[Bug tree-optimization/45685] [4.6 Regression] missed conditional move opportunity in loop

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45685

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
          Component|rtl-optimization            |tree-optimization
         AssignedTo|ebotcazou at gcc dot        |unassigned at gcc dot
                   |gnu.org                     |gnu.org

--- Comment #12 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2010-11-24 
18:31:18 UTC ---
Clearly ifcvt.c is overwhelmed here and somewhat shoots itself in the foot.
The noce_emit_store_flag transformation in pass n creates insns that block the
cond_move_process_if_block conversion in pass n+1 because the new insns are
(rightfully) deemed unsuitable.  Quite tricky to overcome in my opinion.

As Jakub said, creating 3 almost identical cond_expr:

  prephitmp.9_39 = [cond_expr] D.2693_11 <= 0 ? -1 : 1;
  prephitmp.10_40 = [cond_expr] D.2693_11 <= 0 ? 1 : -1;
  prephitmp.11_41 = [cond_expr] D.2693_11 <= 0 ? 1 : -1;

for only one in the source code:

      int val = (products[i] > 0) ? 1 : -1;

is simply unreasonable.  Thus recategorizing.