same tuning decisions as -@option{-m68020-40} and @option{-m68020-60} respectively. - -GCC defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__} -when tuning for 680x0 architecture @var{arch}. It also defines -@samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std} -option is used. If GCC is tuning for a range of architectures, -as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60}, -it defines the macros for every architecture in the range. - -GCC also defines the macro @samp{__m@var{uarch}__} when tuning for -ColdFire microarchitecture @var{uarch}, where @var{uarch} is one -of the arguments given above. - -@item -m68000 -@itemx -mc68000 -@opindex m68000 -@opindex mc68000 -Generate output for a 68000. This is the default -when the compiler is configured for 68000-based systems. -It is equivalent to @option{-march=68000}. - -Use this option for microcontrollers with a 68000 or EC000 core, -including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. - -@item -m68010 -@opindex m68010 -Generate output for a 68010. This is the default -when the compiler is configured for 68010-based systems. -It is equivalent to @option{-march=68010}. - -@item -m68020 -@itemx -mc68020 -@opindex m68020 -@opindex mc68020 -Generate output for a 68020. This is the default -when the compiler is configured for 68020-based systems. -It is equivalent to @option{-march=68020}. - -@item -m68030 -@opindex m68030 -Generate output for a 68030. This is the default when the compiler is -configured for 68030-based systems. It is equivalent to -@option{-march=68030}. - -@item -m68040 -@opindex m68040 -Generate output for a 68040. This is the default when the compiler is -configured for 68040-based systems. It is equivalent to -@option{-march=68040}. - -This option inhibits the use of 68881/68882 instructions that have to be -emulated by software on the 68040. Use this option if your 68040 does not -have code to emulate those instructions. - -@item -m68060 -@opindex m68060 -Generate output for a 68060. This is the default when the compiler is -configured for 68060-based systems. It is equivalent to -@option{-march=68060}. - -This option inhibits the use of 68020 and 68881/68882 instructions that -have to be emulated by software on the 68060. Use this option if your 68060 -does not have code to emulate those instructions. - -@item -mcpu32 -@opindex mcpu32 -Generate output for a CPU32. This is the default -when the compiler is configured for CPU32-based systems. -It is equivalent to @option{-march=cpu32}. - -Use this option for microcontrollers with a -CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, -68336, 68340, 68341, 68349 and 68360. - -@item -m5200 -@opindex m5200 -Generate output for a 520X ColdFire CPU@. This is the default -when the compiler is configured for 520X-based systems. -It is equivalent to @option{-mcpu=5206}, and is now deprecated -in favor of that option. - -Use this option for microcontroller with a 5200 core, including -the MCF5202, MCF5203, MCF5204 and MCF5206. - -@item -m5206e -@opindex m5206e -Generate output for a 5206e ColdFire CPU@. The option is now -deprecated in favor of the equivalent @option{-mcpu=5206e}. - -@item -m528x -@opindex m528x -Generate output for a member of the ColdFire 528X family. -The option is now deprecated in favor of the equivalent -@option{-mcpu=528x}. - -@item -m5307 -@opindex m5307 -Generate output for a ColdFire 5307 CPU@. The option is now deprecated -in favor of the equivalent @option{-mcpu=5307}. - -@item -m5407 -@opindex m5407 -Generate output for a ColdFire 5407 CPU@. The option is now deprecated -in favor of the equivalent @option{-mcpu=5407}. - -@item -mcfv4e -@opindex mcfv4e -Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x). -This includes use of hardware floating-point instructions. -The option is equivalent to @option{-mcpu=547x}, and is now -deprecated in favor of that option. - -@item -m68020-40 -@opindex m68020-40 -Generate output for a 68040, without using any of the new instructions. -This results in code that can run relatively efficiently on either a -68020/68881 or a 68030 or a 68040. The generated code does use the -68881 instructions that are emulated on the 68040. - -The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}. - -@item -m68020-60 -@opindex m68020-60 -Generate output for a 68060, without using any of the new instructions. -This results in code that can run relatively efficiently on either a -68020/68881 or a 68030 or a 68040. The generated code does use the -68881 instructions that are emulated on the 68060. - -The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}. - -@item -mhard-float -@itemx -m68881 -@opindex mhard-float -@opindex m68881 -Generate floating-point instructions. This is the default for 68020 -and above, and for ColdFire devices that have an FPU@. It defines the -macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__} -on ColdFire targets. - -@item -msoft-float -@opindex msoft-float -Do not generate floating-point instructions; use library calls instead. -This is the default for 68000, 68010, and 68832 targets. It is also -the default for ColdFire devices that have no FPU. - -@item -mdiv -@itemx -mno-div -@opindex mdiv -@opindex mno-div -Generate (do not generate) ColdFire hardware divide and remainder -instructions. If @option{-march} is used without @option{-mcpu}, -the default is ``on'' for ColdFire architectures and ``off'' for M680x0 -architectures. Otherwise, the default is taken from the target CPU -(either the default CPU, or the one specified by @option{-mcpu}). For -example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for -@option{-mcpu=5206e}. - -GCC defines the macro @samp{__mcfhwdiv__} when this option is enabled. - -@item -mshort -@opindex mshort -Consider type @code{int} to be 16 bits wide, like @code{short int}. -Additionally, parameters passed on the stack are also aligned to a -16-bit boundary even on targets whose API mandates promotion to 32-bit. - -@item -mno-short -@opindex mno-short -Do not consider type @code{int} to be 16 bits wide. This is the default. - -@item -mnobitfield -@itemx -mno-bitfield -@opindex mnobitfield -@opindex mno-bitfield -Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} -and @option{-m5200} options imply @w{@option{-mnobitfield}}. - -@item -mbitfield -@opindex mbitfield -Do use the bit-field instructions. The @option{-m68020} option implies -@option{-mbitfield}. This is the default if you use a configuration -designed for a 68020. - -@item -mrtd -@opindex mrtd -Use a different function-calling convention, in which functions -that take a fixed number of arguments return with the @code{rtd} -instruction, which pops their arguments while returning. This -saves one instruction in the caller since there is no need to pop -the arguments there. - -This calling convention is incompatible with the one normally -used on Unix, so you cannot use it if you need to call libraries -compiled with the Unix compiler. - -Also, you must provide function prototypes for all functions that -take variable numbers of arguments (including @code{printf}); -otherwise incorrect code is generated for calls to those -functions. - -In addition, seriously incorrect code results if you call a -function with too many arguments. (Normally, extra arguments are -harmlessly ignored.) - -The @code{rtd} instruction is supported by the 68010, 68020, 68030, -68040, 68060 and CPU32 processors, but not by the 68000 or 5200. - -@item -mno-rtd -@opindex mno-rtd -Do not use the calling conventions selected by @option{-mrtd}. -This is the default. - -@item -malign-int -@itemx -mno-align-int -@opindex malign-int -@opindex mno-align-int -Control whether GCC aligns @code{int}, @code{long}, @code{long long}, -@code{float}, @code{double}, and @code{long double} variables on a 32-bit -boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). -Aligning variables on 32-bit boundaries produces code that runs somewhat -faster on processors with 32-bit busses at the expense of more memory. - -@strong{Warning:} if you use the @option{-malign-int} switch, GCC -aligns structures containing the above types differently than -most published application binary interface specifications for the m68k. - -@item -mpcrel -@opindex mpcrel -Use the pc-relative addressing mode of the 68000 directly, instead of -using a global offset table. At present, this option implies @option{-fpic}, -allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is -not presently supported with @option{-mpcrel}, though this could be supported for -68020 and higher processors. - -@item -mno-strict-align -@itemx -mstrict-align -@opindex mno-strict-align -@opindex mstrict-align -Do not (do) assume that unaligned memory references are handled by -the system. - -@item -msep-data -Generate code that allows the data segment to be located in a different -area of memory from the text segment. This allows for execute-in-place in -an environment without virtual memory management. This option implies -@option{-fPIC}. - -@item -mno-sep-data -Generate code that assumes that the data segment follows the text segment. -This is the default. - -@item -mid-shared-library -Generate code that supports shared libraries via the library ID method. -This allows for execute-in-place and shared libraries in an environment -without virtual memory management. This option implies @option{-fPIC}. - -@item -mno-id-shared-library -Generate code that doesn't assume ID-based shared libraries are being used. -This is the default. - -@item -mshared-library-id=n -Specifies the identification number of the ID-based shared library being -compiled. Specifying a value of 0 generates more compact code; specifying -other values forces the allocation of that number to the current -library, but is no more space- or time-efficient than omitting this option. - -@item -mxgot -@itemx -mno-xgot -@opindex mxgot -@opindex mno-xgot -When generating position-independent code for ColdFire, generate code -that works if the GOT has more than 8192 entries. This code is -larger and slower than code generated without this option. On M680x0 -processors, this option is not needed; @option{-fPIC} suffices. - -GCC normally uses a single instruction to load values from the GOT@. -While this is relatively efficient, it only works if the GOT -is smaller than about 64k. Anything larger causes the linker -to report an error such as: - -@cindex relocation truncated to fit (ColdFire) -@smallexample -relocation truncated to fit: R_68K_GOT16O foobar -@end smallexample - -If this happens, you should recompile your code with @option{-mxgot}. -It should then work with very large GOTs. However, code generated with -@option{-mxgot} is less efficient, since it takes 4 instructions to fetch -the value of a global symbol. - -Note that some linkers, including newer versions of the GNU linker, -can create multiple GOTs and sort GOT entries. If you have such a linker, -you should only need to use @option{-mxgot} when compiling a single -object file that accesses more than 8192 GOT entries. Very few do. - -These options have no effect unless GCC is generating -position-independent code. - -@end table - -@node MCore Options -@subsection MCore Options -@cindex MCore options - -These are the @samp{-m} options defined for the Motorola M*Core -processors. - -@table @gcctabopt - -@item -mhardlit -@itemx -mno-hardlit -@opindex mhardlit -@opindex mno-hardlit -Inline constants into the code stream if it can be done in two -instructions or less. - -@item -mdiv -@itemx -mno-div -@opindex mdiv -@opindex mno-div -Use the divide instruction. (Enabled by default). - -@item -mrelax-immediate -@itemx -mno-relax-immediate -@opindex mrelax-immediate -@opindex mno-relax-immediate -Allow arbitrary-sized immediates in bit operations. - -@item -mwide-bitfields -@itemx -mno-wide-bitfields -@opindex mwide-bitfields -@opindex mno-wide-bitfields -Always treat bit-fields as @code{int}-sized. - -@item -m4byte-functions -@itemx -mno-4byte-functions -@opindex m4byte-functions -@opindex mno-4byte-functions -Force all functions to be aligned to a 4-byte boundary. - -@item -mcallgraph-data -@itemx -mno-callgraph-data -@opindex mcallgraph-data -@opindex mno-callgraph-data -Emit callgraph information. - -@item -mslow-bytes -@itemx -mno-slow-bytes -@opindex mslow-bytes -@opindex mno-slow-bytes -Prefer word access when reading byte quantities. - -@item -mlittle-endian -@itemx -mbig-endian -@opindex mlittle-endian -@opindex mbig-endian -Generate code for a little-endian target. - -@item -m210 -@itemx -m340 -@opindex m210 -@opindex m340 -Generate code for the 210 processor. - -@item -mno-lsim -@opindex mno-lsim -Assume that runtime support has been provided and so omit the -simulator library (@file{libsim.a)} from the linker command line. - -@item -mstack-increment=@var{size} -@opindex mstack-increment -Set the maximum amount for a single stack increment operation. Large -values can increase the speed of programs that contain functions -that need a large amount of stack space, but they can also trigger a -segmentation fault if the stack is extended too much. The default -value is 0x1000. - -@end table - -@node MeP Options -@subsection MeP Options -@cindex MeP options - -@table @gcctabopt - -@item -mabsdiff -@opindex mabsdiff -Enables the @code{abs} instruction, which is the absolute difference -between two registers. - -@item -mall-opts -@opindex mall-opts -Enables all the optional instructions---average, multiply, divide, bit -operations, leading zero, absolute difference, min/max, clip, and -saturation. - - -@item -maverage -@opindex maverage -Enables the @code{ave} instruction, which computes the average of two -registers. - -@item -mbased=@var{n} -@opindex mbased= -Variables of size @var{n} bytes or smaller are placed in the -@code{.based} section by default. Based variables use the @code{$tp} -register as a base register, and there is a 128-byte limit to the -@code{.based} section. - -@item -mbitops -@opindex mbitops -Enables the bit operation instructions---bit test (@code{btstm}), set -(@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and -test-and-set (@code{tas}). - -@item -mc=@var{name} -@opindex mc= -Selects which section constant data is placed in. @var{name} may -be @code{tiny}, @code{near}, or @code{far}. - -@item -mclip -@opindex mclip -Enables the @code{clip} instruction. Note that @code{-mclip} is not -useful unless you also provide @code{-mminmax}. - -@item -mconfig=@var{name} -@opindex mconfig= -Selects one of the built-in core configurations. Each MeP chip has -one or more modules in it; each module has a core CPU and a variety of -coprocessors, optional instructions, and peripherals. The -@code{MeP-Integrator} tool, not part of GCC, provides these -configurations through this option; using this option is the same as -using all the corresponding command-line options. The default -configuration is @code{default}. - -@item -mcop -@opindex mcop -Enables the coprocessor instructions. By default, this is a 32-bit -coprocessor. Note that the coprocessor is normally enabled via the -@code{-mconfig=} option. - -@item -mcop32 -@opindex mcop32 -Enables the 32-bit coprocessor's instructions. - -@item -mcop64 -@opindex mcop64 -Enables the 64-bit coprocessor's instructions. - -@item -mivc2 -@opindex mivc2 -Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor. - -@item -mdc -@opindex mdc -Causes constant variables to be placed in the @code{.near} section. - -@item -mdiv -@opindex mdiv -Enables the @code{div} and @code{divu} instructions. - -@item -meb -@opindex meb -Generate big-endian code. - -@item -mel -@opindex mel -Generate little-endian code. - -@item -mio-volatile -@opindex mio-volatile -Tells the compiler that any variable marked with the @code{io} -attribute is to be considered volatile. - -@item -ml -@opindex ml -Causes variables to be assigned to the @code{.far} section by default. - -@item -mleadz -@opindex mleadz -Enables the @code{leadz} (leading zero) instruction. - -@item -mm -@opindex mm -Causes variables to be assigned to the @code{.near} section by default. - -@item -mminmax -@opindex mminmax -Enables the @code{min} and @code{max} instructions. - -@item -mmult -@opindex mmult -Enables the multiplication and multiply-accumulate instructions. - -@item -mno-opts -@opindex mno-opts -Disables all the optional instructions enabled by @code{-mall-opts}. - -@item -mrepeat -@opindex mrepeat -Enables the @code{repeat} and @code{erepeat} instructions, used for -low-overhead looping. - -@item -ms -@opindex ms -Causes all variables to default to the @code{.tiny} section. Note -that there is a 65536-byte limit to this section. Accesses to these -variables use the @code{%gp} base register. - -@item -msatur -@opindex msatur -Enables the saturation instructions. Note that the compiler does not -currently generate these itself, but this option is included for -compatibility with other tools, like @code{as}. - -@item -msdram -@opindex msdram -Link the SDRAM-based runtime instead of the default ROM-based runtime. - -@item -msim -@opindex msim -Link the simulator runtime libraries. - -@item -msimnovec -@opindex msimnovec -Link the simulator runtime libraries, excluding built-in support -for reset and exception vectors and tables. - -@item -mtf -@opindex mtf -Causes all functions to default to the @code{.far} section. Without -this option, functions default to the @code{.near} section. - -@item -mtiny=@var{n} -@opindex mtiny= -Variables that are @var{n} bytes or smaller are allocated to the -@code{.tiny} section. These variables use the @code{$gp} base -register. The default for this option is 4, but note that there's a -65536-byte limit to the @code{.tiny} section. - -@end table - -@node MicroBlaze Options -@subsection MicroBlaze Options -@cindex MicroBlaze Options - -@table @gcctabopt - -@item -msoft-float -@opindex msoft-float -Use software emulation for floating point (default). - -@item -mhard-float -@opindex mhard-float -Use hardware floating-point instructions. - -@item -mmemcpy -@opindex mmemcpy -Do not optimize block moves, use @code{memcpy}. - -@item -mno-clearbss -@opindex mno-clearbss -This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead. - -@item -mcpu=@var{cpu-type} -@opindex mcpu= -Use features of, and schedule code for, the given CPU. -Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}}, -where @var{X} is a major version, @var{YY} is the minor version, and -@var{Z} is compatibility code. Example values are @samp{v3.00.a}, -@samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v5.00.b}, @samp{v6.00.a}. - -@item -mxl-soft-mul -@opindex mxl-soft-mul -Use software multiply emulation (default). - -@item -mxl-soft-div -@opindex mxl-soft-div -Use software emulation for divides (default). - -@item -mxl-barrel-shift -@opindex mxl-barrel-shift -Use the hardware barrel shifter. - -@item -mxl-pattern-compare -@opindex mxl-pattern-compare -Use pattern compare instructions. - -@item -msmall-divides -@opindex msmall-divides -Use table lookup optimization for small signed integer divisions. - -@item -mxl-stack-check -@opindex mxl-stack-check -This option is deprecated. Use @option{-fstack-check} instead. - -@item -mxl-gp-opt -@opindex mxl-gp-opt -Use GP-relative @code{.sdata}/@code{.sbss} sections. - -@item -mxl-multiply-high -@opindex mxl-multiply-high -Use multiply high instructions for high part of 32x32 multiply. - -@item -mxl-float-convert -@opindex mxl-float-convert -Use hardware floating-point conversion instructions. - -@item -mxl-float-sqrt -@opindex mxl-float-sqrt -Use hardware floating-point square root instruction. - -@item -mbig-endian -@opindex mbig-endian -Generate code for a big-endian target. - -@item -mlittle-endian -@opindex mlittle-endian -Generate code for a little-endian target. - -@item -mxl-reorder -@opindex mxl-reorder -Use reorder instructions (swap and byte reversed load/store). - -@item -mxl-mode-@var{app-model} -Select application model @var{app-model}. Valid models are -@table @samp -@item executable -normal executable (default), uses startup code @file{crt0.o}. - -@item xmdstub -for use with Xilinx Microprocessor Debugger (XMD) based -software intrusive debug agent called xmdstub. This uses startup file -@file{crt1.o} and sets the start address of the program to 0x800. - -@item bootstrap -for applications that are loaded using a bootloader. -This model uses startup file @file{crt2.o} which does not contain a processor -reset vector handler. This is suitable for transferring control on a -processor reset to the bootloader rather than the application. - -@item novectors -for applications that do not require any of the -MicroBlaze vectors. This option may be useful for applications running -within a monitoring application. This model uses @file{crt3.o} as a startup file. -@end table - -Option @option{-xl-mode-@var{app-model}} is a deprecated alias for -@option{-mxl-mode-@var{app-model}}. - -@end table - -@node MIPS Options -@subsection MIPS Options -@cindex MIPS options - -@table @gcctabopt - -@item -EB -@opindex EB -Generate big-endian code. - -@item -EL -@opindex EL -Generate little-endian code. This is the default for @samp{mips*el-*-*} -configurations. - -@item -march=@var{arch} -@opindex march -Generate code that runs on @var{arch}, which can be the name of a -generic MIPS ISA, or the name of a particular processor. -The ISA names are: -@samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, -@samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}. -The processor names are: -@samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc}, -@samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd}, -@samp{5kc}, @samp{5kf}, -@samp{20kc}, -@samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1}, -@samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1}, -@samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn}, -@samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2}, -@samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1}, -@samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a}, -@samp{m4k}, -@samp{octeon}, @samp{octeon+}, @samp{octeon2}, -@samp{orion}, -@samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400}, -@samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r6000}, @samp{r8000}, -@samp{rm7000}, @samp{rm9000}, -@samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000}, -@samp{sb1}, -@samp{sr71000}, -@samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300}, -@samp{vr5000}, @samp{vr5400}, @samp{vr5500}, -@samp{xlr} and @samp{xlp}. -The special value @samp{from-abi} selects the -most compatible architecture for the selected ABI (that is, -@samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@. - -The native Linux/GNU toolchain also supports the value @samp{native}, -which selects the best architecture option for the host processor. -@option{-march=native} has no effect if GCC does not recognize -the processor. - -In processor names, a final @samp{000} can be abbreviated as @samp{k} -(for example, @option{-march=r2k}). Prefixes are optional, and -@samp{vr} may be written @samp{r}. - -Names of the form @samp{@var{n}f2_1} refer to processors with -FPUs clocked at half the rate of the core, names of the form -@samp{@var{n}f1_1} refer to processors with FPUs clocked at the same -rate as the core, and names of the form @samp{@var{n}f3_2} refer to -processors with FPUs clocked a ratio of 3:2 with respect to the core. -For compatibility reasons, @samp{@var{n}f} is accepted as a synonym -for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are -accepted as synonyms for @samp{@var{n}f1_1}. - -GCC defines two macros based on the value of this option. The first -is @samp{_MIPS_ARCH}, which gives the name of target architecture, as -a string. The second has the form @samp{_MIPS_ARCH_@var{foo}}, -where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@. -For example, @option{-march=r2000} sets @samp{_MIPS_ARCH} -to @samp{"r2000"} and defines the macro @samp{_MIPS_ARCH_R2000}. - -Note that the @samp{_MIPS_ARCH} macro uses the processor names given -above. In other words, it has the full prefix and does not -abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi}, -the macro names the resolved architecture (either @samp{"mips1"} or -@samp{"mips3"}). It names the default architecture when no -@option{-march} option is given. - -@item -mtune=@var{arch} -@opindex mtune -Optimize for @var{arch}. Among other things, this option controls -the way instructions are scheduled, and the perceived cost of arithmetic -operations. The list of @var{arch} values is the same as for -@option{-march}. - -When this option is not used, GCC optimizes for the processor -specified by @option{-march}. By using @option{-march} and -@option{-mtune} together, it is possible to generate code that -runs on a family of processors, but optimize the code for one -particular member of that family. - -@option{-mtune} defines the macros @samp{_MIPS_TUNE} and -@samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the -@option{-march} ones described above. - -@item -mips1 -@opindex mips1 -Equivalent to @option{-march=mips1}. - -@item -mips2 -@opindex mips2 -Equivalent to @option{-march=mips2}. - -@item -mips3 -@opindex mips3 -Equivalent to @option{-march=mips3}. - -@item -mips4 -@opindex mips4 -Equivalent to @option{-march=mips4}. - -@item -mips32 -@opindex mips32 -Equivalent to @option{-march=mips32}. - -@item -mips32r2 -@opindex mips32r2 -Equivalent to @option{-march=mips32r2}. - -@item -mips64 -@opindex mips64 -Equivalent to @option{-march=mips64}. - -@item -mips64r2 -@opindex mips64r2 -Equivalent to @option{-march=mips64r2}. - -@item -mips16 -@itemx -mno-mips16 -@opindex mips16 -@opindex mno-mips16 -Generate (do not generate) MIPS16 code. If GCC is targeting a -MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@. - -MIPS16 code generation can also be controlled on a per-function basis -by means of @code{mips16} and @code{nomips16} attributes. -@xref{Function Attributes}, for more information. - -@item -mflip-mips16 -@opindex mflip-mips16 -Generate MIPS16 code on alternating functions. This option is provided -for regression testing of mixed MIPS16/non-MIPS16 code generation, and is -not intended for ordinary use in compiling user code. - -@item -minterlink-mips16 -@itemx -mno-interlink-mips16 -@opindex minterlink-mips16 -@opindex mno-interlink-mips16 -Require (do not require) that non-MIPS16 code be link-compatible with -MIPS16 code. - -For example, non-MIPS16 code cannot jump directly to MIPS16 code; -it must either use a call or an indirect jump. @option{-minterlink-mips16} -therefore disables direct jumps unless GCC knows that the target of the -jump is not MIPS16. - -@item -mabi=32 -@itemx -mabi=o64 -@itemx -mabi=n32 -@itemx -mabi=64 -@itemx -mabi=eabi -@opindex mabi=32 -@opindex mabi=o64 -@opindex mabi=n32 -@opindex mabi=64 -@opindex mabi=eabi -Generate code for the given ABI@. - -Note that the EABI has a 32-bit and a 64-bit variant. GCC normally -generates 64-bit code when you select a 64-bit architecture, but you -can use @option{-mgp32} to get 32-bit code instead. - -For information about the O64 ABI, see -@uref{http://gcc.gnu.org/@/projects/@/mipso64-abi.html}. - -GCC supports a variant of the o32 ABI in which floating-point registers -are 64 rather than 32 bits wide. You can select this combination with -@option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1} -and @code{mfhc1} instructions and is therefore only supported for -MIPS32R2 processors. - -The register assignments for arguments and return values remain the -same, but each scalar value is passed in a single 64-bit register -rather than a pair of 32-bit registers. For example, scalar -floating-point values are returned in @samp{$f0} only, not a -@samp{$f0}/@samp{$f1} pair. The set of call-saved registers also -remains the same, but all 64 bits are saved. - -@item -mabicalls -@itemx -mno-abicalls -@opindex mabicalls -@opindex mno-abicalls -Generate (do not generate) code that is suitable for SVR4-style -dynamic objects. @option{-mabicalls} is the default for SVR4-based -systems. - -@item -mshared -@itemx -mno-shared -Generate (do not generate) code that is fully position-independent, -and that can therefore be linked into shared libraries. This option -only affects @option{-mabicalls}. - -All @option{-mabicalls} code has traditionally been position-independent, -regardless of options like @option{-fPIC} and @option{-fpic}. However, -as an extension, the GNU toolchain allows executables to use absolute -accesses for locally-binding symbols. It can also use shorter GP -initialization sequences and generate direct calls to locally-defined -functions. This mode is selected by @option{-mno-shared}. - -@option{-mno-shared} depends on binutils 2.16 or higher and generates -objects that can only be linked by the GNU linker. However, the option -does not affect the ABI of the final executable; it only affects the ABI -of relocatable objects. Using @option{-mno-shared} generally makes -executables both smaller and quicker. - -@option{-mshared} is the default. - -@item -mplt -@itemx -mno-plt -@opindex mplt -@opindex mno-plt -Assume (do not assume) that the static and dynamic linkers -support PLTs and copy relocations. This option only affects -@option{-mno-shared -mabicalls}. For the n64 ABI, this option -has no effect without @option{-msym32}. - -You can make @option{-mplt} the default by configuring -GCC with @option{--with-mips-plt}. The default is -@option{-mno-plt} otherwise. - -@item -mxgot -@itemx -mno-xgot -@opindex mxgot -@opindex mno-xgot -Lift (do not lift) the usual restrictions on the size of the global -offset table. - -GCC normally uses a single instruction to load values from the GOT@. -While this is relatively efficient, it only works if the GOT -is smaller than about 64k. Anything larger causes the linker -to report an error such as: - -@cindex relocation truncated to fit (MIPS) -@smallexample -relocation truncated to fit: R_MIPS_GOT16 foobar -@end smallexample - -If this happens, you should recompile your code with @option{-mxgot}. -This works with very large GOTs, although the code is also -less efficient, since it takes three instructions to fetch the -value of a global symbol. - -Note that some linkers can create multiple GOTs. If you have such a -linker, you should only need to use @option{-mxgot} when a single object -file accesses more than 64k's worth of GOT entries. Very few do. - -These options have no effect unless GCC is generating position -independent code. - -@item -mgp32 -@opindex mgp32 -Assume that general-purpose registers are 32 bits wide. - -@item -mgp64 -@opindex mgp64 -Assume that general-purpose registers are 64 bits wide. - -@item -mfp32 -@opindex mfp32 -Assume that floating-point registers are 32 bits wide. - -@item -mfp64 -@opindex mfp64 -Assume that floating-point registers are 64 bits wide. - -@item -mhard-float -@opindex mhard-float -Use floating-point coprocessor instructions. - -@item -msoft-float -@opindex msoft-float -Do not use floating-point coprocessor instructions. Implement -floating-point calculations using library calls instead. - -@item -mno-float -@opindex mno-float -Equivalent to @option{-msoft-float}, but additionally asserts that the -program being compiled does not perform any floating-point operations. -This option is presently supported only by some bare-metal MIPS -configurations, where it may select a special set of libraries -that lack all floating-point support (including, for example, the -floating-point @code{printf} formats). -If code compiled with @code{-mno-float} accidentally contains -floating-point operations, it is likely to suffer a link-time -or run-time failure. - -@item -msingle-float -@opindex msingle-float -Assume that the floating-point coprocessor only supports single-precision -operations. - -@item -mdouble-float -@opindex mdouble-float -Assume that the floating-point coprocessor supports double-precision -operations. This is the default. - -@item -mllsc -@itemx -mno-llsc -@opindex mllsc -@opindex mno-llsc -Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to -implement atomic memory built-in functions. When neither option is -specified, GCC uses the instructions if the target architecture -supports them. - -@option{-mllsc} is useful if the runtime environment can emulate the -instructions and @option{-mno-llsc} can be useful when compiling for -nonstandard ISAs. You can make either option the default by -configuring GCC with @option{--with-llsc} and @option{--without-llsc} -respectively. @option{--with-llsc} is the default for some -configurations; see the installation documentation for details. - -@item -mdsp -@itemx -mno-dsp -@opindex mdsp -@opindex mno-dsp -Use (do not use) revision 1 of the MIPS DSP ASE@. -@xref{MIPS DSP Built-in Functions}. This option defines the -preprocessor macro @samp{__mips_dsp}. It also defines -@samp{__mips_dsp_rev} to 1. - -@item -mdspr2 -@itemx -mno-dspr2 -@opindex mdspr2 -@opindex mno-dspr2 -Use (do not use) revision 2 of the MIPS DSP ASE@. -@xref{MIPS DSP Built-in Functions}. This option defines the -preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}. -It also defines @samp{__mips_dsp_rev} to 2. - -@item -msmartmips -@itemx -mno-smartmips -@opindex msmartmips -@opindex mno-smartmips -Use (do not use) the MIPS SmartMIPS ASE. - -@item -mpaired-single -@itemx -mno-paired-single -@opindex mpaired-single -@opindex mno-paired-single -Use (do not use) paired-single floating-point instructions. -@xref{MIPS Paired-Single Support}. This option requires -hardware floating-point support to be enabled. - -@item -mdmx -@itemx -mno-mdmx -@opindex mdmx -@opindex mno-mdmx -Use (do not use) MIPS Digital Media Extension instructions. -This option can only be used when generating 64-bit code and requires -hardware floating-point support to be enabled. - -@item -mips3d -@itemx -mno-mips3d -@opindex mips3d -@opindex mno-mips3d -Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}. -The option @option{-mips3d} implies @option{-mpaired-single}. - -@item -mmt -@itemx -mno-mt -@opindex mmt -@opindex mno-mt -Use (do not use) MT Multithreading instructions. - -@item -mmcu -@itemx -mno-mcu -@opindex mmcu -@opindex mno-mcu -Use (do not use) the MIPS MCU ASE instructions. - -@item -mlong64 -@opindex mlong64 -Force @code{long} types to be 64 bits wide. See @option{-mlong32} for -an explanation of the default and the way that the pointer size is -determined. - -@item -mlong32 -@opindex mlong32 -Force @code{long}, @code{int}, and pointer types to be 32 bits wide. - -The default size of @code{int}s, @code{long}s and pointers depends on -the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI -uses 64-bit @code{long}s, as does the 64-bit EABI; the others use -32-bit @code{long}s. Pointers are the same size as @code{long}s, -or the same size as integer registers, whichever is smaller. - -@item -msym32 -@itemx -mno-sym32 -@opindex msym32 -@opindex mno-sym32 -Assume (do not assume) that all symbols have 32-bit values, regardless -of the selected ABI@. This option is useful in combination with -@option{-mabi=64} and @option{-mno-abicalls} because it allows GCC -to generate shorter and faster references to symbolic addresses. - -@item -G @var{num} -@opindex G -Put definitions of externally-visible data in a small data section -if that data is no bigger than @var{num} bytes. GCC can then generate -more efficient accesses to the data; see @option{-mgpopt} for details. - -The default @option{-G} option depends on the configuration. - -@item -mlocal-sdata -@itemx -mno-local-sdata -@opindex mlocal-sdata -@opindex mno-local-sdata -Extend (do not extend) the @option{-G} behavior to local data too, -such as to static variables in C@. @option{-mlocal-sdata} is the -default for all configurations. - -If the linker complains that an application is using too much small data, -you might want to try rebuilding the less performance-critical parts with -@option{-mno-local-sdata}. You might also want to build large -libraries with @option{-mno-local-sdata}, so that the libraries leave -more room for the main program. - -@item -mextern-sdata -@itemx -mno-extern-sdata -@opindex mextern-sdata -@opindex mno-extern-sdata -Assume (do not assume) that externally-defined data is in -a small data section if the size of that data is within the @option{-G} limit. -@option{-mextern-sdata} is the default for all configurations. - -If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G -@var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var} -that is no bigger than @var{num} bytes, you must make sure that @var{Var} -is placed in a small data section. If @var{Var} is defined by another -module, you must either compile that module with a high-enough -@option{-G} setting or attach a @code{section} attribute to @var{Var}'s -definition. If @var{Var} is common, you must link the application -with a high-enough @option{-G} setting. - -The easiest way of satisfying these restrictions is to compile -and link every module with the same @option{-G} option. However, -you may wish to build a library that supports several different -small data limits. You can do this by compiling the library with -the highest supported @option{-G} setting and additionally using -@option{-mno-extern-sdata} to stop the library from making assumptions -about externally-defined data. - -@item -mgpopt -@itemx -mno-gpopt -@opindex mgpopt -@opindex mno-gpopt -Use (do not use) GP-relative accesses for symbols that are known to be -in a small data section; see @option{-G}, @option{-mlocal-sdata} and -@option{-mextern-sdata}. @option{-mgpopt} is the default for all -configurations. - -@option{-mno-gpopt} is useful for cases where the @code{$gp} register -might not hold the value of @code{_gp}. For example, if the code is -part of a library that might be used in a boot monitor, programs that -call boot monitor routines pass an unknown value in @code{$gp}. -(In such situations, the boot monitor itself is usually compiled -with @option{-G0}.) - -@option{-mno-gpopt} implies @option{-mno-local-sdata} and -@option{-mno-extern-sdata}. - -@item -membedded-data -@itemx -mno-embedded-data -@opindex membedded-data -@opindex mno-embedded-data -Allocate variables to the read-only data section first if possible, then -next in the small data section if possible, otherwise in data. This gives -slightly slower code than the default, but reduces the amount of RAM required -when executing, and thus may be preferred for some embedded systems. - -@item -muninit-const-in-rodata -@itemx -mno-uninit-const-in-rodata -@opindex muninit-const-in-rodata -@opindex mno-uninit-const-in-rodata -Put uninitialized @code{const} variables in the read-only data section. -This option is only meaningful in conjunction with @option{-membedded-data}. - -@item -mcode-readable=@var{setting} -@opindex mcode-readable -Specify whether GCC may generate code that reads from executable sections. -There are three possible settings: - -@table @gcctabopt -@item -mcode-readable=yes -Instructions may freely access executable sections. This is the -default setting. - -@item -mcode-readable=pcrel -MIPS16 PC-relative load instructions can access executable sections, -but other instructions must not do so. This option is useful on 4KSc -and 4KSd processors when the code TLBs have the Read Inhibit bit set. -It is also useful on processors that can be configured to have a dual -instruction/data SRAM interface and that, like the M4K, automatically -redirect PC-relative loads to the instruction RAM. - -@item -mcode-readable=no -Instructions must not access executable sections. This option can be -useful on targets that are configured to have a dual instruction/data -SRAM interface but that (unlike the M4K) do not automatically redirect -PC-relative loads to the instruction RAM. -@end table - -@item -msplit-addresses -@itemx -mno-split-addresses -@opindex msplit-addresses -@opindex mno-split-addresses -Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler -relocation operators. This option has been superseded by -@option{-mexplicit-relocs} but is retained for backwards compatibility. - -@item -mexplicit-relocs -@itemx -mno-explicit-relocs -@opindex mexplicit-relocs -@opindex mno-explicit-relocs -Use (do not use) assembler relocation operators when dealing with symbolic -addresses. The alternative, selected by @option{-mno-explicit-relocs}, -is to use assembler macros instead. - -@option{-mexplicit-relocs} is the default if GCC was configured -to use an assembler that supports relocation operators. - -@item -mcheck-zero-division -@itemx -mno-check-zero-division -@opindex mcheck-zero-division -@opindex mno-check-zero-division -Trap (do not trap) on integer division by zero. - -The default is @option{-mcheck-zero-division}. - -@item -mdivide-traps -@itemx -mdivide-breaks -@opindex mdivide-traps -@opindex mdivide-breaks -MIPS systems check for division by zero by generating either a -conditional trap or a break instruction. Using traps results in -smaller code, but is only supported on MIPS II and later. Also, some -versions of the Linux kernel have a bug that prevents trap from -generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to -allow conditional traps on architectures that support them and -@option{-mdivide-breaks} to force the use of breaks. - -The default is usually @option{-mdivide-traps}, but this can be -overridden at configure time using @option{--with-divide=breaks}. -Divide-by-zero checks can be completely disabled using -@option{-mno-check-zero-division}. - -@item -mmemcpy -@itemx -mno-memcpy -@opindex mmemcpy -@opindex mno-memcpy -Force (do not force) the use of @code{memcpy()} for non-trivial block -moves. The default is @option{-mno-memcpy}, which allows GCC to inline -most constant-sized copies. - -@item -mlong-calls -@itemx -mno-long-calls -@opindex mlong-calls -@opindex mno-long-calls -Disable (do not disable) use of the @code{jal} instruction. Calling -functions using @code{jal} is more efficient but requires the caller -and callee to be in the same 256 megabyte segment. - -This option has no effect on abicalls code. The default is -@option{-mno-long-calls}. - -@item -mmad -@itemx -mno-mad -@opindex mmad -@opindex mno-mad -Enable (disable) use of the @code{mad}, @code{madu} and @code{mul} -instructions, as provided by the R4650 ISA@. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Enable (disable) use of the floating-point multiply-accumulate -instructions, when they are available. The default is -@option{-mfused-madd}. - -On the R8000 CPU when multiply-accumulate instructions are used, -the intermediate product is calculated to infinite precision -and is not subject to the FCSR Flush to Zero bit. This may be -undesirable in some circumstances. On other processors the result -is numerically identical to the equivalent computation using -separate multiply, add, subtract and negate instructions. - -@item -nocpp -@opindex nocpp -Tell the MIPS assembler to not run its preprocessor over user -assembler files (with a @samp{.s} suffix) when assembling them. - -@item -mfix-24k -@item -mno-fix-24k -@opindex mfix-24k -@opindex mno-fix-24k -Work around the 24K E48 (lost data on stores during refill) errata. -The workarounds are implemented by the assembler rather than by GCC@. - -@item -mfix-r4000 -@itemx -mno-fix-r4000 -@opindex mfix-r4000 -@opindex mno-fix-r4000 -Work around certain R4000 CPU errata: -@itemize @minus -@item -A double-word or a variable shift may give an incorrect result if executed -immediately after starting an integer division. -@item -A double-word or a variable shift may give an incorrect result if executed -while an integer multiplication is in progress. -@item -An integer division may give an incorrect result if started in a delay slot -of a taken branch or a jump. -@end itemize - -@item -mfix-r4400 -@itemx -mno-fix-r4400 -@opindex mfix-r4400 -@opindex mno-fix-r4400 -Work around certain R4400 CPU errata: -@itemize @minus -@item -A double-word or a variable shift may give an incorrect result if executed -immediately after starting an integer division. -@end itemize - -@item -mfix-r10000 -@itemx -mno-fix-r10000 -@opindex mfix-r10000 -@opindex mno-fix-r10000 -Work around certain R10000 errata: -@itemize @minus -@item -@code{ll}/@code{sc} sequences may not behave atomically on revisions -prior to 3.0. They may deadlock on revisions 2.6 and earlier. -@end itemize - -This option can only be used if the target architecture supports -branch-likely instructions. @option{-mfix-r10000} is the default when -@option{-march=r10000} is used; @option{-mno-fix-r10000} is the default -otherwise. - -@item -mfix-vr4120 -@itemx -mno-fix-vr4120 -@opindex mfix-vr4120 -Work around certain VR4120 errata: -@itemize @minus -@item -@code{dmultu} does not always produce the correct result. -@item -@code{div} and @code{ddiv} do not always produce the correct result if one -of the operands is negative. -@end itemize -The workarounds for the division errata rely on special functions in -@file{libgcc.a}. At present, these functions are only provided by -the @code{mips64vr*-elf} configurations. - -Other VR4120 errata require a NOP to be inserted between certain pairs of -instructions. These errata are handled by the assembler, not by GCC itself. - -@item -mfix-vr4130 -@opindex mfix-vr4130 -Work around the VR4130 @code{mflo}/@code{mfhi} errata. The -workarounds are implemented by the assembler rather than by GCC, -although GCC avoids using @code{mflo} and @code{mfhi} if the -VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi} -instructions are available instead. - -@item -mfix-sb1 -@itemx -mno-fix-sb1 -@opindex mfix-sb1 -Work around certain SB-1 CPU core errata. -(This flag currently works around the SB-1 revision 2 -``F1'' and ``F2'' floating-point errata.) - -@item -mr10k-cache-barrier=@var{setting} -@opindex mr10k-cache-barrier -Specify whether GCC should insert cache barriers to avoid the -side-effects of speculation on R10K processors. - -In common with many processors, the R10K tries to predict the outcome -of a conditional branch and speculatively executes instructions from -the ``taken'' branch. It later aborts these instructions if the -predicted outcome is wrong. However, on the R10K, even aborted -instructions can have side effects. - -This problem only affects kernel stores and, depending on the system, -kernel loads. As an example, a speculatively-executed store may load -the target memory into cache and mark the cache line as dirty, even if -the store itself is later aborted. If a DMA operation writes to the -same area of memory before the ``dirty'' line is flushed, the cached -data overwrites the DMA-ed data. See the R10K processor manual -for a full description, including other potential problems. - -One workaround is to insert cache barrier instructions before every memory -access that might be speculatively executed and that might have side -effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}} -controls GCC's implementation of this workaround. It assumes that -aborted accesses to any byte in the following regions does not have -side effects: - -@enumerate -@item -the memory occupied by the current function's stack frame; - -@item -the memory occupied by an incoming stack argument; - -@item -the memory occupied by an object with a link-time-constant address. -@end enumerate - -It is the kernel's responsibility to ensure that speculative -accesses to these regions are indeed safe. - -If the input program contains a function declaration such as: - -@smallexample -void foo (void); -@end smallexample - -then the implementation of @code{foo} must allow @code{j foo} and -@code{jal foo} to be executed speculatively. GCC honors this -restriction for functions it compiles itself. It expects non-GCC -functions (such as hand-written assembly code) to do the same. - -The option has three forms: - -@table @gcctabopt -@item -mr10k-cache-barrier=load-store -Insert a cache barrier before a load or store that might be -speculatively executed and that might have side effects even -if aborted. - -@item -mr10k-cache-barrier=store -Insert a cache barrier before a store that might be speculatively -executed and that might have side effects even if aborted. - -@item -mr10k-cache-barrier=none -Disable the insertion of cache barriers. This is the default setting. -@end table - -@item -mflush-func=@var{func} -@itemx -mno-flush-func -@opindex mflush-func -Specifies the function to call to flush the I and D caches, or to not -call any such function. If called, the function must take the same -arguments as the common @code{_flush_func()}, that is, the address of the -memory range for which the cache is being flushed, the size of the -memory range, and the number 3 (to flush both caches). The default -depends on the target GCC was configured for, but commonly is either -@samp{_flush_func} or @samp{__cpu_flush}. - -@item mbranch-cost=@var{num} -@opindex mbranch-cost -Set the cost of branches to roughly @var{num} ``simple'' instructions. -This cost is only a heuristic and is not guaranteed to produce -consistent results across releases. A zero cost redundantly selects -the default, which is based on the @option{-mtune} setting. - -@item -mbranch-likely -@itemx -mno-branch-likely -@opindex mbranch-likely -@opindex mno-branch-likely -Enable or disable use of Branch Likely instructions, regardless of the -default for the selected architecture. By default, Branch Likely -instructions may be generated if they are supported by the selected -architecture. An exception is for the MIPS32 and MIPS64 architectures -and processors that implement those architectures; for those, Branch -Likely instructions are not be generated by default because the MIPS32 -and MIPS64 architectures specifically deprecate their use. - -@item -mfp-exceptions -@itemx -mno-fp-exceptions -@opindex mfp-exceptions -Specifies whether FP exceptions are enabled. This affects how -FP instructions are scheduled for some processors. -The default is that FP exceptions are -enabled. - -For instance, on the SB-1, if FP exceptions are disabled, and we are emitting -64-bit code, then we can use both FP pipes. Otherwise, we can only use one -FP pipe. - -@item -mvr4130-align -@itemx -mno-vr4130-align -@opindex mvr4130-align -The VR4130 pipeline is two-way superscalar, but can only issue two -instructions together if the first one is 8-byte aligned. When this -option is enabled, GCC aligns pairs of instructions that it -thinks should execute in parallel. - -This option only has an effect when optimizing for the VR4130. -It normally makes code faster, but at the expense of making it bigger. -It is enabled by default at optimization level @option{-O3}. - -@item -msynci -@itemx -mno-synci -@opindex msynci -Enable (disable) generation of @code{synci} instructions on -architectures that support it. The @code{synci} instructions (if -enabled) are generated when @code{__builtin___clear_cache()} is -compiled. - -This option defaults to @code{-mno-synci}, but the default can be -overridden by configuring with @code{--with-synci}. - -When compiling code for single processor systems, it is generally safe -to use @code{synci}. However, on many multi-core (SMP) systems, it -does not invalidate the instruction caches on all cores and may lead -to undefined behavior. - -@item -mrelax-pic-calls -@itemx -mno-relax-pic-calls -@opindex mrelax-pic-calls -Try to turn PIC calls that are normally dispatched via register -@code{$25} into direct calls. This is only possible if the linker can -resolve the destination at link-time and if the destination is within -range for a direct call. - -@option{-mrelax-pic-calls} is the default if GCC was configured to use -an assembler and a linker that support the @code{.reloc} assembly -directive and @code{-mexplicit-relocs} is in effect. With -@code{-mno-explicit-relocs}, this optimization can be performed by the -assembler and the linker alone without help from the compiler. - -@item -mmcount-ra-address -@itemx -mno-mcount-ra-address -@opindex mmcount-ra-address -@opindex mno-mcount-ra-address -Emit (do not emit) code that allows @code{_mcount} to modify the -calling function's return address. When enabled, this option extends -the usual @code{_mcount} interface with a new @var{ra-address} -parameter, which has type @code{intptr_t *} and is passed in register -@code{$12}. @code{_mcount} can then modify the return address by -doing both of the following: -@itemize -@item -Returning the new address in register @code{$31}. -@item -Storing the new address in @code{*@var{ra-address}}, -if @var{ra-address} is nonnull. -@end itemize - -The default is @option{-mno-mcount-ra-address}. - -@end table - -@node MMIX Options -@subsection MMIX Options -@cindex MMIX Options - -These options are defined for the MMIX: - -@table @gcctabopt -@item -mlibfuncs -@itemx -mno-libfuncs -@opindex mlibfuncs -@opindex mno-libfuncs -Specify that intrinsic library functions are being compiled, passing all -values in registers, no matter the size. - -@item -mepsilon -@itemx -mno-epsilon -@opindex mepsilon -@opindex mno-epsilon -Generate floating-point comparison instructions that compare with respect -to the @code{rE} epsilon register. - -@item -mabi=mmixware -@itemx -mabi=gnu -@opindex mabi=mmixware -@opindex mabi=gnu -Generate code that passes function parameters and return values that (in -the called function) are seen as registers @code{$0} and up, as opposed to -the GNU ABI which uses global registers @code{$231} and up. - -@item -mzero-extend -@itemx -mno-zero-extend -@opindex mzero-extend -@opindex mno-zero-extend -When reading data from memory in sizes shorter than 64 bits, use (do not -use) zero-extending load instructions by default, rather than -sign-extending ones. - -@item -mknuthdiv -@itemx -mno-knuthdiv -@opindex mknuthdiv -@opindex mno-knuthdiv -Make the result of a division yielding a remainder have the same sign as -the divisor. With the default, @option{-mno-knuthdiv}, the sign of the -remainder follows the sign of the dividend. Both methods are -arithmetically valid, the latter being almost exclusively used. - -@item -mtoplevel-symbols -@itemx -mno-toplevel-symbols -@opindex mtoplevel-symbols -@opindex mno-toplevel-symbols -Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly -code can be used with the @code{PREFIX} assembly directive. - -@item -melf -@opindex melf -Generate an executable in the ELF format, rather than the default -@samp{mmo} format used by the @command{mmix} simulator. - -@item -mbranch-predict -@itemx -mno-branch-predict -@opindex mbranch-predict -@opindex mno-branch-predict -Use (do not use) the probable-branch instructions, when static branch -prediction indicates a probable branch. - -@item -mbase-addresses -@itemx -mno-base-addresses -@opindex mbase-addresses -@opindex mno-base-addresses -Generate (do not generate) code that uses @emph{base addresses}. Using a -base address automatically generates a request (handled by the assembler -and the linker) for a constant to be set up in a global register. The -register is used for one or more base address requests within the range 0 -to 255 from the value held in the register. The generally leads to short -and fast code, but the number of different data items that can be -addressed is limited. This means that a program that uses lots of static -data may require @option{-mno-base-addresses}. - -@item -msingle-exit -@itemx -mno-single-exit -@opindex msingle-exit -@opindex mno-single-exit -Force (do not force) generated code to have a single exit point in each -function. -@end table - -@node MN10300 Options -@subsection MN10300 Options -@cindex MN10300 options - -These @option{-m} options are defined for Matsushita MN10300 architectures: - -@table @gcctabopt -@item -mmult-bug -@opindex mmult-bug -Generate code to avoid bugs in the multiply instructions for the MN10300 -processors. This is the default. - -@item -mno-mult-bug -@opindex mno-mult-bug -Do not generate code to avoid bugs in the multiply instructions for the -MN10300 processors. - -@item -mam33 -@opindex mam33 -Generate code using features specific to the AM33 processor. - -@item -mno-am33 -@opindex mno-am33 -Do not generate code using features specific to the AM33 processor. This -is the default. - -@item -mam33-2 -@opindex mam33-2 -Generate code using features specific to the AM33/2.0 processor. - -@item -mam34 -@opindex mam34 -Generate code using features specific to the AM34 processor. - -@item -mtune=@var{cpu-type} -@opindex mtune -Use the timing characteristics of the indicated CPU type when -scheduling instructions. This does not change the targeted processor -type. The CPU type must be one of @samp{mn10300}, @samp{am33}, -@samp{am33-2} or @samp{am34}. - -@item -mreturn-pointer-on-d0 -@opindex mreturn-pointer-on-d0 -When generating a function that returns a pointer, return the pointer -in both @code{a0} and @code{d0}. Otherwise, the pointer is returned -only in @code{a0}, and attempts to call such functions without a prototype -result in errors. Note that this option is on by default; use -@option{-mno-return-pointer-on-d0} to disable it. - -@item -mno-crt0 -@opindex mno-crt0 -Do not link in the C run-time initialization object file. - -@item -mrelax -@opindex mrelax -Indicate to the linker that it should perform a relaxation optimization pass -to shorten branches, calls and absolute memory addresses. This option only -has an effect when used on the command line for the final link step. - -This option makes symbolic debugging impossible. - -@item -mliw -@opindex mliw -Allow the compiler to generate @emph{Long Instruction Word} -instructions if the target is the @samp{AM33} or later. This is the -default. This option defines the preprocessor macro @samp{__LIW__}. - -@item -mnoliw -@opindex mnoliw -Do not allow the compiler to generate @emph{Long Instruction Word} -instructions. This option defines the preprocessor macro -@samp{__NO_LIW__}. - -@item -msetlb -@opindex msetlb -Allow the compiler to generate the @emph{SETLB} and @emph{Lcc} -instructions if the target is the @samp{AM33} or later. This is the -default. This option defines the preprocessor macro @samp{__SETLB__}. - -@item -mnosetlb -@opindex mnosetlb -Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc} -instructions. This option defines the preprocessor macro -@samp{__NO_SETLB__}. - -@end table - -@node Moxie Options -@subsection Moxie Options -@cindex Moxie Options - -@table @gcctabopt - -@item -meb -@opindex meb -Generate big-endian code. This is the default for @samp{moxie-*-*} -configurations. - -@item -mel -@opindex mel -Generate little-endian code. - -@item -mno-crt0 -@opindex mno-crt0 -Do not link in the C run-time initialization object file. - -@end table - -@node PDP-11 Options -@subsection PDP-11 Options -@cindex PDP-11 Options - -These options are defined for the PDP-11: - -@table @gcctabopt -@item -mfpu -@opindex mfpu -Use hardware FPP floating point. This is the default. (FIS floating -point on the PDP-11/40 is not supported.) - -@item -msoft-float -@opindex msoft-float -Do not use hardware floating point. - -@item -mac0 -@opindex mac0 -Return floating-point results in ac0 (fr0 in Unix assembler syntax). - -@item -mno-ac0 -@opindex mno-ac0 -Return floating-point results in memory. This is the default. - -@item -m40 -@opindex m40 -Generate code for a PDP-11/40. - -@item -m45 -@opindex m45 -Generate code for a PDP-11/45. This is the default. - -@item -m10 -@opindex m10 -Generate code for a PDP-11/10. - -@item -mbcopy-builtin -@opindex mbcopy-builtin -Use inline @code{movmemhi} patterns for copying memory. This is the -default. - -@item -mbcopy -@opindex mbcopy -Do not use inline @code{movmemhi} patterns for copying memory. - -@item -mint16 -@itemx -mno-int32 -@opindex mint16 -@opindex mno-int32 -Use 16-bit @code{int}. This is the default. - -@item -mint32 -@itemx -mno-int16 -@opindex mint32 -@opindex mno-int16 -Use 32-bit @code{int}. - -@item -mfloat64 -@itemx -mno-float32 -@opindex mfloat64 -@opindex mno-float32 -Use 64-bit @code{float}. This is the default. - -@item -mfloat32 -@itemx -mno-float64 -@opindex mfloat32 -@opindex mno-float64 -Use 32-bit @code{float}. - -@item -mabshi -@opindex mabshi -Use @code{abshi2} pattern. This is the default. - -@item -mno-abshi -@opindex mno-abshi -Do not use @code{abshi2} pattern. - -@item -mbranch-expensive -@opindex mbranch-expensive -Pretend that branches are expensive. This is for experimenting with -code generation only. - -@item -mbranch-cheap -@opindex mbranch-cheap -Do not pretend that branches are expensive. This is the default. - -@item -munix-asm -@opindex munix-asm -Use Unix assembler syntax. This is the default when configured for -@samp{pdp11-*-bsd}. - -@item -mdec-asm -@opindex mdec-asm -Use DEC assembler syntax. This is the default when configured for any -PDP-11 target other than @samp{pdp11-*-bsd}. -@end table - -@node picoChip Options -@subsection picoChip Options -@cindex picoChip options - -These @samp{-m} options are defined for picoChip implementations: - -@table @gcctabopt - -@item -mae=@var{ae_type} -@opindex mcpu -Set the instruction set, register set, and instruction scheduling -parameters for array element type @var{ae_type}. Supported values -for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}. - -@option{-mae=ANY} selects a completely generic AE type. Code -generated with this option runs on any of the other AE types. The -code is not as efficient as it would be if compiled for a specific -AE type, and some types of operation (e.g., multiplication) do not -work properly on all types of AE. - -@option{-mae=MUL} selects a MUL AE type. This is the most useful AE type -for compiled code, and is the default. - -@option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this -option may suffer from poor performance of byte (char) manipulation, -since the DSP AE does not provide hardware support for byte load/stores. - -@item -msymbol-as-address -Enable the compiler to directly use a symbol name as an address in a -load/store instruction, without first loading it into a -register. Typically, the use of this option generates larger -programs, which run faster than when the option isn't used. However, the -results vary from program to program, so it is left as a user option, -rather than being permanently enabled. - -@item -mno-inefficient-warnings -Disables warnings about the generation of inefficient code. These -warnings can be generated, for example, when compiling code that -performs byte-level memory operations on the MAC AE type. The MAC AE has -no hardware support for byte-level memory operations, so all byte -load/stores must be synthesized from word load/store operations. This is -inefficient and a warning is generated to indicate -that you should rewrite the code to avoid byte operations, or to target -an AE type that has the necessary hardware support. This option disables -these warnings. - -@end table - -@node PowerPC Options -@subsection PowerPC Options -@cindex PowerPC options - -These are listed under @xref{RS/6000 and PowerPC Options}. - -@node RL78 Options -@subsection RL78 Options -@cindex RL78 Options - -@table @gcctabopt - -@item -msim -@opindex msim -Links in additional target libraries to support operation within a -simulator. - -@item -mmul=none -@itemx -mmul=g13 -@itemx -mmul=rl78 -@opindex mmul -Specifies the type of hardware multiplication support to be used. The -default is @code{none}, which uses software multiplication functions. -The @code{g13} option is for the hardware multiply/divide peripheral -only on the RL78/G13 targets. The @code{rl78} option is for the -standard hardware multiplication defined in the RL78 software manual. - -@end table - -@node RS/6000 and PowerPC Options -@subsection IBM RS/6000 and PowerPC Options -@cindex RS/6000 and PowerPC Options -@cindex IBM RS/6000 and PowerPC Options - -These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: -@table @gcctabopt -@item -mpowerpc-gpopt -@itemx -mno-powerpc-gpopt -@itemx -mpowerpc-gfxopt -@itemx -mno-powerpc-gfxopt -@need 800 -@itemx -mpowerpc64 -@itemx -mno-powerpc64 -@itemx -mmfcrf -@itemx -mno-mfcrf -@itemx -mpopcntb -@itemx -mno-popcntb -@itemx -mpopcntd -@itemx -mno-popcntd -@itemx -mfprnd -@itemx -mno-fprnd -@need 800 -@itemx -mcmpb -@itemx -mno-cmpb -@itemx -mmfpgpr -@itemx -mno-mfpgpr -@itemx -mhard-dfp -@itemx -mno-hard-dfp -@opindex mpowerpc-gpopt -@opindex mno-powerpc-gpopt -@opindex mpowerpc-gfxopt -@opindex mno-powerpc-gfxopt -@opindex mpowerpc64 -@opindex mno-powerpc64 -@opindex mmfcrf -@opindex mno-mfcrf -@opindex mpopcntb -@opindex mno-popcntb -@opindex mpopcntd -@opindex mno-popcntd -@opindex mfprnd -@opindex mno-fprnd -@opindex mcmpb -@opindex mno-cmpb -@opindex mmfpgpr -@opindex mno-mfpgpr -@opindex mhard-dfp -@opindex mno-hard-dfp -You use these options to specify which instructions are available on the -processor you are using. The default value of these options is -determined when configuring GCC@. Specifying the -@option{-mcpu=@var{cpu_type}} overrides the specification of these -options. We recommend you use the @option{-mcpu=@var{cpu_type}} option -rather than the options listed above. - -Specifying @option{-mpowerpc-gpopt} allows -GCC to use the optional PowerPC architecture instructions in the -General Purpose group, including floating-point square root. Specifying -@option{-mpowerpc-gfxopt} allows GCC to -use the optional PowerPC architecture instructions in the Graphics -group, including floating-point select. - -The @option{-mmfcrf} option allows GCC to generate the move from -condition register field instruction implemented on the POWER4 -processor and other processors that support the PowerPC V2.01 -architecture. -The @option{-mpopcntb} option allows GCC to generate the popcount and -double-precision FP reciprocal estimate instruction implemented on the -POWER5 processor and other processors that support the PowerPC V2.02 -architecture. -The @option{-mpopcntd} option allows GCC to generate the popcount -instruction implemented on the POWER7 processor and other processors -that support the PowerPC V2.06 architecture. -The @option{-mfprnd} option allows GCC to generate the FP round to -integer instructions implemented on the POWER5+ processor and other -processors that support the PowerPC V2.03 architecture. -The @option{-mcmpb} option allows GCC to generate the compare bytes -instruction implemented on the POWER6 processor and other processors -that support the PowerPC V2.05 architecture. -The @option{-mmfpgpr} option allows GCC to generate the FP move to/from -general-purpose register instructions implemented on the POWER6X -processor and other processors that support the extended PowerPC V2.05 -architecture. -The @option{-mhard-dfp} option allows GCC to generate the decimal -floating-point instructions implemented on some POWER processors. - -The @option{-mpowerpc64} option allows GCC to generate the additional -64-bit instructions that are found in the full PowerPC64 architecture -and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to -@option{-mno-powerpc64}. - -@item -mcpu=@var{cpu_type} -@opindex mcpu -Set architecture type, register usage, and -instruction scheduling parameters for machine type @var{cpu_type}. -Supported values for @var{cpu_type} are @samp{401}, @samp{403}, -@samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp}, -@samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603}, -@samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740}, -@samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823}, -@samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2}, -@samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500}, -@samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5}, -@samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+}, -@samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8}, @samp{powerpc}, -@samp{powerpc64}, and @samp{rs64}. - -@option{-mcpu=powerpc}, and @option{-mcpu=powerpc64} specify pure 32-bit -PowerPC and 64-bit PowerPC architecture machine -types, with an appropriate, generic processor model assumed for -scheduling purposes. - -The other options specify a specific processor. Code generated under -those options runs best on that processor, and may not run at all on -others. - -The @option{-mcpu} options automatically enable or disable the -following options: - -@gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol --mpopcntb -mpopcntd -mpowerpc64 @gol --mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol --msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx} - -The particular options set for any particular CPU varies between -compiler versions, depending on what setting seems to produce optimal -code for that CPU; it doesn't necessarily reflect the actual hardware's -capabilities. If you wish to set an individual option to a particular -value, you may specify it after the @option{-mcpu} option, like -@option{-mcpu=970 -mno-altivec}. - -On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are -not enabled or disabled by the @option{-mcpu} option at present because -AIX does not have full support for these options. You may still -enable or disable them individually if you're sure it'll work in your -environment. - -@item -mtune=@var{cpu_type} -@opindex mtune -Set the instruction scheduling parameters for machine type -@var{cpu_type}, but do not set the architecture type or register usage, -as @option{-mcpu=@var{cpu_type}} does. The same -values for @var{cpu_type} are used for @option{-mtune} as for -@option{-mcpu}. If both are specified, the code generated uses the -architecture and registers set by @option{-mcpu}, but the -scheduling parameters set by @option{-mtune}. - -@item -mcmodel=small -@opindex mcmodel=small -Generate PowerPC64 code for the small model: The TOC is limited to -64k. - -@item -mcmodel=medium -@opindex mcmodel=medium -Generate PowerPC64 code for the medium model: The TOC and other static -data may be up to a total of 4G in size. - -@item -mcmodel=large -@opindex mcmodel=large -Generate PowerPC64 code for the large model: The TOC may be up to 4G -in size. Other data and code is only limited by the 64-bit address -space. - -@item -maltivec -@itemx -mno-altivec -@opindex maltivec -@opindex mno-altivec -Generate code that uses (does not use) AltiVec instructions, and also -enable the use of built-in functions that allow more direct access to -the AltiVec instruction set. You may also need to set -@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI -enhancements. - -@item -mvrsave -@itemx -mno-vrsave -@opindex mvrsave -@opindex mno-vrsave -Generate VRSAVE instructions when generating AltiVec code. - -@item -mgen-cell-microcode -@opindex mgen-cell-microcode -Generate Cell microcode instructions. - -@item -mwarn-cell-microcode -@opindex mwarn-cell-microcode -Warn when a Cell microcode instruction is emitted. An example -of a Cell microcode instruction is a variable shift. - -@item -msecure-plt -@opindex msecure-plt -Generate code that allows @command{ld} and @command{ld.so} -to build executables and shared -libraries with non-executable @code{.plt} and @code{.got} sections. -This is a PowerPC -32-bit SYSV ABI option. - -@item -mbss-plt -@opindex mbss-plt -Generate code that uses a BSS @code{.plt} section that @command{ld.so} -fills in, and -requires @code{.plt} and @code{.got} -sections that are both writable and executable. -This is a PowerPC 32-bit SYSV ABI option. - -@item -misel -@itemx -mno-isel -@opindex misel -@opindex mno-isel -This switch enables or disables the generation of ISEL instructions. - -@item -misel=@var{yes/no} -This switch has been deprecated. Use @option{-misel} and -@option{-mno-isel} instead. - -@item -mspe -@itemx -mno-spe -@opindex mspe -@opindex mno-spe -This switch enables or disables the generation of SPE simd -instructions. - -@item -mpaired -@itemx -mno-paired -@opindex mpaired -@opindex mno-paired -This switch enables or disables the generation of PAIRED simd -instructions. - -@item -mspe=@var{yes/no} -This option has been deprecated. Use @option{-mspe} and -@option{-mno-spe} instead. - -@item -mvsx -@itemx -mno-vsx -@opindex mvsx -@opindex mno-vsx -Generate code that uses (does not use) vector/scalar (VSX) -instructions, and also enable the use of built-in functions that allow -more direct access to the VSX instruction set. - -@item -mfloat-gprs=@var{yes/single/double/no} -@itemx -mfloat-gprs -@opindex mfloat-gprs -This switch enables or disables the generation of floating-point -operations on the general-purpose registers for architectures that -support it. - -The argument @var{yes} or @var{single} enables the use of -single-precision floating-point operations. - -The argument @var{double} enables the use of single and -double-precision floating-point operations. - -The argument @var{no} disables floating-point operations on the -general-purpose registers. - -This option is currently only available on the MPC854x. - -@item -m32 -@itemx -m64 -@opindex m32 -@opindex m64 -Generate code for 32-bit or 64-bit environments of Darwin and SVR4 -targets (including GNU/Linux). The 32-bit environment sets int, long -and pointer to 32 bits and generates code that runs on any PowerPC -variant. The 64-bit environment sets int to 32 bits and long and -pointer to 64 bits, and generates code for PowerPC64, as for -@option{-mpowerpc64}. - -@item -mfull-toc -@itemx -mno-fp-in-toc -@itemx -mno-sum-in-toc -@itemx -mminimal-toc -@opindex mfull-toc -@opindex mno-fp-in-toc -@opindex mno-sum-in-toc -@opindex mminimal-toc -Modify generation of the TOC (Table Of Contents), which is created for -every executable file. The @option{-mfull-toc} option is selected by -default. In that case, GCC allocates at least one TOC entry for -each unique non-automatic variable reference in your program. GCC -also places floating-point constants in the TOC@. However, only -16,384 entries are available in the TOC@. - -If you receive a linker error message that saying you have overflowed -the available TOC space, you can reduce the amount of TOC space used -with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. -@option{-mno-fp-in-toc} prevents GCC from putting floating-point -constants in the TOC and @option{-mno-sum-in-toc} forces GCC to -generate code to calculate the sum of an address and a constant at -run time instead of putting that sum into the TOC@. You may specify one -or both of these options. Each causes GCC to produce very slightly -slower and larger code at the expense of conserving TOC space. - -If you still run out of space in the TOC even when you specify both of -these options, specify @option{-mminimal-toc} instead. This option causes -GCC to make only one TOC entry for every file. When you specify this -option, GCC produces code that is slower and larger but which -uses extremely little TOC space. You may wish to use this option -only on files that contain less frequently-executed code. - -@item -maix64 -@itemx -maix32 -@opindex maix64 -@opindex maix32 -Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit -@code{long} type, and the infrastructure needed to support them. -Specifying @option{-maix64} implies @option{-mpowerpc64}, -while @option{-maix32} disables the 64-bit ABI and -implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. - -@item -mxl-compat -@itemx -mno-xl-compat -@opindex mxl-compat -@opindex mno-xl-compat -Produce code that conforms more closely to IBM XL compiler semantics -when using AIX-compatible ABI@. Pass floating-point arguments to -prototyped functions beyond the register save area (RSA) on the stack -in addition to argument FPRs. Do not assume that most significant -double in 128-bit long double value is properly rounded when comparing -values and converting to double. Use XL symbol names for long double -support routines. - -The AIX calling convention was extended but not initially documented to -handle an obscure K&R C case of calling a function that takes the -address of its arguments with fewer arguments than declared. IBM XL -compilers access floating-point arguments that do not fit in the -RSA from the stack when a subroutine is compiled without -optimization. Because always storing floating-point arguments on the -stack is inefficient and rarely needed, this option is not enabled by -default and only is necessary when calling subroutines compiled by IBM -XL compilers without optimization. - -@item -mpe -@opindex mpe -Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an -application written to use message passing with special startup code to -enable the application to run. The system must have PE installed in the -standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file -must be overridden with the @option{-specs=} option to specify the -appropriate directory location. The Parallel Environment does not -support threads, so the @option{-mpe} option and the @option{-pthread} -option are incompatible. - -@item -malign-natural -@itemx -malign-power -@opindex malign-natural -@opindex malign-power -On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -@option{-malign-natural} overrides the ABI-defined alignment of larger -types, such as floating-point doubles, on their natural size-based boundary. -The option @option{-malign-power} instructs GCC to follow the ABI-specified -alignment rules. GCC defaults to the standard alignment defined in the ABI@. - -On 64-bit Darwin, natural alignment is the default, and @option{-malign-power} -is not supported. - -@item -msoft-float -@itemx -mhard-float -@opindex msoft-float -@opindex mhard-float -Generate code that does not use (uses) the floating-point register set. -Software floating-point emulation is provided if you use the -@option{-msoft-float} option, and pass the option to GCC when linking. - -@item -msingle-float -@itemx -mdouble-float -@opindex msingle-float -@opindex mdouble-float -Generate code for single- or double-precision floating-point operations. -@option{-mdouble-float} implies @option{-msingle-float}. - -@item -msimple-fpu -@opindex msimple-fpu -Do not generate @code{sqrt} and @code{div} instructions for hardware -floating-point unit. - -@item -mfpu=@var{name} -@opindex mfpu -Specify type of floating-point unit. Valid values for @var{name} are -@samp{sp_lite} (equivalent to @option{-msingle-float -msimple-fpu}), -@samp{dp_lite} (equivalent to @option{-mdouble-float -msimple-fpu}), -@samp{sp_full} (equivalent to @option{-msingle-float}), -and @samp{dp_full} (equivalent to @option{-mdouble-float}). - -@item -mxilinx-fpu -@opindex mxilinx-fpu -Perform optimizations for the floating-point unit on Xilinx PPC 405/440. - -@item -mmultiple -@itemx -mno-multiple -@opindex mmultiple -@opindex mno-multiple -Generate code that uses (does not use) the load multiple word -instructions and the store multiple word instructions. These -instructions are generated by default on POWER systems, and not -generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian -PowerPC systems, since those instructions do not work when the -processor is in little-endian mode. The exceptions are PPC740 and -PPC750 which permit these instructions in little-endian mode. - -@item -mstring -@itemx -mno-string -@opindex mstring -@opindex mno-string -Generate code that uses (does not use) the load string instructions -and the store string word instructions to save multiple registers and -do small block moves. These instructions are generated by default on -POWER systems, and not generated on PowerPC systems. Do not use -@option{-mstring} on little-endian PowerPC systems, since those -instructions do not work when the processor is in little-endian mode. -The exceptions are PPC740 and PPC750 which permit these instructions -in little-endian mode. - -@item -mupdate -@itemx -mno-update -@opindex mupdate -@opindex mno-update -Generate code that uses (does not use) the load or store instructions -that update the base register to the address of the calculated memory -location. These instructions are generated by default. If you use -@option{-mno-update}, there is a small window between the time that the -stack pointer is updated and the address of the previous frame is -stored, which means code that walks the stack frame across interrupts or -signals may get corrupted data. - -@item -mavoid-indexed-addresses -@itemx -mno-avoid-indexed-addresses -@opindex mavoid-indexed-addresses -@opindex mno-avoid-indexed-addresses -Generate code that tries to avoid (not avoid) the use of indexed load -or store instructions. These instructions can incur a performance -penalty on Power6 processors in certain situations, such as when -stepping through large arrays that cross a 16M boundary. This option -is enabled by default when targeting Power6 and disabled otherwise. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Generate code that uses (does not use) the floating-point multiply and -accumulate instructions. These instructions are generated by default -if hardware floating point is used. The machine-dependent -@option{-mfused-madd} option is now mapped to the machine-independent -@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is -mapped to @option{-ffp-contract=off}. - -@item -mmulhw -@itemx -mno-mulhw -@opindex mmulhw -@opindex mno-mulhw -Generate code that uses (does not use) the half-word multiply and -multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. -These instructions are generated by default when targeting those -processors. - -@item -mdlmzb -@itemx -mno-dlmzb -@opindex mdlmzb -@opindex mno-dlmzb -Generate code that uses (does not use) the string-search @samp{dlmzb} -instruction on the IBM 405, 440, 464 and 476 processors. This instruction is -generated by default when targeting those processors. - -@item -mno-bit-align -@itemx -mbit-align -@opindex mno-bit-align -@opindex mbit-align -On System V.4 and embedded PowerPC systems do not (do) force structures -and unions that contain bit-fields to be aligned to the base type of the -bit-field. - -For example, by default a structure containing nothing but 8 -@code{unsigned} bit-fields of length 1 is aligned to a 4-byte -boundary and has a size of 4 bytes. By using @option{-mno-bit-align}, -the structure is aligned to a 1-byte boundary and is 1 byte in -size. - -@item -mno-strict-align -@itemx -mstrict-align -@opindex mno-strict-align -@opindex mstrict-align -On System V.4 and embedded PowerPC systems do not (do) assume that -unaligned memory references are handled by the system. - -@item -mrelocatable -@itemx -mno-relocatable -@opindex mrelocatable -@opindex mno-relocatable -Generate code that allows (does not allow) a static executable to be -relocated to a different address at run time. A simple embedded -PowerPC system loader should relocate the entire contents of -@code{.got2} and 4-byte locations listed in the @code{.fixup} section, -a table of 32-bit addresses generated by this option. For this to -work, all objects linked together must be compiled with -@option{-mrelocatable} or @option{-mrelocatable-lib}. -@option{-mrelocatable} code aligns the stack to an 8-byte boundary. - -@item -mrelocatable-lib -@itemx -mno-relocatable-lib -@opindex mrelocatable-lib -@opindex mno-relocatable-lib -Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a -@code{.fixup} section to allow static executables to be relocated at -run time, but @option{-mrelocatable-lib} does not use the smaller stack -alignment of @option{-mrelocatable}. Objects compiled with -@option{-mrelocatable-lib} may be linked with objects compiled with -any combination of the @option{-mrelocatable} options. - -@item -mno-toc -@itemx -mtoc -@opindex mno-toc -@opindex mtoc -On System V.4 and embedded PowerPC systems do not (do) assume that -register 2 contains a pointer to a global area pointing to the addresses -used in the program. - -@item -mlittle -@itemx -mlittle-endian -@opindex mlittle -@opindex mlittle-endian -On System V.4 and embedded PowerPC systems compile code for the -processor in little-endian mode. The @option{-mlittle-endian} option is -the same as @option{-mlittle}. - -@item -mbig -@itemx -mbig-endian -@opindex mbig -@opindex mbig-endian -On System V.4 and embedded PowerPC systems compile code for the -processor in big-endian mode. The @option{-mbig-endian} option is -the same as @option{-mbig}. - -@item -mdynamic-no-pic -@opindex mdynamic-no-pic -On Darwin and Mac OS X systems, compile code so that it is not -relocatable, but that its external references are relocatable. The -resulting code is suitable for applications, but not shared -libraries. - -@item -msingle-pic-base -@opindex msingle-pic-base -Treat the register used for PIC addressing as read-only, rather than -loading it in the prologue for each function. The runtime system is -responsible for initializing this register with an appropriate value -before execution begins. - -@item -mprioritize-restricted-insns=@var{priority} -@opindex mprioritize-restricted-insns -This option controls the priority that is assigned to -dispatch-slot restricted instructions during the second scheduling -pass. The argument @var{priority} takes the value @samp{0}, @samp{1}, -or @samp{2} to assign no, highest, or second-highest (respectively) -priority to dispatch-slot restricted -instructions. - -@item -msched-costly-dep=@var{dependence_type} -@opindex msched-costly-dep -This option controls which dependences are considered costly -by the target during instruction scheduling. The argument -@var{dependence_type} takes one of the following values: - -@table @asis -@item @samp{no} -No dependence is costly. - -@item @samp{all} -All dependences are costly. - -@item @samp{true_store_to_load} -A true dependence from store to load is costly. - -@item @samp{store_to_load} -Any dependence from store to load is costly. - -@item @var{number} -Any dependence for which the latency is greater than or equal to -@var{number} is costly. -@end table - -@item -minsert-sched-nops=@var{scheme} -@opindex minsert-sched-nops -This option controls which NOP insertion scheme is used during -the second scheduling pass. The argument @var{scheme} takes one of the -following values: - -@table @asis -@item @samp{no} -Don't insert NOPs. - -@item @samp{pad} -Pad with NOPs any dispatch group that has vacant issue slots, -according to the scheduler's grouping. - -@item @samp{regroup_exact} -Insert NOPs to force costly dependent insns into -separate groups. Insert exactly as many NOPs as needed to force an insn -to a new group, according to the estimated processor grouping. - -@item @var{number} -Insert NOPs to force costly dependent insns into -separate groups. Insert @var{number} NOPs to force an insn to a new group. -@end table - -@item -mcall-sysv -@opindex mcall-sysv -On System V.4 and embedded PowerPC systems compile code using calling -conventions that adhere to the March 1995 draft of the System V -Application Binary Interface, PowerPC processor supplement. This is the -default unless you configured GCC using @samp{powerpc-*-eabiaix}. - -@item -mcall-sysv-eabi -@itemx -mcall-eabi -@opindex mcall-sysv-eabi -@opindex mcall-eabi -Specify both @option{-mcall-sysv} and @option{-meabi} options. - -@item -mcall-sysv-noeabi -@opindex mcall-sysv-noeabi -Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. - -@item -mcall-aixdesc -@opindex m -On System V.4 and embedded PowerPC systems compile code for the AIX -operating system. - -@item -mcall-linux -@opindex mcall-linux -On System V.4 and embedded PowerPC systems compile code for the -Linux-based GNU system. - -@item -mcall-freebsd -@opindex mcall-freebsd -On System V.4 and embedded PowerPC systems compile code for the -FreeBSD operating system. - -@item -mcall-netbsd -@opindex mcall-netbsd -On System V.4 and embedded PowerPC systems compile code for the -NetBSD operating system. - -@item -mcall-openbsd -@opindex mcall-netbsd -On System V.4 and embedded PowerPC systems compile code for the -OpenBSD operating system. - -@item -maix-struct-return -@opindex maix-struct-return -Return all structures in memory (as specified by the AIX ABI)@. - -@item -msvr4-struct-return -@opindex msvr4-struct-return -Return structures smaller than 8 bytes in registers (as specified by the -SVR4 ABI)@. - -@item -mabi=@var{abi-type} -@opindex mabi -Extend the current ABI with a particular extension, or remove such extension. -Valid values are @var{altivec}, @var{no-altivec}, @var{spe}, -@var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@. - -@item -mabi=spe -@opindex mabi=spe -Extend the current ABI with SPE ABI extensions. This does not change -the default ABI, instead it adds the SPE ABI extensions to the current -ABI@. - -@item -mabi=no-spe -@opindex mabi=no-spe -Disable Book-E SPE ABI extensions for the current ABI@. - -@item -mabi=ibmlongdouble -@opindex mabi=ibmlongdouble -Change the current ABI to use IBM extended-precision long double. -This is a PowerPC 32-bit SYSV ABI option. - -@item -mabi=ieeelongdouble -@opindex mabi=ieeelongdouble -Change the current ABI to use IEEE extended-precision long double. -This is a PowerPC 32-bit Linux ABI option. - -@item -mprototype -@itemx -mno-prototype -@opindex mprototype -@opindex mno-prototype -On System V.4 and embedded PowerPC systems assume that all calls to -variable argument functions are properly prototyped. Otherwise, the -compiler must insert an instruction before every non-prototyped call to -set or clear bit 6 of the condition code register (@var{CR}) to -indicate whether floating-point values are passed in the floating-point -registers in case the function takes variable arguments. With -@option{-mprototype}, only calls to prototyped variable argument functions -set or clear the bit. - -@item -msim -@opindex msim -On embedded PowerPC systems, assume that the startup module is called -@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and -@file{libc.a}. This is the default for @samp{powerpc-*-eabisim} -configurations. - -@item -mmvme -@opindex mmvme -On embedded PowerPC systems, assume that the startup module is called -@file{crt0.o} and the standard C libraries are @file{libmvme.a} and -@file{libc.a}. - -@item -mads -@opindex mads -On embedded PowerPC systems, assume that the startup module is called -@file{crt0.o} and the standard C libraries are @file{libads.a} and -@file{libc.a}. - -@item -myellowknife -@opindex myellowknife -On embedded PowerPC systems, assume that the startup module is called -@file{crt0.o} and the standard C libraries are @file{libyk.a} and -@file{libc.a}. - -@item -mvxworks -@opindex mvxworks -On System V.4 and embedded PowerPC systems, specify that you are -compiling for a VxWorks system. - -@item -memb -@opindex memb -On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags -header to indicate that @samp{eabi} extended relocations are used. - -@item -meabi -@itemx -mno-eabi -@opindex meabi -@opindex mno-eabi -On System V.4 and embedded PowerPC systems do (do not) adhere to the -Embedded Applications Binary Interface (EABI), which is a set of -modifications to the System V.4 specifications. Selecting @option{-meabi} -means that the stack is aligned to an 8-byte boundary, a function -@code{__eabi} is called from @code{main} to set up the EABI -environment, and the @option{-msdata} option can use both @code{r2} and -@code{r13} to point to two separate small data areas. Selecting -@option{-mno-eabi} means that the stack is aligned to a 16-byte boundary, -no EABI initialization function is called from @code{main}, and the -@option{-msdata} option only uses @code{r13} to point to a single -small data area. The @option{-meabi} option is on by default if you -configured GCC using one of the @samp{powerpc*-*-eabi*} options. - -@item -msdata=eabi -@opindex msdata=eabi -On System V.4 and embedded PowerPC systems, put small initialized -@code{const} global and static data in the @samp{.sdata2} section, which -is pointed to by register @code{r2}. Put small initialized -non-@code{const} global and static data in the @samp{.sdata} section, -which is pointed to by register @code{r13}. Put small uninitialized -global and static data in the @samp{.sbss} section, which is adjacent to -the @samp{.sdata} section. The @option{-msdata=eabi} option is -incompatible with the @option{-mrelocatable} option. The -@option{-msdata=eabi} option also sets the @option{-memb} option. - -@item -msdata=sysv -@opindex msdata=sysv -On System V.4 and embedded PowerPC systems, put small global and static -data in the @samp{.sdata} section, which is pointed to by register -@code{r13}. Put small uninitialized global and static data in the -@samp{.sbss} section, which is adjacent to the @samp{.sdata} section. -The @option{-msdata=sysv} option is incompatible with the -@option{-mrelocatable} option. - -@item -msdata=default -@itemx -msdata -@opindex msdata=default -@opindex msdata -On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, -compile code the same as @option{-msdata=eabi}, otherwise compile code the -same as @option{-msdata=sysv}. - -@item -msdata=data -@opindex msdata=data -On System V.4 and embedded PowerPC systems, put small global -data in the @samp{.sdata} section. Put small uninitialized global -data in the @samp{.sbss} section. Do not use register @code{r13} -to address small data however. This is the default behavior unless -other @option{-msdata} options are used. - -@item -msdata=none -@itemx -mno-sdata -@opindex msdata=none -@opindex mno-sdata -On embedded PowerPC systems, put all initialized global and static data -in the @samp{.data} section, and all uninitialized data in the -@samp{.bss} section. - -@item -mblock-move-inline-limit=@var{num} -@opindex mblock-move-inline-limit -Inline all block moves (such as calls to @code{memcpy} or structure -copies) less than or equal to @var{num} bytes. The minimum value for -@var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit -targets. The default value is target-specific. - -@item -G @var{num} -@opindex G -@cindex smaller data references (PowerPC) -@cindex .sdata/.sdata2 references (PowerPC) -On embedded PowerPC systems, put global and static items less than or -equal to @var{num} bytes into the small data or BSS sections instead of -the normal data or BSS section. By default, @var{num} is 8. The -@option{-G @var{num}} switch is also passed to the linker. -All modules should be compiled with the same @option{-G @var{num}} value. - -@item -mregnames -@itemx -mno-regnames -@opindex mregnames -@opindex mno-regnames -On System V.4 and embedded PowerPC systems do (do not) emit register -names in the assembly language output using symbolic forms. - -@item -mlongcall -@itemx -mno-longcall -@opindex mlongcall -@opindex mno-longcall -By default assume that all calls are far away so that a longer and more -expensive calling sequence is required. This is required for calls -farther than 32 megabytes (33,554,432 bytes) from the current location. -A short call is generated if the compiler knows -the call cannot be that far away. This setting can be overridden by -the @code{shortcall} function attribute, or by @code{#pragma -longcall(0)}. - -Some linkers are capable of detecting out-of-range calls and generating -glue code on the fly. On these systems, long calls are unnecessary and -generate slower code. As of this writing, the AIX linker can do this, -as can the GNU linker for PowerPC/64. It is planned to add this feature -to the GNU linker for 32-bit PowerPC systems as well. - -On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr -callee, L42}, plus a @dfn{branch island} (glue code). The two target -addresses represent the callee and the branch island. The -Darwin/PPC linker prefers the first address and generates a @code{bl -callee} if the PPC @code{bl} instruction reaches the callee directly; -otherwise, the linker generates @code{bl L42} to call the branch -island. The branch island is appended to the body of the -calling function; it computes the full 32-bit address of the callee -and jumps to it. - -On Mach-O (Darwin) systems, this option directs the compiler emit to -the glue for every direct call, and the Darwin linker decides whether -to use or discard it. - -In the future, GCC may ignore all longcall specifications -when the linker is known to generate glue. - -@item -mtls-markers -@itemx -mno-tls-markers -@opindex mtls-markers -@opindex mno-tls-markers -Mark (do not mark) calls to @code{__tls_get_addr} with a relocation -specifying the function argument. The relocation allows the linker to -reliably associate function call with argument setup instructions for -TLS optimization, which in turn allows GCC to better schedule the -sequence. - -@item -pthread -@opindex pthread -Adds support for multithreading with the @dfn{pthreads} library. -This option sets flags for both the preprocessor and linker. - -@item -mrecip -@itemx -mno-recip -@opindex mrecip -This option enables use of the reciprocal estimate and -reciprocal square root estimate instructions with additional -Newton-Raphson steps to increase precision instead of doing a divide or -square root and divide for floating-point arguments. You should use -the @option{-ffast-math} option when using @option{-mrecip} (or at -least @option{-funsafe-math-optimizations}, -@option{-finite-math-only}, @option{-freciprocal-math} and -@option{-fno-trapping-math}). Note that while the throughput of the -sequence is generally higher than the throughput of the non-reciprocal -instruction, the precision of the sequence can be decreased by up to 2 -ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square -roots. - -@item -mrecip=@var{opt} -@opindex mrecip=opt -This option controls which reciprocal estimate instructions -may be used. @var{opt} is a comma-separated list of options, which may -be preceded by a @code{!} to invert the option: -@code{all}: enable all estimate instructions, -@code{default}: enable the default instructions, equivalent to @option{-mrecip}, -@code{none}: disable all estimate instructions, equivalent to @option{-mno-recip}; -@code{div}: enable the reciprocal approximation instructions for both single and double precision; -@code{divf}: enable the single-precision reciprocal approximation instructions; -@code{divd}: enable the double-precision reciprocal approximation instructions; -@code{rsqrt}: enable the reciprocal square root approximation instructions for both single and double precision; -@code{rsqrtf}: enable the single-precision reciprocal square root approximation instructions; -@code{rsqrtd}: enable the double-precision reciprocal square root approximation instructions; - -So, for example, @option{-mrecip=all,!rsqrtd} enables -all of the reciprocal estimate instructions, except for the -@code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions -which handle the double-precision reciprocal square root calculations. - -@item -mrecip-precision -@itemx -mno-recip-precision -@opindex mrecip-precision -Assume (do not assume) that the reciprocal estimate instructions -provide higher-precision estimates than is mandated by the PowerPC -ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or -@option{-mcpu=power8} automatically selects @option{-mrecip-precision}. -The double-precision square root estimate instructions are not generated by -default on low-precision machines, since they do not provide an -estimate that converges after three steps. - -@item -mveclibabi=@var{type} -@opindex mveclibabi -Specifies the ABI type to use for vectorizing intrinsics using an -external library. The only type supported at present is @code{mass}, -which specifies to use IBM's Mathematical Acceleration Subsystem -(MASS) libraries for vectorizing intrinsics using external libraries. -GCC currently emits calls to @code{acosd2}, @code{acosf4}, -@code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4}, -@code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4}, -@code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4}, -@code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4}, -@code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4}, -@code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4}, -@code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4}, -@code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4}, -@code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4}, -@code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4}, -@code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2}, -@code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2}, -@code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code -for power7. Both @option{-ftree-vectorize} and -@option{-funsafe-math-optimizations} must also be enabled. The MASS -libraries must be specified at link time. - -@item -mfriz -@itemx -mno-friz -@opindex mfriz -Generate (do not generate) the @code{friz} instruction when the -@option{-funsafe-math-optimizations} option is used to optimize -rounding of floating-point values to 64-bit integer and back to floating -point. The @code{friz} instruction does not return the same value if -the floating-point number is too large to fit in an integer. - -@item -mpointers-to-nested-functions -@itemx -mno-pointers-to-nested-functions -@opindex mpointers-to-nested-functions -Generate (do not generate) code to load up the static chain register -(@var{r11}) when calling through a pointer on AIX and 64-bit Linux -systems where a function pointer points to a 3-word descriptor giving -the function address, TOC value to be loaded in register @var{r2}, and -static chain value to be loaded in register @var{r11}. The -@option{-mpointers-to-nested-functions} is on by default. You cannot -call through pointers to nested functions or pointers -to functions compiled in other languages that use the static chain if -you use the @option{-mno-pointers-to-nested-functions}. - -@item -msave-toc-indirect -@itemx -mno-save-toc-indirect -@opindex msave-toc-indirect -Generate (do not generate) code to save the TOC value in the reserved -stack location in the function prologue if the function calls through -a pointer on AIX and 64-bit Linux systems. If the TOC value is not -saved in the prologue, it is saved just before the call through the -pointer. The @option{-mno-save-toc-indirect} option is the default. -@end table - -@node RX Options -@subsection RX Options -@cindex RX Options - -These command-line options are defined for RX targets: - -@table @gcctabopt -@item -m64bit-doubles -@itemx -m32bit-doubles -@opindex m64bit-doubles -@opindex m32bit-doubles -Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) -or 32 bits (@option{-m32bit-doubles}) in size. The default is -@option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only -works on 32-bit values, which is why the default is -@option{-m32bit-doubles}. - -@item -fpu -@itemx -nofpu -@opindex fpu -@opindex nofpu -Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX -floating-point hardware. The default is enabled for the @var{RX600} -series and disabled for the @var{RX200} series. - -Floating-point instructions are only generated for 32-bit floating-point -values, however, so the FPU hardware is not used for doubles if the -@option{-m64bit-doubles} option is used. - -@emph{Note} If the @option{-fpu} option is enabled then -@option{-funsafe-math-optimizations} is also enabled automatically. -This is because the RX FPU instructions are themselves unsafe. - -@item -mcpu=@var{name} -@opindex -mcpu -Selects the type of RX CPU to be targeted. Currently three types are -supported, the generic @var{RX600} and @var{RX200} series hardware and -the specific @var{RX610} CPU. The default is @var{RX600}. - -The only difference between @var{RX600} and @var{RX610} is that the -@var{RX610} does not support the @code{MVTIPL} instruction. - -The @var{RX200} series does not have a hardware floating-point unit -and so @option{-nofpu} is enabled by default when this type is -selected. - -@item -mbig-endian-data -@itemx -mlittle-endian-data -@opindex mbig-endian-data -@opindex mlittle-endian-data -Store data (but not code) in the big-endian format. The default is -@option{-mlittle-endian-data}, i.e.@: to store data in the little-endian -format. - -@item -msmall-data-limit=@var{N} -@opindex msmall-data-limit -Specifies the maximum size in bytes of global and static variables -which can be placed into the small data area. Using the small data -area can lead to smaller and faster code, but the size of area is -limited and it is up to the programmer to ensure that the area does -not overflow. Also when the small data area is used one of the RX's -registers (usually @code{r13}) is reserved for use pointing to this -area, so it is no longer available for use by the compiler. This -could result in slower and/or larger code if variables are pushed onto -the stack instead of being held in this register. - -Note, common variables (variables that have not been initialized) and -constants are not placed into the small data area as they are assigned -to other sections in the output executable. - -The default value is zero, which disables this feature. Note, this -feature is not enabled by default with higher optimization levels -(@option{-O2} etc) because of the potentially detrimental effects of -reserving a register. It is up to the programmer to experiment and -discover whether this feature is of benefit to their program. See the -description of the @option{-mpid} option for a description of how the -actual register to hold the small data area pointer is chosen. - -@item -msim -@itemx -mno-sim -@opindex msim -@opindex mno-sim -Use the simulator runtime. The default is to use the libgloss -board-specific runtime. - -@item -mas100-syntax -@itemx -mno-as100-syntax -@opindex mas100-syntax -@opindex mno-as100-syntax -When generating assembler output use a syntax that is compatible with -Renesas's AS100 assembler. This syntax can also be handled by the GAS -assembler, but it has some restrictions so it is not generated by default. - -@item -mmax-constant-size=@var{N} -@opindex mmax-constant-size -Specifies the maximum size, in bytes, of a constant that can be used as -an operand in a RX instruction. Although the RX instruction set does -allow constants of up to 4 bytes in length to be used in instructions, -a longer value equates to a longer instruction. Thus in some -circumstances it can be beneficial to restrict the size of constants -that are used in instructions. Constants that are too big are instead -placed into a constant pool and referenced via register indirection. - -The value @var{N} can be between 0 and 4. A value of 0 (the default) -or 4 means that constants of any size are allowed. - -@item -mrelax -@opindex mrelax -Enable linker relaxation. Linker relaxation is a process whereby the -linker attempts to reduce the size of a program by finding shorter -versions of various instructions. Disabled by default. - -@item -mint-register=@var{N} -@opindex mint-register -Specify the number of registers to reserve for fast interrupt handler -functions. The value @var{N} can be between 0 and 4. A value of 1 -means that register @code{r13} is reserved for the exclusive use -of fast interrupt handlers. A value of 2 reserves @code{r13} and -@code{r12}. A value of 3 reserves @code{r13}, @code{r12} and -@code{r11}, and a value of 4 reserves @code{r13} through @code{r10}. -A value of 0, the default, does not reserve any registers. - -@item -msave-acc-in-interrupts -@opindex msave-acc-in-interrupts -Specifies that interrupt handler functions should preserve the -accumulator register. This is only necessary if normal code might use -the accumulator register, for example because it performs 64-bit -multiplications. The default is to ignore the accumulator as this -makes the interrupt handlers faster. - -@item -mpid -@itemx -mno-pid -@opindex mpid -@opindex mno-pid -Enables the generation of position independent data. When enabled any -access to constant data is done via an offset from a base address -held in a register. This allows the location of constant data to be -determined at run time without requiring the executable to be -relocated, which is a benefit to embedded applications with tight -memory constraints. Data that can be modified is not affected by this -option. - -Note, using this feature reserves a register, usually @code{r13}, for -the constant data base address. This can result in slower and/or -larger code, especially in complicated functions. - -The actual register chosen to hold the constant data base address -depends upon whether the @option{-msmall-data-limit} and/or the -@option{-mint-register} command-line options are enabled. Starting -with register @code{r13} and proceeding downwards, registers are -allocated first to satisfy the requirements of @option{-mint-register}, -then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it -is possible for the small data area register to be @code{r8} if both -@option{-mint-register=4} and @option{-mpid} are specified on the -command line. - -By default this feature is not enabled. The default can be restored -via the @option{-mno-pid} command-line option. - -@item -mno-warn-multiple-fast-interrupts -@itemx -mwarn-multiple-fast-interrupts -@opindex mno-warn-multiple-fast-interrupts -@opindex mwarn-multiple-fast-interrupts -Prevents GCC from issuing a warning message if it finds more than one -fast interrupt handler when it is compiling a file. The default is to -issue a warning for each extra fast interrupt handler found, as the RX -only supports one such interrupt. - -@end table - -@emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}} -has special significance to the RX port when used with the -@code{interrupt} function attribute. This attribute indicates a -function intended to process fast interrupts. GCC ensures -that it only uses the registers @code{r10}, @code{r11}, @code{r12} -and/or @code{r13} and only provided that the normal use of the -corresponding registers have been restricted via the -@option{-ffixed-@var{reg}} or @option{-mint-register} command-line -options. - -@node S/390 and zSeries Options -@subsection S/390 and zSeries Options -@cindex S/390 and zSeries Options - -These are the @samp{-m} options defined for the S/390 and zSeries architecture. - -@table @gcctabopt -@item -mhard-float -@itemx -msoft-float -@opindex mhard-float -@opindex msoft-float -Use (do not use) the hardware floating-point instructions and registers -for floating-point operations. When @option{-msoft-float} is specified, -functions in @file{libgcc.a} are used to perform floating-point -operations. When @option{-mhard-float} is specified, the compiler -generates IEEE floating-point instructions. This is the default. - -@item -mhard-dfp -@itemx -mno-hard-dfp -@opindex mhard-dfp -@opindex mno-hard-dfp -Use (do not use) the hardware decimal-floating-point instructions for -decimal-floating-point operations. When @option{-mno-hard-dfp} is -specified, functions in @file{libgcc.a} are used to perform -decimal-floating-point operations. When @option{-mhard-dfp} is -specified, the compiler generates decimal-floating-point hardware -instructions. This is the default for @option{-march=z9-ec} or higher. - -@item -mlong-double-64 -@itemx -mlong-double-128 -@opindex mlong-double-64 -@opindex mlong-double-128 -These switches control the size of @code{long double} type. A size -of 64 bits makes the @code{long double} type equivalent to the @code{double} -type. This is the default. - -@item -mbackchain -@itemx -mno-backchain -@opindex mbackchain -@opindex mno-backchain -Store (do not store) the address of the caller's frame as backchain pointer -into the callee's stack frame. -A backchain may be needed to allow debugging using tools that do not understand -DWARF 2 call frame information. -When @option{-mno-packed-stack} is in effect, the backchain pointer is stored -at the bottom of the stack frame; when @option{-mpacked-stack} is in effect, -the backchain is placed into the topmost word of the 96/160 byte register -save area. - -In general, code compiled with @option{-mbackchain} is call-compatible with -code compiled with @option{-mmo-backchain}; however, use of the backchain -for debugging purposes usually requires that the whole binary is built with -@option{-mbackchain}. Note that the combination of @option{-mbackchain}, -@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order -to build a linux kernel use @option{-msoft-float}. - -The default is to not maintain the backchain. - -@item -mpacked-stack -@itemx -mno-packed-stack -@opindex mpacked-stack -@opindex mno-packed-stack -Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is -specified, the compiler uses the all fields of the 96/160 byte register save -area only for their default purpose; unused fields still take up stack space. -When @option{-mpacked-stack} is specified, register save slots are densely -packed at the top of the register save area; unused space is reused for other -purposes, allowing for more efficient use of the available stack space. -However, when @option{-mbackchain} is also in effect, the topmost word of -the save area is always used to store the backchain, and the return address -register is always saved two words below the backchain. - -As long as the stack frame backchain is not used, code generated with -@option{-mpacked-stack} is call-compatible with code generated with -@option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for -S/390 or zSeries generated code that uses the stack frame backchain at run -time, not just for debugging purposes. Such code is not call-compatible -with code compiled with @option{-mpacked-stack}. Also, note that the -combination of @option{-mbackchain}, -@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order -to build a linux kernel use @option{-msoft-float}. - -The default is to not use the packed stack layout. - -@item -msmall-exec -@itemx -mno-small-exec -@opindex msmall-exec -@opindex mno-small-exec -Generate (or do not generate) code using the @code{bras} instruction -to do subroutine calls. -This only works reliably if the total executable size does not -exceed 64k. The default is to use the @code{basr} instruction instead, -which does not have this limitation. - -@item -m64 -@itemx -m31 -@opindex m64 -@opindex m31 -When @option{-m31} is specified, generate code compliant to the -GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate -code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in -particular to generate 64-bit instructions. For the @samp{s390} -targets, the default is @option{-m31}, while the @samp{s390x} -targets default to @option{-m64}. - -@item -mzarch -@itemx -mesa -@opindex mzarch -@opindex mesa -When @option{-mzarch} is specified, generate code using the -instructions available on z/Architecture. -When @option{-mesa} is specified, generate code using the -instructions available on ESA/390. Note that @option{-mesa} is -not possible with @option{-m64}. -When generating code compliant to the GNU/Linux for S/390 ABI, -the default is @option{-mesa}. When generating code compliant -to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}. - -@item -mmvcle -@itemx -mno-mvcle -@opindex mmvcle -@opindex mno-mvcle -Generate (or do not generate) code using the @code{mvcle} instruction -to perform block moves. When @option{-mno-mvcle} is specified, -use a @code{mvc} loop instead. This is the default unless optimizing for -size. - -@item -mdebug -@itemx -mno-debug -@opindex mdebug -@opindex mno-debug -Print (or do not print) additional debug information when compiling. -The default is to not print debug information. - -@item -march=@var{cpu-type} -@opindex march -Generate code that runs on @var{cpu-type}, which is the name of a system -representing a certain processor type. Possible values for -@var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990}, -@samp{z9-109}, @samp{z9-ec} and @samp{z10}. -When generating code using the instructions available on z/Architecture, -the default is @option{-march=z900}. Otherwise, the default is -@option{-march=g5}. - -@item -mtune=@var{cpu-type} -@opindex mtune -Tune to @var{cpu-type} everything applicable about the generated code, -except for the ABI and the set of available instructions. -The list of @var{cpu-type} values is the same as for @option{-march}. -The default is the value used for @option{-march}. - -@item -mtpf-trace -@itemx -mno-tpf-trace -@opindex mtpf-trace -@opindex mno-tpf-trace -Generate code that adds (does not add) in TPF OS specific branches to trace -routines in the operating system. This option is off by default, even -when compiling for the TPF OS@. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Generate code that uses (does not use) the floating-point multiply and -accumulate instructions. These instructions are generated by default if -hardware floating point is used. - -@item -mwarn-framesize=@var{framesize} -@opindex mwarn-framesize -Emit a warning if the current function exceeds the given frame size. Because -this is a compile-time check it doesn't need to be a real problem when the program -runs. It is intended to identify functions that most probably cause -a stack overflow. It is useful to be used in an environment with limited stack -size e.g.@: the linux kernel. - -@item -mwarn-dynamicstack -@opindex mwarn-dynamicstack -Emit a warning if the function calls @code{alloca} or uses dynamically-sized -arrays. This is generally a bad idea with a limited stack size. - -@item -mstack-guard=@var{stack-guard} -@itemx -mstack-size=@var{stack-size} -@opindex mstack-guard -@opindex mstack-size -If these options are provided the S/390 back end emits additional instructions in -the function prologue that trigger a trap if the stack size is @var{stack-guard} -bytes above the @var{stack-size} (remember that the stack on S/390 grows downward). -If the @var{stack-guard} option is omitted the smallest power of 2 larger than -the frame size of the compiled function is chosen. -These options are intended to be used to help debugging stack overflow problems. -The additionally emitted code causes only little overhead and hence can also be -used in production-like systems without greater performance degradation. The given -values have to be exact powers of 2 and @var{stack-size} has to be greater than -@var{stack-guard} without exceeding 64k. -In order to be efficient the extra code makes the assumption that the stack starts -at an address aligned to the value given by @var{stack-size}. -The @var{stack-guard} option can only be used in conjunction with @var{stack-size}. -@end table - -@node Score Options -@subsection Score Options -@cindex Score Options - -These options are defined for Score implementations: - -@table @gcctabopt -@item -meb -@opindex meb -Compile code for big-endian mode. This is the default. - -@item -mel -@opindex mel -Compile code for little-endian mode. - -@item -mnhwloop -@opindex mnhwloop -Disable generation of @code{bcnz} instructions. - -@item -muls -@opindex muls -Enable generation of unaligned load and store instructions. - -@item -mmac -@opindex mmac -Enable the use of multiply-accumulate instructions. Disabled by default. - -@item -mscore5 -@opindex mscore5 -Specify the SCORE5 as the target architecture. - -@item -mscore5u -@opindex mscore5u -Specify the SCORE5U of the target architecture. - -@item -mscore7 -@opindex mscore7 -Specify the SCORE7 as the target architecture. This is the default. - -@item -mscore7d -@opindex mscore7d -Specify the SCORE7D as the target architecture. -@end table - -@node SH Options -@subsection SH Options - -These @samp{-m} options are defined for the SH implementations: - -@table @gcctabopt -@item -m1 -@opindex m1 -Generate code for the SH1. - -@item -m2 -@opindex m2 -Generate code for the SH2. - -@item -m2e -Generate code for the SH2e. - -@item -m2a-nofpu -@opindex m2a-nofpu -Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way -that the floating-point unit is not used. - -@item -m2a-single-only -@opindex m2a-single-only -Generate code for the SH2a-FPU, in such a way that no double-precision -floating-point operations are used. - -@item -m2a-single -@opindex m2a-single -Generate code for the SH2a-FPU assuming the floating-point unit is in -single-precision mode by default. - -@item -m2a -@opindex m2a -Generate code for the SH2a-FPU assuming the floating-point unit is in -double-precision mode by default. - -@item -m3 -@opindex m3 -Generate code for the SH3. - -@item -m3e -@opindex m3e -Generate code for the SH3e. - -@item -m4-nofpu -@opindex m4-nofpu -Generate code for the SH4 without a floating-point unit. - -@item -m4-single-only -@opindex m4-single-only -Generate code for the SH4 with a floating-point unit that only -supports single-precision arithmetic. - -@item -m4-single -@opindex m4-single -Generate code for the SH4 assuming the floating-point unit is in -single-precision mode by default. - -@item -m4 -@opindex m4 -Generate code for the SH4. - -@item -m4a-nofpu -@opindex m4a-nofpu -Generate code for the SH4al-dsp, or for a SH4a in such a way that the -floating-point unit is not used. - -@item -m4a-single-only -@opindex m4a-single-only -Generate code for the SH4a, in such a way that no double-precision -floating-point operations are used. - -@item -m4a-single -@opindex m4a-single -Generate code for the SH4a assuming the floating-point unit is in -single-precision mode by default. - -@item -m4a -@opindex m4a -Generate code for the SH4a. - -@item -m4al -@opindex m4al -Same as @option{-m4a-nofpu}, except that it implicitly passes -@option{-dsp} to the assembler. GCC doesn't generate any DSP -instructions at the moment. - -@item -mb -@opindex mb -Compile code for the processor in big-endian mode. - -@item -ml -@opindex ml -Compile code for the processor in little-endian mode. - -@item -mdalign -@opindex mdalign -Align doubles at 64-bit boundaries. Note that this changes the calling -conventions, and thus some functions from the standard C library do -not work unless you recompile it first with @option{-mdalign}. - -@item -mrelax -@opindex mrelax -Shorten some address references at link time, when possible; uses the -linker option @option{-relax}. - -@item -mbigtable -@opindex mbigtable -Use 32-bit offsets in @code{switch} tables. The default is to use -16-bit offsets. - -@item -mbitops -@opindex mbitops -Enable the use of bit manipulation instructions on SH2A. - -@item -mfmovd -@opindex mfmovd -Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for -alignment constraints. - -@item -mhitachi -@opindex mhitachi -Comply with the calling conventions defined by Renesas. - -@item -mrenesas -@opindex mhitachi -Comply with the calling conventions defined by Renesas. - -@item -mno-renesas -@opindex mhitachi -Comply with the calling conventions defined for GCC before the Renesas -conventions were available. This option is the default for all -targets of the SH toolchain. - -@item -mnomacsave -@opindex mnomacsave -Mark the @code{MAC} register as call-clobbered, even if -@option{-mhitachi} is given. - -@item -mieee -@itemx -mno-ieee -@opindex mieee -@opindex mnoieee -Control the IEEE compliance of floating-point comparisons, which affects the -handling of cases where the result of a comparison is unordered. By default -@option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is -enabled @option{-mno-ieee} is implicitly set, which results in faster -floating-point greater-equal and less-equal comparisons. The implcit settings -can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}. - -@item -minline-ic_invalidate -@opindex minline-ic_invalidate -Inline code to invalidate instruction cache entries after setting up -nested function trampolines. -This option has no effect if @option{-musermode} is in effect and the selected -code generation option (e.g. @option{-m4}) does not allow the use of the @code{icbi} -instruction. -If the selected code generation option does not allow the use of the @code{icbi} -instruction, and @option{-musermode} is not in effect, the inlined code -manipulates the instruction cache address array directly with an associative -write. This not only requires privileged mode at run time, but it also -fails if the cache line had been mapped via the TLB and has become unmapped. - -@item -misize -@opindex misize -Dump instruction size and location in the assembly code. - -@item -mpadstruct -@opindex mpadstruct -This option is deprecated. It pads structures to multiple of 4 bytes, -which is incompatible with the SH ABI@. - -@item -matomic-model=@var{model} -@opindex matomic-model=@var{model} -Sets the model of atomic operations and additional parameters as a comma -separated list. For details on the atomic built-in functions see -@ref{__atomic Builtins}. The following models and parameters are supported: - -@table @samp - -@item none -Disable compiler generated atomic sequences and emit library calls for atomic -operations. This is the default if the target is not @code{sh-*-linux*}. - -@item soft-gusa -Generate GNU/Linux compatible gUSA software atomic sequences for the atomic -built-in functions. The generated atomic sequences require additional support -from the interrupt/exception handling code of the system and are only suitable -for SH3* and SH4* single-core systems. This option is enabled by default when -the target is @code{sh-*-linux*} and SH3* or SH4*. When the target is SH4A, -this option will also partially utilize the hardware atomic instructions -@code{movli.l} and @code{movco.l} to create more efficient code, unless -@samp{strict} is specified. - -@item soft-tcb -Generate software atomic sequences that use a variable in the thread control -block. This is a variation of the gUSA sequences which can also be used on -SH1* and SH2* targets. The generated atomic sequences require additional -support from the interrupt/exception handling code of the system and are only -suitable for single-core systems. When using this model, the @samp{gbr-offset=} -parameter has to be specified as well. - -@item soft-imask -Generate software atomic sequences that temporarily disable interrupts by -setting @code{SR.IMASK = 1111}. This model works only when the program runs -in privileged mode and is only suitable for single-core systems. Additional -support from the interrupt/exception handling code of the system is not -required. This model is enabled by default when the target is -@code{sh-*-linux*} and SH1* or SH2*. - -@item hard-llcs -Generate hardware atomic sequences using the @code{movli.l} and @code{movco.l} -instructions only. This is only available on SH4A and is suitable for -multi-core systems. Since the hardware instructions support only 32 bit atomic -variables access to 8 or 16 bit variables is emulated with 32 bit accesses. -Code compiled with this option will also be compatible with other software -atomic model interrupt/exception handling systems if executed on an SH4A -system. Additional support from the interrupt/exception handling code of the -system is not required for this model. - -@item gbr-offset= -This parameter specifies the offset in bytes of the variable in the thread -control block structure that should be used by the generated atomic sequences -when the @samp{soft-tcb} model has been selected. For other models this -parameter is ignored. The specified value must be an integer multiple of four -and in the range 0-1020. - -@item strict -This parameter prevents mixed usage of multiple atomic models, even though they -would be compatible, and will make the compiler generate atomic sequences of the -specified model only. - -@end table - -@item -mtas -@opindex mtas -Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}. -Notice that depending on the particular hardware and software configuration -this can degrade overall performance due to the operand cache line flushes -that are implied by the @code{tas.b} instruction. On multi-core SH4A -processors the @code{tas.b} instruction must be used with caution since it -can result in data corruption for certain cache configurations. - -@item -mspace -@opindex mspace -Optimize for space instead of speed. Implied by @option{-Os}. - -@item -mprefergot -@opindex mprefergot -When generating position-independent code, emit function calls using -the Global Offset Table instead of the Procedure Linkage Table. - -@item -musermode -@opindex musermode -Don't generate privileged mode only code. This option -implies @option{-mno-inline-ic_invalidate} -if the inlined code would not work in user mode. -This is the default when the target is @code{sh-*-linux*}. - -@item -multcost=@var{number} -@opindex multcost=@var{number} -Set the cost to assume for a multiply insn. - -@item -mdiv=@var{strategy} -@opindex mdiv=@var{strategy} -Set the division strategy to be used for integer division operations. -For SHmedia @var{strategy} can be one of: - -@table @samp - -@item fp -Performs the operation in floating point. This has a very high latency, -but needs only a few instructions, so it might be a good choice if -your code has enough easily-exploitable ILP to allow the compiler to -schedule the floating-point instructions together with other instructions. -Division by zero causes a floating-point exception. - -@item inv -Uses integer operations to calculate the inverse of the divisor, -and then multiplies the dividend with the inverse. This strategy allows -CSE and hoisting of the inverse calculation. Division by zero calculates -an unspecified result, but does not trap. - -@item inv:minlat -A variant of @samp{inv} where, if no CSE or hoisting opportunities -have been found, or if the entire operation has been hoisted to the same -place, the last stages of the inverse calculation are intertwined with the -final multiply to reduce the overall latency, at the expense of using a few -more instructions, and thus offering fewer scheduling opportunities with -other code. - -@item call -Calls a library function that usually implements the @samp{inv:minlat} -strategy. -This gives high code density for @code{m5-*media-nofpu} compilations. - -@item call2 -Uses a different entry point of the same library function, where it -assumes that a pointer to a lookup table has already been set up, which -exposes the pointer load to CSE and code hoisting optimizations. - -@item inv:call -@itemx inv:call2 -@itemx inv:fp -Use the @samp{inv} algorithm for initial -code generation, but if the code stays unoptimized, revert to the @samp{call}, -@samp{call2}, or @samp{fp} strategies, respectively. Note that the -potentially-trapping side effect of division by zero is carried by a -separate instruction, so it is possible that all the integer instructions -are hoisted out, but the marker for the side effect stays where it is. -A recombination to floating-point operations or a call is not possible -in that case. - -@item inv20u -@itemx inv20l -Variants of the @samp{inv:minlat} strategy. In the case -that the inverse calculation is not separated from the multiply, they speed -up division where the dividend fits into 20 bits (plus sign where applicable) -by inserting a test to skip a number of operations in this case; this test -slows down the case of larger dividends. @samp{inv20u} assumes the case of a such -a small dividend to be unlikely, and @samp{inv20l} assumes it to be likely. - -@end table - -For targets other than SHmedia @var{strategy} can be one of: - -@table @samp - -@item call-div1 -Calls a library function that uses the single-step division instruction -@code{div1} to perform the operation. Division by zero calculates an -unspecified result and does not trap. This is the default except for SH4, -SH2A and SHcompact. - -@item call-fp -Calls a library function that performs the operation in double precision -floating point. Division by zero causes a floating-point exception. This is -the default for SHcompact with FPU. Specifying this for targets that do not -have a double precision FPU will default to @code{call-div1}. - -@item call-table -Calls a library function that uses a lookup table for small divisors and -the @code{div1} instruction with case distinction for larger divisors. Division -by zero calculates an unspecified result and does not trap. This is the default -for SH4. Specifying this for targets that do not have dynamic shift -instructions will default to @code{call-div1}. - -@end table - -When a division strategy has not been specified the default strategy will be -selected based on the current target. For SH2A the default strategy is to -use the @code{divs} and @code{divu} instructions instead of library function -calls. - -@item -maccumulate-outgoing-args -@opindex maccumulate-outgoing-args -Reserve space once for outgoing arguments in the function prologue rather -than around each call. Generally beneficial for performance and size. Also -needed for unwinding to avoid changing the stack frame around conditional code. - -@item -mdivsi3_libfunc=@var{name} -@opindex mdivsi3_libfunc=@var{name} -Set the name of the library function used for 32-bit signed division to -@var{name}. -This only affects the name used in the @samp{call} and @samp{inv:call} -division strategies, and the compiler still expects the same -sets of input/output/clobbered registers as if this option were not present. - -@item -mfixed-range=@var{register-range} -@opindex mfixed-range -Generate code treating the given register range as fixed registers. -A fixed register is one that the register allocator can not use. This is -useful when compiling kernel code. A register range is specified as -two registers separated by a dash. Multiple register ranges can be -specified separated by a comma. - -@item -mindexed-addressing -@opindex mindexed-addressing -Enable the use of the indexed addressing mode for SHmedia32/SHcompact. -This is only safe if the hardware and/or OS implement 32-bit wrap-around -semantics for the indexed addressing mode. The architecture allows the -implementation of processors with 64-bit MMU, which the OS could use to -get 32-bit addressing, but since no current hardware implementation supports -this or any other way to make the indexed addressing mode safe to use in -the 32-bit ABI, the default is @option{-mno-indexed-addressing}. - -@item -mgettrcost=@var{number} -@opindex mgettrcost=@var{number} -Set the cost assumed for the @code{gettr} instruction to @var{number}. -The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise. - -@item -mpt-fixed -@opindex mpt-fixed -Assume @code{pt*} instructions won't trap. This generally generates -better-scheduled code, but is unsafe on current hardware. -The current architecture -definition says that @code{ptabs} and @code{ptrel} trap when the target -anded with 3 is 3. -This has the unintentional effect of making it unsafe to schedule these -instructions before a branch, or hoist them out of a loop. For example, -@code{__do_global_ctors}, a part of @file{libgcc} -that runs constructors at program -startup, calls functions in a list which is delimited by @minus{}1. With the -@option{-mpt-fixed} option, the @code{ptabs} is done before testing against @minus{}1. -That means that all the constructors run a bit more quickly, but when -the loop comes to the end of the list, the program crashes because @code{ptabs} -loads @minus{}1 into a target register. - -Since this option is unsafe for any -hardware implementing the current architecture specification, the default -is @option{-mno-pt-fixed}. Unless specified explicitly with -@option{-mgettrcost}, @option{-mno-pt-fixed} also implies @option{-mgettrcost=100}; -this deters register allocation from using target registers for storing -ordinary integers. - -@item -minvalid-symbols -@opindex minvalid-symbols -Assume symbols might be invalid. Ordinary function symbols generated by -the compiler are always valid to load with -@code{movi}/@code{shori}/@code{ptabs} or -@code{movi}/@code{shori}/@code{ptrel}, -but with assembler and/or linker tricks it is possible -to generate symbols that cause @code{ptabs} or @code{ptrel} to trap. -This option is only meaningful when @option{-mno-pt-fixed} is in effect. -It prevents cross-basic-block CSE, hoisting and most scheduling -of symbol loads. The default is @option{-mno-invalid-symbols}. - -@item -mbranch-cost=@var{num} -@opindex mbranch-cost=@var{num} -Assume @var{num} to be the cost for a branch instruction. Higher numbers -make the compiler try to generate more branch-free code if possible. -If not specified the value is selected depending on the processor type that -is being compiled for. - -@item -mzdcbranch -@itemx -mno-zdcbranch -@opindex mzdcbranch -@opindex mno-zdcbranch -Assume (do not assume) that zero displacement conditional branch instructions -@code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the -compiler will try to prefer zero displacement branch code sequences. This is -enabled by default when generating code for SH4 and SH4A. It can be explicitly -disabled by specifying @option{-mno-zdcbranch}. - -@item -mcbranchdi -@opindex mcbranchdi -Enable the @code{cbranchdi4} instruction pattern. - -@item -mcmpeqdi -@opindex mcmpeqdi -Emit the @code{cmpeqdi_t} instruction pattern even when @option{-mcbranchdi} -is in effect. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Generate code that uses (does not use) the floating-point multiply and -accumulate instructions. These instructions are generated by default -if hardware floating point is used. The machine-dependent -@option{-mfused-madd} option is now mapped to the machine-independent -@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is -mapped to @option{-ffp-contract=off}. - -@item -mfsca -@itemx -mno-fsca -@opindex mfsca -@opindex mno-fsca -Allow or disallow the compiler to emit the @code{fsca} instruction for sine -and cosine approximations. The option @code{-mfsca} must be used in -combination with @code{-funsafe-math-optimizations}. It is enabled by default -when generating code for SH4A. Using @code{-mno-fsca} disables sine and cosine -approximations even if @code{-funsafe-math-optimizations} is in effect. - -@item -mfsrra -@itemx -mno-fsrra -@opindex mfsrra -@opindex mno-fsrra -Allow or disallow the compiler to emit the @code{fsrra} instruction for -reciprocal square root approximations. The option @code{-mfsrra} must be used -in combination with @code{-funsafe-math-optimizations} and -@code{-ffinite-math-only}. It is enabled by default when generating code for -SH4A. Using @code{-mno-fsrra} disables reciprocal square root approximations -even if @code{-funsafe-math-optimizations} and @code{-ffinite-math-only} are -in effect. - -@item -mpretend-cmove -@opindex mpretend-cmove -Prefer zero-displacement conditional branches for conditional move instruction -patterns. This can result in faster code on the SH4 processor. - -@end table - -@node Solaris 2 Options -@subsection Solaris 2 Options -@cindex Solaris 2 options - -These @samp{-m} options are supported on Solaris 2: - -@table @gcctabopt -@item -mimpure-text -@opindex mimpure-text -@option{-mimpure-text}, used in addition to @option{-shared}, tells -the compiler to not pass @option{-z text} to the linker when linking a -shared object. Using this option, you can link position-dependent -code into a shared object. - -@option{-mimpure-text} suppresses the ``relocations remain against -allocatable but non-writable sections'' linker error message. -However, the necessary relocations trigger copy-on-write, and the -shared object is not actually shared across processes. Instead of -using @option{-mimpure-text}, you should compile all source code with -@option{-fpic} or @option{-fPIC}. - -@end table - -These switches are supported in addition to the above on Solaris 2: - -@table @gcctabopt -@item -pthreads -@opindex pthreads -Add support for multithreading using the POSIX threads library. This -option sets flags for both the preprocessor and linker. This option does -not affect the thread safety of object code produced by the compiler or -that of libraries supplied with it. - -@item -pthread -@opindex pthread -This is a synonym for @option{-pthreads}. -@end table - -@node SPARC Options -@subsection SPARC Options -@cindex SPARC options - -These @samp{-m} options are supported on the SPARC: - -@table @gcctabopt -@item -mno-app-regs -@itemx -mapp-regs -@opindex mno-app-regs -@opindex mapp-regs -Specify @option{-mapp-regs} to generate output using the global registers -2 through 4, which the SPARC SVR4 ABI reserves for applications. This -is the default. - -To be fully SVR4 ABI-compliant at the cost of some performance loss, -specify @option{-mno-app-regs}. You should compile libraries and system -software with this option. - -@item -mflat -@itemx -mno-flat -@opindex mflat -@opindex mno-flat -With @option{-mflat}, the compiler does not generate save/restore instructions -and uses a ``flat'' or single register window model. This model is compatible -with the regular register window model. The local registers and the input -registers (0--5) are still treated as ``call-saved'' registers and are -saved on the stack as needed. - -With @option{-mno-flat} (the default), the compiler generates save/restore -instructions (except for leaf functions). This is the normal operating mode. - -@item -mfpu -@itemx -mhard-float -@opindex mfpu -@opindex mhard-float -Generate output containing floating-point instructions. This is the -default. - -@item -mno-fpu -@itemx -msoft-float -@opindex mno-fpu -@opindex msoft-float -Generate output containing library calls for floating point. -@strong{Warning:} the requisite libraries are not available for all SPARC -targets. Normally the facilities of the machine's usual C compiler are -used, but this cannot be done directly in cross-compilation. You must make -your own arrangements to provide suitable library functions for -cross-compilation. The embedded targets @samp{sparc-*-aout} and -@samp{sparclite-*-*} do provide software floating-point support. - -@option{-msoft-float} changes the calling convention in the output file; -therefore, it is only useful if you compile @emph{all} of a program with -this option. In particular, you need to compile @file{libgcc.a}, the -library that comes with GCC, with @option{-msoft-float} in order for -this to work. - -@item -mhard-quad-float -@opindex mhard-quad-float -Generate output containing quad-word (long double) floating-point -instructions. - -@item -msoft-quad-float -@opindex msoft-quad-float -Generate output containing library calls for quad-word (long double) -floating-point instructions. The functions called are those specified -in the SPARC ABI@. This is the default. - -As of this writing, there are no SPARC implementations that have hardware -support for the quad-word floating-point instructions. They all invoke -a trap handler for one of these instructions, and then the trap handler -emulates the effect of the instruction. Because of the trap handler overhead, -this is much slower than calling the ABI library routines. Thus the -@option{-msoft-quad-float} option is the default. - -@item -mno-unaligned-doubles -@itemx -munaligned-doubles -@opindex mno-unaligned-doubles -@opindex munaligned-doubles -Assume that doubles have 8-byte alignment. This is the default. - -With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte -alignment only if they are contained in another type, or if they have an -absolute address. Otherwise, it assumes they have 4-byte alignment. -Specifying this option avoids some rare compatibility problems with code -generated by other compilers. It is not the default because it results -in a performance loss, especially for floating-point code. - -@item -mno-faster-structs -@itemx -mfaster-structs -@opindex mno-faster-structs -@opindex mfaster-structs -With @option{-mfaster-structs}, the compiler assumes that structures -should have 8-byte alignment. This enables the use of pairs of -@code{ldd} and @code{std} instructions for copies in structure -assignment, in place of twice as many @code{ld} and @code{st} pairs. -However, the use of this changed alignment directly violates the SPARC -ABI@. Thus, it's intended only for use on targets where the developer -acknowledges that their resulting code is not directly in line with -the rules of the ABI@. - -@item -mcpu=@var{cpu_type} -@opindex mcpu -Set the instruction set, register set, and instruction scheduling parameters -for machine type @var{cpu_type}. Supported values for @var{cpu_type} are -@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc}, -@samp{leon}, @samp{sparclite}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, -@samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, -@samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, @samp{niagara3}, -and @samp{niagara4}. - -Native Solaris and GNU/Linux toolchains also support the value @samp{native}, -which selects the best architecture option for the host processor. -@option{-mcpu=native} has no effect if GCC does not recognize -the processor. - -Default instruction scheduling parameters are used for values that select -an architecture and not an implementation. These are @samp{v7}, @samp{v8}, -@samp{sparclite}, @samp{sparclet}, @samp{v9}. - -Here is a list of each supported architecture and their supported -implementations. - -@table @asis -@item v7 -cypress - -@item v8 -supersparc, hypersparc, leon - -@item sparclite -f930, f934, sparclite86x - -@item sparclet -tsc701 - -@item v9 -ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4 -@end table - -By default (unless configured otherwise), GCC generates code for the V7 -variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler -additionally optimizes it for the Cypress CY7C602 chip, as used in the -SPARCStation/SPARCServer 3xx series. This is also appropriate for the older -SPARCStation 1, 2, IPX etc. - -With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC -architecture. The only difference from V7 code is that the compiler emits -the integer multiply and integer divide instructions which exist in SPARC-V8 -but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally -optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and -2000 series. - -With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of -the SPARC architecture. This adds the integer multiply, integer divide step -and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7. -With @option{-mcpu=f930}, the compiler additionally optimizes it for the -Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With -@option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu -MB86934 chip, which is the more recent SPARClite with FPU@. - -With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of -the SPARC architecture. This adds the integer multiply, multiply/accumulate, -integer divide step and scan (@code{ffs}) instructions which exist in SPARClet -but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally -optimizes it for the TEMIC SPARClet chip. - -With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC -architecture. This adds 64-bit integer and floating-point move instructions, -3 additional floating-point condition code registers and conditional move -instructions. With @option{-mcpu=ultrasparc}, the compiler additionally -optimizes it for the Sun UltraSPARC I/II/IIi chips. With -@option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the -Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With -@option{-mcpu=niagara}, the compiler additionally optimizes it for -Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler -additionally optimizes it for Sun UltraSPARC T2 chips. With -@option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun -UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler -additionally optimizes it for Sun UltraSPARC T4 chips. - -@item -mtune=@var{cpu_type} -@opindex mtune -Set the instruction scheduling parameters for machine type -@var{cpu_type}, but do not set the instruction set or register set that the -option @option{-mcpu=@var{cpu_type}} does. - -The same values for @option{-mcpu=@var{cpu_type}} can be used for -@option{-mtune=@var{cpu_type}}, but the only useful values are those -that select a particular CPU implementation. Those are @samp{cypress}, -@samp{supersparc}, @samp{hypersparc}, @samp{leon}, @samp{f930}, @samp{f934}, -@samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, @samp{ultrasparc3}, -@samp{niagara}, @samp{niagara2}, @samp{niagara3} and @samp{niagara4}. With -native Solaris and GNU/Linux toolchains, @samp{native} can also be used. - -@item -mv8plus -@itemx -mno-v8plus -@opindex mv8plus -@opindex mno-v8plus -With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The -difference from the V8 ABI is that the global and out registers are -considered 64 bits wide. This is enabled by default on Solaris in 32-bit -mode for all SPARC-V9 processors. - -@item -mvis -@itemx -mno-vis -@opindex mvis -@opindex mno-vis -With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC -Visual Instruction Set extensions. The default is @option{-mno-vis}. - -@item -mvis2 -@itemx -mno-vis2 -@opindex mvis2 -@opindex mno-vis2 -With @option{-mvis2}, GCC generates code that takes advantage of -version 2.0 of the UltraSPARC Visual Instruction Set extensions. The -default is @option{-mvis2} when targeting a cpu that supports such -instructions, such as UltraSPARC-III and later. Setting @option{-mvis2} -also sets @option{-mvis}. - -@item -mvis3 -@itemx -mno-vis3 -@opindex mvis3 -@opindex mno-vis3 -With @option{-mvis3}, GCC generates code that takes advantage of -version 3.0 of the UltraSPARC Visual Instruction Set extensions. The -default is @option{-mvis3} when targeting a cpu that supports such -instructions, such as niagara-3 and later. Setting @option{-mvis3} -also sets @option{-mvis2} and @option{-mvis}. - -@item -mcbcond -@itemx -mno-cbcond -@opindex mcbcond -@opindex mno-cbcond -With @option{-mcbcond}, GCC generates code that takes advantage of -compare-and-branch instructions, as defined in the Sparc Architecture 2011. -The default is @option{-mcbcond} when targeting a cpu that supports such -instructions, such as niagara-4 and later. - -@item -mpopc -@itemx -mno-popc -@opindex mpopc -@opindex mno-popc -With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC -population count instruction. The default is @option{-mpopc} -when targeting a cpu that supports such instructions, such as Niagara-2 and -later. - -@item -mfmaf -@itemx -mno-fmaf -@opindex mfmaf -@opindex mno-fmaf -With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC -Fused Multiply-Add Floating-point extensions. The default is @option{-mfmaf} -when targeting a cpu that supports such instructions, such as Niagara-3 and -later. - -@item -mfix-at697f -@opindex mfix-at697f -Enable the documented workaround for the single erratum of the Atmel AT697F -processor (which corresponds to erratum #13 of the AT697E processor). -@end table - -These @samp{-m} options are supported in addition to the above -on SPARC-V9 processors in 64-bit environments: - -@table @gcctabopt -@item -m32 -@itemx -m64 -@opindex m32 -@opindex m64 -Generate code for a 32-bit or 64-bit environment. -The 32-bit environment sets int, long and pointer to 32 bits. -The 64-bit environment sets int to 32 bits and long and pointer -to 64 bits. - -@item -mcmodel=@var{which} -@opindex mcmodel -Set the code model to one of - -@table @samp -@item medlow -The Medium/Low code model: 64-bit addresses, programs -must be linked in the low 32 bits of memory. Programs can be statically -or dynamically linked. - -@item medmid -The Medium/Middle code model: 64-bit addresses, programs -must be linked in the low 44 bits of memory, the text and data segments must -be less than 2GB in size and the data segment must be located within 2GB of -the text segment. - -@item medany -The Medium/Anywhere code model: 64-bit addresses, programs -may be linked anywhere in memory, the text and data segments must be less -than 2GB in size and the data segment must be located within 2GB of the -text segment. - -@item embmedany -The Medium/Anywhere code model for embedded systems: -64-bit addresses, the text and data segments must be less than 2GB in -size, both starting anywhere in memory (determined at link time). The -global register %g4 points to the base of the data segment. Programs -are statically linked and PIC is not supported. -@end table - -@item -mmemory-model=@var{mem-model} -@opindex mmemory-model -Set the memory model in force on the processor to one of - -@table @samp -@item default -The default memory model for the processor and operating system. - -@item rmo -Relaxed Memory Order - -@item pso -Partial Store Order - -@item tso -Total Store Order - -@item sc -Sequential Consistency -@end table - -These memory models are formally defined in Appendix D of the Sparc V9 -architecture manual, as set in the processor's @code{PSTATE.MM} field. - -@item -mstack-bias -@itemx -mno-stack-bias -@opindex mstack-bias -@opindex mno-stack-bias -With @option{-mstack-bias}, GCC assumes that the stack pointer, and -frame pointer if present, are offset by @minus{}2047 which must be added back -when making stack frame references. This is the default in 64-bit mode. -Otherwise, assume no such offset is present. -@end table - -@node SPU Options -@subsection SPU Options -@cindex SPU options - -These @samp{-m} options are supported on the SPU: - -@table @gcctabopt -@item -mwarn-reloc -@itemx -merror-reloc -@opindex mwarn-reloc -@opindex merror-reloc - -The loader for SPU does not handle dynamic relocations. By default, GCC -gives an error when it generates code that requires a dynamic -relocation. @option{-mno-error-reloc} disables the error, -@option{-mwarn-reloc} generates a warning instead. - -@item -msafe-dma -@itemx -munsafe-dma -@opindex msafe-dma -@opindex munsafe-dma - -Instructions that initiate or test completion of DMA must not be -reordered with respect to loads and stores of the memory that is being -accessed. -With @option{-munsafe-dma} you must use the @code{volatile} keyword to protect -memory accesses, but that can lead to inefficient code in places where the -memory is known to not change. Rather than mark the memory as volatile, -you can use @option{-msafe-dma} to tell the compiler to treat -the DMA instructions as potentially affecting all memory. - -@item -mbranch-hints -@opindex mbranch-hints - -By default, GCC generates a branch hint instruction to avoid -pipeline stalls for always-taken or probably-taken branches. A hint -is not generated closer than 8 instructions away from its branch. -There is little reason to disable them, except for debugging purposes, -or to make an object a little bit smaller. - -@item -msmall-mem -@itemx -mlarge-mem -@opindex msmall-mem -@opindex mlarge-mem - -By default, GCC generates code assuming that addresses are never larger -than 18 bits. With @option{-mlarge-mem} code is generated that assumes -a full 32-bit address. - -@item -mstdmain -@opindex mstdmain - -By default, GCC links against startup code that assumes the SPU-style -main function interface (which has an unconventional parameter list). -With @option{-mstdmain}, GCC links your program against startup -code that assumes a C99-style interface to @code{main}, including a -local copy of @code{argv} strings. - -@item -mfixed-range=@var{register-range} -@opindex mfixed-range -Generate code treating the given register range as fixed registers. -A fixed register is one that the register allocator cannot use. This is -useful when compiling kernel code. A register range is specified as -two registers separated by a dash. Multiple register ranges can be -specified separated by a comma. - -@item -mea32 -@itemx -mea64 -@opindex mea32 -@opindex mea64 -Compile code assuming that pointers to the PPU address space accessed -via the @code{__ea} named address space qualifier are either 32 or 64 -bits wide. The default is 32 bits. As this is an ABI-changing option, -all object code in an executable must be compiled with the same setting. - -@item -maddress-space-conversion -@itemx -mno-address-space-conversion -@opindex maddress-space-conversion -@opindex mno-address-space-conversion -Allow/disallow treating the @code{__ea} address space as superset -of the generic address space. This enables explicit type casts -between @code{__ea} and generic pointer as well as implicit -conversions of generic pointers to @code{__ea} pointers. The -default is to allow address space pointer conversions. - -@item -mcache-size=@var{cache-size} -@opindex mcache-size -This option controls the version of libgcc that the compiler links to an -executable and selects a software-managed cache for accessing variables -in the @code{__ea} address space with a particular cache size. Possible -options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64} -and @samp{128}. The default cache size is 64KB. - -@item -matomic-updates -@itemx -mno-atomic-updates -@opindex matomic-updates -@opindex mno-atomic-updates -This option controls the version of libgcc that the compiler links to an -executable and selects whether atomic updates to the software-managed -cache of PPU-side variables are used. If you use atomic updates, changes -to a PPU variable from SPU code using the @code{__ea} named address space -qualifier do not interfere with changes to other PPU variables residing -in the same cache line from PPU code. If you do not use atomic updates, -such interference may occur; however, writing back cache lines is -more efficient. The default behavior is to use atomic updates. - -@item -mdual-nops -@itemx -mdual-nops=@var{n} -@opindex mdual-nops -By default, GCC inserts nops to increase dual issue when it expects -it to increase performance. @var{n} can be a value from 0 to 10. A -smaller @var{n} inserts fewer nops. 10 is the default, 0 is the -same as @option{-mno-dual-nops}. Disabled with @option{-Os}. - -@item -mhint-max-nops=@var{n} -@opindex mhint-max-nops -Maximum number of nops to insert for a branch hint. A branch hint must -be at least 8 instructions away from the branch it is affecting. GCC -inserts up to @var{n} nops to enforce this, otherwise it does not -generate the branch hint. - -@item -mhint-max-distance=@var{n} -@opindex mhint-max-distance -The encoding of the branch hint instruction limits the hint to be within -256 instructions of the branch it is affecting. By default, GCC makes -sure it is within 125. - -@item -msafe-hints -@opindex msafe-hints -Work around a hardware bug that causes the SPU to stall indefinitely. -By default, GCC inserts the @code{hbrp} instruction to make sure -this stall won't happen. - -@end table - -@node System V Options -@subsection Options for System V - -These additional options are available on System V Release 4 for -compatibility with other compilers on those systems: - -@table @gcctabopt -@item -G -@opindex G -Create a shared object. -It is recommended that @option{-symbolic} or @option{-shared} be used instead. - -@item -Qy -@opindex Qy -Identify the versions of each tool used by the compiler, in a -@code{.ident} assembler directive in the output. - -@item -Qn -@opindex Qn -Refrain from adding @code{.ident} directives to the output file (this is -the default). - -@item -YP,@var{dirs} -@opindex YP -Search the directories @var{dirs}, and no others, for libraries -specified with @option{-l}. - -@item -Ym,@var{dir} -@opindex Ym -Look in the directory @var{dir} to find the M4 preprocessor. -The assembler uses this option. -@c This is supposed to go with a -Yd for predefined M4 macro files, but -@c the generic assembler that comes with Solaris takes just -Ym. -@end table - -@node TILE-Gx Options -@subsection TILE-Gx Options -@cindex TILE-Gx options - -These @samp{-m} options are supported on the TILE-Gx: - -@table @gcctabopt -@item -mcmodel=small -@opindex mcmodel=small -Generate code for the small model. The distance for direct calls is -limited to 500M in either direction. PC-relative addresses are 32 -bits. Absolute addresses support the full address range. - -@item -mcmodel=large -@opindex mcmodel=large -Generate code for the large model. There is no limitation on call -distance, pc-relative addresses, or absolute addresses. - -@item -mcpu=@var{name} -@opindex mcpu -Selects the type of CPU to be targeted. Currently the only supported -type is @samp{tilegx}. - -@item -m32 -@itemx -m64 -@opindex m32 -@opindex m64 -Generate code for a 32-bit or 64-bit environment. The 32-bit -environment sets int, long, and pointer to 32 bits. The 64-bit -environment sets int to 32 bits and long and pointer to 64 bits. -@end table - -@node TILEPro Options -@subsection TILEPro Options -@cindex TILEPro options - -These @samp{-m} options are supported on the TILEPro: - -@table @gcctabopt -@item -mcpu=@var{name} -@opindex mcpu -Selects the type of CPU to be targeted. Currently the only supported -type is @samp{tilepro}. - -@item -m32 -@opindex m32 -Generate code for a 32-bit environment, which sets int, long, and -pointer to 32 bits. This is the only supported behavior so the flag -is essentially ignored. -@end table - -@node V850 Options -@subsection V850 Options -@cindex V850 Options - -These @samp{-m} options are defined for V850 implementations: - -@table @gcctabopt -@item -mlong-calls -@itemx -mno-long-calls -@opindex mlong-calls -@opindex mno-long-calls -Treat all calls as being far away (near). If calls are assumed to be -far away, the compiler always loads the function's address into a -register, and calls indirect through the pointer. - -@item -mno-ep -@itemx -mep -@opindex mno-ep -@opindex mep -Do not optimize (do optimize) basic blocks that use the same index -pointer 4 or more times to copy pointer into the @code{ep} register, and -use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} -option is on by default if you optimize. - -@item -mno-prolog-function -@itemx -mprolog-function -@opindex mno-prolog-function -@opindex mprolog-function -Do not use (do use) external functions to save and restore registers -at the prologue and epilogue of a function. The external functions -are slower, but use less code space if more than one function saves -the same number of registers. The @option{-mprolog-function} option -is on by default if you optimize. - -@item -mspace -@opindex mspace -Try to make the code as small as possible. At present, this just turns -on the @option{-mep} and @option{-mprolog-function} options. - -@item -mtda=@var{n} -@opindex mtda -Put static or global variables whose size is @var{n} bytes or less into -the tiny data area that register @code{ep} points to. The tiny data -area can hold up to 256 bytes in total (128 bytes for byte references). - -@item -msda=@var{n} -@opindex msda -Put static or global variables whose size is @var{n} bytes or less into -the small data area that register @code{gp} points to. The small data -area can hold up to 64 kilobytes. - -@item -mzda=@var{n} -@opindex mzda -Put static or global variables whose size is @var{n} bytes or less into -the first 32 kilobytes of memory. - -@item -mv850 -@opindex mv850 -Specify that the target processor is the V850. - -@item -mv850e3v5 -@opindex mv850e3v5 -Specify that the target processor is the V850E3V5. The preprocessor -constant @samp{__v850e3v5__} is defined if this option is used. - -@item -mv850e2v4 -@opindex mv850e2v4 -Specify that the target processor is the V850E3V5. This is an alias for -the @option{-mv850e3v5} option. - -@item -mv850e2v3 -@opindex mv850e2v3 -Specify that the target processor is the V850E2V3. The preprocessor -constant @samp{__v850e2v3__} is defined if this option is used. - -@item -mv850e2 -@opindex mv850e2 -Specify that the target processor is the V850E2. The preprocessor -constant @samp{__v850e2__} is defined if this option is used. - -@item -mv850e1 -@opindex mv850e1 -Specify that the target processor is the V850E1. The preprocessor -constants @samp{__v850e1__} and @samp{__v850e__} are defined if -this option is used. - -@item -mv850es -@opindex mv850es -Specify that the target processor is the V850ES. This is an alias for -the @option{-mv850e1} option. - -@item -mv850e -@opindex mv850e -Specify that the target processor is the V850E@. The preprocessor -constant @samp{__v850e__} is defined if this option is used. - -If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1} -nor @option{-mv850e2} nor @option{-mv850e2v3} nor @option{-mv850e3v5} -are defined then a default target processor is chosen and the -relevant @samp{__v850*__} preprocessor constant is defined. - -The preprocessor constants @samp{__v850} and @samp{__v851__} are always -defined, regardless of which processor variant is the target. - -@item -mdisable-callt -@itemx -mno-disable-callt -@opindex mdisable-callt -@opindex mno-disable-callt -This option suppresses generation of the @code{CALLT} instruction for the -v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 -architecture. - -This option is enabled by default when the RH850 ABI is -in use (see @option{-mrh850-abi}), and disabled by default when the -GCC ABI is in use. If @code{CALLT} instructions are being generated -then the C preprocessor symbol @code{__V850_CALLT__} will be defined. - -@item -mrelax -@itemx -mno-relax -@opindex mrelax -@opindex mno-relax -Pass on (or do not pass on) the @option{-mrelax} command line option -to the assembler. - -@item -mlong-jumps -@itemx -mno-long-jumps -@opindex mlong-jumps -@opindex mno-long-jumps -Disable (or re-enable) the generation of PC-relative jump instructions. - -@item -msoft-float -@itemx -mhard-float -@opindex msoft-float -@opindex mhard-float -Disable (or re-enable) the generation of hardware floating point -instructions. This option is only significant when the target -architecture is @samp{V850E2V3} or higher. If hardware floating point -instructions are being generated then the C preprocessor symbol -@code{__FPU_OK__} will be defined, otherwise the symbol -@code{__NO_FPU__} will be defined. - -@item -mloop -@opindex mloop -Enables the use of the e3v5 LOOP instruction. The use of this -instruction is not enabled by default when the e3v5 architecture is -selected because its use is still experimental. - -@item -mrh850-abi -@itemx -mghs -@opindex mrh850-abi -@opindex mghs -Enables support for the RH850 version of the V850 ABI. This is the -default. With this version of the ABI the following rules apply: - -@itemize -@item -Integer sized structures and unions are returned via a memory pointer -rather than a register. - -@item -Large structures and unions (more than 8 bytes in size) are passed by -value. - -@item -Functions are aligned to 16-bit boundaries. - -@item -The @option{-m8byte-align} command line option is supported. - -@item -The @option{-mdisable-callt} command line option is enabled by -default. The @option{-mno-disable-callt} command line option is not -supported. -@end itemize - -When this version of the ABI is enabled the C preprocessor symbol -@code{__V850_RH850_ABI__} is defined. - -@item -mgcc-abi -@opindex mgcc-abi -Enables support for the old GCC version of the V850 ABI. With this -version of the ABI the following rules apply: - -@itemize -@item -Integer sized structures and unions are returned in register @code{r10}. - -@item -Large structures and unions (more than 8 bytes in size) are passed by -reference. - -@item -Functions are aligned to 32-bit boundaries, unless optimizing for -size. - -@item -The @option{-m8byte-align} command line option is not supported. - -@item -The @option{-mdisable-callt} command line option is supported but not -enabled by default. -@end itemize - -When this version of the ABI is enabled the C preprocessor symbol -@code{__V850_GCC_ABI__} is defined. - -@item -m8byte-align -@itemx -mno-8byte-align -@opindex m8byte-align -@opindex mno-8byte-align -Enables support for @code{doubles} and @code{long long} types to be -aligned on 8-byte boundaries. The default is to restrict the -alignment of all objects to at most 4-bytes. When -@option{-m8byte-align} is in effect the C preprocessor symbol -@code{__V850_8BYTE_ALIGN__} will be defined. - -@item -mbig-switch -@opindex mbig-switch -Generate code suitable for big switch tables. Use this option only if -the assembler/linker complain about out of range branches within a switch -table. - -@item -mapp-regs -@opindex mapp-regs -This option causes r2 and r5 to be used in the code generated by -the compiler. This setting is the default. - -@item -mno-app-regs -@opindex mno-app-regs -This option causes r2 and r5 to be treated as fixed registers. - -@end table - -@node VAX Options -@subsection VAX Options -@cindex VAX options - -These @samp{-m} options are defined for the VAX: - -@table @gcctabopt -@item -munix -@opindex munix -Do not output certain jump instructions (@code{aobleq} and so on) -that the Unix assembler for the VAX cannot handle across long -ranges. - -@item -mgnu -@opindex mgnu -Do output those jump instructions, on the assumption that the -GNU assembler is being used. - -@item -mg -@opindex mg -Output code for G-format floating-point numbers instead of D-format. -@end table - -@node VMS Options -@subsection VMS Options - -These @samp{-m} options are defined for the VMS implementations: - -@table @gcctabopt -@item -mvms-return-codes -@opindex mvms-return-codes -Return VMS condition codes from @code{main}. The default is to return POSIX-style -condition (e.g.@ error) codes. - -@item -mdebug-main=@var{prefix} -@opindex mdebug-main=@var{prefix} -Flag the first routine whose name starts with @var{prefix} as the main -routine for the debugger. - -@item -mmalloc64 -@opindex mmalloc64 -Default to 64-bit memory allocation routines. - -@item -mpointer-size=@var{size} -@opindex -mpointer-size=@var{size} -Set the default size of pointers. Possible options for @var{size} are -@samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long} -for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers. -The later option disables @code{pragma pointer_size}. -@end table - -@node VxWorks Options -@subsection VxWorks Options -@cindex VxWorks Options - -The options in this section are defined for all VxWorks targets. -Options specific to the target hardware are listed with the other -options for that target. - -@table @gcctabopt -@item -mrtp -@opindex mrtp -GCC can generate code for both VxWorks kernels and real time processes -(RTPs). This option switches from the former to the latter. It also -defines the preprocessor macro @code{__RTP__}. - -@item -non-static -@opindex non-static -Link an RTP executable against shared libraries rather than static -libraries. The options @option{-static} and @option{-shared} can -also be used for RTPs (@pxref{Link Options}); @option{-static} -is the default. - -@item -Bstatic -@itemx -Bdynamic -@opindex Bstatic -@opindex Bdynamic -These options are passed down to the linker. They are defined for -compatibility with Diab. - -@item -Xbind-lazy -@opindex Xbind-lazy -Enable lazy binding of function calls. This option is equivalent to -@option{-Wl,-z,now} and is defined for compatibility with Diab. - -@item -Xbind-now -@opindex Xbind-now -Disable lazy binding of function calls. This option is the default and -is defined for compatibility with Diab. -@end table - -@node x86-64 Options -@subsection x86-64 Options -@cindex x86-64 options - -These are listed under @xref{i386 and x86-64 Options}. - -@node Xstormy16 Options -@subsection Xstormy16 Options -@cindex Xstormy16 Options - -These options are defined for Xstormy16: - -@table @gcctabopt -@item -msim -@opindex msim -Choose startup files and linker script suitable for the simulator. -@end table - -@node Xtensa Options -@subsection Xtensa Options -@cindex Xtensa Options - -These options are supported for Xtensa targets: - -@table @gcctabopt -@item -mconst16 -@itemx -mno-const16 -@opindex mconst16 -@opindex mno-const16 -Enable or disable use of @code{CONST16} instructions for loading -constant values. The @code{CONST16} instruction is currently not a -standard option from Tensilica. When enabled, @code{CONST16} -instructions are always used in place of the standard @code{L32R} -instructions. The use of @code{CONST16} is enabled by default only if -the @code{L32R} instruction is not available. - -@item -mfused-madd -@itemx -mno-fused-madd -@opindex mfused-madd -@opindex mno-fused-madd -Enable or disable use of fused multiply/add and multiply/subtract -instructions in the floating-point option. This has no effect if the -floating-point option is not also enabled. Disabling fused multiply/add -and multiply/subtract instructions forces the compiler to use separate -instructions for the multiply and add/subtract operations. This may be -desirable in some cases where strict IEEE 754-compliant results are -required: the fused multiply add/subtract instructions do not round the -intermediate result, thereby producing results with @emph{more} bits of -precision than specified by the IEEE standard. Disabling fused multiply -add/subtract instructions also ensures that the program output is not -sensitive to the compiler's ability to combine multiply and add/subtract -operations. - -@item -mserialize-volatile -@itemx -mno-serialize-volatile -@opindex mserialize-volatile -@opindex mno-serialize-volatile -When this option is enabled, GCC inserts @code{MEMW} instructions before -@code{volatile} memory references to guarantee sequential consistency. -The default is @option{-mserialize-volatile}. Use -@option{-mno-serialize-volatile} to omit the @code{MEMW} instructions. - -@item -mforce-no-pic -@opindex mforce-no-pic -For targets, like GNU/Linux, where all user-mode Xtensa code must be -position-independent code (PIC), this option disables PIC for compiling -kernel code. - -@item -mtext-section-literals -@itemx -mno-text-section-literals -@opindex mtext-section-literals -@opindex mno-text-section-literals -Control the treatment of literal pools. The default is -@option{-mno-text-section-literals}, which places literals in a separate -section in the output file. This allows the literal pool to be placed -in a data RAM/ROM, and it also allows the linker to combine literal -pools from separate object files to remove redundant literals and -improve code size. With @option{-mtext-section-literals}, the literals -are interspersed in the text section in order to keep them as close as -possible to their references. This may be necessary for large assembly -files. - -@item -mtarget-align -@itemx -mno-target-align -@opindex mtarget-align -@opindex mno-target-align -When this option is enabled, GCC instructs the assembler to -automatically align instructions to reduce branch penalties at the -expense of some code density. The assembler attempts to widen density -instructions to align branch targets and the instructions following call -instructions. If there are not enough preceding safe density -instructions to align a target, no widening is performed. The -default is @option{-mtarget-align}. These options do not affect the -treatment of auto-aligned instructions like @code{LOOP}, which the -assembler always aligns, either by widening density instructions or -by inserting NOP instructions. - -@item -mlongcalls -@itemx -mno-longcalls -@opindex mlongcalls -@opindex mno-longcalls -When this option is enabled, GCC instructs the assembler to translate -direct calls to indirect calls unless it can determine that the target -of a direct call is in the range allowed by the call instruction. This -translation typically occurs for calls to functions in other source -files. Specifically, the assembler translates a direct @code{CALL} -instruction into an @code{L32R} followed by a @code{CALLX} instruction. -The default is @option{-mno-longcalls}. This option should be used in -programs where the call target can potentially be out of range. This -option is implemented in the assembler, not the compiler, so the -assembly code generated by GCC still shows direct call -instructions---look at the disassembled object code to see the actual -instructions. Note that the assembler uses an indirect call for -every cross-file call, not just those that really are out of range. -@end table - -@node zSeries Options -@subsection zSeries Options -@cindex zSeries options - -These are listed under @xref{S/390 and zSeries Options}. - -@node Code Gen Options -@section Options for Code Generation Conventions -@cindex code generation conventions -@cindex options, code generation -@cindex run-time options - -These machine-independent options control the interface conventions -used in code generation. - -Most of them have both positive and negative forms; the negative form -of @option{-ffoo} is @option{-fno-foo}. In the table below, only -one of the forms is listed---the one that is not the default. You -can figure out the other form by either removing @samp{no-} or adding -it. - -@table @gcctabopt -@item -fbounds-check -@opindex fbounds-check -For front ends that support it, generate additional code to check that -indices used to access arrays are within the declared range. This is -currently only supported by the Java and Fortran front ends, where -this option defaults to true and false respectively. - -@item -fstack-reuse=@var{reuse-level} -@opindex fstack_reuse -This option controls stack space reuse for user declared local/auto variables -and compiler generated temporaries. @var{reuse_level} can be @samp{all}, -@samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all -local variables and temporaries, @samp{named_vars} enables the reuse only for -user defined local variables with names, and @samp{none} disables stack reuse -completely. The default value is @samp{all}. The option is needed when the -program extends the lifetime of a scoped local variable or a compiler generated -temporary beyond the end point defined by the language. When a lifetime of -a variable ends, and if the variable lives in memory, the optimizing compiler -has the freedom to reuse its stack space with other temporaries or scoped -local variables whose live range does not overlap with it. Legacy code extending -local lifetime will likely to break with the stack reuse optimization. - -For example, - -@smallexample - int *p; - @{ - int local1; - - p = &local1; - local1 = 10; - .... - @} - @{ - int local2; - local2 = 20; - ... - @} - - if (*p == 10) // out of scope use of local1 - @{ - - @} -@end smallexample - -Another example: -@smallexample - - struct A - @{ - A(int k) : i(k), j(k) @{ @} - int i; - int j; - @}; - - A *ap; - - void foo(const A& ar) - @{ - ap = &ar; - @} - - void bar() - @{ - foo(A(10)); // temp object's lifetime ends when foo returns - - @{ - A a(20); - .... - @} - ap->i+= 10; // ap references out of scope temp whose space - // is reused with a. What is the value of ap->i? - @} - -@end smallexample - -The lifetime of a compiler generated temporary is well defined by the C++ -standard. When a lifetime of a temporary ends, and if the temporary lives -in memory, the optimizing compiler has the freedom to reuse its stack -space with other temporaries or scoped local variables whose live range -does not overlap with it. However some of the legacy code relies on -the behavior of older compilers in which temporaries' stack space is -not reused, the aggressive stack reuse can lead to runtime errors. This -option is used to control the temporary stack reuse optimization. - -@item -ftrapv -@opindex ftrapv -This option generates traps for signed overflow on addition, subtraction, -multiplication operations. - -@item -fwrapv -@opindex fwrapv -This option instructs the compiler to assume that signed arithmetic -overflow of addition, subtraction and multiplication wraps around -using twos-complement representation. This flag enables some optimizations -and disables others. This option is enabled by default for the Java -front end, as required by the Java language specification. - -@item -fexceptions -@opindex fexceptions -Enable exception handling. Generates extra code needed to propagate -exceptions. For some targets, this implies GCC generates frame -unwind information for all functions, which can produce significant data -size overhead, although it does not affect execution. If you do not -specify this option, GCC enables it by default for languages like -C++ that normally require exception handling, and disables it for -languages like C that do not normally require it. However, you may need -to enable this option when compiling C code that needs to interoperate -properly with exception handlers written in C++. You may also wish to -disable this option if you are compiling older C++ programs that don't -use exception handling. - -@item -fnon-call-exceptions -@opindex fnon-call-exceptions -Generate code that allows trapping instructions to throw exceptions. -Note that this requires platform-specific runtime support that does -not exist everywhere. Moreover, it only allows @emph{trapping} -instructions to throw exceptions, i.e.@: memory references or floating-point -instructions. It does not allow exceptions to be thrown from -arbitrary signal handlers such as @code{SIGALRM}. - -@item -fdelete-dead-exceptions -@opindex fdelete-dead-exceptions -Consider that instructions that may throw exceptions but don't otherwise -contribute to the execution of the program can be optimized away. -This option is enabled by default for the Ada front end, as permitted by -the Ada language specification. -Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. - -@item -funwind-tables -@opindex funwind-tables -Similar to @option{-fexceptions}, except that it just generates any needed -static data, but does not affect the generated code in any other way. -You normally do not need to enable this option; instead, a language processor -that needs this handling enables it on your behalf. - -@item -fasynchronous-unwind-tables -@opindex fasynchronous-unwind-tables -Generate unwind table in DWARF 2 format, if supported by target machine. The -table is exact at each instruction boundary, so it can be used for stack -unwinding from asynchronous events (such as debugger or garbage collector). - -@item -fpcc-struct-return -@opindex fpcc-struct-return -Return ``short'' @code{struct} and @code{union} values in memory like -longer ones, rather than in registers. This convention is less -efficient, but it has the advantage of allowing intercallability between -GCC-compiled files and files compiled with other compilers, particularly -the Portable C Compiler (pcc). - -The precise convention for returning structures in memory depends -on the target configuration macros. - -Short structures and unions are those whose size and alignment match -that of some integer type. - -@strong{Warning:} code compiled with the @option{-fpcc-struct-return} -switch is not binary compatible with code compiled with the -@option{-freg-struct-return} switch. -Use it to conform to a non-default application binary interface. - -@item -freg-struct-return -@opindex freg-struct-return -Return @code{struct} and @code{union} values in registers when possible. -This is more efficient for small structures than -@option{-fpcc-struct-return}. - -If you specify neither @option{-fpcc-struct-return} nor -@option{-freg-struct-return}, GCC defaults to whichever convention is -standard for the target. If there is no standard convention, GCC -defaults to @option{-fpcc-struct-return}, except on targets where GCC is -the principal compiler. In those cases, we can choose the standard, and -we chose the more efficient register return alternative. - -@strong{Warning:} code compiled with the @option{-freg-struct-return} -switch is not binary compatible with code compiled with the -@option{-fpcc-struct-return} switch. -Use it to conform to a non-default application binary interface. - -@item -fshort-enums -@opindex fshort-enums -Allocate to an @code{enum} type only as many bytes as it needs for the -declared range of possible values. Specifically, the @code{enum} type -is equivalent to the smallest integer type that has enough room. - -@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate -code that is not binary compatible with code generated without that switch. -Use it to conform to a non-default application binary interface. - -@item -fshort-double -@opindex fshort-double -Use the same size for @code{double} as for @code{float}. - -@strong{Warning:} the @option{-fshort-double} switch causes GCC to generate -code that is not binary compatible with code generated without that switch. -Use it to conform to a non-default application binary interface. - -@item -fshort-wchar -@opindex fshort-wchar -Override the underlying type for @samp{wchar_t} to be @samp{short -unsigned int} instead of the default for the target. This option is -useful for building programs to run under WINE@. - -@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate -code that is not binary compatible with code generated without that switch. -Use it to conform to a non-default application binary interface. - -@item -fno-common -@opindex fno-common -In C code, controls the placement of uninitialized global variables. -Unix C compilers have traditionally permitted multiple definitions of -such variables in different compilation units by placing the variables -in a common block. -This is the behavior specified by @option{-fcommon}, and is the default -for GCC on most targets. -On the other hand, this behavior is not required by ISO C, and on some -targets may carry a speed or code size penalty on variable references. -The @option{-fno-common} option specifies that the compiler should place -uninitialized global variables in the data section of the object file, -rather than generating them as common blocks. -This has the effect that if the same variable is declared -(without @code{extern}) in two different compilations, -you get a multiple-definition error when you link them. -In this case, you must compile with @option{-fcommon} instead. -Compiling with @option{-fno-common} is useful on targets for which -it provides better performance, or if you wish to verify that the -program will work on other systems that always treat uninitialized -variable declarations this way. - -@item -fno-ident -@opindex fno-ident -Ignore the @samp{#ident} directive. - -@item -finhibit-size-directive -@opindex finhibit-size-directive -Don't output a @code{.size} assembler directive, or anything else that -would cause trouble if the function is split in the middle, and the -two halves are placed at locations far apart in memory. This option is -used when compiling @file{crtstuff.c}; you should not need to use it -for anything else. - -@item -fverbose-asm -@opindex fverbose-asm -Put extra commentary information in the generated assembly code to -make it more readable. This option is generally only of use to those -who actually need to read the generated assembly code (perhaps while -debugging the compiler itself). - -@option{-fno-verbose-asm}, the default, causes the -extra information to be omitted and is useful when comparing two assembler -files. - -@item -frecord-gcc-switches -@opindex frecord-gcc-switches -This switch causes the command line used to invoke the -compiler to be recorded into the object file that is being created. -This switch is only implemented on some targets and the exact format -of the recording is target and binary file format dependent, but it -usually takes the form of a section containing ASCII text. This -switch is related to the @option{-fverbose-asm} switch, but that -switch only records information in the assembler output file as -comments, so it never reaches the object file. -See also @option{-grecord-gcc-switches} for another -way of storing compiler options into the object file. - -@item -fpic -@opindex fpic -@cindex global offset table -@cindex PIC -Generate position-independent code (PIC) suitable for use in a shared -library, if supported for the target machine. Such code accesses all -constant addresses through a global offset table (GOT)@. The dynamic -loader resolves the GOT entries when the program starts (the dynamic -loader is not part of GCC; it is part of the operating system). If -the GOT size for the linked executable exceeds a machine-specific -maximum size, you get an error message from the linker indicating that -@option{-fpic} does not work; in that case, recompile with @option{-fPIC} -instead. (These maximums are 8k on the SPARC and 32k -on the m68k and RS/6000. The 386 has no such limit.) - -Position-independent code requires special support, and therefore works -only on certain machines. For the 386, GCC supports PIC for System V -but not for the Sun 386i. Code generated for the IBM RS/6000 is always -position-independent. - -When this flag is set, the macros @code{__pic__} and @code{__PIC__} -are defined to 1. - -@item -fPIC -@opindex fPIC -If supported for the target machine, emit position-independent code, -suitable for dynamic linking and avoiding any limit on the size of the -global offset table. This option makes a difference on the m68k, -PowerPC and SPARC@. - -Position-independent code requires special support, and therefore works -only on certain machines. - -When this flag is set, the macros @code{__pic__} and @code{__PIC__} -are defined to 2. - -@item -fpie -@itemx -fPIE -@opindex fpie -@opindex fPIE -These options are similar to @option{-fpic} and @option{-fPIC}, but -generated position independent code can be only linked into executables. -Usually these options are used when @option{-pie} GCC option is -used during linking. - -@option{-fpie} and @option{-fPIE} both define the macros -@code{__pie__} and @code{__PIE__}. The macros have the value 1 -for @option{-fpie} and 2 for @option{-fPIE}. - -@item -fno-jump-tables -@opindex fno-jump-tables -Do not use jump tables for switch statements even where it would be -more efficient than other code generation strategies. This option is -of use in conjunction with @option{-fpic} or @option{-fPIC} for -building code that forms part of a dynamic linker and cannot -reference the address of a jump table. On some targets, jump tables -do not require a GOT and this option is not needed. - -@item -ffixed-@var{reg} -@opindex ffixed -Treat the register named @var{reg} as a fixed register; generated code -should never refer to it (except perhaps as a stack pointer, frame -pointer or in some other fixed role). - -@var{reg} must be the name of a register. The register names accepted -are machine-specific and are defined in the @code{REGISTER_NAMES} -macro in the machine description macro file. - -This flag does not have a negative form, because it specifies a -three-way choice. - -@item -fcall-used-@var{reg} -@opindex fcall-used -Treat the register named @var{reg} as an allocable register that is -clobbered by function calls. It may be allocated for temporaries or -variables that do not live across a call. Functions compiled this way -do not save and restore the register @var{reg}. - -It is an error to use this flag with the frame pointer or stack pointer. -Use of this flag for other registers that have fixed pervasive roles in -the machine's execution model produces disastrous results. - -This flag does not have a negative form, because it specifies a -three-way choice. - -@item -fcall-saved-@var{reg} -@opindex fcall-saved -Treat the register named @var{reg} as an allocable register saved by -functions. It may be allocated even for temporaries or variables that -live across a call. Functions compiled this way save and restore -the register @var{reg} if they use it. - -It is an error to use this flag with the frame pointer or stack pointer. -Use of this flag for other registers that have fixed pervasive roles in -the machine's execution model produces disastrous results. - -A different sort of disaster results from the use of this flag for -a register in which function values may be returned. - -This flag does not have a negative form, because it specifies a -three-way choice. - -@item -fpack-struct[=@var{n}] -@opindex fpack-struct -Without a value specified, pack all structure members together without -holes. When a value is specified (which must be a small power of two), pack -structure members according to this value, representing the maximum -alignment (that is, objects with default alignment requirements larger than -this are output potentially unaligned at the next fitting location. - -@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate -code that is not binary compatible with code generated without that switch. -Additionally, it makes the code suboptimal. -Use it to conform to a non-default application binary interface. - -@item -finstrument-functions -@opindex finstrument-functions -Generate instrumentation calls for entry and exit to functions. Just -after function entry and just before function exit, the following -profiling functions are called with the address of the current -function and its call site. (On some platforms, -@code{__builtin_return_address} does not work beyond the current -function, so the call site information may not be available to the -profiling functions otherwise.) - -@smallexample -void __cyg_profile_func_enter (void *this_fn, - void *call_site); -void __cyg_profile_func_exit (void *this_fn, - void *call_site); -@end smallexample - -The first argument is the address of the start of the current function, -which may be looked up exactly in the symbol table. - -This instrumentation is also done for functions expanded inline in other -functions. The profiling calls indicate where, conceptually, the -inline function is entered and exited. This means that addressable -versions of such functions must be available. If all your uses of a -function are expanded inline, this may mean an additional expansion of -code size. If you use @samp{extern inline} in your C code, an -addressable version of such functions must be provided. (This is -normally the case anyway, but if you get lucky and the optimizer always -expands the functions inline, you might have gotten away without -providing static copies.) - -A function may be given the attribute @code{no_instrument_function}, in -which case this instrumentation is not done. This can be used, for -example, for the profiling functions listed above, high-priority -interrupt routines, and any functions from which the profiling functions -cannot safely be called (perhaps signal handlers, if the profiling -routines generate output or allocate memory). - -@item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} -@opindex finstrument-functions-exclude-file-list - -Set the list of functions that are excluded from instrumentation (see -the description of @code{-finstrument-functions}). If the file that -contains a function definition matches with one of @var{file}, then -that function is not instrumented. The match is done on substrings: -if the @var{file} parameter is a substring of the file name, it is -considered to be a match. - -For example: - -@smallexample --finstrument-functions-exclude-file-list=/bits/stl,include/sys -@end smallexample - -@noindent -excludes any inline function defined in files whose pathnames -contain @code{/bits/stl} or @code{include/sys}. - -If, for some reason, you want to include letter @code{','} in one of -@var{sym}, write @code{'\,'}. For example, -@code{-finstrument-functions-exclude-file-list='\,\,tmp'} -(note the single quote surrounding the option). - -@item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} -@opindex finstrument-functions-exclude-function-list - -This is similar to @code{-finstrument-functions-exclude-file-list}, -but this option sets the list of function names to be excluded from -instrumentation. The function name to be matched is its user-visible -name, such as @code{vector<int> blah(const vector<int> &)}, not the -internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The -match is done on substrings: if the @var{sym} parameter is a substring -of the function name, it is considered to be a match. For C99 and C++ -extended identifiers, the function name must be given in UTF-8, not -using universal character names. - -@item -fstack-check -@opindex fstack-check -Generate code to verify that you do not go beyond the boundary of the -stack. You should specify this flag if you are running in an -environment with multiple threads, but you only rarely need to specify it in -a single-threaded environment since stack overflow is automatically -detected on nearly all systems if there is only one stack. - -Note that this switch does not actually cause checking to be done; the -operating system or the language runtime must do that. The switch causes -generation of code to ensure that they see the stack being extended. - -You can additionally specify a string parameter: @code{no} means no -checking, @code{generic} means force the use of old-style checking, -@code{specific} means use the best checking method and is equivalent -to bare @option{-fstack-check}. - -Old-style checking is a generic mechanism that requires no specific -target support in the compiler but comes with the following drawbacks: - -@enumerate -@item -Modified allocation strategy for large objects: they are always -allocated dynamically if their size exceeds a fixed threshold. - -@item -Fixed limit on the size of the static frame of functions: when it is -topped by a particular function, stack checking is not reliable and -a warning is issued by the compiler. - -@item -Inefficiency: because of both the modified allocation strategy and the -generic implementation, code performance is hampered. -@end enumerate - -Note that old-style stack checking is also the fallback method for -@code{specific} if no target support has been added in the compiler. - -@item -fstack-limit-register=@var{reg} -@itemx -fstack-limit-symbol=@var{sym} -@itemx -fno-stack-limit -@opindex fstack-limit-register -@opindex fstack-limit-symbol -@opindex fno-stack-limit -Generate code to ensure that the stack does not grow beyond a certain value, -either the value of a register or the address of a symbol. If a larger -stack is required, a signal is raised at run time. For most targets, -the signal is raised before the stack overruns the boundary, so -it is possible to catch the signal without taking special precautions. - -For instance, if the stack starts at absolute address @samp{0x80000000} -and grows downwards, you can use the flags -@option{-fstack-limit-symbol=__stack_limit} and -@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit -of 128KB@. Note that this may only work with the GNU linker. - -@item -fsplit-stack -@opindex fsplit-stack -Generate code to automatically split the stack before it overflows. -The resulting program has a discontiguous stack which can only -overflow if the program is unable to allocate any more memory. This -is most useful when running threaded programs, as it is no longer -necessary to calculate a good stack size to use for each thread. This -is currently only implemented for the i386 and x86_64 back ends running -GNU/Linux. - -When code compiled with @option{-fsplit-stack} calls code compiled -without @option{-fsplit-stack}, there may not be much stack space -available for the latter code to run. If compiling all code, -including library code, with @option{-fsplit-stack} is not an option, -then the linker can fix up these calls so that the code compiled -without @option{-fsplit-stack} always has a large stack. Support for -this is implemented in the gold linker in GNU binutils release 2.21 -and later. - -@item -fleading-underscore -@opindex fleading-underscore -This option and its counterpart, @option{-fno-leading-underscore}, forcibly -change the way C symbols are represented in the object file. One use -is to help link with legacy assembly code. - -@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to -generate code that is not binary compatible with code generated without that -switch. Use it to conform to a non-default application binary interface. -Not all targets provide complete support for this switch. - -@item -ftls-model=@var{model} -@opindex ftls-model -Alter the thread-local storage model to be used (@pxref{Thread-Local}). -The @var{model} argument should be one of @code{global-dynamic}, -@code{local-dynamic}, @code{initial-exec} or @code{local-exec}. - -The default without @option{-fpic} is @code{initial-exec}; with -@option{-fpic} the default is @code{global-dynamic}. - -@item -fvisibility=@var{default|internal|hidden|protected} -@opindex fvisibility -Set the default ELF image symbol visibility to the specified option---all -symbols are marked with this unless overridden within the code. -Using this feature can very substantially improve linking and -load times of shared object libraries, produce more optimized -code, provide near-perfect API export and prevent symbol clashes. -It is @strong{strongly} recommended that you use this in any shared objects -you distribute. - -Despite the nomenclature, @code{default} always means public; i.e., -available to be linked against from outside the shared object. -@code{protected} and @code{internal} are pretty useless in real-world -usage so the only other commonly used option is @code{hidden}. -The default if @option{-fvisibility} isn't specified is -@code{default}, i.e., make every -symbol public---this causes the same behavior as previous versions of -GCC@. - -A good explanation of the benefits offered by ensuring ELF -symbols have the correct visibility is given by ``How To Write -Shared Libraries'' by Ulrich Drepper (which can be found at -@w{@uref{http://people.redhat.com/~drepper/}})---however a superior -solution made possible by this option to marking things hidden when -the default is public is to make the default hidden and mark things -public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden} -and @code{__attribute__ ((visibility("default")))} instead of -@code{__declspec(dllexport)} you get almost identical semantics with -identical syntax. This is a great boon to those working with -cross-platform projects. - -For those adding visibility support to existing code, you may find -@samp{#pragma GCC visibility} of use. This works by you enclosing -the declarations you wish to set visibility for with (for example) -@samp{#pragma GCC visibility push(hidden)} and -@samp{#pragma GCC visibility pop}. -Bear in mind that symbol visibility should be viewed @strong{as -part of the API interface contract} and thus all new code should -always specify visibility when it is not the default; i.e., declarations -only for use within the local DSO should @strong{always} be marked explicitly -as hidden as so to avoid PLT indirection overheads---making this -abundantly clear also aids readability and self-documentation of the code. -Note that due to ISO C++ specification requirements, @code{operator new} and -@code{operator delete} must always be of default visibility. - -Be aware that headers from outside your project, in particular system -headers and headers from any other library you use, may not be -expecting to be compiled with visibility other than the default. You -may need to explicitly say @samp{#pragma GCC visibility push(default)} -before including any such headers. - -@samp{extern} declarations are not affected by @option{-fvisibility}, so -a lot of code can be recompiled with @option{-fvisibility=hidden} with -no modifications. However, this means that calls to @code{extern} -functions with no explicit visibility use the PLT, so it is more -effective to use @code{__attribute ((visibility))} and/or -@code{#pragma GCC visibility} to tell the compiler which @code{extern} -declarations should be treated as hidden. - -Note that @option{-fvisibility} does affect C++ vague linkage -entities. This means that, for instance, an exception class that is -be thrown between DSOs must be explicitly marked with default -visibility so that the @samp{type_info} nodes are unified between -the DSOs. - -An overview of these techniques, their benefits and how to use them -is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}. - -@item -fstrict-volatile-bitfields -@opindex fstrict-volatile-bitfields -This option should be used if accesses to volatile bit-fields (or other -structure fields, although the compiler usually honors those types -anyway) should use a single access of the width of the -field's type, aligned to a natural alignment if possible. For -example, targets with memory-mapped peripheral registers might require -all such accesses to be 16 bits wide; with this flag you can -declare all peripheral bit-fields as @code{unsigned short} (assuming short -is 16 bits on these targets) to force GCC to use 16-bit accesses -instead of, perhaps, a more efficient 32-bit access. - -If this option is disabled, the compiler uses the most efficient -instruction. In the previous example, that might be a 32-bit load -instruction, even though that accesses bytes that do not contain -any portion of the bit-field, or memory-mapped registers unrelated to -the one being updated. - -If the target requires strict alignment, and honoring the field -type would require violating this alignment, a warning is issued. -If the field has @code{packed} attribute, the access is done without -honoring the field type. If the field doesn't have @code{packed} -attribute, the access is done honoring the field type. In both cases, -GCC assumes that the user knows something about the target hardware -that it is unaware of. - -The default value of this option is determined by the application binary -interface for the target processor. - -@item -fsync-libcalls -@opindex fsync-libcalls -This option controls whether any out-of-line instance of the @code{__sync} -family of functions may be used to implement the C++11 @code{__atomic} -family of functions. - -The default value of this option is enabled, thus the only useful form -of the option is @option{-fno-sync-libcalls}. This option is used in -the implementation of the @file{libatomic} runtime library. - -@end table - -@c man end - -@node Environment Variables -@section Environment Variables Affecting GCC -@cindex environment variables - -@c man begin ENVIRONMENT -This section describes several environment variables that affect how GCC -operates. Some of them work by specifying directories or prefixes to use -when searching for various kinds of files. Some are used to specify other -aspects of the compilation environment. - -Note that you can also specify places to search using options such as -@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These -take precedence over places specified using environment variables, which -in turn take precedence over those specified by the configuration of GCC@. -@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, -GNU Compiler Collection (GCC) Internals}. - -@table @env -@item LANG -@itemx LC_CTYPE -@c @itemx LC_COLLATE -@itemx LC_MESSAGES -@c @itemx LC_MONETARY -@c @itemx LC_NUMERIC -@c @itemx LC_TIME -@itemx LC_ALL -@findex LANG -@findex LC_CTYPE -@c @findex LC_COLLATE -@findex LC_MESSAGES -@c @findex LC_MONETARY -@c @findex LC_NUMERIC -@c @findex LC_TIME -@findex LC_ALL -@cindex locale -These environment variables control the way that GCC uses -localization information which allows GCC to work with different -national conventions. GCC inspects the locale categories -@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do -so. These locale categories can be set to any value supported by your -installation. A typical value is @samp{en_GB.UTF-8} for English in the United -Kingdom encoded in UTF-8. - -The @env{LC_CTYPE} environment variable specifies character -classification. GCC uses it to determine the character boundaries in -a string; this is needed for some multibyte encodings that contain quote -and escape characters that are otherwise interpreted as a string -end or escape. - -The @env{LC_MESSAGES} environment variable specifies the language to -use in diagnostic messages. - -If the @env{LC_ALL} environment variable is set, it overrides the value -of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} -and @env{LC_MESSAGES} default to the value of the @env{LANG} -environment variable. If none of these variables are set, GCC -defaults to traditional C English behavior. - -@item TMPDIR -@findex TMPDIR -If @env{TMPDIR} is set, it specifies the directory to use for temporary -files. GCC uses temporary files to hold the output of one stage of -compilation which is to be used as input to the next stage: for example, -the output of the preprocessor, which is the input to the compiler -proper. - -@item GCC_COMPARE_DEBUG -@findex GCC_COMPARE_DEBUG -Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing -@option{-fcompare-debug} to the compiler driver. See the documentation -of this option for more details. - -@item GCC_EXEC_PREFIX -@findex GCC_EXEC_PREFIX -If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the -names of the subprograms executed by the compiler. No slash is added -when this prefix is combined with the name of a subprogram, but you can -specify a prefix that ends with a slash if you wish. - -If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out -an appropriate prefix to use based on the pathname it is invoked with. - -If GCC cannot find the subprogram using the specified prefix, it -tries looking in the usual places for the subprogram. - -The default value of @env{GCC_EXEC_PREFIX} is -@file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to -the installed compiler. In many cases @var{prefix} is the value -of @code{prefix} when you ran the @file{configure} script. - -Other prefixes specified with @option{-B} take precedence over this prefix. - -This prefix is also used for finding files such as @file{crt0.o} that are -used for linking. - -In addition, the prefix is used in an unusual way in finding the -directories to search for header files. For each of the standard -directories whose name normally begins with @samp{/usr/local/lib/gcc} -(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries -replacing that beginning with the specified prefix to produce an -alternate directory name. Thus, with @option{-Bfoo/}, GCC searches -@file{foo/bar} just before it searches the standard directory -@file{/usr/local/lib/bar}. -If a standard directory begins with the configured -@var{prefix} then the value of @var{prefix} is replaced by -@env{GCC_EXEC_PREFIX} when looking for header files. - -@item COMPILER_PATH -@findex COMPILER_PATH -The value of @env{COMPILER_PATH} is a colon-separated list of -directories, much like @env{PATH}. GCC tries the directories thus -specified when searching for subprograms, if it can't find the -subprograms using @env{GCC_EXEC_PREFIX}. - -@item LIBRARY_PATH -@findex LIBRARY_PATH -The value of @env{LIBRARY_PATH} is a colon-separated list of -directories, much like @env{PATH}. When configured as a native compiler, -GCC tries the directories thus specified when searching for special -linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking -using GCC also uses these directories when searching for ordinary -libraries for the @option{-l} option (but directories specified with -@option{-L} come first). - -@item LANG -@findex LANG -@cindex locale definition -This variable is used to pass locale information to the compiler. One way in -which this information is used is to determine the character set to be used -when character literals, string literals and comments are parsed in C and C++. -When the compiler is configured to allow multibyte characters, -the following values for @env{LANG} are recognized: - -@table @samp -@item C-JIS -Recognize JIS characters. -@item C-SJIS -Recognize SJIS characters. -@item C-EUCJP -Recognize EUCJP characters. -@end table - -If @env{LANG} is not defined, or if it has some other value, then the -compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to -recognize and translate multibyte characters. -@end table - -@noindent -Some additional environment variables affect the behavior of the -preprocessor. - -@include cppenv.texi - -@c man end - -@node Precompiled Headers -@section Using Precompiled Headers -@cindex precompiled headers -@cindex speed of compilation - -Often large projects have many header files that are included in every -source file. The time the compiler takes to process these header files -over and over again can account for nearly all of the time required to -build the project. To make builds faster, GCC allows you to -@dfn{precompile} a header file. - -To create a precompiled header file, simply compile it as you would any -other file, if necessary using the @option{-x} option to make the driver -treat it as a C or C++ header file. You may want to use a -tool like @command{make} to keep the precompiled header up-to-date when -the headers it contains change. - -A precompiled header file is searched for when @code{#include} is -seen in the compilation. As it searches for the included file -(@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the -compiler looks for a precompiled header in each directory just before it -looks for the include file in that directory. The name searched for is -the name specified in the @code{#include} with @samp{.gch} appended. If -the precompiled header file can't be used, it is ignored. - -For instance, if you have @code{#include "all.h"}, and you have -@file{all.h.gch} in the same directory as @file{all.h}, then the -precompiled header file is used if possible, and the original -header is used otherwise. - -Alternatively, you might decide to put the precompiled header file in a -directory and use @option{-I} to ensure that directory is searched -before (or instead of) the directory containing the original header. -Then, if you want to check that the precompiled header file is always -used, you can put a file of the same name as the original header in this -directory containing an @code{#error} command. - -This also works with @option{-include}. So yet another way to use -precompiled headers, good for projects not designed with precompiled -header files in mind, is to simply take most of the header files used by -a project, include them from another header file, precompile that header -file, and @option{-include} the precompiled header. If the header files -have guards against multiple inclusion, they are skipped because -they've already been included (in the precompiled header). - -If you need to precompile the same header file for different -languages, targets, or compiler options, you can instead make a -@emph{directory} named like @file{all.h.gch}, and put each precompiled -header in the directory, perhaps using @option{-o}. It doesn't matter -what you call the files in the directory; every precompiled header in -the directory is considered. The first precompiled header -encountered in the directory that is valid for this compilation is -used; they're searched in no particular order. - -There are many other possibilities, limited only by your imagination, -good sense, and the constraints of your build system. - -A precompiled header file can be used only when these conditions apply: - -@itemize -@item -Only one precompiled header can be used in a particular compilation. - -@item -A precompiled header can't be used once the first C token is seen. You -can have preprocessor directives before a precompiled header; you cannot -include a precompiled header from inside another header. - -@item -The precompiled header file must be produced for the same language as -the current compilation. You can't use a C precompiled header for a C++ -compilation. - -@item -The precompiled header file must have been produced by the same compiler -binary as the current compilation is using. - -@item -Any macros defined before the precompiled header is included must -either be defined in the same way as when the precompiled header was -generated, or must not affect the precompiled header, which usually -means that they don't appear in the precompiled header at all. - -The @option{-D} option is one way to define a macro before a -precompiled header is included; using a @code{#define} can also do it. -There are also some options that define macros implicitly, like -@option{-O} and @option{-Wdeprecated}; the same rule applies to macros -defined this way. - -@item If debugging information is output when using the precompiled -header, using @option{-g} or similar, the same kind of debugging information -must have been output when building the precompiled header. However, -a precompiled header built using @option{-g} can be used in a compilation -when no debugging information is being output. - -@item The same @option{-m} options must generally be used when building -and using the precompiled header. @xref{Submodel Options}, -for any cases where this rule is relaxed. - -@item Each of the following options must be the same when building and using -the precompiled header: - -@gccoptlist{-fexceptions} - -@item -Some other command-line options starting with @option{-f}, -@option{-p}, or @option{-O} must be defined in the same way as when -the precompiled header was generated. At present, it's not clear -which options are safe to change and which are not; the safest choice -is to use exactly the same options when generating and using the -precompiled header. The following are known to be safe: - -@gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol --fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol --fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol --pedantic-errors} - -@end itemize - -For all of these except the last, the compiler automatically -ignores the precompiled header if the conditions aren't met. If you -find an option combination that doesn't work and doesn't cause the -precompiled header to be ignored, please consider filing a bug report, -see @ref{Bugs}. - -If you do use differing options when generating and using the -precompiled header, the actual behavior is a mixture of the -behavior for the options. For instance, if you use @option{-g} to -generate the precompiled header but not when using it, you may or may -not get debugging information for routines in the precompiled header. |