https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671
--- Comment #41 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #38)
> Simplified testcase for discussion (is not "miscompiled"):
>
> struct S {
> union { int i; } u;
> };
>
> int main()
> {
> S s;
> new (&s.u.i) float (2.0);
> S q = s;
> if (*reinterpret_cast<float *>(&q.u.i) != 2.0)
> abort ();
> }
>
> so you say q = s is valid because the object representation of the union
> is copied. I say after storing 2.0 to s.u.i the access 's' in q = s is
> invalid as you are accessing the stored value (a float) via a glvalue of
> inappropriate type.
I say what's wrong with this testcase is that storing a float in an int field
is undefined.
