re PR tree-optimization/55011 (GCC in an infinite loop at -O2 in VRP)

2012-10-22  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/55011
	* tree-vrp.c (update_value_range): For invalid lattice transitions
	drop to VARYING.

	* gcc.dg/torture/pr55011.c: New testcase.

From-SVN: r192689

gcc/ChangeLog

+2012-10-22  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/55011
+	* tree-vrp.c (update_value_range): For invalid lattice transitions
+	drop to VARYING.
+
 2012-10-22  Julian Brown  <julian@codesourcery.com>
 
 	* config/arm/arm.h (CANNOT_CHANGE_MODE_CLASS): Avoid subreg'ing

gcc/testsuite/ChangeLog

+2012-10-22  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/55011
+	* gcc.dg/torture/pr55011.c: New testcase.
+
 2012-10-22  Greta Yorsh  <Greta.Yorsh@arm.com>
 
 	* gcc.target/arm/pr40457-1.c: Adjust expected output.

gcc/testsuite/gcc.dg/torture/pr55011.c

+/* { dg-do compile } */
+
+char a;
+
+void f(void)
+{
+  char b = 2;
+
+  for(;;)
+    {
+      unsigned short s = 1, *p = &s, *i;
+
+      for(*i = 0; *i < 4; ++*i)
+	if(a | (*p /= (b += !!a)) <= 63739)
+	  return;
+
+      if(!s)
+	a = 0;
+
+      for(;;);
+    }
+}

gcc/tree-vrp.c

@@ -819,8 +819,19 @@ update_value_range (const_tree var, value_range_t *new_vr)
 	   || !vrp_bitmap_equal_p (old_vr->equiv, new_vr->equiv);
 
   if (is_new)
-    set_value_range (old_vr, new_vr->type, new_vr->min, new_vr->max,
-	             new_vr->equiv);
+    {
+      /* Do not allow transitions up the lattice.  The following
+         is slightly more awkward than just new_vr->type < old_vr->type
+	 because VR_RANGE and VR_ANTI_RANGE need to be considered
+	 the same.  We may not have is_new when transitioning to
+	 UNDEFINED or from VARYING.  */
+      if (new_vr->type == VR_UNDEFINED
+	  || old_vr->type == VR_VARYING)
+	set_value_range_to_varying (old_vr);
+      else
+	set_value_range (old_vr, new_vr->type, new_vr->min, new_vr->max,
+			 new_vr->equiv);
+    }
 
   BITMAP_FREE (new_vr->equiv);