1 // Copyright 2014 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef V8_LAYOUT_DESCRIPTOR_H_
6 #define V8_LAYOUT_DESCRIPTOR_H_
10 #include "src/objects.h"
15 // LayoutDescriptor is a bit vector defining which fields contain non-tagged
16 // values. It could either be a fixed typed array (slow form) or a Smi
17 // if the length fits (fast form).
18 // Each bit in the layout represents a FIELD. The bits are referenced by
19 // field_index which is a field number. If the bit is set then the corresponding
20 // field contains a non-tagged value and therefore must be skipped by GC.
21 // Otherwise the field is considered tagged. If the queried bit lays "outside"
22 // of the descriptor then the field is also considered tagged.
23 // Once a layout descriptor is created it is allowed only to append properties
25 class LayoutDescriptor : public JSTypedArray {
27 V8_INLINE bool IsTagged(int field_index);
29 // Queries the contiguous region of fields that are either tagged or not.
30 // Returns true if the given field is tagged or false otherwise and writes
31 // the length of the contiguous region to |out_sequence_length|.
32 // If the sequence is longer than |max_sequence_length| then
33 // |out_sequence_length| is set to |max_sequence_length|.
34 bool IsTagged(int field_index, int max_sequence_length,
35 int* out_sequence_length);
37 // Returns true if this is a layout of the object having only tagged fields.
38 V8_INLINE bool IsFastPointerLayout();
39 V8_INLINE static bool IsFastPointerLayout(Object* layout_descriptor);
41 // Returns true if the layout descriptor is in non-Smi form.
42 V8_INLINE bool IsSlowLayout();
44 V8_INLINE static LayoutDescriptor* cast(Object* object);
45 V8_INLINE static const LayoutDescriptor* cast(const Object* object);
47 V8_INLINE static LayoutDescriptor* cast_gc_safe(Object* object);
49 // Builds layout descriptor optimized for given |map| by |num_descriptors|
50 // elements of given descriptors array. The |map|'s descriptors could be
52 static Handle<LayoutDescriptor> New(Handle<Map> map,
53 Handle<DescriptorArray> descriptors,
56 // Modifies |map|'s layout descriptor or creates a new one if necessary by
57 // appending property with |details| to it.
58 static Handle<LayoutDescriptor> ShareAppend(Handle<Map> map,
59 PropertyDetails details);
61 // Creates new layout descriptor by appending property with |details| to
62 // |map|'s layout descriptor and if it is still fast then returns it.
63 // Otherwise the |full_layout_descriptor| is returned.
64 static Handle<LayoutDescriptor> AppendIfFastOrUseFull(
65 Handle<Map> map, PropertyDetails details,
66 Handle<LayoutDescriptor> full_layout_descriptor);
68 // Layout descriptor that corresponds to an object all fields of which are
69 // tagged (FastPointerLayout).
70 V8_INLINE static LayoutDescriptor* FastPointerLayout();
72 // Check that this layout descriptor corresponds to given map.
73 bool IsConsistentWithMap(Map* map, bool check_tail = false);
75 // Trims this layout descriptor to given number of descriptors. This happens
76 // only when corresponding descriptors array is trimmed.
77 // The layout descriptor could be trimmed if it was slow or it could
79 LayoutDescriptor* Trim(Heap* heap, Map* map, DescriptorArray* descriptors,
83 // For our gdb macros, we should perhaps change these in the future.
86 void Print(std::ostream& os); // NOLINT
89 // Capacity of layout descriptors in bits.
90 V8_INLINE int capacity();
92 V8_INLINE uint32_t get_scalar(int index);
93 V8_INLINE void set(int index, uint32_t value);
95 static Handle<LayoutDescriptor> NewForTesting(Isolate* isolate, int length);
96 LayoutDescriptor* SetTaggedForTesting(int field_index, bool tagged);
99 static const int kNumberOfBits = 32;
101 V8_INLINE static Handle<LayoutDescriptor> New(Isolate* isolate, int length);
102 V8_INLINE static LayoutDescriptor* FromSmi(Smi* smi);
104 V8_INLINE static bool InobjectUnboxedField(int inobject_properties,
105 PropertyDetails details);
107 // Calculates minimal layout descriptor capacity required for given
108 // |map|, |descriptors| and |num_descriptors|.
109 V8_INLINE static int CalculateCapacity(Map* map, DescriptorArray* descriptors,
110 int num_descriptors);
112 // Calculates the length of the slow-mode backing store array by given layout
113 // descriptor length.
114 V8_INLINE static int GetSlowModeBackingStoreLength(int length);
116 // Fills in clean |layout_descriptor| according to given |map|, |descriptors|
117 // and |num_descriptors|.
118 V8_INLINE static LayoutDescriptor* Initialize(
119 LayoutDescriptor* layout_descriptor, Map* map,
120 DescriptorArray* descriptors, int num_descriptors);
122 static Handle<LayoutDescriptor> EnsureCapacity(
123 Isolate* isolate, Handle<LayoutDescriptor> layout_descriptor,
126 // Returns false if requested field_index is out of bounds.
127 V8_INLINE bool GetIndexes(int field_index, int* layout_word_index,
128 int* layout_bit_index);
130 V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetRawData(int field_index) {
131 return SetTagged(field_index, false);
134 V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetTagged(int field_index,
139 // LayoutDescriptorHelper is a helper class for querying layout descriptor
140 // about whether the field at given offset is tagged or not.
141 class LayoutDescriptorHelper {
143 inline explicit LayoutDescriptorHelper(Map* map);
145 bool all_fields_tagged() { return all_fields_tagged_; }
146 inline bool IsTagged(int offset_in_bytes);
148 // Queries the contiguous region of fields that are either tagged or not.
149 // Returns true if fields starting at |offset_in_bytes| are tagged or false
150 // otherwise and writes the offset of the end of the contiguous region to
151 // |out_end_of_contiguous_region_offset|. The |end_offset| value is the
152 // upper bound for |out_end_of_contiguous_region_offset|.
153 bool IsTagged(int offset_in_bytes, int end_offset,
154 int* out_end_of_contiguous_region_offset);
157 bool all_fields_tagged_;
159 LayoutDescriptor* layout_descriptor_;
162 } // namespace v8::internal
164 #endif // V8_LAYOUT_DESCRIPTOR_H_