Never hchange nan-hole to hole or hole to nan-hole.

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 79 matching lines @@
   V(Change)                                    \
   V(CheckFunction)                             \
   V(CheckHeapObject)                           \
   V(CheckInstanceType)                         \
   V(CheckMaps)                                 \
   V(CheckMapValue)                             \
   V(CheckSmi)                                  \
   V(ClampToUint8)                              \
   V(ClassOfTestAndBranch)                      \
   V(CompareNumericAndBranch)                   \
+  V(CompareHoleAndBranch)                      \
   V(CompareGeneric)                            \
   V(CompareObjectEqAndBranch)                  \
   V(CompareMap)                                \
   V(Constant)                                  \
   V(Context)                                   \
   V(DateField)                                 \
   V(DebugBreak)                                \
   V(DeclareGlobals)                            \
   V(Deoptimize)                                \
   V(Div)                                       \
@@ skipping 685 matching lines @@
 
   // Mark this HValue as dead and to be removed from other HValues' use lists.
   void Kill();
 
   int flags() const { return flags_; }
   void SetFlag(Flag f) { flags_ |= (1 << f); }
   void ClearFlag(Flag f) { flags_ &= ~(1 << f); }
   bool CheckFlag(Flag f) const { return (flags_ & (1 << f)) != 0; }
 
   // Returns true if the flag specified is set for all uses, false otherwise.
-  bool CheckUsesForFlag(Flag f);
+  bool CheckUsesForFlag(Flag f) const;
   // Returns true if the flag specified is set for all uses, and this set
   // of uses is non-empty.
-  bool HasAtLeastOneUseWithFlagAndNoneWithout(Flag f);
+  bool HasAtLeastOneUseWithFlagAndNoneWithout(Flag f) const;
 
   GVNFlagSet gvn_flags() const { return gvn_flags_; }
   void SetGVNFlag(GVNFlag f) { gvn_flags_.Add(f); }
   void ClearGVNFlag(GVNFlag f) { gvn_flags_.Remove(f); }
   bool CheckGVNFlag(GVNFlag f) const { return gvn_flags_.Contains(f); }
   void SetAllSideEffects() { gvn_flags_.Add(AllSideEffectsFlagSet()); }
   void ClearAllSideEffects() {
     gvn_flags_.Remove(AllSideEffectsFlagSet());
   }
   bool HasSideEffects() const {
@@ skipping 692 matching lines @@
     set_representation(required_representation);
   }
 };
 
 
 class HChange: public HUnaryOperation {
  public:
   HChange(HValue* value,
           Representation to,
           bool is_truncating_to_smi,
-          bool is_truncating_to_int32,
-          bool allow_undefined_as_nan)
+          bool is_truncating_to_int32)
       : HUnaryOperation(value) {
     ASSERT(!value->representation().IsNone());
     ASSERT(!to.IsNone());
     ASSERT(!value->representation().Equals(to));
     set_representation(to);
     SetFlag(kUseGVN);
-    if (allow_undefined_as_nan) SetFlag(kAllowUndefinedAsNaN);
     if (is_truncating_to_smi) SetFlag(kTruncatingToSmi);
     if (is_truncating_to_int32) SetFlag(kTruncatingToInt32);
     if (value->representation().IsSmi() || value->type().IsSmi()) {
       set_type(HType::Smi());
     } else {
       set_type(HType::TaggedNumber());
       if (to.IsTagged()) SetGVNFlag(kChangesNewSpacePromotion);
     }
   }
 
+  bool can_convert_undefined_to_nan() {
+    return CheckUsesForFlag(kAllowUndefinedAsNaN);
+  }
+
   virtual HValue* EnsureAndPropagateNotMinusZero(BitVector* visited);
   virtual HType CalculateInferredType();
   virtual HValue* Canonicalize();
 
   Representation from() const { return value()->representation(); }
   Representation to() const { return representation(); }
-  bool allow_undefined_as_nan() const {
-    return CheckFlag(kAllowUndefinedAsNaN);
-  }
   bool deoptimize_on_minus_zero() const {
     return CheckFlag(kBailoutOnMinusZero);
   }
   virtual Representation RequiredInputRepresentation(int index) {
     return from();
   }
 
   virtual Range* InferRange(Zone* zone);
 
   virtual void PrintDataTo(StringStream* stream);
@@ skipping 2379 matching lines @@
   virtual void PrintDataTo(StringStream* stream);
 
   DECLARE_CONCRETE_INSTRUCTION(CompareNumericAndBranch)
 
  private:
   Representation observed_input_representation_[2];
   Token::Value token_;
 };
 
 
+class HCompareHoleAndBranch: public HTemplateControlInstruction<2, 1> {
+ public:
+  // TODO(danno): make this private when the IfBuilder properly constructs
+  // control flow instructions.
+  explicit HCompareHoleAndBranch(HValue* object) {
+    SetFlag(kFlexibleRepresentation);
+    SetFlag(kAllowUndefinedAsNaN);
+    SetOperandAt(0, object);
+  }
+
+  DECLARE_INSTRUCTION_FACTORY_P1(HCompareHoleAndBranch, HValue*);
+
+  HValue* object() { return OperandAt(0); }
+
+  virtual void InferRepresentation(HInferRepresentationPhase* h_infer);
+
+  virtual Representation RequiredInputRepresentation(int index) {
+    return representation();
+  }
+
+  virtual void PrintDataTo(StringStream* stream);
+
+  DECLARE_CONCRETE_INSTRUCTION(CompareHoleAndBranch)
+};
+
+
 class HCompareObjectEqAndBranch: public HTemplateControlInstruction<2, 2> {
  public:
   // TODO(danno): make this private when the IfBuilder properly constructs
   // control flow instructions.
   HCompareObjectEqAndBranch(HValue* left,
                             HValue* right) {
     SetOperandAt(0, left);
     SetOperandAt(1, right);
   }
 
@@ skipping 363 matching lines @@
       decomposition->Apply(right(), left()->GetInteger32Constant());
       return true;
     } else if (right()->IsInteger32Constant()) {
       decomposition->Apply(left(), right()->GetInteger32Constant());
       return true;
     } else {
       return false;
     }
   }
 
+  virtual void RepresentationChanged(Representation to) {
+    if (to.IsTagged()) ClearFlag(kAllowUndefinedAsNaN);
+    HArithmeticBinaryOperation::RepresentationChanged(to);
+  }
+
   DECLARE_CONCRETE_INSTRUCTION(Add)
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
 
   virtual Range* InferRange(Zone* zone);
 
  private:
   HAdd(HValue* context, HValue* left, HValue* right)
       : HArithmeticBinaryOperation(context, left, right) {
@@ skipping 2437 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_