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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.
4 :
5 : #ifndef V8_LAYOUT_DESCRIPTOR_H_
6 : #define V8_LAYOUT_DESCRIPTOR_H_
7 :
8 : #include <iosfwd>
9 :
10 : #include "src/objects.h"
11 :
12 : namespace v8 {
13 : namespace internal {
14 :
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
24 : // to it. GC uses layout descriptors to iterate objects. Avoid heap pointers
25 : // in a layout descriptor because they can lead to data races in GC when
26 : // GC moves objects in parallel.
27 : class LayoutDescriptor : public ByteArray {
28 : public:
29 : V8_INLINE bool IsTagged(int field_index);
30 :
31 : // Queries the contiguous region of fields that are either tagged or not.
32 : // Returns true if the given field is tagged or false otherwise and writes
33 : // the length of the contiguous region to |out_sequence_length|.
34 : // If the sequence is longer than |max_sequence_length| then
35 : // |out_sequence_length| is set to |max_sequence_length|.
36 : bool IsTagged(int field_index, int max_sequence_length,
37 : int* out_sequence_length);
38 :
39 : // Returns true if this is a layout of the object having only tagged fields.
40 : V8_INLINE bool IsFastPointerLayout();
41 : V8_INLINE static bool IsFastPointerLayout(Object* layout_descriptor);
42 :
43 : // Returns true if the layout descriptor is in non-Smi form.
44 : V8_INLINE bool IsSlowLayout();
45 :
46 : V8_INLINE static LayoutDescriptor* cast(Object* object);
47 : V8_INLINE static const LayoutDescriptor* cast(const Object* object);
48 :
49 : V8_INLINE static LayoutDescriptor* cast_gc_safe(Object* object);
50 :
51 : // Builds layout descriptor optimized for given |map| by |num_descriptors|
52 : // elements of given descriptors array. The |map|'s descriptors could be
53 : // different.
54 : static Handle<LayoutDescriptor> New(Handle<Map> map,
55 : Handle<DescriptorArray> descriptors,
56 : int num_descriptors);
57 :
58 : // Modifies |map|'s layout descriptor or creates a new one if necessary by
59 : // appending property with |details| to it.
60 : static Handle<LayoutDescriptor> ShareAppend(Handle<Map> map,
61 : PropertyDetails details);
62 :
63 : // Creates new layout descriptor by appending property with |details| to
64 : // |map|'s layout descriptor and if it is still fast then returns it.
65 : // Otherwise the |full_layout_descriptor| is returned.
66 : static Handle<LayoutDescriptor> AppendIfFastOrUseFull(
67 : Handle<Map> map, PropertyDetails details,
68 : Handle<LayoutDescriptor> full_layout_descriptor);
69 :
70 : // Layout descriptor that corresponds to an object all fields of which are
71 : // tagged (FastPointerLayout).
72 : V8_INLINE static LayoutDescriptor* FastPointerLayout();
73 :
74 : // Check that this layout descriptor corresponds to given map.
75 : bool IsConsistentWithMap(Map* map, bool check_tail = false);
76 :
77 : // Trims this layout descriptor to given number of descriptors. This happens
78 : // only when corresponding descriptors array is trimmed.
79 : // The layout descriptor could be trimmed if it was slow or it could
80 : // become fast.
81 : LayoutDescriptor* Trim(Heap* heap, Map* map, DescriptorArray* descriptors,
82 : int num_descriptors);
83 :
84 : #ifdef OBJECT_PRINT
85 : // For our gdb macros, we should perhaps change these in the future.
86 : void Print();
87 :
88 : void ShortPrint(std::ostream& os);
89 : void Print(std::ostream& os); // NOLINT
90 : #endif
91 :
92 : // Capacity of layout descriptors in bits.
93 : V8_INLINE int capacity();
94 :
95 : static Handle<LayoutDescriptor> NewForTesting(Isolate* isolate, int length);
96 : LayoutDescriptor* SetTaggedForTesting(int field_index, bool tagged);
97 :
98 : private:
99 : static const int kBitsPerLayoutWord = 32;
100 135536 : int number_of_layout_words() { return length() / kUInt32Size; }
101 1201638 : uint32_t get_layout_word(int index) const { return get_uint32(index); }
102 358602 : void set_layout_word(int index, uint32_t value) { set_uint32(index, value); }
103 :
104 : V8_INLINE static Handle<LayoutDescriptor> New(Isolate* isolate, int length);
105 : V8_INLINE static LayoutDescriptor* FromSmi(Smi* smi);
106 :
107 : V8_INLINE static bool InobjectUnboxedField(int inobject_properties,
108 : PropertyDetails details);
109 :
110 : // Calculates minimal layout descriptor capacity required for given
111 : // |map|, |descriptors| and |num_descriptors|.
112 : V8_INLINE static int CalculateCapacity(Map* map, DescriptorArray* descriptors,
113 : int num_descriptors);
114 :
115 : // Calculates the length of the slow-mode backing store array by given layout
116 : // descriptor length.
117 : V8_INLINE static int GetSlowModeBackingStoreLength(int length);
118 :
119 : // Fills in clean |layout_descriptor| according to given |map|, |descriptors|
120 : // and |num_descriptors|.
121 : V8_INLINE static LayoutDescriptor* Initialize(
122 : LayoutDescriptor* layout_descriptor, Map* map,
123 : DescriptorArray* descriptors, int num_descriptors);
124 :
125 : static Handle<LayoutDescriptor> EnsureCapacity(
126 : Isolate* isolate, Handle<LayoutDescriptor> layout_descriptor,
127 : int new_capacity);
128 :
129 : // Returns false if requested field_index is out of bounds.
130 : V8_INLINE bool GetIndexes(int field_index, int* layout_word_index,
131 : int* layout_bit_index);
132 :
133 : V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetRawData(int field_index);
134 :
135 : V8_INLINE MUST_USE_RESULT LayoutDescriptor* SetTagged(int field_index,
136 : bool tagged);
137 : };
138 :
139 :
140 : // LayoutDescriptorHelper is a helper class for querying layout descriptor
141 : // about whether the field at given offset is tagged or not.
142 : class LayoutDescriptorHelper {
143 : public:
144 : inline explicit LayoutDescriptorHelper(Map* map);
145 :
146 : bool all_fields_tagged() { return all_fields_tagged_; }
147 : inline bool IsTagged(int offset_in_bytes);
148 :
149 : // Queries the contiguous region of fields that are either tagged or not.
150 : // Returns true if fields starting at |offset_in_bytes| are tagged or false
151 : // otherwise and writes the offset of the end of the contiguous region to
152 : // |out_end_of_contiguous_region_offset|. The |end_offset| value is the
153 : // upper bound for |out_end_of_contiguous_region_offset|.
154 : bool IsTagged(int offset_in_bytes, int end_offset,
155 : int* out_end_of_contiguous_region_offset);
156 :
157 : private:
158 : bool all_fields_tagged_;
159 : int header_size_;
160 : LayoutDescriptor* layout_descriptor_;
161 : };
162 : } // namespace internal
163 : } // namespace v8
164 :
165 : #endif // V8_LAYOUT_DESCRIPTOR_H_
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