[Bug tree-optimization/92765] [10 Regression] Wrong code caused by folding of -Wstring-compare since r276773

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92765

--- Comment #18 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Also, note that union doesn't have to be visible on the access path, e.g.
union U { struct S { char a[2]; char b[2]; char c[2]; } s; struct T { char
d[6]; } t; } u;

__attribute__((noipa)) void
bar (char *p)
{
  if (__builtin_strcmp (p, "a") != 0)
    __builtin_abort ();
  __builtin_strcpy (u.t.d, "abcde");
}

__attribute__((noipa)) void
foo (void *x)
{
  struct S *s = (struct S *) x;
  char *p = (char *) &s->b;
  bar (p);
  struct T *t = (struct T *) x;
  if (__builtin_strcmp (&t->d[2], "cde"))
    __builtin_abort ();
}

int
main ()
{
  __builtin_strcpy (u.s.b, "a");
  foo (&u);
  return 0;
}

is miscompiled too, there is no type punning through union, only active union
member is ever read...