gcc/

	Backport from trunk r230150.
	2015-11-11  Richard Biener  <rguenth@gcc.gnu.org>
	    Jiong Wang	    <jiong.wang@arm.com>

	PR tree-optimization/68234
	* tree-vrp.c (vrp_visit_phi_node): Extend SCEV check to those loop PHI
	node which estimiated to be VR_VARYING initially.

	gcc/testsuite/
	Backport from trunk r230150.
	2015-11-11  Richard Biener  <rguenth@gcc.gnu.org>
	    Jiong Wang	    <jiong.wang@arm.com>

	* gcc.dg/tree-ssa/pr68234.c: New testcase.

Change-Id: Id0e4ece65bdb060513995d88572eb52dd67ddb6f

2 files changed, 49 insertions, 14 deletions

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr68234.c b/gcc/testsuite/gcc.dg/tree-ssa/pr68234.c
new file mode 100644
index 00000000000..e7c2a95aa4c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr68234.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp2" } */
+
+extern int nc;
+void ff (unsigned long long);
+
+void
+f (void)
+{
+  unsigned char resp[1024];
+  int c;
+  int bl = 0;
+  unsigned long long *dwords = (unsigned long long *) (resp + 5);
+  for (c = 0; c < nc; c++)
+    {
+      /* PR middle-end/68234, this signed division should be optimized into
+	 right shift as vrp pass should deduct range info of 'bl' falls into
+	 positive number.  */
+      ff (dwords[bl / 64]);
+      bl++;
+    }
+}
+
+/* { dg-final { scan-tree-dump ">> 6" "vrp2" } } */
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 877b7d580a7..ec43bc64729 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -8977,20 +8977,11 @@ vrp_visit_phi_node (gphi *phi)
 
       /* If we dropped either bound to +-INF then if this is a loop
 	 PHI node SCEV may known more about its value-range.  */
-      if ((cmp_min > 0 || cmp_min < 0
+      if (cmp_min > 0 || cmp_min < 0
 	   || cmp_max < 0 || cmp_max > 0)
-	  && (l = loop_containing_stmt (phi))
-	  && l->header == gimple_bb (phi))
-	adjust_range_with_scev (&vr_result, l, phi, lhs);
-
-      /* If we will end up with a (-INF, +INF) range, set it to
-	 VARYING.  Same if the previous max value was invalid for
-	 the type and we end up with vr_result.min > vr_result.max.  */
-      if ((vrp_val_is_max (vr_result.max)
-	   && vrp_val_is_min (vr_result.min))
-	  || compare_values (vr_result.min,
-			     vr_result.max) > 0)
-	goto varying;
+	goto scev_check;
+
+      goto infinite_check;
     }
 
   /* If the new range is different than the previous value, keep
@@ -9016,8 +9007,28 @@ update_range:
   /* Nothing changed, don't add outgoing edges.  */
   return SSA_PROP_NOT_INTERESTING;
 
-  /* No match found.  Set the LHS to VARYING.  */
 varying:
+  set_value_range_to_varying (&vr_result);
+
+scev_check:
+  /* If this is a loop PHI node SCEV may known more about its value-range.
+     scev_check can be reached from two paths, one is a fall through from above
+     "varying" label, the other is direct goto from code block which tries to
+     avoid infinite simulation.  */
+  if ((l = loop_containing_stmt (phi))
+      && l->header == gimple_bb (phi))
+    adjust_range_with_scev (&vr_result, l, phi, lhs);
+
+infinite_check:
+  /* If we will end up with a (-INF, +INF) range, set it to
+     VARYING.  Same if the previous max value was invalid for
+     the type and we end up with vr_result.min > vr_result.max.  */
+  if ((vr_result.type == VR_RANGE || vr_result.type == VR_ANTI_RANGE)
+      && !((vrp_val_is_max (vr_result.max) && vrp_val_is_min (vr_result.min))
+	   || compare_values (vr_result.min, vr_result.max) > 0))
+    goto update_range;
+
+  /* No match found.  Set the LHS to VARYING.  */
   set_value_range_to_varying (lhs_vr);
   return SSA_PROP_VARYING;
 }