[Bug middle-end/49628] [4.7 Regression] 447.dealII in SPEC CPU 2006 failed to build

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49628

Richard Guenther <rguenth at gcc dot gnu.org> changed:

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

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-07-04 15:06:51 UTC ---
Vectorizing the loop

<bb 8>:
  # __position_11 = PHI <__position_34(9), __position$_M_current_15(7)>
  D.2964_46 = __x_copy.values[0];
  __position_11->values[0] = D.2964_46;
  D.2964_51 = __x_copy.values[1];
  __position_11->values[1] = D.2964_51;
  D.2964_56 = __x_copy.values[2];
  __position_11->values[2] = D.2964_56;
  __position_34 = __position_11 + 24;
  if (D.2961_29 != __position_34)
    goto <bb 9>;
  else
    goto <bb 10>;

<bb 9>:
  goto <bb 8>;

I wonder where we are supposed to set GROUP_SIZE here and how it possibly
can connect to my change ... ah, the invariant loads from __x_copy.values
no longer will inhibit vectorization early.  The group is now indeed
the __x_copy.values[] loads.

The following fixes it (or rather, avoids looking at this group):

Index: gcc/tree-vect-data-refs.c
===================================================================
--- gcc/tree-vect-data-refs.c   (revision 175802)
+++ gcc/tree-vect-data-refs.c   (working copy)
@@ -1495,12 +1495,19 @@ vect_enhance_data_refs_alignment (loop_v
           && GROUP_FIRST_ELEMENT (stmt_info) != stmt)
         continue;

+      /* For invariant accesses there is nothing to enhance.  */
+      if (integer_zerop (DR_STEP (dr)))
+       continue;
+
       supportable_dr_alignment = vect_supportable_dr_alignment (dr, true);
       do_peeling = vector_alignment_reachable_p (dr);
       if (do_peeling)