Limit non-constant step prefetching only to the innermost loops.

2010-06-09  Changpeng Fang  <changpeng.fang@amd.com>

	* tree-ssa-loop-prefetch.c (gather_memory_references_ref):
	Do not the gather memory reference in the outer loop if the step
	is not a constant.

From-SVN: r160515

gcc/ChangeLog

 2010-06-09  Changpeng Fang  <changpeng.fang@amd.com>
 
+	* tree-ssa-loop-prefetch.c (gather_memory_references_ref):
+	Do not the gather memory reference in the outer loop if the step
+	is not a constant.
+
+2010-06-09  Changpeng Fang  <changpeng.fang@amd.com>
+
         * tree-ssa-loop-prefetch.c (PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO) :
         Change the PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO threshold value from
         8 to 4.  Minor change of the related comments.

gcc/tree-ssa-loop-prefetch.c

@@ -513,6 +513,10 @@ gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs,
   if (step == NULL_TREE)
     return false;
 
+  /* Limit non-constant step prefetching only to the innermost loops.  */
+  if (!cst_and_fits_in_hwi (step) && loop->inner != NULL)
+    return false;
+
   /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP
      are integer constants.  */
   agrp = find_or_create_group (refs, base, step);