[Bug ipa/59831] [4.9 Regression] ice in cgraph_speculative_call_info with -O3

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59831

--- Comment #4 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Created attachment 31996
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31996&action=edit
Proposed fix

OK, here we have
A& C::operator[](int) (struct C * const this, int p1)
{        
  int (*__vtbl_ptr_type) () * _3;
  int (*__vtbl_ptr_type) () _4;
  struct A & _8;

  <bb 2>:
  _3 = this_2(D)->_vptr.C;
  _4 = *_3;
  OBJ_TYPE_REF(_4;(struct C)this_2(D)->0) (this_2(D));
  _8 = B::operator[] (this_2(D), p1_6(D)); 
  return _8;

}

that is devirtualizable in the context of:

void sort(C&, C&) (struct C & p1, struct C & p2)
{
  <bb 2>:

  <bb 3>:
  C::operator[] (p2_3(D), 0);
  C::operator[] (p1_5(D), 0);
  C::operator[] (p2_3(D), 0);

  <bb 4>:
  goto <bb 3>;

}

used exclusively from:

void sort(C&, C&) (struct C & p1, struct C & p2)
{
  <bb 2>:

  <bb 3>:
  C::operator[] (p2_3(D), 0);
  C::operator[] (p1_5(D), 0);
  C::operator[] (p2_3(D), 0);

  <bb 4>:
  goto <bb 3>;

}

ipa-cp does:

Evaluating opportunities for void sort(C&, C&)/10.
 - Creating a specialized node of void sort(C&, C&)/10 for all known contexts.
    replacing param #1 p2 with const &b
                Accounting size:2.00, time:0.00 on new predicate:(not inlined)
     the new node is void sort.constprop(C&)/30.
     Aggregate replacements: 0[0]=&MEM[(void *)&_ZTV1C + 16B]

Evaluating opportunities for void sort(C&, C&)/10.
  Marking node as dead: void sort(C&, C&)/10.

Evaluating opportunities for A& C::operator[](int)/1.
 - considering value &b for param #0 this (caller_count: 3)
     good_cloning_opportunity_p (time: 1, size: 17, freq_sum: 201000) ->
evaluation: 11823, threshold: 500
  Creating a specialized node of A& C::operator[](int)/1.
    adding an extra known scalar value 0 for param #1 p1
    replacing param #0 this with const &b
    replacing param #1 p1 with const 0
                Accounting size:1.00, time:1.00 on predicate:(true)
                Accounting size:3.00, time:2.00 on new predicate:(not inlined)
                Accounting size:0.50, time:0.50 on new predicate:(op0[ref
offset: 0] changed) && (not inlined)
                Accounting size:0.50, time:0.50 on new predicate:(op0[ref
offset: 0] changed)
     the new node is A& C::operator[].constprop()/31.

Evaluating opportunities for A& C::operator[](int)/1.

Evaluating opportunities for virtual int C::m_fn1()/0.
 - considering value &b for param #0 this (caller_count: 1)
     good_cloning_opportunity_p (time: 2, size: 3, freq_sum: 800) ->
evaluation: 533, threshold: 500
  Creating a specialized node of virtual int C::m_fn1()/0.
    replacing param #0 this with const &b
                Accounting size:3.00, time:2.00 on new predicate:(not inlined)
     the new node is int C::m_fn1.constprop()/32.

Evaluating opportunities for virtual int C::m_fn1()/0.

For some reason it gets right the aggregate value, but misses the
devirtualization.

devirtualization_time_bonus properly anticipates the devirtualization to
happen.

The problem is that later we replace BINFO by a constant.  This is going throug
gimple_extract_binfo_from_cst that is known to be buggy.

This patch removes it and uses equivalent functionality of ipa-devirt.