https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101641
Bug ID: 101641
Summary: Bogus redundant store removal
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
union u {
long x;
long long y;
};
__attribute__((noinline,noclone))
long test(long *px, long long *py, union u *pu)
{
*px = 0;
*py = 1;
long xy = pu->y;
pu->x = xy;
return *px;
}
int main ()
{
union u u;
if (test (&u.x, &u.y, &u) != 1)
__builtin_abort ();
return 0;
}
is miscompiled at -O2+ as FRE removes the seemingly redundant store to
pu->x but that's needed to make the read via *px pick up the value stored
via *py = 1 rather than (correctly) disambiguating against that and
running into *px = 0.
