Improve handling of property loads on the proto chain.

src/hydrogen.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 6012 matching lines @@
   }
 
   // Handle a load of a constant known function.
   if (lookup.IsConstantFunction()) {
     AddInstruction(new(zone()) HCheckNonSmi(object));
     AddInstruction(HCheckMaps::NewWithTransitions(object, map, zone()));
     Handle<JSFunction> function(lookup.GetConstantFunctionFromMap(*map));
     return new(zone()) HConstant(function, Representation::Tagged());
   }
 
+  // Handle a load from a known field somewhere in the protoype chain.
+  LookupInPrototypes(map, name, &lookup);
+  if (lookup.IsField()) {
+    Handle<JSObject> prototype(JSObject::cast(map->prototype()));
+    Handle<JSObject> holder(lookup.holder());
+    Handle<Map> holder_map(holder->map());
+    AddInstruction(new(zone()) HCheckNonSmi(object));
+    AddInstruction(HCheckMaps::NewWithTransitions(object, map, zone()));
+    HInstruction* holder_value =
+        AddInstruction(new(zone()) HCheckPrototypeMaps(prototype, holder));
+    return BuildLoadNamedField(holder_value, holder_map, &lookup, false);
+  }
+
   // No luck, do a generic load.
   return BuildLoadNamedGeneric(object, name, expr);
 }
 
 
 HInstruction* HGraphBuilder::BuildLoadKeyedGeneric(HValue* object,
                                                    HValue* key) {
   HValue* context = environment()->LookupContext();
   return new(zone()) HLoadKeyedGeneric(context, object, key);
 }
@@ skipping 3930 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal