http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49771
Ira Rosen <irar at il dot ibm.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |irar at il dot ibm.com
--- Comment #3 from Ira Rosen <irar at il dot ibm.com> 2011-07-18 15:55:49 UTC
---
(In reply to comment #2)
> That commit looks bogus, the change it made is:
> # ivtmp.37_45 = PHI <ivtmp.37_43(6), ivtmp.37_46(2)>
> vect_pa.7_44 = (vector(4) int *) ivtmp.37_45;
> - D.2731_1 = vect_pa.7_44 < &a;
> - D.2733_14 = vect_pa.7_44 > &a[1000];
> + D.2731_1 = vect_pa.7_44 <= &a;
> + D.2733_14 = vect_pa.7_44 >= &a[1000];
> D.2734_23 = D.2733_14 | D.2731_1;
> if (D.2734_23 != 0)
>
> vect_pa.7_44 is the pointer that goes from &a[0] to &a[999]. While in this
> case it is fine to change the second > to >=, changing the first one is of
> course wrong, because in the first iteration it will overlap, yet this test
> will say that they do not.
> What is weird is that segment_length_a in vect_create_cond_for_alias_checks
> is 0 instead of 4 (sizeof (int)) I'd expect, while segment_length_b is the
> expected 4000. Apparently DR_STEP in the first case is 0.
The step of a[i] is indeed 0 in the j loop.
> I wonder whether
> the change of the comparison should only be done if one segment length is
> empty
> (and thus clearly doesn't include all bytes of the read/store), or something
> similar.
We can create a segment of length sizeof(type) for the zero step case:
Index: tree-vect-loop-manip.c
===================================================================
--- tree-vect-loop-manip.c (revision 176389)
+++ tree-vect-loop-manip.c (working copy)
@@ -2356,9 +2356,14 @@ static tree
vect_vfa_segment_size (struct data_reference *dr, tree length_factor)
{
tree segment_length;
- segment_length = size_binop (MULT_EXPR,
- fold_convert (sizetype, DR_STEP (dr)),
- fold_convert (sizetype, length_factor));
+
+ if (!compare_tree_int (DR_STEP (dr), 0))
+ segment_length = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr)));
+ else
+ segment_length = size_binop (MULT_EXPR,
+ fold_convert (sizetype, DR_STEP (dr)),
+ fold_convert (sizetype, length_factor));
+
if (vect_supportable_dr_alignment (dr, false)
== dr_explicit_realign_optimized)
{
(tested only with the vectorizer testsuite).
Ira
