[Bug tree-optimization/93946] New: Bogus redundant store removal

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93946

            Bug ID: 93946
           Summary: Bogus redundant store removal
           Product: gcc
           Version: 10.0
            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 long i; long f; };
struct a {union U u;};
struct aa {struct a a;};
struct b {union U u;};
struct bb {struct b b;};

long
foo (struct bb *bv, void *ptr)
{
  struct aa *a = ptr;
  struct bb *b = ptr;
  bv->b.u.f = 1;
  a->a.u.i = 0;
  b->b.u.f = 0;
  return bv->b.u.f;
}

int
main ()
{
  union C {struct aa aa; struct bb bb;} v;
  if (foo (&v.bb, &v) != 0)
    __builtin_abort ();
  return 0;
}


we treat b->b.u.f = 0 as redundant because the alias-set of that and the
a->a.u.i = 0 store are actually the same.