[Bug tree-optimization/55334] mgrid regression (ipa-cp disables vectorization)

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55334

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-11-16 13:29:05 UTC ---
Ah, on the #c5 testcase the problem seems to be const float * vs. float *,

  /* If the references do not access the same object, we do not know
     whether they alias or not.  */
  if (!operand_equal_p (DR_BASE_OBJECT (a), DR_BASE_OBJECT (b), 0))
    {
      DDR_ARE_DEPENDENT (res) = chrec_dont_know;
      return res;
    }

operand_equal_p here fails because, while both base objects are MEM_REFs and
operand_equal_p (TREE_OPERAND (DR_BASE_OBJECT (a), 0), TREE_OPERAND
(DR_BASE_OBJECT (b), 0), 0) is true, the second operand of one MEM_REF is
const float *, while on the other MEM_REF it is float *, and operand_equal_p
for that tests:
...
2570  && (TYPE_MAIN_VARIANT (TREE_TYPE (TREE_OPERAND (arg0, 1)))
2571      == TYPE_MAIN_VARIANT (TREE_TYPE (TREE_OPERAND (arg1, 1))))
2572  && OP_SAME (0) && OP_SAME (1));
and the TYPE_MAIN_VARIANT check fails.  In this case I believe we don't care
whether it points to const float or float.  Not sure if we should change
operand_equal_p to try harder if TYPE_MAIN_VARIANT of the two types isn't
equal,
but TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (TREE_OPERAND (argX, 1))))
is equal, and both pointers have the same deref alias set, or perhaps just
change the above spot to try harder on MEM_REFs if it failed.