[Bug target/79671] [7 Regression] mapnik miscompilation on armv7hl since r235622

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671

--- Comment #38 from Richard Biener <rguenth at gcc dot gnu.org> ---
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.