PR middle-end/35535 part I

[Jan Hubicka]

Hi,
PR 35545 has trivial testcase of feedback directed devirtualization:
int main()
{
 int i;
  A* ap = 0;

  for (i = 0; i < 10000; i++)
  {
     if (i%7==0)
        ap = new A();
     else
        ap = new B();
    ap->foo();
    ....

Here we should devirtualize since B's foo is dominating target and we correctly 
do so.
We however do more, we trace the code into:
  for (i = 0; i < 10000; i++)
  {
     if (i%7==0)
        {
          ap = new A();
          ap->foo();
        }
     else
        {
          ap = new B();
          ap->foo();
        }
that should allow us to devirtualize completely.  Instead of doing that we get 
stuck
on stupid
  <bb 5>:
  ap_8 = operator new (16);
  ap_8->i = 0;
  ap_8->_vptr.A = &MEM[(void *)&_ZTV1A + 16B];
  _19 = foo;
  PROF_26 = [obj_type_ref] OBJ_TYPE_REF(_19;(struct A)ap_8->0);
  if (PROF_26 == foo)
    goto <bb 8>;
  else
    goto <bb 7>;

  <bb 6>:
  ap_13 = operator new (16);
  MEM[(struct B *)ap_13].D.2237.i = 0;
  MEM[(struct B *)ap_13].b = 0;
  MEM[(struct B *)ap_13].D.2237._vptr.A = &MEM[(void *)&_ZTV1B + 16B];
  _1 = foo;
  PROF_30 = [obj_type_ref] OBJ_TYPE_REF(_1;(struct A)ap_13->0);
  if (PROF_30 == foo)
    goto <bb 8>;
  else
    goto <bb 7>;

There are several reasons for it
 1) most of our passes do not expect OBJ_TYPE_REF in arguments and cowardly
    consider it volatile
 2) tracer happens too late and there is no VRP pass to cleanup afterwards
 3) folding machinery expect OBJ_TYPE_REF to be only in argument.

After some consideration I decided to not update gimple_ic to remove 
OBJ_TYPE_REF,
since this is a perfect example where OBJ_TYPE_REF may be useful after inlining:
in a more complex cases a type based devirt may kick in and save a day even
late after unrolling/tracing and other code specialization.

This is first trivial patch to make VRP behaving correctly.
Bootstrapped/regtested x86_64-linux OK?

        * tree-vrp.c (extract_range_from_unary_expr_1): Add OBJ_TYPE_REF
Index: tree-vrp.c
===================================================================
--- tree-vrp.c  (revision 206040)
+++ tree-vrp.c  (working copy)
@@ -3202,9 +3202,9 @@ extract_range_from_unary_expr_1 (value_r
     }
 
   /* Handle operations that we express in terms of others.  */
-  if (code == PAREN_EXPR)
+  if (code == PAREN_EXPR || code == OBJ_TYPE_REF)
     {
-      /* PAREN_EXPR is a simple copy.  */
+      /* PAREN_EXPR and OBJ_TYPE_REF are simple copies.  */
       copy_value_range (vr, &vr0);
       return;
     }