Remove purely informative definitions from the graph.

src/hydrogen-instructions.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 801 matching lines @@
   static const int kNoRedefinedOperand = -1;
   virtual int RedefinedOperandIndex() { return kNoRedefinedOperand; }
   bool IsInformativeDefinition() {
     return RedefinedOperandIndex() != kNoRedefinedOperand;
   }
   HValue* RedefinedOperand() {
     return IsInformativeDefinition() ? OperandAt(RedefinedOperandIndex())
                                      : NULL;
   }
 
+  // A purely informative definition is an idef that will not emit code and
+  // should therefore be removed from the graph in the RestoreActualValues
+  // phase (so that live ranges will be shorter).
+  virtual bool IsPurelyInformativeDefinition() { return false; }
+
   // This method must always return the original HValue SSA definition
   // (regardless of any iDef of this value).
   HValue* ActualValue() {
     return IsInformativeDefinition() ? RedefinedOperand()->ActualValue()
                                      : this;
   }
 
   virtual void AddInformativeDefinitions() {}
 
   void UpdateRedefinedUsesWhileSettingUpInformativeDefinitions() {
@@ skipping 447 matching lines @@
   static HNumericConstraint* AddToGraph(HValue* constrained_value,
                                         NumericRelation relation,
                                         HValue* related_value,
                                         HInstruction* insertion_point = NULL);
 
   HValue* constrained_value() { return OperandAt(0); }
   HValue* related_value() { return OperandAt(1); }
   NumericRelation relation() { return relation_; }
 
   virtual int RedefinedOperandIndex() { return 0; }
+  virtual bool IsPurelyInformativeDefinition() { return true; }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return representation();
   }
 
   virtual void PrintDataTo(StringStream* stream);
 
   virtual bool IsRelationTrueInternal(NumericRelation other_relation,
                                       HValue* other_related_value) {
     if (related_value() == other_related_value) {
@@ skipping 2053 matching lines @@
   virtual bool IsRelationTrueInternal(NumericRelation relation,
                                       HValue* related_value);
 
   virtual void PrintDataTo(StringStream* stream);
   virtual void InferRepresentation(HInferRepresentation* h_infer);
 
   HValue* index() { return OperandAt(0); }
   HValue* length() { return OperandAt(1); }
 
   virtual int RedefinedOperandIndex() { return 0; }
+  virtual bool IsPurelyInformativeDefinition() { return skip_check(); }
   virtual void AddInformativeDefinitions();
 
   DECLARE_CONCRETE_INSTRUCTION(BoundsCheck)
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
   BoundsCheckKeyMode key_mode_;
   bool skip_check_;
 };
 
@@ skipping 2642 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_