Improve dead phi elimination....

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
===================================================================
--- src/hydrogen-instructions.h	(revision 7081)
+++ src/hydrogen-instructions.h	(working copy)
@@ -461,9 +461,9 @@
   int id() const { return id_; }
   void set_id(int id) { id_ = id; }
 
-  const ZoneList<HValue*>* uses() const { return &uses_; }
+  ZoneList<HValue*>* uses() { return &uses_; }
 
-  virtual bool EmitAtUses() const { return false; }
+  virtual bool EmitAtUses() { return false; }
   Representation representation() const { return representation_; }
   void ChangeRepresentation(Representation r) {
     // Representation was already set and is allowed to be changed.
@@ -1800,7 +1800,8 @@
   explicit HPhi(int merged_index)
       : inputs_(2),
         merged_index_(merged_index),
-        phi_id_(-1) {
+        phi_id_(-1),
+        is_live_(false) {
     for (int i = 0; i < Representation::kNumRepresentations; i++) {
       non_phi_uses_[i] = 0;
       indirect_uses_[i] = 0;
@@ -1834,6 +1835,7 @@
   virtual HValue* OperandAt(int index) { return inputs_[index]; }
   HValue* GetRedundantReplacement();
   void AddInput(HValue* value);
+  bool HasRealUses();
 
   bool IsReceiver() { return merged_index_ == 0; }
 
@@ -1872,6 +1874,8 @@
     return indirect_uses_[Representation::kDouble];
   }
   int phi_id() { return phi_id_; }
+  bool is_live() { return is_live_; }
+  void set_is_live(bool b) { is_live_ = b; }
 
  protected:
   virtual void DeleteFromGraph();
@@ -1886,6 +1890,7 @@
   int non_phi_uses_[Representation::kNumRepresentations];
   int indirect_uses_[Representation::kNumRepresentations];
   int phi_id_;
+  bool is_live_;
 };
 
 
@@ -1916,7 +1921,7 @@
     return Representation::None();
   }
 
-  virtual bool EmitAtUses() const { return !representation().IsDouble(); }
+  virtual bool EmitAtUses() { return !representation().IsDouble(); }
   virtual void PrintDataTo(StringStream* stream);
   virtual HType CalculateInferredType();
   bool IsInteger() const { return handle_->IsSmi(); }
@@ -2191,7 +2196,7 @@
 
   void SetInputRepresentation(Representation r);
 
-  virtual bool EmitAtUses() const {
+  virtual bool EmitAtUses() {
     return !HasSideEffects() && (uses()->length() <= 1);
   }
 
@@ -2232,7 +2237,7 @@
     SetFlag(kUseGVN);
   }
 
-  virtual bool EmitAtUses() const {
+  virtual bool EmitAtUses() {
     return !HasSideEffects() && (uses()->length() <= 1);
   }
 
@@ -2255,7 +2260,7 @@
     SetFlag(kUseGVN);
   }
 
-  virtual bool EmitAtUses() const {
+  virtual bool EmitAtUses() {
     return !HasSideEffects() && (uses()->length() <= 1);
   }
 
@@ -2315,7 +2320,7 @@
     SetFlag(kUseGVN);
   }
 
-  virtual bool EmitAtUses() const {
+  virtual bool EmitAtUses() {
     return !HasSideEffects() && (uses()->length() <= 1);
   }
 
@@ -2437,7 +2442,7 @@
   HValue* left() { return OperandAt(1); }
   HValue* right() { return OperandAt(2); }
 
-  virtual bool EmitAtUses() const {
+  virtual bool EmitAtUses() {
     return !HasSideEffects() && (uses()->length() <= 1);
   }