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diff --git a/gcc-4.2.1-5666.3/gcc/doc/tm.texi b/gcc-4.2.1-5666.3/gcc/doc/tm.texi new file mode 100644 index 000000000..606b5a295 --- /dev/null +++ b/gcc-4.2.1-5666.3/gcc/doc/tm.texi @@ -0,0 +1,10019 @@ +@c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001, +@c 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Target Macros +@chapter Target Description Macros and Functions +@cindex machine description macros +@cindex target description macros +@cindex macros, target description +@cindex @file{tm.h} macros + +In addition to the file @file{@var{machine}.md}, a machine description +includes a C header file conventionally given the name +@file{@var{machine}.h} and a C source file named @file{@var{machine}.c}. +The header file defines numerous macros that convey the information +about the target machine that does not fit into the scheme of the +@file{.md} file. The file @file{tm.h} should be a link to +@file{@var{machine}.h}. The header file @file{config.h} includes +@file{tm.h} and most compiler source files include @file{config.h}. The +source file defines a variable @code{targetm}, which is a structure +containing pointers to functions and data relating to the target +machine. @file{@var{machine}.c} should also contain their definitions, +if they are not defined elsewhere in GCC, and other functions called +through the macros defined in the @file{.h} file. + +@menu +* Target Structure:: The @code{targetm} variable. +* Driver:: Controlling how the driver runs the compilation passes. +* Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}. +* Per-Function Data:: Defining data structures for per-function information. +* Storage Layout:: Defining sizes and alignments of data. +* Type Layout:: Defining sizes and properties of basic user data types. +* Registers:: Naming and describing the hardware registers. +* Register Classes:: Defining the classes of hardware registers. +* Old Constraints:: The old way to define machine-specific constraints. +* Stack and Calling:: Defining which way the stack grows and by how much. +* Varargs:: Defining the varargs macros. +* Trampolines:: Code set up at run time to enter a nested function. +* Library Calls:: Controlling how library routines are implicitly called. +* Addressing Modes:: Defining addressing modes valid for memory operands. +* Anchored Addresses:: Defining how @option{-fsection-anchors} should work. +* Condition Code:: Defining how insns update the condition code. +* Costs:: Defining relative costs of different operations. +* Scheduling:: Adjusting the behavior of the instruction scheduler. +* Sections:: Dividing storage into text, data, and other sections. +* PIC:: Macros for position independent code. +* Assembler Format:: Defining how to write insns and pseudo-ops to output. +* Debugging Info:: Defining the format of debugging output. +* Floating Point:: Handling floating point for cross-compilers. +* Mode Switching:: Insertion of mode-switching instructions. +* Target Attributes:: Defining target-specific uses of @code{__attribute__}. +* MIPS Coprocessors:: MIPS coprocessor support and how to customize it. +* PCH Target:: Validity checking for precompiled headers. +* C++ ABI:: Controlling C++ ABI changes. +* Misc:: Everything else. +@end menu + +@node Target Structure +@section The Global @code{targetm} Variable +@cindex target hooks +@cindex target functions + +@deftypevar {struct gcc_target} targetm +The target @file{.c} file must define the global @code{targetm} variable +which contains pointers to functions and data relating to the target +machine. The variable is declared in @file{target.h}; +@file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is +used to initialize the variable, and macros for the default initializers +for elements of the structure. The @file{.c} file should override those +macros for which the default definition is inappropriate. For example: +@smallexample +#include "target.h" +#include "target-def.h" + +/* @r{Initialize the GCC target structure.} */ + +#undef TARGET_COMP_TYPE_ATTRIBUTES +#define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes + +struct gcc_target targetm = TARGET_INITIALIZER; +@end smallexample +@end deftypevar + +Where a macro should be defined in the @file{.c} file in this manner to +form part of the @code{targetm} structure, it is documented below as a +``Target Hook'' with a prototype. Many macros will change in future +from being defined in the @file{.h} file to being part of the +@code{targetm} structure. + +@node Driver +@section Controlling the Compilation Driver, @file{gcc} +@cindex driver +@cindex controlling the compilation driver + +@c prevent bad page break with this line +You can control the compilation driver. + +@defmac SWITCH_TAKES_ARG (@var{char}) +A C expression which determines whether the option @option{-@var{char}} +takes arguments. The value should be the number of arguments that +option takes--zero, for many options. + +By default, this macro is defined as +@code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options +properly. You need not define @code{SWITCH_TAKES_ARG} unless you +wish to add additional options which take arguments. Any redefinition +should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for +additional options. +@end defmac + +@defmac WORD_SWITCH_TAKES_ARG (@var{name}) +A C expression which determines whether the option @option{-@var{name}} +takes arguments. The value should be the number of arguments that +option takes--zero, for many options. This macro rather than +@code{SWITCH_TAKES_ARG} is used for multi-character option names. + +By default, this macro is defined as +@code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options +properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you +wish to add additional options which take arguments. Any redefinition +should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for +additional options. +@end defmac + +@defmac SWITCH_CURTAILS_COMPILATION (@var{char}) +A C expression which determines whether the option @option{-@var{char}} +stops compilation before the generation of an executable. The value is +boolean, nonzero if the option does stop an executable from being +generated, zero otherwise. + +By default, this macro is defined as +@code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard +options properly. You need not define +@code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional +options which affect the generation of an executable. Any redefinition +should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check +for additional options. +@end defmac + +@defmac SWITCHES_NEED_SPACES +A string-valued C expression which enumerates the options for which +the linker needs a space between the option and its argument. + +If this macro is not defined, the default value is @code{""}. +@end defmac + +@defmac TARGET_OPTION_TRANSLATE_TABLE +If defined, a list of pairs of strings, the first of which is a +potential command line target to the @file{gcc} driver program, and the +second of which is a space-separated (tabs and other whitespace are not +supported) list of options with which to replace the first option. The +target defining this list is responsible for assuring that the results +are valid. Replacement options may not be the @code{--opt} style, they +must be the @code{-opt} style. It is the intention of this macro to +provide a mechanism for substitution that affects the multilibs chosen, +such as one option that enables many options, some of which select +multilibs. Example nonsensical definition, where @option{-malt-abi}, +@option{-EB}, and @option{-mspoo} cause different multilibs to be chosen: + +@smallexample +#define TARGET_OPTION_TRANSLATE_TABLE \ +@{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \ +@{ "-compat", "-EB -malign=4 -mspoo" @} +@end smallexample +@end defmac + +@defmac DRIVER_SELF_SPECS +A list of specs for the driver itself. It should be a suitable +initializer for an array of strings, with no surrounding braces. + +The driver applies these specs to its own command line between loading +default @file{specs} files (but not command-line specified ones) and +choosing the multilib directory or running any subcommands. It +applies them in the order given, so each spec can depend on the +options added by earlier ones. It is also possible to remove options +using @samp{%<@var{option}} in the usual way. + +This macro can be useful when a port has several interdependent target +options. It provides a way of standardizing the command line so +that the other specs are easier to write. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac OPTION_DEFAULT_SPECS +A list of specs used to support configure-time default options (i.e.@: +@option{--with} options) in the driver. It should be a suitable initializer +for an array of structures, each containing two strings, without the +outermost pair of surrounding braces. + +The first item in the pair is the name of the default. This must match +the code in @file{config.gcc} for the target. The second item is a spec +to apply if a default with this name was specified. The string +@samp{%(VALUE)} in the spec will be replaced by the value of the default +everywhere it occurs. + +The driver will apply these specs to its own command line between loading +default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using +the same mechanism as @code{DRIVER_SELF_SPECS}. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CPP_SPEC +A C string constant that tells the GCC driver program options to +pass to CPP@. It can also specify how to translate options you +give to GCC into options for GCC to pass to the CPP@. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CPLUSPLUS_CPP_SPEC +This macro is just like @code{CPP_SPEC}, but is used for C++, rather +than C@. If you do not define this macro, then the value of +@code{CPP_SPEC} (if any) will be used instead. +@end defmac + +@defmac CC1_SPEC +A C string constant that tells the GCC driver program options to +pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language +front ends. +It can also specify how to translate options you give to GCC into options +for GCC to pass to front ends. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CC1PLUS_SPEC +A C string constant that tells the GCC driver program options to +pass to @code{cc1plus}. It can also specify how to translate options you +give to GCC into options for GCC to pass to the @code{cc1plus}. + +Do not define this macro if it does not need to do anything. +Note that everything defined in CC1_SPEC is already passed to +@code{cc1plus} so there is no need to duplicate the contents of +CC1_SPEC in CC1PLUS_SPEC@. +@end defmac + +@defmac ASM_SPEC +A C string constant that tells the GCC driver program options to +pass to the assembler. It can also specify how to translate options +you give to GCC into options for GCC to pass to the assembler. +See the file @file{sun3.h} for an example of this. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac ASM_FINAL_SPEC +A C string constant that tells the GCC driver program how to +run any programs which cleanup after the normal assembler. +Normally, this is not needed. See the file @file{mips.h} for +an example of this. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac AS_NEEDS_DASH_FOR_PIPED_INPUT +Define this macro, with no value, if the driver should give the assembler +an argument consisting of a single dash, @option{-}, to instruct it to +read from its standard input (which will be a pipe connected to the +output of the compiler proper). This argument is given after any +@option{-o} option specifying the name of the output file. + +If you do not define this macro, the assembler is assumed to read its +standard input if given no non-option arguments. If your assembler +cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct; +see @file{mips.h} for instance. +@end defmac + +@defmac LINK_SPEC +A C string constant that tells the GCC driver program options to +pass to the linker. It can also specify how to translate options you +give to GCC into options for GCC to pass to the linker. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac LIB_SPEC +Another C string constant used much like @code{LINK_SPEC}. The difference +between the two is that @code{LIB_SPEC} is used at the end of the +command given to the linker. + +If this macro is not defined, a default is provided that +loads the standard C library from the usual place. See @file{gcc.c}. +@end defmac + +@defmac LIBGCC_SPEC +Another C string constant that tells the GCC driver program +how and when to place a reference to @file{libgcc.a} into the +linker command line. This constant is placed both before and after +the value of @code{LIB_SPEC}. + +If this macro is not defined, the GCC driver provides a default that +passes the string @option{-lgcc} to the linker. +@end defmac + +@defmac REAL_LIBGCC_SPEC +By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the +@code{LIBGCC_SPEC} is not directly used by the driver program but is +instead modified to refer to different versions of @file{libgcc.a} +depending on the values of the command line flags @option{-static}, +@option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On +targets where these modifications are inappropriate, define +@code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the +driver how to place a reference to @file{libgcc} on the link command +line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified. +@end defmac + +@defmac USE_LD_AS_NEEDED +A macro that controls the modifications to @code{LIBGCC_SPEC} +mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be +generated that uses --as-needed and the shared libgcc in place of the +static exception handler library, when linking without any of +@code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}. +@end defmac + +@defmac LINK_EH_SPEC +If defined, this C string constant is added to @code{LINK_SPEC}. +When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects +the modifications to @code{LIBGCC_SPEC} mentioned in +@code{REAL_LIBGCC_SPEC}. +@end defmac + +@defmac STARTFILE_SPEC +Another C string constant used much like @code{LINK_SPEC}. The +difference between the two is that @code{STARTFILE_SPEC} is used at +the very beginning of the command given to the linker. + +If this macro is not defined, a default is provided that loads the +standard C startup file from the usual place. See @file{gcc.c}. +@end defmac + +@defmac ENDFILE_SPEC +Another C string constant used much like @code{LINK_SPEC}. The +difference between the two is that @code{ENDFILE_SPEC} is used at +the very end of the command given to the linker. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac THREAD_MODEL_SPEC +GCC @code{-v} will print the thread model GCC was configured to use. +However, this doesn't work on platforms that are multilibbed on thread +models, such as AIX 4.3. On such platforms, define +@code{THREAD_MODEL_SPEC} such that it evaluates to a string without +blanks that names one of the recognized thread models. @code{%*}, the +default value of this macro, will expand to the value of +@code{thread_file} set in @file{config.gcc}. +@end defmac + +@defmac SYSROOT_SUFFIX_SPEC +Define this macro to add a suffix to the target sysroot when GCC is +configured with a sysroot. This will cause GCC to search for usr/lib, +et al, within sysroot+suffix. +@end defmac + +@defmac SYSROOT_HEADERS_SUFFIX_SPEC +Define this macro to add a headers_suffix to the target sysroot when +GCC is configured with a sysroot. This will cause GCC to pass the +updated sysroot+headers_suffix to CPP, causing it to search for +usr/include, et al, within sysroot+headers_suffix. +@end defmac + +@defmac EXTRA_SPECS +Define this macro to provide additional specifications to put in the +@file{specs} file that can be used in various specifications like +@code{CC1_SPEC}. + +The definition should be an initializer for an array of structures, +containing a string constant, that defines the specification name, and a +string constant that provides the specification. + +Do not define this macro if it does not need to do anything. + +@code{EXTRA_SPECS} is useful when an architecture contains several +related targets, which have various @code{@dots{}_SPECS} which are similar +to each other, and the maintainer would like one central place to keep +these definitions. + +For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to +define either @code{_CALL_SYSV} when the System V calling sequence is +used or @code{_CALL_AIX} when the older AIX-based calling sequence is +used. + +The @file{config/rs6000/rs6000.h} target file defines: + +@smallexample +#define EXTRA_SPECS \ + @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @}, + +#define CPP_SYS_DEFAULT "" +@end smallexample + +The @file{config/rs6000/sysv.h} target file defines: +@smallexample +#undef CPP_SPEC +#define CPP_SPEC \ +"%@{posix: -D_POSIX_SOURCE @} \ +%@{mcall-sysv: -D_CALL_SYSV @} \ +%@{!mcall-sysv: %(cpp_sysv_default) @} \ +%@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}" + +#undef CPP_SYSV_DEFAULT +#define CPP_SYSV_DEFAULT "-D_CALL_SYSV" +@end smallexample + +while the @file{config/rs6000/eabiaix.h} target file defines +@code{CPP_SYSV_DEFAULT} as: + +@smallexample +#undef CPP_SYSV_DEFAULT +#define CPP_SYSV_DEFAULT "-D_CALL_AIX" +@end smallexample +@end defmac + +@defmac LINK_LIBGCC_SPECIAL_1 +Define this macro if the driver program should find the library +@file{libgcc.a}. If you do not define this macro, the driver program will pass +the argument @option{-lgcc} to tell the linker to do the search. +@end defmac + +@defmac LINK_GCC_C_SEQUENCE_SPEC +The sequence in which libgcc and libc are specified to the linker. +By default this is @code{%G %L %G}. +@end defmac + +@defmac LINK_COMMAND_SPEC +A C string constant giving the complete command line need to execute the +linker. When you do this, you will need to update your port each time a +change is made to the link command line within @file{gcc.c}. Therefore, +define this macro only if you need to completely redefine the command +line for invoking the linker and there is no other way to accomplish +the effect you need. Overriding this macro may be avoidable by overriding +@code{LINK_GCC_C_SEQUENCE_SPEC} instead. +@end defmac + +@defmac LINK_ELIMINATE_DUPLICATE_LDIRECTORIES +A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search +directories from linking commands. Do not give it a nonzero value if +removing duplicate search directories changes the linker's semantics. +@end defmac + +@defmac MULTILIB_DEFAULTS +Define this macro as a C expression for the initializer of an array of +string to tell the driver program which options are defaults for this +target and thus do not need to be handled specially when using +@code{MULTILIB_OPTIONS}. + +Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in +the target makefile fragment or if none of the options listed in +@code{MULTILIB_OPTIONS} are set by default. +@xref{Target Fragment}. +@end defmac + +@defmac RELATIVE_PREFIX_NOT_LINKDIR +Define this macro to tell @command{gcc} that it should only translate +a @option{-B} prefix into a @option{-L} linker option if the prefix +indicates an absolute file name. +@end defmac + +@defmac MD_EXEC_PREFIX +If defined, this macro is an additional prefix to try after +@code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched +when the @option{-b} option is used, or the compiler is built as a cross +compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it +to the list of directories used to find the assembler in @file{configure.in}. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX +Define this macro as a C string constant if you wish to override the +standard choice of @code{libdir} as the default prefix to +try when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX_1 +Define this macro as a C string constant if you wish to override the +standard choice of @code{/lib} as a prefix to try after the default prefix +when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX_2 +Define this macro as a C string constant if you wish to override the +standard choice of @code{/lib} as yet another prefix to try after the +default prefix when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac MD_STARTFILE_PREFIX +If defined, this macro supplies an additional prefix to try after the +standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the +@option{-b} option is used, or when the compiler is built as a cross +compiler. +@end defmac + +@defmac MD_STARTFILE_PREFIX_1 +If defined, this macro supplies yet another prefix to try after the +standard prefixes. It is not searched when the @option{-b} option is +used, or when the compiler is built as a cross compiler. +@end defmac + +@defmac INIT_ENVIRONMENT +Define this macro as a C string constant if you wish to set environment +variables for programs called by the driver, such as the assembler and +loader. The driver passes the value of this macro to @code{putenv} to +initialize the necessary environment variables. +@end defmac + +@defmac LOCAL_INCLUDE_DIR +Define this macro as a C string constant if you wish to override the +standard choice of @file{/usr/local/include} as the default prefix to +try when searching for local header files. @code{LOCAL_INCLUDE_DIR} +comes before @code{SYSTEM_INCLUDE_DIR} in the search order. + +Cross compilers do not search either @file{/usr/local/include} or its +replacement. +@end defmac + +@defmac MODIFY_TARGET_NAME +Define this macro if you wish to define command-line switches that +modify the default target name. + +For each switch, you can include a string to be appended to the first +part of the configuration name or a string to be deleted from the +configuration name, if present. The definition should be an initializer +for an array of structures. Each array element should have three +elements: the switch name (a string constant, including the initial +dash), one of the enumeration codes @code{ADD} or @code{DELETE} to +indicate whether the string should be inserted or deleted, and the string +to be inserted or deleted (a string constant). + +For example, on a machine where @samp{64} at the end of the +configuration name denotes a 64-bit target and you want the @option{-32} +and @option{-64} switches to select between 32- and 64-bit targets, you would +code + +@smallexample +#define MODIFY_TARGET_NAME \ + @{ @{ "-32", DELETE, "64"@}, \ + @{"-64", ADD, "64"@}@} +@end smallexample +@end defmac + +@defmac SYSTEM_INCLUDE_DIR +Define this macro as a C string constant if you wish to specify a +system-specific directory to search for header files before the standard +directory. @code{SYSTEM_INCLUDE_DIR} comes before +@code{STANDARD_INCLUDE_DIR} in the search order. + +Cross compilers do not use this macro and do not search the directory +specified. +@end defmac + +@defmac STANDARD_INCLUDE_DIR +Define this macro as a C string constant if you wish to override the +standard choice of @file{/usr/include} as the default prefix to +try when searching for header files. + +Cross compilers ignore this macro and do not search either +@file{/usr/include} or its replacement. +@end defmac + +@defmac STANDARD_INCLUDE_COMPONENT +The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}. +See @code{INCLUDE_DEFAULTS}, below, for the description of components. +If you do not define this macro, no component is used. +@end defmac + +@defmac INCLUDE_DEFAULTS +Define this macro if you wish to override the entire default search path +for include files. For a native compiler, the default search path +usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR}, +@code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and +@code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR} +and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile}, +and specify private search areas for GCC@. The directory +@code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs. + +The definition should be an initializer for an array of structures. +Each array element should have four elements: the directory name (a +string constant), the component name (also a string constant), a flag +for C++-only directories, +and a flag showing that the includes in the directory don't need to be +wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of +the array with a null element. + +The component name denotes what GNU package the include file is part of, +if any, in all uppercase letters. For example, it might be @samp{GCC} +or @samp{BINUTILS}. If the package is part of a vendor-supplied +operating system, code the component name as @samp{0}. + +For example, here is the definition used for VAX/VMS: + +@smallexample +#define INCLUDE_DEFAULTS \ +@{ \ + @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \ + @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \ + @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \ + @{ ".", 0, 0, 0@}, \ + @{ 0, 0, 0, 0@} \ +@} +@end smallexample +@end defmac + +Here is the order of prefixes tried for exec files: + +@enumerate +@item +Any prefixes specified by the user with @option{-B}. + +@item +The environment variable @code{GCC_EXEC_PREFIX}, if any. + +@item +The directories specified by the environment variable @code{COMPILER_PATH}. + +@item +The macro @code{STANDARD_EXEC_PREFIX}. + +@item +@file{/usr/lib/gcc/}. + +@item +The macro @code{MD_EXEC_PREFIX}, if any. +@end enumerate + +Here is the order of prefixes tried for startfiles: + +@enumerate +@item +Any prefixes specified by the user with @option{-B}. + +@item +The environment variable @code{GCC_EXEC_PREFIX}, if any. + +@item +The directories specified by the environment variable @code{LIBRARY_PATH} +(or port-specific name; native only, cross compilers do not use this). + +@item +The macro @code{STANDARD_EXEC_PREFIX}. + +@item +@file{/usr/lib/gcc/}. + +@item +The macro @code{MD_EXEC_PREFIX}, if any. + +@item +The macro @code{MD_STARTFILE_PREFIX}, if any. + +@item +The macro @code{STANDARD_STARTFILE_PREFIX}. + +@item +@file{/lib/}. + +@item +@file{/usr/lib/}. +@end enumerate + +@node Run-time Target +@section Run-time Target Specification +@cindex run-time target specification +@cindex predefined macros +@cindex target specifications + +@c prevent bad page break with this line +Here are run-time target specifications. + +@defmac TARGET_CPU_CPP_BUILTINS () +This function-like macro expands to a block of code that defines +built-in preprocessor macros and assertions for the target cpu, using +the functions @code{builtin_define}, @code{builtin_define_std} and +@code{builtin_assert}. When the front end +calls this macro it provides a trailing semicolon, and since it has +finished command line option processing your code can use those +results freely. + +@code{builtin_assert} takes a string in the form you pass to the +command-line option @option{-A}, such as @code{cpu=mips}, and creates +the assertion. @code{builtin_define} takes a string in the form +accepted by option @option{-D} and unconditionally defines the macro. + +@code{builtin_define_std} takes a string representing the name of an +object-like macro. If it doesn't lie in the user's namespace, +@code{builtin_define_std} defines it unconditionally. Otherwise, it +defines a version with two leading underscores, and another version +with two leading and trailing underscores, and defines the original +only if an ISO standard was not requested on the command line. For +example, passing @code{unix} defines @code{__unix}, @code{__unix__} +and possibly @code{unix}; passing @code{_mips} defines @code{__mips}, +@code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64} +defines only @code{_ABI64}. + +You can also test for the C dialect being compiled. The variable +@code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus} +or @code{clk_objective_c}. Note that if we are preprocessing +assembler, this variable will be @code{clk_c} but the function-like +macro @code{preprocessing_asm_p()} will return true, so you might want +to check for that first. If you need to check for strict ANSI, the +variable @code{flag_iso} can be used. The function-like macro +@code{preprocessing_trad_p()} can be used to check for traditional +preprocessing. +@end defmac + +@defmac TARGET_OS_CPP_BUILTINS () +Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional +and is used for the target operating system instead. +@end defmac + +@defmac TARGET_OBJFMT_CPP_BUILTINS () +Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional +and is used for the target object format. @file{elfos.h} uses this +macro to define @code{__ELF__}, so you probably do not need to define +it yourself. +@end defmac + +@deftypevar {extern int} target_flags +This variable is declared in @file{options.h}, which is included before +any target-specific headers. +@end deftypevar + +@deftypevar {Target Hook} int TARGET_DEFAULT_TARGET_FLAGS +This variable specifies the initial value of @code{target_flags}. +Its default setting is 0. +@end deftypevar + +@cindex optional hardware or system features +@cindex features, optional, in system conventions + +@deftypefn {Target Hook} bool TARGET_HANDLE_OPTION (size_t @var{code}, const char *@var{arg}, int @var{value}) +This hook is called whenever the user specifies one of the +target-specific options described by the @file{.opt} definition files +(@pxref{Options}). It has the opportunity to do some option-specific +processing and should return true if the option is valid. The default +definition does nothing but return true. + +@var{code} specifies the @code{OPT_@var{name}} enumeration value +associated with the selected option; @var{name} is just a rendering of +the option name in which non-alphanumeric characters are replaced by +underscores. @var{arg} specifies the string argument and is null if +no argument was given. If the option is flagged as a @code{UInteger} +(@pxref{Option properties}), @var{value} is the numeric value of the +argument. Otherwise @var{value} is 1 if the positive form of the +option was used and 0 if the ``no-'' form was. +@end deftypefn + +@defmac TARGET_VERSION +This macro is a C statement to print on @code{stderr} a string +describing the particular machine description choice. Every machine +description should define @code{TARGET_VERSION}. For example: + +@smallexample +#ifdef MOTOROLA +#define TARGET_VERSION \ + fprintf (stderr, " (68k, Motorola syntax)"); +#else +#define TARGET_VERSION \ + fprintf (stderr, " (68k, MIT syntax)"); +#endif +@end smallexample +@end defmac + +@defmac OVERRIDE_OPTIONS +Sometimes certain combinations of command options do not make sense on +a particular target machine. You can define a macro +@code{OVERRIDE_OPTIONS} to take account of this. This macro, if +defined, is executed once just after all the command options have been +parsed. + +Don't use this macro to turn on various extra optimizations for +@option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for. +@end defmac + +@defmac C_COMMON_OVERRIDE_OPTIONS +This is similar to @code{OVERRIDE_OPTIONS} but is only used in the C +language frontends (C, Objective-C, C++, Objective-C++) and so can be +used to alter option flag variables which only exist in those +frontends. +@end defmac + +@defmac OPTIMIZATION_OPTIONS (@var{level}, @var{size}) +Some machines may desire to change what optimizations are performed for +various optimization levels. This macro, if defined, is executed once +just after the optimization level is determined and before the remainder +of the command options have been parsed. Values set in this macro are +used as the default values for the other command line options. + +@var{level} is the optimization level specified; 2 if @option{-O2} is +specified, 1 if @option{-O} is specified, and 0 if neither is specified. + +@var{size} is nonzero if @option{-Os} is specified and zero otherwise. + +You should not use this macro to change options that are not +machine-specific. These should uniformly selected by the same +optimization level on all supported machines. Use this macro to enable +machine-specific optimizations. + +@strong{Do not examine @code{write_symbols} in +this macro!} The debugging options are not supposed to alter the +generated code. +@end defmac + +@defmac CAN_DEBUG_WITHOUT_FP +Define this macro if debugging can be performed even without a frame +pointer. If this macro is defined, GCC will turn on the +@option{-fomit-frame-pointer} option whenever @option{-O} is specified. +@end defmac + +@node Per-Function Data +@section Defining data structures for per-function information. +@cindex per-function data +@cindex data structures + +If the target needs to store information on a per-function basis, GCC +provides a macro and a couple of variables to allow this. Note, just +using statics to store the information is a bad idea, since GCC supports +nested functions, so you can be halfway through encoding one function +when another one comes along. + +GCC defines a data structure called @code{struct function} which +contains all of the data specific to an individual function. This +structure contains a field called @code{machine} whose type is +@code{struct machine_function *}, which can be used by targets to point +to their own specific data. + +If a target needs per-function specific data it should define the type +@code{struct machine_function} and also the macro @code{INIT_EXPANDERS}. +This macro should be used to initialize the function pointer +@code{init_machine_status}. This pointer is explained below. + +One typical use of per-function, target specific data is to create an +RTX to hold the register containing the function's return address. This +RTX can then be used to implement the @code{__builtin_return_address} +function, for level 0. + +Note---earlier implementations of GCC used a single data area to hold +all of the per-function information. Thus when processing of a nested +function began the old per-function data had to be pushed onto a +stack, and when the processing was finished, it had to be popped off the +stack. GCC used to provide function pointers called +@code{save_machine_status} and @code{restore_machine_status} to handle +the saving and restoring of the target specific information. Since the +single data area approach is no longer used, these pointers are no +longer supported. + +@defmac INIT_EXPANDERS +Macro called to initialize any target specific information. This macro +is called once per function, before generation of any RTL has begun. +The intention of this macro is to allow the initialization of the +function pointer @code{init_machine_status}. +@end defmac + +@deftypevar {void (*)(struct function *)} init_machine_status +If this function pointer is non-@code{NULL} it will be called once per +function, before function compilation starts, in order to allow the +target to perform any target specific initialization of the +@code{struct function} structure. It is intended that this would be +used to initialize the @code{machine} of that structure. + +@code{struct machine_function} structures are expected to be freed by GC@. +Generally, any memory that they reference must be allocated by using +@code{ggc_alloc}, including the structure itself. +@end deftypevar + +@node Storage Layout +@section Storage Layout +@cindex storage layout + +Note that the definitions of the macros in this table which are sizes or +alignments measured in bits do not need to be constant. They can be C +expressions that refer to static variables, such as the @code{target_flags}. +@xref{Run-time Target}. + +@defmac BITS_BIG_ENDIAN +Define this macro to have the value 1 if the most significant bit in a +byte has the lowest number; otherwise define it to have the value zero. +This means that bit-field instructions count from the most significant +bit. If the machine has no bit-field instructions, then this must still +be defined, but it doesn't matter which value it is defined to. This +macro need not be a constant. + +This macro does not affect the way structure fields are packed into +bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}. +@end defmac + +@defmac BYTES_BIG_ENDIAN +Define this macro to have the value 1 if the most significant byte in a +word has the lowest number. This macro need not be a constant. +@end defmac + +@defmac WORDS_BIG_ENDIAN +Define this macro to have the value 1 if, in a multiword object, the +most significant word has the lowest number. This applies to both +memory locations and registers; GCC fundamentally assumes that the +order of words in memory is the same as the order in registers. This +macro need not be a constant. +@end defmac + +@defmac LIBGCC2_WORDS_BIG_ENDIAN +Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a +constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be +used only when compiling @file{libgcc2.c}. Typically the value will be set +based on preprocessor defines. +@end defmac + +@defmac FLOAT_WORDS_BIG_ENDIAN +Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or +@code{TFmode} floating point numbers are stored in memory with the word +containing the sign bit at the lowest address; otherwise define it to +have the value 0. This macro need not be a constant. + +You need not define this macro if the ordering is the same as for +multi-word integers. +@end defmac + +@defmac BITS_PER_UNIT +Define this macro to be the number of bits in an addressable storage +unit (byte). If you do not define this macro the default is 8. +@end defmac + +@defmac BITS_PER_WORD +Number of bits in a word. If you do not define this macro, the default +is @code{BITS_PER_UNIT * UNITS_PER_WORD}. +@end defmac + +@defmac MAX_BITS_PER_WORD +Maximum number of bits in a word. If this is undefined, the default is +@code{BITS_PER_WORD}. Otherwise, it is the constant value that is the +largest value that @code{BITS_PER_WORD} can have at run-time. +@end defmac + +@defmac UNITS_PER_WORD +Number of storage units in a word; normally the size of a general-purpose +register, a power of two from 1 or 8. +@end defmac + +@defmac MIN_UNITS_PER_WORD +Minimum number of units in a word. If this is undefined, the default is +@code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the +smallest value that @code{UNITS_PER_WORD} can have at run-time. +@end defmac + +@defmac UNITS_PER_SIMD_WORD +Number of units in the vectors that the vectorizer can produce. +The default is equal to @code{UNITS_PER_WORD}, because the vectorizer +can do some transformations even in absence of specialized @acronym{SIMD} +hardware. +@end defmac + +@defmac POINTER_SIZE +Width of a pointer, in bits. You must specify a value no wider than the +width of @code{Pmode}. If it is not equal to the width of @code{Pmode}, +you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify +a value the default is @code{BITS_PER_WORD}. +@end defmac + +@defmac POINTERS_EXTEND_UNSIGNED +A C expression whose value is greater than zero if pointers that need to be +extended from being @code{POINTER_SIZE} bits wide to @code{Pmode} are to +be zero-extended and zero if they are to be sign-extended. If the value +is less then zero then there must be an "ptr_extend" instruction that +extends a pointer from @code{POINTER_SIZE} to @code{Pmode}. + +You need not define this macro if the @code{POINTER_SIZE} is equal +to the width of @code{Pmode}. +@end defmac + +@defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type}) +A macro to update @var{m} and @var{unsignedp} when an object whose type +is @var{type} and which has the specified mode and signedness is to be +stored in a register. This macro is only called when @var{type} is a +scalar type. + +On most RISC machines, which only have operations that operate on a full +register, define this macro to set @var{m} to @code{word_mode} if +@var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most +cases, only integer modes should be widened because wider-precision +floating-point operations are usually more expensive than their narrower +counterparts. + +For most machines, the macro definition does not change @var{unsignedp}. +However, some machines, have instructions that preferentially handle +either signed or unsigned quantities of certain modes. For example, on +the DEC Alpha, 32-bit loads from memory and 32-bit add instructions +sign-extend the result to 64 bits. On such machines, set +@var{unsignedp} according to which kind of extension is more efficient. + +Do not define this macro if it would never modify @var{m}. +@end defmac + +@defmac PROMOTE_FUNCTION_MODE +Like @code{PROMOTE_MODE}, but is applied to outgoing function arguments or +function return values, as specified by @code{TARGET_PROMOTE_FUNCTION_ARGS} +and @code{TARGET_PROMOTE_FUNCTION_RETURN}, respectively. + +The default is @code{PROMOTE_MODE}. +@end defmac + +@deftypefn {Target Hook} bool TARGET_PROMOTE_FUNCTION_ARGS (tree @var{fntype}) +This target hook should return @code{true} if the promotion described by +@code{PROMOTE_FUNCTION_MODE} should be done for outgoing function +arguments. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_PROMOTE_FUNCTION_RETURN (tree @var{fntype}) +This target hook should return @code{true} if the promotion described by +@code{PROMOTE_FUNCTION_MODE} should be done for the return value of +functions. + +If this target hook returns @code{true}, @code{TARGET_FUNCTION_VALUE} +must perform the same promotions done by @code{PROMOTE_FUNCTION_MODE}. +@end deftypefn + +@defmac PARM_BOUNDARY +Normal alignment required for function parameters on the stack, in +bits. All stack parameters receive at least this much alignment +regardless of data type. On most machines, this is the same as the +size of an integer. +@end defmac + +@defmac STACK_BOUNDARY +Define this macro to the minimum alignment enforced by hardware for the +stack pointer on this machine. The definition is a C expression for the +desired alignment (measured in bits). This value is used as a default +if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines, +this should be the same as @code{PARM_BOUNDARY}. +@end defmac + +@defmac PREFERRED_STACK_BOUNDARY +Define this macro if you wish to preserve a certain alignment for the +stack pointer, greater than what the hardware enforces. The definition +is a C expression for the desired alignment (measured in bits). This +macro must evaluate to a value equal to or larger than +@code{STACK_BOUNDARY}. +@end defmac + +@defmac FUNCTION_BOUNDARY +Alignment required for a function entry point, in bits. +@end defmac + +@defmac BIGGEST_ALIGNMENT +Biggest alignment that any data type can require on this machine, in bits. +@end defmac + +@c APPLE LOCAL begin 5946347 ms_struct support +@defmac BIGGEST_MS_STRUCT_ALIGNMENT +Define this macro if the target supports Microsoft structure alignment +(@code{TARGET_MS_BITFIELD_LAYOUT_P}) and the target definition of +BIGGEST_ALIGNMENT is smaller than is needed for ms_struct records. It should +defined as the largest field alignment required by the target for Microsoft +aligned structure fields. + +By default, @code{BIGGEST_MS_STRUCT_ALIGNMENT} is defined to be equivalent to +@code{BIGGEST_ALIGNMENT}. +@end defmac + +@defmac TARGET_FIELD_MS_STRUCT_ALIGN +Define this macro if the target supports Microsoft structure alignment +(@code{TARGET_MS_BITFIELD_LAYOUT_P}) and the standard type alignment +of non-aggregate types is not sufficient for the MS structure alignment rules. + +The @code{TARGET_FIELD_MS_STRUCT_ALIGN} macro should return the alignment required +for the field passed as its argument. + +By default, the type alignment of the field will be used, i.e., +@code{TYPE_ALIGN (TREE_TYPE (FIELD))}. +@end defmac +@c APPLE LOCAL end 5946347 ms_struct support + +@defmac MINIMUM_ATOMIC_ALIGNMENT +If defined, the smallest alignment, in bits, that can be given to an +object that can be referenced in one operation, without disturbing any +nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger +on machines that don't have byte or half-word store operations. +@end defmac + +@defmac BIGGEST_FIELD_ALIGNMENT +Biggest alignment that any structure or union field can require on this +machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for +structure and union fields only, unless the field alignment has been set +by the @code{__attribute__ ((aligned (@var{n})))} construct. +@end defmac + +@defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed}) +An expression for the alignment of a structure field @var{field} if the +alignment computed in the usual way (including applying of +@code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the +alignment) is @var{computed}. It overrides alignment only if the +field alignment has not been set by the +@code{__attribute__ ((aligned (@var{n})))} construct. +@end defmac + +@defmac MAX_OFILE_ALIGNMENT +Biggest alignment supported by the object file format of this machine. +Use this macro to limit the alignment which can be specified using the +@code{__attribute__ ((aligned (@var{n})))} construct. If not defined, +the default value is @code{BIGGEST_ALIGNMENT}. +@end defmac + +@defmac DATA_ALIGNMENT (@var{type}, @var{basic-align}) +If defined, a C expression to compute the alignment for a variable in +the static store. @var{type} is the data type, and @var{basic-align} is +the alignment that the object would ordinarily have. The value of this +macro is used instead of that alignment to align the object. + +If this macro is not defined, then @var{basic-align} is used. + +@findex strcpy +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. Another is to cause character +arrays to be word-aligned so that @code{strcpy} calls that copy +constants to character arrays can be done inline. +@end defmac + +@defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align}) +If defined, a C expression to compute the alignment given to a constant +that is being placed in memory. @var{constant} is the constant and +@var{basic-align} is the alignment that the object would ordinarily +have. The value of this macro is used instead of that alignment to +align the object. + +If this macro is not defined, then @var{basic-align} is used. + +The typical use of this macro is to increase alignment for string +constants to be word aligned so that @code{strcpy} calls that copy +constants can be done inline. +@end defmac + +@defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align}) +If defined, a C expression to compute the alignment for a variable in +the local store. @var{type} is the data type, and @var{basic-align} is +the alignment that the object would ordinarily have. The value of this +macro is used instead of that alignment to align the object. + +If this macro is not defined, then @var{basic-align} is used. + +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. +@end defmac + +@defmac EMPTY_FIELD_BOUNDARY +Alignment in bits to be given to a structure bit-field that follows an +empty field such as @code{int : 0;}. + +If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro. +@end defmac + +@defmac STRUCTURE_SIZE_BOUNDARY +Number of bits which any structure or union's size must be a multiple of. +Each structure or union's size is rounded up to a multiple of this. + +If you do not define this macro, the default is the same as +@code{BITS_PER_UNIT}. +@end defmac + +@defmac STRICT_ALIGNMENT +Define this macro to be the value 1 if instructions will fail to work +if given data not on the nominal alignment. If instructions will merely +go slower in that case, define this macro as 0. +@end defmac + +@defmac PCC_BITFIELD_TYPE_MATTERS +Define this if you wish to imitate the way many other C compilers handle +alignment of bit-fields and the structures that contain them. + +The behavior is that the type written for a named bit-field (@code{int}, +@code{short}, or other integer type) imposes an alignment for the entire +structure, as if the structure really did contain an ordinary field of +that type. In addition, the bit-field is placed within the structure so +that it would fit within such a field, not crossing a boundary for it. + +Thus, on most machines, a named bit-field whose type is written as +@code{int} would not cross a four-byte boundary, and would force +four-byte alignment for the whole structure. (The alignment used may +not be four bytes; it is controlled by the other alignment parameters.) + +An unnamed bit-field will not affect the alignment of the containing +structure. + +If the macro is defined, its definition should be a C expression; +a nonzero value for the expression enables this behavior. + +Note that if this macro is not defined, or its value is zero, some +bit-fields may cross more than one alignment boundary. The compiler can +support such references if there are @samp{insv}, @samp{extv}, and +@samp{extzv} insns that can directly reference memory. + +The other known way of making bit-fields work is to define +@code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}. +Then every structure can be accessed with fullwords. + +Unless the machine has bit-field instructions or you define +@code{STRUCTURE_SIZE_BOUNDARY} that way, you must define +@code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value. + +If your aim is to make GCC use the same conventions for laying out +bit-fields as are used by another compiler, here is how to investigate +what the other compiler does. Compile and run this program: + +@smallexample +struct foo1 +@{ + char x; + char :0; + char y; +@}; + +struct foo2 +@{ + char x; + int :0; + char y; +@}; + +main () +@{ + printf ("Size of foo1 is %d\n", + sizeof (struct foo1)); + printf ("Size of foo2 is %d\n", + sizeof (struct foo2)); + exit (0); +@} +@end smallexample + +If this prints 2 and 5, then the compiler's behavior is what you would +get from @code{PCC_BITFIELD_TYPE_MATTERS}. +@end defmac + +@defmac BITFIELD_NBYTES_LIMITED +Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited +to aligning a bit-field within the structure. +@end defmac + +@deftypefn {Target Hook} bool TARGET_ALIGN_ANON_BITFIELDS (void) +When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine +whether unnamed bitfields affect the alignment of the containing +structure. The hook should return true if the structure should inherit +the alignment requirements of an unnamed bitfield's type. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_NARROW_VOLATILE_BITFIELDS (void) +This target hook should return @code{true} if accesses to volatile bitfields +should use the narrowest mode possible. It should return @code{false} if +these accesses should use the bitfield container type. + +The default is @code{!TARGET_STRICT_ALIGN}. +@end deftypefn + +@defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode}) +Return 1 if a structure or array containing @var{field} should be accessed using +@code{BLKMODE}. + +If @var{field} is the only field in the structure, @var{mode} is its +mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the +case where structures of one field would require the structure's mode to +retain the field's mode. + +Normally, this is not needed. See the file @file{c4x.h} for an example +of how to use this macro to prevent a structure having a floating point +field from being accessed in an integer mode. +@end defmac + +@defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified}) +Define this macro as an expression for the alignment of a type (given +by @var{type} as a tree node) if the alignment computed in the usual +way is @var{computed} and the alignment explicitly specified was +@var{specified}. + +The default is to use @var{specified} if it is larger; otherwise, use +the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT} +@end defmac + +@defmac MAX_FIXED_MODE_SIZE +An integer expression for the size in bits of the largest integer +machine mode that should actually be used. All integer machine modes of +this size or smaller can be used for structures and unions with the +appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE +(DImode)} is assumed. +@end defmac + +@defmac STACK_SAVEAREA_MODE (@var{save_level}) +If defined, an expression of type @code{enum machine_mode} that +specifies the mode of the save area operand of a +@code{save_stack_@var{level}} named pattern (@pxref{Standard Names}). +@var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or +@code{SAVE_NONLOCAL} and selects which of the three named patterns is +having its mode specified. + +You need not define this macro if it always returns @code{Pmode}. You +would most commonly define this macro if the +@code{save_stack_@var{level}} patterns need to support both a 32- and a +64-bit mode. +@end defmac + +@defmac STACK_SIZE_MODE +If defined, an expression of type @code{enum machine_mode} that +specifies the mode of the size increment operand of an +@code{allocate_stack} named pattern (@pxref{Standard Names}). + +You need not define this macro if it always returns @code{word_mode}. +You would most commonly define this macro if the @code{allocate_stack} +pattern needs to support both a 32- and a 64-bit mode. +@end defmac + +@defmac TARGET_FLOAT_FORMAT +A code distinguishing the floating point format of the target machine. +There are four defined values: + +@ftable @code +@item IEEE_FLOAT_FORMAT +This code indicates IEEE floating point. It is the default; there is no +need to define @code{TARGET_FLOAT_FORMAT} when the format is IEEE@. + +@item VAX_FLOAT_FORMAT +This code indicates the ``F float'' (for @code{float}) and ``D float'' +or ``G float'' formats (for @code{double}) used on the VAX and PDP-11@. + +@item IBM_FLOAT_FORMAT +This code indicates the format used on the IBM System/370. + +@item C4X_FLOAT_FORMAT +This code indicates the format used on the TMS320C3x/C4x. +@end ftable + +If your target uses a floating point format other than these, you must +define a new @var{name}_FLOAT_FORMAT code for it, and add support for +it to @file{real.c}. + +The ordering of the component words of floating point values stored in +memory is controlled by @code{FLOAT_WORDS_BIG_ENDIAN}. +@end defmac + +@defmac MODE_HAS_NANS (@var{mode}) +When defined, this macro should be true if @var{mode} has a NaN +representation. The compiler assumes that NaNs are not equal to +anything (including themselves) and that addition, subtraction, +multiplication and division all return NaNs when one operand is +NaN@. + +By default, this macro is true if @var{mode} is a floating-point +mode and the target floating-point format is IEEE@. +@end defmac + +@defmac MODE_HAS_INFINITIES (@var{mode}) +This macro should be true if @var{mode} can represent infinity. At +present, the compiler uses this macro to decide whether @samp{x - x} +is always defined. By default, the macro is true when @var{mode} +is a floating-point mode and the target format is IEEE@. +@end defmac + +@defmac MODE_HAS_SIGNED_ZEROS (@var{mode}) +True if @var{mode} distinguishes between positive and negative zero. +The rules are expected to follow the IEEE standard: + +@itemize @bullet +@item +@samp{x + x} has the same sign as @samp{x}. + +@item +If the sum of two values with opposite sign is zero, the result is +positive for all rounding modes expect towards @minus{}infinity, for +which it is negative. + +@item +The sign of a product or quotient is negative when exactly one +of the operands is negative. +@end itemize + +The default definition is true if @var{mode} is a floating-point +mode and the target format is IEEE@. +@end defmac + +@defmac MODE_HAS_SIGN_DEPENDENT_ROUNDING (@var{mode}) +If defined, this macro should be true for @var{mode} if it has at +least one rounding mode in which @samp{x} and @samp{-x} can be +rounded to numbers of different magnitude. Two such modes are +towards @minus{}infinity and towards +infinity. + +The default definition of this macro is true if @var{mode} is +a floating-point mode and the target format is IEEE@. +@end defmac + +@defmac ROUND_TOWARDS_ZERO +If defined, this macro should be true if the prevailing rounding +mode is towards zero. A true value has the following effects: + +@itemize @bullet +@item +@code{MODE_HAS_SIGN_DEPENDENT_ROUNDING} will be false for all modes. + +@item +@file{libgcc.a}'s floating-point emulator will round towards zero +rather than towards nearest. + +@item +The compiler's floating-point emulator will round towards zero after +doing arithmetic, and when converting from the internal float format to +the target format. +@end itemize + +The macro does not affect the parsing of string literals. When the +primary rounding mode is towards zero, library functions like +@code{strtod} might still round towards nearest, and the compiler's +parser should behave like the target's @code{strtod} where possible. + +Not defining this macro is equivalent to returning zero. +@end defmac + +@defmac LARGEST_EXPONENT_IS_NORMAL (@var{size}) +This macro should return true if floats with @var{size} +bits do not have a NaN or infinity representation, but use the largest +exponent for normal numbers instead. + +Defining this macro to true for @var{size} causes @code{MODE_HAS_NANS} +and @code{MODE_HAS_INFINITIES} to be false for @var{size}-bit modes. +It also affects the way @file{libgcc.a} and @file{real.c} emulate +floating-point arithmetic. + +The default definition of this macro returns false for all sizes. +@end defmac + +@deftypefn {Target Hook} bool TARGET_VECTOR_OPAQUE_P (tree @var{type}) +This target hook should return @code{true} a vector is opaque. That +is, if no cast is needed when copying a vector value of type +@var{type} into another vector lvalue of the same size. Vector opaque +types cannot be initialized. The default is that there are no such +types. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (tree @var{record_type}) +This target hook returns @code{true} if bit-fields in the given +@var{record_type} are to be laid out following the rules of Microsoft +Visual C/C++, namely: (i) a bit-field won't share the same storage +unit with the previous bit-field if their underlying types have +different sizes, and the bit-field will be aligned to the highest +alignment of the underlying types of itself and of the previous +bit-field; (ii) a zero-sized bit-field will affect the alignment of +the whole enclosing structure, even if it is unnamed; except that +(iii) a zero-sized bit-field will be disregarded unless it follows +another bit-field of nonzero size. If this hook returns @code{true}, +other macros that control bit-field layout are ignored. + +When a bit-field is inserted into a packed record, the whole size +of the underlying type is used by one or more same-size adjacent +bit-fields (that is, if its long:3, 32 bits is used in the record, +and any additional adjacent long bit-fields are packed into the same +chunk of 32 bits. However, if the size changes, a new field of that +size is allocated). In an unpacked record, this is the same as using +alignment, but not equivalent when packing. + +If both MS bit-fields and @samp{__attribute__((packed))} are used, +the latter will take precedence. If @samp{__attribute__((packed))} is +used on a single field when MS bit-fields are in use, it will take +precedence for that field, but the alignment of the rest of the structure +may affect its placement. +@end deftypefn + +@deftypefn {Target Hook} {bool} TARGET_DECIMAL_FLOAT_SUPPORTED_P (void) +Returns true if the target supports decimal floating point. +@end deftypefn + +@c APPLE LOCAL begin mangle_type 7105099 +@deftypefn {Target Hook} {const char *} TARGET_MANGLE_TYPE (tree @var{type}) +If your target defines any fundamental types, or any types your target +uses should be mangled differently from the default, define this hook +to return the appropriate encoding for these types as part of a C++ +mangled name. The @var{type} argument is the tree structure representing +the type to be mangled. The hook may be applied to trees which are +not target-specific fundamental types; it should return @code{NULL} +for all such types, as well as arguments it does not recognize. If the +return value is not @code{NULL}, it must point to a statically-allocated +string constant. +@c APPLE LOCAL end mangle_type 7105099 + +Target-specific fundamental types might be new fundamental types or +qualified versions of ordinary fundamental types. Encode new +fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name} +is the name used for the type in source code, and @var{n} is the +length of @var{name} in decimal. Encode qualified versions of +ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where +@var{name} is the name used for the type qualifier in source code, +@var{n} is the length of @var{name} as above, and @var{code} is the +code used to represent the unqualified version of this type. (See +@code{write_builtin_type} in @file{cp/mangle.c} for the list of +codes.) In both cases the spaces are for clarity; do not include any +spaces in your string. + +@c APPLE LOCAL begin mangle_type 7105099 +This hook is applied to types prior to typedef resolution. If the mangled +name for a particular type depends only on that type's main variant, you +can perform typedef resolution yourself using @code{TYPE_MAIN_VARIANT} +before mangling. +@c APPLE LOCAL end mangle_type 7105099 + +The default version of this hook always returns @code{NULL}, which is +appropriate for a target that does not define any new fundamental +types. +@end deftypefn + +@node Type Layout +@section Layout of Source Language Data Types + +These macros define the sizes and other characteristics of the standard +basic data types used in programs being compiled. Unlike the macros in +the previous section, these apply to specific features of C and related +languages, rather than to fundamental aspects of storage layout. + +@defmac INT_TYPE_SIZE +A C expression for the size in bits of the type @code{int} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac SHORT_TYPE_SIZE +A C expression for the size in bits of the type @code{short} on the +target machine. If you don't define this, the default is half a word. +(If this would be less than one storage unit, it is rounded up to one +unit.) +@end defmac + +@defmac LONG_TYPE_SIZE +A C expression for the size in bits of the type @code{long} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac ADA_LONG_TYPE_SIZE +On some machines, the size used for the Ada equivalent of the type +@code{long} by a native Ada compiler differs from that used by C@. In +that situation, define this macro to be a C expression to be used for +the size of that type. If you don't define this, the default is the +value of @code{LONG_TYPE_SIZE}. +@end defmac + +@defmac LONG_LONG_TYPE_SIZE +A C expression for the size in bits of the type @code{long long} on the +target machine. If you don't define this, the default is two +words. If you want to support GNU Ada on your machine, the value of this +macro must be at least 64. +@end defmac + +@defmac CHAR_TYPE_SIZE +A C expression for the size in bits of the type @code{char} on the +target machine. If you don't define this, the default is +@code{BITS_PER_UNIT}. +@end defmac + +@defmac BOOL_TYPE_SIZE +A C expression for the size in bits of the C++ type @code{bool} and +C99 type @code{_Bool} on the target machine. If you don't define +this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}. +@end defmac + +@defmac FLOAT_TYPE_SIZE +A C expression for the size in bits of the type @code{float} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac DOUBLE_TYPE_SIZE +A C expression for the size in bits of the type @code{double} on the +target machine. If you don't define this, the default is two +words. +@end defmac + +@defmac LONG_DOUBLE_TYPE_SIZE +A C expression for the size in bits of the type @code{long double} on +the target machine. If you don't define this, the default is two +words. +@end defmac + +@defmac LIBGCC2_LONG_DOUBLE_TYPE_SIZE +Define this macro if @code{LONG_DOUBLE_TYPE_SIZE} is not constant or +if you want routines in @file{libgcc2.a} for a size other than +@code{LONG_DOUBLE_TYPE_SIZE}. If you don't define this, the +default is @code{LONG_DOUBLE_TYPE_SIZE}. +@end defmac + +@defmac LIBGCC2_HAS_DF_MODE +Define this macro if neither @code{LIBGCC2_DOUBLE_TYPE_SIZE} nor +@code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is +@code{DFmode} but you want @code{DFmode} routines in @file{libgcc2.a} +anyway. If you don't define this and either @code{LIBGCC2_DOUBLE_TYPE_SIZE} +or @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64 then the default is 1, +otherwise it is 0. +@end defmac + +@defmac LIBGCC2_HAS_XF_MODE +Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not +@code{XFmode} but you want @code{XFmode} routines in @file{libgcc2.a} +anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} +is 80 then the default is 1, otherwise it is 0. +@end defmac + +@defmac LIBGCC2_HAS_TF_MODE +Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not +@code{TFmode} but you want @code{TFmode} routines in @file{libgcc2.a} +anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} +is 128 then the default is 1, otherwise it is 0. +@end defmac + +@defmac SF_SIZE +@defmacx DF_SIZE +@defmacx XF_SIZE +@defmacx TF_SIZE +Define these macros to be the size in bits of the mantissa of +@code{SFmode}, @code{DFmode}, @code{XFmode} and @code{TFmode} values, +if the defaults in @file{libgcc2.h} are inappropriate. By default, +@code{FLT_MANT_DIG} is used for @code{SF_SIZE}, @code{LDBL_MANT_DIG} +for @code{XF_SIZE} and @code{TF_SIZE}, and @code{DBL_MANT_DIG} or +@code{LDBL_MANT_DIG} for @code{DF_SIZE} according to whether +@code{LIBGCC2_DOUBLE_TYPE_SIZE} or +@code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64. +@end defmac + +@defmac TARGET_FLT_EVAL_METHOD +A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h}, +assuming, if applicable, that the floating-point control word is in its +default state. If you do not define this macro the value of +@code{FLT_EVAL_METHOD} will be zero. +@end defmac + +@defmac WIDEST_HARDWARE_FP_SIZE +A C expression for the size in bits of the widest floating-point format +supported by the hardware. If you define this macro, you must specify a +value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}. +If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE} +is the default. +@end defmac + +@defmac DEFAULT_SIGNED_CHAR +An expression whose value is 1 or 0, according to whether the type +@code{char} should be signed or unsigned by default. The user can +always override this default with the options @option{-fsigned-char} +and @option{-funsigned-char}. +@end defmac + +@deftypefn {Target Hook} bool TARGET_DEFAULT_SHORT_ENUMS (void) +This target hook should return true if the compiler should give an +@code{enum} type only as many bytes as it takes to represent the range +of possible values of that type. It should return false if all +@code{enum} types should be allocated like @code{int}. + +The default is to return false. +@end deftypefn + +@defmac SIZE_TYPE +A C expression for a string describing the name of the data type to use +for size values. The typedef name @code{size_t} is defined using the +contents of the string. + +The string can contain more than one keyword. If so, separate them with +spaces, and write first any length keyword, then @code{unsigned} if +appropriate, and finally @code{int}. The string must exactly match one +of the data type names defined in the function +@code{init_decl_processing} in the file @file{c-decl.c}. You may not +omit @code{int} or change the order---that would cause the compiler to +crash on startup. + +If you don't define this macro, the default is @code{"long unsigned +int"}. +@end defmac + +@defmac PTRDIFF_TYPE +A C expression for a string describing the name of the data type to use +for the result of subtracting two pointers. The typedef name +@code{ptrdiff_t} is defined using the contents of the string. See +@code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is @code{"long int"}. +@end defmac + +@defmac WCHAR_TYPE +A C expression for a string describing the name of the data type to use +for wide characters. The typedef name @code{wchar_t} is defined using +the contents of the string. See @code{SIZE_TYPE} above for more +information. + +If you don't define this macro, the default is @code{"int"}. +@end defmac + +@defmac WCHAR_TYPE_SIZE +A C expression for the size in bits of the data type for wide +characters. This is used in @code{cpp}, which cannot make use of +@code{WCHAR_TYPE}. +@end defmac + +@defmac WINT_TYPE +A C expression for a string describing the name of the data type to +use for wide characters passed to @code{printf} and returned from +@code{getwc}. The typedef name @code{wint_t} is defined using the +contents of the string. See @code{SIZE_TYPE} above for more +information. + +If you don't define this macro, the default is @code{"unsigned int"}. +@end defmac + +@defmac INTMAX_TYPE +A C expression for a string describing the name of the data type that +can represent any value of any standard or extended signed integer type. +The typedef name @code{intmax_t} is defined using the contents of the +string. See @code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is the first of +@code{"int"}, @code{"long int"}, or @code{"long long int"} that has as +much precision as @code{long long int}. +@end defmac + +@defmac UINTMAX_TYPE +A C expression for a string describing the name of the data type that +can represent any value of any standard or extended unsigned integer +type. The typedef name @code{uintmax_t} is defined using the contents +of the string. See @code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is the first of +@code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long +unsigned int"} that has as much precision as @code{long long unsigned +int}. +@end defmac + +@defmac TARGET_PTRMEMFUNC_VBIT_LOCATION +The C++ compiler represents a pointer-to-member-function with a struct +that looks like: + +@smallexample + struct @{ + union @{ + void (*fn)(); + ptrdiff_t vtable_index; + @}; + ptrdiff_t delta; + @}; +@end smallexample + +@noindent +The C++ compiler must use one bit to indicate whether the function that +will be called through a pointer-to-member-function is virtual. +Normally, we assume that the low-order bit of a function pointer must +always be zero. Then, by ensuring that the vtable_index is odd, we can +distinguish which variant of the union is in use. But, on some +platforms function pointers can be odd, and so this doesn't work. In +that case, we use the low-order bit of the @code{delta} field, and shift +the remainder of the @code{delta} field to the left. + +GCC will automatically make the right selection about where to store +this bit using the @code{FUNCTION_BOUNDARY} setting for your platform. +However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY} +set such that functions always start at even addresses, but the lowest +bit of pointers to functions indicate whether the function at that +address is in ARM or Thumb mode. If this is the case of your +architecture, you should define this macro to +@code{ptrmemfunc_vbit_in_delta}. + +In general, you should not have to define this macro. On architectures +in which function addresses are always even, according to +@code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to +@code{ptrmemfunc_vbit_in_pfn}. +@end defmac + +@defmac TARGET_VTABLE_USES_DESCRIPTORS +Normally, the C++ compiler uses function pointers in vtables. This +macro allows the target to change to use ``function descriptors'' +instead. Function descriptors are found on targets for whom a +function pointer is actually a small data structure. Normally the +data structure consists of the actual code address plus a data +pointer to which the function's data is relative. + +If vtables are used, the value of this macro should be the number +of words that the function descriptor occupies. +@end defmac + +@defmac TARGET_VTABLE_ENTRY_ALIGN +By default, the vtable entries are void pointers, the so the alignment +is the same as pointer alignment. The value of this macro specifies +the alignment of the vtable entry in bits. It should be defined only +when special alignment is necessary. */ +@end defmac + +@defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE +There are a few non-descriptor entries in the vtable at offsets below +zero. If these entries must be padded (say, to preserve the alignment +specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number +of words in each data entry. +@end defmac + +@node Registers +@section Register Usage +@cindex register usage + +This section explains how to describe what registers the target machine +has, and how (in general) they can be used. + +The description of which registers a specific instruction can use is +done with register classes; see @ref{Register Classes}. For information +on using registers to access a stack frame, see @ref{Frame Registers}. +For passing values in registers, see @ref{Register Arguments}. +For returning values in registers, see @ref{Scalar Return}. + +@menu +* Register Basics:: Number and kinds of registers. +* Allocation Order:: Order in which registers are allocated. +* Values in Registers:: What kinds of values each reg can hold. +* Leaf Functions:: Renumbering registers for leaf functions. +* Stack Registers:: Handling a register stack such as 80387. +@end menu + +@node Register Basics +@subsection Basic Characteristics of Registers + +@c prevent bad page break with this line +Registers have various characteristics. + +@defmac FIRST_PSEUDO_REGISTER +Number of hardware registers known to the compiler. They receive +numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first +pseudo register's number really is assigned the number +@code{FIRST_PSEUDO_REGISTER}. +@end defmac + +@defmac FIXED_REGISTERS +@cindex fixed register +An initializer that says which registers are used for fixed purposes +all throughout the compiled code and are therefore not available for +general allocation. These would include the stack pointer, the frame +pointer (except on machines where that can be used as a general +register when no frame pointer is needed), the program counter on +machines where that is considered one of the addressable registers, +and any other numbered register with a standard use. + +This information is expressed as a sequence of numbers, separated by +commas and surrounded by braces. The @var{n}th number is 1 if +register @var{n} is fixed, 0 otherwise. + +The table initialized from this macro, and the table initialized by +the following one, may be overridden at run time either automatically, +by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by +the user with the command options @option{-ffixed-@var{reg}}, +@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}. +@end defmac + +@defmac CALL_USED_REGISTERS +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +Like @code{FIXED_REGISTERS} but has 1 for each register that is +clobbered (in general) by function calls as well as for fixed +registers. This macro therefore identifies the registers that are not +available for general allocation of values that must live across +function calls. + +If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler +automatically saves it on function entry and restores it on function +exit, if the register is used within the function. +@end defmac + +@defmac CALL_REALLY_USED_REGISTERS +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +Like @code{CALL_USED_REGISTERS} except this macro doesn't require +that the entire set of @code{FIXED_REGISTERS} be included. +(@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}). +This macro is optional. If not specified, it defaults to the value +of @code{CALL_USED_REGISTERS}. +@end defmac + +@defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode}) +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +A C expression that is nonzero if it is not permissible to store a +value of mode @var{mode} in hard register number @var{regno} across a +call without some part of it being clobbered. For most machines this +macro need not be defined. It is only required for machines that do not +preserve the entire contents of a register across a call. +@end defmac + +@findex fixed_regs +@findex call_used_regs +@findex global_regs +@findex reg_names +@findex reg_class_contents +@defmac CONDITIONAL_REGISTER_USAGE +Zero or more C statements that may conditionally modify five variables +@code{fixed_regs}, @code{call_used_regs}, @code{global_regs}, +@code{reg_names}, and @code{reg_class_contents}, to take into account +any dependence of these register sets on target flags. The first three +of these are of type @code{char []} (interpreted as Boolean vectors). +@code{global_regs} is a @code{const char *[]}, and +@code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is +called, @code{fixed_regs}, @code{call_used_regs}, +@code{reg_class_contents}, and @code{reg_names} have been initialized +from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS}, +@code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively. +@code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}}, +@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}} +command options have been applied. + +You need not define this macro if it has no work to do. + +@cindex disabling certain registers +@cindex controlling register usage +If the usage of an entire class of registers depends on the target +flags, you may indicate this to GCC by using this macro to modify +@code{fixed_regs} and @code{call_used_regs} to 1 for each of the +registers in the classes which should not be used by GCC@. Also define +the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT} +to return @code{NO_REGS} if it +is called with a letter for a class that shouldn't be used. + +(However, if this class is not included in @code{GENERAL_REGS} and all +of the insn patterns whose constraints permit this class are +controlled by target switches, then GCC will automatically avoid using +these registers when the target switches are opposed to them.) +@end defmac + +@defmac INCOMING_REGNO (@var{out}) +Define this macro if the target machine has register windows. This C +expression returns the register number as seen by the called function +corresponding to the register number @var{out} as seen by the calling +function. Return @var{out} if register number @var{out} is not an +outbound register. +@end defmac + +@defmac OUTGOING_REGNO (@var{in}) +Define this macro if the target machine has register windows. This C +expression returns the register number as seen by the calling function +corresponding to the register number @var{in} as seen by the called +function. Return @var{in} if register number @var{in} is not an inbound +register. +@end defmac + +@defmac LOCAL_REGNO (@var{regno}) +Define this macro if the target machine has register windows. This C +expression returns true if the register is call-saved but is in the +register window. Unlike most call-saved registers, such registers +need not be explicitly restored on function exit or during non-local +gotos. +@end defmac + +@defmac PC_REGNUM +If the program counter has a register number, define this as that +register number. Otherwise, do not define it. +@end defmac + +@node Allocation Order +@subsection Order of Allocation of Registers +@cindex order of register allocation +@cindex register allocation order + +@c prevent bad page break with this line +Registers are allocated in order. + +@defmac REG_ALLOC_ORDER +If defined, an initializer for a vector of integers, containing the +numbers of hard registers in the order in which GCC should prefer +to use them (from most preferred to least). + +If this macro is not defined, registers are used lowest numbered first +(all else being equal). + +One use of this macro is on machines where the highest numbered +registers must always be saved and the save-multiple-registers +instruction supports only sequences of consecutive registers. On such +machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists +the highest numbered allocable register first. +@end defmac + +@defmac ORDER_REGS_FOR_LOCAL_ALLOC +A C statement (sans semicolon) to choose the order in which to allocate +hard registers for pseudo-registers local to a basic block. + +Store the desired register order in the array @code{reg_alloc_order}. +Element 0 should be the register to allocate first; element 1, the next +register; and so on. + +The macro body should not assume anything about the contents of +@code{reg_alloc_order} before execution of the macro. + +On most machines, it is not necessary to define this macro. +@end defmac + +@node Values in Registers +@subsection How Values Fit in Registers + +This section discusses the macros that describe which kinds of values +(specifically, which machine modes) each register can hold, and how many +consecutive registers are needed for a given mode. + +@defmac HARD_REGNO_NREGS (@var{regno}, @var{mode}) +A C expression for the number of consecutive hard registers, starting +at register number @var{regno}, required to hold a value of mode +@var{mode}. + +On a machine where all registers are exactly one word, a suitable +definition of this macro is + +@smallexample +#define HARD_REGNO_NREGS(REGNO, MODE) \ + ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \ + / UNITS_PER_WORD) +@end smallexample +@end defmac + +@defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode}) +A C expression that is nonzero if a value of mode @var{mode}, stored +in memory, ends with padding that causes it to take up more space than +in registers starting at register number @var{regno} (as determined by +multiplying GCC's notion of the size of the register when containing +this mode by the number of registers returned by +@code{HARD_REGNO_NREGS}). By default this is zero. + +For example, if a floating-point value is stored in three 32-bit +registers but takes up 128 bits in memory, then this would be +nonzero. + +This macros only needs to be defined if there are cases where +@code{subreg_regno_offset} and @code{subreg_offset_representable_p} +would otherwise wrongly determine that a @code{subreg} can be +represented by an offset to the register number, when in fact such a +@code{subreg} would contain some of the padding not stored in +registers and so not be representable. +@end defmac + +@defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode}) +For values of @var{regno} and @var{mode} for which +@code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression +returning the greater number of registers required to hold the value +including any padding. In the example above, the value would be four. +@end defmac + +@defmac REGMODE_NATURAL_SIZE (@var{mode}) +Define this macro if the natural size of registers that hold values +of mode @var{mode} is not the word size. It is a C expression that +should give the natural size in bytes for the specified mode. It is +used by the register allocator to try to optimize its results. This +happens for example on SPARC 64-bit where the natural size of +floating-point registers is still 32-bit. +@end defmac + +@defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode}) +A C expression that is nonzero if it is permissible to store a value +of mode @var{mode} in hard register number @var{regno} (or in several +registers starting with that one). For a machine where all registers +are equivalent, a suitable definition is + +@smallexample +#define HARD_REGNO_MODE_OK(REGNO, MODE) 1 +@end smallexample + +You need not include code to check for the numbers of fixed registers, +because the allocation mechanism considers them to be always occupied. + +@cindex register pairs +On some machines, double-precision values must be kept in even/odd +register pairs. You can implement that by defining this macro to reject +odd register numbers for such modes. + +The minimum requirement for a mode to be OK in a register is that the +@samp{mov@var{mode}} instruction pattern support moves between the +register and other hard register in the same class and that moving a +value into the register and back out not alter it. + +Since the same instruction used to move @code{word_mode} will work for +all narrower integer modes, it is not necessary on any machine for +@code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided +you define patterns @samp{movhi}, etc., to take advantage of this. This +is useful because of the interaction between @code{HARD_REGNO_MODE_OK} +and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes +to be tieable. + +Many machines have special registers for floating point arithmetic. +Often people assume that floating point machine modes are allowed only +in floating point registers. This is not true. Any registers that +can hold integers can safely @emph{hold} a floating point machine +mode, whether or not floating arithmetic can be done on it in those +registers. Integer move instructions can be used to move the values. + +On some machines, though, the converse is true: fixed-point machine +modes may not go in floating registers. This is true if the floating +registers normalize any value stored in them, because storing a +non-floating value there would garble it. In this case, +@code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in +floating registers. But if the floating registers do not automatically +normalize, if you can store any bit pattern in one and retrieve it +unchanged without a trap, then any machine mode may go in a floating +register, so you can define this macro to say so. + +The primary significance of special floating registers is rather that +they are the registers acceptable in floating point arithmetic +instructions. However, this is of no concern to +@code{HARD_REGNO_MODE_OK}. You handle it by writing the proper +constraints for those instructions. + +On some machines, the floating registers are especially slow to access, +so that it is better to store a value in a stack frame than in such a +register if floating point arithmetic is not being done. As long as the +floating registers are not in class @code{GENERAL_REGS}, they will not +be used unless some pattern's constraint asks for one. +@end defmac + +@defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to}) +A C expression that is nonzero if it is OK to rename a hard register +@var{from} to another hard register @var{to}. + +One common use of this macro is to prevent renaming of a register to +another register that is not saved by a prologue in an interrupt +handler. + +The default is always nonzero. +@end defmac + +@defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2}) +A C expression that is nonzero if a value of mode +@var{mode1} is accessible in mode @var{mode2} without copying. + +If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and +@code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for +any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})} +should be nonzero. If they differ for any @var{r}, you should define +this macro to return zero unless some other mechanism ensures the +accessibility of the value in a narrower mode. + +You should define this macro to return nonzero in as many cases as +possible since doing so will allow GCC to perform better register +allocation. +@end defmac + +@defmac AVOID_CCMODE_COPIES +Define this macro if the compiler should avoid copies to/from @code{CCmode} +registers. You should only define this macro if support for copying to/from +@code{CCmode} is incomplete. +@end defmac + +@node Leaf Functions +@subsection Handling Leaf Functions + +@cindex leaf functions +@cindex functions, leaf +On some machines, a leaf function (i.e., one which makes no calls) can run +more efficiently if it does not make its own register window. Often this +means it is required to receive its arguments in the registers where they +are passed by the caller, instead of the registers where they would +normally arrive. + +The special treatment for leaf functions generally applies only when +other conditions are met; for example, often they may use only those +registers for its own variables and temporaries. We use the term ``leaf +function'' to mean a function that is suitable for this special +handling, so that functions with no calls are not necessarily ``leaf +functions''. + +GCC assigns register numbers before it knows whether the function is +suitable for leaf function treatment. So it needs to renumber the +registers in order to output a leaf function. The following macros +accomplish this. + +@defmac LEAF_REGISTERS +Name of a char vector, indexed by hard register number, which +contains 1 for a register that is allowable in a candidate for leaf +function treatment. + +If leaf function treatment involves renumbering the registers, then the +registers marked here should be the ones before renumbering---those that +GCC would ordinarily allocate. The registers which will actually be +used in the assembler code, after renumbering, should not be marked with 1 +in this vector. + +Define this macro only if the target machine offers a way to optimize +the treatment of leaf functions. +@end defmac + +@defmac LEAF_REG_REMAP (@var{regno}) +A C expression whose value is the register number to which @var{regno} +should be renumbered, when a function is treated as a leaf function. + +If @var{regno} is a register number which should not appear in a leaf +function before renumbering, then the expression should yield @minus{}1, which +will cause the compiler to abort. + +Define this macro only if the target machine offers a way to optimize the +treatment of leaf functions, and registers need to be renumbered to do +this. +@end defmac + +@findex current_function_is_leaf +@findex current_function_uses_only_leaf_regs +@code{TARGET_ASM_FUNCTION_PROLOGUE} and +@code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions +specially. They can test the C variable @code{current_function_is_leaf} +which is nonzero for leaf functions. @code{current_function_is_leaf} is +set prior to local register allocation and is valid for the remaining +compiler passes. They can also test the C variable +@code{current_function_uses_only_leaf_regs} which is nonzero for leaf +functions which only use leaf registers. +@code{current_function_uses_only_leaf_regs} is valid after all passes +that modify the instructions have been run and is only useful if +@code{LEAF_REGISTERS} is defined. +@c changed this to fix overfull. ALSO: why the "it" at the beginning +@c of the next paragraph?! --mew 2feb93 + +@node Stack Registers +@subsection Registers That Form a Stack + +There are special features to handle computers where some of the +``registers'' form a stack. Stack registers are normally written by +pushing onto the stack, and are numbered relative to the top of the +stack. + +Currently, GCC can only handle one group of stack-like registers, and +they must be consecutively numbered. Furthermore, the existing +support for stack-like registers is specific to the 80387 floating +point coprocessor. If you have a new architecture that uses +stack-like registers, you will need to do substantial work on +@file{reg-stack.c} and write your machine description to cooperate +with it, as well as defining these macros. + +@defmac STACK_REGS +Define this if the machine has any stack-like registers. +@end defmac + +@defmac FIRST_STACK_REG +The number of the first stack-like register. This one is the top +of the stack. +@end defmac + +@defmac LAST_STACK_REG +The number of the last stack-like register. This one is the bottom of +the stack. +@end defmac + +@node Register Classes +@section Register Classes +@cindex register class definitions +@cindex class definitions, register + +On many machines, the numbered registers are not all equivalent. +For example, certain registers may not be allowed for indexed addressing; +certain registers may not be allowed in some instructions. These machine +restrictions are described to the compiler using @dfn{register classes}. + +You define a number of register classes, giving each one a name and saying +which of the registers belong to it. Then you can specify register classes +that are allowed as operands to particular instruction patterns. + +@findex ALL_REGS +@findex NO_REGS +In general, each register will belong to several classes. In fact, one +class must be named @code{ALL_REGS} and contain all the registers. Another +class must be named @code{NO_REGS} and contain no registers. Often the +union of two classes will be another class; however, this is not required. + +@findex GENERAL_REGS +One of the classes must be named @code{GENERAL_REGS}. There is nothing +terribly special about the name, but the operand constraint letters +@samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is +the same as @code{ALL_REGS}, just define it as a macro which expands +to @code{ALL_REGS}. + +Order the classes so that if class @var{x} is contained in class @var{y} +then @var{x} has a lower class number than @var{y}. + +The way classes other than @code{GENERAL_REGS} are specified in operand +constraints is through machine-dependent operand constraint letters. +You can define such letters to correspond to various classes, then use +them in operand constraints. + +You should define a class for the union of two classes whenever some +instruction allows both classes. For example, if an instruction allows +either a floating point (coprocessor) register or a general register for a +certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS} +which includes both of them. Otherwise you will get suboptimal code. + +You must also specify certain redundant information about the register +classes: for each class, which classes contain it and which ones are +contained in it; for each pair of classes, the largest class contained +in their union. + +When a value occupying several consecutive registers is expected in a +certain class, all the registers used must belong to that class. +Therefore, register classes cannot be used to enforce a requirement for +a register pair to start with an even-numbered register. The way to +specify this requirement is with @code{HARD_REGNO_MODE_OK}. + +Register classes used for input-operands of bitwise-and or shift +instructions have a special requirement: each such class must have, for +each fixed-point machine mode, a subclass whose registers can transfer that +mode to or from memory. For example, on some machines, the operations for +single-byte values (@code{QImode}) are limited to certain registers. When +this is so, each register class that is used in a bitwise-and or shift +instruction must have a subclass consisting of registers from which +single-byte values can be loaded or stored. This is so that +@code{PREFERRED_RELOAD_CLASS} can always have a possible value to return. + +@deftp {Data type} {enum reg_class} +An enumerated type that must be defined with all the register class names +as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS} +must be the last register class, followed by one more enumerated value, +@code{LIM_REG_CLASSES}, which is not a register class but rather +tells how many classes there are. + +Each register class has a number, which is the value of casting +the class name to type @code{int}. The number serves as an index +in many of the tables described below. +@end deftp + +@defmac N_REG_CLASSES +The number of distinct register classes, defined as follows: + +@smallexample +#define N_REG_CLASSES (int) LIM_REG_CLASSES +@end smallexample +@end defmac + +@defmac REG_CLASS_NAMES +An initializer containing the names of the register classes as C string +constants. These names are used in writing some of the debugging dumps. +@end defmac + +@defmac REG_CLASS_CONTENTS +An initializer containing the contents of the register classes, as integers +which are bit masks. The @var{n}th integer specifies the contents of class +@var{n}. The way the integer @var{mask} is interpreted is that +register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1. + +When the machine has more than 32 registers, an integer does not suffice. +Then the integers are replaced by sub-initializers, braced groupings containing +several integers. Each sub-initializer must be suitable as an initializer +for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}. +In this situation, the first integer in each sub-initializer corresponds to +registers 0 through 31, the second integer to registers 32 through 63, and +so on. +@end defmac + +@defmac REGNO_REG_CLASS (@var{regno}) +A C expression whose value is a register class containing hard register +@var{regno}. In general there is more than one such class; choose a class +which is @dfn{minimal}, meaning that no smaller class also contains the +register. +@end defmac + +@defmac BASE_REG_CLASS +A macro whose definition is the name of the class to which a valid +base register must belong. A base register is one used in an address +which is the register value plus a displacement. +@end defmac + +@defmac MODE_BASE_REG_CLASS (@var{mode}) +This is a variation of the @code{BASE_REG_CLASS} macro which allows +the selection of a base register in a mode dependent manner. If +@var{mode} is VOIDmode then it should return the same value as +@code{BASE_REG_CLASS}. +@end defmac + +@defmac MODE_BASE_REG_REG_CLASS (@var{mode}) +A C expression whose value is the register class to which a valid +base register must belong in order to be used in a base plus index +register address. You should define this macro if base plus index +addresses have different requirements than other base register uses. +@end defmac + +@defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{outer_code}, @var{index_code}) +A C expression whose value is the register class to which a valid +base register must belong. @var{outer_code} and @var{index_code} define the +context in which the base register occurs. @var{outer_code} is the code of +the immediately enclosing expression (@code{MEM} for the top level of an +address, @code{ADDRESS} for something that occurs in an +@code{address_operand}). @var{index_code} is the code of the corresponding +index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise. +@end defmac + +@defmac INDEX_REG_CLASS +A macro whose definition is the name of the class to which a valid +index register must belong. An index register is one used in an +address where its value is either multiplied by a scale factor or +added to another register (as well as added to a displacement). +@end defmac + +@defmac REGNO_OK_FOR_BASE_P (@var{num}) +A C expression which is nonzero if register number @var{num} is +suitable for use as a base register in operand addresses. It may be +either a suitable hard register or a pseudo register that has been +allocated such a hard register. +@end defmac + +@defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode}) +A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that +that expression may examine the mode of the memory reference in +@var{mode}. You should define this macro if the mode of the memory +reference affects whether a register may be used as a base register. If +you define this macro, the compiler will use it instead of +@code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for addresses +that appear outside a @code{MEM}, i.e. as an @code{address_operand}. + +@end defmac + +@defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode}) +A C expression which is nonzero if register number @var{num} is suitable for +use as a base register in base plus index operand addresses, accessing +memory in mode @var{mode}. It may be either a suitable hard register or a +pseudo register that has been allocated such a hard register. You should +define this macro if base plus index addresses have different requirements +than other base register uses. + +Use of this macro is deprecated; please use the more general +@code{REGNO_MODE_CODE_OK_FOR_BASE_P}. +@end defmac + +@defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{outer_code}, @var{index_code}) +A C expression that is just like @code{REGNO_MODE_OK_FOR_BASE_P}, except that +that expression may examine the context in which the register appears in the +memory reference. @var{outer_code} is the code of the immediately enclosing +expression (@code{MEM} if at the top level of the address, @code{ADDRESS} for +something that occurs in an @code{address_operand}). @var{index_code} is the +code of the corresponding index expression if @var{outer_code} is @code{PLUS}; +@code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses +that appear outside a @code{MEM}, i.e. as an @code{address_operand}. +@end defmac + +@defmac REGNO_OK_FOR_INDEX_P (@var{num}) +A C expression which is nonzero if register number @var{num} is +suitable for use as an index register in operand addresses. It may be +either a suitable hard register or a pseudo register that has been +allocated such a hard register. + +The difference between an index register and a base register is that +the index register may be scaled. If an address involves the sum of +two registers, neither one of them scaled, then either one may be +labeled the ``base'' and the other the ``index''; but whichever +labeling is used must fit the machine's constraints of which registers +may serve in each capacity. The compiler will try both labelings, +looking for one that is valid, and will reload one or both registers +only if neither labeling works. +@end defmac + +@defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class}) +A C expression that places additional restrictions on the register class +to use when it is necessary to copy value @var{x} into a register in class +@var{class}. The value is a register class; perhaps @var{class}, or perhaps +another, smaller class. On many machines, the following definition is +safe: + +@smallexample +#define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS +@end smallexample + +Sometimes returning a more restrictive class makes better code. For +example, on the 68000, when @var{x} is an integer constant that is in range +for a @samp{moveq} instruction, the value of this macro is always +@code{DATA_REGS} as long as @var{class} includes the data registers. +Requiring a data register guarantees that a @samp{moveq} will be used. + +One case where @code{PREFERRED_RELOAD_CLASS} must not return +@var{class} is if @var{x} is a legitimate constant which cannot be +loaded into some register class. By returning @code{NO_REGS} you can +force @var{x} into a memory location. For example, rs6000 can load +immediate values into general-purpose registers, but does not have an +instruction for loading an immediate value into a floating-point +register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when +@var{x} is a floating-point constant. If the constant can't be loaded +into any kind of register, code generation will be better if +@code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead +of using @code{PREFERRED_RELOAD_CLASS}. + +If an insn has pseudos in it after register allocation, reload will go +through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS} +to find the best one. Returning @code{NO_REGS}, in this case, makes +reload add a @code{!} in front of the constraint: the x86 back-end uses +this feature to discourage usage of 387 registers when math is done in +the SSE registers (and vice versa). +@end defmac + +@defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class}) +Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of +input reloads. If you don't define this macro, the default is to use +@var{class}, unchanged. + +You can also use @code{PREFERRED_OUTPUT_RELOAD_CLASS} to discourage +reload from using some alternatives, like @code{PREFERRED_RELOAD_CLASS}. +@end defmac + +@defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class}) +A C expression that places additional restrictions on the register class +to use when it is necessary to be able to hold a value of mode +@var{mode} in a reload register for which class @var{class} would +ordinarily be used. + +Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when +there are certain modes that simply can't go in certain reload classes. + +The value is a register class; perhaps @var{class}, or perhaps another, +smaller class. + +Don't define this macro unless the target machine has limitations which +require the macro to do something nontrivial. +@end defmac + +@deftypefn {Target Hook} enum reg_class TARGET_SECONDARY_RELOAD (bool @var{in_p}, rtx @var{x}, enum reg_class @var{reload_class}, enum machine_mode @var{reload_mode}, secondary_reload_info *@var{sri}) +Many machines have some registers that cannot be copied directly to or +from memory or even from other types of registers. An example is the +@samp{MQ} register, which on most machines, can only be copied to or +from general registers, but not memory. Below, we shall be using the +term 'intermediate register' when a move operation cannot be performed +directly, but has to be done by copying the source into the intermediate +register first, and then copying the intermediate register to the +destination. An intermediate register always has the same mode as +source and destination. Since it holds the actual value being copied, +reload might apply optimizations to re-use an intermediate register +and eliding the copy from the source when it can determine that the +intermediate register still holds the required value. + +Another kind of secondary reload is required on some machines which +allow copying all registers to and from memory, but require a scratch +register for stores to some memory locations (e.g., those with symbolic +address on the RT, and those with certain symbolic address on the SPARC +when compiling PIC)@. Scratch registers need not have the same mode +as the value being copied, and usually hold a different value that +that being copied. Special patterns in the md file are needed to +describe how the copy is performed with the help of the scratch register; +these patterns also describe the number, register class(es) and mode(s) +of the scratch register(s). + +In some cases, both an intermediate and a scratch register are required. + +For input reloads, this target hook is called with nonzero @var{in_p}, +and @var{x} is an rtx that needs to be copied to a register in of class +@var{reload_class} in @var{reload_mode}. For output reloads, this target +hook is called with zero @var{in_p}, and a register of class @var{reload_mode} +needs to be copied to rtx @var{x} in @var{reload_mode}. + +If copying a register of @var{reload_class} from/to @var{x} requires +an intermediate register, the hook @code{secondary_reload} should +return the register class required for this intermediate register. +If no intermediate register is required, it should return NO_REGS. +If more than one intermediate register is required, describe the one +that is closest in the copy chain to the reload register. + +If scratch registers are needed, you also have to describe how to +perform the copy from/to the reload register to/from this +closest intermediate register. Or if no intermediate register is +required, but still a scratch register is needed, describe the +copy from/to the reload register to/from the reload operand @var{x}. + +You do this by setting @code{sri->icode} to the instruction code of a pattern +in the md file which performs the move. Operands 0 and 1 are the output +and input of this copy, respectively. Operands from operand 2 onward are +for scratch operands. These scratch operands must have a mode, and a +single-register-class +@c [later: or memory] +output constraint. + +When an intermediate register is used, the @code{secondary_reload} +hook will be called again to determine how to copy the intermediate +register to/from the reload operand @var{x}, so your hook must also +have code to handle the register class of the intermediate operand. + +@c [For later: maybe we'll allow multi-alternative reload patterns - +@c the port maintainer could name a mov<mode> pattern that has clobbers - +@c and match the constraints of input and output to determine the required +@c alternative. A restriction would be that constraints used to match +@c against reloads registers would have to be written as register class +@c constraints, or we need a new target macro / hook that tells us if an +@c arbitrary constraint can match an unknown register of a given class. +@c Such a macro / hook would also be useful in other places.] + + +@var{x} might be a pseudo-register or a @code{subreg} of a +pseudo-register, which could either be in a hard register or in memory. +Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is +in memory and the hard register number if it is in a register. + +Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are +currently not supported. For the time being, you will have to continue +to use @code{SECONDARY_MEMORY_NEEDED} for that purpose. + +@code{copy_cost} also uses this target hook to find out how values are +copied. If you want it to include some extra cost for the need to allocate +(a) scratch register(s), set @code{sri->extra_cost} to the additional cost. +Or if two dependent moves are supposed to have a lower cost than the sum +of the individual moves due to expected fortuitous scheduling and/or special +forwarding logic, you can set @code{sri->extra_cost} to a negative amount. +@end deftypefn + +@defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +@defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +@defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +These macros are obsolete, new ports should use the target hook +@code{TARGET_SECONDARY_RELOAD} instead. + +These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD} +target hook. Older ports still define these macros to indicate to the +reload phase that it may +need to allocate at least one register for a reload in addition to the +register to contain the data. Specifically, if copying @var{x} to a +register @var{class} in @var{mode} requires an intermediate register, +you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the +largest register class all of whose registers can be used as +intermediate registers or scratch registers. + +If copying a register @var{class} in @var{mode} to @var{x} requires an +intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS} +was supposed to be defined be defined to return the largest register +class required. If the +requirements for input and output reloads were the same, the macro +@code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both +macros identically. + +The values returned by these macros are often @code{GENERAL_REGS}. +Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x} +can be directly copied to or from a register of @var{class} in +@var{mode} without requiring a scratch register. Do not define this +macro if it would always return @code{NO_REGS}. + +If a scratch register is required (either with or without an +intermediate register), you were supposed to define patterns for +@samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required +(@pxref{Standard Names}. These patterns, which were normally +implemented with a @code{define_expand}, should be similar to the +@samp{mov@var{m}} patterns, except that operand 2 is the scratch +register. + +These patterns need constraints for the reload register and scratch +register that +contain a single register class. If the original reload register (whose +class is @var{class}) can meet the constraint given in the pattern, the +value returned by these macros is used for the class of the scratch +register. Otherwise, two additional reload registers are required. +Their classes are obtained from the constraints in the insn pattern. + +@var{x} might be a pseudo-register or a @code{subreg} of a +pseudo-register, which could either be in a hard register or in memory. +Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is +in memory and the hard register number if it is in a register. + +These macros should not be used in the case where a particular class of +registers can only be copied to memory and not to another class of +registers. In that case, secondary reload registers are not needed and +would not be helpful. Instead, a stack location must be used to perform +the copy and the @code{mov@var{m}} pattern should use memory as an +intermediate storage. This case often occurs between floating-point and +general registers. +@end defmac + +@defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m}) +Certain machines have the property that some registers cannot be copied +to some other registers without using memory. Define this macro on +those machines to be a C expression that is nonzero if objects of mode +@var{m} in registers of @var{class1} can only be copied to registers of +class @var{class2} by storing a register of @var{class1} into memory +and loading that memory location into a register of @var{class2}. + +Do not define this macro if its value would always be zero. +@end defmac + +@defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode}) +Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler +allocates a stack slot for a memory location needed for register copies. +If this macro is defined, the compiler instead uses the memory location +defined by this macro. + +Do not define this macro if you do not define +@code{SECONDARY_MEMORY_NEEDED}. +@end defmac + +@defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode}) +When the compiler needs a secondary memory location to copy between two +registers of mode @var{mode}, it normally allocates sufficient memory to +hold a quantity of @code{BITS_PER_WORD} bits and performs the store and +load operations in a mode that many bits wide and whose class is the +same as that of @var{mode}. + +This is right thing to do on most machines because it ensures that all +bits of the register are copied and prevents accesses to the registers +in a narrower mode, which some machines prohibit for floating-point +registers. + +However, this default behavior is not correct on some machines, such as +the DEC Alpha, that store short integers in floating-point registers +differently than in integer registers. On those machines, the default +widening will not work correctly and you must define this macro to +suppress that widening in some cases. See the file @file{alpha.h} for +details. + +Do not define this macro if you do not define +@code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that +is @code{BITS_PER_WORD} bits wide is correct for your machine. +@end defmac + +@defmac SMALL_REGISTER_CLASSES +On some machines, it is risky to let hard registers live across arbitrary +insns. Typically, these machines have instructions that require values +to be in specific registers (like an accumulator), and reload will fail +if the required hard register is used for another purpose across such an +insn. + +Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero +value on these machines. When this macro has a nonzero value, the +compiler will try to minimize the lifetime of hard registers. + +It is always safe to define this macro with a nonzero value, but if you +unnecessarily define it, you will reduce the amount of optimizations +that can be performed in some cases. If you do not define this macro +with a nonzero value when it is required, the compiler will run out of +spill registers and print a fatal error message. For most machines, you +should not define this macro at all. +@end defmac + +@defmac CLASS_LIKELY_SPILLED_P (@var{class}) +A C expression whose value is nonzero if pseudos that have been assigned +to registers of class @var{class} would likely be spilled because +registers of @var{class} are needed for spill registers. + +The default value of this macro returns 1 if @var{class} has exactly one +register and zero otherwise. On most machines, this default should be +used. Only define this macro to some other expression if pseudos +allocated by @file{local-alloc.c} end up in memory because their hard +registers were needed for spill registers. If this macro returns nonzero +for those classes, those pseudos will only be allocated by +@file{global.c}, which knows how to reallocate the pseudo to another +register. If there would not be another register available for +reallocation, you should not change the definition of this macro since +the only effect of such a definition would be to slow down register +allocation. +@end defmac + +@defmac CLASS_MAX_NREGS (@var{class}, @var{mode}) +A C expression for the maximum number of consecutive registers +of class @var{class} needed to hold a value of mode @var{mode}. + +This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact, +the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})} +should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno}, +@var{mode})} for all @var{regno} values in the class @var{class}. + +This macro helps control the handling of multiple-word values +in the reload pass. +@end defmac + +@defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class}) +If defined, a C expression that returns nonzero for a @var{class} for which +a change from mode @var{from} to mode @var{to} is invalid. + +For the example, loading 32-bit integer or floating-point objects into +floating-point registers on the Alpha extends them to 64 bits. +Therefore loading a 64-bit object and then storing it as a 32-bit object +does not store the low-order 32 bits, as would be the case for a normal +register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS} +as below: + +@smallexample +#define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \ + (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \ + ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0) +@end smallexample +@end defmac + +@node Old Constraints +@section Obsolete Macros for Defining Constraints +@cindex defining constraints, obsolete method +@cindex constraints, defining, obsolete method + +Machine-specific constraints can be defined with these macros instead +of the machine description constructs described in @ref{Define +Constraints}. This mechanism is obsolete. New ports should not use +it; old ports should convert to the new mechanism. + +@defmac CONSTRAINT_LEN (@var{char}, @var{str}) +For the constraint at the start of @var{str}, which starts with the letter +@var{c}, return the length. This allows you to have register class / +constant / extra constraints that are longer than a single letter; +you don't need to define this macro if you can do with single-letter +constraints only. The definition of this macro should use +DEFAULT_CONSTRAINT_LEN for all the characters that you don't want +to handle specially. +There are some sanity checks in genoutput.c that check the constraint lengths +for the md file, so you can also use this macro to help you while you are +transitioning from a byzantine single-letter-constraint scheme: when you +return a negative length for a constraint you want to re-use, genoutput +will complain about every instance where it is used in the md file. +@end defmac + +@defmac REG_CLASS_FROM_LETTER (@var{char}) +A C expression which defines the machine-dependent operand constraint +letters for register classes. If @var{char} is such a letter, the +value should be the register class corresponding to it. Otherwise, +the value should be @code{NO_REGS}. The register letter @samp{r}, +corresponding to class @code{GENERAL_REGS}, will not be passed +to this macro; you do not need to handle it. +@end defmac + +@defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str}) +Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string +passed in @var{str}, so that you can use suffixes to distinguish between +different variants. +@end defmac + +@defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c}) +A C expression that defines the machine-dependent operand constraint +letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify +particular ranges of integer values. If @var{c} is one of those +letters, the expression should check that @var{value}, an integer, is in +the appropriate range and return 1 if so, 0 otherwise. If @var{c} is +not one of those letters, the value should be 0 regardless of +@var{value}. +@end defmac + +@defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str}) +Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint +string passed in @var{str}, so that you can use suffixes to distinguish +between different variants. +@end defmac + +@defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c}) +A C expression that defines the machine-dependent operand constraint +letters that specify particular ranges of @code{const_double} values +(@samp{G} or @samp{H}). + +If @var{c} is one of those letters, the expression should check that +@var{value}, an RTX of code @code{const_double}, is in the appropriate +range and return 1 if so, 0 otherwise. If @var{c} is not one of those +letters, the value should be 0 regardless of @var{value}. + +@code{const_double} is used for all floating-point constants and for +@code{DImode} fixed-point constants. A given letter can accept either +or both kinds of values. It can use @code{GET_MODE} to distinguish +between these kinds. +@end defmac + +@defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str}) +Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint +string passed in @var{str}, so that you can use suffixes to distinguish +between different variants. +@end defmac + +@defmac EXTRA_CONSTRAINT (@var{value}, @var{c}) +A C expression that defines the optional machine-dependent constraint +letters that can be used to segregate specific types of operands, usually +memory references, for the target machine. Any letter that is not +elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} / +@code{REG_CLASS_FROM_CONSTRAINT} +may be used. Normally this macro will not be defined. + +If it is required for a particular target machine, it should return 1 +if @var{value} corresponds to the operand type represented by the +constraint letter @var{c}. If @var{c} is not defined as an extra +constraint, the value returned should be 0 regardless of @var{value}. + +For example, on the ROMP, load instructions cannot have their output +in r0 if the memory reference contains a symbolic address. Constraint +letter @samp{Q} is defined as representing a memory address that does +@emph{not} contain a symbolic address. An alternative is specified with +a @samp{Q} constraint on the input and @samp{r} on the output. The next +alternative specifies @samp{m} on the input and a register class that +does not include r0 on the output. +@end defmac + +@defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str}) +Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed +in @var{str}, so that you can use suffixes to distinguish between different +variants. +@end defmac + +@defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str}) +A C expression that defines the optional machine-dependent constraint +letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should +be treated like memory constraints by the reload pass. + +It should return 1 if the operand type represented by the constraint +at the start of @var{str}, the first letter of which is the letter @var{c}, + comprises a subset of all memory references including +all those whose address is simply a base register. This allows the reload +pass to reload an operand, if it does not directly correspond to the operand +type of @var{c}, by copying its address into a base register. + +For example, on the S/390, some instructions do not accept arbitrary +memory references, but only those that do not make use of an index +register. The constraint letter @samp{Q} is defined via +@code{EXTRA_CONSTRAINT} as representing a memory address of this type. +If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT}, +a @samp{Q} constraint can handle any memory operand, because the +reload pass knows it can be reloaded by copying the memory address +into a base register if required. This is analogous to the way +a @samp{o} constraint can handle any memory operand. +@end defmac + +@defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str}) +A C expression that defines the optional machine-dependent constraint +letters, amongst those accepted by @code{EXTRA_CONSTRAINT} / +@code{EXTRA_CONSTRAINT_STR}, that should +be treated like address constraints by the reload pass. + +It should return 1 if the operand type represented by the constraint +at the start of @var{str}, which starts with the letter @var{c}, comprises +a subset of all memory addresses including +all those that consist of just a base register. This allows the reload +pass to reload an operand, if it does not directly correspond to the operand +type of @var{str}, by copying it into a base register. + +Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only +be used with the @code{address_operand} predicate. It is treated +analogously to the @samp{p} constraint. +@end defmac + +@node Stack and Calling +@section Stack Layout and Calling Conventions +@cindex calling conventions + +@c prevent bad page break with this line +This describes the stack layout and calling conventions. + +@menu +* Frame Layout:: +* Exception Handling:: +* Stack Checking:: +* Frame Registers:: +* Elimination:: +* Stack Arguments:: +* Register Arguments:: +* Scalar Return:: +* Aggregate Return:: +* Caller Saves:: +* Function Entry:: +* Profiling:: +* Tail Calls:: +* Stack Smashing Protection:: +@end menu + +@node Frame Layout +@subsection Basic Stack Layout +@cindex stack frame layout +@cindex frame layout + +@c prevent bad page break with this line +Here is the basic stack layout. + +@defmac STACK_GROWS_DOWNWARD +Define this macro if pushing a word onto the stack moves the stack +pointer to a smaller address. + +When we say, ``define this macro if @dots{}'', it means that the +compiler checks this macro only with @code{#ifdef} so the precise +definition used does not matter. +@end defmac + +@defmac STACK_PUSH_CODE +This macro defines the operation used when something is pushed +on the stack. In RTL, a push operation will be +@code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})} + +The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC}, +and @code{POST_INC}. Which of these is correct depends on +the stack direction and on whether the stack pointer points +to the last item on the stack or whether it points to the +space for the next item on the stack. + +The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is +defined, which is almost always right, and @code{PRE_INC} otherwise, +which is often wrong. +@end defmac + +@defmac FRAME_GROWS_DOWNWARD +Define this macro to nonzero value if the addresses of local variable slots +are at negative offsets from the frame pointer. +@end defmac + +@defmac ARGS_GROW_DOWNWARD +Define this macro if successive arguments to a function occupy decreasing +addresses on the stack. +@end defmac + +@defmac STARTING_FRAME_OFFSET +Offset from the frame pointer to the first local variable slot to be allocated. + +If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by +subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}. +Otherwise, it is found by adding the length of the first slot to the +value @code{STARTING_FRAME_OFFSET}. +@c i'm not sure if the above is still correct.. had to change it to get +@c rid of an overfull. --mew 2feb93 +@end defmac + +@defmac STACK_ALIGNMENT_NEEDED +Define to zero to disable final alignment of the stack during reload. +The nonzero default for this macro is suitable for most ports. + +On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there +is a register save block following the local block that doesn't require +alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable +stack alignment and do it in the backend. +@end defmac + +@defmac STACK_POINTER_OFFSET +Offset from the stack pointer register to the first location at which +outgoing arguments are placed. If not specified, the default value of +zero is used. This is the proper value for most machines. + +If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above +the first location at which outgoing arguments are placed. +@end defmac + +@defmac FIRST_PARM_OFFSET (@var{fundecl}) +Offset from the argument pointer register to the first argument's +address. On some machines it may depend on the data type of the +function. + +If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above +the first argument's address. +@end defmac + +@defmac STACK_DYNAMIC_OFFSET (@var{fundecl}) +Offset from the stack pointer register to an item dynamically allocated +on the stack, e.g., by @code{alloca}. + +The default value for this macro is @code{STACK_POINTER_OFFSET} plus the +length of the outgoing arguments. The default is correct for most +machines. See @file{function.c} for details. +@end defmac + +@defmac INITIAL_FRAME_ADDRESS_RTX +A C expression whose value is RTL representing the address of the initial +stack frame. This address is passed to @code{RETURN_ADDR_RTX} and +@code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable +default value will be used. Define this macro in order to make frame pointer +elimination work in the presence of @code{__builtin_frame_address (count)} and +@code{__builtin_return_address (count)} for @code{count} not equal to zero. +@end defmac + +@defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr}) +A C expression whose value is RTL representing the address in a stack +frame where the pointer to the caller's frame is stored. Assume that +@var{frameaddr} is an RTL expression for the address of the stack frame +itself. + +If you don't define this macro, the default is to return the value +of @var{frameaddr}---that is, the stack frame address is also the +address of the stack word that points to the previous frame. +@end defmac + +@defmac SETUP_FRAME_ADDRESSES +If defined, a C expression that produces the machine-specific code to +setup the stack so that arbitrary frames can be accessed. For example, +on the SPARC, we must flush all of the register windows to the stack +before we can access arbitrary stack frames. You will seldom need to +define this macro. +@end defmac + +@deftypefn {Target Hook} bool TARGET_BUILTIN_SETJMP_FRAME_VALUE () +This target hook should return an rtx that is used to store +the address of the current frame into the built in @code{setjmp} buffer. +The default value, @code{virtual_stack_vars_rtx}, is correct for most +machines. One reason you may need to define this target hook is if +@code{hard_frame_pointer_rtx} is the appropriate value on your machine. +@end deftypefn + +@defmac FRAME_ADDR_RTX (@var{frameaddr}) +A C expression whose value is RTL representing the value of the frame +address for the current frame. @var{frameaddr} is the frame pointer +of the current frame. This is used for __builtin_frame_address. +You need only define this macro if the frame address is not the same +as the frame pointer. Most machines do not need to define it. +@end defmac + +@defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr}) +A C expression whose value is RTL representing the value of the return +address for the frame @var{count} steps up from the current frame, after +the prologue. @var{frameaddr} is the frame pointer of the @var{count} +frame, or the frame pointer of the @var{count} @minus{} 1 frame if +@code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined. + +The value of the expression must always be the correct address when +@var{count} is zero, but may be @code{NULL_RTX} if there is not way to +determine the return address of other frames. +@end defmac + +@defmac RETURN_ADDR_IN_PREVIOUS_FRAME +Define this if the return address of a particular stack frame is accessed +from the frame pointer of the previous stack frame. +@end defmac + +@defmac INCOMING_RETURN_ADDR_RTX +A C expression whose value is RTL representing the location of the +incoming return address at the beginning of any function, before the +prologue. This RTL is either a @code{REG}, indicating that the return +value is saved in @samp{REG}, or a @code{MEM} representing a location in +the stack. + +You only need to define this macro if you want to support call frame +debugging information like that provided by DWARF 2. + +If this RTL is a @code{REG}, you should also define +@code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}. +@end defmac + +@defmac DWARF_ALT_FRAME_RETURN_COLUMN +A C expression whose value is an integer giving a DWARF 2 column +number that may be used as an alternate return column. This should +be defined only if @code{DWARF_FRAME_RETURN_COLUMN} is set to a +general register, but an alternate column needs to be used for +signal frames. +@end defmac + +@defmac DWARF_ZERO_REG +A C expression whose value is an integer giving a DWARF 2 register +number that is considered to always have the value zero. This should +only be defined if the target has an architected zero register, and +someone decided it was a good idea to use that register number to +terminate the stack backtrace. New ports should avoid this. +@end defmac + +@deftypefn {Target Hook} void TARGET_DWARF_HANDLE_FRAME_UNSPEC (const char *@var{label}, rtx @var{pattern}, int @var{index}) +This target hook allows the backend to emit frame-related insns that +contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging +info engine will invoke it on insns of the form +@smallexample +(set (reg) (unspec [...] UNSPEC_INDEX)) +@end smallexample +and +@smallexample +(set (reg) (unspec_volatile [...] UNSPECV_INDEX)). +@end smallexample +to let the backend emit the call frame instructions. @var{label} is +the CFI label attached to the insn, @var{pattern} is the pattern of +the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}. +@end deftypefn + +@defmac INCOMING_FRAME_SP_OFFSET +A C expression whose value is an integer giving the offset, in bytes, +from the value of the stack pointer register to the top of the stack +frame at the beginning of any function, before the prologue. The top of +the frame is defined to be the value of the stack pointer in the +previous frame, just before the call instruction. + +You only need to define this macro if you want to support call frame +debugging information like that provided by DWARF 2. +@end defmac + +@defmac ARG_POINTER_CFA_OFFSET (@var{fundecl}) +A C expression whose value is an integer giving the offset, in bytes, +from the argument pointer to the canonical frame address (cfa). The +final value should coincide with that calculated by +@code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable +during virtual register instantiation. + +The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)}, +which is correct for most machines; in general, the arguments are found +immediately before the stack frame. Note that this is not the case on +some targets that save registers into the caller's frame, such as SPARC +and rs6000, and so such targets need to define this macro. + +You only need to define this macro if the default is incorrect, and you +want to support call frame debugging information like that provided by +DWARF 2. +@end defmac + +@defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl}) +If defined, a C expression whose value is an integer giving the offset +in bytes from the frame pointer to the canonical frame address (cfa). +The final value should coincide with that calculated by +@code{INCOMING_FRAME_SP_OFFSET}. + +Normally the CFA is calculated as an offset from the argument pointer, +via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is +variable due to the ABI, this may not be possible. If this macro is +defined, it implies that the virtual register instantiation should be +based on the frame pointer instead of the argument pointer. Only one +of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET} +should be defined. +@end defmac + +@defmac CFA_FRAME_BASE_OFFSET (@var{fundecl}) +If defined, a C expression whose value is an integer giving the offset +in bytes from the canonical frame address (cfa) to the frame base used +in DWARF 2 debug information. The default is zero. A different value +may reduce the size of debug information on some ports. +@end defmac + +@node Exception Handling +@subsection Exception Handling Support +@cindex exception handling + +@defmac EH_RETURN_DATA_REGNO (@var{N}) +A C expression whose value is the @var{N}th register number used for +data by exception handlers, or @code{INVALID_REGNUM} if fewer than +@var{N} registers are usable. + +The exception handling library routines communicate with the exception +handlers via a set of agreed upon registers. Ideally these registers +should be call-clobbered; it is possible to use call-saved registers, +but may negatively impact code size. The target must support at least +2 data registers, but should define 4 if there are enough free registers. + +You must define this macro if you want to support call frame exception +handling like that provided by DWARF 2. +@end defmac + +@defmac EH_RETURN_STACKADJ_RTX +A C expression whose value is RTL representing a location in which +to store a stack adjustment to be applied before function return. +This is used to unwind the stack to an exception handler's call frame. +It will be assigned zero on code paths that return normally. + +Typically this is a call-clobbered hard register that is otherwise +untouched by the epilogue, but could also be a stack slot. + +Do not define this macro if the stack pointer is saved and restored +by the regular prolog and epilog code in the call frame itself; in +this case, the exception handling library routines will update the +stack location to be restored in place. Otherwise, you must define +this macro if you want to support call frame exception handling like +that provided by DWARF 2. +@end defmac + +@defmac EH_RETURN_HANDLER_RTX +A C expression whose value is RTL representing a location in which +to store the address of an exception handler to which we should +return. It will not be assigned on code paths that return normally. + +Typically this is the location in the call frame at which the normal +return address is stored. For targets that return by popping an +address off the stack, this might be a memory address just below +the @emph{target} call frame rather than inside the current call +frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already +been assigned, so it may be used to calculate the location of the +target call frame. + +Some targets have more complex requirements than storing to an +address calculable during initial code generation. In that case +the @code{eh_return} instruction pattern should be used instead. + +If you want to support call frame exception handling, you must +define either this macro or the @code{eh_return} instruction pattern. +@end defmac + +@defmac RETURN_ADDR_OFFSET +If defined, an integer-valued C expression for which rtl will be generated +to add it to the exception handler address before it is searched in the +exception handling tables, and to subtract it again from the address before +using it to return to the exception handler. +@end defmac + +@defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global}) +This macro chooses the encoding of pointers embedded in the exception +handling sections. If at all possible, this should be defined such +that the exception handling section will not require dynamic relocations, +and so may be read-only. + +@var{code} is 0 for data, 1 for code labels, 2 for function pointers. +@var{global} is true if the symbol may be affected by dynamic relocations. +The macro should return a combination of the @code{DW_EH_PE_*} defines +as found in @file{dwarf2.h}. + +If this macro is not defined, pointers will not be encoded but +represented directly. +@end defmac + +@defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done}) +This macro allows the target to emit whatever special magic is required +to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}. +Generic code takes care of pc-relative and indirect encodings; this must +be defined if the target uses text-relative or data-relative encodings. + +This is a C statement that branches to @var{done} if the format was +handled. @var{encoding} is the format chosen, @var{size} is the number +of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF} +to be emitted. +@end defmac + +@defmac MD_UNWIND_SUPPORT +A string specifying a file to be #include'd in unwind-dw2.c. The file +so included typically defines @code{MD_FALLBACK_FRAME_STATE_FOR}. +@end defmac + +@defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs}) +This macro allows the target to add cpu and operating system specific +code to the call-frame unwinder for use when there is no unwind data +available. The most common reason to implement this macro is to unwind +through signal frames. + +This macro is called from @code{uw_frame_state_for} in @file{unwind-dw2.c} +and @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; +@var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra} +for the address of the code being executed and @code{context->cfa} for +the stack pointer value. If the frame can be decoded, the register save +addresses should be updated in @var{fs} and the macro should evaluate to +@code{_URC_NO_REASON}. If the frame cannot be decoded, the macro should +evaluate to @code{_URC_END_OF_STACK}. + +For proper signal handling in Java this macro is accompanied by +@code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers. +@end defmac + +@defmac MD_HANDLE_UNWABI (@var{context}, @var{fs}) +This macro allows the target to add operating system specific code to the +call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive, +usually used for signal or interrupt frames. + +This macro is called from @code{uw_update_context} in @file{unwind-ia64.c}. +@var{context} is an @code{_Unwind_Context}; +@var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi} +for the abi and context in the @code{.unwabi} directive. If the +@code{.unwabi} directive can be handled, the register save addresses should +be updated in @var{fs}. +@end defmac + +@defmac TARGET_USES_WEAK_UNWIND_INFO +A C expression that evaluates to true if the target requires unwind +info to be given comdat linkage. Define it to be @code{1} if comdat +linkage is necessary. The default is @code{0}. +@end defmac + +@node Stack Checking +@subsection Specifying How Stack Checking is Done + +GCC will check that stack references are within the boundaries of +the stack, if the @option{-fstack-check} is specified, in one of three ways: + +@enumerate +@item +If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC +will assume that you have arranged for stack checking to be done at +appropriate places in the configuration files, e.g., in +@code{TARGET_ASM_FUNCTION_PROLOGUE}. GCC will do not other special +processing. + +@item +If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern +called @code{check_stack} in your @file{md} file, GCC will call that +pattern with one argument which is the address to compare the stack +value against. You must arrange for this pattern to report an error if +the stack pointer is out of range. + +@item +If neither of the above are true, GCC will generate code to periodically +``probe'' the stack pointer using the values of the macros defined below. +@end enumerate + +Normally, you will use the default values of these macros, so GCC +will use the third approach. + +@defmac STACK_CHECK_BUILTIN +A nonzero value if stack checking is done by the configuration files in a +machine-dependent manner. You should define this macro if stack checking +is require by the ABI of your machine or if you would like to have to stack +checking in some more efficient way than GCC's portable approach. +The default value of this macro is zero. +@end defmac + +@defmac STACK_CHECK_PROBE_INTERVAL +An integer representing the interval at which GCC must generate stack +probe instructions. You will normally define this macro to be no larger +than the size of the ``guard pages'' at the end of a stack area. The +default value of 4096 is suitable for most systems. +@end defmac + +@defmac STACK_CHECK_PROBE_LOAD +A integer which is nonzero if GCC should perform the stack probe +as a load instruction and zero if GCC should use a store instruction. +The default is zero, which is the most efficient choice on most systems. +@end defmac + +@defmac STACK_CHECK_PROTECT +The number of bytes of stack needed to recover from a stack overflow, +for languages where such a recovery is supported. The default value of +75 words should be adequate for most machines. +@end defmac + +@defmac STACK_CHECK_MAX_FRAME_SIZE +The maximum size of a stack frame, in bytes. GCC will generate probe +instructions in non-leaf functions to ensure at least this many bytes of +stack are available. If a stack frame is larger than this size, stack +checking will not be reliable and GCC will issue a warning. The +default is chosen so that GCC only generates one instruction on most +systems. You should normally not change the default value of this macro. +@end defmac + +@defmac STACK_CHECK_FIXED_FRAME_SIZE +GCC uses this value to generate the above warning message. It +represents the amount of fixed frame used by a function, not including +space for any callee-saved registers, temporaries and user variables. +You need only specify an upper bound for this amount and will normally +use the default of four words. +@end defmac + +@defmac STACK_CHECK_MAX_VAR_SIZE +The maximum size, in bytes, of an object that GCC will place in the +fixed area of the stack frame when the user specifies +@option{-fstack-check}. +GCC computed the default from the values of the above macros and you will +normally not need to override that default. +@end defmac + +@need 2000 +@node Frame Registers +@subsection Registers That Address the Stack Frame + +@c prevent bad page break with this line +This discusses registers that address the stack frame. + +@defmac STACK_POINTER_REGNUM +The register number of the stack pointer register, which must also be a +fixed register according to @code{FIXED_REGISTERS}. On most machines, +the hardware determines which register this is. +@end defmac + +@defmac FRAME_POINTER_REGNUM +The register number of the frame pointer register, which is used to +access automatic variables in the stack frame. On some machines, the +hardware determines which register this is. On other machines, you can +choose any register you wish for this purpose. +@end defmac + +@defmac HARD_FRAME_POINTER_REGNUM +On some machines the offset between the frame pointer and starting +offset of the automatic variables is not known until after register +allocation has been done (for example, because the saved registers are +between these two locations). On those machines, define +@code{FRAME_POINTER_REGNUM} the number of a special, fixed register to +be used internally until the offset is known, and define +@code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number +used for the frame pointer. + +You should define this macro only in the very rare circumstances when it +is not possible to calculate the offset between the frame pointer and +the automatic variables until after register allocation has been +completed. When this macro is defined, you must also indicate in your +definition of @code{ELIMINABLE_REGS} how to eliminate +@code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM} +or @code{STACK_POINTER_REGNUM}. + +Do not define this macro if it would be the same as +@code{FRAME_POINTER_REGNUM}. +@end defmac + +@defmac ARG_POINTER_REGNUM +The register number of the arg pointer register, which is used to access +the function's argument list. On some machines, this is the same as the +frame pointer register. On some machines, the hardware determines which +register this is. On other machines, you can choose any register you +wish for this purpose. If this is not the same register as the frame +pointer register, then you must mark it as a fixed register according to +@code{FIXED_REGISTERS}, or arrange to be able to eliminate it +(@pxref{Elimination}). +@end defmac + +@defmac RETURN_ADDRESS_POINTER_REGNUM +The register number of the return address pointer register, which is used to +access the current function's return address from the stack. On some +machines, the return address is not at a fixed offset from the frame +pointer or stack pointer or argument pointer. This register can be defined +to point to the return address on the stack, and then be converted by +@code{ELIMINABLE_REGS} into either the frame pointer or stack pointer. + +Do not define this macro unless there is no other way to get the return +address from the stack. +@end defmac + +@defmac STATIC_CHAIN_REGNUM +@defmacx STATIC_CHAIN_INCOMING_REGNUM +Register numbers used for passing a function's static chain pointer. If +register windows are used, the register number as seen by the called +function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register +number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If +these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need +not be defined. + +The static chain register need not be a fixed register. + +If the static chain is passed in memory, these macros should not be +defined; instead, the next two macros should be defined. +@end defmac + +@defmac STATIC_CHAIN +@defmacx STATIC_CHAIN_INCOMING +If the static chain is passed in memory, these macros provide rtx giving +@code{mem} expressions that denote where they are stored. +@code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations +as seen by the calling and called functions, respectively. Often the former +will be at an offset from the stack pointer and the latter at an offset from +the frame pointer. + +@findex stack_pointer_rtx +@findex frame_pointer_rtx +@findex arg_pointer_rtx +The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and +@code{arg_pointer_rtx} will have been initialized prior to the use of these +macros and should be used to refer to those items. + +If the static chain is passed in a register, the two previous macros should +be defined instead. +@end defmac + +@defmac DWARF_FRAME_REGISTERS +This macro specifies the maximum number of hard registers that can be +saved in a call frame. This is used to size data structures used in +DWARF2 exception handling. + +Prior to GCC 3.0, this macro was needed in order to establish a stable +exception handling ABI in the face of adding new hard registers for ISA +extensions. In GCC 3.0 and later, the EH ABI is insulated from changes +in the number of hard registers. Nevertheless, this macro can still be +used to reduce the runtime memory requirements of the exception handling +routines, which can be substantial if the ISA contains a lot of +registers that are not call-saved. + +If this macro is not defined, it defaults to +@code{FIRST_PSEUDO_REGISTER}. +@end defmac + +@defmac PRE_GCC3_DWARF_FRAME_REGISTERS + +This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided +for backward compatibility in pre GCC 3.0 compiled code. + +If this macro is not defined, it defaults to +@code{DWARF_FRAME_REGISTERS}. +@end defmac + +@defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno}) + +Define this macro if the target's representation for dwarf registers +is different than the internal representation for unwind column. +Given a dwarf register, this macro should return the internal unwind +column number to use instead. + +See the PowerPC's SPE target for an example. +@end defmac + +@defmac DWARF_FRAME_REGNUM (@var{regno}) + +Define this macro if the target's representation for dwarf registers +used in .eh_frame or .debug_frame is different from that used in other +debug info sections. Given a GCC hard register number, this macro +should return the .eh_frame register number. The default is +@code{DBX_REGISTER_NUMBER (@var{regno})}. + +@end defmac + +@defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh}) + +Define this macro to map register numbers held in the call frame info +that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that +should be output in .debug_frame (@code{@var{for_eh}} is zero) and +.eh_frame (@code{@var{for_eh}} is nonzero). The default is to +return @code{@var{regno}}. + +@end defmac + +@node Elimination +@subsection Eliminating Frame Pointer and Arg Pointer + +@c prevent bad page break with this line +This is about eliminating the frame pointer and arg pointer. + +@defmac FRAME_POINTER_REQUIRED +A C expression which is nonzero if a function must have and use a frame +pointer. This expression is evaluated in the reload pass. If its value is +nonzero the function will have a frame pointer. + +The expression can in principle examine the current function and decide +according to the facts, but on most machines the constant 0 or the +constant 1 suffices. Use 0 when the machine allows code to be generated +with no frame pointer, and doing so saves some time or space. Use 1 +when there is no possible advantage to avoiding a frame pointer. + +In certain cases, the compiler does not know how to produce valid code +without a frame pointer. The compiler recognizes those cases and +automatically gives the function a frame pointer regardless of what +@code{FRAME_POINTER_REQUIRED} says. You don't need to worry about +them. + +In a function that does not require a frame pointer, the frame pointer +register can be allocated for ordinary usage, unless you mark it as a +fixed register. See @code{FIXED_REGISTERS} for more information. +@end defmac + +@findex get_frame_size +@defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var}) +A C statement to store in the variable @var{depth-var} the difference +between the frame pointer and the stack pointer values immediately after +the function prologue. The value would be computed from information +such as the result of @code{get_frame_size ()} and the tables of +registers @code{regs_ever_live} and @code{call_used_regs}. + +If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and +need not be defined. Otherwise, it must be defined even if +@code{FRAME_POINTER_REQUIRED} is defined to always be true; in that +case, you may set @var{depth-var} to anything. +@end defmac + +@defmac ELIMINABLE_REGS +If defined, this macro specifies a table of register pairs used to +eliminate unneeded registers that point into the stack frame. If it is not +defined, the only elimination attempted by the compiler is to replace +references to the frame pointer with references to the stack pointer. + +The definition of this macro is a list of structure initializations, each +of which specifies an original and replacement register. + +On some machines, the position of the argument pointer is not known until +the compilation is completed. In such a case, a separate hard register +must be used for the argument pointer. This register can be eliminated by +replacing it with either the frame pointer or the argument pointer, +depending on whether or not the frame pointer has been eliminated. + +In this case, you might specify: +@smallexample +#define ELIMINABLE_REGS \ +@{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \ + @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \ + @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@} +@end smallexample + +Note that the elimination of the argument pointer with the stack pointer is +specified first since that is the preferred elimination. +@end defmac + +@defmac CAN_ELIMINATE (@var{from-reg}, @var{to-reg}) +A C expression that returns nonzero if the compiler is allowed to try +to replace register number @var{from-reg} with register number +@var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS} +is defined, and will usually be the constant 1, since most of the cases +preventing register elimination are things that the compiler already +knows about. +@end defmac + +@defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var}) +This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It +specifies the initial difference between the specified pair of +registers. This macro must be defined if @code{ELIMINABLE_REGS} is +defined. +@end defmac + +@node Stack Arguments +@subsection Passing Function Arguments on the Stack +@cindex arguments on stack +@cindex stack arguments + +The macros in this section control how arguments are passed +on the stack. See the following section for other macros that +control passing certain arguments in registers. + +@deftypefn {Target Hook} bool TARGET_PROMOTE_PROTOTYPES (tree @var{fntype}) +This target hook returns @code{true} if an argument declared in a +prototype as an integral type smaller than @code{int} should actually be +passed as an @code{int}. In addition to avoiding errors in certain +cases of mismatch, it also makes for better code on certain machines. +The default is to not promote prototypes. +@end deftypefn + +@defmac PUSH_ARGS +A C expression. If nonzero, push insns will be used to pass +outgoing arguments. +If the target machine does not have a push instruction, set it to zero. +That directs GCC to use an alternate strategy: to +allocate the entire argument block and then store the arguments into +it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too. +@end defmac + +@defmac PUSH_ARGS_REVERSED +A C expression. If nonzero, function arguments will be evaluated from +last to first, rather than from first to last. If this macro is not +defined, it defaults to @code{PUSH_ARGS} on targets where the stack +and args grow in opposite directions, and 0 otherwise. +@end defmac + +@defmac PUSH_ROUNDING (@var{npushed}) +A C expression that is the number of bytes actually pushed onto the +stack when an instruction attempts to push @var{npushed} bytes. + +On some machines, the definition + +@smallexample +#define PUSH_ROUNDING(BYTES) (BYTES) +@end smallexample + +@noindent +will suffice. But on other machines, instructions that appear +to push one byte actually push two bytes in an attempt to maintain +alignment. Then the definition should be + +@smallexample +#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) +@end smallexample +@end defmac + +@findex current_function_outgoing_args_size +@defmac ACCUMULATE_OUTGOING_ARGS +A C expression. If nonzero, the maximum amount of space required for outgoing arguments +will be computed and placed into the variable +@code{current_function_outgoing_args_size}. No space will be pushed +onto the stack for each call; instead, the function prologue should +increase the stack frame size by this amount. + +Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS} +is not proper. +@end defmac + +@defmac REG_PARM_STACK_SPACE (@var{fndecl}) +Define this macro if functions should assume that stack space has been +allocated for arguments even when their values are passed in +registers. + +The value of this macro is the size, in bytes, of the area reserved for +arguments passed in registers for the function represented by @var{fndecl}, +which can be zero if GCC is calling a library function. + +This space can be allocated by the caller, or be a part of the +machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says +which. +@end defmac +@c above is overfull. not sure what to do. --mew 5feb93 did +@c something, not sure if it looks good. --mew 10feb93 + +@defmac OUTGOING_REG_PARM_STACK_SPACE +Define this if it is the responsibility of the caller to allocate the area +reserved for arguments passed in registers. + +If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls +whether the space for these arguments counts in the value of +@code{current_function_outgoing_args_size}. +@end defmac + +@defmac STACK_PARMS_IN_REG_PARM_AREA +Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the +stack parameters don't skip the area specified by it. +@c i changed this, makes more sens and it should have taken care of the +@c overfull.. not as specific, tho. --mew 5feb93 + +Normally, when a parameter is not passed in registers, it is placed on the +stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro +suppresses this behavior and causes the parameter to be passed on the +stack in its natural location. +@end defmac + +@defmac RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size}) +A C expression that should indicate the number of bytes of its own +arguments that a function pops on returning, or 0 if the +function pops no arguments and the caller must therefore pop them all +after the function returns. + +@var{fundecl} is a C variable whose value is a tree node that describes +the function in question. Normally it is a node of type +@code{FUNCTION_DECL} that describes the declaration of the function. +From this you can obtain the @code{DECL_ATTRIBUTES} of the function. + +@var{funtype} is a C variable whose value is a tree node that +describes the function in question. Normally it is a node of type +@code{FUNCTION_TYPE} that describes the data type of the function. +From this it is possible to obtain the data types of the value and +arguments (if known). + +When a call to a library function is being considered, @var{fundecl} +will contain an identifier node for the library function. Thus, if +you need to distinguish among various library functions, you can do so +by their names. Note that ``library function'' in this context means +a function used to perform arithmetic, whose name is known specially +in the compiler and was not mentioned in the C code being compiled. + +@var{stack-size} is the number of bytes of arguments passed on the +stack. If a variable number of bytes is passed, it is zero, and +argument popping will always be the responsibility of the calling function. + +On the VAX, all functions always pop their arguments, so the definition +of this macro is @var{stack-size}. On the 68000, using the standard +calling convention, no functions pop their arguments, so the value of +the macro is always 0 in this case. But an alternative calling +convention is available in which functions that take a fixed number of +arguments pop them but other functions (such as @code{printf}) pop +nothing (the caller pops all). When this convention is in use, +@var{funtype} is examined to determine whether a function takes a fixed +number of arguments. +@end defmac + +@defmac CALL_POPS_ARGS (@var{cum}) +A C expression that should indicate the number of bytes a call sequence +pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS} +when compiling a function call. + +@var{cum} is the variable in which all arguments to the called function +have been accumulated. + +On certain architectures, such as the SH5, a call trampoline is used +that pops certain registers off the stack, depending on the arguments +that have been passed to the function. Since this is a property of the +call site, not of the called function, @code{RETURN_POPS_ARGS} is not +appropriate. +@end defmac + +@node Register Arguments +@subsection Passing Arguments in Registers +@cindex arguments in registers +@cindex registers arguments + +This section describes the macros which let you control how various +types of arguments are passed in registers or how they are arranged in +the stack. + +@defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) +A C expression that controls whether a function argument is passed +in a register, and which register. + +The arguments are @var{cum}, which summarizes all the previous +arguments; @var{mode}, the machine mode of the argument; @var{type}, +the data type of the argument as a tree node or 0 if that is not known +(which happens for C support library functions); and @var{named}, +which is 1 for an ordinary argument and 0 for nameless arguments that +correspond to @samp{@dots{}} in the called function's prototype. +@var{type} can be an incomplete type if a syntax error has previously +occurred. + +The value of the expression is usually either a @code{reg} RTX for the +hard register in which to pass the argument, or zero to pass the +argument on the stack. + +For machines like the VAX and 68000, where normally all arguments are +pushed, zero suffices as a definition. + +The value of the expression can also be a @code{parallel} RTX@. This is +used when an argument is passed in multiple locations. The mode of the +@code{parallel} should be the mode of the entire argument. The +@code{parallel} holds any number of @code{expr_list} pairs; each one +describes where part of the argument is passed. In each +@code{expr_list} the first operand must be a @code{reg} RTX for the hard +register in which to pass this part of the argument, and the mode of the +register RTX indicates how large this part of the argument is. The +second operand of the @code{expr_list} is a @code{const_int} which gives +the offset in bytes into the entire argument of where this part starts. +As a special exception the first @code{expr_list} in the @code{parallel} +RTX may have a first operand of zero. This indicates that the entire +argument is also stored on the stack. + +The last time this macro is called, it is called with @code{MODE == +VOIDmode}, and its result is passed to the @code{call} or @code{call_value} +pattern as operands 2 and 3 respectively. + +@cindex @file{stdarg.h} and register arguments +The usual way to make the ISO library @file{stdarg.h} work on a machine +where some arguments are usually passed in registers, is to cause +nameless arguments to be passed on the stack instead. This is done +by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0. + +@cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG} +@cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG} +You may use the hook @code{targetm.calls.must_pass_in_stack} +in the definition of this macro to determine if this argument is of a +type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE} +is not defined and @code{FUNCTION_ARG} returns nonzero for such an +argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is +defined, the argument will be computed in the stack and then loaded into +a register. +@end defmac + +@deftypefn {Target Hook} bool TARGET_MUST_PASS_IN_STACK (enum machine_mode @var{mode}, tree @var{type}) +This target hook should return @code{true} if we should not pass @var{type} +solely in registers. The file @file{expr.h} defines a +definition that is usually appropriate, refer to @file{expr.h} for additional +documentation. +@end deftypefn + +@defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) +Define this macro if the target machine has ``register windows'', so +that the register in which a function sees an arguments is not +necessarily the same as the one in which the caller passed the +argument. + +For such machines, @code{FUNCTION_ARG} computes the register in which +the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should +be defined in a similar fashion to tell the function being called +where the arguments will arrive. + +If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG} +serves both purposes. +@end defmac + +@deftypefn {Target Hook} int TARGET_ARG_PARTIAL_BYTES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named}) +This target hook returns the number of bytes at the beginning of an +argument that must be put in registers. The value must be zero for +arguments that are passed entirely in registers or that are entirely +pushed on the stack. + +On some machines, certain arguments must be passed partially in +registers and partially in memory. On these machines, typically the +first few words of arguments are passed in registers, and the rest +on the stack. If a multi-word argument (a @code{double} or a +structure) crosses that boundary, its first few words must be passed +in registers and the rest must be pushed. This macro tells the +compiler when this occurs, and how many bytes should go in registers. + +@code{FUNCTION_ARG} for these arguments should return the first +register to be used by the caller for this argument; likewise +@code{FUNCTION_INCOMING_ARG}, for the called function. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_PASS_BY_REFERENCE (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named}) +This target hook should return @code{true} if an argument at the +position indicated by @var{cum} should be passed by reference. This +predicate is queried after target independent reasons for being +passed by reference, such as @code{TREE_ADDRESSABLE (type)}. + +If the hook returns true, a copy of that argument is made in memory and a +pointer to the argument is passed instead of the argument itself. +The pointer is passed in whatever way is appropriate for passing a pointer +to that type. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CALLEE_COPIES (CUMULATIVE_ARGS *@var{cum}, enum machine_mode @var{mode}, tree @var{type}, bool @var{named}) +The function argument described by the parameters to this hook is +known to be passed by reference. The hook should return true if the +function argument should be copied by the callee instead of copied +by the caller. + +For any argument for which the hook returns true, if it can be +determined that the argument is not modified, then a copy need +not be generated. + +The default version of this hook always returns false. +@end deftypefn + +@defmac CUMULATIVE_ARGS +A C type for declaring a variable that is used as the first argument of +@code{FUNCTION_ARG} and other related values. For some target machines, +the type @code{int} suffices and can hold the number of bytes of +argument so far. + +There is no need to record in @code{CUMULATIVE_ARGS} anything about the +arguments that have been passed on the stack. The compiler has other +variables to keep track of that. For target machines on which all +arguments are passed on the stack, there is no need to store anything in +@code{CUMULATIVE_ARGS}; however, the data structure must exist and +should not be empty, so use @code{int}. +@end defmac + +@defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args}) +A C statement (sans semicolon) for initializing the variable +@var{cum} for the state at the beginning of the argument list. The +variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype} +is the tree node for the data type of the function which will receive +the args, or 0 if the args are to a compiler support library function. +For direct calls that are not libcalls, @var{fndecl} contain the +declaration node of the function. @var{fndecl} is also set when +@code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function +being compiled. @var{n_named_args} is set to the number of named +arguments, including a structure return address if it is passed as a +parameter, when making a call. When processing incoming arguments, +@var{n_named_args} is set to @minus{}1. + +When processing a call to a compiler support library function, +@var{libname} identifies which one. It is a @code{symbol_ref} rtx which +contains the name of the function, as a string. @var{libname} is 0 when +an ordinary C function call is being processed. Thus, each time this +macro is called, either @var{libname} or @var{fntype} is nonzero, but +never both of them at once. +@end defmac + +@defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname}) +Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls, +it gets a @code{MODE} argument instead of @var{fntype}, that would be +@code{NULL}. @var{indirect} would always be zero, too. If this macro +is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, +0)} is used instead. +@end defmac + +@defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname}) +Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of +finding the arguments for the function being compiled. If this macro is +undefined, @code{INIT_CUMULATIVE_ARGS} is used instead. + +The value passed for @var{libname} is always 0, since library routines +with special calling conventions are never compiled with GCC@. The +argument @var{libname} exists for symmetry with +@code{INIT_CUMULATIVE_ARGS}. +@c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe. +@c --mew 5feb93 i switched the order of the sentences. --mew 10feb93 +@end defmac + +@defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named}) +A C statement (sans semicolon) to update the summarizer variable +@var{cum} to advance past an argument in the argument list. The +values @var{mode}, @var{type} and @var{named} describe that argument. +Once this is done, the variable @var{cum} is suitable for analyzing +the @emph{following} argument with @code{FUNCTION_ARG}, etc. + +This macro need not do anything if the argument in question was passed +on the stack. The compiler knows how to track the amount of stack space +used for arguments without any special help. +@end defmac + +@defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type}) +If defined, a C expression which determines whether, and in which direction, +to pad out an argument with extra space. The value should be of type +@code{enum direction}: either @code{upward} to pad above the argument, +@code{downward} to pad below, or @code{none} to inhibit padding. + +The @emph{amount} of padding is always just enough to reach the next +multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control +it. + +This macro has a default definition which is right for most systems. +For little-endian machines, the default is to pad upward. For +big-endian machines, the default is to pad downward for an argument of +constant size shorter than an @code{int}, and upward otherwise. +@end defmac + +@defmac PAD_VARARGS_DOWN +If defined, a C expression which determines whether the default +implementation of va_arg will attempt to pad down before reading the +next argument, if that argument is smaller than its aligned space as +controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such +arguments are padded down if @code{BYTES_BIG_ENDIAN} is true. +@end defmac + +@defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first}) +Specify padding for the last element of a block move between registers and +memory. @var{first} is nonzero if this is the only element. Defining this +macro allows better control of register function parameters on big-endian +machines, without using @code{PARALLEL} rtl. In particular, +@code{MUST_PASS_IN_STACK} need not test padding and mode of types in +registers, as there is no longer a "wrong" part of a register; For example, +a three byte aggregate may be passed in the high part of a register if so +required. +@end defmac + +@defmac FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type}) +If defined, a C expression that gives the alignment boundary, in bits, +of an argument with the specified mode and type. If it is not defined, +@code{PARM_BOUNDARY} is used for all arguments. +@end defmac + +@defmac FUNCTION_ARG_REGNO_P (@var{regno}) +A C expression that is nonzero if @var{regno} is the number of a hard +register in which function arguments are sometimes passed. This does +@emph{not} include implicit arguments such as the static chain and +the structure-value address. On many machines, no registers can be +used for this purpose since all function arguments are pushed on the +stack. +@end defmac + +@deftypefn {Target Hook} bool TARGET_SPLIT_COMPLEX_ARG (tree @var{type}) +This hook should return true if parameter of type @var{type} are passed +as two scalar parameters. By default, GCC will attempt to pack complex +arguments into the target's word size. Some ABIs require complex arguments +to be split and treated as their individual components. For example, on +AIX64, complex floats should be passed in a pair of floating point +registers, even though a complex float would fit in one 64-bit floating +point register. + +The default value of this hook is @code{NULL}, which is treated as always +false. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_BUILD_BUILTIN_VA_LIST (void) +This hook returns a type node for @code{va_list} for the target. +The default version of the hook returns @code{void*}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_GIMPLIFY_VA_ARG_EXPR (tree @var{valist}, tree @var{type}, tree *@var{pre_p}, tree *@var{post_p}) +This hook performs target-specific gimplification of +@code{VA_ARG_EXPR}. The first two parameters correspond to the +arguments to @code{va_arg}; the latter two are as in +@code{gimplify.c:gimplify_expr}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VALID_POINTER_MODE (enum machine_mode @var{mode}) +Define this to return nonzero if the port can handle pointers +with machine mode @var{mode}. The default version of this +hook returns true for both @code{ptr_mode} and @code{Pmode}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCALAR_MODE_SUPPORTED_P (enum machine_mode @var{mode}) +Define this to return nonzero if the port is prepared to handle +insns involving scalar mode @var{mode}. For a scalar mode to be +considered supported, all the basic arithmetic and comparisons +must work. + +The default version of this hook returns true for any mode +required to handle the basic C types (as defined by the port). +Included here are the double-word arithmetic supported by the +code in @file{optabs.c}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VECTOR_MODE_SUPPORTED_P (enum machine_mode @var{mode}) +Define this to return nonzero if the port is prepared to handle +insns involving vector mode @var{mode}. At the very least, it +must have move patterns for this mode. +@end deftypefn + +@node Scalar Return +@subsection How Scalar Function Values Are Returned +@cindex return values in registers +@cindex values, returned by functions +@cindex scalars, returned as values + +This section discusses the macros that control returning scalars as +values---values that can fit in registers. + +@deftypefn {Target Hook} rtx TARGET_FUNCTION_VALUE (tree @var{ret_type}, tree @var{fn_decl_or_type}, bool @var{outgoing}) + +Define this to return an RTX representing the place where a function +returns or receives a value of data type @var{ret_type}, a tree node +node representing a data type. @var{fn_decl_or_type} is a tree node +representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a +function being called. If @var{outgoing} is false, the hook should +compute the register in which the caller will see the return value. +Otherwise, the hook should return an RTX representing the place where +a function returns a value. + +On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant. +(Actually, on most machines, scalar values are returned in the same +place regardless of mode.) The value of the expression is usually a +@code{reg} RTX for the hard register where the return value is stored. +The value can also be a @code{parallel} RTX, if the return value is in +multiple places. See @code{FUNCTION_ARG} for an explanation of the +@code{parallel} form. + +If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply +the same promotion rules specified in @code{PROMOTE_MODE} if +@var{valtype} is a scalar type. + +If the precise function being called is known, @var{func} is a tree +node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null +pointer. This makes it possible to use a different value-returning +convention for specific functions when all their calls are +known. + +Some target machines have ``register windows'' so that the register in +which a function returns its value is not the same as the one in which +the caller sees the value. For such machines, you should return +different RTX depending on @var{outgoing}. + +@code{TARGET_FUNCTION_VALUE} is not used for return values with +aggregate data types, because these are returned in another way. See +@code{TARGET_STRUCT_VALUE_RTX} and related macros, below. +@end deftypefn + +@defmac FUNCTION_VALUE (@var{valtype}, @var{func}) +This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for +a new target instead. +@end defmac + +@defmac FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func}) +This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for +a new target instead. +@end defmac + +@defmac LIBCALL_VALUE (@var{mode}) +A C expression to create an RTX representing the place where a library +function returns a value of mode @var{mode}. If the precise function +being called is known, @var{func} is a tree node +(@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null +pointer. This makes it possible to use a different value-returning +convention for specific functions when all their calls are +known. + +Note that ``library function'' in this context means a compiler +support routine, used to perform arithmetic, whose name is known +specially by the compiler and was not mentioned in the C code being +compiled. + +The definition of @code{LIBRARY_VALUE} need not be concerned aggregate +data types, because none of the library functions returns such types. +@end defmac + +@defmac FUNCTION_VALUE_REGNO_P (@var{regno}) +A C expression that is nonzero if @var{regno} is the number of a hard +register in which the values of called function may come back. + +A register whose use for returning values is limited to serving as the +second of a pair (for a value of type @code{double}, say) need not be +recognized by this macro. So for most machines, this definition +suffices: + +@smallexample +#define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) +@end smallexample + +If the machine has register windows, so that the caller and the called +function use different registers for the return value, this macro +should recognize only the caller's register numbers. +@end defmac + +@defmac APPLY_RESULT_SIZE +Define this macro if @samp{untyped_call} and @samp{untyped_return} +need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for +saving and restoring an arbitrary return value. +@end defmac + +@deftypefn {Target Hook} bool TARGET_RETURN_IN_MSB (tree @var{type}) +This hook should return true if values of type @var{type} are returned +at the most significant end of a register (in other words, if they are +padded at the least significant end). You can assume that @var{type} +is returned in a register; the caller is required to check this. + +Note that the register provided by @code{TARGET_FUNCTION_VALUE} must +be able to hold the complete return value. For example, if a 1-, 2- +or 3-byte structure is returned at the most significant end of a +4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an +@code{SImode} rtx. +@end deftypefn + +@node Aggregate Return +@subsection How Large Values Are Returned +@cindex aggregates as return values +@cindex large return values +@cindex returning aggregate values +@cindex structure value address + +When a function value's mode is @code{BLKmode} (and in some other +cases), the value is not returned according to +@code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the +caller passes the address of a block of memory in which the value +should be stored. This address is called the @dfn{structure value +address}. + +This section describes how to control returning structure values in +memory. + +@deftypefn {Target Hook} bool TARGET_RETURN_IN_MEMORY (tree @var{type}, tree @var{fntype}) +This target hook should return a nonzero value to say to return the +function value in memory, just as large structures are always returned. +Here @var{type} will be the data type of the value, and @var{fntype} +will be the type of the function doing the returning, or @code{NULL} for +libcalls. + +Note that values of mode @code{BLKmode} must be explicitly handled +by this function. Also, the option @option{-fpcc-struct-return} +takes effect regardless of this macro. On most systems, it is +possible to leave the hook undefined; this causes a default +definition to be used, whose value is the constant 1 for @code{BLKmode} +values, and 0 otherwise. + +Do not use this hook to indicate that structures and unions should always +be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN} +to indicate this. +@end deftypefn + +@defmac DEFAULT_PCC_STRUCT_RETURN +Define this macro to be 1 if all structure and union return values must be +in memory. Since this results in slower code, this should be defined +only if needed for compatibility with other compilers or with an ABI@. +If you define this macro to be 0, then the conventions used for structure +and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY} +target hook. + +If not defined, this defaults to the value 1. +@end defmac + +@deftypefn {Target Hook} rtx TARGET_STRUCT_VALUE_RTX (tree @var{fndecl}, int @var{incoming}) +This target hook should return the location of the structure value +address (normally a @code{mem} or @code{reg}), or 0 if the address is +passed as an ``invisible'' first argument. Note that @var{fndecl} may +be @code{NULL}, for libcalls. You do not need to define this target +hook if the address is always passed as an ``invisible'' first +argument. + +On some architectures the place where the structure value address +is found by the called function is not the same place that the +caller put it. This can be due to register windows, or it could +be because the function prologue moves it to a different place. +@var{incoming} is @code{1} or @code{2} when the location is needed in +the context of the called function, and @code{0} in the context of +the caller. + +If @var{incoming} is nonzero and the address is to be found on the +stack, return a @code{mem} which refers to the frame pointer. If +@var{incoming} is @code{2}, the result is being used to fetch the +structure value address at the beginning of a function. If you need +to emit adjusting code, you should do it at this point. +@end deftypefn + +@defmac PCC_STATIC_STRUCT_RETURN +Define this macro if the usual system convention on the target machine +for returning structures and unions is for the called function to return +the address of a static variable containing the value. + +Do not define this if the usual system convention is for the caller to +pass an address to the subroutine. + +This macro has effect in @option{-fpcc-struct-return} mode, but it does +nothing when you use @option{-freg-struct-return} mode. +@end defmac + +@node Caller Saves +@subsection Caller-Saves Register Allocation + +If you enable it, GCC can save registers around function calls. This +makes it possible to use call-clobbered registers to hold variables that +must live across calls. + +@defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls}) +A C expression to determine whether it is worthwhile to consider placing +a pseudo-register in a call-clobbered hard register and saving and +restoring it around each function call. The expression should be 1 when +this is worth doing, and 0 otherwise. + +If you don't define this macro, a default is used which is good on most +machines: @code{4 * @var{calls} < @var{refs}}. +@end defmac + +@defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs}) +A C expression specifying which mode is required for saving @var{nregs} +of a pseudo-register in call-clobbered hard register @var{regno}. If +@var{regno} is unsuitable for caller save, @code{VOIDmode} should be +returned. For most machines this macro need not be defined since GCC +will select the smallest suitable mode. +@end defmac + +@node Function Entry +@subsection Function Entry and Exit +@cindex function entry and exit +@cindex prologue +@cindex epilogue + +This section describes the macros that output function entry +(@dfn{prologue}) and exit (@dfn{epilogue}) code. + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) +If defined, a function that outputs the assembler code for entry to a +function. The prologue is responsible for setting up the stack frame, +initializing the frame pointer register, saving registers that must be +saved, and allocating @var{size} additional bytes of storage for the +local variables. @var{size} is an integer. @var{file} is a stdio +stream to which the assembler code should be output. + +The label for the beginning of the function need not be output by this +macro. That has already been done when the macro is run. + +@findex regs_ever_live +To determine which registers to save, the macro can refer to the array +@code{regs_ever_live}: element @var{r} is nonzero if hard register +@var{r} is used anywhere within the function. This implies the function +prologue should save register @var{r}, provided it is not one of the +call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use +@code{regs_ever_live}.) + +On machines that have ``register windows'', the function entry code does +not save on the stack the registers that are in the windows, even if +they are supposed to be preserved by function calls; instead it takes +appropriate steps to ``push'' the register stack, if any non-call-used +registers are used in the function. + +@findex frame_pointer_needed +On machines where functions may or may not have frame-pointers, the +function entry code must vary accordingly; it must set up the frame +pointer if one is wanted, and not otherwise. To determine whether a +frame pointer is in wanted, the macro can refer to the variable +@code{frame_pointer_needed}. The variable's value will be 1 at run +time in a function that needs a frame pointer. @xref{Elimination}. + +The function entry code is responsible for allocating any stack space +required for the function. This stack space consists of the regions +listed below. In most cases, these regions are allocated in the +order listed, with the last listed region closest to the top of the +stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and +the highest address if it is not defined). You can use a different order +for a machine if doing so is more convenient or required for +compatibility reasons. Except in cases where required by standard +or by a debugger, there is no reason why the stack layout used by GCC +need agree with that used by other compilers for a machine. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file}) +If defined, a function that outputs assembler code at the end of a +prologue. This should be used when the function prologue is being +emitted as RTL, and you have some extra assembler that needs to be +emitted. @xref{prologue instruction pattern}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file}) +If defined, a function that outputs assembler code at the start of an +epilogue. This should be used when the function epilogue is being +emitted as RTL, and you have some extra assembler that needs to be +emitted. @xref{epilogue instruction pattern}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) +If defined, a function that outputs the assembler code for exit from a +function. The epilogue is responsible for restoring the saved +registers and stack pointer to their values when the function was +called, and returning control to the caller. This macro takes the +same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the +registers to restore are determined from @code{regs_ever_live} and +@code{CALL_USED_REGISTERS} in the same way. + +On some machines, there is a single instruction that does all the work +of returning from the function. On these machines, give that +instruction the name @samp{return} and do not define the macro +@code{TARGET_ASM_FUNCTION_EPILOGUE} at all. + +Do not define a pattern named @samp{return} if you want the +@code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target +switches to control whether return instructions or epilogues are used, +define a @samp{return} pattern with a validity condition that tests the +target switches appropriately. If the @samp{return} pattern's validity +condition is false, epilogues will be used. + +On machines where functions may or may not have frame-pointers, the +function exit code must vary accordingly. Sometimes the code for these +two cases is completely different. To determine whether a frame pointer +is wanted, the macro can refer to the variable +@code{frame_pointer_needed}. The variable's value will be 1 when compiling +a function that needs a frame pointer. + +Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and +@code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially. +The C variable @code{current_function_is_leaf} is nonzero for such a +function. @xref{Leaf Functions}. + +On some machines, some functions pop their arguments on exit while +others leave that for the caller to do. For example, the 68020 when +given @option{-mrtd} pops arguments in functions that take a fixed +number of arguments. + +@findex current_function_pops_args +Your definition of the macro @code{RETURN_POPS_ARGS} decides which +functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE} +needs to know what was decided. The variable that is called +@code{current_function_pops_args} is the number of bytes of its +arguments that a function should pop. @xref{Scalar Return}. +@c what is the "its arguments" in the above sentence referring to, pray +@c tell? --mew 5feb93 +@end deftypefn + +@itemize @bullet +@item +@findex current_function_pretend_args_size +A region of @code{current_function_pretend_args_size} bytes of +uninitialized space just underneath the first argument arriving on the +stack. (This may not be at the very start of the allocated stack region +if the calling sequence has pushed anything else since pushing the stack +arguments. But usually, on such machines, nothing else has been pushed +yet, because the function prologue itself does all the pushing.) This +region is used on machines where an argument may be passed partly in +registers and partly in memory, and, in some cases to support the +features in @code{<stdarg.h>}. + +@item +An area of memory used to save certain registers used by the function. +The size of this area, which may also include space for such things as +the return address and pointers to previous stack frames, is +machine-specific and usually depends on which registers have been used +in the function. Machines with register windows often do not require +a save area. + +@item +A region of at least @var{size} bytes, possibly rounded up to an allocation +boundary, to contain the local variables of the function. On some machines, +this region and the save area may occur in the opposite order, with the +save area closer to the top of the stack. + +@item +@cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames +Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of +@code{current_function_outgoing_args_size} bytes to be used for outgoing +argument lists of the function. @xref{Stack Arguments}. +@end itemize + +@defmac EXIT_IGNORE_STACK +Define this macro as a C expression that is nonzero if the return +instruction or the function epilogue ignores the value of the stack +pointer; in other words, if it is safe to delete an instruction to +adjust the stack pointer before a return from the function. The +default is 0. + +Note that this macro's value is relevant only for functions for which +frame pointers are maintained. It is never safe to delete a final +stack adjustment in a function that has no frame pointer, and the +compiler knows this regardless of @code{EXIT_IGNORE_STACK}. +@end defmac + +@defmac EPILOGUE_USES (@var{regno}) +Define this macro as a C expression that is nonzero for registers that are +used by the epilogue or the @samp{return} pattern. The stack and frame +pointer registers are already assumed to be used as needed. +@end defmac + +@defmac EH_USES (@var{regno}) +Define this macro as a C expression that is nonzero for registers that are +used by the exception handling mechanism, and so should be considered live +on entry to an exception edge. +@end defmac + +@defmac DELAY_SLOTS_FOR_EPILOGUE +Define this macro if the function epilogue contains delay slots to which +instructions from the rest of the function can be ``moved''. The +definition should be a C expression whose value is an integer +representing the number of delay slots there. +@end defmac + +@defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n}) +A C expression that returns 1 if @var{insn} can be placed in delay +slot number @var{n} of the epilogue. + +The argument @var{n} is an integer which identifies the delay slot now +being considered (since different slots may have different rules of +eligibility). It is never negative and is always less than the number +of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns). +If you reject a particular insn for a given delay slot, in principle, it +may be reconsidered for a subsequent delay slot. Also, other insns may +(at least in principle) be considered for the so far unfilled delay +slot. + +@findex current_function_epilogue_delay_list +@findex final_scan_insn +The insns accepted to fill the epilogue delay slots are put in an RTL +list made with @code{insn_list} objects, stored in the variable +@code{current_function_epilogue_delay_list}. The insn for the first +delay slot comes first in the list. Your definition of the macro +@code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by +outputting the insns in this list, usually by calling +@code{final_scan_insn}. + +You need not define this macro if you did not define +@code{DELAY_SLOTS_FOR_EPILOGUE}. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_MI_THUNK (FILE *@var{file}, tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, tree @var{function}) +A function that outputs the assembler code for a thunk +function, used to implement C++ virtual function calls with multiple +inheritance. The thunk acts as a wrapper around a virtual function, +adjusting the implicit object parameter before handing control off to +the real function. + +First, emit code to add the integer @var{delta} to the location that +contains the incoming first argument. Assume that this argument +contains a pointer, and is the one used to pass the @code{this} pointer +in C++. This is the incoming argument @emph{before} the function prologue, +e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of +all other incoming arguments. + +Then, if @var{vcall_offset} is nonzero, an additional adjustment should be +made after adding @code{delta}. In particular, if @var{p} is the +adjusted pointer, the following adjustment should be made: + +@smallexample +p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)] +@end smallexample + +After the additions, emit code to jump to @var{function}, which is a +@code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does +not touch the return address. Hence returning from @var{FUNCTION} will +return to whoever called the current @samp{thunk}. + +The effect must be as if @var{function} had been called directly with +the adjusted first argument. This macro is responsible for emitting all +of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE} +and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked. + +The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function} +have already been extracted from it.) It might possibly be useful on +some targets, but probably not. + +If you do not define this macro, the target-independent code in the C++ +front end will generate a less efficient heavyweight thunk that calls +@var{function} instead of jumping to it. The generic approach does +not support varargs. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ASM_CAN_OUTPUT_MI_THUNK (tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, tree @var{function}) +A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able +to output the assembler code for the thunk function specified by the +arguments it is passed, and false otherwise. In the latter case, the +generic approach will be used by the C++ front end, with the limitations +previously exposed. +@end deftypefn + +@node Profiling +@subsection Generating Code for Profiling +@cindex profiling, code generation + +These macros will help you generate code for profiling. + +@defmac FUNCTION_PROFILER (@var{file}, @var{labelno}) +A C statement or compound statement to output to @var{file} some +assembler code to call the profiling subroutine @code{mcount}. + +@findex mcount +The details of how @code{mcount} expects to be called are determined by +your operating system environment, not by GCC@. To figure them out, +compile a small program for profiling using the system's installed C +compiler and look at the assembler code that results. + +Older implementations of @code{mcount} expect the address of a counter +variable to be loaded into some register. The name of this variable is +@samp{LP} followed by the number @var{labelno}, so you would generate +the name using @samp{LP%d} in a @code{fprintf}. +@end defmac + +@defmac PROFILE_HOOK +A C statement or compound statement to output to @var{file} some assembly +code to call the profiling subroutine @code{mcount} even the target does +not support profiling. +@end defmac + +@defmac NO_PROFILE_COUNTERS +Define this macro to be an expression with a nonzero value if the +@code{mcount} subroutine on your system does not need a counter variable +allocated for each function. This is true for almost all modern +implementations. If you define this macro, you must not use the +@var{labelno} argument to @code{FUNCTION_PROFILER}. +@end defmac + +@defmac PROFILE_BEFORE_PROLOGUE +Define this macro if the code for function profiling should come before +the function prologue. Normally, the profiling code comes after. +@end defmac + +@node Tail Calls +@subsection Permitting tail calls +@cindex tail calls + +@deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp}) +True if it is ok to do sibling call optimization for the specified +call expression @var{exp}. @var{decl} will be the called function, +or @code{NULL} if this is an indirect call. + +It is not uncommon for limitations of calling conventions to prevent +tail calls to functions outside the current unit of translation, or +during PIC compilation. The hook is used to enforce these restrictions, +as the @code{sibcall} md pattern can not fail, or fall over to a +``normal'' call. The criteria for successful sibling call optimization +may vary greatly between different architectures. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_EXTRA_LIVE_ON_ENTRY (bitmap *@var{regs}) +Add any hard registers to @var{regs} that are live on entry to the +function. This hook only needs to be defined to provide registers that +cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved +registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM, +TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES, +FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM. +@end deftypefn + +@node Stack Smashing Protection +@subsection Stack smashing protection +@cindex stack smashing protection + +@deftypefn {Target Hook} tree TARGET_STACK_PROTECT_GUARD (void) +This hook returns a @code{DECL} node for the external variable to use +for the stack protection guard. This variable is initialized by the +runtime to some random value and is used to initialize the guard value +that is placed at the top of the local stack frame. The type of this +variable must be @code{ptr_type_node}. + +The default version of this hook creates a variable called +@samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_STACK_PROTECT_FAIL (void) +This hook returns a tree expression that alerts the runtime that the +stack protect guard variable has been modified. This expression should +involve a call to a @code{noreturn} function. + +The default version of this hook invokes a function called +@samp{__stack_chk_fail}, taking no arguments. This function is +normally defined in @file{libgcc2.c}. +@end deftypefn + +@node Varargs +@section Implementing the Varargs Macros +@cindex varargs implementation + +GCC comes with an implementation of @code{<varargs.h>} and +@code{<stdarg.h>} that work without change on machines that pass arguments +on the stack. Other machines require their own implementations of +varargs, and the two machine independent header files must have +conditionals to include it. + +ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in +the calling convention for @code{va_start}. The traditional +implementation takes just one argument, which is the variable in which +to store the argument pointer. The ISO implementation of +@code{va_start} takes an additional second argument. The user is +supposed to write the last named argument of the function here. + +However, @code{va_start} should not use this argument. The way to find +the end of the named arguments is with the built-in functions described +below. + +@defmac __builtin_saveregs () +Use this built-in function to save the argument registers in memory so +that the varargs mechanism can access them. Both ISO and traditional +versions of @code{va_start} must use @code{__builtin_saveregs}, unless +you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead. + +On some machines, @code{__builtin_saveregs} is open-coded under the +control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On +other machines, it calls a routine written in assembler language, +found in @file{libgcc2.c}. + +Code generated for the call to @code{__builtin_saveregs} appears at the +beginning of the function, as opposed to where the call to +@code{__builtin_saveregs} is written, regardless of what the code is. +This is because the registers must be saved before the function starts +to use them for its own purposes. +@c i rewrote the first sentence above to fix an overfull hbox. --mew +@c 10feb93 +@end defmac + +@defmac __builtin_args_info (@var{category}) +Use this built-in function to find the first anonymous arguments in +registers. + +In general, a machine may have several categories of registers used for +arguments, each for a particular category of data types. (For example, +on some machines, floating-point registers are used for floating-point +arguments while other arguments are passed in the general registers.) +To make non-varargs functions use the proper calling convention, you +have defined the @code{CUMULATIVE_ARGS} data type to record how many +registers in each category have been used so far + +@code{__builtin_args_info} accesses the same data structure of type +@code{CUMULATIVE_ARGS} after the ordinary argument layout is finished +with it, with @var{category} specifying which word to access. Thus, the +value indicates the first unused register in a given category. + +Normally, you would use @code{__builtin_args_info} in the implementation +of @code{va_start}, accessing each category just once and storing the +value in the @code{va_list} object. This is because @code{va_list} will +have to update the values, and there is no way to alter the +values accessed by @code{__builtin_args_info}. +@end defmac + +@defmac __builtin_next_arg (@var{lastarg}) +This is the equivalent of @code{__builtin_args_info}, for stack +arguments. It returns the address of the first anonymous stack +argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it +returns the address of the location above the first anonymous stack +argument. Use it in @code{va_start} to initialize the pointer for +fetching arguments from the stack. Also use it in @code{va_start} to +verify that the second parameter @var{lastarg} is the last named argument +of the current function. +@end defmac + +@defmac __builtin_classify_type (@var{object}) +Since each machine has its own conventions for which data types are +passed in which kind of register, your implementation of @code{va_arg} +has to embody these conventions. The easiest way to categorize the +specified data type is to use @code{__builtin_classify_type} together +with @code{sizeof} and @code{__alignof__}. + +@code{__builtin_classify_type} ignores the value of @var{object}, +considering only its data type. It returns an integer describing what +kind of type that is---integer, floating, pointer, structure, and so on. + +The file @file{typeclass.h} defines an enumeration that you can use to +interpret the values of @code{__builtin_classify_type}. +@end defmac + +These machine description macros help implement varargs: + +@deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN_SAVEREGS (void) +If defined, this hook produces the machine-specific code for a call to +@code{__builtin_saveregs}. This code will be moved to the very +beginning of the function, before any parameter access are made. The +return value of this function should be an RTX that contains the value +to use as the return of @code{__builtin_saveregs}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SETUP_INCOMING_VARARGS (CUMULATIVE_ARGS *@var{args_so_far}, enum machine_mode @var{mode}, tree @var{type}, int *@var{pretend_args_size}, int @var{second_time}) +This target hook offers an alternative to using +@code{__builtin_saveregs} and defining the hook +@code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous +register arguments into the stack so that all the arguments appear to +have been passed consecutively on the stack. Once this is done, you can +use the standard implementation of varargs that works for machines that +pass all their arguments on the stack. + +The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data +structure, containing the values that are obtained after processing the +named arguments. The arguments @var{mode} and @var{type} describe the +last named argument---its machine mode and its data type as a tree node. + +The target hook should do two things: first, push onto the stack all the +argument registers @emph{not} used for the named arguments, and second, +store the size of the data thus pushed into the @code{int}-valued +variable pointed to by @var{pretend_args_size}. The value that you +store here will serve as additional offset for setting up the stack +frame. + +Because you must generate code to push the anonymous arguments at +compile time without knowing their data types, +@code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that +have just a single category of argument register and use it uniformly +for all data types. + +If the argument @var{second_time} is nonzero, it means that the +arguments of the function are being analyzed for the second time. This +happens for an inline function, which is not actually compiled until the +end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should +not generate any instructions in this case. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_STRICT_ARGUMENT_NAMING (CUMULATIVE_ARGS *@var{ca}) +Define this hook to return @code{true} if the location where a function +argument is passed depends on whether or not it is a named argument. + +This hook controls how the @var{named} argument to @code{FUNCTION_ARG} +is set for varargs and stdarg functions. If this hook returns +@code{true}, the @var{named} argument is always true for named +arguments, and false for unnamed arguments. If it returns @code{false}, +but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true}, +then all arguments are treated as named. Otherwise, all named arguments +except the last are treated as named. + +You need not define this hook if it always returns zero. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_PRETEND_OUTGOING_VARARGS_NAMED +If you need to conditionally change ABIs so that one works with +@code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither +@code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was +defined, then define this hook to return @code{true} if +@code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise. +Otherwise, you should not define this hook. +@end deftypefn + +@node Trampolines +@section Trampolines for Nested Functions +@cindex trampolines for nested functions +@cindex nested functions, trampolines for + +A @dfn{trampoline} is a small piece of code that is created at run time +when the address of a nested function is taken. It normally resides on +the stack, in the stack frame of the containing function. These macros +tell GCC how to generate code to allocate and initialize a +trampoline. + +The instructions in the trampoline must do two things: load a constant +address into the static chain register, and jump to the real address of +the nested function. On CISC machines such as the m68k, this requires +two instructions, a move immediate and a jump. Then the two addresses +exist in the trampoline as word-long immediate operands. On RISC +machines, it is often necessary to load each address into a register in +two parts. Then pieces of each address form separate immediate +operands. + +The code generated to initialize the trampoline must store the variable +parts---the static chain value and the function address---into the +immediate operands of the instructions. On a CISC machine, this is +simply a matter of copying each address to a memory reference at the +proper offset from the start of the trampoline. On a RISC machine, it +may be necessary to take out pieces of the address and store them +separately. + +@defmac TRAMPOLINE_TEMPLATE (@var{file}) +A C statement to output, on the stream @var{file}, assembler code for a +block of data that contains the constant parts of a trampoline. This +code should not include a label---the label is taken care of +automatically. + +If you do not define this macro, it means no template is needed +for the target. Do not define this macro on systems where the block move +code to copy the trampoline into place would be larger than the code +to generate it on the spot. +@end defmac + +@defmac TRAMPOLINE_SECTION +Return the section into which the trampoline template is to be placed +(@pxref{Sections}). The default value is @code{readonly_data_section}. +@end defmac + +@defmac TRAMPOLINE_SIZE +A C expression for the size in bytes of the trampoline, as an integer. +@end defmac + +@defmac TRAMPOLINE_ALIGNMENT +Alignment required for trampolines, in bits. + +If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT} +is used for aligning trampolines. +@end defmac + +@defmac INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain}) +A C statement to initialize the variable parts of a trampoline. +@var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is +an RTX for the address of the nested function; @var{static_chain} is an +RTX for the static chain value that should be passed to the function +when it is called. +@end defmac + +@defmac TRAMPOLINE_ADJUST_ADDRESS (@var{addr}) +A C statement that should perform any machine-specific adjustment in +the address of the trampoline. Its argument contains the address that +was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be +used for a function call should be different from the address in which +the template was stored, the different address should be assigned to +@var{addr}. If this macro is not defined, @var{addr} will be used for +function calls. + +@cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines +@cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines +If this macro is not defined, by default the trampoline is allocated as +a stack slot. This default is right for most machines. The exceptions +are machines where it is impossible to execute instructions in the stack +area. On such machines, you may have to implement a separate stack, +using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE} +and @code{TARGET_ASM_FUNCTION_EPILOGUE}. + +@var{fp} points to a data structure, a @code{struct function}, which +describes the compilation status of the immediate containing function of +the function which the trampoline is for. The stack slot for the +trampoline is in the stack frame of this containing function. Other +allocation strategies probably must do something analogous with this +information. +@end defmac + +Implementing trampolines is difficult on many machines because they have +separate instruction and data caches. Writing into a stack location +fails to clear the memory in the instruction cache, so when the program +jumps to that location, it executes the old contents. + +Here are two possible solutions. One is to clear the relevant parts of +the instruction cache whenever a trampoline is set up. The other is to +make all trampolines identical, by having them jump to a standard +subroutine. The former technique makes trampoline execution faster; the +latter makes initialization faster. + +To clear the instruction cache when a trampoline is initialized, define +the following macro. + +@defmac CLEAR_INSN_CACHE (@var{beg}, @var{end}) +If defined, expands to a C expression clearing the @emph{instruction +cache} in the specified interval. The definition of this macro would +typically be a series of @code{asm} statements. Both @var{beg} and +@var{end} are both pointer expressions. +@end defmac + +The operating system may also require the stack to be made executable +before calling the trampoline. To implement this requirement, define +the following macro. + +@defmac ENABLE_EXECUTE_STACK +Define this macro if certain operations must be performed before executing +code located on the stack. The macro should expand to a series of C +file-scope constructs (e.g.@: functions) and provide a unique entry point +named @code{__enable_execute_stack}. The target is responsible for +emitting calls to the entry point in the code, for example from the +@code{INITIALIZE_TRAMPOLINE} macro. +@end defmac + +To use a standard subroutine, define the following macro. In addition, +you must make sure that the instructions in a trampoline fill an entire +cache line with identical instructions, or else ensure that the +beginning of the trampoline code is always aligned at the same point in +its cache line. Look in @file{m68k.h} as a guide. + +@defmac TRANSFER_FROM_TRAMPOLINE +Define this macro if trampolines need a special subroutine to do their +work. The macro should expand to a series of @code{asm} statements +which will be compiled with GCC@. They go in a library function named +@code{__transfer_from_trampoline}. + +If you need to avoid executing the ordinary prologue code of a compiled +C function when you jump to the subroutine, you can do so by placing a +special label of your own in the assembler code. Use one @code{asm} +statement to generate an assembler label, and another to make the label +global. Then trampolines can use that label to jump directly to your +special assembler code. +@end defmac + +@node Library Calls +@section Implicit Calls to Library Routines +@cindex library subroutine names +@cindex @file{libgcc.a} + +@c prevent bad page break with this line +Here is an explanation of implicit calls to library routines. + +@defmac DECLARE_LIBRARY_RENAMES +This macro, if defined, should expand to a piece of C code that will get +expanded when compiling functions for libgcc.a. It can be used to +provide alternate names for GCC's internal library functions if there +are ABI-mandated names that the compiler should provide. +@end defmac + +@findex init_one_libfunc +@findex set_optab_libfunc +@deftypefn {Target Hook} void TARGET_INIT_LIBFUNCS (void) +This hook should declare additional library routines or rename +existing ones, using the functions @code{set_optab_libfunc} and +@code{init_one_libfunc} defined in @file{optabs.c}. +@code{init_optabs} calls this macro after initializing all the normal +library routines. + +The default is to do nothing. Most ports don't need to define this hook. +@end deftypefn + +@defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison}) +This macro should return @code{true} if the library routine that +implements the floating point comparison operator @var{comparison} in +mode @var{mode} will return a boolean, and @var{false} if it will +return a tristate. + +GCC's own floating point libraries return tristates from the +comparison operators, so the default returns false always. Most ports +don't need to define this macro. +@end defmac + +@defmac TARGET_LIB_INT_CMP_BIASED +This macro should evaluate to @code{true} if the integer comparison +functions (like @code{__cmpdi2}) return 0 to indicate that the first +operand is smaller than the second, 1 to indicate that they are equal, +and 2 to indicate that the first operand is greater than the second. +If this macro evaluates to @code{false} the comparison functions return +@minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines +in @file{libgcc.a}, you do not need to define this macro. +@end defmac + +@cindex US Software GOFAST, floating point emulation library +@cindex floating point emulation library, US Software GOFAST +@cindex GOFAST, floating point emulation library +@findex gofast_maybe_init_libfuncs +@defmac US_SOFTWARE_GOFAST +Define this macro if your system C library uses the US Software GOFAST +library to provide floating point emulation. + +In addition to defining this macro, your architecture must set +@code{TARGET_INIT_LIBFUNCS} to @code{gofast_maybe_init_libfuncs}, or +else call that function from its version of that hook. It is defined +in @file{config/gofast.h}, which must be included by your +architecture's @file{@var{cpu}.c} file. See @file{sparc/sparc.c} for +an example. + +If this macro is defined, the +@code{TARGET_FLOAT_LIB_COMPARE_RETURNS_BOOL} target hook must return +false for @code{SFmode} and @code{DFmode} comparisons. +@end defmac + +@cindex @code{EDOM}, implicit usage +@findex matherr +@defmac TARGET_EDOM +The value of @code{EDOM} on the target machine, as a C integer constant +expression. If you don't define this macro, GCC does not attempt to +deposit the value of @code{EDOM} into @code{errno} directly. Look in +@file{/usr/include/errno.h} to find the value of @code{EDOM} on your +system. + +If you do not define @code{TARGET_EDOM}, then compiled code reports +domain errors by calling the library function and letting it report the +error. If mathematical functions on your system use @code{matherr} when +there is an error, then you should leave @code{TARGET_EDOM} undefined so +that @code{matherr} is used normally. +@end defmac + +@cindex @code{errno}, implicit usage +@defmac GEN_ERRNO_RTX +Define this macro as a C expression to create an rtl expression that +refers to the global ``variable'' @code{errno}. (On certain systems, +@code{errno} may not actually be a variable.) If you don't define this +macro, a reasonable default is used. +@end defmac + +@cindex C99 math functions, implicit usage +@defmac TARGET_C99_FUNCTIONS +When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into +@code{sinf} and similarly for other functions defined by C99 standard. The +default is nonzero that should be proper value for most modern systems, however +number of existing systems lacks support for these functions in the runtime so +they needs this macro to be redefined to 0. +@end defmac + +@defmac NEXT_OBJC_RUNTIME +Define this macro to generate code for Objective-C message sending using +the calling convention of the NeXT system. This calling convention +involves passing the object, the selector and the method arguments all +at once to the method-lookup library function. + +The default calling convention passes just the object and the selector +to the lookup function, which returns a pointer to the method. +@end defmac + +@node Addressing Modes +@section Addressing Modes +@cindex addressing modes + +@c prevent bad page break with this line +This is about addressing modes. + +@defmac HAVE_PRE_INCREMENT +@defmacx HAVE_PRE_DECREMENT +@defmacx HAVE_POST_INCREMENT +@defmacx HAVE_POST_DECREMENT +A C expression that is nonzero if the machine supports pre-increment, +pre-decrement, post-increment, or post-decrement addressing respectively. +@end defmac + +@defmac HAVE_PRE_MODIFY_DISP +@defmacx HAVE_POST_MODIFY_DISP +A C expression that is nonzero if the machine supports pre- or +post-address side-effect generation involving constants other than +the size of the memory operand. +@end defmac + +@defmac HAVE_PRE_MODIFY_REG +@defmacx HAVE_POST_MODIFY_REG +A C expression that is nonzero if the machine supports pre- or +post-address side-effect generation involving a register displacement. +@end defmac + +@defmac CONSTANT_ADDRESS_P (@var{x}) +A C expression that is 1 if the RTX @var{x} is a constant which +is a valid address. On most machines, this can be defined as +@code{CONSTANT_P (@var{x})}, but a few machines are more restrictive +in which constant addresses are supported. +@end defmac + +@defmac CONSTANT_P (@var{x}) +@code{CONSTANT_P}, which is defined by target-independent code, +accepts integer-values expressions whose values are not explicitly +known, such as @code{symbol_ref}, @code{label_ref}, and @code{high} +expressions and @code{const} arithmetic expressions, in addition to +@code{const_int} and @code{const_double} expressions. +@end defmac + +@defmac MAX_REGS_PER_ADDRESS +A number, the maximum number of registers that can appear in a valid +memory address. Note that it is up to you to specify a value equal to +the maximum number that @code{GO_IF_LEGITIMATE_ADDRESS} would ever +accept. +@end defmac + +@defmac GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label}) +A C compound statement with a conditional @code{goto @var{label};} +executed if @var{x} (an RTX) is a legitimate memory address on the +target machine for a memory operand of mode @var{mode}. + +It usually pays to define several simpler macros to serve as +subroutines for this one. Otherwise it may be too complicated to +understand. + +This macro must exist in two variants: a strict variant and a +non-strict one. The strict variant is used in the reload pass. It +must be defined so that any pseudo-register that has not been +allocated a hard register is considered a memory reference. In +contexts where some kind of register is required, a pseudo-register +with no hard register must be rejected. + +The non-strict variant is used in other passes. It must be defined to +accept all pseudo-registers in every context where some kind of +register is required. + +@findex REG_OK_STRICT +Compiler source files that want to use the strict variant of this +macro define the macro @code{REG_OK_STRICT}. You should use an +@code{#ifdef REG_OK_STRICT} conditional to define the strict variant +in that case and the non-strict variant otherwise. + +Subroutines to check for acceptable registers for various purposes (one +for base registers, one for index registers, and so on) are typically +among the subroutines used to define @code{GO_IF_LEGITIMATE_ADDRESS}. +Then only these subroutine macros need have two variants; the higher +levels of macros may be the same whether strict or not. + +Normally, constant addresses which are the sum of a @code{symbol_ref} +and an integer are stored inside a @code{const} RTX to mark them as +constant. Therefore, there is no need to recognize such sums +specifically as legitimate addresses. Normally you would simply +recognize any @code{const} as legitimate. + +Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant +sums that are not marked with @code{const}. It assumes that a naked +@code{plus} indicates indexing. If so, then you @emph{must} reject such +naked constant sums as illegitimate addresses, so that none of them will +be given to @code{PRINT_OPERAND_ADDRESS}. + +@cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation +On some machines, whether a symbolic address is legitimate depends on +the section that the address refers to. On these machines, define the +target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information +into the @code{symbol_ref}, and then check for it here. When you see a +@code{const}, you will have to look inside it to find the +@code{symbol_ref} in order to determine the section. @xref{Assembler +Format}. +@end defmac + +@defmac FIND_BASE_TERM (@var{x}) +A C expression to determine the base term of address @var{x}. +This macro is used in only one place: `find_base_term' in alias.c. + +It is always safe for this macro to not be defined. It exists so +that alias analysis can understand machine-dependent addresses. + +The typical use of this macro is to handle addresses containing +a label_ref or symbol_ref within an UNSPEC@. +@end defmac + +@defmac LEGITIMIZE_ADDRESS (@var{x}, @var{oldx}, @var{mode}, @var{win}) +A C compound statement that attempts to replace @var{x} with a valid +memory address for an operand of mode @var{mode}. @var{win} will be a +C statement label elsewhere in the code; the macro definition may use + +@smallexample +GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{win}); +@end smallexample + +@noindent +to avoid further processing if the address has become legitimate. + +@findex break_out_memory_refs +@var{x} will always be the result of a call to @code{break_out_memory_refs}, +and @var{oldx} will be the operand that was given to that function to produce +@var{x}. + +The code generated by this macro should not alter the substructure of +@var{x}. If it transforms @var{x} into a more legitimate form, it +should assign @var{x} (which will always be a C variable) a new value. + +It is not necessary for this macro to come up with a legitimate +address. The compiler has standard ways of doing so in all cases. In +fact, it is safe to omit this macro. But often a +machine-dependent strategy can generate better code. +@end defmac + +@defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) +A C compound statement that attempts to replace @var{x}, which is an address +that needs reloading, with a valid memory address for an operand of mode +@var{mode}. @var{win} will be a C statement label elsewhere in the code. +It is not necessary to define this macro, but it might be useful for +performance reasons. + +For example, on the i386, it is sometimes possible to use a single +reload register instead of two by reloading a sum of two pseudo +registers into a register. On the other hand, for number of RISC +processors offsets are limited so that often an intermediate address +needs to be generated in order to address a stack slot. By defining +@code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses +generated for adjacent some stack slots can be made identical, and thus +be shared. + +@emph{Note}: This macro should be used with caution. It is necessary +to know something of how reload works in order to effectively use this, +and it is quite easy to produce macros that build in too much knowledge +of reload internals. + +@emph{Note}: This macro must be able to reload an address created by a +previous invocation of this macro. If it fails to handle such addresses +then the compiler may generate incorrect code or abort. + +@findex push_reload +The macro definition should use @code{push_reload} to indicate parts that +need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually +suitable to be passed unaltered to @code{push_reload}. + +The code generated by this macro must not alter the substructure of +@var{x}. If it transforms @var{x} into a more legitimate form, it +should assign @var{x} (which will always be a C variable) a new value. +This also applies to parts that you change indirectly by calling +@code{push_reload}. + +@findex strict_memory_address_p +The macro definition may use @code{strict_memory_address_p} to test if +the address has become legitimate. + +@findex copy_rtx +If you want to change only a part of @var{x}, one standard way of doing +this is to use @code{copy_rtx}. Note, however, that is unshares only a +single level of rtl. Thus, if the part to be changed is not at the +top level, you'll need to replace first the top level. +It is not necessary for this macro to come up with a legitimate +address; but often a machine-dependent strategy can generate better code. +@end defmac + +@defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label}) +A C statement or compound statement with a conditional @code{goto +@var{label};} executed if memory address @var{x} (an RTX) can have +different meanings depending on the machine mode of the memory +reference it is used for or if the address is valid for some modes +but not others. + +Autoincrement and autodecrement addresses typically have mode-dependent +effects because the amount of the increment or decrement is the size +of the operand being addressed. Some machines have other mode-dependent +addresses. Many RISC machines have no mode-dependent addresses. + +You may assume that @var{addr} is a valid address for the machine. +@end defmac + +@defmac LEGITIMATE_CONSTANT_P (@var{x}) +A C expression that is nonzero if @var{x} is a legitimate constant for +an immediate operand on the target machine. You can assume that +@var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact, +@samp{1} is a suitable definition for this macro on machines where +anything @code{CONSTANT_P} is valid. +@end defmac + +@deftypefn {Target Hook} rtx TARGET_DELEGITIMIZE_ADDRESS (rtx @var{x}) +This hook is used to undo the possibly obfuscating effects of the +@code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target +macros. Some backend implementations of these macros wrap symbol +references inside an @code{UNSPEC} rtx to represent PIC or similar +addressing modes. This target hook allows GCC's optimizers to understand +the semantics of these opaque @code{UNSPEC}s by converting them back +into their original form. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CANNOT_FORCE_CONST_MEM (rtx @var{x}) +This hook should return true if @var{x} is of a form that cannot (or +should not) be spilled to the constant pool. The default version of +this hook returns false. + +The primary reason to define this hook is to prevent reload from +deciding that a non-legitimate constant would be better reloaded +from the constant pool instead of spilling and reloading a register +holding the constant. This restriction is often true of addresses +of TLS symbols for various targets. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_USE_BLOCKS_FOR_CONSTANT_P (enum machine_mode @var{mode}, rtx @var{x}) +This hook should return true if pool entries for constant @var{x} can +be placed in an @code{object_block} structure. @var{mode} is the mode +of @var{x}. + +The default version returns false for all constants. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD (void) +This hook should return the DECL of a function @var{f} that given an +address @var{addr} as an argument returns a mask @var{m} that can be +used to extract from two vectors the relevant data that resides in +@var{addr} in case @var{addr} is not properly aligned. + +The autovectrizer, when vectorizing a load operation from an address +@var{addr} that may be unaligned, will generate two vector loads from +the two aligned addresses around @var{addr}. It then generates a +@code{REALIGN_LOAD} operation to extract the relevant data from the +two loaded vectors. The first two arguments to @code{REALIGN_LOAD}, +@var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and +the third argument, @var{OFF}, defines how the data will be extracted +from these two vectors: if @var{OFF} is 0, then the returned vector is +@var{v2}; otherwise, the returned vector is composed from the last +@var{VS}-@var{OFF} elements of @var{v1} concatenated to the first +@var{OFF} elements of @var{v2}. + +If this hook is defined, the autovectorizer will generate a call +to @var{f} (using the DECL tree that this hook returns) and will +use the return value of @var{f} as the argument @var{OFF} to +@code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f} +should comply with the semantics expected by @code{REALIGN_LOAD} +described above. +If this hook is not defined, then @var{addr} will be used as +the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low +log2(@var{VS})-1 bits of @var{addr} will be considered. +@end deftypefn + +@node Anchored Addresses +@section Anchored Addresses +@cindex anchored addresses +@cindex @option{-fsection-anchors} + +GCC usually addresses every static object as a separate entity. +For example, if we have: + +@smallexample +static int a, b, c; +int foo (void) @{ return a + b + c; @} +@end smallexample + +the code for @code{foo} will usually calculate three separate symbolic +addresses: those of @code{a}, @code{b} and @code{c}. On some targets, +it would be better to calculate just one symbolic address and access +the three variables relative to it. The equivalent pseudocode would +be something like: + +@smallexample +int foo (void) +@{ + register int *xr = &x; + return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; +@} +@end smallexample + +(which isn't valid C). We refer to shared addresses like @code{x} as +``section anchors''. Their use is controlled by @option{-fsection-anchors}. + +The hooks below describe the target properties that GCC needs to know +in order to make effective use of section anchors. It won't use +section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET} +or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value. + +@deftypevar {Target Hook} HOST_WIDE_INT TARGET_MIN_ANCHOR_OFFSET +The minimum offset that should be applied to a section anchor. +On most targets, it should be the smallest offset that can be +applied to a base register while still giving a legitimate address +for every mode. The default value is 0. +@end deftypevar + +@deftypevar {Target Hook} HOST_WIDE_INT TARGET_MAX_ANCHOR_OFFSET +Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive) +offset that should be applied to section anchors. The default +value is 0. +@end deftypevar + +@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_ANCHOR (rtx @var{x}) +Write the assembly code to define section anchor @var{x}, which is a +@code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true. +The hook is called with the assembly output position set to the beginning +of @code{SYMBOL_REF_BLOCK (@var{x})}. + +If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses +it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}. +If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition +is @code{NULL}, which disables the use of section anchors altogether. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_USE_ANCHORS_FOR_SYMBOL_P (rtx @var{x}) +Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF} +@var{x}. You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and +@samp{!SYMBOL_REF_ANCHOR_P (@var{x})}. + +The default version is correct for most targets, but you might need to +intercept this hook to handle things like target-specific attributes +or target-specific sections. +@end deftypefn + +@node Condition Code +@section Condition Code Status +@cindex condition code status + +@c prevent bad page break with this line +This describes the condition code status. + +@findex cc_status +The file @file{conditions.h} defines a variable @code{cc_status} to +describe how the condition code was computed (in case the interpretation of +the condition code depends on the instruction that it was set by). This +variable contains the RTL expressions on which the condition code is +currently based, and several standard flags. + +Sometimes additional machine-specific flags must be defined in the machine +description header file. It can also add additional machine-specific +information by defining @code{CC_STATUS_MDEP}. + +@defmac CC_STATUS_MDEP +C code for a data type which is used for declaring the @code{mdep} +component of @code{cc_status}. It defaults to @code{int}. + +This macro is not used on machines that do not use @code{cc0}. +@end defmac + +@defmac CC_STATUS_MDEP_INIT +A C expression to initialize the @code{mdep} field to ``empty''. +The default definition does nothing, since most machines don't use +the field anyway. If you want to use the field, you should probably +define this macro to initialize it. + +This macro is not used on machines that do not use @code{cc0}. +@end defmac + +@defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn}) +A C compound statement to set the components of @code{cc_status} +appropriately for an insn @var{insn} whose body is @var{exp}. It is +this macro's responsibility to recognize insns that set the condition +code as a byproduct of other activity as well as those that explicitly +set @code{(cc0)}. + +This macro is not used on machines that do not use @code{cc0}. + +If there are insns that do not set the condition code but do alter +other machine registers, this macro must check to see whether they +invalidate the expressions that the condition code is recorded as +reflecting. For example, on the 68000, insns that store in address +registers do not set the condition code, which means that usually +@code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such +insns. But suppose that the previous insn set the condition code +based on location @samp{a4@@(102)} and the current insn stores a new +value in @samp{a4}. Although the condition code is not changed by +this, it will no longer be true that it reflects the contents of +@samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter +@code{cc_status} in this case to say that nothing is known about the +condition code value. + +The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal +with the results of peephole optimization: insns whose patterns are +@code{parallel} RTXs containing various @code{reg}, @code{mem} or +constants which are just the operands. The RTL structure of these +insns is not sufficient to indicate what the insns actually do. What +@code{NOTICE_UPDATE_CC} should do when it sees one is just to run +@code{CC_STATUS_INIT}. + +A possible definition of @code{NOTICE_UPDATE_CC} is to call a function +that looks at an attribute (@pxref{Insn Attributes}) named, for example, +@samp{cc}. This avoids having detailed information about patterns in +two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}. +@end defmac + +@defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y}) +Returns a mode from class @code{MODE_CC} to be used when comparison +operation code @var{op} is applied to rtx @var{x} and @var{y}. For +example, on the SPARC, @code{SELECT_CC_MODE} is defined as (see +@pxref{Jump Patterns} for a description of the reason for this +definition) + +@smallexample +#define SELECT_CC_MODE(OP,X,Y) \ + (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ + ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \ + : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ + || GET_CODE (X) == NEG) \ + ? CC_NOOVmode : CCmode)) +@end smallexample + +You should define this macro if and only if you define extra CC modes +in @file{@var{machine}-modes.def}. +@end defmac + +@defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1}) +On some machines not all possible comparisons are defined, but you can +convert an invalid comparison into a valid one. For example, the Alpha +does not have a @code{GT} comparison, but you can use an @code{LT} +comparison instead and swap the order of the operands. + +On such machines, define this macro to be a C statement to do any +required conversions. @var{code} is the initial comparison code +and @var{op0} and @var{op1} are the left and right operands of the +comparison, respectively. You should modify @var{code}, @var{op0}, and +@var{op1} as required. + +GCC will not assume that the comparison resulting from this macro is +valid but will see if the resulting insn matches a pattern in the +@file{md} file. + +You need not define this macro if it would never change the comparison +code or operands. +@end defmac + +@defmac REVERSIBLE_CC_MODE (@var{mode}) +A C expression whose value is one if it is always safe to reverse a +comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE} +can ever return @var{mode} for a floating-point inequality comparison, +then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero. + +You need not define this macro if it would always returns zero or if the +floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}. +For example, here is the definition used on the SPARC, where floating-point +inequality comparisons are always given @code{CCFPEmode}: + +@smallexample +#define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode) +@end smallexample +@end defmac + +@defmac REVERSE_CONDITION (@var{code}, @var{mode}) +A C expression whose value is reversed condition code of the @var{code} for +comparison done in CC_MODE @var{mode}. The macro is used only in case +@code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case +machine has some non-standard way how to reverse certain conditionals. For +instance in case all floating point conditions are non-trapping, compiler may +freely convert unordered compares to ordered one. Then definition may look +like: + +@smallexample +#define REVERSE_CONDITION(CODE, MODE) \ + ((MODE) != CCFPmode ? reverse_condition (CODE) \ + : reverse_condition_maybe_unordered (CODE)) +@end smallexample +@end defmac + +@defmac REVERSE_CONDEXEC_PREDICATES_P (@var{op1}, @var{op2}) +A C expression that returns true if the conditional execution predicate +@var{op1}, a comparison operation, is the inverse of @var{op2} and vice +versa. Define this to return 0 if the target has conditional execution +predicates that cannot be reversed safely. There is no need to validate +that the arguments of op1 and op2 are the same, this is done separately. +If no expansion is specified, this macro is defined as follows: + +@smallexample +#define REVERSE_CONDEXEC_PREDICATES_P (x, y) \ + (GET_CODE ((x)) == reversed_comparison_code ((y), NULL)) +@end smallexample +@end defmac + +@deftypefn {Target Hook} bool TARGET_FIXED_CONDITION_CODE_REGS (unsigned int *, unsigned int *) +On targets which do not use @code{(cc0)}, and which use a hard +register rather than a pseudo-register to hold condition codes, the +regular CSE passes are often not able to identify cases in which the +hard register is set to a common value. Use this hook to enable a +small pass which optimizes such cases. This hook should return true +to enable this pass, and it should set the integers to which its +arguments point to the hard register numbers used for condition codes. +When there is only one such register, as is true on most systems, the +integer pointed to by the second argument should be set to +@code{INVALID_REGNUM}. + +The default version of this hook returns false. +@end deftypefn + +@deftypefn {Target Hook} enum machine_mode TARGET_CC_MODES_COMPATIBLE (enum machine_mode, enum machine_mode) +On targets which use multiple condition code modes in class +@code{MODE_CC}, it is sometimes the case that a comparison can be +validly done in more than one mode. On such a system, define this +target hook to take two mode arguments and to return a mode in which +both comparisons may be validly done. If there is no such mode, +return @code{VOIDmode}. + +The default version of this hook checks whether the modes are the +same. If they are, it returns that mode. If they are different, it +returns @code{VOIDmode}. +@end deftypefn + +@node Costs +@section Describing Relative Costs of Operations +@cindex costs of instructions +@cindex relative costs +@cindex speed of instructions + +These macros let you describe the relative speed of various operations +on the target machine. + +@defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to}) +A C expression for the cost of moving data of mode @var{mode} from a +register in class @var{from} to one in class @var{to}. The classes are +expressed using the enumeration values such as @code{GENERAL_REGS}. A +value of 2 is the default; other values are interpreted relative to +that. + +It is not required that the cost always equal 2 when @var{from} is the +same as @var{to}; on some machines it is expensive to move between +registers if they are not general registers. + +If reload sees an insn consisting of a single @code{set} between two +hard registers, and if @code{REGISTER_MOVE_COST} applied to their +classes returns a value of 2, reload does not check to ensure that the +constraints of the insn are met. Setting a cost of other than 2 will +allow reload to verify that the constraints are met. You should do this +if the @samp{mov@var{m}} pattern's constraints do not allow such copying. +@end defmac + +@defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) +A C expression for the cost of moving data of mode @var{mode} between a +register of class @var{class} and memory; @var{in} is zero if the value +is to be written to memory, nonzero if it is to be read in. This cost +is relative to those in @code{REGISTER_MOVE_COST}. If moving between +registers and memory is more expensive than between two registers, you +should define this macro to express the relative cost. + +If you do not define this macro, GCC uses a default cost of 4 plus +the cost of copying via a secondary reload register, if one is +needed. If your machine requires a secondary reload register to copy +between memory and a register of @var{class} but the reload mechanism is +more complex than copying via an intermediate, define this macro to +reflect the actual cost of the move. + +GCC defines the function @code{memory_move_secondary_cost} if +secondary reloads are needed. It computes the costs due to copying via +a secondary register. If your machine copies from memory using a +secondary register in the conventional way but the default base value of +4 is not correct for your machine, define this macro to add some other +value to the result of that function. The arguments to that function +are the same as to this macro. +@end defmac + +@defmac BRANCH_COST +A C expression for the cost of a branch instruction. A value of 1 is +the default; other values are interpreted relative to that. +@end defmac + +Here are additional macros which do not specify precise relative costs, +but only that certain actions are more expensive than GCC would +ordinarily expect. + +@defmac SLOW_BYTE_ACCESS +Define this macro as a C expression which is nonzero if accessing less +than a word of memory (i.e.@: a @code{char} or a @code{short}) is no +faster than accessing a word of memory, i.e., if such access +require more than one instruction or if there is no difference in cost +between byte and (aligned) word loads. + +When this macro is not defined, the compiler will access a field by +finding the smallest containing object; when it is defined, a fullword +load will be used if alignment permits. Unless bytes accesses are +faster than word accesses, using word accesses is preferable since it +may eliminate subsequent memory access if subsequent accesses occur to +other fields in the same word of the structure, but to different bytes. +@end defmac + +@defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment}) +Define this macro to be the value 1 if memory accesses described by the +@var{mode} and @var{alignment} parameters have a cost many times greater +than aligned accesses, for example if they are emulated in a trap +handler. + +When this macro is nonzero, the compiler will act as if +@code{STRICT_ALIGNMENT} were nonzero when generating code for block +moves. This can cause significantly more instructions to be produced. +Therefore, do not set this macro nonzero if unaligned accesses only add a +cycle or two to the time for a memory access. + +If the value of this macro is always zero, it need not be defined. If +this macro is defined, it should produce a nonzero value when +@code{STRICT_ALIGNMENT} is nonzero. +@end defmac + +@defmac MOVE_RATIO +The threshold of number of scalar memory-to-memory move insns, @emph{below} +which a sequence of insns should be generated instead of a +string move insn or a library call. Increasing the value will always +make code faster, but eventually incurs high cost in increased code size. + +Note that on machines where the corresponding move insn is a +@code{define_expand} that emits a sequence of insns, this macro counts +the number of such sequences. + +If you don't define this, a reasonable default is used. +@end defmac + +@defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment}) +A C expression used to determine whether @code{move_by_pieces} will be used to +copy a chunk of memory, or whether some other block move mechanism +will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less +than @code{MOVE_RATIO}. +@end defmac + +@defmac MOVE_MAX_PIECES +A C expression used by @code{move_by_pieces} to determine the largest unit +a load or store used to copy memory is. Defaults to @code{MOVE_MAX}. +@end defmac + +@defmac CLEAR_RATIO +The threshold of number of scalar move insns, @emph{below} which a sequence +of insns should be generated to clear memory instead of a string clear insn +or a library call. Increasing the value will always make code faster, but +eventually incurs high cost in increased code size. + +If you don't define this, a reasonable default is used. +@end defmac + +@defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment}) +A C expression used to determine whether @code{clear_by_pieces} will be used +to clear a chunk of memory, or whether some other block clear mechanism +will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less +than @code{CLEAR_RATIO}. +@end defmac + +@defmac STORE_BY_PIECES_P (@var{size}, @var{alignment}) +A C expression used to determine whether @code{store_by_pieces} will be +used to set a chunk of memory to a constant value, or whether some other +mechanism will be used. Used by @code{__builtin_memset} when storing +values other than constant zero and by @code{__builtin_strcpy} when +when called with a constant source string. +Defaults to 1 if @code{move_by_pieces_ninsns} returns less +than @code{MOVE_RATIO}. +@end defmac + +@defmac USE_LOAD_POST_INCREMENT (@var{mode}) +A C expression used to determine whether a load postincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_INCREMENT}. +@end defmac + +@defmac USE_LOAD_POST_DECREMENT (@var{mode}) +A C expression used to determine whether a load postdecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_DECREMENT}. +@end defmac + +@defmac USE_LOAD_PRE_INCREMENT (@var{mode}) +A C expression used to determine whether a load preincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_INCREMENT}. +@end defmac + +@defmac USE_LOAD_PRE_DECREMENT (@var{mode}) +A C expression used to determine whether a load predecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_DECREMENT}. +@end defmac + +@defmac USE_STORE_POST_INCREMENT (@var{mode}) +A C expression used to determine whether a store postincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_INCREMENT}. +@end defmac + +@defmac USE_STORE_POST_DECREMENT (@var{mode}) +A C expression used to determine whether a store postdecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_DECREMENT}. +@end defmac + +@defmac USE_STORE_PRE_INCREMENT (@var{mode}) +This macro is used to determine whether a store preincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_INCREMENT}. +@end defmac + +@defmac USE_STORE_PRE_DECREMENT (@var{mode}) +This macro is used to determine whether a store predecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_DECREMENT}. +@end defmac + +@defmac NO_FUNCTION_CSE +Define this macro if it is as good or better to call a constant +function address than to call an address kept in a register. +@end defmac + +@defmac RANGE_TEST_NON_SHORT_CIRCUIT +Define this macro if a non-short-circuit operation produced by +@samp{fold_range_test ()} is optimal. This macro defaults to true if +@code{BRANCH_COST} is greater than or equal to the value 2. +@end defmac + +@deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, int @var{code}, int @var{outer_code}, int *@var{total}) +This target hook describes the relative costs of RTL expressions. + +The cost may depend on the precise form of the expression, which is +available for examination in @var{x}, and the rtx code of the expression +in which it is contained, found in @var{outer_code}. @var{code} is the +expression code---redundant, since it can be obtained with +@code{GET_CODE (@var{x})}. + +In implementing this hook, you can use the construct +@code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast +instructions. + +On entry to the hook, @code{*@var{total}} contains a default estimate +for the cost of the expression. The hook should modify this value as +necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)} +for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus +operations, and @code{COSTS_N_INSNS (1)} for all other operations. + +When optimizing for code size, i.e.@: when @code{optimize_size} is +nonzero, this target hook should be used to estimate the relative +size cost of an expression, again relative to @code{COSTS_N_INSNS}. + +The hook returns true when all subexpressions of @var{x} have been +processed, and false when @code{rtx_cost} should recurse. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address}) +This hook computes the cost of an addressing mode that contains +@var{address}. If not defined, the cost is computed from +the @var{address} expression and the @code{TARGET_RTX_COST} hook. + +For most CISC machines, the default cost is a good approximation of the +true cost of the addressing mode. However, on RISC machines, all +instructions normally have the same length and execution time. Hence +all addresses will have equal costs. + +In cases where more than one form of an address is known, the form with +the lowest cost will be used. If multiple forms have the same, lowest, +cost, the one that is the most complex will be used. + +For example, suppose an address that is equal to the sum of a register +and a constant is used twice in the same basic block. When this macro +is not defined, the address will be computed in a register and memory +references will be indirect through that register. On machines where +the cost of the addressing mode containing the sum is no higher than +that of a simple indirect reference, this will produce an additional +instruction and possibly require an additional register. Proper +specification of this macro eliminates this overhead for such machines. + +This hook is never called with an invalid address. + +On machines where an address involving more than one register is as +cheap as an address computation involving only one register, defining +@code{TARGET_ADDRESS_COST} to reflect this can cause two registers to +be live over a region of code where only one would have been if +@code{TARGET_ADDRESS_COST} were not defined in that manner. This effect +should be considered in the definition of this macro. Equivalent costs +should probably only be given to addresses with different numbers of +registers on machines with lots of registers. +@end deftypefn + +@node Scheduling +@section Adjusting the Instruction Scheduler + +The instruction scheduler may need a fair amount of machine-specific +adjustment in order to produce good code. GCC provides several target +hooks for this purpose. It is usually enough to define just a few of +them: try the first ones in this list first. + +@deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void) +This hook returns the maximum number of instructions that can ever +issue at the same time on the target machine. The default is one. +Although the insn scheduler can define itself the possibility of issue +an insn on the same cycle, the value can serve as an additional +constraint to issue insns on the same simulated processor cycle (see +hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}). +This value must be constant over the entire compilation. If you need +it to vary depending on what the instructions are, you must use +@samp{TARGET_SCHED_VARIABLE_ISSUE}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more}) +This hook is executed by the scheduler after it has scheduled an insn +from the ready list. It should return the number of insns which can +still be issued in the current cycle. The default is +@samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and +@code{USE}, which normally are not counted against the issue rate. +You should define this hook if some insns take more machine resources +than others, so that fewer insns can follow them in the same cycle. +@var{file} is either a null pointer, or a stdio stream to write any +debug output to. @var{verbose} is the verbose level provided by +@option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that +was scheduled. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost}) +This function corrects the value of @var{cost} based on the +relationship between @var{insn} and @var{dep_insn} through the +dependence @var{link}. It should return the new value. The default +is to make no adjustment to @var{cost}. This can be used for example +to specify to the scheduler using the traditional pipeline description +that an output- or anti-dependence does not incur the same cost as a +data-dependence. If the scheduler using the automaton based pipeline +description, the cost of anti-dependence is zero and the cost of +output-dependence is maximum of one and the difference of latency +times of the first and the second insns. If these values are not +acceptable, you could use the hook to modify them too. See also +@pxref{Processor pipeline description}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority}) +This hook adjusts the integer scheduling priority @var{priority} of +@var{insn}. It should return the new priority. Increase the priority to +execute @var{insn} earlier, reduce the priority to execute @var{insn} +later. Do not define this hook if you do not need to adjust the +scheduling priorities of insns. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock}) +This hook is executed by the scheduler after it has scheduled the ready +list, to allow the machine description to reorder it (for example to +combine two small instructions together on @samp{VLIW} machines). +@var{file} is either a null pointer, or a stdio stream to write any +debug output to. @var{verbose} is the verbose level provided by +@option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready +list of instructions that are ready to be scheduled. @var{n_readyp} is +a pointer to the number of elements in the ready list. The scheduler +reads the ready list in reverse order, starting with +@var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock} +is the timer tick of the scheduler. You may modify the ready list and +the number of ready insns. The return value is the number of insns that +can issue this cycle; normally this is just @code{issue_rate}. See also +@samp{TARGET_SCHED_REORDER2}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock}) +Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That +function is called whenever the scheduler starts a new cycle. This one +is called once per iteration over a cycle, immediately after +@samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and +return the number of insns to be scheduled in the same cycle. Defining +this hook can be useful if there are frequent situations where +scheduling one insn causes other insns to become ready in the same +cycle. These other insns can then be taken into account properly. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx @var{head}, rtx @var{tail}) +This hook is called after evaluation forward dependencies of insns in +chain given by two parameter values (@var{head} and @var{tail} +correspondingly) but before insns scheduling of the insn chain. For +example, it can be used for better insn classification if it requires +analysis of dependencies. This hook can use backward and forward +dependencies of the insn scheduler because they are already +calculated. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready}) +This hook is executed by the scheduler at the beginning of each block of +instructions that are to be scheduled. @var{file} is either a null +pointer, or a stdio stream to write any debug output to. @var{verbose} +is the verbose level provided by @option{-fsched-verbose-@var{n}}. +@var{max_ready} is the maximum number of insns in the current scheduling +region that can be live at the same time. This can be used to allocate +scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose}) +This hook is executed by the scheduler at the end of each block of +instructions that are to be scheduled. It can be used to perform +cleanup of any actions done by the other scheduling hooks. @var{file} +is either a null pointer, or a stdio stream to write any debug output +to. @var{verbose} is the verbose level provided by +@option{-fsched-verbose-@var{n}}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT_GLOBAL (FILE *@var{file}, int @var{verbose}, int @var{old_max_uid}) +This hook is executed by the scheduler after function level initializations. +@var{file} is either a null pointer, or a stdio stream to write any debug output to. +@var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. +@var{old_max_uid} is the maximum insn uid when scheduling begins. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FINISH_GLOBAL (FILE *@var{file}, int @var{verbose}) +This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}. +@var{file} is either a null pointer, or a stdio stream to write any debug output to. +@var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_DFA_PRE_CYCLE_INSN (void) +The hook returns an RTL insn. The automaton state used in the +pipeline hazard recognizer is changed as if the insn were scheduled +when the new simulated processor cycle starts. Usage of the hook may +simplify the automaton pipeline description for some @acronym{VLIW} +processors. If the hook is defined, it is used only for the automaton +based pipeline description. The default is not to change the state +when the new simulated processor cycle starts. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void) +The hook can be used to initialize data used by the previous hook. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_DFA_POST_CYCLE_INSN (void) +The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used +to changed the state as if the insn were scheduled when the new +simulated processor cycle finishes. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void) +The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but +used to initialize data used by the previous hook. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void) +This hook controls better choosing an insn from the ready insn queue +for the @acronym{DFA}-based insn scheduler. Usually the scheduler +chooses the first insn from the queue. If the hook returns a positive +value, an additional scheduler code tries all permutations of +@samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()} +subsequent ready insns to choose an insn whose issue will result in +maximal number of issued insns on the same cycle. For the +@acronym{VLIW} processor, the code could actually solve the problem of +packing simple insns into the @acronym{VLIW} insn. Of course, if the +rules of @acronym{VLIW} packing are described in the automaton. + +This code also could be used for superscalar @acronym{RISC} +processors. Let us consider a superscalar @acronym{RISC} processor +with 3 pipelines. Some insns can be executed in pipelines @var{A} or +@var{B}, some insns can be executed only in pipelines @var{B} or +@var{C}, and one insn can be executed in pipeline @var{B}. The +processor may issue the 1st insn into @var{A} and the 2nd one into +@var{B}. In this case, the 3rd insn will wait for freeing @var{B} +until the next cycle. If the scheduler issues the 3rd insn the first, +the processor could issue all 3 insns per cycle. + +Actually this code demonstrates advantages of the automaton based +pipeline hazard recognizer. We try quickly and easy many insn +schedules to choose the best one. + +The default is no multipass scheduling. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx) + +This hook controls what insns from the ready insn queue will be +considered for the multipass insn scheduling. If the hook returns +zero for insn passed as the parameter, the insn will be not chosen to +be issued. + +The default is that any ready insns can be chosen to be issued. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *, int, rtx, int, int, int *) + +This hook is called by the insn scheduler before issuing insn passed +as the third parameter on given cycle. If the hook returns nonzero, +the insn is not issued on given processors cycle. Instead of that, +the processor cycle is advanced. If the value passed through the last +parameter is zero, the insn ready queue is not sorted on the new cycle +start as usually. The first parameter passes file for debugging +output. The second one passes the scheduler verbose level of the +debugging output. The forth and the fifth parameter values are +correspondingly processor cycle on which the previous insn has been +issued and the current processor cycle. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCHED_IS_COSTLY_DEPENDENCE (rtx @var{insn1}, rtx @var{insn2}, rtx @var{dep_link}, int @var{dep_cost}, int @var{distance}) +This hook is used to define which dependences are considered costly by +the target, so costly that it is not advisable to schedule the insns that +are involved in the dependence too close to one another. The parameters +to this hook are as follows: The second parameter @var{insn2} is dependent +upon the first parameter @var{insn1}. The dependence between @var{insn1} +and @var{insn2} is represented by the third parameter @var{dep_link}. The +fourth parameter @var{cost} is the cost of the dependence, and the fifth +parameter @var{distance} is the distance in cycles between the two insns. +The hook returns @code{true} if considering the distance between the two +insns the dependence between them is considered costly by the target, +and @code{false} otherwise. + +Defining this hook can be useful in multiple-issue out-of-order machines, +where (a) it's practically hopeless to predict the actual data/resource +delays, however: (b) there's a better chance to predict the actual grouping +that will be formed, and (c) correctly emulating the grouping can be very +important. In such targets one may want to allow issuing dependent insns +closer to one another---i.e., closer than the dependence distance; however, +not in cases of "costly dependences", which this hooks allows to define. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST_2 (rtx @var{insn}, int @var{dep_type}, rtx @var{dep_insn}, int @var{cost}) +This hook is a modified version of @samp{TARGET_SCHED_ADJUST_COST}. Instead +of passing dependence as a second parameter, it passes a type of that +dependence. This is useful to calculate cost of dependence between insns +not having the corresponding link. If @samp{TARGET_SCHED_ADJUST_COST_2} is +defined it is used instead of @samp{TARGET_SCHED_ADJUST_COST}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_H_I_D_EXTENDED (void) +This hook is called by the insn scheduler after emitting a new instruction to +the instruction stream. The hook notifies a target backend to extend its +per instruction data structures. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_SPECULATE_INSN (rtx @var{insn}, int @var{request}, rtx *@var{new_pat}) +This hook is called by the insn scheduler when @var{insn} has only +speculative dependencies and therefore can be scheduled speculatively. +The hook is used to check if the pattern of @var{insn} has a speculative +version and, in case of successful check, to generate that speculative +pattern. The hook should return 1, if the instruction has a speculative form, +or -1, if it doesn't. @var{request} describes the type of requested +speculation. If the return value equals 1 then @var{new_pat} is assigned +the generated speculative pattern. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_NEEDS_BLOCK_P (rtx @var{insn}) +This hook is called by the insn scheduler during generation of recovery code +for @var{insn}. It should return nonzero, if the corresponding check +instruction should branch to recovery code, or zero otherwise. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_SCHED_GEN_CHECK (rtx @var{insn}, rtx @var{label}, int @var{mutate_p}) +This hook is called by the insn scheduler to generate a pattern for recovery +check instruction. If @var{mutate_p} is zero, then @var{insn} is a +speculative instruction for which the check should be generated. +@var{label} is either a label of a basic block, where recovery code should +be emitted, or a null pointer, when requested check doesn't branch to +recovery code (a simple check). If @var{mutate_p} is nonzero, then +a pattern for a branchy check corresponding to a simple check denoted by +@var{insn} should be generated. In this case @var{label} can't be null. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD_SPEC (rtx @var{insn}) +This hook is used as a workaround for +@samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD} not being +called on the first instruction of the ready list. The hook is used to +discard speculative instruction that stand first in the ready list from +being scheduled on the current cycle. For non-speculative instructions, +the hook should always return nonzero. For example, in the ia64 backend +the hook is used to cancel data speculative insns when the ALAT table +is nearly full. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_FLAGS (unsigned int *@var{flags}, spec_info_t @var{spec_info}) +This hook is used by the insn scheduler to find out what features should be +enabled/used. @var{flags} initially may have either the SCHED_RGN or SCHED_EBB +bit set. This denotes the scheduler pass for which the data should be +provided. The target backend should modify @var{flags} by modifying +the bits corresponding to the following features: USE_DEPS_LIST, USE_GLAT, +DETACH_LIFE_INFO, and DO_SPECULATION. For the DO_SPECULATION feature +an additional structure @var{spec_info} should be filled by the target. +The structure describes speculation types that can be used in the scheduler. +@end deftypefn + +@node Sections +@section Dividing the Output into Sections (Texts, Data, @dots{}) +@c the above section title is WAY too long. maybe cut the part between +@c the (...)? --mew 10feb93 + +An object file is divided into sections containing different types of +data. In the most common case, there are three sections: the @dfn{text +section}, which holds instructions and read-only data; the @dfn{data +section}, which holds initialized writable data; and the @dfn{bss +section}, which holds uninitialized data. Some systems have other kinds +of sections. + +@file{varasm.c} provides several well-known sections, such as +@code{text_section}, @code{data_section} and @code{bss_section}. +The normal way of controlling a @code{@var{foo}_section} variable +is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro, +as described below. The macros are only read once, when @file{varasm.c} +initializes itself, so their values must be run-time constants. +They may however depend on command-line flags. + +@emph{Note:} Some run-time files, such @file{crtstuff.c}, also make +use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them +to be string literals. + +Some assemblers require a different string to be written every time a +section is selected. If your assembler falls into this category, you +should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use +@code{get_unnamed_section} to set up the sections. + +You must always create a @code{text_section}, either by defining +@code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section} +in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of +@code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not +create a distinct @code{readonly_data_section}, the default is to +reuse @code{text_section}. + +All the other @file{varasm.c} sections are optional, and are null +if the target does not provide them. + +@defmac TEXT_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation that should precede instructions and read-only data. +Normally @code{"\t.text"} is right. +@end defmac + +@defmac HOT_TEXT_SECTION_NAME +If defined, a C string constant for the name of the section containing most +frequently executed functions of the program. If not defined, GCC will provide +a default definition if the target supports named sections. +@end defmac + +@defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME +If defined, a C string constant for the name of the section containing unlikely +executed functions in the program. +@end defmac + +@defmac DATA_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation to identify the following data as writable initialized +data. Normally @code{"\t.data"} is right. +@end defmac + +@defmac SDATA_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +initialized, writable small data. +@end defmac + +@defmac READONLY_DATA_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation to identify the following data as read-only initialized +data. +@end defmac + +@defmac BSS_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +uninitialized global data. If not defined, and neither +@code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined, +uninitialized global data will be output in the data section if +@option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be +used. +@end defmac + +@defmac SBSS_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +uninitialized, writable small data. +@end defmac + +@defmac INIT_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +initialization code. If not defined, GCC will assume such a section does +not exist. This section has no corresponding @code{init_section} +variable; it is used entirely in runtime code. +@end defmac + +@defmac FINI_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +finalization code. If not defined, GCC will assume such a section does +not exist. This section has no corresponding @code{fini_section} +variable; it is used entirely in runtime code. +@end defmac + +@defmac INIT_ARRAY_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +part of the @code{.init_array} (or equivalent) section. If not +defined, GCC will assume such a section does not exist. Do not define +both this macro and @code{INIT_SECTION_ASM_OP}. +@end defmac + +@defmac FINI_ARRAY_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +part of the @code{.fini_array} (or equivalent) section. If not +defined, GCC will assume such a section does not exist. Do not define +both this macro and @code{FINI_SECTION_ASM_OP}. +@end defmac + +@defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function}) +If defined, an ASM statement that switches to a different section +via @var{section_op}, calls @var{function}, and switches back to +the text section. This is used in @file{crtstuff.c} if +@code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls +to initialization and finalization functions from the init and fini +sections. By default, this macro uses a simple function call. Some +ports need hand-crafted assembly code to avoid dependencies on +registers initialized in the function prologue or to ensure that +constant pools don't end up too far way in the text section. +@end defmac + +@defmac TARGET_LIBGCC_SDATA_SECTION +If defined, a string which names the section into which small +variables defined in crtstuff and libgcc should go. This is useful +when the target has options for optimizing access to small data, and +you want the crtstuff and libgcc routines to be conservative in what +they expect of your application yet liberal in what your application +expects. For example, for targets with a @code{.sdata} section (like +MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't +require small data support from your application, but use this macro +to put small data into @code{.sdata} so that your application can +access these variables whether it uses small data or not. +@end defmac + +@defmac FORCE_CODE_SECTION_ALIGN +If defined, an ASM statement that aligns a code section to some +arbitrary boundary. This is used to force all fragments of the +@code{.init} and @code{.fini} sections to have to same alignment +and thus prevent the linker from having to add any padding. +@end defmac + +@defmac JUMP_TABLES_IN_TEXT_SECTION +Define this macro to be an expression with a nonzero value if jump +tables (for @code{tablejump} insns) should be output in the text +section, along with the assembler instructions. Otherwise, the +readonly data section is used. + +This macro is irrelevant if there is no separate readonly data section. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_INIT_SECTIONS (void) +Define this hook if you need to do something special to set up the +@file{varasm.c} sections, or if your target has some special sections +of its own that you need to create. + +GCC calls this hook after processing the command line, but before writing +any assembly code, and before calling any of the section-returning hooks +described below. +@end deftypefn + +@deftypefn {Target Hook} TARGET_ASM_RELOC_RW_MASK (void) +Return a mask describing how relocations should be treated when +selecting sections. Bit 1 should be set if global relocations +should be placed in a read-write section; bit 0 should be set if +local relocations should be placed in a read-write section. + +The default version of this function returns 3 when @option{-fpic} +is in effect, and 0 otherwise. The hook is typically redefined +when the target cannot support (some kinds of) dynamic relocations +in read-only sections even in executables. +@end deftypefn + +@deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align}) +Return the section into which @var{exp} should be placed. You can +assume that @var{exp} is either a @code{VAR_DECL} node or a constant of +some sort. @var{reloc} indicates whether the initial value of @var{exp} +requires link-time relocations. Bit 0 is set when variable contains +local relocations only, while bit 1 is set for global relocations. +@var{align} is the constant alignment in bits. + +The default version of this function takes care of putting read-only +variables in @code{readonly_data_section}. + +See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}. +@end deftypefn + +@defmac USE_SELECT_SECTION_FOR_FUNCTIONS +Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called +for @code{FUNCTION_DECL}s as well as for variables and constants. + +In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the +function has been determined to be likely to be called, and nonzero if +it is unlikely to be called. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc}) +Build up a unique section name, expressed as a @code{STRING_CST} node, +and assign it to @samp{DECL_SECTION_NAME (@var{decl})}. +As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether +the initial value of @var{exp} requires link-time relocations. + +The default version of this function appends the symbol name to the +ELF section name that would normally be used for the symbol. For +example, the function @code{foo} would be placed in @code{.text.foo}. +Whatever the actual target object format, this is often good enough. +@end deftypefn + +@deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl}) +Return the readonly data section associated with +@samp{DECL_SECTION_NAME (@var{decl})}. +The default version of this function selects @code{.gnu.linkonce.r.name} if +the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name} +if function is in @code{.text.name}, and the normal readonly-data section +otherwise. +@end deftypefn + +@deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_RTX_SECTION (enum machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align}) +Return the section into which a constant @var{x}, of mode @var{mode}, +should be placed. You can assume that @var{x} is some kind of +constant in RTL@. The argument @var{mode} is redundant except in the +case of a @code{const_int} rtx. @var{align} is the constant alignment +in bits. + +The default version of this function takes care of putting symbolic +constants in @code{flag_pic} mode in @code{data_section} and everything +else in @code{readonly_data_section}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p}) +Define this hook if references to a symbol or a constant must be +treated differently depending on something about the variable or +function named by the symbol (such as what section it is in). + +The hook is executed immediately after rtl has been created for +@var{decl}, which may be a variable or function declaration or +an entry in the constant pool. In either case, @var{rtl} is the +rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})} +in this hook; that field may not have been initialized yet. + +In the case of a constant, it is safe to assume that the rtl is +a @code{mem} whose address is a @code{symbol_ref}. Most decls +will also have this form, but that is not guaranteed. Global +register variables, for instance, will have a @code{reg} for their +rtl. (Normally the right thing to do with such unusual rtl is +leave it alone.) + +The @var{new_decl_p} argument will be true if this is the first time +that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will +be false for subsequent invocations, which will happen for duplicate +declarations. Whether or not anything must be done for the duplicate +declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}. +@var{new_decl_p} is always true when the hook is called for a constant. + +@cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO} +The usual thing for this hook to do is to record flags in the +@code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}. +Historically, the name string was modified if it was necessary to +encode more than one bit of information, but this practice is now +discouraged; use @code{SYMBOL_REF_FLAGS}. + +The default definition of this hook, @code{default_encode_section_info} +in @file{varasm.c}, sets a number of commonly-useful bits in +@code{SYMBOL_REF_FLAGS}. Check whether the default does what you need +before overriding it. +@end deftypefn + +@deftypefn {Target Hook} const char *TARGET_STRIP_NAME_ENCODING (const char *name) +Decode @var{name} and return the real name part, sans +the characters that @code{TARGET_ENCODE_SECTION_INFO} +may have added. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (tree @var{exp}) +Returns true if @var{exp} should be placed into a ``small data'' section. +The default version of this hook always returns false. +@end deftypefn + +@deftypevar {Target Hook} bool TARGET_HAVE_SRODATA_SECTION +Contains the value true if the target places read-only +``small data'' into a separate section. The default value is false. +@end deftypevar + +@deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (tree @var{exp}) +Returns true if @var{exp} names an object for which name resolution +rules must resolve to the current ``module'' (dynamic shared library +or executable image). + +The default version of this hook implements the name resolution rules +for ELF, which has a looser model of global name binding than other +currently supported object file formats. +@end deftypefn + +@deftypevar {Target Hook} bool TARGET_HAVE_TLS +Contains the value true if the target supports thread-local storage. +The default value is false. +@end deftypevar + + +@node PIC +@section Position Independent Code +@cindex position independent code +@cindex PIC + +This section describes macros that help implement generation of position +independent code. Simply defining these macros is not enough to +generate valid PIC; you must also add support to the macros +@code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}, as +well as @code{LEGITIMIZE_ADDRESS}. You must modify the definition of +@samp{movsi} to do something appropriate when the source operand +contains a symbolic address. You may also need to alter the handling of +switch statements so that they use relative addresses. +@c i rearranged the order of the macros above to try to force one of +@c them to the next line, to eliminate an overfull hbox. --mew 10feb93 + +@defmac PIC_OFFSET_TABLE_REGNUM +The register number of the register used to address a table of static +data addresses in memory. In some cases this register is defined by a +processor's ``application binary interface'' (ABI)@. When this macro +is defined, RTL is generated for this register once, as with the stack +pointer and frame pointer registers. If this macro is not defined, it +is up to the machine-dependent files to allocate such a register (if +necessary). Note that this register must be fixed when in use (e.g.@: +when @code{flag_pic} is true). +@end defmac + +@defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED +Define this macro if the register defined by +@code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define +this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined. +@end defmac + +@defmac LEGITIMATE_PIC_OPERAND_P (@var{x}) +A C expression that is nonzero if @var{x} is a legitimate immediate +operand on the target machine when generating position independent code. +You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not +check this. You can also assume @var{flag_pic} is true, so you need not +check it either. You need not define this macro if all constants +(including @code{SYMBOL_REF}) can be immediate operands when generating +position independent code. +@end defmac + +@node Assembler Format +@section Defining the Output Assembler Language + +This section describes macros whose principal purpose is to describe how +to write instructions in assembler language---rather than what the +instructions do. + +@menu +* File Framework:: Structural information for the assembler file. +* Data Output:: Output of constants (numbers, strings, addresses). +* Uninitialized Data:: Output of uninitialized variables. +* Label Output:: Output and generation of labels. +* Initialization:: General principles of initialization + and termination routines. +* Macros for Initialization:: + Specific macros that control the handling of + initialization and termination routines. +* Instruction Output:: Output of actual instructions. +* Dispatch Tables:: Output of jump tables. +* Exception Region Output:: Output of exception region code. +* Alignment Output:: Pseudo ops for alignment and skipping data. +@end menu + +@node File Framework +@subsection The Overall Framework of an Assembler File +@cindex assembler format +@cindex output of assembler code + +@c prevent bad page break with this line +This describes the overall framework of an assembly file. + +@deftypefn {Target Hook} void TARGET_ASM_FILE_START () +@findex default_file_start +Output to @code{asm_out_file} any text which the assembler expects to +find at the beginning of a file. The default behavior is controlled +by two flags, documented below. Unless your target's assembler is +quite unusual, if you override the default, you should call +@code{default_file_start} at some point in your target hook. This +lets other target files rely on these variables. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF +If this flag is true, the text of the macro @code{ASM_APP_OFF} will be +printed as the very first line in the assembly file, unless +@option{-fverbose-asm} is in effect. (If that macro has been defined +to the empty string, this variable has no effect.) With the normal +definition of @code{ASM_APP_OFF}, the effect is to notify the GNU +assembler that it need not bother stripping comments or extra +whitespace from its input. This allows it to work a bit faster. + +The default is false. You should not set it to true unless you have +verified that your port does not generate any extra whitespace or +comments that will cause GAS to issue errors in NO_APP mode. +@end deftypevr + +@deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE +If this flag is true, @code{output_file_directive} will be called +for the primary source file, immediately after printing +@code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect +this to be done. The default is false. +@end deftypevr + +@deftypefn {Target Hook} void TARGET_ASM_FILE_END () +Output to @code{asm_out_file} any text which the assembler expects +to find at the end of a file. The default is to output nothing. +@end deftypefn + +@deftypefun void file_end_indicate_exec_stack () +Some systems use a common convention, the @samp{.note.GNU-stack} +special section, to indicate whether or not an object file relies on +the stack being executable. If your system uses this convention, you +should define @code{TARGET_ASM_FILE_END} to this function. If you +need to do other things in that hook, have your hook function call +this function. +@end deftypefun + +@defmac ASM_COMMENT_START +A C string constant describing how to begin a comment in the target +assembler language. The compiler assumes that the comment will end at +the end of the line. +@end defmac + +@defmac ASM_APP_ON +A C string constant for text to be output before each @code{asm} +statement or group of consecutive ones. Normally this is +@code{"#APP"}, which is a comment that has no effect on most +assemblers but tells the GNU assembler that it must check the lines +that follow for all valid assembler constructs. +@end defmac + +@defmac ASM_APP_OFF +A C string constant for text to be output after each @code{asm} +statement or group of consecutive ones. Normally this is +@code{"#NO_APP"}, which tells the GNU assembler to resume making the +time-saving assumptions that are valid for ordinary compiler output. +@end defmac + +@defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) +A C statement to output COFF information or DWARF debugging information +which indicates that filename @var{name} is the current source file to +the stdio stream @var{stream}. + +This macro need not be defined if the standard form of output +for the file format in use is appropriate. +@end defmac + +@defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string}) +A C statement to output the string @var{string} to the stdio stream +@var{stream}. If you do not call the function @code{output_quoted_string} +in your config files, GCC will only call it to output filenames to +the assembler source. So you can use it to canonicalize the format +of the filename using this macro. +@end defmac + +@defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string}) +A C statement to output something to the assembler file to handle a +@samp{#ident} directive containing the text @var{string}. If this +macro is not defined, nothing is output for a @samp{#ident} directive. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align}) +Output assembly directives to switch to section @var{name}. The section +should have attributes as specified by @var{flags}, which is a bit mask +of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align} +is nonzero, it contains an alignment in bytes to be used for the section, +otherwise some target default should be used. Only targets that must +specify an alignment within the section directive need pay attention to +@var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS +This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. +@end deftypefn + +@anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS} +@deftypefn {Target Hook} bool TARGET_HAVE_SWITCHABLE_BSS_SECTIONS +This flag is true if we can create zeroed data by switching to a BSS +section and then using @code{ASM_OUTPUT_SKIP} to allocate the space. +This is true on most ELF targets. +@end deftypefn + +@deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc}) +Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION} +based on a variable or function decl, a section name, and whether or not the +declaration's initializer may contain runtime relocations. @var{decl} may be + null, in which case read-write data should be assumed. + +The default version of this function handles choosing code vs data, +read-only vs read-write data, and @code{flag_pic}. You should only +need to override this if your target has special flags that might be +set via @code{__attribute__}. +@end deftypefn + +@need 2000 +@node Data Output +@subsection Output of Data + + +@deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP +These hooks specify assembly directives for creating certain kinds +of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a +byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an +aligned two-byte object, and so on. Any of the hooks may be +@code{NULL}, indicating that no suitable directive is available. + +The compiler will print these strings at the start of a new line, +followed immediately by the object's initial value. In most cases, +the string should contain a tab, a pseudo-op, and then another tab. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p}) +The @code{assemble_integer} function uses this hook to output an +integer object. @var{x} is the object's value, @var{size} is its size +in bytes and @var{aligned_p} indicates whether it is aligned. The +function should return @code{true} if it was able to output the +object. If it returns false, @code{assemble_integer} will try to +split the object into smaller parts. + +The default implementation of this hook will use the +@code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false} +when the relevant string is @code{NULL}. +@end deftypefn + +@defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail}) +A C statement to recognize @var{rtx} patterns that +@code{output_addr_const} can't deal with, and output assembly code to +@var{stream} corresponding to the pattern @var{x}. This may be used to +allow machine-dependent @code{UNSPEC}s to appear within constants. + +If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must +@code{goto fail}, so that a standard error message is printed. If it +prints an error message itself, by calling, for example, +@code{output_operand_lossage}, it may just complete normally. +@end defmac + +@defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len}) +A C statement to output to the stdio stream @var{stream} an assembler +instruction to assemble a string constant containing the @var{len} +bytes at @var{ptr}. @var{ptr} will be a C expression of type +@code{char *} and @var{len} a C expression of type @code{int}. + +If the assembler has a @code{.ascii} pseudo-op as found in the +Berkeley Unix assembler, do not define the macro +@code{ASM_OUTPUT_ASCII}. +@end defmac + +@defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n}) +A C statement to output word @var{n} of a function descriptor for +@var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS} +is defined, and is otherwise unused. +@end defmac + +@defmac CONSTANT_POOL_BEFORE_FUNCTION +You may define this macro as a C expression. You should define the +expression to have a nonzero value if GCC should output the constant +pool for a function before the code for the function, or a zero value if +GCC should output the constant pool after the function. If you do +not define this macro, the usual case, GCC will output the constant +pool before the function. +@end defmac + +@defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size}) +A C statement to output assembler commands to define the start of the +constant pool for a function. @var{funname} is a string giving +the name of the function. Should the return type of the function +be required, it can be obtained via @var{fundecl}. @var{size} +is the size, in bytes, of the constant pool that will be written +immediately after this call. + +If no constant-pool prefix is required, the usual case, this macro need +not be defined. +@end defmac + +@defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto}) +A C statement (with or without semicolon) to output a constant in the +constant pool, if it needs special treatment. (This macro need not do +anything for RTL expressions that can be output normally.) + +The argument @var{file} is the standard I/O stream to output the +assembler code on. @var{x} is the RTL expression for the constant to +output, and @var{mode} is the machine mode (in case @var{x} is a +@samp{const_int}). @var{align} is the required alignment for the value +@var{x}; you should output an assembler directive to force this much +alignment. + +The argument @var{labelno} is a number to use in an internal label for +the address of this pool entry. The definition of this macro is +responsible for outputting the label definition at the proper place. +Here is how to do this: + +@smallexample +@code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno}); +@end smallexample + +When you output a pool entry specially, you should end with a +@code{goto} to the label @var{jumpto}. This will prevent the same pool +entry from being output a second time in the usual manner. + +You need not define this macro if it would do nothing. +@end defmac + +@defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size}) +A C statement to output assembler commands to at the end of the constant +pool for a function. @var{funname} is a string giving the name of the +function. Should the return type of the function be required, you can +obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the +constant pool that GCC wrote immediately before this call. + +If no constant-pool epilogue is required, the usual case, you need not +define this macro. +@end defmac + +@defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}) +Define this macro as a C expression which is nonzero if @var{C} is +used as a logical line separator by the assembler. + +If you do not define this macro, the default is that only +the character @samp{;} is treated as a logical line separator. +@end defmac + +@deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN +@deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN +These target hooks are C string constants, describing the syntax in the +assembler for grouping arithmetic expressions. If not overridden, they +default to normal parentheses, which is correct for most assemblers. +@end deftypevr + + These macros are provided by @file{real.h} for writing the definitions +of @code{ASM_OUTPUT_DOUBLE} and the like: + +@defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l}) +These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the +target's floating point representation, and store its bit pattern in +the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and +@code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a +simple @code{long int}. For the others, it should be an array of +@code{long int}. The number of elements in this array is determined +by the size of the desired target floating point data type: 32 bits of +it go in each @code{long int} array element. Each array element holds +32 bits of the result, even if @code{long int} is wider than 32 bits +on the host machine. + +The array element values are designed so that you can print them out +using @code{fprintf} in the order they should appear in the target +machine's memory. +@end defmac + +@node Uninitialized Data +@subsection Output of Uninitialized Variables + +Each of the macros in this section is used to do the whole job of +outputting a single uninitialized variable. + +@defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a common-label named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. + +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +This macro controls how the assembler definitions of uninitialized +common global variables are output. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the +variable to be output, if there is one, or @code{NULL_TREE} if there +is no corresponding variable. If you define this macro, GCC will use it +in place of both @code{ASM_OUTPUT_COMMON} and +@code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see +the variable's decl in order to chose what to output. +@end defmac + +@defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of uninitialized global @var{decl} named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. + +Try to use function @code{asm_output_bss} defined in @file{varasm.c} when +defining this macro. If unable, use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name itself; +before and after that, output the additional assembler syntax for defining +the name, and a newline. + +There are two ways of handling global BSS. One is to define either +this macro or its aligned counterpart, @code{ASM_OUTPUT_ALIGNED_BSS}. +The other is to have @code{TARGET_ASM_SELECT_SECTION} return a +switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}). +You do not need to do both. + +Some languages do not have @code{common} data, and require a +non-common form of global BSS in order to handle uninitialized globals +efficiently. C++ is one example of this. However, if the target does +not support global BSS, the front end may choose to make globals +common in order to save space in the object file. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. + +Try to use function @code{asm_output_aligned_bss} defined in file +@file{varasm.c} when defining this macro. +@end defmac + +@defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a local-common-label named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. + +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +This macro controls how the assembler definitions of uninitialized +static variables are output. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the +variable to be output, if there is one, or @code{NULL_TREE} if there +is no corresponding variable. If you define this macro, GCC will use it +in place of both @code{ASM_OUTPUT_DECL} and +@code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see +the variable's decl in order to chose what to output. +@end defmac + +@node Label Output +@subsection Output and Generation of Labels + +@c prevent bad page break with this line +This is about outputting labels. + +@findex assemble_name +@defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a label named @var{name}. +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. A default +definition of this macro is provided which is correct for most systems. +@end defmac + +@findex assemble_name_raw +@defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name}) +Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known +to refer to a compiler-generated label. The default definition uses +@code{assemble_name_raw}, which is like @code{assemble_name} except +that it is more efficient. +@end defmac + +@defmac SIZE_ASM_OP +A C string containing the appropriate assembler directive to specify the +size of a symbol, without any arguments. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other +systems, the default is not to define this macro. + +Define this macro only if it is correct to use the default definitions +of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE} +for your system. If you need your own custom definitions of those +macros, or if you do not need explicit symbol sizes at all, do not +define this macro. +@end defmac + +@defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler that the size of the +symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}. +If you define @code{SIZE_ASM_OP}, a default definition of this macro is +provided. +@end defmac + +@defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler to calculate the size of +the symbol @var{name} by subtracting its address from the current +address. + +If you define @code{SIZE_ASM_OP}, a default definition of this macro is +provided. The default assumes that the assembler recognizes a special +@samp{.} symbol as referring to the current address, and can calculate +the difference between this and another symbol. If your assembler does +not recognize @samp{.} or cannot do calculations with it, you will need +to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique. +@end defmac + +@defmac TYPE_ASM_OP +A C string containing the appropriate assembler directive to specify the +type of a symbol, without any arguments. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other +systems, the default is not to define this macro. + +Define this macro only if it is correct to use the default definition of +@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own +custom definition of this macro, or if you do not need explicit symbol +types at all, do not define this macro. +@end defmac + +@defmac TYPE_OPERAND_FMT +A C string which specifies (using @code{printf} syntax) the format of +the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems, +the default is not to define this macro. + +Define this macro only if it is correct to use the default definition of +@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own +custom definition of this macro, or if you do not need explicit symbol +types at all, do not define this macro. +@end defmac + +@defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler that the type of the +symbol @var{name} is @var{type}. @var{type} is a C string; currently, +that string is always either @samp{"function"} or @samp{"object"}, but +you should not count on this. + +If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default +definition of this macro is provided. +@end defmac + +@defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of a +function which is being defined. This macro is responsible for +outputting the label definition (perhaps using +@code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the +@code{FUNCTION_DECL} tree node representing the function. + +If this macro is not defined, then the function name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the size of a function +which is being defined. The argument @var{name} is the name of the +function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node +representing the function. + +If this macro is not defined, then the function size is not defined. + +You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of an +initialized variable which is being defined. This macro must output the +label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument +@var{decl} is the @code{VAR_DECL} tree node representing the variable. + +If this macro is not defined, then the variable name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or +@code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro. +@end defmac + +@defmac ASM_DECLARE_CONSTANT_NAME (@var{stream}, @var{name}, @var{exp}, @var{size}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of a +constant which is being defined. This macro is responsible for +outputting the label definition (perhaps using +@code{ASM_OUTPUT_LABEL}). The argument @var{exp} is the +value of the constant, and @var{size} is the size of the constant +in bytes. @var{name} will be an internal label. + +If this macro is not defined, then the @var{name} is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for claiming a register @var{regno} +for a global variable @var{decl} with name @var{name}. + +If you don't define this macro, that is equivalent to defining it to do +nothing. +@end defmac + +@defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend}) +A C statement (sans semicolon) to finish up declaring a variable name +once the compiler has processed its initializer fully and thus has had a +chance to determine the size of an array when controlled by an +initializer. This is used on systems where it's necessary to declare +something about the size of the object. + +If you don't define this macro, that is equivalent to defining it to do +nothing. + +You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or +@code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name}) +This target hook is a function to output to the stdio stream +@var{stream} some commands that will make the label @var{name} global; +that is, available for reference from other files. + +The default implementation relies on a proper definition of +@code{GLOBAL_ASM_OP}. +@end deftypefn + +@defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} some commands that will make the label @var{name} weak; +that is, available for reference from other files but only used if +no other definition is available. Use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name +itself; before and after that, output the additional assembler syntax +for making that name weak, and a newline. + +If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not +support weak symbols and you should not define the @code{SUPPORTS_WEAK} +macro. +@end defmac + +@defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value}) +Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and +@code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function +or variable decl. If @var{value} is not @code{NULL}, this C statement +should output to the stdio stream @var{stream} assembler code which +defines (equates) the weak symbol @var{name} to have the value +@var{value}. If @var{value} is @code{NULL}, it should output commands +to make @var{name} weak. +@end defmac + +@defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value}) +Outputs a directive that enables @var{name} to be used to refer to +symbol @var{value} with weak-symbol semantics. @code{decl} is the +declaration of @code{name}. +@end defmac + +@defmac SUPPORTS_WEAK +A C expression which evaluates to true if the target supports weak symbols. + +If you don't define this macro, @file{defaults.h} provides a default +definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL} +is defined, the default definition is @samp{1}; otherwise, it is +@samp{0}. Define this macro if you want to control weak symbol support +with a compiler flag such as @option{-melf}. +@end defmac + +@defmac MAKE_DECL_ONE_ONLY (@var{decl}) +A C statement (sans semicolon) to mark @var{decl} to be emitted as a +public symbol such that extra copies in multiple translation units will +be discarded by the linker. Define this macro if your object file +format provides support for this concept, such as the @samp{COMDAT} +section flags in the Microsoft Windows PE/COFF format, and this support +requires changes to @var{decl}, such as putting it in a separate section. +@end defmac + +@defmac SUPPORTS_ONE_ONLY +A C expression which evaluates to true if the target supports one-only +semantics. + +If you don't define this macro, @file{varasm.c} provides a default +definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default +definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if +you want to control one-only symbol support with a compiler flag, or if +setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to +be emitted as one-only. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, const char *@var{visibility}) +This target hook is a function to output to @var{asm_out_file} some +commands that will make the symbol(s) associated with @var{decl} have +hidden, protected or internal visibility as specified by @var{visibility}. +@end deftypefn + +@defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC +A C expression that evaluates to true if the target's linker expects +that weak symbols do not appear in a static archive's table of contents. +The default is @code{0}. + +Leaving weak symbols out of an archive's table of contents means that, +if a symbol will only have a definition in one translation unit and +will have undefined references from other translation units, that +symbol should not be weak. Defining this macro to be nonzero will +thus have the effect that certain symbols that would normally be weak +(explicit template instantiations, and vtables for polymorphic classes +with noninline key methods) will instead be nonweak. + +The C++ ABI requires this macro to be zero. Define this macro for +targets where full C++ ABI compliance is impossible and where linker +restrictions require weak symbols to be left out of a static archive's +table of contents. +@end defmac + +@defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name of an external +symbol named @var{name} which is referenced in this compilation but +not defined. The value of @var{decl} is the tree node for the +declaration. + +This macro need not be defined if it does not need to output anything. +The GNU assembler and most Unix assemblers don't require anything. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_EXTERNAL_LIBCALL (rtx @var{symref}) +This target hook is a function to output to @var{asm_out_file} an assembler +pseudo-op to declare a library function name external. The name of the +library function is given by @var{symref}, which is a @code{symbol_ref}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_MARK_DECL_PRESERVED (tree @var{decl}) +This target hook is a function to output to @var{asm_out_file} an assembler +directive to annotate used symbol. Darwin target use .no_dead_code_strip +directive. +@end deftypefn + +@defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a reference in assembler syntax to a label named +@var{name}. This should add @samp{_} to the front of the name, if that +is customary on your operating system, as it is in most Berkeley Unix +systems. This macro is used in @code{assemble_name}. +@end defmac + +@defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym}) +A C statement (sans semicolon) to output a reference to +@code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name} +will be used to output the name of the symbol. This macro may be used +to modify the way a symbol is referenced depending on information +encoded by @code{TARGET_ENCODE_SECTION_INFO}. +@end defmac + +@defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf}) +A C statement (sans semicolon) to output a reference to @var{buf}, the +result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined, +@code{assemble_name} will be used to output the name of the symbol. +This macro is not used by @code{output_asm_label}, or the @code{%l} +specifier that calls it; the intention is that this macro should be set +when it is necessary to output a label differently when its address is +being taken. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno}) +A function to output to the stdio stream @var{stream} a label whose +name is made from the string @var{prefix} and the number @var{labelno}. + +It is absolutely essential that these labels be distinct from the labels +used for user-level functions and variables. Otherwise, certain programs +will have name conflicts with internal labels. + +It is desirable to exclude internal labels from the symbol table of the +object file. Most assemblers have a naming convention for labels that +should be excluded; on many systems, the letter @samp{L} at the +beginning of a label has this effect. You should find out what +convention your system uses, and follow it. + +The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}. +@end deftypefn + +@defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num}) +A C statement to output to the stdio stream @var{stream} a debug info +label whose name is made from the string @var{prefix} and the number +@var{num}. This is useful for VLIW targets, where debug info labels +may need to be treated differently than branch target labels. On some +systems, branch target labels must be at the beginning of instruction +bundles, but debug info labels can occur in the middle of instruction +bundles. + +If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be +used. +@end defmac + +@defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num}) +A C statement to store into the string @var{string} a label whose name +is made from the string @var{prefix} and the number @var{num}. + +This string, when output subsequently by @code{assemble_name}, should +produce the output that @code{(*targetm.asm_out.internal_label)} would produce +with the same @var{prefix} and @var{num}. + +If the string begins with @samp{*}, then @code{assemble_name} will +output the rest of the string unchanged. It is often convenient for +@code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the +string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets +to output the string, and may change it. (Of course, +@code{ASM_OUTPUT_LABELREF} is also part of your machine description, so +you should know what it does on your machine.) +@end defmac + +@defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number}) +A C expression to assign to @var{outvar} (which is a variable of type +@code{char *}) a newly allocated string made from the string +@var{name} and the number @var{number}, with some suitable punctuation +added. Use @code{alloca} to get space for the string. + +The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to +produce an assembler label for an internal static variable whose name is +@var{name}. Therefore, the string must be such as to result in valid +assembler code. The argument @var{number} is different each time this +macro is executed; it prevents conflicts between similarly-named +internal static variables in different scopes. + +Ideally this string should not be a valid C identifier, to prevent any +conflict with the user's own symbols. Most assemblers allow periods +or percent signs in assembler symbols; putting at least one of these +between the name and the number will suffice. + +If this macro is not defined, a default definition will be provided +which is correct for most systems. +@end defmac + +@defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol @var{name} to have the value @var{value}. + +@findex SET_ASM_OP +If @code{SET_ASM_OP} is defined, a default definition is provided which is +correct for most systems. +@end defmac + +@defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol whose tree node is @var{decl_of_name} +to have the value of the tree node @var{decl_of_value}. This macro will +be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if +the tree nodes are available. + +@findex SET_ASM_OP +If @code{SET_ASM_OP} is defined, a default definition is provided which is +correct for most systems. +@end defmac + +@defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value}) +A C statement that evaluates to true if the assembler code which defines +(equates) the symbol whose tree node is @var{decl_of_name} to have the value +of the tree node @var{decl_of_value} should be emitted near the end of the +current compilation unit. The default is to not defer output of defines. +This macro affects defines output by @samp{ASM_OUTPUT_DEF} and +@samp{ASM_OUTPUT_DEF_FROM_DECLS}. +@end defmac + +@defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the weak symbol @var{name} to have the value +@var{value}. If @var{value} is @code{NULL}, it defines @var{name} as +an undefined weak symbol. + +Define this macro if the target only supports weak aliases; define +@code{ASM_OUTPUT_DEF} instead if possible. +@end defmac + +@defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name}) +Define this macro to override the default assembler names used for +Objective-C methods. + +The default name is a unique method number followed by the name of the +class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of +the category is also included in the assembler name (e.g.@: +@samp{_1_Foo_Bar}). + +These names are safe on most systems, but make debugging difficult since +the method's selector is not present in the name. Therefore, particular +systems define other ways of computing names. + +@var{buf} is an expression of type @code{char *} which gives you a +buffer in which to store the name; its length is as long as +@var{class_name}, @var{cat_name} and @var{sel_name} put together, plus +50 characters extra. + +The argument @var{is_inst} specifies whether the method is an instance +method or a class method; @var{class_name} is the name of the class; +@var{cat_name} is the name of the category (or @code{NULL} if the method is not +in a category); and @var{sel_name} is the name of the selector. + +On systems where the assembler can handle quoted names, you can use this +macro to provide more human-readable names. +@end defmac + +@defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} commands to declare that the label @var{name} is an +Objective-C class reference. This is only needed for targets whose +linkers have special support for NeXT-style runtimes. +@end defmac + +@defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} commands to declare that the label @var{name} is an +unresolved Objective-C class reference. This is only needed for targets +whose linkers have special support for NeXT-style runtimes. +@end defmac + +@node Initialization +@subsection How Initialization Functions Are Handled +@cindex initialization routines +@cindex termination routines +@cindex constructors, output of +@cindex destructors, output of + +The compiled code for certain languages includes @dfn{constructors} +(also called @dfn{initialization routines})---functions to initialize +data in the program when the program is started. These functions need +to be called before the program is ``started''---that is to say, before +@code{main} is called. + +Compiling some languages generates @dfn{destructors} (also called +@dfn{termination routines}) that should be called when the program +terminates. + +To make the initialization and termination functions work, the compiler +must output something in the assembler code to cause those functions to +be called at the appropriate time. When you port the compiler to a new +system, you need to specify how to do this. + +There are two major ways that GCC currently supports the execution of +initialization and termination functions. Each way has two variants. +Much of the structure is common to all four variations. + +@findex __CTOR_LIST__ +@findex __DTOR_LIST__ +The linker must build two lists of these functions---a list of +initialization functions, called @code{__CTOR_LIST__}, and a list of +termination functions, called @code{__DTOR_LIST__}. + +Each list always begins with an ignored function pointer (which may hold +0, @minus{}1, or a count of the function pointers after it, depending on +the environment). This is followed by a series of zero or more function +pointers to constructors (or destructors), followed by a function +pointer containing zero. + +Depending on the operating system and its executable file format, either +@file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup +time and exit time. Constructors are called in reverse order of the +list; destructors in forward order. + +The best way to handle static constructors works only for object file +formats which provide arbitrarily-named sections. A section is set +aside for a list of constructors, and another for a list of destructors. +Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each +object file that defines an initialization function also puts a word in +the constructor section to point to that function. The linker +accumulates all these words into one contiguous @samp{.ctors} section. +Termination functions are handled similarly. + +This method will be chosen as the default by @file{target-def.h} if +@code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not +support arbitrary sections, but does support special designated +constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP} +and @code{DTORS_SECTION_ASM_OP} to achieve the same effect. + +When arbitrary sections are available, there are two variants, depending +upon how the code in @file{crtstuff.c} is called. On systems that +support a @dfn{.init} section which is executed at program startup, +parts of @file{crtstuff.c} are compiled into that section. The +program is linked by the @command{gcc} driver like this: + +@smallexample +ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o +@end smallexample + +The prologue of a function (@code{__init}) appears in the @code{.init} +section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise +for the function @code{__fini} in the @dfn{.fini} section. Normally these +files are provided by the operating system or by the GNU C library, but +are provided by GCC for a few targets. + +The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets) +compiled from @file{crtstuff.c}. They contain, among other things, code +fragments within the @code{.init} and @code{.fini} sections that branch +to routines in the @code{.text} section. The linker will pull all parts +of a section together, which results in a complete @code{__init} function +that invokes the routines we need at startup. + +To use this variant, you must define the @code{INIT_SECTION_ASM_OP} +macro properly. + +If no init section is available, when GCC compiles any function called +@code{main} (or more accurately, any function designated as a program +entry point by the language front end calling @code{expand_main_function}), +it inserts a procedure call to @code{__main} as the first executable code +after the function prologue. The @code{__main} function is defined +in @file{libgcc2.c} and runs the global constructors. + +In file formats that don't support arbitrary sections, there are again +two variants. In the simplest variant, the GNU linker (GNU @code{ld}) +and an `a.out' format must be used. In this case, +@code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs} +entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__}, +and with the address of the void function containing the initialization +code as its value. The GNU linker recognizes this as a request to add +the value to a @dfn{set}; the values are accumulated, and are eventually +placed in the executable as a vector in the format described above, with +a leading (ignored) count and a trailing zero element. +@code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init +section is available, the absence of @code{INIT_SECTION_ASM_OP} causes +the compilation of @code{main} to call @code{__main} as above, starting +the initialization process. + +The last variant uses neither arbitrary sections nor the GNU linker. +This is preferable when you want to do dynamic linking and when using +file formats which the GNU linker does not support, such as `ECOFF'@. In +this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and +termination functions are recognized simply by their names. This requires +an extra program in the linkage step, called @command{collect2}. This program +pretends to be the linker, for use with GCC; it does its job by running +the ordinary linker, but also arranges to include the vectors of +initialization and termination functions. These functions are called +via @code{__main} as described above. In order to use this method, +@code{use_collect2} must be defined in the target in @file{config.gcc}. + +@ifinfo +The following section describes the specific macros that control and +customize the handling of initialization and termination functions. +@end ifinfo + +@node Macros for Initialization +@subsection Macros Controlling Initialization Routines + +Here are the macros that control how the compiler handles initialization +and termination functions: + +@defmac INIT_SECTION_ASM_OP +If defined, a C string constant, including spacing, for the assembler +operation to identify the following data as initialization code. If not +defined, GCC will assume such a section does not exist. When you are +using special sections for initialization and termination functions, this +macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to +run the initialization functions. +@end defmac + +@defmac HAS_INIT_SECTION +If defined, @code{main} will not call @code{__main} as described above. +This macro should be defined for systems that control start-up code +on a symbol-by-symbol basis, such as OSF/1, and should not +be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}. +@end defmac + +@defmac LD_INIT_SWITCH +If defined, a C string constant for a switch that tells the linker that +the following symbol is an initialization routine. +@end defmac + +@defmac LD_FINI_SWITCH +If defined, a C string constant for a switch that tells the linker that +the following symbol is a finalization routine. +@end defmac + +@defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func}) +If defined, a C statement that will write a function that can be +automatically called when a shared library is loaded. The function +should call @var{func}, which takes no arguments. If not defined, and +the object format requires an explicit initialization function, then a +function called @code{_GLOBAL__DI} will be generated. + +This function and the following one are used by collect2 when linking a +shared library that needs constructors or destructors, or has DWARF2 +exception tables embedded in the code. +@end defmac + +@defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func}) +If defined, a C statement that will write a function that can be +automatically called when a shared library is unloaded. The function +should call @var{func}, which takes no arguments. If not defined, and +the object format requires an explicit finalization function, then a +function called @code{_GLOBAL__DD} will be generated. +@end defmac + +@defmac INVOKE__main +If defined, @code{main} will call @code{__main} despite the presence of +@code{INIT_SECTION_ASM_OP}. This macro should be defined for systems +where the init section is not actually run automatically, but is still +useful for collecting the lists of constructors and destructors. +@end defmac + +@defmac SUPPORTS_INIT_PRIORITY +If nonzero, the C++ @code{init_priority} attribute is supported and the +compiler should emit instructions to control the order of initialization +of objects. If zero, the compiler will issue an error message upon +encountering an @code{init_priority} attribute. +@end defmac + +@deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS +This value is true if the target supports some ``native'' method of +collecting constructors and destructors to be run at startup and exit. +It is false if we must use @command{collect2}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority}) +If defined, a function that outputs assembler code to arrange to call +the function referenced by @var{symbol} at initialization time. + +Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking +no arguments and with no return value. If the target supports initialization +priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY}; +otherwise it must be @code{DEFAULT_INIT_PRIORITY}. + +If this macro is not defined by the target, a suitable default will +be chosen if (1) the target supports arbitrary section names, (2) the +target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2} +is not defined. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority}) +This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination +functions rather than initialization functions. +@end deftypefn + +If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine +generated for the generated object file will have static linkage. + +If your system uses @command{collect2} as the means of processing +constructors, then that program normally uses @command{nm} to scan +an object file for constructor functions to be called. + +On certain kinds of systems, you can define this macro to make +@command{collect2} work faster (and, in some cases, make it work at all): + +@defmac OBJECT_FORMAT_COFF +Define this macro if the system uses COFF (Common Object File Format) +object files, so that @command{collect2} can assume this format and scan +object files directly for dynamic constructor/destructor functions. + +This macro is effective only in a native compiler; @command{collect2} as +part of a cross compiler always uses @command{nm} for the target machine. +@end defmac + +@defmac REAL_NM_FILE_NAME +Define this macro as a C string constant containing the file name to use +to execute @command{nm}. The default is to search the path normally for +@command{nm}. + +If your system supports shared libraries and has a program to list the +dynamic dependencies of a given library or executable, you can define +these macros to enable support for running initialization and +termination functions in shared libraries: +@end defmac + +@defmac LDD_SUFFIX +Define this macro to a C string constant containing the name of the program +which lists dynamic dependencies, like @command{"ldd"} under SunOS 4. +@end defmac + +@defmac PARSE_LDD_OUTPUT (@var{ptr}) +Define this macro to be C code that extracts filenames from the output +of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable +of type @code{char *} that points to the beginning of a line of output +from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the +code must advance @var{ptr} to the beginning of the filename on that +line. Otherwise, it must set @var{ptr} to @code{NULL}. +@end defmac + +@node Instruction Output +@subsection Output of Assembler Instructions + +@c prevent bad page break with this line +This describes assembler instruction output. + +@defmac REGISTER_NAMES +A C initializer containing the assembler's names for the machine +registers, each one as a C string constant. This is what translates +register numbers in the compiler into assembler language. +@end defmac + +@defmac ADDITIONAL_REGISTER_NAMES +If defined, a C initializer for an array of structures containing a name +and a register number. This macro defines additional names for hard +registers, thus allowing the @code{asm} option in declarations to refer +to registers using alternate names. +@end defmac + +@defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr}) +Define this macro if you are using an unusual assembler that +requires different names for the machine instructions. + +The definition is a C statement or statements which output an +assembler instruction opcode to the stdio stream @var{stream}. The +macro-operand @var{ptr} is a variable of type @code{char *} which +points to the opcode name in its ``internal'' form---the form that is +written in the machine description. The definition should output the +opcode name to @var{stream}, performing any translation you desire, and +increment the variable @var{ptr} to point at the end of the opcode +so that it will not be output twice. + +In fact, your macro definition may process less than the entire opcode +name, or more than the opcode name; but if you want to process text +that includes @samp{%}-sequences to substitute operands, you must take +care of the substitution yourself. Just be sure to increment +@var{ptr} over whatever text should not be output normally. + +@findex recog_data.operand +If you need to look at the operand values, they can be found as the +elements of @code{recog_data.operand}. + +If the macro definition does nothing, the instruction is output +in the usual way. +@end defmac + +@defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands}) +If defined, a C statement to be executed just prior to the output of +assembler code for @var{insn}, to modify the extracted operands so +they will be output differently. + +Here the argument @var{opvec} is the vector containing the operands +extracted from @var{insn}, and @var{noperands} is the number of +elements of the vector which contain meaningful data for this insn. +The contents of this vector are what will be used to convert the insn +template into assembler code, so you can change the assembler output +by changing the contents of the vector. + +This macro is useful when various assembler syntaxes share a single +file of instruction patterns; by defining this macro differently, you +can cause a large class of instructions to be output differently (such +as with rearranged operands). Naturally, variations in assembler +syntax affecting individual insn patterns ought to be handled by +writing conditional output routines in those patterns. + +If this macro is not defined, it is equivalent to a null statement. +@end defmac + +@defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code}) +A C compound statement to output to stdio stream @var{stream} the +assembler syntax for an instruction operand @var{x}. @var{x} is an +RTL expression. + +@var{code} is a value that can be used to specify one of several ways +of printing the operand. It is used when identical operands must be +printed differently depending on the context. @var{code} comes from +the @samp{%} specification that was used to request printing of the +operand. If the specification was just @samp{%@var{digit}} then +@var{code} is 0; if the specification was @samp{%@var{ltr} +@var{digit}} then @var{code} is the ASCII code for @var{ltr}. + +@findex reg_names +If @var{x} is a register, this macro should print the register's name. +The names can be found in an array @code{reg_names} whose type is +@code{char *[]}. @code{reg_names} is initialized from +@code{REGISTER_NAMES}. + +When the machine description has a specification @samp{%@var{punct}} +(a @samp{%} followed by a punctuation character), this macro is called +with a null pointer for @var{x} and the punctuation character for +@var{code}. +@end defmac + +@defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code}) +A C expression which evaluates to true if @var{code} is a valid +punctuation character for use in the @code{PRINT_OPERAND} macro. If +@code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no +punctuation characters (except for the standard one, @samp{%}) are used +in this way. +@end defmac + +@defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x}) +A C compound statement to output to stdio stream @var{stream} the +assembler syntax for an instruction operand that is a memory reference +whose address is @var{x}. @var{x} is an RTL expression. + +@cindex @code{TARGET_ENCODE_SECTION_INFO} usage +On some machines, the syntax for a symbolic address depends on the +section that the address refers to. On these machines, define the hook +@code{TARGET_ENCODE_SECTION_INFO} to store the information into the +@code{symbol_ref}, and then check for it here. @xref{Assembler +Format}. +@end defmac + +@findex dbr_sequence_length +@defmac DBR_OUTPUT_SEQEND (@var{file}) +A C statement, to be executed after all slot-filler instructions have +been output. If necessary, call @code{dbr_sequence_length} to +determine the number of slots filled in a sequence (zero if not +currently outputting a sequence), to decide how many no-ops to output, +or whatever. + +Don't define this macro if it has nothing to do, but it is helpful in +reading assembly output if the extent of the delay sequence is made +explicit (e.g.@: with white space). +@end defmac + +@findex final_sequence +Note that output routines for instructions with delay slots must be +prepared to deal with not being output as part of a sequence +(i.e.@: when the scheduling pass is not run, or when no slot fillers could be +found.) The variable @code{final_sequence} is null when not +processing a sequence, otherwise it contains the @code{sequence} rtx +being output. + +@findex asm_fprintf +@defmac REGISTER_PREFIX +@defmacx LOCAL_LABEL_PREFIX +@defmacx USER_LABEL_PREFIX +@defmacx IMMEDIATE_PREFIX +If defined, C string expressions to be used for the @samp{%R}, @samp{%L}, +@samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see +@file{final.c}). These are useful when a single @file{md} file must +support multiple assembler formats. In that case, the various @file{tm.h} +files can define these macros differently. +@end defmac + +@defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format}) +If defined this macro should expand to a series of @code{case} +statements which will be parsed inside the @code{switch} statement of +the @code{asm_fprintf} function. This allows targets to define extra +printf formats which may useful when generating their assembler +statements. Note that uppercase letters are reserved for future +generic extensions to asm_fprintf, and so are not available to target +specific code. The output file is given by the parameter @var{file}. +The varargs input pointer is @var{argptr} and the rest of the format +string, starting the character after the one that is being switched +upon, is pointed to by @var{format}. +@end defmac + +@defmac ASSEMBLER_DIALECT +If your target supports multiple dialects of assembler language (such as +different opcodes), define this macro as a C expression that gives the +numeric index of the assembler language dialect to use, with zero as the +first variant. + +If this macro is defined, you may use constructs of the form +@smallexample +@samp{@{option0|option1|option2@dots{}@}} +@end smallexample +@noindent +in the output templates of patterns (@pxref{Output Template}) or in the +first argument of @code{asm_fprintf}. This construct outputs +@samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of +@code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters +within these strings retain their usual meaning. If there are fewer +alternatives within the braces than the value of +@code{ASSEMBLER_DIALECT}, the construct outputs nothing. + +If you do not define this macro, the characters @samp{@{}, @samp{|} and +@samp{@}} do not have any special meaning when used in templates or +operands to @code{asm_fprintf}. + +Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX}, +@code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express +the variations in assembler language syntax with that mechanism. Define +@code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax +if the syntax variant are larger and involve such things as different +opcodes or operand order. +@end defmac + +@defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno}) +A C expression to output to @var{stream} some assembler code +which will push hard register number @var{regno} onto the stack. +The code need not be optimal, since this macro is used only when +profiling. +@end defmac + +@defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno}) +A C expression to output to @var{stream} some assembler code +which will pop hard register number @var{regno} off of the stack. +The code need not be optimal, since this macro is used only when +profiling. +@end defmac + +@node Dispatch Tables +@subsection Output of Dispatch Tables + +@c prevent bad page break with this line +This concerns dispatch tables. + +@cindex dispatch table +@defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel}) +A C statement to output to the stdio stream @var{stream} an assembler +pseudo-instruction to generate a difference between two labels. +@var{value} and @var{rel} are the numbers of two internal labels. The +definitions of these labels are output using +@code{(*targetm.asm_out.internal_label)}, and they must be printed in the same +way here. For example, + +@smallexample +fprintf (@var{stream}, "\t.word L%d-L%d\n", + @var{value}, @var{rel}) +@end smallexample + +You must provide this macro on machines where the addresses in a +dispatch table are relative to the table's own address. If defined, GCC +will also use this macro on all machines when producing PIC@. +@var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the +mode and flags can be read. +@end defmac + +@defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value}) +This macro should be provided on machines where the addresses +in a dispatch table are absolute. + +The definition should be a C statement to output to the stdio stream +@var{stream} an assembler pseudo-instruction to generate a reference to +a label. @var{value} is the number of an internal label whose +definition is output using @code{(*targetm.asm_out.internal_label)}. +For example, + +@smallexample +fprintf (@var{stream}, "\t.word L%d\n", @var{value}) +@end smallexample +@end defmac + +@defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table}) +Define this if the label before a jump-table needs to be output +specially. The first three arguments are the same as for +@code{(*targetm.asm_out.internal_label)}; the fourth argument is the +jump-table which follows (a @code{jump_insn} containing an +@code{addr_vec} or @code{addr_diff_vec}). + +This feature is used on system V to output a @code{swbeg} statement +for the table. + +If this macro is not defined, these labels are output with +@code{(*targetm.asm_out.internal_label)}. +@end defmac + +@defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table}) +Define this if something special must be output at the end of a +jump-table. The definition should be a C statement to be executed +after the assembler code for the table is written. It should write +the appropriate code to stdio stream @var{stream}. The argument +@var{table} is the jump-table insn, and @var{num} is the label-number +of the preceding label. + +If this macro is not defined, nothing special is output at the end of +the jump-table. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_EMIT_UNWIND_LABEL (@var{stream}, @var{decl}, @var{for_eh}, @var{empty}) +This target hook emits a label at the beginning of each FDE@. It +should be defined on targets where FDEs need special labels, and it +should write the appropriate label, for the FDE associated with the +function declaration @var{decl}, to the stdio stream @var{stream}. +The third argument, @var{for_eh}, is a boolean: true if this is for an +exception table. The fourth argument, @var{empty}, is a boolean: +true if this is a placeholder label for an omitted FDE@. + +The default is that FDEs are not given nonlocal labels. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL (@var{stream}) +This target hook emits a label at the beginning of the exception table. +It should be defined on targets where it is desirable for the table +to be broken up according to function. + +The default is that no label is emitted. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_UNWIND_EMIT (FILE * @var{stream}, rtx @var{insn}) +This target hook emits and assembly directives required to unwind the +given instruction. This is only used when TARGET_UNWIND_INFO is set. +@end deftypefn + +@node Exception Region Output +@subsection Assembler Commands for Exception Regions + +@c prevent bad page break with this line + +This describes commands marking the start and the end of an exception +region. + +@defmac EH_FRAME_SECTION_NAME +If defined, a C string constant for the name of the section containing +exception handling frame unwind information. If not defined, GCC will +provide a default definition if the target supports named sections. +@file{crtstuff.c} uses this macro to switch to the appropriate section. + +You should define this symbol if your target supports DWARF 2 frame +unwind information and the default definition does not work. +@end defmac + +@defmac EH_FRAME_IN_DATA_SECTION +If defined, DWARF 2 frame unwind information will be placed in the +data section even though the target supports named sections. This +might be necessary, for instance, if the system linker does garbage +collection and sections cannot be marked as not to be collected. + +Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is +also defined. +@end defmac + +@defmac EH_TABLES_CAN_BE_READ_ONLY +Define this macro to 1 if your target is such that no frame unwind +information encoding used with non-PIC code will ever require a +runtime relocation, but the linker may not support merging read-only +and read-write sections into a single read-write section. +@end defmac + +@defmac MASK_RETURN_ADDR +An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so +that it does not contain any extraneous set bits in it. +@end defmac + +@defmac DWARF2_UNWIND_INFO +Define this macro to 0 if your target supports DWARF 2 frame unwind +information, but it does not yet work with exception handling. +Otherwise, if your target supports this information (if it defines +@samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP} +or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of 1. + +If @code{TARGET_UNWIND_INFO} is defined, the target specific unwinder +will be used in all cases. Defining this macro will enable the generation +of DWARF 2 frame debugging information. + +If @code{TARGET_UNWIND_INFO} is not defined, and this macro is defined to 1, +the DWARF 2 unwinder will be the default exception handling mechanism; +otherwise, the @code{setjmp}/@code{longjmp}-based scheme will be used by +default. +@end defmac + +@defmac TARGET_UNWIND_INFO +Define this macro if your target has ABI specified unwind tables. Usually +these will be output by @code{TARGET_UNWIND_EMIT}. +@end defmac + +@deftypevar {Target Hook} bool TARGET_UNWIND_TABLES_DEFAULT +This variable should be set to @code{true} if the target ABI requires unwinding +tables even when exceptions are not used. +@end deftypevar + +@defmac MUST_USE_SJLJ_EXCEPTIONS +This macro need only be defined if @code{DWARF2_UNWIND_INFO} is +runtime-variable. In that case, @file{except.h} cannot correctly +determine the corresponding definition of @code{MUST_USE_SJLJ_EXCEPTIONS}, +so the target must provide it directly. +@end defmac + +@defmac DONT_USE_BUILTIN_SETJMP +Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme +should use the @code{setjmp}/@code{longjmp} functions from the C library +instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery. +@end defmac + +@defmac DWARF_CIE_DATA_ALIGNMENT +This macro need only be defined if the target might save registers in the +function prologue at an offset to the stack pointer that is not aligned to +@code{UNITS_PER_WORD}. The definition should be the negative minimum +alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive +minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if +the target supports DWARF 2 frame unwind information. +@end defmac + +@deftypevar {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO +Contains the value true if the target should add a zero word onto the +end of a Dwarf-2 frame info section when used for exception handling. +Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and +true otherwise. +@end deftypevar + +@deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg}) +Given a register, this hook should return a parallel of registers to +represent where to find the register pieces. Define this hook if the +register and its mode are represented in Dwarf in non-contiguous +locations, or if the register should be represented in more than one +register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}. +If not defined, the default is to return @code{NULL_RTX}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ASM_TTYPE (rtx @var{sym}) +This hook is used to output a reference from a frame unwinding table to +the type_info object identified by @var{sym}. It should return @code{true} +if the reference was output. Returning @code{false} will cause the +reference to be output using the normal Dwarf2 routines. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ARM_EABI_UNWINDER +This hook should be set to @code{true} on targets that use an ARM EABI +based unwinding library, and @code{false} on other targets. This effects +the format of unwinding tables, and how the unwinder in entered after +running a cleanup. The default is @code{false}. +@end deftypefn + +@node Alignment Output +@subsection Assembler Commands for Alignment + +@c prevent bad page break with this line +This describes commands for alignment. + +@defmac JUMP_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which is +a common destination of jumps and has no fallthru incoming edge. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @var{align_jumps} in the target's +@code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's +selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation. +@end defmac + +@defmac LABEL_ALIGN_AFTER_BARRIER (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which follows +a @code{BARRIER}. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. +@end defmac + +@defmac LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP +The maximum number of bytes to skip when applying +@code{LABEL_ALIGN_AFTER_BARRIER}. This works only if +@code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. +@end defmac + +@defmac LOOP_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which follows +a @code{NOTE_INSN_LOOP_BEG} note. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @code{align_loops} in the target's +@code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's +selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation. +@end defmac + +@defmac LOOP_ALIGN_MAX_SKIP +The maximum number of bytes to skip when applying @code{LOOP_ALIGN}. +This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. +@end defmac + +@defmac LABEL_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}. +If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment, +the maximum of the specified values is used. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @code{align_labels} in the target's +@code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's +selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation. +@end defmac + +@defmac LABEL_ALIGN_MAX_SKIP +The maximum number of bytes to skip when applying @code{LABEL_ALIGN}. +This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. +@end defmac + +@defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes}) +A C statement to output to the stdio stream @var{stream} an assembler +instruction to advance the location counter by @var{nbytes} bytes. +Those bytes should be zero when loaded. @var{nbytes} will be a C +expression of type @code{int}. +@end defmac + +@defmac ASM_NO_SKIP_IN_TEXT +Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the +text section because it fails to put zeros in the bytes that are skipped. +This is true on many Unix systems, where the pseudo--op to skip bytes +produces no-op instructions rather than zeros when used in the text +section. +@end defmac + +@defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power}) +A C statement to output to the stdio stream @var{stream} an assembler +command to advance the location counter to a multiple of 2 to the +@var{power} bytes. @var{power} will be a C expression of type @code{int}. +@end defmac + +@defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power}) +Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used +for padding, if necessary. +@end defmac + +@defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip}) +A C statement to output to the stdio stream @var{stream} an assembler +command to advance the location counter to a multiple of 2 to the +@var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to +satisfy the alignment request. @var{power} and @var{max_skip} will be +a C expression of type @code{int}. +@end defmac + +@need 3000 +@node Debugging Info +@section Controlling Debugging Information Format + +@c prevent bad page break with this line +This describes how to specify debugging information. + +@menu +* All Debuggers:: Macros that affect all debugging formats uniformly. +* DBX Options:: Macros enabling specific options in DBX format. +* DBX Hooks:: Hook macros for varying DBX format. +* File Names and DBX:: Macros controlling output of file names in DBX format. +* SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. +* VMS Debug:: Macros for VMS debug format. +@end menu + +@node All Debuggers +@subsection Macros Affecting All Debugging Formats + +@c prevent bad page break with this line +These macros affect all debugging formats. + +@defmac DBX_REGISTER_NUMBER (@var{regno}) +A C expression that returns the DBX register number for the compiler +register number @var{regno}. In the default macro provided, the value +of this expression will be @var{regno} itself. But sometimes there are +some registers that the compiler knows about and DBX does not, or vice +versa. In such cases, some register may need to have one number in the +compiler and another for DBX@. + +If two registers have consecutive numbers inside GCC, and they can be +used as a pair to hold a multiword value, then they @emph{must} have +consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}. +Otherwise, debuggers will be unable to access such a pair, because they +expect register pairs to be consecutive in their own numbering scheme. + +If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that +does not preserve register pairs, then what you must do instead is +redefine the actual register numbering scheme. +@end defmac + +@defmac DEBUGGER_AUTO_OFFSET (@var{x}) +A C expression that returns the integer offset value for an automatic +variable having address @var{x} (an RTL expression). The default +computation assumes that @var{x} is based on the frame-pointer and +gives the offset from the frame-pointer. This is required for targets +that produce debugging output for DBX or COFF-style debugging output +for SDB and allow the frame-pointer to be eliminated when the +@option{-g} options is used. +@end defmac + +@defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x}) +A C expression that returns the integer offset value for an argument +having address @var{x} (an RTL expression). The nominal offset is +@var{offset}. +@end defmac + +@defmac PREFERRED_DEBUGGING_TYPE +A C expression that returns the type of debugging output GCC should +produce when the user specifies just @option{-g}. Define +this if you have arranged for GCC to support more than one format of +debugging output. Currently, the allowable values are @code{DBX_DEBUG}, +@code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG}, +@code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}. + +When the user specifies @option{-ggdb}, GCC normally also uses the +value of this macro to select the debugging output format, but with two +exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the +value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is +defined, GCC uses @code{DBX_DEBUG}. + +The value of this macro only affects the default debugging output; the +user can always get a specific type of output by using @option{-gstabs}, +@option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}. +@end defmac + +@node DBX Options +@subsection Specific Options for DBX Output + +@c prevent bad page break with this line +These are specific options for DBX output. + +@defmac DBX_DEBUGGING_INFO +Define this macro if GCC should produce debugging output for DBX +in response to the @option{-g} option. +@end defmac + +@defmac XCOFF_DEBUGGING_INFO +Define this macro if GCC should produce XCOFF format debugging output +in response to the @option{-g} option. This is a variant of DBX format. +@end defmac + +@defmac DEFAULT_GDB_EXTENSIONS +Define this macro to control whether GCC should by default generate +GDB's extended version of DBX debugging information (assuming DBX-format +debugging information is enabled at all). If you don't define the +macro, the default is 1: always generate the extended information +if there is any occasion to. +@end defmac + +@defmac DEBUG_SYMS_TEXT +Define this macro if all @code{.stabs} commands should be output while +in the text section. +@end defmac + +@defmac ASM_STABS_OP +A C string constant, including spacing, naming the assembler pseudo op to +use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol. +If you don't define this macro, @code{"\t.stabs\t"} is used. This macro +applies only to DBX debugging information format. +@end defmac + +@defmac ASM_STABD_OP +A C string constant, including spacing, naming the assembler pseudo op to +use instead of @code{"\t.stabd\t"} to define a debugging symbol whose +value is the current location. If you don't define this macro, +@code{"\t.stabd\t"} is used. This macro applies only to DBX debugging +information format. +@end defmac + +@defmac ASM_STABN_OP +A C string constant, including spacing, naming the assembler pseudo op to +use instead of @code{"\t.stabn\t"} to define a debugging symbol with no +name. If you don't define this macro, @code{"\t.stabn\t"} is used. This +macro applies only to DBX debugging information format. +@end defmac + +@defmac DBX_NO_XREFS +Define this macro if DBX on your system does not support the construct +@samp{xs@var{tagname}}. On some systems, this construct is used to +describe a forward reference to a structure named @var{tagname}. +On other systems, this construct is not supported at all. +@end defmac + +@defmac DBX_CONTIN_LENGTH +A symbol name in DBX-format debugging information is normally +continued (split into two separate @code{.stabs} directives) when it +exceeds a certain length (by default, 80 characters). On some +operating systems, DBX requires this splitting; on others, splitting +must not be done. You can inhibit splitting by defining this macro +with the value zero. You can override the default splitting-length by +defining this macro as an expression for the length you desire. +@end defmac + +@defmac DBX_CONTIN_CHAR +Normally continuation is indicated by adding a @samp{\} character to +the end of a @code{.stabs} string when a continuation follows. To use +a different character instead, define this macro as a character +constant for the character you want to use. Do not define this macro +if backslash is correct for your system. +@end defmac + +@defmac DBX_STATIC_STAB_DATA_SECTION +Define this macro if it is necessary to go to the data section before +outputting the @samp{.stabs} pseudo-op for a non-global static +variable. +@end defmac + +@defmac DBX_TYPE_DECL_STABS_CODE +The value to use in the ``code'' field of the @code{.stabs} directive +for a typedef. The default is @code{N_LSYM}. +@end defmac + +@defmac DBX_STATIC_CONST_VAR_CODE +The value to use in the ``code'' field of the @code{.stabs} directive +for a static variable located in the text section. DBX format does not +provide any ``right'' way to do this. The default is @code{N_FUN}. +@end defmac + +@defmac DBX_REGPARM_STABS_CODE +The value to use in the ``code'' field of the @code{.stabs} directive +for a parameter passed in registers. DBX format does not provide any +``right'' way to do this. The default is @code{N_RSYM}. +@end defmac + +@defmac DBX_REGPARM_STABS_LETTER +The letter to use in DBX symbol data to identify a symbol as a parameter +passed in registers. DBX format does not customarily provide any way to +do this. The default is @code{'P'}. +@end defmac + +@defmac DBX_FUNCTION_FIRST +Define this macro if the DBX information for a function and its +arguments should precede the assembler code for the function. Normally, +in DBX format, the debugging information entirely follows the assembler +code. +@end defmac + +@defmac DBX_BLOCKS_FUNCTION_RELATIVE +Define this macro, with value 1, if the value of a symbol describing +the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be +relative to the start of the enclosing function. Normally, GCC uses +an absolute address. +@end defmac + +@defmac DBX_LINES_FUNCTION_RELATIVE +Define this macro, with value 1, if the value of a symbol indicating +the current line number (@code{N_SLINE}) should be relative to the +start of the enclosing function. Normally, GCC uses an absolute address. +@end defmac + +@defmac DBX_USE_BINCL +Define this macro if GCC should generate @code{N_BINCL} and +@code{N_EINCL} stabs for included header files, as on Sun systems. This +macro also directs GCC to output a type number as a pair of a file +number and a type number within the file. Normally, GCC does not +generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single +number for a type number. +@end defmac + +@node DBX Hooks +@subsection Open-Ended Hooks for DBX Format + +@c prevent bad page break with this line +These are hooks for DBX format. + +@defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name}) +Define this macro to say how to output to @var{stream} the debugging +information for the start of a scope level for variable names. The +argument @var{name} is the name of an assembler symbol (for use with +@code{assemble_name}) whose value is the address where the scope begins. +@end defmac + +@defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name}) +Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level. +@end defmac + +@defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl}) +Define this macro if the target machine requires special handling to +output an @code{N_FUN} entry for the function @var{decl}. +@end defmac + +@defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter}) +A C statement to output DBX debugging information before code for line +number @var{line} of the current source file to the stdio stream +@var{stream}. @var{counter} is the number of time the macro was +invoked, including the current invocation; it is intended to generate +unique labels in the assembly output. + +This macro should not be defined if the default output is correct, or +if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}. +@end defmac + +@defmac NO_DBX_FUNCTION_END +Some stabs encapsulation formats (in particular ECOFF), cannot handle the +@code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct. +On those machines, define this macro to turn this feature off without +disturbing the rest of the gdb extensions. +@end defmac + +@defmac NO_DBX_BNSYM_ENSYM +Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx +extension construct. On those machines, define this macro to turn this +feature off without disturbing the rest of the gdb extensions. +@end defmac + +@node File Names and DBX +@subsection File Names in DBX Format + +@c prevent bad page break with this line +This describes file names in DBX format. + +@defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name}) +A C statement to output DBX debugging information to the stdio stream +@var{stream}, which indicates that file @var{name} is the main source +file---the file specified as the input file for compilation. +This macro is called only once, at the beginning of compilation. + +This macro need not be defined if the standard form of output +for DBX debugging information is appropriate. + +It may be necessary to refer to a label equal to the beginning of the +text section. You can use @samp{assemble_name (stream, ltext_label_name)} +to do so. If you do this, you must also set the variable +@var{used_ltext_label_name} to @code{true}. +@end defmac + +@defmac NO_DBX_MAIN_SOURCE_DIRECTORY +Define this macro, with value 1, if GCC should not emit an indication +of the current directory for compilation and current source language at +the beginning of the file. +@end defmac + +@defmac NO_DBX_GCC_MARKER +Define this macro, with value 1, if GCC should not emit an indication +that this object file was compiled by GCC@. The default is to emit +an @code{N_OPT} stab at the beginning of every source file, with +@samp{gcc2_compiled.} for the string and value 0. +@end defmac + +@defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name}) +A C statement to output DBX debugging information at the end of +compilation of the main source file @var{name}. Output should be +written to the stdio stream @var{stream}. + +If you don't define this macro, nothing special is output at the end +of compilation, which is correct for most machines. +@end defmac + +@defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END +Define this macro @emph{instead of} defining +@code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at +the end of compilation is a @code{N_SO} stab with an empty string, +whose value is the highest absolute text address in the file. +@end defmac + +@need 2000 +@node SDB and DWARF +@subsection Macros for SDB and DWARF Output + +@c prevent bad page break with this line +Here are macros for SDB and DWARF output. + +@defmac SDB_DEBUGGING_INFO +Define this macro if GCC should produce COFF-style debugging output +for SDB in response to the @option{-g} option. +@end defmac + +@defmac DWARF2_DEBUGGING_INFO +Define this macro if GCC should produce dwarf version 2 format +debugging output in response to the @option{-g} option. + +@deftypefn {Target Hook} int TARGET_DWARF_CALLING_CONVENTION (tree @var{function}) +Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to +be emitted for each function. Instead of an integer return the enum +value for the @code{DW_CC_} tag. +@end deftypefn + +To support optional call frame debugging information, you must also +define @code{INCOMING_RETURN_ADDR_RTX} and either set +@code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the +prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save} +as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't. +@end defmac + +@defmac DWARF2_FRAME_INFO +Define this macro to a nonzero value if GCC should always output +Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO} +(@pxref{Exception Region Output} is nonzero, GCC will output this +information not matter how you define @code{DWARF2_FRAME_INFO}. +@end defmac + +@defmac DWARF2_ASM_LINE_DEBUG_INFO +Define this macro to be a nonzero value if the assembler can generate Dwarf 2 +line debug info sections. This will result in much more compact line number +tables, and hence is desirable if it works. +@end defmac + +@defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) +A C statement to issue assembly directives that create a difference +@var{lab1} minus @var{lab2}, using an integer of the given @var{size}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{section}) +A C statement to issue assembly directives that create a +section-relative reference to the given @var{label}, using an integer of the +given @var{size}. The label is known to be defined in the given @var{section}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label}) +A C statement to issue assembly directives that create a self-relative +reference to the given @var{label}, using an integer of the given @var{size}. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_DWARF_DTPREL (FILE *@var{FILE}, int @var{size}, rtx @var{x}) +If defined, this target hook is a function which outputs a DTP-relative +reference to the given TLS symbol of the specified size. +@end deftypefn + +@defmac PUT_SDB_@dots{} +Define these macros to override the assembler syntax for the special +SDB assembler directives. See @file{sdbout.c} for a list of these +macros and their arguments. If the standard syntax is used, you need +not define them yourself. +@end defmac + +@defmac SDB_DELIM +Some assemblers do not support a semicolon as a delimiter, even between +SDB assembler directives. In that case, define this macro to be the +delimiter to use (usually @samp{\n}). It is not necessary to define +a new set of @code{PUT_SDB_@var{op}} macros if this is the only change +required. +@end defmac + +@defmac SDB_ALLOW_UNKNOWN_REFERENCES +Define this macro to allow references to unknown structure, +union, or enumeration tags to be emitted. Standard COFF does not +allow handling of unknown references, MIPS ECOFF has support for +it. +@end defmac + +@defmac SDB_ALLOW_FORWARD_REFERENCES +Define this macro to allow references to structure, union, or +enumeration tags that have not yet been seen to be handled. Some +assemblers choke if forward tags are used, while some require it. +@end defmac + +@defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}) +A C statement to output SDB debugging information before code for line +number @var{line} of the current source file to the stdio stream +@var{stream}. The default is to emit an @code{.ln} directive. +@end defmac + +@need 2000 +@node VMS Debug +@subsection Macros for VMS Debug Format + +@c prevent bad page break with this line +Here are macros for VMS debug format. + +@defmac VMS_DEBUGGING_INFO +Define this macro if GCC should produce debugging output for VMS +in response to the @option{-g} option. The default behavior for VMS +is to generate minimal debug info for a traceback in the absence of +@option{-g} unless explicitly overridden with @option{-g0}. This +behavior is controlled by @code{OPTIMIZATION_OPTIONS} and +@code{OVERRIDE_OPTIONS}. +@end defmac + +@node Floating Point +@section Cross Compilation and Floating Point +@cindex cross compilation and floating point +@cindex floating point and cross compilation + +While all modern machines use twos-complement representation for integers, +there are a variety of representations for floating point numbers. This +means that in a cross-compiler the representation of floating point numbers +in the compiled program may be different from that used in the machine +doing the compilation. + +Because different representation systems may offer different amounts of +range and precision, all floating point constants must be represented in +the target machine's format. Therefore, the cross compiler cannot +safely use the host machine's floating point arithmetic; it must emulate +the target's arithmetic. To ensure consistency, GCC always uses +emulation to work with floating point values, even when the host and +target floating point formats are identical. + +The following macros are provided by @file{real.h} for the compiler to +use. All parts of the compiler which generate or optimize +floating-point calculations must use these macros. They may evaluate +their operands more than once, so operands must not have side effects. + +@defmac REAL_VALUE_TYPE +The C data type to be used to hold a floating point value in the target +machine's format. Typically this is a @code{struct} containing an +array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque +quantity. +@end defmac + +@deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) +Compares for equality the two values, @var{x} and @var{y}. If the target +floating point format supports negative zeroes and/or NaNs, +@samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and +@samp{REAL_VALUES_EQUAL (NaN, NaN)} is false. +@end deftypefn + +@deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) +Tests whether @var{x} is less than @var{y}. +@end deftypefn + +@deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x}) +Truncates @var{x} to a signed integer, rounding toward zero. +@end deftypefn + +@deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x}) +Truncates @var{x} to an unsigned integer, rounding toward zero. If +@var{x} is negative, returns zero. +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode}) +Converts @var{string} into a floating point number in the target machine's +representation for mode @var{mode}. This routine can handle both +decimal and hexadecimal floating point constants, using the syntax +defined by the C language for both. +@end deftypefn + +@deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x}) +Returns 1 if @var{x} is negative (including negative zero), 0 otherwise. +@end deftypefn + +@deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x}) +Determines whether @var{x} represents infinity (positive or negative). +@end deftypefn + +@deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x}) +Determines whether @var{x} represents a ``NaN'' (not-a-number). +@end deftypefn + +@deftypefn Macro void REAL_ARITHMETIC (REAL_VALUE_TYPE @var{output}, enum tree_code @var{code}, REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) +Calculates an arithmetic operation on the two floating point values +@var{x} and @var{y}, storing the result in @var{output} (which must be a +variable). + +The operation to be performed is specified by @var{code}. Only the +following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR}, +@code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}. + +If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the +target's floating point format cannot represent infinity, it will call +@code{abort}. Callers should check for this situation first, using +@code{MODE_HAS_INFINITIES}. @xref{Storage Layout}. +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x}) +Returns the negative of the floating point value @var{x}. +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x}) +Returns the absolute value of @var{x}. +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x}) +Truncates the floating point value @var{x} to fit in @var{mode}. The +return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an +appropriate bit pattern to be output asa floating constant whose +precision accords with mode @var{mode}. +@end deftypefn + +@deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x}) +Converts a floating point value @var{x} into a double-precision integer +which is then stored into @var{low} and @var{high}. If the value is not +integral, it is truncated. +@end deftypefn + +@deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, enum machine_mode @var{mode}) +Converts a double-precision integer found in @var{low} and @var{high}, +into a floating point value which is then stored into @var{x}. The +value is truncated to fit in mode @var{mode}. +@end deftypefn + +@node Mode Switching +@section Mode Switching Instructions +@cindex mode switching +The following macros control mode switching optimizations: + +@defmac OPTIMIZE_MODE_SWITCHING (@var{entity}) +Define this macro if the port needs extra instructions inserted for mode +switching in an optimizing compilation. + +For an example, the SH4 can perform both single and double precision +floating point operations, but to perform a single precision operation, +the FPSCR PR bit has to be cleared, while for a double precision +operation, this bit has to be set. Changing the PR bit requires a general +purpose register as a scratch register, hence these FPSCR sets have to +be inserted before reload, i.e.@: you can't put this into instruction emitting +or @code{TARGET_MACHINE_DEPENDENT_REORG}. + +You can have multiple entities that are mode-switched, and select at run time +which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should +return nonzero for any @var{entity} that needs mode-switching. +If you define this macro, you also have to define +@code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED}, +@code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}. +@code{MODE_AFTER}, @code{MODE_ENTRY}, and @code{MODE_EXIT} +are optional. +@end defmac + +@defmac NUM_MODES_FOR_MODE_SWITCHING +If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as +initializer for an array of integers. Each initializer element +N refers to an entity that needs mode switching, and specifies the number +of different modes that might need to be set for this entity. +The position of the initializer in the initializer---starting counting at +zero---determines the integer that is used to refer to the mode-switched +entity in question. +In macros that take mode arguments / yield a mode result, modes are +represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode +switch is needed / supplied. +@end defmac + +@defmac MODE_NEEDED (@var{entity}, @var{insn}) +@var{entity} is an integer specifying a mode-switched entity. If +@code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to +return an integer value not larger than the corresponding element in +@code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must +be switched into prior to the execution of @var{insn}. +@end defmac + +@defmac MODE_AFTER (@var{mode}, @var{insn}) +If this macro is defined, it is evaluated for every @var{insn} during +mode switching. It determines the mode that an insn results in (if +different from the incoming mode). +@end defmac + +@defmac MODE_ENTRY (@var{entity}) +If this macro is defined, it is evaluated for every @var{entity} that needs +mode switching. It should evaluate to an integer, which is a mode that +@var{entity} is assumed to be switched to at function entry. If @code{MODE_ENTRY} +is defined then @code{MODE_EXIT} must be defined. +@end defmac + +@defmac MODE_EXIT (@var{entity}) +If this macro is defined, it is evaluated for every @var{entity} that needs +mode switching. It should evaluate to an integer, which is a mode that +@var{entity} is assumed to be switched to at function exit. If @code{MODE_EXIT} +is defined then @code{MODE_ENTRY} must be defined. +@end defmac + +@defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n}) +This macro specifies the order in which modes for @var{entity} are processed. +0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the +lowest. The value of the macro should be an integer designating a mode +for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode} +(@var{entity}, @var{n}) shall be a bijection in 0 @dots{} +@code{num_modes_for_mode_switching[@var{entity}] - 1}. +@end defmac + +@defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live}) +Generate one or more insns to set @var{entity} to @var{mode}. +@var{hard_reg_live} is the set of hard registers live at the point where +the insn(s) are to be inserted. +@end defmac + +@node Target Attributes +@section Defining target-specific uses of @code{__attribute__} +@cindex target attributes +@cindex machine attributes +@cindex attributes, target-specific + +Target-specific attributes may be defined for functions, data and types. +These are described using the following target hooks; they also need to +be documented in @file{extend.texi}. + +@deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE +If defined, this target hook points to an array of @samp{struct +attribute_spec} (defined in @file{tree.h}) specifying the machine +specific attributes for this target and some of the restrictions on the +entities to which these attributes are applied and the arguments they +take. +@end deftypevr + +@deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) +If defined, this target hook is a function which returns zero if the attributes on +@var{type1} and @var{type2} are incompatible, one if they are compatible, +and two if they are nearly compatible (which causes a warning to be +generated). If this is not defined, machine-specific attributes are +supposed always to be compatible. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type}) +If defined, this target hook is a function which assigns default attributes to +newly defined @var{type}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) +Define this target hook if the merging of type attributes needs special +handling. If defined, the result is a list of the combined +@code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed +that @code{comptypes} has already been called and returned 1. This +function may call @code{merge_attributes} to handle machine-independent +merging. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl}) +Define this target hook if the merging of decl attributes needs special +handling. If defined, the result is a list of the combined +@code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}. +@var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of +when this is needed are when one attribute overrides another, or when an +attribute is nullified by a subsequent definition. This function may +call @code{merge_attributes} to handle machine-independent merging. + +@findex TARGET_DLLIMPORT_DECL_ATTRIBUTES +If the only target-specific handling you require is @samp{dllimport} +for Microsoft Windows targets, you should define the macro +@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler +will then define a function called +@code{merge_dllimport_decl_attributes} which can then be defined as +the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also +add @code{handle_dll_attribute} in the attribute table for your port +to perform initial processing of the @samp{dllimport} and +@samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and +@file{i386/i386.c}, for example. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VALID_DLLIMPORT_ATTRIBUTE_P (tree @var{decl}) +@var{decl} is a variable or function with @code{__attribute__((dllimport))} +specified. Use this hook if the target needs to add extra validation +checks to @code{handle_dll_attribute}. +@end deftypefn + +@defmac TARGET_DECLSPEC +Define this macro to a nonzero value if you want to treat +@code{__declspec(X)} as equivalent to @code{__attribute((X))}. By +default, this behavior is enabled only for targets that define +@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation +of @code{__declspec} is via a built-in macro, but you should not rely +on this implementation detail. +@end defmac + +@deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr}) +Define this target hook if you want to be able to add attributes to a decl +when it is being created. This is normally useful for back ends which +wish to implement a pragma by using the attributes which correspond to +the pragma's effect. The @var{node} argument is the decl which is being +created. The @var{attr_ptr} argument is a pointer to the attribute list +for this decl. The list itself should not be modified, since it may be +shared with other decls, but attributes may be chained on the head of +the list and @code{*@var{attr_ptr}} modified to point to the new +attributes, or a copy of the list may be made if further changes are +needed. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl}) +@cindex inlining +This target hook returns @code{true} if it is ok to inline @var{fndecl} +into the current function, despite its having target-specific +attributes, @code{false} otherwise. By default, if a function has a +target specific attribute attached to it, it will not be inlined. +@end deftypefn + +@node MIPS Coprocessors +@section Defining coprocessor specifics for MIPS targets. +@cindex MIPS coprocessor-definition macros + +The MIPS specification allows MIPS implementations to have as many as 4 +coprocessors, each with as many as 32 private registers. GCC supports +accessing these registers and transferring values between the registers +and memory using asm-ized variables. For example: + +@smallexample + register unsigned int cp0count asm ("c0r1"); + unsigned int d; + + d = cp0count + 3; +@end smallexample + +(``c0r1'' is the default name of register 1 in coprocessor 0; alternate +names may be added as described below, or the default names may be +overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.) + +Coprocessor registers are assumed to be epilogue-used; sets to them will +be preserved even if it does not appear that the register is used again +later in the function. + +Another note: according to the MIPS spec, coprocessor 1 (if present) is +the FPU@. One accesses COP1 registers through standard mips +floating-point support; they are not included in this mechanism. + +There is one macro used in defining the MIPS coprocessor interface which +you may want to override in subtargets; it is described below. + +@defmac ALL_COP_ADDITIONAL_REGISTER_NAMES +A comma-separated list (with leading comma) of pairs describing the +alternate names of coprocessor registers. The format of each entry should be +@smallexample +@{ @var{alternatename}, @var{register_number}@} +@end smallexample +Default: empty. +@end defmac + +@node PCH Target +@section Parameters for Precompiled Header Validity Checking +@cindex parameters, precompiled headers + +@deftypefn {Target Hook} void *TARGET_GET_PCH_VALIDITY (size_t *@var{sz}) +This hook returns the data needed by @code{TARGET_PCH_VALID_P} and sets +@samp{*@var{sz}} to the size of the data in bytes. +@end deftypefn + +@deftypefn {Target Hook} const char *TARGET_PCH_VALID_P (const void *@var{data}, size_t @var{sz}) +This hook checks whether the options used to create a PCH file are +compatible with the current settings. It returns @code{NULL} +if so and a suitable error message if not. Error messages will +be presented to the user and must be localized using @samp{_(@var{msg})}. + +@var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY} +when the PCH file was created and @var{sz} is the size of that data in bytes. +It's safe to assume that the data was created by the same version of the +compiler, so no format checking is needed. + +The default definition of @code{default_pch_valid_p} should be +suitable for most targets. +@end deftypefn + +@deftypefn {Target Hook} const char *TARGET_CHECK_PCH_TARGET_FLAGS (int @var{pch_flags}) +If this hook is nonnull, the default implementation of +@code{TARGET_PCH_VALID_P} will use it to check for compatible values +of @code{target_flags}. @var{pch_flags} specifies the value that +@code{target_flags} had when the PCH file was created. The return +value is the same as for @code{TARGET_PCH_VALID_P}. +@end deftypefn + +@node C++ ABI +@section C++ ABI parameters +@cindex parameters, c++ abi + +@deftypefn {Target Hook} tree TARGET_CXX_GUARD_TYPE (void) +Define this hook to override the integer type used for guard variables. +These are used to implement one-time construction of static objects. The +default is long_long_integer_type_node. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_GUARD_MASK_BIT (void) +This hook determines how guard variables are used. It should return +@code{false} (the default) if first byte should be used. A return value of +@code{true} indicates the least significant bit should be used. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_CXX_GET_COOKIE_SIZE (tree @var{type}) +This hook returns the size of the cookie to use when allocating an array +whose elements have the indicated @var{type}. Assumes that it is already +known that a cookie is needed. The default is +@code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the +IA64/Generic C++ ABI@. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_COOKIE_HAS_SIZE (void) +This hook should return @code{true} if the element size should be stored in +array cookies. The default is to return @code{false}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_CXX_IMPORT_EXPORT_CLASS (tree @var{type}, int @var{import_export}) +If defined by a backend this hook allows the decision made to export +class @var{type} to be overruled. Upon entry @var{import_export} +will contain 1 if the class is going to be exported, @minus{}1 if it is going +to be imported and 0 otherwise. This function should return the +modified value and perform any other actions necessary to support the +backend's targeted operating system. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_CDTOR_RETURNS_THIS (void) +This hook should return @code{true} if constructors and destructors return +the address of the object created/destroyed. The default is to return +@code{false}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_KEY_METHOD_MAY_BE_INLINE (void) +This hook returns true if the key method for a class (i.e., the method +which, if defined in the current translation unit, causes the virtual +table to be emitted) may be an inline function. Under the standard +Itanium C++ ABI the key method may be an inline function so long as +the function is not declared inline in the class definition. Under +some variants of the ABI, an inline function can never be the key +method. The default is to return @code{true}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY (tree @var{decl}) +@var{decl} is a virtual table, virtual table table, typeinfo object, +or other similar implicit class data object that will be emitted with +external linkage in this translation unit. No ELF visibility has been +explicitly specified. If the target needs to specify a visibility +other than that of the containing class, use this hook to set +@code{DECL_VISIBILITY} and @code{DECL_VISIBILITY_SPECIFIED}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT (void) +This hook returns true (the default) if virtual tables and other +similar implicit class data objects are always COMDAT if they have +external linkage. If this hook returns false, then class data for +classes whose virtual table will be emitted in only one translation +unit will not be COMDAT. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_USE_AEABI_ATEXIT (void) +This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI) +should be used to register static destructors when @option{-fuse-cxa-atexit} +is in effect. The default is to return false to use @code{__cxa_atexit}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_CXX_ADJUST_CLASS_AT_DEFINITION (tree @var{type}) +@var{type} is a C++ class (i.e., RECORD_TYPE or UNION_TYPE) that has just been +defined. Use this hook to make adjustments to the class (eg, tweak +visibility or perform any other required target modifications). +@end deftypefn + +@c APPLE LOCAL begin mainline 4.3 2006-01-10 4871915 +@deftypefn {Target Hook} bool TARGET_CXX_LIBRARY_RTTI_COMDAT (void) +This hook returns true (the default) if the RTTI information for +the basic types which is defined in the C++ runtime should always +be COMDAT, false if it should not be COMDAT. +@end deftypefn + +@c APPLE LOCAL end mainline 4.3 2006-01-10 4871915 +@node Misc +@section Miscellaneous Parameters +@cindex parameters, miscellaneous + +@c prevent bad page break with this line +Here are several miscellaneous parameters. + +@defmac HAS_LONG_COND_BRANCH +Define this boolean macro to indicate whether or not your architecture +has conditional branches that can span all of memory. It is used in +conjunction with an optimization that partitions hot and cold basic +blocks into separate sections of the executable. If this macro is +set to false, gcc will convert any conditional branches that attempt +to cross between sections into unconditional branches or indirect jumps. +@end defmac + +@defmac HAS_LONG_UNCOND_BRANCH +Define this boolean macro to indicate whether or not your architecture +has unconditional branches that can span all of memory. It is used in +conjunction with an optimization that partitions hot and cold basic +blocks into separate sections of the executable. If this macro is +set to false, gcc will convert any unconditional branches that attempt +to cross between sections into indirect jumps. +@end defmac + +@defmac CASE_VECTOR_MODE +An alias for a machine mode name. This is the machine mode that +elements of a jump-table should have. +@end defmac + +@defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body}) +Optional: return the preferred mode for an @code{addr_diff_vec} +when the minimum and maximum offset are known. If you define this, +it enables extra code in branch shortening to deal with @code{addr_diff_vec}. +To make this work, you also have to define @code{INSN_ALIGN} and +make the alignment for @code{addr_diff_vec} explicit. +The @var{body} argument is provided so that the offset_unsigned and scale +flags can be updated. +@end defmac + +@defmac CASE_VECTOR_PC_RELATIVE +Define this macro to be a C expression to indicate when jump-tables +should contain relative addresses. You need not define this macro if +jump-tables never contain relative addresses, or jump-tables should +contain relative addresses only when @option{-fPIC} or @option{-fPIC} +is in effect. +@end defmac + +@defmac CASE_VALUES_THRESHOLD +Define this to be the smallest number of different values for which it +is best to use a jump-table instead of a tree of conditional branches. +The default is four for machines with a @code{casesi} instruction and +five otherwise. This is best for most machines. +@end defmac + +@defmac CASE_USE_BIT_TESTS +Define this macro to be a C expression to indicate whether C switch +statements may be implemented by a sequence of bit tests. This is +advantageous on processors that can efficiently implement left shift +of 1 by the number of bits held in a register, but inappropriate on +targets that would require a loop. By default, this macro returns +@code{true} if the target defines an @code{ashlsi3} pattern, and +@code{false} otherwise. +@end defmac + +@defmac WORD_REGISTER_OPERATIONS +Define this macro if operations between registers with integral mode +smaller than a word are always performed on the entire register. +Most RISC machines have this property and most CISC machines do not. +@end defmac + +@defmac LOAD_EXTEND_OP (@var{mem_mode}) +Define this macro to be a C expression indicating when insns that read +memory in @var{mem_mode}, an integral mode narrower than a word, set the +bits outside of @var{mem_mode} to be either the sign-extension or the +zero-extension of the data read. Return @code{SIGN_EXTEND} for values +of @var{mem_mode} for which the +insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and +@code{UNKNOWN} for other modes. + +This macro is not called with @var{mem_mode} non-integral or with a width +greater than or equal to @code{BITS_PER_WORD}, so you may return any +value in this case. Do not define this macro if it would always return +@code{UNKNOWN}. On machines where this macro is defined, you will normally +define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}. + +You may return a non-@code{UNKNOWN} value even if for some hard registers +the sign extension is not performed, if for the @code{REGNO_REG_CLASS} +of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero +when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any +integral mode larger than this but not larger than @code{word_mode}. + +You must return @code{UNKNOWN} if for some hard registers that allow this +mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to +@code{word_mode}, but that they can change to another integral mode that +is larger then @var{mem_mode} but still smaller than @code{word_mode}. +@end defmac + +@defmac SHORT_IMMEDIATES_SIGN_EXTEND +Define this macro if loading short immediate values into registers sign +extends. +@end defmac + +@defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC +Define this macro if the same instructions that convert a floating +point number to a signed fixed point number also convert validly to an +unsigned one. +@end defmac + +@deftypefn {Target Hook} int TARGET_MIN_DIVISIONS_FOR_RECIP_MUL (enum machine_mode @var{mode}) +When @option{-ffast-math} is in effect, GCC tries to optimize +divisions by the same divisor, by turning them into multiplications by +the reciprocal. This target hook specifies the minimum number of divisions +that should be there for GCC to perform the optimization for a variable +of mode @var{mode}. The default implementation returns 3 if the machine +has an instruction for the division, and 2 if it does not. +@end deftypefn + +@defmac MOVE_MAX +The maximum number of bytes that a single instruction can move quickly +between memory and registers or between two memory locations. +@end defmac + +@defmac MAX_MOVE_MAX +The maximum number of bytes that a single instruction can move quickly +between memory and registers or between two memory locations. If this +is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the +constant value that is the largest value that @code{MOVE_MAX} can have +at run-time. +@end defmac + +@defmac SHIFT_COUNT_TRUNCATED +A C expression that is nonzero if on this machine the number of bits +actually used for the count of a shift operation is equal to the number +of bits needed to represent the size of the object being shifted. When +this macro is nonzero, the compiler will assume that it is safe to omit +a sign-extend, zero-extend, and certain bitwise `and' instructions that +truncates the count of a shift operation. On machines that have +instructions that act on bit-fields at variable positions, which may +include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED} +also enables deletion of truncations of the values that serve as +arguments to bit-field instructions. + +If both types of instructions truncate the count (for shifts) and +position (for bit-field operations), or if no variable-position bit-field +instructions exist, you should define this macro. + +However, on some machines, such as the 80386 and the 680x0, truncation +only applies to shift operations and not the (real or pretended) +bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on +such machines. Instead, add patterns to the @file{md} file that include +the implied truncation of the shift instructions. + +You need not define this macro if it would always have the value of zero. +@end defmac + +@anchor{TARGET_SHIFT_TRUNCATION_MASK} +@deftypefn {Target Hook} int TARGET_SHIFT_TRUNCATION_MASK (enum machine_mode @var{mode}) +This function describes how the standard shift patterns for @var{mode} +deal with shifts by negative amounts or by more than the width of the mode. +@xref{shift patterns}. + +On many machines, the shift patterns will apply a mask @var{m} to the +shift count, meaning that a fixed-width shift of @var{x} by @var{y} is +equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If +this is true for mode @var{mode}, the function should return @var{m}, +otherwise it should return 0. A return value of 0 indicates that no +particular behavior is guaranteed. + +Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does +@emph{not} apply to general shift rtxes; it applies only to instructions +that are generated by the named shift patterns. + +The default implementation of this function returns +@code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED} +and 0 otherwise. This definition is always safe, but if +@code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns +nevertheless truncate the shift count, you may get better code +by overriding it. +@end deftypefn + +@defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec}) +A C expression which is nonzero if on this machine it is safe to +``convert'' an integer of @var{inprec} bits to one of @var{outprec} +bits (where @var{outprec} is smaller than @var{inprec}) by merely +operating on it as if it had only @var{outprec} bits. + +On many machines, this expression can be 1. + +@c rearranged this, removed the phrase "it is reported that". this was +@c to fix an overfull hbox. --mew 10feb93 +When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for +modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result. +If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in +such cases may improve things. +@end defmac + +@deftypefn {Target Hook} int TARGET_MODE_REP_EXTENDED (enum machine_mode @var{mode}, enum machine_mode @var{rep_mode}) +The representation of an integral mode can be such that the values +are always extended to a wider integral mode. Return +@code{SIGN_EXTEND} if values of @var{mode} are represented in +sign-extended form to @var{rep_mode}. Return @code{UNKNOWN} +otherwise. (Currently, none of the targets use zero-extended +representation this way so unlike @code{LOAD_EXTEND_OP}, +@code{TARGET_MODE_REP_EXTENDED} is expected to return either +@code{SIGN_EXTEND} or @code{UNKNOWN}. Also no target extends +@var{mode} to @var{mode_rep} so that @var{mode_rep} is not the next +widest integral mode and currently we take advantage of this fact.) + +Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN} +value even if the extension is not performed on certain hard registers +as long as for the @code{REGNO_REG_CLASS} of these hard registers +@code{CANNOT_CHANGE_MODE_CLASS} returns nonzero. + +Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP} +describe two related properties. If you define +@code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want +to define @code{LOAD_EXTEND_OP (mode)} to return the same type of +extension. + +In order to enforce the representation of @code{mode}, +@code{TRULY_NOOP_TRUNCATION} should return false when truncating to +@code{mode}. +@end deftypefn + +@defmac STORE_FLAG_VALUE +A C expression describing the value returned by a comparison operator +with an integral mode and stored by a store-flag instruction +(@samp{s@var{cond}}) when the condition is true. This description must +apply to @emph{all} the @samp{s@var{cond}} patterns and all the +comparison operators whose results have a @code{MODE_INT} mode. + +A value of 1 or @minus{}1 means that the instruction implementing the +comparison operator returns exactly 1 or @minus{}1 when the comparison is true +and 0 when the comparison is false. Otherwise, the value indicates +which bits of the result are guaranteed to be 1 when the comparison is +true. This value is interpreted in the mode of the comparison +operation, which is given by the mode of the first operand in the +@samp{s@var{cond}} pattern. Either the low bit or the sign bit of +@code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by +the compiler. + +If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will +generate code that depends only on the specified bits. It can also +replace comparison operators with equivalent operations if they cause +the required bits to be set, even if the remaining bits are undefined. +For example, on a machine whose comparison operators return an +@code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as +@samp{0x80000000}, saying that just the sign bit is relevant, the +expression + +@smallexample +(ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0)) +@end smallexample + +@noindent +can be converted to + +@smallexample +(ashift:SI @var{x} (const_int @var{n})) +@end smallexample + +@noindent +where @var{n} is the appropriate shift count to move the bit being +tested into the sign bit. + +There is no way to describe a machine that always sets the low-order bit +for a true value, but does not guarantee the value of any other bits, +but we do not know of any machine that has such an instruction. If you +are trying to port GCC to such a machine, include an instruction to +perform a logical-and of the result with 1 in the pattern for the +comparison operators and let us know at @email{gcc@@gcc.gnu.org}. + +Often, a machine will have multiple instructions that obtain a value +from a comparison (or the condition codes). Here are rules to guide the +choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions +to be used: + +@itemize @bullet +@item +Use the shortest sequence that yields a valid definition for +@code{STORE_FLAG_VALUE}. It is more efficient for the compiler to +``normalize'' the value (convert it to, e.g., 1 or 0) than for the +comparison operators to do so because there may be opportunities to +combine the normalization with other operations. + +@item +For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being +slightly preferred on machines with expensive jumps and 1 preferred on +other machines. + +@item +As a second choice, choose a value of @samp{0x80000001} if instructions +exist that set both the sign and low-order bits but do not define the +others. + +@item +Otherwise, use a value of @samp{0x80000000}. +@end itemize + +Many machines can produce both the value chosen for +@code{STORE_FLAG_VALUE} and its negation in the same number of +instructions. On those machines, you should also define a pattern for +those cases, e.g., one matching + +@smallexample +(set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C}))) +@end smallexample + +Some machines can also perform @code{and} or @code{plus} operations on +condition code values with less instructions than the corresponding +@samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those +machines, define the appropriate patterns. Use the names @code{incscc} +and @code{decscc}, respectively, for the patterns which perform +@code{plus} or @code{minus} operations on condition code values. See +@file{rs6000.md} for some examples. The GNU Superoptizer can be used to +find such instruction sequences on other machines. + +If this macro is not defined, the default value, 1, is used. You need +not define @code{STORE_FLAG_VALUE} if the machine has no store-flag +instructions, or if the value generated by these instructions is 1. +@end defmac + +@defmac FLOAT_STORE_FLAG_VALUE (@var{mode}) +A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is +returned when comparison operators with floating-point results are true. +Define this macro on machines that have comparison operations that return +floating-point values. If there are no such operations, do not define +this macro. +@end defmac + +@defmac VECTOR_STORE_FLAG_VALUE (@var{mode}) +A C expression that gives a rtx representing the nonzero true element +for vector comparisons. The returned rtx should be valid for the inner +mode of @var{mode} which is guaranteed to be a vector mode. Define +this macro on machines that have vector comparison operations that +return a vector result. If there are no such operations, do not define +this macro. Typically, this macro is defined as @code{const1_rtx} or +@code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent +the compiler optimizing such vector comparison operations for the +given mode. +@end defmac + +@defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) +@defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) +A C expression that evaluates to true if the architecture defines a value +for @code{clz} or @code{ctz} with a zero operand. If so, @var{value} +should be set to this value. If this macro is not defined, the value of +@code{clz} or @code{ctz} is assumed to be undefined. + +This macro must be defined if the target's expansion for @code{ffs} +relies on a particular value to get correct results. Otherwise it +is not necessary, though it may be used to optimize some corner cases. + +Note that regardless of this macro the ``definedness'' of @code{clz} +and @code{ctz} at zero do @emph{not} extend to the builtin functions +visible to the user. Thus one may be free to adjust the value at will +to match the target expansion of these operations without fear of +breaking the API@. +@end defmac + +@defmac Pmode +An alias for the machine mode for pointers. On most machines, define +this to be the integer mode corresponding to the width of a hardware +pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines. +On some machines you must define this to be one of the partial integer +modes, such as @code{PSImode}. + +The width of @code{Pmode} must be at least as large as the value of +@code{POINTER_SIZE}. If it is not equal, you must define the macro +@code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended +to @code{Pmode}. +@end defmac + +@defmac FUNCTION_MODE +An alias for the machine mode used for memory references to functions +being called, in @code{call} RTL expressions. On most machines this +should be @code{QImode}. +@end defmac + +@defmac STDC_0_IN_SYSTEM_HEADERS +In normal operation, the preprocessor expands @code{__STDC__} to the +constant 1, to signify that GCC conforms to ISO Standard C@. On some +hosts, like Solaris, the system compiler uses a different convention, +where @code{__STDC__} is normally 0, but is 1 if the user specifies +strict conformance to the C Standard. + +Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host +convention when processing system header files, but when processing user +files @code{__STDC__} will always expand to 1. +@end defmac + +@defmac NO_IMPLICIT_EXTERN_C +Define this macro if the system header files support C++ as well as C@. +This macro inhibits the usual method of using system header files in +C++, which is to pretend that the file's contents are enclosed in +@samp{extern "C" @{@dots{}@}}. +@end defmac + +@findex #pragma +@findex pragma +@defmac REGISTER_TARGET_PRAGMAS () +Define this macro if you want to implement any target-specific pragmas. +If defined, it is a C expression which makes a series of calls to +@code{c_register_pragma} or @code{c_register_pragma_with_expansion} +for each pragma. The macro may also do any +setup required for the pragmas. + +The primary reason to define this macro is to provide compatibility with +other compilers for the same target. In general, we discourage +definition of target-specific pragmas for GCC@. + +If the pragma can be implemented by attributes then you should consider +defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well. + +Preprocessor macros that appear on pragma lines are not expanded. All +@samp{#pragma} directives that do not match any registered pragma are +silently ignored, unless the user specifies @option{-Wunknown-pragmas}. +@end defmac + +@deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) +@deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) + +Each call to @code{c_register_pragma} or +@code{c_register_pragma_with_expansion} establishes one pragma. The +@var{callback} routine will be called when the preprocessor encounters a +pragma of the form + +@smallexample +#pragma [@var{space}] @var{name} @dots{} +@end smallexample + +@var{space} is the case-sensitive namespace of the pragma, or +@code{NULL} to put the pragma in the global namespace. The callback +routine receives @var{pfile} as its first argument, which can be passed +on to cpplib's functions if necessary. You can lex tokens after the +@var{name} by calling @code{pragma_lex}. Tokens that are not read by the +callback will be silently ignored. The end of the line is indicated by +a token of type @code{CPP_EOF}. Macro expansion occurs on the +arguments of pragmas registered with +@code{c_register_pragma_with_expansion} but not on the arguments of +pragmas registered with @code{c_register_pragma}. + +For an example use of this routine, see @file{c4x.h} and the callback +routines defined in @file{c4x-c.c}. + +Note that the use of @code{pragma_lex} is specific to the C and C++ +compilers. It will not work in the Java or Fortran compilers, or any +other language compilers for that matter. Thus if @code{pragma_lex} is going +to be called from target-specific code, it must only be done so when +building the C and C++ compilers. This can be done by defining the +variables @code{c_target_objs} and @code{cxx_target_objs} in the +target entry in the @file{config.gcc} file. These variables should name +the target-specific, language-specific object file which contains the +code that uses @code{pragma_lex}. Note it will also be necessary to add a +rule to the makefile fragment pointed to by @code{tmake_file} that shows +how to build this object file. +@end deftypefun + +@findex #pragma +@findex pragma +@defmac HANDLE_SYSV_PRAGMA +Define this macro (to a value of 1) if you want the System V style +pragmas @samp{#pragma pack(<n>)} and @samp{#pragma weak <name> +[=<value>]} to be supported by gcc. + +The pack pragma specifies the maximum alignment (in bytes) of fields +within a structure, in much the same way as the @samp{__aligned__} and +@samp{__packed__} @code{__attribute__}s do. A pack value of zero resets +the behavior to the default. + +A subtlety for Microsoft Visual C/C++ style bit-field packing +(e.g.@: -mms-bitfields) for targets that support it: +When a bit-field is inserted into a packed record, the whole size +of the underlying type is used by one or more same-size adjacent +bit-fields (that is, if its long:3, 32 bits is used in the record, +and any additional adjacent long bit-fields are packed into the same +chunk of 32 bits. However, if the size changes, a new field of that +size is allocated). + +If both MS bit-fields and @samp{__attribute__((packed))} are used, +the latter will take precedence. If @samp{__attribute__((packed))} is +used on a single field when MS bit-fields are in use, it will take +precedence for that field, but the alignment of the rest of the structure +may affect its placement. + +The weak pragma only works if @code{SUPPORTS_WEAK} and +@code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation +of specifically named weak labels, optionally with a value. +@end defmac + +@findex #pragma +@findex pragma +@defmac HANDLE_PRAGMA_PACK_PUSH_POP +Define this macro (to a value of 1) if you want to support the Win32 +style pragmas @samp{#pragma pack(push[,@var{n}])} and @samp{#pragma +pack(pop)}. The @samp{pack(push,[@var{n}])} pragma specifies the maximum +alignment (in bytes) of fields within a structure, in much the same way as +the @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A +pack value of zero resets the behavior to the default. Successive +invocations of this pragma cause the previous values to be stacked, so +that invocations of @samp{#pragma pack(pop)} will return to the previous +value. +@end defmac + +@defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION +Define this macro, as well as +@code{HANDLE_SYSV_PRAGMA}, if macros should be expanded in the +arguments of @samp{#pragma pack}. +@end defmac + +@defmac TARGET_DEFAULT_PACK_STRUCT +If your target requires a structure packing default other than 0 (meaning +the machine default), define this macro to the necessary value (in bytes). +This must be a value that would also be valid to use with +@samp{#pragma pack()} (that is, a small power of two). +@end defmac + +@defmac DOLLARS_IN_IDENTIFIERS +Define this macro to control use of the character @samp{$} in +identifier names for the C family of languages. 0 means @samp{$} is +not allowed by default; 1 means it is allowed. 1 is the default; +there is no need to define this macro in that case. +@end defmac + +@defmac NO_DOLLAR_IN_LABEL +Define this macro if the assembler does not accept the character +@samp{$} in label names. By default constructors and destructors in +G++ have @samp{$} in the identifiers. If this macro is defined, +@samp{.} is used instead. +@end defmac + +@defmac NO_DOT_IN_LABEL +Define this macro if the assembler does not accept the character +@samp{.} in label names. By default constructors and destructors in G++ +have names that use @samp{.}. If this macro is defined, these names +are rewritten to avoid @samp{.}. +@end defmac + +@defmac INSN_SETS_ARE_DELAYED (@var{insn}) +Define this macro as a C expression that is nonzero if it is safe for the +delay slot scheduler to place instructions in the delay slot of @var{insn}, +even if they appear to use a resource set or clobbered in @var{insn}. +@var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that +every @code{call_insn} has this behavior. On machines where some @code{insn} +or @code{jump_insn} is really a function call and hence has this behavior, +you should define this macro. + +You need not define this macro if it would always return zero. +@end defmac + +@defmac INSN_REFERENCES_ARE_DELAYED (@var{insn}) +Define this macro as a C expression that is nonzero if it is safe for the +delay slot scheduler to place instructions in the delay slot of @var{insn}, +even if they appear to set or clobber a resource referenced in @var{insn}. +@var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where +some @code{insn} or @code{jump_insn} is really a function call and its operands +are registers whose use is actually in the subroutine it calls, you should +define this macro. Doing so allows the delay slot scheduler to move +instructions which copy arguments into the argument registers into the delay +slot of @var{insn}. + +You need not define this macro if it would always return zero. +@end defmac + +@defmac MULTIPLE_SYMBOL_SPACES +Define this macro as a C expression that is nonzero if, in some cases, +global symbols from one translation unit may not be bound to undefined +symbols in another translation unit without user intervention. For +instance, under Microsoft Windows symbols must be explicitly imported +from shared libraries (DLLs). + +You need not define this macro if it would always evaluate to zero. +@end defmac + +@deftypefn {Target Hook} tree TARGET_MD_ASM_CLOBBERS (tree @var{outputs}, tree @var{inputs}, tree @var{clobbers}) +This target hook should add to @var{clobbers} @code{STRING_CST} trees for +any hard regs the port wishes to automatically clobber for an asm. +It should return the result of the last @code{tree_cons} used to add a +clobber. The @var{outputs}, @var{inputs} and @var{clobber} lists are the +corresponding parameters to the asm and may be inspected to avoid +clobbering a register that is an input or output of the asm. You can use +@code{tree_overlaps_hard_reg_set}, declared in @file{tree.h}, to test +for overlap with regards to asm-declared registers. +@end deftypefn + +@defmac MATH_LIBRARY +Define this macro as a C string constant for the linker argument to link +in the system math library, or @samp{""} if the target does not have a +separate math library. + +You need only define this macro if the default of @samp{"-lm"} is wrong. +@end defmac + +@defmac LIBRARY_PATH_ENV +Define this macro as a C string constant for the environment variable that +specifies where the linker should look for libraries. + +You need only define this macro if the default of @samp{"LIBRARY_PATH"} +is wrong. +@end defmac + +@defmac TARGET_POSIX_IO +Define this macro if the target supports the following POSIX@ file +functions, access, mkdir and file locking with fcntl / F_SETLKW@. +Defining @code{TARGET_POSIX_IO} will enable the test coverage code +to use file locking when exiting a program, which avoids race conditions +if the program has forked. It will also create directories at run-time +for cross-profiling. +@end defmac + +@defmac MAX_CONDITIONAL_EXECUTE + +A C expression for the maximum number of instructions to execute via +conditional execution instructions instead of a branch. A value of +@code{BRANCH_COST}+1 is the default if the machine does not use cc0, and +1 if it does use cc0. +@end defmac + +@defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr}) +Used if the target needs to perform machine-dependent modifications on the +conditionals used for turning basic blocks into conditionally executed code. +@var{ce_info} points to a data structure, @code{struct ce_if_block}, which +contains information about the currently processed blocks. @var{true_expr} +and @var{false_expr} are the tests that are used for converting the +then-block and the else-block, respectively. Set either @var{true_expr} or +@var{false_expr} to a null pointer if the tests cannot be converted. +@end defmac + +@defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr}) +Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated +if-statements into conditions combined by @code{and} and @code{or} operations. +@var{bb} contains the basic block that contains the test that is currently +being processed and about to be turned into a condition. +@end defmac + +@defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn}) +A C expression to modify the @var{PATTERN} of an @var{INSN} that is to +be converted to conditional execution format. @var{ce_info} points to +a data structure, @code{struct ce_if_block}, which contains information +about the currently processed blocks. +@end defmac + +@defmac IFCVT_MODIFY_FINAL (@var{ce_info}) +A C expression to perform any final machine dependent modifications in +converting code to conditional execution. The involved basic blocks +can be found in the @code{struct ce_if_block} structure that is pointed +to by @var{ce_info}. +@end defmac + +@defmac IFCVT_MODIFY_CANCEL (@var{ce_info}) +A C expression to cancel any machine dependent modifications in +converting code to conditional execution. The involved basic blocks +can be found in the @code{struct ce_if_block} structure that is pointed +to by @var{ce_info}. +@end defmac + +@defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info}) +A C expression to initialize any extra fields in a @code{struct ce_if_block} +structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro. +@end defmac + +@defmac IFCVT_EXTRA_FIELDS +If defined, it should expand to a set of field declarations that will be +added to the @code{struct ce_if_block} structure. These should be initialized +by the @code{IFCVT_INIT_EXTRA_FIELDS} macro. +@end defmac + +@deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG () +If non-null, this hook performs a target-specific pass over the +instruction stream. The compiler will run it at all optimization levels, +just before the point at which it normally does delayed-branch scheduling. + +The exact purpose of the hook varies from target to target. Some use +it to do transformations that are necessary for correctness, such as +laying out in-function constant pools or avoiding hardware hazards. +Others use it as an opportunity to do some machine-dependent optimizations. + +You need not implement the hook if it has nothing to do. The default +definition is null. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_INIT_BUILTINS () +Define this hook if you have any machine-specific built-in functions +that need to be defined. It should be a function that performs the +necessary setup. + +Machine specific built-in functions can be useful to expand special machine +instructions that would otherwise not normally be generated because +they have no equivalent in the source language (for example, SIMD vector +instructions or prefetch instructions). + +To create a built-in function, call the function +@code{lang_hooks.builtin_function} +which is defined by the language front end. You can use any type nodes set +up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2}; +only language front ends that use those two functions will call +@samp{TARGET_INIT_BUILTINS}. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore}) + +Expand a call to a machine specific built-in function that was set up by +@samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the +function call; the result should go to @var{target} if that is +convenient, and have mode @var{mode} if that is convenient. +@var{subtarget} may be used as the target for computing one of +@var{exp}'s operands. @var{ignore} is nonzero if the value is to be +ignored. This function should return the result of the call to the +built-in function. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_RESOLVE_OVERLOADED_BUILTIN (tree @var{fndecl}, tree @var{arglist}) + +Select a replacement for a machine specific built-in function that +was set up by @samp{TARGET_INIT_BUILTINS}. This is done +@emph{before} regular type checking, and so allows the target to +implement a crude form of function overloading. @var{fndecl} is the +declaration of the built-in function. @var{arglist} is the list of +arguments passed to the built-in function. The result is a +complete expression that implements the operation, usually +another @code{CALL_EXPR}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_FOLD_BUILTIN (tree @var{fndecl}, tree @var{arglist}, bool @var{ignore}) + +Fold a call to a machine specific built-in function that was set up by +@samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the +built-in function. @var{arglist} is the list of arguments passed to +the built-in function. The result is another tree containing a +simplified expression for the call's result. If @var{ignore} is true +the value will be ignored. +@end deftypefn + +@deftypefn {Target Hook} const char * TARGET_INVALID_WITHIN_DOLOOP (rtx @var{insn}) + +Take an instruction in @var{insn} and return NULL if it is valid within a +low-overhead loop, otherwise return a string why doloop could not be applied. + +Many targets use special registers for low-overhead looping. For any +instruction that clobbers these this function should return a string indicating +the reason why the doloop could not be applied. +By default, the RTL loop optimizer does not use a present doloop pattern for +loops containing function calls or branch on table instructions. +@end deftypefn + +@defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2}) + +Take a branch insn in @var{branch1} and another in @var{branch2}. +Return true if redirecting @var{branch1} to the destination of +@var{branch2} is possible. + +On some targets, branches may have a limited range. Optimizing the +filling of delay slots can result in branches being redirected, and this +may in turn cause a branch offset to overflow. +@end defmac + +@deftypefn {Target Hook} bool TARGET_COMMUTATIVE_P (rtx @var{x}, @var{outer_code}) +This target hook returns @code{true} if @var{x} is considered to be commutative. +Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider +PLUS to be commutative inside a MEM. @var{outer_code} is the rtx code +of the enclosing rtl, if known, otherwise it is UNKNOWN. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_ALLOCATE_INITIAL_VALUE (rtx @var{hard_reg}) + +When the initial value of a hard register has been copied in a pseudo +register, it is often not necessary to actually allocate another register +to this pseudo register, because the original hard register or a stack slot +it has been saved into can be used. @code{TARGET_ALLOCATE_INITIAL_VALUE} +is called at the start of register allocation once for each hard register +that had its initial value copied by using +@code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}. +Possible values are @code{NULL_RTX}, if you don't want +to do any special allocation, a @code{REG} rtx---that would typically be +the hard register itself, if it is known not to be clobbered---or a +@code{MEM}. +If you are returning a @code{MEM}, this is only a hint for the allocator; +it might decide to use another register anyways. +You may use @code{current_function_leaf_function} in the hook, functions +that use @code{REG_N_SETS}, to determine if the hard +register in question will not be clobbered. +The default value of this hook is @code{NULL}, which disables any special +allocation. +@end deftypefn + +@defmac TARGET_OBJECT_SUFFIX +Define this macro to be a C string representing the suffix for object +files on your target machine. If you do not define this macro, GCC will +use @samp{.o} as the suffix for object files. +@end defmac + +@defmac TARGET_EXECUTABLE_SUFFIX +Define this macro to be a C string representing the suffix to be +automatically added to executable files on your target machine. If you +do not define this macro, GCC will use the null string as the suffix for +executable files. +@end defmac + +@defmac COLLECT_EXPORT_LIST +If defined, @code{collect2} will scan the individual object files +specified on its command line and create an export list for the linker. +Define this macro for systems like AIX, where the linker discards +object files that are not referenced from @code{main} and uses export +lists. +@end defmac + +@defmac MODIFY_JNI_METHOD_CALL (@var{mdecl}) +Define this macro to a C expression representing a variant of the +method call @var{mdecl}, if Java Native Interface (JNI) methods +must be invoked differently from other methods on your target. +For example, on 32-bit Microsoft Windows, JNI methods must be invoked using +the @code{stdcall} calling convention and this macro is then +defined as this expression: + +@smallexample +build_type_attribute_variant (@var{mdecl}, + build_tree_list + (get_identifier ("stdcall"), + NULL)) +@end smallexample +@end defmac + +@deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void) +This target hook returns @code{true} past the point in which new jump +instructions could be created. On machines that require a register for +every jump such as the SHmedia ISA of SH5, this point would typically be +reload, so this target hook should be defined to a function such as: + +@smallexample +static bool +cannot_modify_jumps_past_reload_p () +@{ + return (reload_completed || reload_in_progress); +@} +@end smallexample +@end deftypefn + +@deftypefn {Target Hook} int TARGET_BRANCH_TARGET_REGISTER_CLASS (void) +This target hook returns a register class for which branch target register +optimizations should be applied. All registers in this class should be +usable interchangeably. After reload, registers in this class will be +re-allocated and loads will be hoisted out of loops and be subjected +to inter-block scheduling. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED (bool @var{after_prologue_epilogue_gen}) +Branch target register optimization will by default exclude callee-saved +registers +that are not already live during the current function; if this target hook +returns true, they will be included. The target code must than make sure +that all target registers in the class returned by +@samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are +saved. @var{after_prologue_epilogue_gen} indicates if prologues and +epilogues have already been generated. Note, even if you only return +true when @var{after_prologue_epilogue_gen} is false, you still are likely +to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET} +to reserve space for caller-saved target registers. +@end deftypefn + +@defmac POWI_MAX_MULTS +If defined, this macro is interpreted as a signed integer C expression +that specifies the maximum number of floating point multiplications +that should be emitted when expanding exponentiation by an integer +constant inline. When this value is defined, exponentiation requiring +more than this number of multiplications is implemented by calling the +system library's @code{pow}, @code{powf} or @code{powl} routines. +The default value places no upper bound on the multiplication count. +@end defmac + +@deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) +This target hook should register any extra include files for the +target. The parameter @var{stdinc} indicates if normal include files +are present. The parameter @var{sysroot} is the system root directory. +The parameter @var{iprefix} is the prefix for the gcc directory. +@end deftypefn + +@deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) +This target hook should register any extra include files for the +target before any standard headers. The parameter @var{stdinc} +indicates if normal include files are present. The parameter +@var{sysroot} is the system root directory. The parameter +@var{iprefix} is the prefix for the gcc directory. +@end deftypefn + +@deftypefn Macro void TARGET_OPTF (char *@var{path}) +This target hook should register special include paths for the target. +The parameter @var{path} is the include to register. On Darwin +systems, this is used for Framework includes, which have semantics +that are different from @option{-I}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl}) +This target hook returns @code{true} if it is safe to use a local alias +for a virtual function @var{fndecl} when constructing thunks, +@code{false} otherwise. By default, the hook returns @code{true} for all +functions, if a target supports aliases (i.e.@: defines +@code{ASM_OUTPUT_DEF}), @code{false} otherwise, +@end deftypefn + +@defmac TARGET_FORMAT_TYPES +If defined, this macro is the name of a global variable containing +target-specific format checking information for the @option{-Wformat} +option. The default is to have no target-specific format checks. +@end defmac + +@defmac TARGET_N_FORMAT_TYPES +If defined, this macro is the number of entries in +@code{TARGET_FORMAT_TYPES}. +@end defmac + +@deftypefn {Target Hook} bool TARGET_RELAXED_ORDERING +If set to @code{true}, means that the target's memory model does not +guarantee that loads which do not depend on one another will access +main memory in the order of the instruction stream; if ordering is +important, an explicit memory barrier must be used. This is true of +many recent processors which implement a policy of ``relaxed,'' +``weak,'' or ``release'' memory consistency, such as Alpha, PowerPC, +and ia64. The default is @code{false}. +@end deftypefn + +@deftypefn {Target Hook} const char *TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN (tree @var{typelist}, tree @var{funcdecl}, tree @var{val}) +If defined, this macro returns the diagnostic message when it is +illegal to pass argument @var{val} to function @var{funcdecl} +with prototype @var{typelist}. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_INVALID_CONVERSION (tree @var{fromtype}, tree @var{totype}) +If defined, this macro returns the diagnostic message when it is +invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL} +if validity should be determined by the front end. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_INVALID_UNARY_OP (int @var{op}, tree @var{type}) +If defined, this macro returns the diagnostic message when it is +invalid to apply operation @var{op} (where unary plus is denoted by +@code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL} +if validity should be determined by the front end. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_INVALID_BINARY_OP (int @var{op}, tree @var{type1}, tree @var{type2}) +If defined, this macro returns the diagnostic message when it is +invalid to apply operation @var{op} to operands of types @var{type1} +and @var{type2}, or @code{NULL} if validity should be determined by +the front end. +@end deftypefn + +@defmac TARGET_USE_JCR_SECTION +This macro determines whether to use the JCR section to register Java +classes. By default, TARGET_USE_JCR_SECTION is defined to 1 if both +SUPPORTS_WEAK and TARGET_HAVE_NAMED_SECTIONS are true, else 0. +@end defmac + +@defmac OBJC_JBLEN +This macro determines the size of the objective C jump buffer for the +NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value. +@end defmac |