Added a simple dead code removal phase.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index a4e9ed72b1505026de7592a09d9cbe493f848598..ae769fea0aefbbf8b0621a0967222e126dbf5c9a 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -667,7 +667,7 @@ class HValue: public ZoneObject {
 
   // Operands.
   virtual int OperandCount() = 0;
-  virtual HValue* OperandAt(int index) = 0;
+  virtual HValue* OperandAt(int index) const = 0;
   void SetOperandAt(int index, HValue* value);
 
   void DeleteAndReplaceWith(HValue* other);
@@ -778,6 +778,10 @@ class HValue: public ZoneObject {
     UNREACHABLE();
   }
 
+  bool IsDead() const {
+    return HasNoUses() && !HasObservableSideEffects() && IsDeletable();
+  }
+
 #ifdef DEBUG
   virtual void Verify() = 0;
 #endif
@@ -862,6 +866,8 @@ class HValue: public ZoneObject {
   GVNFlagSet gvn_flags_;
 
  private:
+  virtual bool IsDeletable() const { return false; }
+
   DISALLOW_COPY_AND_ASSIGN(HValue);
 };
 
@@ -930,7 +936,7 @@ template<int V>
 class HTemplateInstruction : public HInstruction {
  public:
   int OperandCount() { return V; }
-  HValue* OperandAt(int i) { return inputs_[i]; }
+  HValue* OperandAt(int i) const { return inputs_[i]; }
 
  protected:
   void InternalSetOperandAt(int i, HValue* value) { inputs_[i] = value; }
@@ -982,7 +988,7 @@ class HTemplateControlInstruction: public HControlInstruction {
   void SetSuccessorAt(int i, HBasicBlock* block) { successors_[i] = block; }
 
   int OperandCount() { return V; }
-  HValue* OperandAt(int i) { return inputs_[i]; }
+  HValue* OperandAt(int i) const { return inputs_[i]; }
 
 
  protected:
@@ -1027,7 +1033,7 @@ class HDeoptimize: public HControlInstruction {
   }
 
   virtual int OperandCount() { return values_.length(); }
-  virtual HValue* OperandAt(int index) { return values_[index]; }
+  virtual HValue* OperandAt(int index) const { return values_[index]; }
   virtual void PrintDataTo(StringStream* stream);
 
   virtual int SuccessorCount() { return 0; }
@@ -1284,6 +1290,9 @@ class HChange: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1303,6 +1312,9 @@ class HClampToUint8: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1341,7 +1353,7 @@ class HSimulate: public HInstruction {
     AddValue(kNoIndex, value);
   }
   virtual int OperandCount() { return values_.length(); }
-  virtual HValue* OperandAt(int index) { return values_[index]; }
+  virtual HValue* OperandAt(int index) const { return values_[index]; }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::None();
@@ -1514,6 +1526,9 @@ class HThisFunction: public HTemplateInstruction<0> {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1532,6 +1547,9 @@ class HContext: public HTemplateInstruction<0> {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1550,6 +1568,9 @@ class HOuterContext: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1595,6 +1616,9 @@ class HGlobalObject: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1614,6 +1638,9 @@ class HGlobalReceiver: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1899,6 +1926,9 @@ class HJSArrayLength: public HTemplateInstruction<2> {
 
  protected:
   virtual bool DataEquals(HValue* other_raw) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1919,6 +1949,9 @@ class HFixedArrayBaseLength: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1939,6 +1972,9 @@ class HMapEnumLength: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1958,6 +1994,9 @@ class HElementsKind: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -1980,6 +2019,9 @@ class HBitNot: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -2062,6 +2104,8 @@ class HUnaryMathOperation: public HTemplateInstruction<2> {
   }
 
  private:
+  virtual bool IsDeletable() const { return true; }
+
   BuiltinFunctionId op_;
 };
 
@@ -2086,6 +2130,9 @@ class HLoadElements: public HTemplateInstruction<2> {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -2109,6 +2156,9 @@ class HLoadExternalArrayPointer: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -2408,7 +2458,7 @@ class HPhi: public HValue {
   }
   virtual HType CalculateInferredType();
   virtual int OperandCount() { return inputs_.length(); }
-  virtual HValue* OperandAt(int index) { return inputs_[index]; }
+  virtual HValue* OperandAt(int index) const { return inputs_[index]; }
   HValue* GetRedundantReplacement();
   void AddInput(HValue* value);
   bool HasRealUses();
@@ -2504,6 +2554,9 @@ class HArgumentsObject: public HTemplateInstruction<0> {
   }
 
   DECLARE_CONCRETE_INSTRUCTION(ArgumentsObject)
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -2632,6 +2685,8 @@ class HConstant: public HTemplateInstruction<0> {
   }
 
  private:
+  virtual bool IsDeletable() const { return true; }
+
   // If this is a numerical constant, handle_ either points to to the
   // HeapObject the constant originated from or is null.  If the
   // constant is non-numeric, handle_ always points to a valid
@@ -2754,6 +2809,9 @@ class HArgumentsElements: public HTemplateInstruction<0> {
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
 
+ private:
+  virtual bool IsDeletable() const { return true; }
+
   bool from_inlined_;
 };
 
@@ -2773,6 +2831,9 @@ class HArgumentsLength: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -2898,6 +2959,8 @@ class HBitwiseBinaryOperation: public HBinaryOperation {
   DECLARE_ABSTRACT_INSTRUCTION(BitwiseBinaryOperation)
 
  private:
+  virtual bool IsDeletable() const { return true; }
+
   Representation observed_input_representation_[3];
 };
 
@@ -2921,6 +2984,9 @@ class HMathFloorOfDiv: public HBinaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -2953,6 +3019,9 @@ class HArithmeticBinaryOperation: public HBinaryOperation {
     }
     return HValue::InferredRepresentation();
   }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -3238,6 +3307,9 @@ class HGetCachedArrayIndex: public HUnaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -3342,7 +3414,7 @@ class HPower: public HTemplateInstruction<2> {
   }
 
   HValue* left() { return OperandAt(0); }
-  HValue* right() { return OperandAt(1); }
+  HValue* right() const { return OperandAt(1); }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return index == 0
@@ -3354,6 +3426,11 @@ class HPower: public HTemplateInstruction<2> {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+ private:
+  virtual bool IsDeletable() const {
+    return !right()->representation().IsTagged();
+  }
 };
 
 
@@ -3371,6 +3448,9 @@ class HRandom: public HTemplateInstruction<1> {
   }
 
   DECLARE_CONCRETE_INSTRUCTION(Random)
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -3761,7 +3841,7 @@ class HLoadGlobalCell: public HTemplateInstruction<0> {
   }
 
   Handle<JSGlobalPropertyCell>  cell() const { return cell_; }
-  bool RequiresHoleCheck();
+  bool RequiresHoleCheck() const;
 
   virtual void PrintDataTo(StringStream* stream);
 
@@ -3783,6 +3863,8 @@ class HLoadGlobalCell: public HTemplateInstruction<0> {
   }
 
  private:
+  virtual bool IsDeletable() const { return !RequiresHoleCheck(); }
+
   Handle<JSGlobalPropertyCell> cell_;
   PropertyDetails details_;
 };
@@ -3943,7 +4025,7 @@ class HLoadContextSlot: public HUnaryOperation {
     return mode_ == kCheckDeoptimize;
   }
 
-  bool RequiresHoleCheck() {
+  bool RequiresHoleCheck() const {
     return mode_ != kNoCheck;
   }
 
@@ -3962,6 +4044,8 @@ class HLoadContextSlot: public HUnaryOperation {
   }
 
  private:
+  virtual bool IsDeletable() const { return !RequiresHoleCheck(); }
+
   int slot_index_;
   Mode mode_;
 };
@@ -4054,6 +4138,8 @@ class HLoadNamedField: public HUnaryOperation {
   }
 
  private:
+  virtual bool IsDeletable() const { return true; }
+
   bool is_in_object_;
   int offset_;
 };
@@ -4200,7 +4286,7 @@ class HLoadKeyedFastElement
 
   virtual void PrintDataTo(StringStream* stream);
 
-  bool RequiresHoleCheck();
+  bool RequiresHoleCheck() const;
 
   DECLARE_CONCRETE_INSTRUCTION(LoadKeyedFastElement)
 
@@ -4214,6 +4300,8 @@ class HLoadKeyedFastElement
   }
 
  private:
+  virtual bool IsDeletable() const { return !RequiresHoleCheck(); }
+
   class ElementsKindField:  public BitField<ElementsKind, 0, 4> {};
   class IndexOffsetField:   public BitField<uint32_t, 4, 27> {};
   class IsDehoistedField:   public BitField<bool, 31, 1> {};
@@ -4260,7 +4348,7 @@ class HLoadKeyedFastDoubleElement
     return Representation::None();
   }
 
-  bool RequiresHoleCheck() {
+  bool RequiresHoleCheck() const {
     return hole_check_mode_ == PERFORM_HOLE_CHECK;
   }
 
@@ -4277,6 +4365,8 @@ class HLoadKeyedFastDoubleElement
   }
 
  private:
+  virtual bool IsDeletable() const { return !RequiresHoleCheck(); }
+
   uint32_t index_offset_;
   bool is_dehoisted_;
   HoleCheckMode hole_check_mode_;
@@ -4341,6 +4431,8 @@ class HLoadKeyedSpecializedArrayElement
   }
 
  private:
+  virtual bool IsDeletable() const { return true; }
+
   ElementsKind elements_kind_;
   uint32_t index_offset_;
   bool is_dehoisted_;
@@ -4722,6 +4814,10 @@ class HStringAdd: public HBinaryOperation {
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
+
+  // TODO(svenpanne) Might be safe, but leave it out until we know for sure.
+  // private:
+  //  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -4756,6 +4852,10 @@ class HStringCharCodeAt: public HTemplateInstruction<3> {
   virtual Range* InferRange(Zone* zone) {
     return new(zone) Range(0, String::kMaxUtf16CodeUnit);
   }
+
+  // TODO(svenpanne) Might be safe, but leave it out until we know for sure.
+  // private:
+  //  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -4782,6 +4882,10 @@ class HStringCharFromCode: public HTemplateInstruction<2> {
   virtual bool DataEquals(HValue* other) { return true; }
 
   DECLARE_CONCRETE_INSTRUCTION(StringCharFromCode)
+
+  // TODO(svenpanne) Might be safe, but leave it out until we know for sure.
+  // private:
+  //  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -4810,6 +4914,9 @@ class HStringLength: public HUnaryOperation {
   virtual Range* InferRange(Zone* zone) {
     return new(zone) Range(0, String::kMaxLength);
   }
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -4836,6 +4943,9 @@ class HAllocateObject: public HTemplateInstruction<1> {
   DECLARE_CONCRETE_INSTRUCTION(AllocateObject)
 
  private:
+  // TODO(svenpanne) Might be safe, but leave it out until we know for sure.
+  //  virtual bool IsDeletable() const { return true; }
+
   Handle<JSFunction> constructor_;
 };
 
@@ -4852,6 +4962,8 @@ class HMaterializedLiteral: public HTemplateInstruction<V> {
   int depth() const { return depth_; }
 
  private:
+  virtual bool IsDeletable() const { return true; }
+
   int literal_index_;
   int depth_;
 };
@@ -5027,6 +5139,8 @@ class HFunctionLiteral: public HTemplateInstruction<1> {
   bool pretenure() const { return pretenure_; }
 
  private:
+  virtual bool IsDeletable() const { return true; }
+
   Handle<SharedFunctionInfo> shared_info_;
   bool pretenure_;
 };
@@ -5051,6 +5165,9 @@ class HTypeof: public HTemplateInstruction<2> {
   }
 
   DECLARE_CONCRETE_INSTRUCTION(Typeof)
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -5069,6 +5186,9 @@ class HToFastProperties: public HUnaryOperation {
   }
 
   DECLARE_CONCRETE_INSTRUCTION(ToFastProperties)
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -5083,6 +5203,9 @@ class HValueOf: public HUnaryOperation {
   }
 
   DECLARE_CONCRETE_INSTRUCTION(ValueOf)
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };
 
 
@@ -5279,6 +5402,9 @@ class HLoadFieldByIndex : public HTemplateInstruction<2> {
   }
 
   DECLARE_CONCRETE_INSTRUCTION(LoadFieldByIndex);
+
+ private:
+  virtual bool IsDeletable() const { return true; }
 };