[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_castFoo *(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

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

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

   What|Removed |Added

 CC||hubicka at gcc dot gnu dot
   ||org, jamborm at gcc dot gnu
   ||dot org
   Target Milestone|--- |4.6.0


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

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

[hjl dot tools at gmail dot com]

--- Comment #1 from hjl dot tools at gmail dot com  2010-09-20 15:27 ---
It is caused by revision 161655:

http://gcc.gnu.org/ml/gcc-cvs/2010-07/msg6.html


-- 

hjl dot tools at gmail dot com changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
 Ever Confirmed|0   |1
   Last reconfirmed|-00-00 00:00:00 |2010-09-20 15:27:10
   date||


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

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

[rguenth at gcc dot gnu dot org]

--- Comment #2 from rguenth at gcc dot gnu dot org  2010-09-20 15:46 ---
Of course it is ;)  Before pointer-conversions became useless we didn't
propagate the invariant address into the OBJ_TYPE_REF expression.

We still have useful function-pointer conversions as well, because
dropping them would wreck CALL_EXPRs, too (we need to preserve the
original function type, similar to the alias-type on MEM_REFs).
I suppose we could do the same for OBJ_TYPE_REFs that I plan(ned) for
CALL_EXPRs - store the pointed-to type via a MEM_REF - thus a
dereferenced address.

You'd then have

  CALL_EXPR (MEM [fnptr], args ...)
  OBJ_TYPE_REF (MEM [fnptr], MEM [objptr], index)

where both TREE_TYPE of the function and the object are kept like the
FE specified them.


-- 


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