Fix IsDeletable() for HStringAdd, HStringCharCodeAt, HStringCharFromCode.

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 405 matching lines @@
   }
 
   bool IsJSObject() const {
     return ((type_ & kJSObject) == kJSObject);
   }
 
   bool IsHeapObject() const {
     return IsHeapNumber() || IsString() || IsBoolean() || IsNonPrimitive();
   }
 
+  bool ToStringOrToNumberCanBeObserved(Representation representation) {
+    switch (type_) {

[Sven Panne, 2013/07/29 11:48:08]

The usual pattern within v8 is:

   switch (foo) {
     case BLAH:
     case BLOH:
       return 42;
     case FOO:
       return 271828;
   }
   UNREACHABLE();
   return 0;  // Make -Wall happy

I'll leave it up to you if you change it or not.

[Michael Starzinger, 2013/07/29 12:30:03]

+1 on this comment.

+    case kTaggedPrimitive:  // fallthru

[Sven Panne, 2013/07/29 11:48:08]

Align.

+      case kTaggedNumber:   // fallthru
+      case kSmi:            // fallthru
+      case kHeapNumber:     // fallthru
+      case kString:         // fallthru
+      case kBoolean: return false;
+      case kJSArray:        // fallthru
+      case kJSObject: return true;
+      case kTagged: break;
+    }
+    return !representation.IsSmiOrInteger32() && !representation.IsDouble();
+  }
+
   static HType TypeFromValue(Handle<Object> value);
 
   const char* ToString();
 
  private:
   enum Type {
     kTagged = 0x1,           // 0000 0000 0000 0001
     kTaggedPrimitive = 0x5,  // 0000 0000 0000 0101
     kTaggedNumber = 0xd,     // 0000 0000 0000 1101
     kSmi = 0x1d,             // 0000 0000 0001 1101
@@ skipping 683 matching lines @@
 
   bool TryGuaranteeRange(HValue* upper_bound);
   virtual bool TryDecompose(DecompositionResult* decomposition) {
     if (RedefinedOperand() != NULL) {
       return RedefinedOperand()->TryDecompose(decomposition);
     } else {
       return false;
     }
   }
 
+  // Returns true conservatively if the program might be able to observe a
+  // ToString() operation on this value.
+  bool ToStringCanBeObserved() const {
+    return type().ToStringOrToNumberCanBeObserved(representation());
+  }
+
+  // Returns true conservatively if the program might be able to observe a
+  // ToNumber() operation on this value.
+  bool ToNumberCanBeObserved() const {
+    return type().ToStringOrToNumberCanBeObserved(representation());
+  }
+
  protected:
   void TryGuaranteeRangeRecursive(RangeEvaluationContext* context);
 
   enum RangeGuaranteeDirection {
     DIRECTION_NONE = 0,
     DIRECTION_UPPER = 1,
     DIRECTION_LOWER = 2,
     DIRECTION_BOTH = DIRECTION_UPPER | DIRECTION_LOWER
   };
   virtual void SetResponsibilityForRange(RangeGuaranteeDirection direction) {}
@@ skipping 2174 matching lines @@
   int phi_id() { return phi_id_; }
 
   static HPhi* cast(HValue* value) {
     ASSERT(value->IsPhi());
     return reinterpret_cast<HPhi*>(value);
   }
   virtual Opcode opcode() const { return HValue::kPhi; }
 
   void SimplifyConstantInputs();
 
-  // TODO(titzer): we can't eliminate the receiver for generating backtraces
-  virtual bool IsDeletable() const { return !IsReceiver(); }
-
  protected:
   virtual void DeleteFromGraph();
   virtual void InternalSetOperandAt(int index, HValue* value) {
     inputs_[index] = value;
   }
 
   virtual bool IsRelationTrueInternal(NumericRelation relation,
                                       HValue* other,
                                       int offset = 0,
                                       int scale = 0);
 
  private:
   ZoneList<HValue*> inputs_;
   int merged_index_;
 
   int non_phi_uses_[Representation::kNumRepresentations];
   int indirect_uses_[Representation::kNumRepresentations];
   int phi_id_;
   InductionVariableData* induction_variable_data_;
+
+  // TODO(titzer): we can't eliminate the receiver for generating backtraces
+  virtual bool IsDeletable() const { return !IsReceiver(); }
 };
 
 
 class HInductionVariableAnnotation : public HUnaryOperation {
  public:
   static HInductionVariableAnnotation* AddToGraph(HPhi* phi,
                                                   NumericRelation relation,
                                                   int operand_index);
 
   NumericRelation relation() { return relation_; }
@@ skipping 291 matching lines @@
   HBinaryOperation(HValue* context, HValue* left, HValue* right)
       : observed_output_representation_(Representation::None()) {
     ASSERT(left != NULL && right != NULL);
     SetOperandAt(0, context);
     SetOperandAt(1, left);
     SetOperandAt(2, right);
     observed_input_representation_[0] = Representation::None();
     observed_input_representation_[1] = Representation::None();
   }
 
-  HValue* context() { return OperandAt(0); }
-  HValue* left() { return OperandAt(1); }
-  HValue* right() { return OperandAt(2); }
+  HValue* context() const { return OperandAt(0); }
+  HValue* left() const { return OperandAt(1); }
+  HValue* right() const { return OperandAt(2); }
 
   // True if switching left and right operands likely generates better code.
   bool AreOperandsBetterSwitched() {
     if (!IsCommutative()) return false;
 
     // Constant operands are better off on the right, they can be inlined in
     // many situations on most platforms.
     if (left()->IsConstant()) return true;
     if (right()->IsConstant()) return false;
 
@@ skipping 233 matching lines @@
       base_ = index();
       offset_ = 0;
       scale_ = 0;
       return false;
     }
   }
 
   virtual Representation RequiredInputRepresentation(int arg_index) {
     return representation();
   }
-  virtual bool IsDeletable() const {
-    return skip_check() && !FLAG_debug_code;
-  }
 
   virtual bool IsRelationTrueInternal(NumericRelation relation,
                                       HValue* related_value,
                                       int offset = 0,
                                       int scale = 0);
 
   virtual void PrintDataTo(StringStream* stream);
   virtual void InferRepresentation(HInferRepresentationPhase* h_infer);
 
   HValue* index() { return OperandAt(0); }
@@ skipping 16 matching lines @@
   }
 
   virtual bool DataEquals(HValue* other) { return true; }
   virtual void TryGuaranteeRangeChanging(RangeEvaluationContext* context);
   bool skip_check_;
   HValue* base_;
   int offset_;
   int scale_;
   RangeGuaranteeDirection responsibility_direction_;
   bool allow_equality_;
+
+ private:
+  virtual bool IsDeletable() const {
+    return skip_check() && !FLAG_debug_code;
+  }
 };
 
 
 class HBoundsCheckBaseIndexInformation: public HTemplateInstruction<2> {
  public:
   explicit HBoundsCheckBaseIndexInformation(HBoundsCheck* check) {
     DecompositionResult decomposition;
     if (check->index()->TryDecompose(&decomposition)) {
       SetOperandAt(0, decomposition.base());
       SetOperandAt(1, check);
@@ skipping 2481 matching lines @@
 
  private:
   HStringAdd(HValue* context, HValue* left, HValue* right, StringAddFlags flags)
       : HBinaryOperation(context, left, right), flags_(flags) {
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetGVNFlag(kDependsOnMaps);
     SetGVNFlag(kChangesNewSpacePromotion);
   }
 
-  // TODO(svenpanne) Might be safe, but leave it out until we know for sure.
-  //  virtual bool IsDeletable() const { return true; }
+  // No side-effects except possible allocation.
+  // NOTE: this instruction _does not_ call ToString() on its inputs.
+  virtual bool IsDeletable() const { return true; }
 
   const StringAddFlags flags_;
 };
 
 
 class HStringCharCodeAt: public HTemplateInstruction<3> {
  public:
   HStringCharCodeAt(HValue* context, HValue* string, HValue* index) {
     SetOperandAt(0, context);
     SetOperandAt(1, string);
     SetOperandAt(2, index);
     set_representation(Representation::Integer32());
     SetFlag(kUseGVN);
     SetGVNFlag(kDependsOnMaps);
     SetGVNFlag(kChangesNewSpacePromotion);
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
     // The index is supposed to be Integer32.
     return index == 2
         ? Representation::Integer32()
         : Representation::Tagged();
   }
 
-  HValue* context() { return OperandAt(0); }
-  HValue* string() { return OperandAt(1); }
-  HValue* index() { return OperandAt(2); }
+  HValue* context() const { return OperandAt(0); }
+  HValue* string() const { return OperandAt(1); }
+  HValue* index() const { return OperandAt(2); }
 
   DECLARE_CONCRETE_INSTRUCTION(StringCharCodeAt)
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
 
   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; }
+ private:
+  // No side effects: runtime function assumes string + number inputs.
+  virtual bool IsDeletable() const { return true; }
 };
 
 
 class HStringCharFromCode: public HTemplateInstruction<2> {
  public:
   static HInstruction* New(Zone* zone,
                            HValue* context,
                            HValue* char_code);
 
   virtual Representation RequiredInputRepresentation(int index) {
     return index == 0
         ? Representation::Tagged()
         : Representation::Integer32();
   }
-  virtual HType CalculateInferredType();
+  virtual HType CalculateInferredType() { return HType::String(); }
 
-  HValue* context() { return OperandAt(0); }
-  HValue* value() { return OperandAt(1); }
+  HValue* context() const { return OperandAt(0); }
+  HValue* value() const { return OperandAt(1); }
 
   virtual bool DataEquals(HValue* other) { return true; }
 
   DECLARE_CONCRETE_INSTRUCTION(StringCharFromCode)
 
  private:
   HStringCharFromCode(HValue* context, HValue* char_code) {
     SetOperandAt(0, context);
     SetOperandAt(1, char_code);
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetGVNFlag(kChangesNewSpacePromotion);
   }
 
-  // TODO(svenpanne) Might be safe, but leave it out until we know for sure.
-  // virtual bool IsDeletable() const { return true; }
+  virtual bool IsDeletable() const {
+    return !value()->ToNumberCanBeObserved();
+  }
 };
 
 
 class HStringLength: public HUnaryOperation {
  public:
   static HInstruction* New(Zone* zone, HValue* string);
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
   }
@@ skipping 388 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_