[Bug tree-optimization/47316] devirtualize calls to virtual methods that are never further overriden

["hubicka at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47316

--- Comment #5 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
The testcase provided now generates:
void foo(A*) (struct A * a)
{
  int (*__vtbl_ptr_type) () * _3;
  int (*__vtbl_ptr_type) () _4;
  int i.0_6;
  int i.1_7;
  void * PROF_9;
  int i.2_11;
  int i.3_12;

  <bb 2>:
  _3 = a_2(D)->_vptr.A;
  _4 = *_3;
  PROF_9 = [obj_type_ref] OBJ_TYPE_REF(_4;(struct A)a_2(D)->0);
  if (PROF_9 == f)
    goto <bb 3>;
  else
    goto <bb 4>;

  <bb 3>:
  i.2_11 ={v} i;
  i.3_12 = i.2_11 + -1;
  i ={v} i.3_12;
  goto <bb 5>;

  <bb 4>:
  OBJ_TYPE_REF(_4;(struct A)a_2(D)->0) (a_2(D));

  <bb 5>:
  i.0_6 ={v} i;
  i.1_7 = i.0_6 + -1;
  i ={v} i.1_7;
  return;

}

where
  PROF_9 = [obj_type_ref] OBJ_TYPE_REF(_4;(struct A)a_2(D)->0);
  if (PROF_9 == f)
    goto <bb 3>;
  else
    goto <bb 4>;

looking at it, I am not sure if we want to keep OBJ_TYPE_REF here.
It is generally ignored except for the call statements themselves.
So either we want to drop it or extend type devirtualization in the folding
machinery to work for non-calls, too.