Preallocate space in descriptor arrays.

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2473 matching lines @@
 
   // Returns true for both shared empty_descriptor_array and for smis, which the
   // map uses to encode additional bit fields when the descriptor array is not
   // yet used.
   inline bool IsEmpty();
 
   // Returns the number of descriptors in the array.
   int number_of_descriptors() {
     ASSERT(length() >= kFirstIndex || IsEmpty());
     int len = length();
-    return len <= kFirstIndex ? 0 : (len - kFirstIndex) / kDescriptorSize;
+    return len == 0 ? 0 : Smi::cast(get(kDescriptorLengthIndex))->value();
   }
 
+  int number_of_descriptors_storage() {
+    int len = length();
+    return len == 0 ? 0 : (len - kFirstIndex) / kDescriptorSize;
+  }
+
+  int NumberOfSlackDescriptors() {
+    return number_of_descriptors_storage() - number_of_descriptors();
+  }
+
+  inline void SetNumberOfDescriptors(int number_of_descriptors);
   inline int number_of_entries() { return number_of_descriptors(); }
 
   bool HasEnumCache() {
     return !IsEmpty() && !get(kEnumCacheIndex)->IsSmi();
   }
 
   void CopyEnumCacheFrom(DescriptorArray* array) {
     set(kEnumCacheIndex, array->get(kEnumCacheIndex));
   }
 
@@ skipping 31 matching lines @@
 
   inline String* GetSortedKey(int descriptor_number);
   inline int GetSortedKeyIndex(int descriptor_number);
   inline void SetSortedKey(int pointer, int descriptor_number);
 
   // Accessor for complete descriptor.
   inline void Get(int descriptor_number, Descriptor* desc);
   inline void Set(int descriptor_number,
                   Descriptor* desc,
                   const WhitenessWitness&);
+  inline void Set(int descriptor_number, Descriptor* desc);
+  inline void EraseDescriptor(Heap* heap, int descriptor_number);
 
   // Append automatically sets the enumeration index. This should only be used
   // to add descriptors in bulk at the end, followed by sorting the descriptor
   // array.
-  inline void Append(Descriptor* desc,
-                     const WhitenessWitness&,
-                     int number_of_set_descriptors);
+  inline void Append(Descriptor* desc, const WhitenessWitness&);
+  inline void Append(Descriptor* desc);
 
   // Transfer a complete descriptor from the src descriptor array to this
   // descriptor array.
   void CopyFrom(int dst_index,
                 DescriptorArray* src,
                 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();
 
   // Search the instance descriptors for given 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, Map* map));
 
   // Allocates a DescriptorArray, but returns the singleton
   // empty descriptor array object if number_of_descriptors is 0.
-  MUST_USE_RESULT static MaybeObject* Allocate(int number_of_descriptors);
+  MUST_USE_RESULT static MaybeObject* Allocate(int number_of_descriptors,
+                                               int slack = 0);
 
   // Casting.
   static inline DescriptorArray* cast(Object* obj);
 
   // Constant for denoting key was not found.
   static const int kNotFound = -1;
 
-  static const int kEnumCacheIndex = 0;
-  static const int kFirstIndex = 1;
+  static const int kDescriptorLengthIndex = 0;
+  static const int kEnumCacheIndex = 1;
+  static const int kFirstIndex = 2;
 
   // The length of the "bridge" to the enum cache.
   static const int kEnumCacheBridgeLength = 2;
   static const int kEnumCacheBridgeCacheIndex = 0;
   static const int kEnumCacheBridgeIndicesCacheIndex = 1;
 
   // Layout description.
-  static const int kEnumCacheOffset = FixedArray::kHeaderSize;
+  static const int kDescriptorLengthOffset = FixedArray::kHeaderSize;
+  static const int kEnumCacheOffset = kDescriptorLengthOffset + kPointerSize;
   static const int kFirstOffset = kEnumCacheOffset + kPointerSize;
 
   // Layout description for the bridge array.
   static const int kEnumCacheBridgeCacheOffset = FixedArray::kHeaderSize;
 
   // Layout of descriptor.
   static const int kDescriptorKey = 0;
   static const int kDescriptorDetails = 1;
   static const int kDescriptorValue = 2;
   static const int kDescriptorSize = 3;
@@ skipping 2410 matching lines @@
   inline void ClearCodeCache(Heap* heap);
 
   // Update code cache.
   static void UpdateCodeCache(Handle<Map> map,
                               Handle<String> name,
                               Handle<Code> code);
   MUST_USE_RESULT MaybeObject* UpdateCodeCache(String* name, Code* code);
 
   // Extend the descriptor array of the map with the list of descriptors.
   // In case of duplicates, the latest descriptor is used.
-  static void CopyAppendCallbackDescriptors(Handle<Map> map,
-                                            Handle<Object> descriptors);
+  static void AppendCallbackDescriptors(Handle<Map> map,
+                                        Handle<Object> descriptors);
+
+  static void EnsureDescriptorSlack(Handle<Map> map, int slack);
 
   // Returns the found code or undefined if absent.
   Object* FindInCodeCache(String* name, Code::Flags flags);
 
   // Returns the non-negative index of the code object if it is in the
   // cache and -1 otherwise.
   int IndexInCodeCache(Object* name, Code* code);
 
   // Removes a code object from the code cache at the given index.
   void RemoveFromCodeCache(String* name, Code* code, int index);
@@ skipping 3950 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_