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// Copyright 2014 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.
#include <iosfwd>
#include "src/objects.h"
namespace v8 {
namespace internal {
// LayoutDescriptor is a bit vector defining which fields contain non-tagged
// values. It could either be a fixed typed array (slow form) or a Smi
// if the length fits (fast form).
// Each bit in the layout represents a FIELD. The bits are referenced by
// field_index which is a field number. If the bit is set then the corresponding
// field contains a non-tagged value and therefore must be skipped by GC.
// Otherwise the field is considered tagged. If the queried bit lays "outside"
// of the descriptor then the field is also considered tagged.
// Once a layout descriptor is created it is allowed only to append properties
// to it.
class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
V8_INLINE bool IsTagged(int field_index);
// Queries the contiguous region of fields that are either tagged or not.
// Returns true if the given field is tagged or false otherwise and writes
// the length of the contiguous region to |out_sequence_length|.
// If the sequence is longer than |max_sequence_length| then
// |out_sequence_length| is set to |max_sequence_length|.
bool IsTagged(int field_index, int max_sequence_length,
int* out_sequence_length);
// Returns true if this is a layout of the object having only tagged fields.
V8_INLINE bool IsFastPointerLayout();
V8_INLINE static bool IsFastPointerLayout(Object* layout_descriptor);
// Returns true if the layout descriptor is in non-Smi form.
V8_INLINE bool IsSlowLayout();
V8_INLINE static LayoutDescriptor* cast(Object* object);
V8_INLINE static const LayoutDescriptor* cast(const Object* object);
V8_INLINE static LayoutDescriptor* cast_gc_safe(Object* object);
// Builds layout descriptor optimized for given |map| by |num_descriptors|
// elements of given descriptors array. The |map|'s descriptors could be
// different.
static Handle<LayoutDescriptor> New(Handle<Map> map,
Handle<DescriptorArray> descriptors,
int num_descriptors);
// Creates new layout descriptor by appending property with |details| to
// |map|'s layout descriptor.
static Handle<LayoutDescriptor> Append(Handle<Map> map,
PropertyDetails details);
// Creates new layout descriptor by appending property with |details| to
// |map|'s layout descriptor and if it is still fast then returns it.
// Otherwise the |full_layout_descriptor| is returned.
static Handle<LayoutDescriptor> AppendIfFastOrUseFull(
Handle<Map> map, PropertyDetails details,
Handle<LayoutDescriptor> full_layout_descriptor);
// Layout descriptor that corresponds to an object all fields of which are
// tagged (FastPointerLayout).
V8_INLINE static LayoutDescriptor* FastPointerLayout();
#ifdef DEBUG
// Check that this layout descriptor corresponds to given map.
bool IsConsistentWithMap(Map* map);
// For our gdb macros, we should perhaps change these in the future.
void Print();
void Print(std::ostream& os); // NOLINT
// Capacity of layout descriptors in bits.
V8_INLINE int capacity();
static Handle<LayoutDescriptor> NewForTesting(Isolate* isolate, int length);
LayoutDescriptor* SetTaggedForTesting(int field_index, bool tagged);
static const int kNumberOfBits = 32;
V8_INLINE static Handle<LayoutDescriptor> New(Isolate* isolate, int length);
V8_INLINE static LayoutDescriptor* FromSmi(Smi* smi);
V8_INLINE static bool InobjectUnboxedField(int inobject_properties,
PropertyDetails details);
static Handle<LayoutDescriptor> EnsureCapacity(
Isolate* isolate, Handle<LayoutDescriptor> layout_descriptor,
int new_capacity);
// Returns false if requested field_index is out of bounds.
V8_INLINE bool GetIndexes(int field_index, int* layout_word_index,
int* layout_bit_index);
V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetRawData(int field_index) {
return SetTagged(field_index, false);
V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetTagged(int field_index,
bool tagged);
// LayoutDescriptorHelper is a helper class for querying layout descriptor
// about whether the field at given offset is tagged or not.
class LayoutDescriptorHelper {
inline explicit LayoutDescriptorHelper(Map* map);
bool all_fields_tagged() { return all_fields_tagged_; }
inline bool IsTagged(int offset_in_bytes);
// Queries the contiguous region of fields that are either tagged or not.
// Returns true if fields starting at |offset_in_bytes| are tagged or false
// otherwise and writes the offset of the end of the contiguous region to
// |out_end_of_contiguous_region_offset|. The |end_offset| value is the
// upper bound for |out_end_of_contiguous_region_offset|.
bool IsTagged(int offset_in_bytes, int end_offset,
int* out_end_of_contiguous_region_offset);
bool all_fields_tagged_;
int header_size_;
LayoutDescriptor* layout_descriptor_;
} // namespace v8::internal