;; Copyright (C) 2001-2021 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 ;; . ;; ;; 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