tree-optimization/98516 - fix SLP permute opt materialization

When materializing on a VEC_PERM node we have to permute the
incoming vectors, not the outgoing one.

2021-01-05  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/98516
	* tree-vect-slp.c (vect_optimize_slp): Permute the incoming
	lanes when materializing on a VEC_PERM node.
	(vectorizable_slp_permutation): Dump the permute properly.

	* gcc.dg/vect/bb-slp-pr98516-1.c: New testcase.
	* gcc.dg/vect/bb-slp-pr98516-2.c: Likewise.

3 files changed, 70 insertions, 5 deletions

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr98516-1.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr98516-1.c
new file mode 100644
index 0000000..c4c244c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr98516-1.c
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+
+double a[4], b[2];
+
+void __attribute__((noipa))
+foo ()
+{
+  double a0 = a[0];
+  double a1 = a[1];
+  double a2 = a[2];
+  double a3 = a[3];
+  b[0] = a1 - a3;
+  b[1] = a0 + a2;
+}
+
+int main()
+{
+  a[0] = 1.;
+  a[1] = 2.;
+  a[2] = 3.;
+  a[3] = 4.;
+  foo ();
+  if (b[0] != -2 || b[1] != 4)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr98516-2.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr98516-2.c
new file mode 100644
index 0000000..f1a9341
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr98516-2.c
@@ -0,0 +1,36 @@
+/* { dg-do run } */
+
+float a[8], b[4];
+
+void __attribute__((noipa))
+foo ()
+{
+  float a0 = a[0];
+  float a1 = a[1];
+  float a2 = a[2];
+  float a3 = a[3];
+  float a4 = a[4];
+  float a5 = a[5];
+  float a6 = a[6];
+  float a7 = a[7];
+  b[0] = a1 - a5;
+  b[1] = a0 + a4;
+  b[2] = a3 - a7;
+  b[3] = a2 + a6;
+}
+
+int main()
+{
+  a[0] = 1.;
+  a[1] = 2.;
+  a[2] = 3.;
+  a[3] = 4.;
+  a[4] = 5.;
+  a[5] = 6.;
+  a[6] = 7.;
+  a[7] = 8.;
+  foo ();
+  if (b[0] != -4 || b[1] != 6 || b[2] != -4 || b[3] != 10)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 49cb635..c9da845 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -3094,15 +3094,18 @@ vect_optimize_slp (vec_info *vinfo)
 	    ;
 	  else if (SLP_TREE_LANE_PERMUTATION (node).exists ())
 	    {
-	      /* If the node if already a permute node we just need to apply
-		 the permutation to the permute node itself.  */
+	      /* If the node is already a permute node we can apply
+		 the permutation to the lane selection, effectively
+		 materializing it on the incoming vectors.  */
 	      if (dump_enabled_p ())
 		dump_printf_loc (MSG_NOTE, vect_location,
 				 "simplifying permute node %p\n",
 				 node);
 
-	      vect_slp_permute (perms[perm], SLP_TREE_LANE_PERMUTATION (node),
-				true);
+	      for (unsigned k = 0;
+		   k < SLP_TREE_LANE_PERMUTATION (node).length (); ++k)
+		SLP_TREE_LANE_PERMUTATION (node)[k].second
+		  = perms[perm][SLP_TREE_LANE_PERMUTATION (node)[k].second];
 	    }
 	  else
 	    {
@@ -5554,7 +5557,7 @@ vectorizable_slp_permutation (vec_info *vinfo, gimple_stmt_iterator *gsi,
 	    dump_printf (MSG_NOTE, ",");
 	  dump_printf (MSG_NOTE, " vops%u[%u][%u]",
 		       vperm[i].first.first, vperm[i].first.second,
-		       vperm[i].first.second);
+		       vperm[i].second);
 	}
       dump_printf (MSG_NOTE, "\n");
     }