https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92152
--- Comment #16 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jan Hubicka from comment #15)
> The following testcase:
> 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;
> }
>
> is misoptimized since GCC 4.6
That is PR93946
