Simple support for const variables in Crankshaft....

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 220 matching lines @@
   Handle<Code> Compile(CompilationInfo* info);
 
   void set_undefined_constant(HConstant* constant) {
     undefined_constant_.set(constant);
   }
   HConstant* GetConstantUndefined() const { return undefined_constant_.get(); }
   HConstant* GetConstant1();
   HConstant* GetConstantMinus1();
   HConstant* GetConstantTrue();
   HConstant* GetConstantFalse();
+  HConstant* GetConstantHole();
 
   HBasicBlock* CreateBasicBlock();
   HArgumentsObject* GetArgumentsObject() const {
     return arguments_object_.get();
   }
   bool HasArgumentsObject() const { return arguments_object_.is_set(); }
 
   void SetArgumentsObject(HArgumentsObject* object) {
     arguments_object_.set(object);
   }
@@ skipping 41 matching lines @@
   HBasicBlock* entry_block_;
   HEnvironment* start_environment_;
   ZoneList<HBasicBlock*> blocks_;
   ZoneList<HValue*> values_;
   ZoneList<HPhi*>* phi_list_;
   SetOncePointer<HConstant> undefined_constant_;
   SetOncePointer<HConstant> constant_1_;
   SetOncePointer<HConstant> constant_minus1_;
   SetOncePointer<HConstant> constant_true_;
   SetOncePointer<HConstant> constant_false_;
+  SetOncePointer<HConstant> constant_hole_;
   SetOncePointer<HArgumentsObject> arguments_object_;
 
   DISALLOW_COPY_AND_ASSIGN(HGraph);
 };
 
 
 Zone* HBasicBlock::zone() { return graph_->zone(); }
 
 
 class HEnvironment: public ZoneObject {
@@ skipping 881 matching lines @@
   const char* filename_;
   HeapStringAllocator string_allocator_;
   StringStream trace_;
   int indent_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_