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

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |redi at gcc dot gnu.org

--- Comment #20 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I believe this all boils down to:
inline void* operator new(__SIZE_TYPE__, void *p) { return p; }
struct A { A (float x) : f (x) {} float f; };
struct B
{
  int x;
  union U
  {
    int a;
    char b[sizeof (float)];
  } u;
  int y;
};

__attribute__((noinline, noclone)) void
bar (B &x, B &y)
{
  if (x.x != 0 || x.y != 3 || y.x != 0 || y.y != 3)
    __builtin_abort ();
  float f;
  __builtin_memcpy (&f, x.u.b, sizeof (float));
  if (f != 3.5f)
    __builtin_abort ();
  __builtin_memcpy (&f, y.u.b, sizeof (float));
  if (f != 3.5f)
    __builtin_abort ();
}

__attribute__((noinline, noclone)) 
B *
baz (B &x)
{
  return &x;
}

__attribute__((noinline, noclone)) void
foo (float x)
{
  B b { 0, {}, 3 }, c;
  B *p = baz (b);
  new (b.u.b) A (x);
  c = *p;
  bar (*p, c);
}

int
main ()
{
  foo (3.5f);
}

which fails also on x86_64-linux at -O2.  And that testcase regressed with
r223126.  Now whether this is valid C++, no idea, placement new is messy.