GCC aliasing rules: more aggressive than C99?

[Florian Weimer]

* Joshua Haberman:

> To me this allows the following:
>
>   int i;
>   union u { int x; } *pu = (union u*)&i;
>   printf("%d\n", pu->x);

I think the cast on the secodn line is undefined, not the access on
the third.