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

src/hydrogen-instructions.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 109 matching lines @@
   V(LeaveInlined)                              \
   V(LoadContextSlot)                           \
   V(LoadElements)                              \
   V(LoadExternalArrayPointer)                  \
   V(LoadFunctionPrototype)                     \
   V(LoadGlobal)                                \
   V(LoadKeyedFastElement)                      \
   V(LoadKeyedGeneric)                          \
   V(LoadNamedField)                            \
   V(LoadNamedGeneric)                          \
+  V(LoadNamedFieldPolymorphic)                 \
   V(LoadPixelArrayElement)                     \
   V(Mod)                                       \
   V(Mul)                                       \
   V(ObjectLiteral)                             \
   V(OsrEntry)                                  \
   V(OuterContext)                              \
   V(Parameter)                                 \
   V(Power)                                     \
   V(PushArgument)                              \
   V(RegExpLiteral)                             \
@@ skipping 2824 matching lines @@
     HLoadNamedField* b = HLoadNamedField::cast(other);
     return is_in_object_ == b->is_in_object_ && offset_ == b->offset_;
   }
 
  private:
   bool is_in_object_;
   int offset_;
 };
 
 
+class HLoadNamedFieldPolymorphic: public HUnaryOperation {
+ public:
+  HLoadNamedFieldPolymorphic(HValue* object,
+                             ZoneMapList* types,
+                             Handle<String> name);
+
+  HValue* object() { return OperandAt(0); }
+  ZoneMapList* types() { return &types_; }
+  Handle<String> name() { return name_; }
+  bool need_generic() { return need_generic_; }
+
+  virtual Representation RequiredInputRepresentation(int index) const {
+    return Representation::Tagged();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(LoadNamedFieldPolymorphic,
+                               "load_named_field_polymorphic")
+
+  static const int kMaxLoadPolymorphism = 4;
+
+ protected:
+  virtual bool DataEquals(HValue* value);
+
+ private:
+  ZoneMapList types_;
+  Handle<String> name_;
+  bool need_generic_;
+};
+
+
+
 class HLoadNamedGeneric: public HBinaryOperation {
  public:
   HLoadNamedGeneric(HValue* context, HValue* object, Handle<Object> name)
       : HBinaryOperation(context, object), name_(name) {
     set_representation(Representation::Tagged());
     SetAllSideEffects();
   }
 
   HValue* context() { return OperandAt(0); }
   HValue* object() { return OperandAt(1); }
@@ skipping 537 matching lines @@
   HValue* object() { return left(); }
   HValue* key() { return right(); }
 };
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_