tree-optimization/93428 - avoid load permutation vector clobbering

With SLP now being a graph with shared nodes across instances we have
to make sure to compute the load permutation of nodes once, not
overwriting the result of earlier analysis.

2020-01-28  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/93428
	* tree-vect-slp.c (vect_build_slp_tree_2): Compute the load
	permutation when the load node is created.
	(vect_analyze_slp_instance): Re-use it here.

	* gcc.dg/torture/pr93428.c: New testcase.

gcc/ChangeLog

+2020-01-29  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/93428
+	* tree-vect-slp.c (vect_build_slp_tree_2): Compute the load
+	permutation when the load node is created.
+	(vect_analyze_slp_instance): Re-use it here.
+
 2020-01-28  Jan Hubicka  <hubicka@ucw.cz>
 
 	* ipa-prop.c (update_indirect_edges_after_inlining): Fix warning.

gcc/testsuite/ChangeLog

+2020-01-29  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/93428
+	* gcc.dg/torture/pr93428.c: New testcase.
+
 2020-01-28  Martin Sebor  <msebor@redhat.com>
 
 	PR middle-end/93437

gcc/testsuite/gcc.dg/torture/pr93428.c

+/* { dg-do compile } */
+/* { dg-additional-options "-ftree-slp-vectorize" } */
+
+int ai[2][8];
+void bar (int *);
+void
+br (void)
+{
+  int qp[9];
+  bar (qp);
+  ai[0][0] = qp[0] + qp[1] + 1 >> 1;
+  ai[0][1] = qp[1] + qp[2] + 1 >> 1;
+  ai[0][2] = qp[2] + qp[3] + 1 >> 1;
+  ai[0][3] = qp[3] + qp[4] + 1 >> 1;
+  ai[0][4] = qp[4] + qp[5] + 1 >> 1;
+  ai[0][5] = qp[5] + qp[6] + 1 >> 1;
+  ai[0][6] = qp[6] + qp[7] + 1 >> 1;
+  ai[0][7] = qp[7] + qp[8] + 1 >> 1;
+  ai[1][0] = qp[0] + qp[1] + 2 * qp[0] + 1 >> 2;
+  ai[1][1] = qp[0] + qp[2] + 2 * qp[1] + 1 >> 2;
+  ai[1][2] = qp[1] + qp[3] + 2 * qp[2] + 1 >> 2;
+  ai[1][3] = qp[2] + qp[4] + 2 * qp[3] + 1 >> 2;
+  ai[1][4] = qp[3] + qp[5] + 2 * qp[4] + 1 >> 2;
+  ai[1][5] = qp[4] + qp[6] + 2 * qp[5] + 1 >> 2;
+  ai[1][6] = qp[5] + qp[7] + 2 * qp[6] + 1 >> 2;
+  ai[1][7] = qp[6] + qp[8] + 2 * qp[7] + 1 >> 2;
+}

gcc/tree-vect-slp.c

@@ -1353,6 +1353,23 @@ vect_build_slp_tree_2 (vec_info *vinfo,
 	  *max_nunits = this_max_nunits;
 	  (*tree_size)++;
 	  node = vect_create_new_slp_node (stmts);
+	  /* And compute the load permutation.  Whether it is actually
+	     a permutation depends on the unrolling factor which is
+	     decided later.  */
+	  vec<unsigned> load_permutation;
+	  int j;
+	  stmt_vec_info load_info;
+	  load_permutation.create (group_size);
+	  stmt_vec_info first_stmt_info
+	    = DR_GROUP_FIRST_ELEMENT (SLP_TREE_SCALAR_STMTS (node)[0]);
+	  FOR_EACH_VEC_ELT (SLP_TREE_SCALAR_STMTS (node), j, load_info)
+	    {
+	      int load_place = vect_get_place_in_interleaving_chain
+		  (load_info, first_stmt_info);
+	      gcc_assert (load_place != -1);
+	      load_permutation.safe_push (load_place);
+	    }
+	  SLP_TREE_LOAD_PERMUTATION (node) = load_permutation;
 	  return node;
 	}
     }
@@ -2254,22 +2271,19 @@ vect_analyze_slp_instance (vec_info *vinfo,
 	  bool loads_permuted = false;
 	  FOR_EACH_VEC_ELT (SLP_INSTANCE_LOADS (new_instance), i, load_node)
 	    {
-	      vec<unsigned> load_permutation;
-	      int j;
+	      if (!SLP_TREE_LOAD_PERMUTATION (load_node).exists ())
+		continue;
+	      unsigned j;
 	      stmt_vec_info load_info;
 	      bool this_load_permuted = false;
-	      load_permutation.create (group_size);
 	      stmt_vec_info first_stmt_info = DR_GROUP_FIRST_ELEMENT
 		  (SLP_TREE_SCALAR_STMTS (load_node)[0]);
 	      FOR_EACH_VEC_ELT (SLP_TREE_SCALAR_STMTS (load_node), j, load_info)
-		{
-		  int load_place = vect_get_place_in_interleaving_chain
-		      (load_info, first_stmt_info);
-		  gcc_assert (load_place != -1);
-		  if (load_place != j)
+		if (SLP_TREE_LOAD_PERMUTATION (load_node)[j] != j)
+		  {
 		    this_load_permuted = true;
-		  load_permutation.safe_push (load_place);
-		}
+		    break;
+		  }
 	      if (!this_load_permuted
 		  /* The load requires permutation when unrolling exposes
 		     a gap either because the group is larger than the SLP
@@ -2278,10 +2292,9 @@ vect_analyze_slp_instance (vec_info *vinfo,
 		      || (group_size == DR_GROUP_SIZE (first_stmt_info)
 			  && DR_GROUP_GAP (first_stmt_info) == 0)))
 		{
-		  load_permutation.release ();
+		  SLP_TREE_LOAD_PERMUTATION (load_node).release ();
 		  continue;
 		}
-	      SLP_TREE_LOAD_PERMUTATION (load_node) = load_permutation;
 	      loads_permuted = true;
 	    }