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

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
===================================================================
--- src/hydrogen-instructions.h	(revision 7299)
+++ src/hydrogen-instructions.h	(working copy)
@@ -127,6 +127,7 @@
   V(LoadKeyedGeneric)                          \
   V(LoadNamedField)                            \
   V(LoadNamedGeneric)                          \
+  V(LoadNamedFieldPolymorphic)                 \
   V(LoadPixelArrayElement)                     \
   V(Mod)                                       \
   V(Mul)                                       \
@@ -2971,6 +2972,37 @@
 };
 
 
+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)