[Bug tree-optimization/47413] Constant Propagation and Virtual Function Tables

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47413

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org

--- Comment #2 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Current mainline gets pretty close:
;; Function int f1337(obj*) (_ZL5f1337P3obj, funcdef_no=19, decl_uid=3418,
cgraph_uid=19, symbol_order=19)

int f1337(obj*) (struct obj * obj)
{
  <bb 2>:
  return 1337;

}



;; Function int main() (main, funcdef_no=22, decl_uid=3427, cgraph_uid=22,
symbol_order=22) (executed once)

Removing basic block 5
int main() ()
{
  struct obj * obj;
  int _1;
  int _10;

  <bb 2>:
  obj_7 = malloc (8);
  if (obj_7 == 0B)
    goto <bb 4>;
  else
    goto <bb 3>;

  <bb 3>:
  obj_7->vtab = &vtab1337;
  _10 = f1337 (obj_7);
  printf ("%d\n", _10);

  <bb 4>:
  # _1 = PHI <0(2), 1(3)>
  return _1;

}

So we are down to one missing inline. After FRE we get:

  <bb 2>:
  obj_13 = malloc (8);
  if (obj_13 == 0B)
    goto <bb 4>;
  else
    goto <bb 3>;

  <bb 3>:
  obj_13->vtab = &vtab1337;

  <bb 4>:
  # _14 = PHI <0B(2), obj_13(3)>
  if (_14 == 0B)
    goto <bb 6>;
  else
    goto <bb 5>;

  <bb 5>:
  _4 = _14->vtab;
  _15 = _4->f;
  _16 = _15 (_14);
  printf ("%d\n", _16);


So purely local problem. I suppose FRE could propagate through by knowing that
on the other path program with segfault?