Line data Source code
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/fixed-array.h"
11 :
12 : // Has to be the last include (doesn't have include guards):
13 : #include "src/objects/object-macros.h"
14 :
15 : namespace v8 {
16 : namespace internal {
17 :
18 : // LayoutDescriptor is a bit vector defining which fields contain non-tagged
19 : // values. It could either be a fixed typed array (slow form) or a Smi
20 : // if the length fits (fast form).
21 : // Each bit in the layout represents a FIELD. The bits are referenced by
22 : // field_index which is a field number. If the bit is set then the corresponding
23 : // field contains a non-tagged value and therefore must be skipped by GC.
24 : // Otherwise the field is considered tagged. If the queried bit lays "outside"
25 : // of the descriptor then the field is also considered tagged.
26 : // Once a layout descriptor is created it is allowed only to append properties
27 : // to it. GC uses layout descriptors to iterate objects. Avoid heap pointers
28 : // in a layout descriptor because they can lead to data races in GC when
29 : // GC moves objects in parallel.
30 : class LayoutDescriptor : public ByteArray {
31 : public:
32 : V8_INLINE bool IsTagged(int field_index);
33 :
34 : // Queries the contiguous region of fields that are either tagged or not.
35 : // Returns true if the given field is tagged or false otherwise and writes
36 : // the length of the contiguous region to |out_sequence_length|.
37 : // If the sequence is longer than |max_sequence_length| then
38 : // |out_sequence_length| is set to |max_sequence_length|.
39 : bool IsTagged(int field_index, int max_sequence_length,
40 : int* out_sequence_length);
41 :
42 : // Returns true if this is a layout of the object having only tagged fields.
43 : V8_INLINE bool IsFastPointerLayout();
44 : V8_INLINE static bool IsFastPointerLayout(Object layout_descriptor);
45 :
46 : // Returns true if the layout descriptor is in non-Smi form.
47 : V8_INLINE bool IsSlowLayout();
48 :
49 : DECL_CAST(LayoutDescriptor)
50 :
51 : V8_INLINE static LayoutDescriptor cast_gc_safe(Object object);
52 :
53 : // Builds layout descriptor optimized for given |map| by |num_descriptors|
54 : // elements of given descriptors array. The |map|'s descriptors could be
55 : // different.
56 : static Handle<LayoutDescriptor> New(Isolate* isolate, Handle<Map> map,
57 : Handle<DescriptorArray> descriptors,
58 : int num_descriptors);
59 :
60 : // Modifies |map|'s layout descriptor or creates a new one if necessary by
61 : // appending property with |details| to it.
62 : static Handle<LayoutDescriptor> ShareAppend(Isolate* isolate, Handle<Map> map,
63 : PropertyDetails details);
64 :
65 : // Creates new layout descriptor by appending property with |details| to
66 : // |map|'s layout descriptor and if it is still fast then returns it.
67 : // Otherwise the |full_layout_descriptor| is returned.
68 : static Handle<LayoutDescriptor> AppendIfFastOrUseFull(
69 : Isolate* isolate, Handle<Map> map, PropertyDetails details,
70 : Handle<LayoutDescriptor> full_layout_descriptor);
71 :
72 : // Layout descriptor that corresponds to an object all fields of which are
73 : // tagged (FastPointerLayout).
74 : V8_INLINE static LayoutDescriptor FastPointerLayout();
75 :
76 : // Check that this layout descriptor corresponds to given map.
77 : bool IsConsistentWithMap(Map map, bool check_tail = false);
78 :
79 : // Trims this layout descriptor to given number of descriptors. This happens
80 : // only when corresponding descriptors array is trimmed.
81 : // The layout descriptor could be trimmed if it was slow or it could
82 : // become fast.
83 : LayoutDescriptor Trim(Heap* heap, Map map, DescriptorArray descriptors,
84 : int num_descriptors);
85 :
86 : #ifdef OBJECT_PRINT
87 : // For our gdb macros, we should perhaps change these in the future.
88 : void Print();
89 :
90 : void ShortPrint(std::ostream& os);
91 : void Print(std::ostream& os); // NOLINT
92 : #endif
93 :
94 : // Capacity of layout descriptors in bits.
95 : V8_INLINE int capacity();
96 :
97 : static Handle<LayoutDescriptor> NewForTesting(Isolate* isolate, int length);
98 : LayoutDescriptor SetTaggedForTesting(int field_index, bool tagged);
99 :
100 : private:
101 : // Exclude sign-bit to simplify encoding.
102 : static constexpr int kBitsInSmiLayout =
103 : SmiValuesAre32Bits() ? 32 : kSmiValueSize - 1;
104 :
105 : static const int kBitsPerLayoutWord = 32;
106 :
107 : V8_INLINE int number_of_layout_words();
108 : V8_INLINE uint32_t get_layout_word(int index) const;
109 : V8_INLINE void set_layout_word(int index, uint32_t value);
110 :
111 : V8_INLINE static Handle<LayoutDescriptor> New(Isolate* isolate, int length);
112 : V8_INLINE static LayoutDescriptor FromSmi(Smi smi);
113 :
114 : V8_INLINE static bool InobjectUnboxedField(int inobject_properties,
115 : PropertyDetails details);
116 :
117 : // Calculates minimal layout descriptor capacity required for given
118 : // |map|, |descriptors| and |num_descriptors|.
119 : V8_INLINE static int CalculateCapacity(Map map, DescriptorArray descriptors,
120 : int num_descriptors);
121 :
122 : // Calculates the length of the slow-mode backing store array by given layout
123 : // descriptor length.
124 : V8_INLINE static int GetSlowModeBackingStoreLength(int length);
125 :
126 : // Fills in clean |layout_descriptor| according to given |map|, |descriptors|
127 : // and |num_descriptors|.
128 : V8_INLINE static LayoutDescriptor Initialize(
129 : LayoutDescriptor layout_descriptor, Map map, DescriptorArray descriptors,
130 : int num_descriptors);
131 :
132 : static Handle<LayoutDescriptor> EnsureCapacity(
133 : Isolate* isolate, Handle<LayoutDescriptor> layout_descriptor,
134 : int new_capacity);
135 :
136 : // Returns false if requested field_index is out of bounds.
137 : V8_INLINE bool GetIndexes(int field_index, int* layout_word_index,
138 : int* layout_bit_index);
139 :
140 : V8_INLINE V8_WARN_UNUSED_RESULT LayoutDescriptor SetRawData(int field_index);
141 :
142 : V8_INLINE V8_WARN_UNUSED_RESULT LayoutDescriptor SetTagged(int field_index,
143 : bool tagged);
144 :
145 10279 : OBJECT_CONSTRUCTORS(LayoutDescriptor, ByteArray);
146 : };
147 :
148 :
149 : // LayoutDescriptorHelper is a helper class for querying layout descriptor
150 : // about whether the field at given offset is tagged or not.
151 : class LayoutDescriptorHelper {
152 : public:
153 : inline explicit LayoutDescriptorHelper(Map map);
154 :
155 : bool all_fields_tagged() { return all_fields_tagged_; }
156 : inline bool IsTagged(int offset_in_bytes);
157 :
158 : // Queries the contiguous region of fields that are either tagged or not.
159 : // Returns true if fields starting at |offset_in_bytes| are tagged or false
160 : // otherwise and writes the offset of the end of the contiguous region to
161 : // |out_end_of_contiguous_region_offset|. The |end_offset| value is the
162 : // upper bound for |out_end_of_contiguous_region_offset|.
163 : bool IsTagged(int offset_in_bytes, int end_offset,
164 : int* out_end_of_contiguous_region_offset);
165 :
166 : private:
167 : bool all_fields_tagged_;
168 : int header_size_;
169 : LayoutDescriptor layout_descriptor_;
170 : };
171 : } // namespace internal
172 : } // namespace v8
173 :
174 : #include "src/objects/object-macros-undef.h"
175 :
176 : #endif // V8_LAYOUT_DESCRIPTOR_H_
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