Make DeltaBlue performance more stable by ignoring type feedback that

src/hydrogen-instructions.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1585 matching lines @@
                                                        HValue* object,
                                                        SmallMapList* types,
                                                        Handle<String> name)
     : types_(Min(types->length(), kMaxLoadPolymorphism)),
       name_(name),
       need_generic_(false) {
   SetOperandAt(0, 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) {
     Handle<Map> map = types->at(i);
     LookupResult lookup(map->GetIsolate());
     map->LookupInDescriptors(NULL, *name, &lookup);
     if (lookup.IsFound()) {
       switch (lookup.type()) {
         case FIELD: {
           int index = lookup.GetLocalFieldIndexFromMap(*map);
           if (index < 0) {
             SetGVNFlag(kDependsOnInobjectFields);
           } else {
             SetGVNFlag(kDependsOnBackingStoreFields);
           }
           types_.Add(types->at(i));
           break;
         }
         case CONSTANT_FUNCTION:
           types_.Add(types->at(i));
           break;
+        case MAP_TRANSITION:

[Michael Starzinger, 2012/05/02 13:39:29]

I think that check is not general enough. We have a transition whenever
"lookup.IsFound() && !lookup.IsProperty()". Esepcially with Sven's new accessor
pairs in mind.

[Sven Panne, 2012/05/02 13:55:00]

Michael's comment is correct, but things are even more tricky, because the
PropertyType alone is not enough to decide if we have a transition or not: In
the CALLBACKS case you have to look into the AccessorPair to decide if we have a
transition or not. And without a holder (see "NULL" above), this won't work...
(see LookupResult::IsProperty).

[Erik Corry, 2012/05/03 10:39:14]

All I want to do is to ignore this particular map when generating optimized
code.  If we actually encounter it we will deopt.  I don't actually care much
whether there is a real map transition from this map to another one.

+          // We should just ignore these since they are not relevant to a load
+          // operation.

[Michael Starzinger, 2012/05/03 14:12:22]

In this case, this comment should contain something like "... and possibly
deoptimize in these cases".

+          map_transitions++;
+          break;
         default:

[Sven Panne, 2012/05/02 13:55:00]

We should never use a default case when doing a switch over the property type,
because this makes finding all the places where things have to be changed when
fiddling around with those types (e.g. adding a new type, changing the behaviour
for a given type, etc.) virtually impossible. I've been down that road several
times in the last few months... :-P

[Erik Corry, 2012/05/03 10:39:14]

I didn't add this default clause.  All it is saying is that if there is another
kind of property then Crankshaft does not understand it and will not generate
optimized code for it.  If a new kind of property is added this is certainly the
correct behaviour, so I see no reason to change this, but you are welcome to try
in a different CL.

           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();
     need_generic_ = true;
   }
 }
 
 
 bool HLoadNamedFieldPolymorphic::DataEquals(HValue* value) {
   HLoadNamedFieldPolymorphic* other = HLoadNamedFieldPolymorphic::cast(value);
@@ skipping 784 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal