Enable GVN for polymorphic loads by not expanding them at the HIR level.

src/hydrogen.h

 // Copyright 2011 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 776 matching lines @@
   // non-NULL reason string.
   void TraceInline(Handle<JSFunction> target, const char* failure_reason);
 
   void HandleGlobalVariableAssignment(Variable* var,
                                       HValue* value,
                                       int position,
                                       int ast_id);
 
   void HandlePropertyAssignment(Assignment* expr);
   void HandleCompoundAssignment(Assignment* expr);
-  void HandlePolymorphicLoadNamedField(Property* expr,
-                                       HValue* object,
-                                       ZoneMapList* types,
-                                       Handle<String> name);
   void HandlePolymorphicStoreNamedField(Assignment* expr,
                                         HValue* object,
                                         HValue* value,
                                         ZoneMapList* types,
                                         Handle<String> name);
   void HandlePolymorphicCallNamed(Call* expr,
                                   HValue* receiver,
                                   ZoneMapList* types,
                                   Handle<String> name);
 
@@ skipping 291 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_