// 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. #ifndef V8_LAYOUT_DESCRIPTOR_H_ #define V8_LAYOUT_DESCRIPTOR_H_ #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> { public: V8_INLINE bool IsTagged(int field_index); // Returns true if this is a layout of the object having only tagged fields. V8_INLINE bool IsFastPointerLayout(); // 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); #endif #ifdef OBJECT_PRINT // For our gdb macros, we should perhaps change these in the future. void Print(); void Print(std::ostream& os); // NOLINT #endif // Capacity of layout descriptors in bits. V8_INLINE int capacity(); V8_INLINE LayoutDescriptor* SetTaggedForTesting(int field_index, bool tagged) { return SetTagged(field_index, tagged); } private: 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, uint32_t* layout_mask); 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); }; // InobjectPropertiesHelper is a helper class for querying layout descriptor // about whether the field at given offset is tagged or not. class InobjectPropertiesHelper { public: inline explicit InobjectPropertiesHelper(Map* map); bool all_fields_tagged() { return all_fields_tagged_; } inline bool IsTagged(int offset_in_bytes); private: bool all_fields_tagged_; int header_size_; LayoutDescriptor* layout_descriptor_; }; } } // namespace v8::internal #endif // V8_LAYOUT_DESCRIPTOR_H_