https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127998
Bug ID: 127998
Summary: Possible missed optimization at O3
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: apowenq at gmail dot com
Target Milestone: ---
Reproducer: https://godbolt.org/z/E1EYjf4qY
Possible some missed case in demanded bits analysis (note that `i1 >> 4`).
$cat prog.c
int src(int v2, int v3) {
if (!(31 <= v2 && v2 <= 32)) __builtin_unreachable();
if (!(192 <= v3 && v3 <= 193)) __builtin_unreachable();
int i0 = v3 ^ 141;
int i1 = v2 ^ i0;
int i2 = i1 >> 4;
return i2;
}
GCC at O3:
"src":
mov eax, edi
xor eax, esi
sar eax, 4
xor eax, 8
ret
LLVM at O3:
src:
shr edi, 4
lea eax, [rdi + 4]
ret
