re PR tree-optimization/91293 (Wrong code with -O3 -mavx2)

2019-07-31  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/91293
	* tree-vect-slp.c (vect_build_slp_tree_2): Do not swap operands
	of reduction stmts.

	* gcc.dg/vect/pr91293-1.c: New testcase.
	* gcc.dg/vect/pr91293-2.c: Likewise.
	* gcc.dg/vect/pr91293-3.c: Likewise.

From-SVN: r273934

gcc/ChangeLog

+2019-07-31  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/91293
+	* tree-vect-slp.c (vect_build_slp_tree_2): Do not swap operands
+	of reduction stmts.
+
 2019-07-31  Matt Thomas  <matt@3am-software.com>
 	    Nick Hudson <nick@nthcliff.demon.co.uk>
 	    Matthew Green <mrg@eterna.com.au>

gcc/testsuite/ChangeLog

+2019-07-31  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/91293
+	* gcc.dg/vect/pr91293-1.c: New testcase.
+	* gcc.dg/vect/pr91293-2.c: Likewise.
+	* gcc.dg/vect/pr91293-3.c: Likewise.
+
 2019-07-31  Jakub Jelinek  <jakub@redhat.com>
 
 	PR tree-optimization/91201

gcc/testsuite/gcc.dg/vect/pr91293-1.c

+/* { dg-do run } */
+/* { dg-additional-options "-msse4.1" { target { sse4_runtime } } } */
+
+long long a;
+unsigned b, c;
+int d = 62;
+void e(long long *f, int p2) { *f = p2; }
+int main()
+{
+  for (int g = 2; g <= d; g++)
+    {
+      b += g + 4;
+      c += 5 - g;
+    }
+  e(&a, b);
+  if (a != 2196)
+    __builtin_abort ();
+  return 0;
+}

gcc/testsuite/gcc.dg/vect/pr91293-2.c

+/* { dg-do run } */
+/* { dg-additional-options "-msse4.1" { target { sse4_runtime } } } */
+
+long long a;
+unsigned b, c;
+int d = 62;
+void e(long long *f, int p2) { *f = p2; }
+int main()
+{
+  for (int g = 2; g <= d; g++)
+    {
+      c += 5 - g;
+      b += g + 4;
+    }
+  e(&a, b);
+  if (a != 2196)
+    __builtin_abort ();
+  return 0;
+}

gcc/testsuite/gcc.dg/vect/pr91293-3.c

+/* { dg-do run } */
+/* { dg-additional-options "-msse4.1" { target { sse4_runtime } } } */
+
+long long a;
+unsigned b, c;
+int d = 62;
+void e(long long *f, int p2) { *f = p2; }
+int xx = 5, yy = 4;
+int main()
+{
+  for (int g = 2; g <= d; g++)
+    {
+      c += xx - g;
+      b += yy + g;
+    }
+  e(&a, b);
+  if (a != 2196)
+    __builtin_abort ();
+  return 0;
+}

gcc/tree-vect-slp.c

@@ -1296,6 +1296,9 @@ vect_build_slp_tree_2 (vec_info *vinfo,
 	  && nops == 2
 	  && oprnds_info[1]->first_dt == vect_internal_def
 	  && is_gimple_assign (stmt_info->stmt)
+	  /* Swapping operands for reductions breaks assumptions later on.  */
+	  && STMT_VINFO_DEF_TYPE (stmt_info) != vect_reduction_def
+	  && STMT_VINFO_DEF_TYPE (stmt_info) != vect_double_reduction_def
 	  /* Do so only if the number of not successful permutes was nor more
 	     than a cut-ff as re-trying the recursive match on
 	     possibly each level of the tree would expose exponential