Change the way we split stores in BB vectorization

The following fixes missed optimizations due to the strange way we
split stores in BB vectorization.  The solution is to split at
the failure boundary and not re-align that to the initial piece
chosen vector size.  Also re-analyze any larger matching rest.

2020-10-28  Richard Biener  <rguenther@suse.de>

	* tree-vect-slp.c (vect_build_slp_instance): Split the store
	group at the failure boundary and also re-analyze a large enough
	matching rest.

	* gcc.dg/vect/bb-slp-68.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-68.c b/gcc/testsuite/gcc.dg/vect/bb-slp-68.c
new file mode 100644 (file)
index 0000000..8718031
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-68.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_double } */
+/* { dg-additional-options "-mavx" { target avx } } */
+
+double x[10], y[6], z[4];
+
+void foo ()
+{
+  x[0] = y[0];
+  x[1] = y[1];
+  x[2] = y[2];
+  x[3] = y[3];
+  x[4] = y[4];
+  x[5] = y[5];
+  x[6] = z[0] + 1.;
+  x[7] = z[1] + 1.;
+  x[8] = z[2] + 1.;
+  x[9] = z[3] + 1.;
+}
+
+/* We want to have the store group split into 4, 2, 4 when using 32byte vectors.  */
+/* { dg-final { scan-tree-dump-not "from scalars" "slp2" } } */

diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 470b67d76b526b0296226cb8d245edf464c3d640..50a2d37eb254c02e788ded0435f00ec0620302d1 100644 (file)
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -2412,15 +2412,21 @@ vect_build_slp_instance (vec_info *vinfo,
                                                               group1_size);
              bool res = vect_analyze_slp_instance (vinfo, bst_map, stmt_info,
                                                    max_tree_size);
-             /* If the first non-match was in the middle of a vector,
-                skip the rest of that vector.  Do not bother to re-analyze
-                single stmt groups.  */
-             if (group1_size < i)
+             /* Split the rest at the failure point and possibly
+                re-analyze the remaining matching part if it has
+                at least two lanes.  */
+             if (group1_size < i
+                 && (i + 1 < group_size
+                     || i - group1_size > 1))
                {
-                 i = group1_size + const_nunits;
-                 if (i + 1 < group_size)
-                   rest = vect_split_slp_store_group (rest, const_nunits);
+                 stmt_vec_info rest2 = rest;
+                 rest = vect_split_slp_store_group (rest, i - group1_size);
+                 if (i - group1_size > 1)
+                   res |= vect_analyze_slp_instance (vinfo, bst_map,
+                                                     rest2, max_tree_size);
                }
+             /* Re-analyze the non-matching tail if it has at least
+                two lanes.  */
              if (i + 1 < group_size)
                res |= vect_analyze_slp_instance (vinfo, bst_map,
                                                  rest, max_tree_size);