| // 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); |
| |
| // 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); |
| #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(); |
| |
| static Handle<LayoutDescriptor> NewForTesting(Isolate* isolate, int length); |
| LayoutDescriptor* SetTaggedForTesting(int field_index, bool 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, |
| 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 { |
| public: |
| 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); |
| |
| private: |
| bool all_fields_tagged_; |
| int header_size_; |
| LayoutDescriptor* layout_descriptor_; |
| }; |
| } |
| } // namespace v8::internal |
| |
| #endif // V8_LAYOUT_DESCRIPTOR_H_ |