Allow constants to be deleted by reinserting them into the graph as needed.

src/hydrogen.h

 // Copyright 2012 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 320 matching lines @@
   // Returns false if there are phi-uses of the arguments-object
   // which are not supported by the optimizing compiler.
   bool CheckArgumentsPhiUses();
 
   // Returns false if there are phi-uses of an uninitialized const
   // which are not supported by the optimizing compiler.
   bool CheckConstPhiUses();
 
   void CollectPhis();
 
-  void set_undefined_constant(HConstant* constant) {
-    undefined_constant_.set(constant);
-  }
-  HConstant* GetConstantUndefined() const { return undefined_constant_.get(); }
+  HConstant* GetConstantUndefined();
   HConstant* GetConstant0();
   HConstant* GetConstant1();
   HConstant* GetConstantMinus1();
   HConstant* GetConstantTrue();
   HConstant* GetConstantFalse();
   HConstant* GetConstantHole();
   HConstant* GetConstantNull();
   HConstant* GetInvalidContext();
 
   bool IsStandardConstant(HConstant* constant);
@@ skipping 94 matching lines @@
       uint32_instructions_ = new(zone()) ZoneList<HInstruction*>(4, zone());
     }
     uint32_instructions_->Add(instr, zone());
   }
 
   void IncrementInNoSideEffectsScope() { no_side_effects_scope_count_++; }
   void DecrementInNoSideEffectsScope() { no_side_effects_scope_count_--; }
   bool IsInsideNoSideEffectsScope() { return no_side_effects_scope_count_ > 0; }
 
  private:
+  HConstant* ReinsertConstantIfNecessary(HConstant* constant);
   HConstant* GetConstant(SetOncePointer<HConstant>* pointer,
                          int32_t integer_value);
 
   template<class Phase>
   void Run() {
     Phase phase(this);
     phase.Run();
   }
 
   void EliminateRedundantBoundsChecksUsingInductionVariables();
 
   Isolate* isolate_;
   int next_block_id_;
   HBasicBlock* entry_block_;
   HEnvironment* start_environment_;
   ZoneList<HBasicBlock*> blocks_;
   ZoneList<HValue*> values_;
   ZoneList<HPhi*>* phi_list_;
   ZoneList<HInstruction*>* uint32_instructions_;
-  SetOncePointer<HConstant> undefined_constant_;
+  SetOncePointer<HConstant> constant_undefined_;
   SetOncePointer<HConstant> constant_0_;
   SetOncePointer<HConstant> constant_1_;
   SetOncePointer<HConstant> constant_minus1_;
   SetOncePointer<HConstant> constant_true_;
   SetOncePointer<HConstant> constant_false_;
   SetOncePointer<HConstant> constant_the_hole_;
   SetOncePointer<HConstant> constant_null_;
   SetOncePointer<HConstant> constant_invalid_context_;
   SetOncePointer<HArgumentsObject> arguments_object_;
 
@@ skipping 1978 matching lines @@
   }
 
  private:
   HGraphBuilder* builder_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_