[Bug tree-optimization/46316] [4.6 regression] incorrect loop optimization

["xinliangli at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46316

--- Comment #13 from davidxl <xinliangli at gmail dot com> 2010-11-08 07:13:03 UTC ---
(In reply to comment #12)
> Won't there be similar problem when using TImode IVs on 64-bit targets (e.g.
> __int128 or int __attribute__((mode (TI)))) ?
> Normally overflows are detected when doing computations on trees rather than
> just in double_int.


yes. The following is the fix to this particular problem.


Index: tree-vrp.c
===================================================================
--- tree-vrp.c    (revision 166426)
+++ tree-vrp.c    (working copy)
@@ -3402,24 +3402,34 @@ adjust_range_with_scev (value_range_t *v
       || get_value_range (init)->type == VR_RANGE))
     {
       value_range_t maxvr = { VR_UNDEFINED, NULL_TREE, NULL_TREE, NULL };
-      double_int dtmp;
-      dtmp = double_int_mul (tree_to_double_int (step),
-                 double_int_sub (loop->nb_iterations_upper_bound,
-                         double_int_one));
-      tem = double_int_to_tree (TREE_TYPE (init), dtmp);
-      /* If the multiplication overflowed we can't do a meaningful
-     adjustment.  */
-      if (double_int_equal_p (dtmp, tree_to_double_int (tem)))
-    {
-      extract_range_from_binary_expr (&maxvr, PLUS_EXPR,
-                      TREE_TYPE (init), init, tem);
-      /* Likewise if the addition did.  */
-      if (maxvr.type == VR_RANGE)
-        {
-          tmin = maxvr.min;
-          tmax = maxvr.max;
-        }
-    }
+      double_int upper_bound_m1, step_int, dtmp;
+      bool unsigned_p;
+
+      upper_bound_m1 = double_int_sub (loop->nb_iterations_upper_bound,
+                                       double_int_one);
+      step_int = tree_to_double_int (step);
+      dtmp = double_int_mul (step_int, upper_bound_m1);
+      unsigned_p = TYPE_UNSIGNED (TREE_TYPE (step));
+      /* Check overflow.  */
+      if (double_int_equal_p (upper_bound_m1,
+                              double_int_div (dtmp, step_int,
+                                              unsigned_p, ROUND_DIV_EXPR)))
+        {
+          tem = double_int_to_tree (TREE_TYPE (init), dtmp);
+          /* If the multiplication overflowed we can't do a meaningful
+             adjustment.  */
+          if (double_int_equal_p (dtmp, tree_to_double_int (tem)))
+            {
+              extract_range_from_binary_expr (&maxvr, PLUS_EXPR,
+                                              TREE_TYPE (init), init, tem);
+              /* Likewise if the addition did.  */
+              if (maxvr.type == VR_RANGE)
+                {
+                  tmin = maxvr.min;
+                  tmax = maxvr.max;
+                }
+            }
+        }
     }

   if (vr->type == VR_VARYING || vr->type == VR_UNDEFINED)