Simple support for const variables in Crankshaft....

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 150 matching lines @@
   V(StringCharFromCode)                        \
   V(StringLength)                              \
   V(Sub)                                       \
   V(Test)                                      \
   V(Throw)                                     \
   V(ToFastProperties)                          \
   V(Typeof)                                    \
   V(TypeofIs)                                  \
   V(UnaryMathOperation)                        \
   V(UnknownOSRValue)                           \
+  V(UseConst)                                  \
   V(ValueOf)
 
 #define GVN_FLAG_LIST(V)                       \
   V(Calls)                                     \
   V(InobjectFields)                            \
   V(BackingStoreFields)                        \
   V(ArrayElements)                             \
   V(SpecializedArrayElements)                  \
   V(GlobalVars)                                \
   V(Maps)                                      \
@@ skipping 831 matching lines @@
   }
 
   virtual Representation RequiredInputRepresentation(int index) const {
     return Representation::Tagged();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(Throw)
 };
 
 
+class HUseConst: public HUnaryOperation {
+ public:
+  explicit HUseConst(HValue* old_value) : HUnaryOperation(old_value) { }
+
+  virtual Representation RequiredInputRepresentation(int index) const {
+    return Representation::None();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(UseConst)
+};
+
+
 class HForceRepresentation: public HTemplateInstruction<1> {
  public:
   HForceRepresentation(HValue* value, Representation required_representation) {
     SetOperandAt(0, value);
     set_representation(required_representation);
   }
 
   HValue* value() { return OperandAt(0); }
 
   virtual HValue* EnsureAndPropagateNotMinusZero(BitVector* visited);
@@ skipping 2968 matching lines @@
 
   DECLARE_CONCRETE_INSTRUCTION(In)
 };
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_