Hi,
When I compile this C code:
#include <stdint.h>
inline int mid_pred(int a, int b, int c)
{
int t= (a-b)&((a-b)>>31);
a-=t;
b+=t;
b-= (b-c)&((b-c)>>31);
b+= (a-b)&((a-b)>>31);
return b;
}
I get this asm output from GCC 4.3.2 (-m68060 -fomit-frame-pointer -O[2/3]):
#NO_APP
.text
.even
.globl _mid_pred
_mid_pred:
movem.l #14336,-(sp)
move.l 16(sp),d2
move.l 20(sp),d1
move.l d2,d0
sub.l d1,d0
move.l d0,d4
add.l d4,d4
subx.l d4,d4
and.l d0,d4
add.l d4,d1
move.l d1,d3
sub.l 24(sp),d3
move.l d3,d0
add.l d0,d0
subx.l d0,d0
and.l d3,d0
sub.l d0,d1
sub.l d4,d2
sub.l d1,d2
move.l d2,d0
add.l d0,d0
subx.l d0,d0
and.l d2,d0
add.l d1,d0
movem.l (sp)+,#28
rts
When I use GCC 4.4.[0/1/2] with -O2/-O3 option I get worse asm output (2
additional move.ls):
#NO_APP
.text
.even
.globl _mid_pred
_mid_pred:
movem.l #14336,-(sp)
move.l 16(sp),d1
move.l 20(sp),d0
move.l d1,d3
sub.l d0,d3
move.l d3,d2
add.l d2,d2
subx.l d2,d2
and.l d3,d2
add.l d2,d0
move.l d0,d4
sub.l 24(sp),d4
move.l d4,d3
add.l d3,d3
subx.l d3,d3
and.l d4,d3
sub.l d3,d0
move.l d0,d3
sub.l d2,d1
sub.l d0,d1
move.l d1,d2
add.l d2,d2
subx.l d2,d2
and.l d1,d2
move.l d2,d0
add.l d3,d0
movem.l (sp)+,#28
rts
The problematic optimization is -fregmove (-m68060 -fomit-frame-pointer -O[2/3]
-fno-regmove):
#NO_APP
.text
.even
.globl _mid_pred
_mid_pred:
movem.l #14336,-(sp)
move.l 16(sp),d0
move.l 20(sp),d1
move.l d0,d2
sub.l d1,d2
move.l d2,d3
add.l d3,d3
subx.l d3,d3
and.l d3,d2
add.l d2,d1
move.l d1,d3
sub.l 24(sp),d3
move.l d3,d4
add.l d4,d4
subx.l d4,d4
and.l d4,d3
sub.l d3,d1
sub.l d2,d0
sub.l d1,d0
move.l d0,d2
add.l d2,d2
subx.l d2,d2
and.l d2,d0
add.l d1,d0
movem.l (sp)+,#28
rts
--
Summary: GCC 4.4.[0/1/2] generates worse code compared to GCC
4.3.2
Product: gcc
Version: 4.4.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ami_stuff at o2 dot pl
GCC host triplet: i686-cygwin
GCC target triplet: m68k-amigaos
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41204
