https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110431
Bug ID: 110431
Summary: Incorrect disambiguation of wide accesess from
store-merging or SLP
Product: gcc
Version: 12.3.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: amonakov at gcc dot gnu.org
Target Milestone: ---
Inspired by bug 110237 comment 19:
int b, a;
int main()
{
int *pa = &a, *pb = &b;
asm("" : "+r"(pa));
asm("" : "+r"(pb));
if (pa + 1 == pb) {
a = 1, b = 2;
long x;
__builtin_memcpy(&x, pa, 4);
__builtin_memcpy(4 + (char *)&x, pa+1, 4);
return (x - 0x0000000200000001) * 131 >> 32;
}
}
https://godbolt.org/z/b67zxMv54
On GIMPLE, both store-merging and SLP vectorization are capable of introducing
merged long-sized access in place of individual int-sized memcpy's, which is
then disambiguated against initial stores on the RTL level, leading to a
miscompilation.
