Sharing of descriptor arrays.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 720d96e0ea22d891ee22f4668b2cd4a866dc8d91..bec7710dee520d34b578b0c92a492499adbf7b16 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -177,6 +177,13 @@ enum TransitionFlag {
   OMIT_TRANSITION
 };
 
+// Indicates whether we are only interested in the descriptors of a particular
+// map, or in all descriptors in the descriptor array.
+enum DescriptorFlag {
+  ALL_DESCRIPTORS,
+  OWN_DESCRIPTORS
+};
+
 
 // Instance size sentinel for objects of variable size.
 const int kVariableSizeSentinel = 0;
@@ -2479,12 +2486,15 @@ class DescriptorArray: public FixedArray {
   }
 
   inline int number_of_entries() { return number_of_descriptors(); }
-  inline int NextEnumerationIndex() { return number_of_descriptors() + 1; }
 
   bool HasEnumCache() {
     return !IsEmpty() && !get(kEnumCacheIndex)->IsSmi();
   }
 
+  void CopyEnumCacheFrom(DescriptorArray* array) {
+    set(kEnumCacheIndex, array->get(kEnumCacheIndex));
+  }
+
   Object* GetEnumCache() {
     ASSERT(HasEnumCache());
     FixedArray* bridge = FixedArray::cast(get(kEnumCacheIndex));
@@ -2539,19 +2549,17 @@ class DescriptorArray: public FixedArray {
                 int src_index,
                 const WhitenessWitness&);
 
+  MUST_USE_RESULT MaybeObject* CopyUpTo(int enumeration_index);
+
   // Sort the instance descriptors by the hash codes of their keys.
   void Sort();
-  inline void SwapSortedKeys(int first, int second);
 
   // Search the instance descriptors for given name.
-  INLINE(int Search(String* name));
+  INLINE(int Search(String* name, int number_of_own_descriptors));
 
   // As the above, but uses DescriptorLookupCache and updates it when
   // necessary.
-  INLINE(int SearchWithCache(String* name));
-
-  // Tells whether the name is present int the array.
-  bool Contains(String* name) { return kNotFound != Search(name); }
+  INLINE(int SearchWithCache(String* name, Map* map));
 
   // Allocates a DescriptorArray, but returns the singleton
   // empty descriptor array object if number_of_descriptors is 0.
@@ -2594,7 +2602,7 @@ class DescriptorArray: public FixedArray {
 
 #ifdef DEBUG
   // Is the descriptor array sorted and without duplicates?
-  bool IsSortedNoDuplicates();
+  bool IsSortedNoDuplicates(int valid_descriptors = -1);
 
   // Is the descriptor array consistent with the back pointers in targets?
   bool IsConsistentWithBackPointers(Map* current_map);
@@ -2647,24 +2655,21 @@ class DescriptorArray: public FixedArray {
            kDescriptorValue;
   }
 
-  // Swap operation on FixedArray without using write barriers.
-  static inline void NoIncrementalWriteBarrierSwap(
-      FixedArray* array, int first, int second);
-
   // Swap first and second descriptor.
-  inline void NoIncrementalWriteBarrierSwapDescriptors(
-      int first, int second);
+  inline void SwapSortedKeys(int first, int second);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(DescriptorArray);
 };
 
 
-template<typename T>
-inline int LinearSearch(T* array, String* name, int len);
+enum SearchMode { ALL_ENTRIES, VALID_ENTRIES };
 
+template<SearchMode search_mode, typename T>
+inline int LinearSearch(T* array, String* name, int len, int valid_entries);
 
-template<typename T>
-inline int Search(T* array, String* name);
+
+template<SearchMode search_mode, typename T>
+inline int Search(T* array, String* name, int valid_entries = 0);
 
 
 // HashTable is a subclass of FixedArray that implements a hash table
@@ -4670,6 +4675,7 @@ class Map: public HeapObject {
   class IsShared:                   public BitField<bool, 22,  1> {};
   class FunctionWithPrototype:      public BitField<bool, 23,  1> {};
   class DictionaryMap:              public BitField<bool, 24,  1> {};
+  class OwnsDescriptors:            public BitField<bool, 25,  1> {};
 
   // Tells whether the object in the prototype property will be used
   // for instances created from this function.  If the prototype
@@ -4790,12 +4796,14 @@ class Map: public HeapObject {
   static bool IsValidElementsTransition(ElementsKind from_kind,
                                         ElementsKind to_kind);
 
+  bool StoresOwnDescriptors() { return HasTransitionArray(); }
   inline bool HasTransitionArray();
   inline bool HasElementsTransition();
   inline Map* elements_transition_map();
   MUST_USE_RESULT inline MaybeObject* set_elements_transition_map(
       Map* transitioned_map);
-  inline void SetTransition(int index, Map* target);
+  inline void SetTransition(int transition_index, Map* target);
+  inline Map* GetTransition(int transition_index);
   MUST_USE_RESULT inline MaybeObject* AddTransition(String* key, Map* target);
   DECL_ACCESSORS(transitions, TransitionArray)
   inline void ClearTransitions(Heap* heap,
@@ -4835,9 +4843,9 @@ class Map: public HeapObject {
 
   // [instance descriptors]: describes the object.
   inline DescriptorArray* instance_descriptors();
+  inline JSGlobalPropertyCell* descriptors_pointer();
   MUST_USE_RESULT inline MaybeObject* SetDescriptors(
-      DescriptorArray* descriptors,
-      WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
+      DescriptorArray* descriptors);
   static void SetDescriptors(Handle<Map> map,
                              Handle<DescriptorArray> descriptors);
   MUST_USE_RESULT inline MaybeObject* InitializeDescriptors(
@@ -4918,17 +4926,29 @@ class Map: public HeapObject {
   }
 
   void SetNumberOfOwnDescriptors(int number) {
+    ASSERT(number <= instance_descriptors()->number_of_descriptors());
     set_bit_field3(NumberOfOwnDescriptorsBits::update(bit_field3(), number));
   }
 
+  inline JSGlobalPropertyCell* RetrieveDescriptorsPointer();
+
   int EnumLength() {
     return EnumLengthBits::decode(bit_field3());
   }
 
-  void SetEnumLength(int index) {
-    set_bit_field3(EnumLengthBits::update(bit_field3(), index));
+  void SetEnumLength(int length) {
+    if (length != kInvalidEnumCache) {
+      ASSERT(length >= 0);
+      ASSERT(length == 0 || instance_descriptors()->HasEnumCache());
+      ASSERT(length <= NumberOfOwnDescriptors());
+    }
+    set_bit_field3(EnumLengthBits::update(bit_field3(), length));
   }
 
+
+  inline bool owns_descriptors();
+  inline void set_owns_descriptors(bool is_shared);
+
   MUST_USE_RESULT MaybeObject* RawCopy(int instance_size);
   MUST_USE_RESULT MaybeObject* CopyWithPreallocatedFieldDescriptors();
   MUST_USE_RESULT MaybeObject* CopyDropDescriptors();
@@ -4936,6 +4956,7 @@ class Map: public HeapObject {
       DescriptorArray* descriptors,
       String* name,
       TransitionFlag flag);
+  MUST_USE_RESULT MaybeObject* ShareDescriptor(Descriptor* descriptor);
   MUST_USE_RESULT MaybeObject* CopyAddDescriptor(Descriptor* descriptor,
                                                  TransitionFlag flag);
   MUST_USE_RESULT MaybeObject* CopyInsertDescriptor(Descriptor* descriptor,
@@ -4964,7 +4985,8 @@ class Map: public HeapObject {
 
   // Returns the number of properties described in instance_descriptors
   // filtering out properties with the specified attributes.
-  int NumberOfDescribedProperties(PropertyAttributes filter = NONE);
+  int NumberOfDescribedProperties(DescriptorFlag which = OWN_DESCRIPTORS,
+                                  PropertyAttributes filter = NONE);
 
   // Casting.
   static inline Map* cast(Object* obj);
@@ -5068,7 +5090,7 @@ class Map: public HeapObject {
 
   static const int kMaxPreAllocatedPropertyFields = 255;
 
-  // Constant for denoting that the Enum Cache field was not yet used.
+  // Constant for denoting that the enum cache is not yet initialized.
   static const int kInvalidEnumCache = EnumLengthBits::kMax;
 
   // Layout description.