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...
