[PATCH] Simple fix to enhance outer-loop vectorization.

[Yuri Rumyantsev <ysrumyan@gmail.com>]

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Hi All,

Here is a simple patch which removes restriction on outer-loop
vectorization -  allow references in inner-loop with zero step. This
case was found in one important benchmark.

Bootstrap and regression testing did not show any new failures.
Is it OK for trunk.

ChangeLog:
2015-05-28  Yuri Rumyantsev  <ysrumyan@gmail.com>

* tree-vect-data-refs.c (vect_analyze_data_ref_access): Allow
consecutive accesses within outer-loop vectorization for references
with zero step in inner-loop.

gcc/testsuite/ChangeLog:
* gcc.dg/vect/fast-math-vect-outer-1.c: New test.

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Index: testsuite/gcc.dg/vect/fast-math-vect-outer-1.c
===================================================================
--- testsuite/gcc.dg/vect/fast-math-vect-outer-1.c	(revision 0)
+++ testsuite/gcc.dg/vect/fast-math-vect-outer-1.c	(working copy)
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_float } */
+/* { dg-require-effective-target vect_simd_clones } */
+/* { dg-additional-options "-fopenmp-simd" } */
+
+extern float *px, *py, *tx, *ty, *x, *y;
+#define N 64
+static void   inline bar(float cx, float cy, float *vx, float *vy)
+{
+  int j;
+  for (j = 0; j < N; ++j)
+    {
+        const float dx  = cx - px[j];
+        const float dy  = cy - py[j];
+        *vx  += dx * tx[j];
+        *vy  -= dy * ty[j];
+    }
+}
+
+void foo ()
+{
+  int i;
+
+#pragma omp simd
+  for (i = 0; i < N; i++)
+    bar(px[i],py[i],x+i,y+i);
+}
+
+/* { dg-final { scan-tree-dump "OUTER LOOP VECTORIZED" "vect" } } */
+/* { dg-final { cleanup-tree-dump "vect" } } */
Index: tree-vect-data-refs.c
===================================================================
--- tree-vect-data-refs.c	(revision 223653)
+++ tree-vect-data-refs.c	(working copy)
@@ -2261,7 +2261,6 @@
   return true;
 }
 
-
 /* Analyze the access pattern of the data-reference DR.
    In case of non-consecutive accesses call vect_analyze_group_access() to
    analyze groups of accesses.  */
@@ -2291,14 +2290,8 @@
   if (loop_vinfo && integer_zerop (step))
     {
       GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt)) = NULL;
-      if (nested_in_vect_loop_p (loop, stmt))
-	{
-	  if (dump_enabled_p ())
-	    dump_printf_loc (MSG_NOTE, vect_location,
-			     "zero step in inner loop of nest\n");
-	  return false;
-	}
-      return DR_IS_READ (dr);
+      if (!nested_in_vect_loop_p (loop, stmt))
+	return DR_IS_READ (dr);
     }
 
   if (loop && nested_in_vect_loop_p (loop, stmt))