[Bug tree-optimization/45734] [4.6 Regression] Devirtualization results in wrong-code

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2010-09-21 10:12 -------
The following is miscompiled since ever (and also ICC miscompiles it), so
I'm not sure if it is valid to use 'f' to refer to the Bar object.

namespace std {
  typedef __SIZE_TYPE__ size_t;
}
inline void* operator new(std::size_t, void* __p) throw() {
  return __p;
}
extern "C" void abort (void);
class Foo {
public:
    virtual void test (void) { abort (); }
};
class Bar : public Foo {
public:
    virtual void test (void) { }
};
int main()
{
  Foo f;
  new (&f) Bar();
  f.test();
  return 0;
}

A variant with using a pointer of type Bar * like

int main()
{
  Foo f;
  static_cast<Foo *>(new (&f) Bar())->test();
  return 0;
}

only breaks on recent trunk.

int main()
{
  Foo f;
  new (&f) Bar();
  (&f)->test();
  return 0;
}

also breaks always.  While

int main()
{
  Foo f, *p;
  p = new (&f) Bar();
  p->test();
  return 0;
}

works.

int main()
{
  Foo f, *p;
  new (&f) Bar();
  ((Foo *)(void *)&f)->test();
  return 0;
}

also works.

Fun.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45734