Improve our simple elimination of hole checks.

src/hydrogen-instructions.h

 // Copyright 2011 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 3183 matching lines @@
   virtual Representation RequiredInputRepresentation(int index) const {
     return Representation::None();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(UnknownOSRValue)
 };
 
 
 class HLoadGlobalCell: public HTemplateInstruction<0> {
  public:
-  HLoadGlobalCell(Handle<JSGlobalPropertyCell> cell, bool check_hole_value)
-      : cell_(cell), check_hole_value_(check_hole_value) {
+  HLoadGlobalCell(Handle<JSGlobalPropertyCell> cell, bool deleteable_or_const)

[Kevin Millikin (Chromium), 2011/09/27 12:01:04]

I'm not thrilled with the bool.  The terminology is also confusing by now.  We
have a mix of "(not) read only" / "(not) don't delete" in older code and "(not)
writable" / "(not) configurable" in newer code.

One suggestion is to store the PropertyAttributes from the lookup:

new(zone()) HLoadGlobalCell(cell, lookup.GetAttributes())

And then use them in RequiresHoleCheck().

That should take up the same amount of space and be more flexible.

+      : cell_(cell), deleteable_or_const_(deleteable_or_const) {
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetFlag(kDependsOnGlobalVars);
   }
 
   Handle<JSGlobalPropertyCell>  cell() const { return cell_; }
-  bool check_hole_value() const { return check_hole_value_; }
+  bool deleteable_or_const() const { return deleteable_or_const_; }
+  bool RequiresHoleCheck() const;
 
   virtual void PrintDataTo(StringStream* stream);
 
   virtual intptr_t Hashcode() {
     ASSERT(!HEAP->allow_allocation(false));
     return reinterpret_cast<intptr_t>(*cell_);
   }
 
   virtual Representation RequiredInputRepresentation(int index) const {
     return Representation::None();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(LoadGlobalCell)
 
  protected:
   virtual bool DataEquals(HValue* other) {
     HLoadGlobalCell* b = HLoadGlobalCell::cast(other);
     return cell_.is_identical_to(b->cell());
   }
 
  private:
   Handle<JSGlobalPropertyCell> cell_;
-  bool check_hole_value_;
+  bool deleteable_or_const_;
 };
 
 
 class HLoadGlobalGeneric: public HTemplateInstruction<2> {
  public:
   HLoadGlobalGeneric(HValue* context,
                      HValue* global_object,
                      Handle<Object> name,
                      bool for_typeof)
       : name_(name),
@@ skipping 20 matching lines @@
  private:
   Handle<Object> name_;
   bool for_typeof_;
 };
 
 
 class HStoreGlobalCell: public HUnaryOperation {
  public:
   HStoreGlobalCell(HValue* value,
                    Handle<JSGlobalPropertyCell> cell,
-                   bool check_hole_value)
+                   bool deleteable_or_const)
       : HUnaryOperation(value),
         cell_(cell),
-        check_hole_value_(check_hole_value) {
+        deleteable_or_const_(deleteable_or_const) {
     SetFlag(kChangesGlobalVars);
   }
 
   Handle<JSGlobalPropertyCell> cell() const { return cell_; }
-  bool check_hole_value() const { return check_hole_value_; }
+  bool deleteable_or_const() const { return deleteable_or_const_; }
+  bool RequiresHoleCheck() const { return deleteable_or_const(); }
 
   virtual Representation RequiredInputRepresentation(int index) const {
     return Representation::Tagged();
   }
   virtual void PrintDataTo(StringStream* stream);
 
   DECLARE_CONCRETE_INSTRUCTION(StoreGlobalCell)
 
  private:
   Handle<JSGlobalPropertyCell> cell_;
-  bool check_hole_value_;
+  bool deleteable_or_const_;
 };
 
 
 class HStoreGlobalGeneric: public HTemplateInstruction<3> {
  public:
   HStoreGlobalGeneric(HValue* context,
                       HValue* global_object,
                       Handle<Object> name,
                       HValue* value,
                       bool strict_mode)
@@ skipping 261 matching lines @@
 
   virtual Representation RequiredInputRepresentation(int index) const {
     // The key is supposed to be Integer32.
     return index == 0
       ? Representation::Tagged()
       : Representation::Integer32();
   }
 
   virtual void PrintDataTo(StringStream* stream);
 
-  bool RequiresHoleCheck() const;
-
   DECLARE_CONCRETE_INSTRUCTION(LoadKeyedFastDoubleElement)
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
 };
 
 
 class HLoadKeyedSpecializedArrayElement: public HTemplateInstruction<2> {
  public:
   HLoadKeyedSpecializedArrayElement(HValue* external_elements,
@@ skipping 653 matching lines @@
 
   DECLARE_CONCRETE_INSTRUCTION(In)
 };
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_