Improve our simple elimination of hole checks.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
===================================================================
--- src/hydrogen-instructions.h	(revision 9445)
+++ src/hydrogen-instructions.h	(working copy)
@@ -3201,15 +3201,16 @@
 
 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);
 
@@ -3232,7 +3233,7 @@
 
  private:
   Handle<JSGlobalPropertyCell> cell_;
-  bool check_hole_value_;
+  bool deleteable_or_const_;
 };
 
 
@@ -3273,15 +3274,16 @@
  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();
@@ -3292,7 +3294,7 @@
 
  private:
   Handle<JSGlobalPropertyCell> cell_;
-  bool check_hole_value_;
+  bool deleteable_or_const_;
 };
 
 
@@ -3574,8 +3576,6 @@
 
   virtual void PrintDataTo(StringStream* stream);
 
-  bool RequiresHoleCheck() const;
-
   DECLARE_CONCRETE_INSTRUCTION(LoadKeyedFastDoubleElement)
 
  protected: