[Bug tree-optimization/81500] [8 Regression] ICE with -O3 in process_use, at tree-vect-stmts.c:506

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81500

--- Comment #4 from rguenther at suse dot de <rguenther at suse dot de> ---
On Fri, 21 Jul 2017, dcb314 at hotmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81500
> 
> --- Comment #3 from David Binderman <dcb314 at hotmail dot com> ---
> Possible duplicate for this reduced code:
> 
> struct a {
>   int b;
>   int c
> };
> struct d {
>   struct a *e
> } f(struct d *g) {
>   int h;
>   int b;
>   for (; h; ++h) {
>     int i = g->e[h].c + 1;
>     g->e[h].c = g->e[h].b;
>     g->e[h].b = b;
>     b = i;
>   }
>   if (b)
>     j();
> }

Yeah.  Fix is obvious:

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: ");
     }