src/objects/descriptor-array.h

// Copyright 2017 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_OBJECTS_DESCRIPTOR_ARRAY_H_
#define V8_OBJECTS_DESCRIPTOR_ARRAY_H_

#include "src/objects.h"
#include "src/objects/fixed-array.h"

// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"

namespace v8 {
namespace internal {

template <typename T>
class Handle;

class Isolate;

// An EnumCache is a pair used to hold keys and indices caches.
class EnumCache : public Tuple2 {
 public:
  DECL_ACCESSORS(keys, FixedArray)
  DECL_ACCESSORS(indices, FixedArray)

  DECL_CAST(EnumCache)

  // Layout description.
  static const int kKeysOffset = kValue1Offset;
  static const int kIndicesOffset = kValue2Offset;

 private:
  DISALLOW_IMPLICIT_CONSTRUCTORS(EnumCache);
};

// A DescriptorArray is a fixed array used to hold instance descriptors.
// The format of these objects is:
//   [0]: Number of descriptors
//   [1]: Enum cache.
//   [2]: first key (and internalized String)
//   [3]: first descriptor details (see PropertyDetails)
//   [4]: first value for constants | Smi(1) when not used
//
//   [2 + number of descriptors * 3]: start of slack
// The "value" fields store either values or field types. A field type is either
// FieldType::None(), FieldType::Any() or a weak reference to a Map. All other
// references are strong.
class DescriptorArray : public WeakFixedArray {
 public:
  // Returns the number of descriptors in the array.
  inline int number_of_descriptors() const;
  inline int number_of_descriptors_storage() const;
  inline int NumberOfSlackDescriptors() const;

  inline void SetNumberOfDescriptors(int number_of_descriptors);
  inline int number_of_entries() const;

  inline EnumCache* GetEnumCache();

  void ClearEnumCache();
  inline void CopyEnumCacheFrom(DescriptorArray* array);
  // Initialize or change the enum cache,
  static void SetEnumCache(Handle<DescriptorArray> descriptors,
                           Isolate* isolate, Handle<FixedArray> keys,
                           Handle<FixedArray> indices);

  // Accessors for fetching instance descriptor at descriptor number.
  inline Name* GetKey(int descriptor_number);
  inline Object** GetKeySlot(int descriptor_number);
  inline Object* GetStrongValue(int descriptor_number);
  inline void SetValue(int descriptor_number, Object* value);
  inline MaybeObject* GetValue(int descriptor_number);
  inline MaybeObject** GetValueSlot(int descriptor_number);
  static inline int GetValueOffset(int descriptor_number);
  inline MaybeObject** GetDescriptorStartSlot(int descriptor_number);
  inline MaybeObject** GetDescriptorEndSlot(int descriptor_number);
  inline PropertyDetails GetDetails(int descriptor_number);
  inline int GetFieldIndex(int descriptor_number);
  inline FieldType* GetFieldType(int descriptor_number);

  inline Name* GetSortedKey(int descriptor_number);
  inline int GetSortedKeyIndex(int descriptor_number);
  inline void SetSortedKey(int pointer, int descriptor_number);

  // Accessor for complete descriptor.
  inline void Set(int descriptor_number, Descriptor* desc);
  inline void Set(int descriptor_number, Name* key, MaybeObject* value,
                  PropertyDetails details);
  void Replace(int descriptor_number, Descriptor* descriptor);

  // Generalizes constness, representation and field type of all field
  // descriptors.
  void GeneralizeAllFields();

  // 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);

  static Handle<DescriptorArray> CopyUpTo(Isolate* isolate,
                                          Handle<DescriptorArray> desc,
                                          int enumeration_index, int slack = 0);

  static Handle<DescriptorArray> CopyUpToAddAttributes(
      Isolate* isolate, Handle<DescriptorArray> desc, int enumeration_index,
      PropertyAttributes attributes, int slack = 0);

  static Handle<DescriptorArray> CopyForFastObjectClone(
      Isolate* isolate, Handle<DescriptorArray> desc, int enumeration_index,
      int slack = 0);

  // Sort the instance descriptors by the hash codes of their keys.
  void Sort();

  // Search the instance descriptors for given name.
  V8_INLINE int Search(Name* name, int number_of_own_descriptors);
  V8_INLINE int Search(Name* name, Map* map);

  // As the above, but uses DescriptorLookupCache and updates it when
  // necessary.
  V8_INLINE int SearchWithCache(Isolate* isolate, Name* name, Map* map);

  bool IsEqualUpTo(DescriptorArray* desc, int nof_descriptors);

  // Allocates a DescriptorArray, but returns the singleton
  // empty descriptor array object if number_of_descriptors is 0.
  static Handle<DescriptorArray> Allocate(
      Isolate* isolate, int number_of_descriptors, int slack,
      PretenureFlag pretenure = NOT_TENURED);

  DECL_CAST(DescriptorArray)

  // Constant for denoting key was not found.
  static const int kNotFound = -1;

  static const int kDescriptorLengthIndex = 0;
  static const int kEnumCacheIndex = 1;
  static const int kFirstIndex = 2;

  // Layout description.
  static const int kDescriptorLengthOffset = FixedArray::kHeaderSize;
  static const int kEnumCacheOffset = kDescriptorLengthOffset + kPointerSize;
  static const int kFirstOffset = kEnumCacheOffset + kPointerSize;

  // Layout of descriptor.
  // Naming is consistent with Dictionary classes for easy templating.
  static const int kEntryKeyIndex = 0;
  static const int kEntryDetailsIndex = 1;
  static const int kEntryValueIndex = 2;
  static const int kEntrySize = 3;

  // Print all the descriptors.
  void PrintDescriptors(std::ostream& os);
  void PrintDescriptorDetails(std::ostream& os, int descriptor,
                              PropertyDetails::PrintMode mode);

  DECL_PRINTER(DescriptorArray)
  DECL_VERIFIER(DescriptorArray)

#ifdef DEBUG
  // Is the descriptor array sorted and without duplicates?
  bool IsSortedNoDuplicates(int valid_descriptors = -1);

  // Are two DescriptorArrays equal?
  bool IsEqualTo(DescriptorArray* other);
#endif

  // Returns the fixed array length required to hold number_of_descriptors
  // descriptors.
  static constexpr int LengthFor(int number_of_descriptors) {
    return ToKeyIndex(number_of_descriptors);
  }

  static constexpr int ToDetailsIndex(int descriptor_number) {
    return kFirstIndex + (descriptor_number * kEntrySize) + kEntryDetailsIndex;
  }

  // Conversion from descriptor number to array indices.
  static constexpr int ToKeyIndex(int descriptor_number) {
    return kFirstIndex + (descriptor_number * kEntrySize) + kEntryKeyIndex;
  }

  static constexpr int ToValueIndex(int descriptor_number) {
    return kFirstIndex + (descriptor_number * kEntrySize) + kEntryValueIndex;
  }

 private:
  inline MaybeObject* get(int index) const;
  inline void set(int index, MaybeObject* value);

  // Transfer a complete descriptor from the src descriptor array to this
  // descriptor array.
  void CopyFrom(int index, DescriptorArray* src);

  // Swap first and second descriptor.
  inline void SwapSortedKeys(int first, int second);

  DISALLOW_IMPLICIT_CONSTRUCTORS(DescriptorArray);
};

}  // namespace internal
}  // namespace v8

#include "src/objects/object-macros-undef.h"

#endif  // V8_OBJECTS_DESCRIPTOR_ARRAY_H_