https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65214
Bug ID: 65214
Summary: [SH] Optimize sign/zero extensions across basic blocks
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: olegendo at gcc dot gnu.org
Target: sh*-*-*
This is an example from gcc.c-torture/execute/pr20187-1.c:
int a = 0x101;
int b = 0x100;
int
test (void)
{
return (((unsigned char) (unsigned long long) ((a ? a : 1) & (a * b)))
? 0 : 1);
}
compiled with -m4 -ml -O2 -fdisable-rtl-dbr:
mov.l .L6,r1
mov.l @r1,r2
mov #1,r1 // r1 is zero extended after constant load
tst r2,r2
bt .L2
exts.b r2,r1
.L2:
mov.l .L7,r3
extu.b r1,r1 // r1 = extu.b (exts.b (r2))
mov.l @r3,r3
mulu.w r2,r3
sts macl,r3
tst r3,r1
movt r0
rts
nop
The extu.b basically overrides result of exts.b. Thus we can replace the
exts.b with extu.b and eliminate one insn:
mov.l .L6,r1
mov.l @r1,r2
mov #1,r1
tst r2,r2
bt .L2
extu.b r2,r1
.L2:
mov.l .L7,r3
mov.l @r3,r3
mulu.w r2,r3
sts macl,r3
tst r3,r1
movt r0
rts
nop
