Allow property indexes to refer to slots inside the object header.

src/property.h

Index: src/property.h
diff --git a/src/property.h b/src/property.h
index 3faa28b85ed08ae6dedd0b68ce43e0caf8a9d9e3..14e3d006767d1ef924df445d8731a066a6ed206d 100644
--- a/src/property.h
+++ b/src/property.h
@@ -132,6 +132,44 @@ class CallbacksDescriptor:  public Descriptor {
 };
 
 
+// Hold a property index value distinguishing if it is a field index or an

[Jakob Kummerow, 2012/11/13 10:44:43]

nit: s/Hold/Holds/

+// index inside the object header.
+class PropertyIndex {
+ public:
+  static PropertyIndex NewFieldIndex(int index) {
+    return PropertyIndex(index, false);
+  }
+  static PropertyIndex NewHeaderIndex(int index) {
+    return PropertyIndex(index, true);
+  }
+
+  bool IsFieldIndex() { return (index_ & kHeaderIndexBit) == 0; }

[Jakob Kummerow, 2012/11/13 10:44:43]

nit: I think for this and the next three methods, unix_hacker_style names would
be appropriate, as they're essentially simple getters.

+  bool IsHeaderIndex() { return (index_ & kHeaderIndexBit) != 0; }
+
+  int FieldIndex() {
+    ASSERT(IsFieldIndex());
+    return value();
+  }
+  int HeaderIndex() {
+    ASSERT(IsHeaderIndex());
+    return value();
+  }
+
+  int RawIndex() { return index_; }

[Jakob Kummerow, 2012/11/13 10:44:43]

I don't see this ever getting called.

+
+ private:
+  static const int kHeaderIndexBit = 1 << 31;
+  static const int kIndexMask = ~kHeaderIndexBit;
+
+  int value() { return index_ & kIndexMask; }
+
+  int index_;
+  PropertyIndex(int index, bool isHeaderBased) :

[Jakob Kummerow, 2012/11/13 10:44:43]

nit1: ':' should be on the second line (see e.g. the LookupResult constructor
right below).

nit2: is_header_based. (Usually, we also prefer enums over bools, but since this
method is local to the class, using a bool is OK.)

nit3: within the "private:" section, please adhere to the ordering statics ->
methods -> fields.

+      index_(index | (isHeaderBased ? kHeaderIndexBit : 0)) {
+    ASSERT(index <= kIndexMask);
+  }
+};
+

[Jakob Kummerow, 2012/11/13 10:44:43]

nit: two lines of whitespace between top-level definitions

 class LookupResult BASE_EMBEDDED {
  public:
   explicit LookupResult(Isolate* isolate)
@@ -278,7 +316,7 @@ class LookupResult BASE_EMBEDDED {
   Object* GetLazyValue() {
     switch (type()) {
       case FIELD:
-        return holder()->FastPropertyAt(GetFieldIndex());
+        return holder()->FastPropertyAt(GetFieldIndex().FieldIndex());
       case NORMAL: {
         Object* value;
         value = holder()->property_dictionary()->ValueAt(GetDictionaryEntry());
@@ -334,10 +372,11 @@ class LookupResult BASE_EMBEDDED {
     return number_;
   }
 
-  int GetFieldIndex() {
+  PropertyIndex GetFieldIndex() {
     ASSERT(lookup_type_ == DESCRIPTOR_TYPE);
     ASSERT(IsField());
-    return Descriptor::IndexFromValue(GetValue());
+    return PropertyIndex::NewFieldIndex(
+        Descriptor::IndexFromValue(GetValue()));
   }
 
   int GetLocalFieldIndexFromMap(Map* map) {