Perform a fix point iteration for GVN.

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 857 matching lines @@
 
   // Updated the inferred type of this instruction and returns true if
   // it has changed.
   bool UpdateInferredType();
 
   virtual HType CalculateInferredType();
 
   // This function must be overridden for instructions which have the
   // kTrackSideEffectDominators flag set, to track instructions that are
   // dominating side effects.
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  // It returns true if it removed an instruction which had side effects.
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) {
     UNREACHABLE();
+    return false;
   }
 
   // Check if this instruction has some reason that prevents elimination.
   bool CannotBeEliminated() const {
     return HasObservableSideEffects() || !IsDeletable();
   }
 
 #ifdef DEBUG
   virtual void Verify() = 0;
 #endif
@@ skipping 1766 matching lines @@
     }
     return check_map;
   }
 
   bool CanOmitMapChecks() { return omit_; }
 
   virtual bool HasEscapingOperandAt(int index) V8_OVERRIDE { return false; }
   virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
     return Representation::Tagged();
   }
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE;
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
   HValue* value() { return OperandAt(0); }
 
   Unique<Map> first_map() const { return map_set_.at(0); }
   UniqueSet<Map> map_set() const { return map_set_; }
 
   bool has_migration_target() const {
     return has_migration_target_;
@@ skipping 2647 matching lines @@
   }
 
   bool MustClearNextMapWord() const {
     return (flags_ & CLEAR_NEXT_MAP_WORD) != 0;
   }
 
   void MakeDoubleAligned() {
     flags_ = static_cast<HAllocate::Flags>(flags_ | ALLOCATE_DOUBLE_ALIGNED);
   }
 
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE;
 
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
   DECLARE_CONCRETE_INSTRUCTION(Allocate)
 
  private:
   enum Flags {
     ALLOCATE_IN_NEW_SPACE = 1 << 0,
     ALLOCATE_IN_OLD_DATA_SPACE = 1 << 1,
@@ skipping 1091 matching lines @@
         if (SmiValuesAre32Bits() && store_mode_ == STORE_TO_INITIALIZED_ENTRY) {
           return Representation::Integer32();
         }
         return field_representation();
       } else if (field_representation().IsExternal()) {
         return Representation::External();
       }
     }
     return Representation::Tagged();
   }
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE {
     ASSERT(side_effect == kChangesNewSpacePromotion);
     new_space_dominator_ = dominator;
+    return false;
   }
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
   void SkipWriteBarrier() { write_barrier_mode_ = SKIP_WRITE_BARRIER; }
   bool IsSkipWriteBarrier() const {
     return write_barrier_mode_ == SKIP_WRITE_BARRIER;
   }
 
   HValue* object() const { return OperandAt(0); }
   HValue* value() const { return OperandAt(1); }
@@ skipping 206 matching lines @@
   void SetDehoisted(bool is_dehoisted) { is_dehoisted_ = is_dehoisted; }
   bool IsUninitialized() { return is_uninitialized_; }
   void SetUninitialized(bool is_uninitialized) {
     is_uninitialized_ = is_uninitialized;
   }
 
   bool IsConstantHoleStore() {
     return value()->IsConstant() && HConstant::cast(value())->IsTheHole();
   }
 
-  virtual void HandleSideEffectDominator(GVNFlag side_effect,
+  virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE {
     ASSERT(side_effect == kChangesNewSpacePromotion);
     new_space_dominator_ = dominator;
+    return false;
   }
 
   HValue* new_space_dominator() const { return new_space_dominator_; }
 
   bool NeedsWriteBarrier() {
     if (value_is_smi()) {
       return false;
     } else {
       return StoringValueNeedsWriteBarrier(value()) &&
           ReceiverObjectNeedsWriteBarrier(elements(), value(),
@@ skipping 729 matching lines @@
   virtual bool IsDeletable() const V8_OVERRIDE { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_