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;; Copyright (C) 2001-2014 Free Software Foundation, Inc.
;;
;; This file is part of GCC.
;;
;; GCC is free software; you can redistribute it and/or modify it under
;; the terms of the GNU General Public License as published by the Free
;; Software Foundation; either version 3, or (at your option) any later
;; version.
;;
;; GCC is distributed in the hope that it will be useful, but WITHOUT ANY
;; WARRANTY; without even the implied warranty of MERCHANTABILITY or
;; FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
;; for more details.
;;
;; Under Section 7 of GPL version 3, you are granted additional
;; permissions described in the GCC Runtime Library Exception, version
;; 3.1, as published by the Free Software Foundation.
;;
;; You should have received a copy of the GNU General Public License and
;; a copy of the GCC Runtime Library Exception along with this program;
;; see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
;; <http://www.gnu.org/licenses/>.
;;
;; This code used to be expanded through interesting expansions in
;; the machine description, compiled from this code:
;;
;; #ifdef L_mulsi3
;; long __Mul (unsigned long a, unsigned long b) __attribute__ ((__const__));
;;
;; /* This must be compiled with the -mexpand-mul flag, to synthesize the
;; multiplication from the mstep instructions. The check for
;; smaller-size multiplication pays off in the order of .5-10%;
;; estimated median 1%, depending on application.
;; FIXME: It can be further optimized if we go to assembler code, as
;; gcc 2.7.2 adds a few unnecessary instructions and does not put the
;; basic blocks in optimal order. */
;; long
;; __Mul (unsigned long a, unsigned long b)
;; {
;; #if defined (__CRIS_arch_version) && __CRIS_arch_version >= 10
;; /* In case other code is compiled without -march=v10, they will
;; contain calls to __Mul, regardless of flags at link-time. The
;; "else"-code below will work, but is unnecessarily slow. This
;; sometimes cuts a few minutes off from simulation time by just
;; returning a "mulu.d". */
;; return a * b;
;; #else
;; unsigned long min;
;;
;; /* Get minimum via the bound insn. */
;; min = a < b ? a : b;
;;
;; /* Can we omit computation of the high part? */
;; if (min > 65535)
;; /* No. Perform full multiplication. */
;; return a * b;
;; else
;; {
;; /* Check if both operands are within 16 bits. */
;; unsigned long max;
;;
;; /* Get maximum, by knowing the minimum.
;; This will partition a and b into max and min.
;; This is not currently something GCC understands,
;; so do this trick by asm. */
;; __asm__ ("xor %1,%0\n\txor %2,%0"
;; : "=r" (max)
;; : "r" (b), "r" (a), "0" (min));
;;
;; if (max > 65535)
;; /* Make GCC understand that only the low part of "min" will be
;; used. */
;; return max * (unsigned short) min;
;; else
;; /* Only the low parts of both operands are necessary. */
;; return ((unsigned short) max) * (unsigned short) min;
;; }
;; #endif /* not __CRIS_arch_version >= 10 */
;; }
;; #endif /* L_mulsi3 */
;;
;; That approach was abandoned since the caveats outweighted the
;; benefits. The expand-multiplication machinery is also removed, so you
;; can't do this anymore.
;;
;; For doubters of there being any benefits, some where: insensitivity to:
;; - ABI changes (mostly for experimentation)
;; - assembler syntax differences (mostly debug format).
;; - insn scheduling issues.
;; Most ABI experiments will presumably happen with arches with mul insns,
;; so that argument doesn't really hold anymore, and it's unlikely there
;; being new arch variants needing insn scheduling and not having mul
;; insns.
;; ELF and a.out have different syntax for local labels: the "wrong"
;; one may not be omitted from the object.
#undef L
#ifdef __AOUT__
# define L(x) x
#else
# define L(x) .x
#endif
.global ___Mul
.type ___Mul,@function
___Mul:
#if defined (__CRIS_arch_version) && __CRIS_arch_version >= 10
;; Can't have the mulu.d last on a cache-line (in the delay-slot of the
;; "ret"), due to hardware bug. See documentation for -mmul-bug-workaround.
;; Not worthwhile to conditionalize here.
.p2alignw 2,0x050f
mulu.d $r11,$r10
ret
nop
#else
;; See if we can avoid multiplying some of the parts, knowing
;; they're zero.
move.d $r11,$r9
bound.d $r10,$r9
cmpu.w 65535,$r9
bls L(L3)
move.d $r10,$r12
;; Nope, have to do all the parts of a 32-bit multiplication.
;; See head comment in optabs.c:expand_doubleword_mult.
move.d $r10,$r13
movu.w $r11,$r9 ; ab*cd = (a*d + b*c)<<16 + b*d
lslq 16,$r13
mstep $r9,$r13 ; d*b
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
mstep $r9,$r13
clear.w $r10
test.d $r10
mstep $r9,$r10 ; d*a
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
mstep $r9,$r10
movu.w $r12,$r12
clear.w $r11
move.d $r11,$r9 ; Doubles as a "test.d" preparing for the mstep.
mstep $r12,$r9 ; b*c
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
mstep $r12,$r9
add.w $r9,$r10
lslq 16,$r10
ret
add.d $r13,$r10
L(L3):
;; Form the maximum in $r10, by knowing the minimum, $r9.
;; (We don't know which one of $r10 or $r11 it is.)
;; Check if the largest operand is still just 16 bits.
xor $r9,$r10
xor $r11,$r10
cmpu.w 65535,$r10
bls L(L5)
movu.w $r9,$r13
;; We have ab*cd = (a*c)<<32 + (a*d + b*c)<<16 + b*d, but c==0
;; so we only need (a*d)<<16 + b*d with d = $r13, ab = $r10.
;; We drop the upper part of (a*d)<<16 as we're only doing a
;; 32-bit-result multiplication.
move.d $r10,$r9
lslq 16,$r9
mstep $r13,$r9 ; b*d
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
mstep $r13,$r9
clear.w $r10
test.d $r10
mstep $r13,$r10 ; a*d
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
lslq 16,$r10
ret
add.d $r9,$r10
L(L5):
;; We have ab*cd = (a*c)<<32 + (a*d + b*c)<<16 + b*d, but a and c==0
;; so b*d (with b=$r13, a=$r10) it is.
lslq 16,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
mstep $r13,$r10
ret
mstep $r13,$r10
#endif
L(Lfe1):
.size ___Mul,L(Lfe1)-___Mul
|
