Keep track of which maps are associated with prototype objects

src/objects.h

Index: src/objects.h
===================================================================
--- src/objects.h	(revision 11658)
+++ src/objects.h	(working copy)
@@ -1583,6 +1583,8 @@
   MUST_USE_RESULT MaybeObject* DeleteNormalizedProperty(String* name,
                                                         DeleteMode mode);
 
+  MUST_USE_RESULT MaybeObject* OptimizeAsPrototype();
+
   // Retrieve interceptors.
   InterceptorInfo* GetNamedInterceptor();
   InterceptorInfo* GetIndexedInterceptor();
@@ -2053,7 +2055,7 @@
   // Maximal number of fast properties for the JSObject. Used to
   // restrict the number of map transitions to avoid an explosion in
   // the number of maps for objects used as dictionaries.
-  inline int MaxFastProperties();
+  inline bool TooManyFastProperties(int properties);
 
   // Maximal number of elements (numbered 0 .. kMaxElementCount - 1).
   // Also maximal value of JSArray's length property.
@@ -2075,7 +2077,8 @@
   static const int kMaxUncheckedOldFastElementsLength = 500;
 
   static const int kInitialMaxFastElementArray = 100000;
-  static const int kMaxFastProperties = 12;
+  static const int kFastPropertiesSoftLimit = 12;
+  static const int kMaxFastProperties = 32;
   static const int kMaxInstanceSize = 255 * kPointerSize;
   // When extending the backing storage for property values, we increase
   // its size by more than the 1 entry necessary, so sequentially adding fields
@@ -4663,9 +4666,16 @@
   // behavior. If true, the map should never be modified, instead a clone
   // should be created and modified.
   inline void set_is_shared(bool value);
-
   inline bool is_shared();
 
+  // Tells whether the map is used for an object that is a prototype for another
+  // object or is the prototype on a function.  Such maps are made faster by
+  // tweaking the heuristics that distinguish between regular object-oriented
+  // objects and the objects that are being used as hash maps.  This flag is
+  // for optimization, not correctness.
+  inline void set_used_for_prototype(bool value);
+  inline bool used_for_prototype();
+
   // Tells whether the instance needs security checks when accessing its
   // properties.
   inline void set_is_access_check_needed(bool access_check_needed);
@@ -4856,7 +4866,7 @@
 
   static const int kMaxCachedPrototypeTransitions = 256;
 
-  Object* GetPrototypeTransition(Object* prototype);
+  Map* GetPrototypeTransition(Object* prototype);

[Michael Starzinger, 2012/05/30 14:08:03]

I know this is not part of this CL, but can we add some comments to
[Get/Put]PrototypeTransition() and also briefly describe the new "the-hole
magic" you are adding?

[Erik Corry, 2012/05/30 15:24:13]

Done.

 
   MUST_USE_RESULT MaybeObject* PutPrototypeTransition(Object* prototype,
                                                       Map* map);
@@ -4949,6 +4959,7 @@
   // Bit positions for bit field 3
   static const int kIsShared = 0;
   static const int kFunctionWithPrototype = 1;
+  static const int kUsedForPrototype = 2;
 
   // Layout of the default cache. It holds alternating name and code objects.
   static const int kCodeCacheEntrySize = 2;