Make DeltaBlue performance more stable by ignoring type feedback that

tells us that a map can transition to another map when we are generating
code for load operations.  This may cause us to deopt if the same routine
is seeing different maps caused by branching in constructors.  If so, I
have a different change that is around 100 times more complicated that
lets us generated Crankshaft code for negative lookups.
Review URL: https://chromiumcodereview.appspot.com/10306010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11524 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.cc

@@ -1603,6 +1603,7 @@ HLoadNamedFieldPolymorphic::HLoadNamedFieldPolymorphic(HValue* context,
   SetOperandAt(1, object);
   set_representation(Representation::Tagged());
   SetGVNFlag(kDependsOnMaps);
+  int map_transitions = 0;
   for (int i = 0;
        i < types->length() && types_.length() < kMaxLoadPolymorphism;
        ++i) {
@@ -1624,13 +1625,20 @@ HLoadNamedFieldPolymorphic::HLoadNamedFieldPolymorphic(HValue* context,
         case CONSTANT_FUNCTION:
           types_.Add(types->at(i));
           break;
+        case MAP_TRANSITION:
+          // We should just ignore these since they are not relevant to a load
+          // operation.  This means we will deopt if we actually see this map
+          // from optimized code.
+          map_transitions++;
+          break;
         default:
           break;
       }
     }
   }
 
-  if (types_.length() == types->length() && FLAG_deoptimize_uncommon_cases) {
+  if (types_.length() + map_transitions == types->length() &&
+      FLAG_deoptimize_uncommon_cases) {
     SetFlag(kUseGVN);
   } else {
     SetAllSideEffects();