[Bug tree-optimization/45791] Missed devirtualization

[hubicka at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45791

--- Comment #5 from Jan Hubicka <hubicka at gcc dot gnu.org> 2010-09-25 
22:17:41 UTC ---
Another testcase where we devirtualize via folding is:
// { dg-do assemble  }
// { dg-options "-g -O2" }

//  Copyright (C) 1999 Free Software Foundation, Inc.
//  Contributed by Nathan Sidwell 21 Nov 1999 <nat...@acm.org>

// This causes assember relocation errors

struct X
{
  virtual ~X () {}
};

struct Y
{
  Y (){};
};

void foo ()
{
  X *x = new X;
  x->~X ();
  Y ys[2];
}

compiled with -O2 we get
  x_3 = operator new (8);
  # DEBUG this => x_3
  x_3->_vptr.X = &_ZTV1X[2];
  # DEBUG x => x_3 
  D.2142_7 = (int (*__vtbl_ptr_type) (void)) __comp_dtor ;
  OBJ_TYPE_REF(D.2142_7;x_3->0) (x_3);
that gets folded only in ccp3. We need FRE to fold:
  x_3->_vptr.X = &_ZTV1X[2];
  # DEBUG x => x_3
  D.2141_6 = &_ZTV1X[2];
  D.2142_7 = *D.2141_6;
  OBJ_TYPE_REF(D.2142_7;x_3->0) (x_3);
into
  x_3 = operator new (8);
  # DEBUG this => x_3
  x_3->_vptr.X = &_ZTV1X[2];
  # DEBUG x => x_3
  D.2141_6 = x_3->_vptr.X;
  D.2142_7 = *D.2141_6;
  OBJ_TYPE_REF(D.2142_7;x_3->0) (x_3);