Reduce space usage of simple transitions and descriptors holders.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 5fa275ef25beec5ac6b406c66d1d26240cbd49df..86a70b043b5ae5db379894ca68f4fd7e4a8080eb 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -177,6 +177,13 @@ enum TransitionFlag {
   OMIT_TRANSITION
 };
 

[Michael Starzinger, 2012/09/19 09:34:55]

Insert second empty newline here.

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

+// Indicates whether the transition is simple: it either adds a property to a

[Michael Starzinger, 2012/09/19 09:34:55]

The comment is slightly confusing to me. Can we rephrase the second part? What
is "it" in this sentence?

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

+// descriptor array; or it modifies the last added property.
+enum SimpleTransitionFlag {
+  SIMPLE_TRANSITION,
+  FULL_TRANSITION
+};
+

[Michael Starzinger, 2012/09/19 09:34:55]

Insert second empty newline here.

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

 // Indicates whether we are only interested in the descriptors of a particular
 // map, or in all descriptors in the descriptor array.
 enum DescriptorFlag {
@@ -4836,7 +4843,10 @@ class Map: public HeapObject {
       Map* transitioned_map);
   inline void SetTransition(int transition_index, Map* target);
   inline Map* GetTransition(int transition_index);
-  MUST_USE_RESULT inline MaybeObject* AddTransition(String* key, Map* target);
+  MUST_USE_RESULT inline MaybeObject* AddTransition(
+      String* key,
+      Map* target,
+      SimpleTransitionFlag flag = SIMPLE_TRANSITION);

[Michael Starzinger, 2012/09/19 09:34:55]

The Google C++ Style Guide doesn't like default arguments. We sometimes break
that rule. But since this method only has two call-sites, I think it's not worth
here.

http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Default_Arguments

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

   DECL_ACCESSORS(transitions, TransitionArray)
   inline void ClearTransitions(Heap* heap,
                                WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
@@ -4987,7 +4997,8 @@ class Map: public HeapObject {
   MUST_USE_RESULT MaybeObject* CopyReplaceDescriptors(
       DescriptorArray* descriptors,
       String* name,
-      TransitionFlag flag);
+      TransitionFlag flag,
+      int descriptor_index = 0);

[Michael Starzinger, 2012/09/19 09:34:55]

Likewise. Although there are more call-sites here. But they are all in
objects.cc, so I also think it's not worth here.

[Toon Verwaest, 2012/09/19 09:53:23]

Done.

   MUST_USE_RESULT MaybeObject* ShareDescriptor(Descriptor* descriptor);
   MUST_USE_RESULT MaybeObject* CopyAddDescriptor(Descriptor* descriptor,
                                                  TransitionFlag flag);