text: // 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_MAP_INL_H_
  #define V8_OBJECTS_MAP_INL_H_
  
  #include "src/objects/map.h"
  
  #include "src/field-type.h"
  #include "src/objects-inl.h"
  #include "src/objects/api-callbacks-inl.h"
  #include "src/objects/descriptor-array.h"
  #include "src/objects/prototype-info-inl.h"
  #include "src/objects/shared-function-info.h"
  #include "src/objects/templates-inl.h"
  #include "src/property.h"
  #include "src/transitions.h"
  
  // For pulling in heap/incremental-marking.h which is needed by
  // ACCESSORS_CHECKED.
  #include "src/heap/heap-inl.h"
  
  // Has to be the last include (doesn't have include guards):
  #include "src/objects/object-macros.h"
  
  namespace v8 {
  namespace internal {
  
  CAST_ACCESSOR(Map)
  
  ACCESSORS(Map, instance_descriptors, DescriptorArray, kDescriptorsOffset)
  ACCESSORS_CHECKED(Map, layout_descriptor, LayoutDescriptor,
                    kLayoutDescriptorOffset, FLAG_unbox_double_fields)
  WEAK_ACCESSORS(Map, raw_transitions, kTransitionsOrPrototypeInfoOffset)
  
  // |bit_field| fields.
  BIT_FIELD_ACCESSORS(Map, bit_field, has_non_instance_prototype,
                      Map::HasNonInstancePrototypeBit)
  BIT_FIELD_ACCESSORS(Map, bit_field, is_callable, Map::IsCallableBit)
  BIT_FIELD_ACCESSORS(Map, bit_field, has_named_interceptor,
                      Map::HasNamedInterceptorBit)
  BIT_FIELD_ACCESSORS(Map, bit_field, has_indexed_interceptor,
                      Map::HasIndexedInterceptorBit)
  BIT_FIELD_ACCESSORS(Map, bit_field, is_undetectable, Map::IsUndetectableBit)
  BIT_FIELD_ACCESSORS(Map, bit_field, is_access_check_needed,
                      Map::IsAccessCheckNeededBit)
  BIT_FIELD_ACCESSORS(Map, bit_field, is_constructor, Map::IsConstructorBit)
  BIT_FIELD_ACCESSORS(Map, bit_field, has_prototype_slot,
                      Map::HasPrototypeSlotBit)
  
  // |bit_field2| fields.
  BIT_FIELD_ACCESSORS(Map, bit_field2, is_extensible, Map::IsExtensibleBit)
  BIT_FIELD_ACCESSORS(Map, bit_field2, is_prototype_map, Map::IsPrototypeMapBit)
  BIT_FIELD_ACCESSORS(Map, bit_field2, is_in_retained_map_list,
                      Map::IsInRetainedMapListBit)
  
  // |bit_field3| fields.
  BIT_FIELD_ACCESSORS(Map, bit_field3, owns_descriptors, Map::OwnsDescriptorsBit)
  BIT_FIELD_ACCESSORS(Map, bit_field3, has_hidden_prototype,
                      Map::HasHiddenPrototypeBit)
  BIT_FIELD_ACCESSORS(Map, bit_field3, is_deprecated, Map::IsDeprecatedBit)
  BIT_FIELD_ACCESSORS(Map, bit_field3, is_migration_target,
                      Map::IsMigrationTargetBit)
  BIT_FIELD_ACCESSORS(Map, bit_field3, is_immutable_proto,
                      Map::IsImmutablePrototypeBit)
  BIT_FIELD_ACCESSORS(Map, bit_field3, new_target_is_base,
                      Map::NewTargetIsBaseBit)
  BIT_FIELD_ACCESSORS(Map, bit_field3, may_have_interesting_symbols,
                      Map::MayHaveInterestingSymbolsBit)
  BIT_FIELD_ACCESSORS(Map, bit_field3, construction_counter,
                      Map::ConstructionCounterBits)
  
  InterceptorInfo* Map::GetNamedInterceptor() {
    DCHECK(has_named_interceptor());
    FunctionTemplateInfo* info = GetFunctionTemplateInfo();
    return InterceptorInfo::cast(info->named_property_handler());
  }
  
  InterceptorInfo* Map::GetIndexedInterceptor() {
    DCHECK(has_indexed_interceptor());
    FunctionTemplateInfo* info = GetFunctionTemplateInfo();
    return InterceptorInfo::cast(info->indexed_property_handler());
  }
  
  bool Map::IsInplaceGeneralizableField(PropertyConstness constness,
                                        Representation representation,
                                        FieldType* field_type) {
    if (FLAG_track_constant_fields && FLAG_modify_map_inplace &&
        (constness == PropertyConstness::kConst)) {
      // VariableMode::kConst -> PropertyConstness::kMutable field generalization
      // may happen in-place.
      return true;
    }
    if (representation.IsHeapObject() && !field_type->IsAny()) {
      return true;
    }
    return false;
  }
  
  bool Map::CanHaveFastTransitionableElementsKind(InstanceType instance_type) {
    return instance_type == JS_ARRAY_TYPE || instance_type == JS_VALUE_TYPE ||
           instance_type == JS_ARGUMENTS_TYPE;
  }
  
  bool Map::CanHaveFastTransitionableElementsKind() const {
    return CanHaveFastTransitionableElementsKind(instance_type());
  }
  
  // static
  void Map::GeneralizeIfCanHaveTransitionableFastElementsKind(
      Isolate* isolate, InstanceType instance_type, PropertyConstness* constness,
      Representation* representation, Handle<FieldType>* field_type) {
    if (CanHaveFastTransitionableElementsKind(instance_type)) {
      // We don't support propagation of field generalization through elements
      // kind transitions because they are inserted into the transition tree
      // before field transitions. In order to avoid complexity of handling
      // such a case we ensure that all maps with transitionable elements kinds
      // do not have fields that can be generalized in-place (without creation
      // of a new map).
      if (FLAG_track_constant_fields && FLAG_modify_map_inplace) {
        // The constness is either already PropertyConstness::kMutable or should
        // become PropertyConstness::kMutable if it was VariableMode::kConst.
        *constness = PropertyConstness::kMutable;
      }
      if (representation->IsHeapObject()) {
        // The field type is either already Any or should become Any if it was
        // something else.
        *field_type = FieldType::Any(isolate);
      }
    }
  }
  
  bool Map::IsUnboxedDoubleField(FieldIndex index) const {
    if (!FLAG_unbox_double_fields) return false;
    if (index.is_hidden_field() || !index.is_inobject()) return false;
    return !layout_descriptor()->IsTagged(index.property_index());
  }
  
  bool Map::TooManyFastProperties(StoreFromKeyed store_mode) const {
    if (UnusedPropertyFields() != 0) return false;
    if (is_prototype_map()) return false;
    int minimum = store_mode == CERTAINLY_NOT_STORE_FROM_KEYED ? 128 : 12;
    int limit = Max(minimum, GetInObjectProperties());
    int external = NumberOfFields() - GetInObjectProperties();
    return external > limit;
  }
  
  PropertyDetails Map::GetLastDescriptorDetails() const {
    return instance_descriptors()->GetDetails(LastAdded());
  }
  
  int Map::LastAdded() const {
    int number_of_own_descriptors = NumberOfOwnDescriptors();
    DCHECK_GT(number_of_own_descriptors, 0);
    return number_of_own_descriptors - 1;
  }
  
  int Map::NumberOfOwnDescriptors() const {
    return NumberOfOwnDescriptorsBits::decode(bit_field3());
  }
  
  void Map::SetNumberOfOwnDescriptors(int number) {
    DCHECK_LE(number, instance_descriptors()->number_of_descriptors());
    CHECK_LE(static_cast<unsigned>(number),
             static_cast<unsigned>(kMaxNumberOfDescriptors));
    set_bit_field3(NumberOfOwnDescriptorsBits::update(bit_field3(), number));
  }
  
  int Map::EnumLength() const { return EnumLengthBits::decode(bit_field3()); }
  
  void Map::SetEnumLength(int length) {
    if (length != kInvalidEnumCacheSentinel) {
      DCHECK_LE(length, NumberOfOwnDescriptors());
      CHECK_LE(static_cast<unsigned>(length),
               static_cast<unsigned>(kMaxNumberOfDescriptors));
    }
    set_bit_field3(EnumLengthBits::update(bit_field3(), length));
  }
  
  FixedArrayBase* Map::GetInitialElements() const {
    FixedArrayBase* result = nullptr;
    if (has_fast_elements() || has_fast_string_wrapper_elements()) {
      result = GetReadOnlyRoots().empty_fixed_array();
    } else if (has_fast_sloppy_arguments_elements()) {
      result = GetReadOnlyRoots().empty_sloppy_arguments_elements();
    } else if (has_fixed_typed_array_elements()) {
      result = GetReadOnlyRoots().EmptyFixedTypedArrayForMap(this);
    } else if (has_dictionary_elements()) {
      result = GetReadOnlyRoots().empty_slow_element_dictionary();
    } else {
      UNREACHABLE();
    }
    DCHECK(!Heap::InNewSpace(result));
    return result;
  }
  
  VisitorId Map::visitor_id() const {
    return static_cast<VisitorId>(
        RELAXED_READ_BYTE_FIELD(this, kVisitorIdOffset));
  }
  
  void Map::set_visitor_id(VisitorId id) {
    CHECK_LT(static_cast<unsigned>(id), 256);
    RELAXED_WRITE_BYTE_FIELD(this, kVisitorIdOffset, static_cast<byte>(id));
  }
  
  int Map::instance_size_in_words() const {
    return RELAXED_READ_BYTE_FIELD(this, kInstanceSizeInWordsOffset);
  }
  
  void Map::set_instance_size_in_words(int value) {
    RELAXED_WRITE_BYTE_FIELD(this, kInstanceSizeInWordsOffset,
                             static_cast<byte>(value));
  }
  
  int Map::instance_size() const {
    return instance_size_in_words() << kPointerSizeLog2;
  }
  
  void Map::set_instance_size(int value) {
    CHECK_EQ(0, value & (kPointerSize - 1));
    value >>= kPointerSizeLog2;
    CHECK_LT(static_cast<unsigned>(value), 256);
    set_instance_size_in_words(value);
  }
  
  int Map::inobject_properties_start_or_constructor_function_index() const {
    return RELAXED_READ_BYTE_FIELD(
        this, kInObjectPropertiesStartOrConstructorFunctionIndexOffset);
  }
  
  void Map::set_inobject_properties_start_or_constructor_function_index(
      int value) {
    CHECK_LT(static_cast<unsigned>(value), 256);
    RELAXED_WRITE_BYTE_FIELD(
        this, kInObjectPropertiesStartOrConstructorFunctionIndexOffset,
        static_cast<byte>(value));
  }
  
  int Map::GetInObjectPropertiesStartInWords() const {
    DCHECK(IsJSObjectMap());
    return inobject_properties_start_or_constructor_function_index();
  }
  
  void Map::SetInObjectPropertiesStartInWords(int value) {
    CHECK(IsJSObjectMap());
    set_inobject_properties_start_or_constructor_function_index(value);
  }
  
  int Map::GetInObjectProperties() const {
    DCHECK(IsJSObjectMap());
    return instance_size_in_words() - GetInObjectPropertiesStartInWords();
  }
  
  int Map::GetConstructorFunctionIndex() const {
    DCHECK(IsPrimitiveMap());
    return inobject_properties_start_or_constructor_function_index();
  }
  
  void Map::SetConstructorFunctionIndex(int value) {
    CHECK(IsPrimitiveMap());
    set_inobject_properties_start_or_constructor_function_index(value);
  }
  
  int Map::GetInObjectPropertyOffset(int index) const {
    return (GetInObjectPropertiesStartInWords() + index) * kPointerSize;
  }
  
  Handle<Map> Map::AddMissingTransitionsForTesting(
      Isolate* isolate, Handle<Map> split_map,
      Handle<DescriptorArray> descriptors,
      Handle<LayoutDescriptor> full_layout_descriptor) {
    return AddMissingTransitions(isolate, split_map, descriptors,
                                 full_layout_descriptor);
  }
  
  InstanceType Map::instance_type() const {
    return static_cast<InstanceType>(
        READ_UINT16_FIELD(this, kInstanceTypeOffset));
  }
  
  void Map::set_instance_type(InstanceType value) {
    WRITE_UINT16_FIELD(this, kInstanceTypeOffset, value);
  }
  
  int Map::UnusedPropertyFields() const {
    int value = used_or_unused_instance_size_in_words();
    DCHECK_IMPLIES(!IsJSObjectMap(), value == 0);
    int unused;
    if (value >= JSObject::kFieldsAdded) {
      unused = instance_size_in_words() - value;
    } else {
      // For out of object properties "used_or_unused_instance_size_in_words"
      // byte encodes the slack in the property array.
      unused = value;
    }
    return unused;
  }
  
  int Map::UnusedInObjectProperties() const {
    // Like Map::UnusedPropertyFields(), but returns 0 for out of object
    // properties.
    int value = used_or_unused_instance_size_in_words();
    DCHECK_IMPLIES(!IsJSObjectMap(), value == 0);
    if (value >= JSObject::kFieldsAdded) {
      return instance_size_in_words() - value;
    }
    return 0;
  }
  
  int Map::used_or_unused_instance_size_in_words() const {
    return RELAXED_READ_BYTE_FIELD(this, kUsedOrUnusedInstanceSizeInWordsOffset);
  }
  
  void Map::set_used_or_unused_instance_size_in_words(int value) {
    CHECK_LE(static_cast<unsigned>(value), 255);
    RELAXED_WRITE_BYTE_FIELD(this, kUsedOrUnusedInstanceSizeInWordsOffset,
                             static_cast<byte>(value));
  }
  
  int Map::UsedInstanceSize() const {
    int words = used_or_unused_instance_size_in_words();
    if (words < JSObject::kFieldsAdded) {
      // All in-object properties are used and the words is tracking the slack
      // in the property array.
      return instance_size();
    }
    return words * kPointerSize;
  }
  
  void Map::SetInObjectUnusedPropertyFields(int value) {
    STATIC_ASSERT(JSObject::kFieldsAdded == JSObject::kHeaderSize / kPointerSize);
    if (!IsJSObjectMap()) {
      CHECK_EQ(0, value);
      set_used_or_unused_instance_size_in_words(0);
      DCHECK_EQ(0, UnusedPropertyFields());
      return;
    }
    CHECK_LE(0, value);
    DCHECK_LE(value, GetInObjectProperties());
    int used_inobject_properties = GetInObjectProperties() - value;
    set_used_or_unused_instance_size_in_words(
        GetInObjectPropertyOffset(used_inobject_properties) / kPointerSize);
    DCHECK_EQ(value, UnusedPropertyFields());
  }
  
  void Map::SetOutOfObjectUnusedPropertyFields(int value) {
    STATIC_ASSERT(JSObject::kFieldsAdded == JSObject::kHeaderSize / kPointerSize);
    CHECK_LT(static_cast<unsigned>(value), JSObject::kFieldsAdded);
    // For out of object properties "used_instance_size_in_words" byte encodes
    // the slack in the property array.
    set_used_or_unused_instance_size_in_words(value);
    DCHECK_EQ(value, UnusedPropertyFields());
  }
  
  void Map::CopyUnusedPropertyFields(Map* map) {
    set_used_or_unused_instance_size_in_words(
        map->used_or_unused_instance_size_in_words());
    DCHECK_EQ(UnusedPropertyFields(), map->UnusedPropertyFields());
  }
  
  void Map::AccountAddedPropertyField() {
    // Update used instance size and unused property fields number.
    STATIC_ASSERT(JSObject::kFieldsAdded == JSObject::kHeaderSize / kPointerSize);
  #ifdef DEBUG
    int new_unused = UnusedPropertyFields() - 1;
    if (new_unused < 0) new_unused += JSObject::kFieldsAdded;
  #endif
    int value = used_or_unused_instance_size_in_words();
    if (value >= JSObject::kFieldsAdded) {
      if (value == instance_size_in_words()) {
        AccountAddedOutOfObjectPropertyField(0);
      } else {
        // The property is added in-object, so simply increment the counter.
        set_used_or_unused_instance_size_in_words(value + 1);
      }
    } else {
      AccountAddedOutOfObjectPropertyField(value);
    }
    DCHECK_EQ(new_unused, UnusedPropertyFields());
  }
  
  void Map::AccountAddedOutOfObjectPropertyField(int unused_in_property_array) {
    unused_in_property_array--;
    if (unused_in_property_array < 0) {
      unused_in_property_array += JSObject::kFieldsAdded;
    }
    CHECK_LT(static_cast<unsigned>(unused_in_property_array),
             JSObject::kFieldsAdded);
    set_used_or_unused_instance_size_in_words(unused_in_property_array);
    DCHECK_EQ(unused_in_property_array, UnusedPropertyFields());
  }
  
  byte Map::bit_field() const { return READ_BYTE_FIELD(this, kBitFieldOffset); }
  
  void Map::set_bit_field(byte value) {
    WRITE_BYTE_FIELD(this, kBitFieldOffset, value);
  }
  
  byte Map::bit_field2() const { return READ_BYTE_FIELD(this, kBitField2Offset); }
  
  void Map::set_bit_field2(byte value) {
    WRITE_BYTE_FIELD(this, kBitField2Offset, value);
  }
  
  bool Map::is_abandoned_prototype_map() const {
    return is_prototype_map() && !owns_descriptors();
  }
  
  bool Map::should_be_fast_prototype_map() const {
    if (!prototype_info()->IsPrototypeInfo()) return false;
    return PrototypeInfo::cast(prototype_info())->should_be_fast_map();
  }
  
  void Map::set_elements_kind(ElementsKind elements_kind) {
    CHECK_LT(static_cast<int>(elements_kind), kElementsKindCount);
    set_bit_field2(Map::ElementsKindBits::update(bit_field2(), elements_kind));
  }
  
  ElementsKind Map::elements_kind() const {
    return Map::ElementsKindBits::decode(bit_field2());
  }
  
  bool Map::has_fast_smi_elements() const {
    return IsSmiElementsKind(elements_kind());
  }
  
  bool Map::has_fast_object_elements() const {
    return IsObjectElementsKind(elements_kind());
  }
  
  bool Map::has_fast_smi_or_object_elements() const {
    return IsSmiOrObjectElementsKind(elements_kind());
  }
  
  bool Map::has_fast_double_elements() const {
    return IsDoubleElementsKind(elements_kind());
  }
  
  bool Map::has_fast_elements() const {
    return IsFastElementsKind(elements_kind());
  }
  
  bool Map::has_sloppy_arguments_elements() const {
    return IsSloppyArgumentsElementsKind(elements_kind());
  }
  
  bool Map::has_fast_sloppy_arguments_elements() const {
    return elements_kind() == FAST_SLOPPY_ARGUMENTS_ELEMENTS;
  }
  
  bool Map::has_fast_string_wrapper_elements() const {
    return elements_kind() == FAST_STRING_WRAPPER_ELEMENTS;
  }
  
  bool Map::has_fixed_typed_array_elements() const {
    return IsFixedTypedArrayElementsKind(elements_kind());
  }
  
  bool Map::has_dictionary_elements() const {
    return IsDictionaryElementsKind(elements_kind());
  }
  
  void Map::set_is_dictionary_map(bool value) {
    uint32_t new_bit_field3 = IsDictionaryMapBit::update(bit_field3(), value);
    new_bit_field3 = IsUnstableBit::update(new_bit_field3, value);
    set_bit_field3(new_bit_field3);
  }
  
  bool Map::is_dictionary_map() const {
    return IsDictionaryMapBit::decode(bit_field3());
  }
  
  void Map::mark_unstable() {
    set_bit_field3(IsUnstableBit::update(bit_field3(), true));
  }
  
  bool Map::is_stable() const { return !IsUnstableBit::decode(bit_field3()); }
  
  bool Map::CanBeDeprecated() const {
    int descriptor = LastAdded();
    for (int i = 0; i <= descriptor; i++) {
      PropertyDetails details = instance_descriptors()->GetDetails(i);
      if (details.representation().IsNone()) return true;
      if (details.representation().IsSmi()) return true;
      if (details.representation().IsDouble()) return true;
      if (details.representation().IsHeapObject()) return true;
      if (details.kind() == kData && details.location() == kDescriptor) {
        return true;
      }
    }
    return false;
  }
  
  void Map::NotifyLeafMapLayoutChange(Isolate* isolate) {
    if (is_stable()) {
      mark_unstable();
      dependent_code()->DeoptimizeDependentCodeGroup(
          isolate, DependentCode::kPrototypeCheckGroup);
    }
  }
  
  bool Map::IsJSObject(InstanceType type) {
    STATIC_ASSERT(LAST_TYPE == LAST_JS_OBJECT_TYPE);
    return type >= FIRST_JS_OBJECT_TYPE;
  }
  
  bool Map::CanTransition() const {
    // Only JSObject and subtypes have map transitions and back pointers.
    return IsJSObject(instance_type());
  }
  
  bool Map::IsBooleanMap() const {
    return this == GetReadOnlyRoots().boolean_map();
  }
  
  bool Map::IsNullMap() const { return this == GetReadOnlyRoots().null_map(); }
  
  bool Map::IsUndefinedMap() const {
    return this == GetReadOnlyRoots().undefined_map();
  }
  
  bool Map::IsNullOrUndefinedMap() const {
    return IsNullMap() || IsUndefinedMap();
  }
  
  bool Map::IsPrimitiveMap() const {
    return instance_type() <= LAST_PRIMITIVE_TYPE;
  }
  bool Map::IsJSReceiverMap() const {
    STATIC_ASSERT(LAST_JS_RECEIVER_TYPE == LAST_TYPE);
    return instance_type() >= FIRST_JS_RECEIVER_TYPE;
  }
  bool Map::IsJSObjectMap() const { return IsJSObject(instance_type()); }
  bool Map::IsJSPromiseMap() const { return instance_type() == JS_PROMISE_TYPE; }
  bool Map::IsJSArrayMap() const { return instance_type() == JS_ARRAY_TYPE; }
  bool Map::IsJSFunctionMap() const {
    return instance_type() == JS_FUNCTION_TYPE;
  }
  bool Map::IsStringMap() const { return instance_type() < FIRST_NONSTRING_TYPE; }
  bool Map::IsJSProxyMap() const { return instance_type() == JS_PROXY_TYPE; }
  bool Map::IsJSGlobalProxyMap() const {
    return instance_type() == JS_GLOBAL_PROXY_TYPE;
  }
  bool Map::IsJSGlobalObjectMap() const {
    return instance_type() == JS_GLOBAL_OBJECT_TYPE;
  }
  bool Map::IsJSTypedArrayMap() const {
    return instance_type() == JS_TYPED_ARRAY_TYPE;
  }
  bool Map::IsJSDataViewMap() const {
    return instance_type() == JS_DATA_VIEW_TYPE;
  }
  
  Object* Map::prototype() const { return READ_FIELD(this, kPrototypeOffset); }
  
  void Map::set_prototype(Object* value, WriteBarrierMode mode) {
    DCHECK(value->IsNull() || value->IsJSReceiver());
    WRITE_FIELD(this, kPrototypeOffset, value);
    CONDITIONAL_WRITE_BARRIER(Heap::FromWritableHeapObject(this), this,
                              kPrototypeOffset, value, mode);
  }
  
  LayoutDescriptor* Map::layout_descriptor_gc_safe() const {
    DCHECK(FLAG_unbox_double_fields);
    Object* layout_desc = RELAXED_READ_FIELD(this, kLayoutDescriptorOffset);
    return LayoutDescriptor::cast_gc_safe(layout_desc);
  }
  
  bool Map::HasFastPointerLayout() const {
    DCHECK(FLAG_unbox_double_fields);
    Object* layout_desc = RELAXED_READ_FIELD(this, kLayoutDescriptorOffset);
    return LayoutDescriptor::IsFastPointerLayout(layout_desc);
  }
  
  void Map::UpdateDescriptors(DescriptorArray* descriptors,
                              LayoutDescriptor* layout_desc) {
    set_instance_descriptors(descriptors);
    if (FLAG_unbox_double_fields) {
      if (layout_descriptor()->IsSlowLayout()) {
        set_layout_descriptor(layout_desc);
      }
  #ifdef VERIFY_HEAP
      // TODO(ishell): remove these checks from VERIFY_HEAP mode.
      if (FLAG_verify_heap) {
        CHECK(layout_descriptor()->IsConsistentWithMap(this));
        CHECK_EQ(Map::GetVisitorId(this), visitor_id());
      }
  #else
      SLOW_DCHECK(layout_descriptor()->IsConsistentWithMap(this));
      DCHECK(visitor_id() == Map::GetVisitorId(this));
  #endif
    }
  }
  
  void Map::InitializeDescriptors(DescriptorArray* descriptors,
                                  LayoutDescriptor* layout_desc) {
    int len = descriptors->number_of_descriptors();
    set_instance_descriptors(descriptors);
    SetNumberOfOwnDescriptors(len);
  
    if (FLAG_unbox_double_fields) {
      set_layout_descriptor(layout_desc);
  #ifdef VERIFY_HEAP
      // TODO(ishell): remove these checks from VERIFY_HEAP mode.
      if (FLAG_verify_heap) {
        CHECK(layout_descriptor()->IsConsistentWithMap(this));
      }
  #else
      SLOW_DCHECK(layout_descriptor()->IsConsistentWithMap(this));
  #endif
      set_visitor_id(Map::GetVisitorId(this));
    }
  }
  
  void Map::set_bit_field3(uint32_t bits) {
    if (kInt32Size != kPointerSize) {
      WRITE_UINT32_FIELD(this, kBitField3Offset + kInt32Size, 0);
    }
    WRITE_UINT32_FIELD(this, kBitField3Offset, bits);
  }
  
  uint32_t Map::bit_field3() const {
    return READ_UINT32_FIELD(this, kBitField3Offset);
  }
  
  LayoutDescriptor* Map::GetLayoutDescriptor() const {
    return FLAG_unbox_double_fields ? layout_descriptor()
                                    : LayoutDescriptor::FastPointerLayout();
  }
  
  void Map::AppendDescriptor(Descriptor* desc) {
    DescriptorArray* descriptors = instance_descriptors();
    int number_of_own_descriptors = NumberOfOwnDescriptors();
    DCHECK(descriptors->number_of_descriptors() == number_of_own_descriptors);
    descriptors->Append(desc);
    SetNumberOfOwnDescriptors(number_of_own_descriptors + 1);
  
    // Properly mark the map if the {desc} is an "interesting symbol".
    if (desc->GetKey()->IsInterestingSymbol()) {
      set_may_have_interesting_symbols(true);
    }
    PropertyDetails details = desc->GetDetails();
    if (details.location() == kField) {
      DCHECK_GT(UnusedPropertyFields(), 0);
      AccountAddedPropertyField();
    }
  
  // This function does not support appending double field descriptors and
  // it should never try to (otherwise, layout descriptor must be updated too).
  #ifdef DEBUG
    DCHECK(details.location() != kField || !details.representation().IsDouble());
  #endif
  }
  
  Object* Map::GetBackPointer() const {
    Object* object = constructor_or_backpointer();
    if (object->IsMap()) {
      return object;
    }
    return GetReadOnlyRoots().undefined_value();
  }
  
  Map* Map::ElementsTransitionMap() {
    DisallowHeapAllocation no_gc;
    // TODO(delphick): While it's safe to pass nullptr for Isolate* here as
    // SearchSpecial doesn't need it, this is really ugly. Perhaps factor out a
    // base class for methods not requiring an Isolate?
    return TransitionsAccessor(nullptr, this, &no_gc)
        .SearchSpecial(GetReadOnlyRoots().elements_transition_symbol());
  }
  
  Object* Map::prototype_info() const {
    DCHECK(is_prototype_map());
    return READ_FIELD(this, Map::kTransitionsOrPrototypeInfoOffset);
  }
  
  void Map::set_prototype_info(Object* value, WriteBarrierMode mode) {
    CHECK(is_prototype_map());
    WRITE_FIELD(this, Map::kTransitionsOrPrototypeInfoOffset, value);
    CONDITIONAL_WRITE_BARRIER(Heap::FromWritableHeapObject(this), this,
                              Map::kTransitionsOrPrototypeInfoOffset, value,
                              mode);
  }
  
  void Map::SetBackPointer(Object* value, WriteBarrierMode mode) {
    CHECK_GE(instance_type(), FIRST_JS_RECEIVER_TYPE);
    CHECK(value->IsMap());
    CHECK(GetBackPointer()->IsUndefined());
    CHECK_IMPLIES(value->IsMap(), Map::cast(value)->GetConstructor() ==
                                      constructor_or_backpointer());
    set_constructor_or_backpointer(value, mode);
  }
  
  ACCESSORS(Map, dependent_code, DependentCode, kDependentCodeOffset)
  ACCESSORS(Map, prototype_validity_cell, Object, kPrototypeValidityCellOffset)
  ACCESSORS(Map, constructor_or_backpointer, Object,
            kConstructorOrBackPointerOffset)
  
  bool Map::IsPrototypeValidityCellValid() const {
    Object* validity_cell = prototype_validity_cell();
    Object* value = validity_cell->IsSmi() ? Smi::cast(validity_cell)
                                           : Cell::cast(validity_cell)->value();
    return value == Smi::FromInt(Map::kPrototypeChainValid);
  }
  
  Object* Map::GetConstructor() const {
    Object* maybe_constructor = constructor_or_backpointer();
    // Follow any back pointers.
    while (maybe_constructor->IsMap()) {
      maybe_constructor =
          Map::cast(maybe_constructor)->constructor_or_backpointer();
    }
    return maybe_constructor;
  }
  
  FunctionTemplateInfo* Map::GetFunctionTemplateInfo() const {
    Object* constructor = GetConstructor();
    if (constructor->IsJSFunction()) {
      DCHECK(JSFunction::cast(constructor)->shared()->IsApiFunction());
      return JSFunction::cast(constructor)->shared()->get_api_func_data();
    }
    DCHECK(constructor->IsFunctionTemplateInfo());
    return FunctionTemplateInfo::cast(constructor);
  }
  
  void Map::SetConstructor(Object* constructor, WriteBarrierMode mode) {
    // Never overwrite a back pointer with a constructor.
    CHECK(!constructor_or_backpointer()->IsMap());
    set_constructor_or_backpointer(constructor, mode);
  }
  
  Handle<Map> Map::CopyInitialMap(Isolate* isolate, Handle<Map> map) {
    return CopyInitialMap(isolate, map, map->instance_size(),
                          map->GetInObjectProperties(),
                          map->UnusedPropertyFields());
  }
  
  bool Map::IsInobjectSlackTrackingInProgress() const {
    return construction_counter() != Map::kNoSlackTracking;
  }
  
  void Map::InobjectSlackTrackingStep(Isolate* isolate) {
    // Slack tracking should only be performed on an initial map.
    DCHECK(GetBackPointer()->IsUndefined());
    if (!IsInobjectSlackTrackingInProgress()) return;
    int counter = construction_counter();
    set_construction_counter(counter - 1);
    if (counter == kSlackTrackingCounterEnd) {
      CompleteInobjectSlackTracking(isolate);
    }
  }
  
  int Map::SlackForArraySize(int old_size, int size_limit) {
    const int max_slack = size_limit - old_size;
    CHECK_LE(0, max_slack);
    if (old_size < 4) {
      DCHECK_LE(1, max_slack);
      return 1;
    }
    return Min(max_slack, old_size / 4);
  }
  
  int NormalizedMapCache::GetIndex(Handle<Map> map) {
    return map->Hash() % NormalizedMapCache::kEntries;
  }
  
  bool NormalizedMapCache::IsNormalizedMapCache(const HeapObject* obj) {
    if (!obj->IsWeakFixedArray()) return false;
    if (WeakFixedArray::cast(obj)->length() != NormalizedMapCache::kEntries) {
      return false;
    }
  #ifdef VERIFY_HEAP
    if (FLAG_verify_heap) {
      NormalizedMapCache* cache =
          reinterpret_cast<NormalizedMapCache*>(const_cast<HeapObject*>(obj));
      cache->NormalizedMapCacheVerify(cache->GetIsolate());
    }
  #endif
    return true;
  }
  
  }  // namespace internal
  }  // namespace v8
  
  #include "src/objects/object-macros-undef.h"
  
  #endif  // V8_OBJECTS_MAP_INL_H_
  