Merging ContentArray into DescriptorArray

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 2411 matching lines @@
  public:
   // 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;
+    return len <= kFirstIndex ? 0 : (len - kFirstIndex) / kDescriptorSize;
   }
 
   int NextEnumerationIndex() {
     if (IsEmpty()) return PropertyDetails::kInitialIndex;
     Object* obj = get(kEnumerationIndexIndex);
     if (obj->IsSmi()) {
       return Smi::cast(obj)->value();
     } else {
       Object* index = FixedArray::cast(obj)->get(kEnumCacheBridgeEnumIndex);
       return Smi::cast(index)->value();
     }
   }
 
   // Set next enumeration index and flush any enum cache.
   void SetNextEnumerationIndex(int value) {
     if (!IsEmpty()) {
       set(kEnumerationIndexIndex, Smi::FromInt(value));
     }
   }
   bool HasEnumCache() {
     return !IsEmpty() && !get(kEnumerationIndexIndex)->IsSmi();
   }
 
   Object* GetEnumCache() {
     ASSERT(HasEnumCache());
     FixedArray* bridge = FixedArray::cast(get(kEnumerationIndexIndex));
     return bridge->get(kEnumCacheBridgeCacheIndex);
   }
 
+  Object** GetEnumCacheSlot() {
+    ASSERT(HasEnumCache());
+    return HeapObject::RawField(reinterpret_cast<HeapObject*>(this),
+                                kEnumerationIndexOffset);
+  }
+
   // TODO(1399): It should be possible to make room for bit_field3 in the map
   //             without overloading the instance descriptors field in the map
   //             (and storing it in the DescriptorArray when the map has one).
   inline int bit_field3_storage();
   inline void set_bit_field3_storage(int value);
 
   // Initialize or change the enum cache,
   // using the supplied storage for the small "bridge".
   void SetEnumCache(FixedArray* bridge_storage,
                     FixedArray* new_cache,
                     Object* new_index_cache);
 
   // Accessors for fetching instance descriptor at descriptor number.
   inline String* GetKey(int descriptor_number);
+  inline Object** GetKeySlot(int descriptor_number);
   inline Object* GetValue(int descriptor_number);
+  inline Object** GetValueSlot(int descriptor_number);
+  inline void SetNullValueUnchecked(int descriptor_number, Heap* heap);
   inline PropertyDetails GetDetails(int descriptor_number);
+  inline void SetDetailsUnchecked(int descriptor_number, Smi* value);
+
+  inline Object* RawGetValue(int descriptor_number);
+  inline PropertyDetails RawGetDetails(int descriptor_number);
+
   inline PropertyType GetType(int descriptor_number);
   inline int GetFieldIndex(int descriptor_number);
   inline JSFunction* GetConstantFunction(int descriptor_number);
   inline Object* GetCallbacksObject(int descriptor_number);
   inline AccessorDescriptor* GetCallbacks(int descriptor_number);
   inline bool IsProperty(int descriptor_number);
   inline bool IsTransitionOnly(int descriptor_number);
   inline bool IsNullDescriptor(int descriptor_number);
 
+  // WhitenessWitness is used to prove that a specific descriptor array is white
+  // (unmarked), so potentially unique heap objects can be freely assigned
+  // without potentially causing memory leaks. A witness is always
+  // stack-allocated right after creating a descriptor array. By allocating a witness,

[Florian Schneider, 2012/05/22 16:53:09]

Long line.

+  // incremental marking is globally disabled. The witness is then passed along
+  // wherever needed to statically prove that the descriptor array is known to
+  // be white.
   class WhitenessWitness {
    public:
     inline explicit WhitenessWitness(DescriptorArray* array);
     inline ~WhitenessWitness();
 
    private:
     IncrementalMarking* marking_;
   };
 
   // Accessor for complete descriptor.
@@ skipping 63 matching lines @@
   // empty descriptor array object if number_of_descriptors is 0.
   MUST_USE_RESULT static MaybeObject* Allocate(int number_of_descriptors);
 
   // Casting.
   static inline DescriptorArray* cast(Object* obj);
 
   // Constant for denoting key was not found.
   static const int kNotFound = -1;
 
   static const int kBitField3StorageIndex = 0;
-  static const int kContentArrayIndex = 1;
-  static const int kEnumerationIndexIndex = 2;
-  static const int kFirstIndex = 3;
+  static const int kEnumerationIndexIndex = 1;
+  static const int kFirstIndex = 2;
 
   // The length of the "bridge" to the enum cache.
   static const int kEnumCacheBridgeLength = 3;
   static const int kEnumCacheBridgeEnumIndex = 0;
   static const int kEnumCacheBridgeCacheIndex = 1;
   static const int kEnumCacheBridgeIndicesCacheIndex = 2;
 
   // Layout description.
   static const int kBitField3StorageOffset = FixedArray::kHeaderSize;
-  static const int kContentArrayOffset = kBitField3StorageOffset + kPointerSize;
-  static const int kEnumerationIndexOffset = kContentArrayOffset + kPointerSize;
+  static const int kEnumerationIndexOffset = kBitField3StorageOffset +
+                                             kPointerSize;
   static const int kFirstOffset = kEnumerationIndexOffset + kPointerSize;
 
   // Layout description for the bridge array.
   static const int kEnumCacheBridgeEnumOffset = FixedArray::kHeaderSize;
   static const int kEnumCacheBridgeCacheOffset =
     kEnumCacheBridgeEnumOffset + kPointerSize;
 
+  // Layout of descriptor.
+  static const int kDescriptorSize = 3;

[Florian Schneider, 2012/05/22 16:53:09]

Maybe sort the constants for the layout by increasing numbers.

+  static const int kDescriptorKey = 0;
+  static const int kDescriptorDetails = 1;
+  static const int kDescriptorValue = 2;
+
 #ifdef OBJECT_PRINT
   // Print all the descriptors.
   inline void PrintDescriptors() {
     PrintDescriptors(stdout);
   }
   void PrintDescriptors(FILE* out);
 #endif
 
 #ifdef DEBUG
   // Is the descriptor array sorted and without duplicates?
@@ skipping 20 matching lines @@
     inline PropertyType type() { return descs_->GetType(index_); }
     inline Object* GetCallbackObject() { return descs_->GetValue(index_); }
 
    private:
     DescriptorArray* descs_;
     int index_;
   };
 
   // Conversion from descriptor number to array indices.
   static int ToKeyIndex(int descriptor_number) {
-    return descriptor_number+kFirstIndex;
+    return kFirstIndex +
+           (descriptor_number * kDescriptorSize) +
+           kDescriptorKey;
   }
 
   static int ToDetailsIndex(int descriptor_number) {
-    return (descriptor_number << 1) + 1;
+    return kFirstIndex +
+           (descriptor_number * kDescriptorSize) +
+           kDescriptorDetails;
   }
 
   static int ToValueIndex(int descriptor_number) {
-    return descriptor_number << 1;
+    return kFirstIndex +
+           (descriptor_number * kDescriptorSize) +
+           kDescriptorValue;
   }
 
   // Swap operation on FixedArray without using write barriers.
   static inline void NoIncrementalWriteBarrierSwap(
       FixedArray* array, int first, int second);
 
   // Swap descriptor first and second.
   inline void NoIncrementalWriteBarrierSwapDescriptors(
       int first, int second);
 
-  FixedArray* GetContentArray() {
-    return FixedArray::cast(get(kContentArrayIndex));
-  }
   DISALLOW_IMPLICIT_CONSTRUCTORS(DescriptorArray);
 };
 
 
 // HashTable is a subclass of FixedArray that implements a hash table
 // that uses open addressing and quadratic probing.
 //
 // In order for the quadratic probing to work, elements that have not
 // yet been used and elements that have been deleted are
 // distinguished.  Probing continues when deleted elements are
@@ skipping 5984 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_