[PATCH] Fix PR81500

[Richard Biener]

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.

Richard.

2017-06-21  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/81500
        * tree-vect-loop.c (vect_is_simple_reduction): Properly fail if
        we didn't identify a reduction path.

        * gcc.dg/torture/pr81500.c: New testcase.

Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c        (revision 250386)
+++ gcc/tree-vect-loop.c        (working copy)
@@ -3243,7 +3243,7 @@ pop:
     }
 
   /* Check whether the reduction path detected is valid.  */
-  bool fail = false;
+  bool fail = path.length () == 0;
   bool neg = false;
   for (unsigned i = 1; i < path.length (); ++i)
     {
@@ -3276,9 +3276,7 @@ pop:
 
   if (dump_enabled_p ())
     {
-      report_vect_op (MSG_MISSED_OPTIMIZATION,
-                     SSA_NAME_DEF_STMT
-                       (USE_FROM_PTR (path[path.length ()-1].second)),
+      report_vect_op (MSG_MISSED_OPTIMIZATION, def_stmt,
                      "reduction: unknown pattern: ");
     }
 
Index: gcc/testsuite/gcc.dg/torture/pr81500.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr81500.c      (nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr81500.c      (working copy)
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+
+typedef int a;
+void c(int *b)
+{
+  int d;
+  a e, f, *g, *h = b;
+  for (; d; d--) {
+      f = *g & 1;
+      *h-- = *g-- | e;
+      e = f;
+  }
+}