tree-vect-slp.c (vect_bb_slp_scalar_cost): Properly confine life to the active subtree.

2017-08-29  Richard Biener  <rguenther@suse.de>
	Dominik Infuehr <dominik.infuehr@theobroma-systems.com>

	* tree-vect-slp.c (vect_bb_slp_scalar_cost): Properly confine
	life to the active subtree.

	* gcc.dg/vect/costmodel/x86_64/costmodel-vect-slp.c: New testcase.

Co-Authored-By: Dominik Infuehr <dominik.infuehr@theobroma-systems.com>

From-SVN: r251398

gcc/ChangeLog

+2017-08-29  Richard Biener  <rguenther@suse.de>
+	Dominik Infuehr <dominik.infuehr@theobroma-systems.com>
+
+	* tree-vect-slp.c (vect_bb_slp_scalar_cost): Properly confine
+	life to the active subtree.
+
 2017-08-28  Jeff Law  <law@redhat.com>
 
 	* tree-ssa-dom.c (edge_info::record_simple_equiv): Call

gcc/testsuite/ChangeLog

+2017-08-29  Richard Biener  <rguenther@suse.de>
+	Dominik Infuehr <dominik.infuehr@theobroma-systems.com>
+
+	* gcc.dg/vect/costmodel/x86_64/costmodel-vect-slp.c: New testcase.
+
 2017-08-28  Jeff Law  <law@redhat.com>
 
 	* gcc.dg/torture/pr57214.c: Fix type of loop counter.

gcc/testsuite/gcc.dg/vect/costmodel/x86_64/costmodel-vect-slp.c

+/* { dg-do compile } */
+/* { dg-additional-options "-fdump-tree-slp-details" } */
+
+#define N 4
+
+int s1[N], s2[N], s3[N];
+void escape(int, int, int, int);
+
+void
+foo ()
+{
+  int t1, t2, t3, t4;
+
+  t1 = s1[0] + s2[0] + s3[0];
+  t2 = s1[1] + s2[1] + s3[1];
+  t3 = s1[2] + s2[2] + s3[2];
+  t4 = s1[3] + s2[3] + s3[3];
+
+  s3[0] = t1 - s1[0] * s2[0];
+  s3[1] = t2 - s1[1] * s2[1];
+  s3[2] = t3 - s1[2] * s2[2];
+  s3[3] = t4 - s1[3] * s2[3];
+
+  escape (t1, t2, t3, t4);
+}
+
+/* { dg-final { scan-tree-dump-not "vectorization is not profitable" "slp2" } } */
+/* { dg-final { scan-tree-dump "basic block vectorized" "slp2" } } */

gcc/tree-vect-slp.c

@@ -2690,9 +2690,18 @@ vect_bb_slp_scalar_cost (basic_block bb,
       scalar_cost += stmt_cost;
     }
 
+  auto_vec<bool, 20> subtree_life;
   FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
-    if (SLP_TREE_DEF_TYPE (child) == vect_internal_def)
-      scalar_cost += vect_bb_slp_scalar_cost (bb, child, life);
+    {
+      if (SLP_TREE_DEF_TYPE (child) == vect_internal_def)
+	{
+	  /* Do not directly pass LIFE to the recursive call, copy it to
+	     confine changes in the callee to the current child/subtree.  */
+	  subtree_life.safe_splice (*life);
+	  scalar_cost += vect_bb_slp_scalar_cost (bb, child, &subtree_life);
+	  subtree_life.truncate (0);
+	}
+    }
 
   return scalar_cost;
 }