1 // Copyright 2012 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_OBJECTS_VISITING_H_
6 #define V8_OBJECTS_VISITING_H_
8 #include "src/allocation.h"
9 #include "src/layout-descriptor.h"
11 // This file provides base classes and auxiliary methods for defining
12 // static object visitors used during GC.
13 // Visiting HeapObject body with a normal ObjectVisitor requires performing
14 // two switches on object's instance type to determine object size and layout
15 // and one or more virtual method calls on visitor itself.
16 // Static visitor is different: it provides a dispatch table which contains
17 // pointers to specialized visit functions. Each map has the visitor_id
18 // field which contains an index of specialized visitor to use.
24 // Base class for all static visitors.
25 class StaticVisitorBase : public AllStatic {
27 #define VISITOR_ID_LIST(V) \
30 V(ShortcutCandidate) \
37 V(FixedFloat64Array) \
48 V(DataObjectGeneric) \
76 V(SharedFunctionInfo) \
84 // For data objects, JS objects and structs along with generic visitor which
85 // can visit object of any size we provide visitors specialized by
86 // object size in words.
87 // Ids of specialized visitors are declared in a linear order (without
88 // holes) starting from the id of visitor specialized for 2 words objects
89 // (base visitor id) and ending with the id of generic visitor.
90 // Method GetVisitorIdForSize depends on this ordering to calculate visitor
91 // id of specialized visitor from given instance size, base visitor id and
92 // generic visitor's id.
94 #define VISITOR_ID_ENUM_DECL(id) kVisit##id,
95 VISITOR_ID_LIST(VISITOR_ID_ENUM_DECL)
96 #undef VISITOR_ID_ENUM_DECL
98 kVisitDataObject = kVisitDataObject2,
99 kVisitJSObject = kVisitJSObject2,
100 kVisitStruct = kVisitStruct2,
101 kMinObjectSizeInWords = 2
104 // Visitor ID should fit in one byte.
105 STATIC_ASSERT(kVisitorIdCount <= 256);
107 // Determine which specialized visitor should be used for given instance type
108 // and instance type.
109 static VisitorId GetVisitorId(int instance_type, int instance_size,
110 bool has_unboxed_fields);
112 // Determine which specialized visitor should be used for given map.
113 static VisitorId GetVisitorId(Map* map);
115 // For visitors that allow specialization by size calculate VisitorId based
116 // on size, base visitor id and generic visitor id.
117 static VisitorId GetVisitorIdForSize(VisitorId base, VisitorId generic,
119 bool has_unboxed_fields) {
120 DCHECK((base == kVisitDataObject) || (base == kVisitStruct) ||
121 (base == kVisitJSObject));
122 DCHECK(IsAligned(object_size, kPointerSize));
123 DCHECK(kMinObjectSizeInWords * kPointerSize <= object_size);
124 DCHECK(object_size <= Page::kMaxRegularHeapObjectSize);
125 DCHECK(!has_unboxed_fields || (base == kVisitJSObject));
127 if (has_unboxed_fields) return generic;
130 Min(base + (object_size >> kPointerSizeLog2) - kMinObjectSizeInWords,
131 static_cast<int>(generic));
133 return static_cast<VisitorId>(visitor_id);
138 template <typename Callback>
139 class VisitorDispatchTable {
141 void CopyFrom(VisitorDispatchTable* other) {
142 // We are not using memcpy to guarantee that during update
143 // every element of callbacks_ array will remain correct
144 // pointer (memcpy might be implemented as a byte copying loop).
145 for (int i = 0; i < StaticVisitorBase::kVisitorIdCount; i++) {
146 base::NoBarrier_Store(&callbacks_[i], other->callbacks_[i]);
150 inline Callback GetVisitorById(StaticVisitorBase::VisitorId id) {
151 return reinterpret_cast<Callback>(callbacks_[id]);
154 inline Callback GetVisitor(Map* map) {
155 return reinterpret_cast<Callback>(callbacks_[map->visitor_id()]);
158 void Register(StaticVisitorBase::VisitorId id, Callback callback) {
159 DCHECK(id < StaticVisitorBase::kVisitorIdCount); // id is unsigned.
160 callbacks_[id] = reinterpret_cast<base::AtomicWord>(callback);
163 template <typename Visitor, StaticVisitorBase::VisitorId base,
164 StaticVisitorBase::VisitorId generic, int object_size_in_words>
165 void RegisterSpecialization() {
166 static const int size = object_size_in_words * kPointerSize;
167 Register(StaticVisitorBase::GetVisitorIdForSize(base, generic, size, false),
168 &Visitor::template VisitSpecialized<size>);
172 template <typename Visitor, StaticVisitorBase::VisitorId base,
173 StaticVisitorBase::VisitorId generic>
174 void RegisterSpecializations() {
175 STATIC_ASSERT((generic - base + StaticVisitorBase::kMinObjectSizeInWords) ==
177 RegisterSpecialization<Visitor, base, generic, 2>();
178 RegisterSpecialization<Visitor, base, generic, 3>();
179 RegisterSpecialization<Visitor, base, generic, 4>();
180 RegisterSpecialization<Visitor, base, generic, 5>();
181 RegisterSpecialization<Visitor, base, generic, 6>();
182 RegisterSpecialization<Visitor, base, generic, 7>();
183 RegisterSpecialization<Visitor, base, generic, 8>();
184 RegisterSpecialization<Visitor, base, generic, 9>();
185 Register(generic, &Visitor::Visit);
189 base::AtomicWord callbacks_[StaticVisitorBase::kVisitorIdCount];
193 template <typename StaticVisitor>
194 class BodyVisitorBase : public AllStatic {
196 INLINE(static void IteratePointers(Heap* heap, HeapObject* object,
197 int start_offset, int end_offset)) {
198 DCHECK(!FLAG_unbox_double_fields || object->map()->HasFastPointerLayout());
199 IterateRawPointers(heap, object, start_offset, end_offset);
202 INLINE(static void IterateBody(Heap* heap, HeapObject* object,
203 int start_offset, int end_offset)) {
204 if (!FLAG_unbox_double_fields || object->map()->HasFastPointerLayout()) {
205 IterateRawPointers(heap, object, start_offset, end_offset);
207 IterateBodyUsingLayoutDescriptor(heap, object, start_offset, end_offset);
212 INLINE(static void IterateRawPointers(Heap* heap, HeapObject* object,
213 int start_offset, int end_offset)) {
214 StaticVisitor::VisitPointers(heap, object,
215 HeapObject::RawField(object, start_offset),
216 HeapObject::RawField(object, end_offset));
219 static void IterateBodyUsingLayoutDescriptor(Heap* heap, HeapObject* object,
222 DCHECK(FLAG_unbox_double_fields);
223 DCHECK(IsAligned(start_offset, kPointerSize) &&
224 IsAligned(end_offset, kPointerSize));
226 LayoutDescriptorHelper helper(object->map());
227 DCHECK(!helper.all_fields_tagged());
228 for (int offset = start_offset; offset < end_offset;) {
229 int end_of_region_offset;
230 if (helper.IsTagged(offset, end_offset, &end_of_region_offset)) {
231 IterateRawPointers(heap, object, offset, end_of_region_offset);
233 offset = end_of_region_offset;
239 template <typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
240 class FlexibleBodyVisitor : public BodyVisitorBase<StaticVisitor> {
242 INLINE(static ReturnType Visit(Map* map, HeapObject* object)) {
243 int object_size = BodyDescriptor::SizeOf(map, object);
244 BodyVisitorBase<StaticVisitor>::IterateBody(
245 map->GetHeap(), object, BodyDescriptor::kStartOffset, object_size);
246 return static_cast<ReturnType>(object_size);
249 template <int object_size>
250 static inline ReturnType VisitSpecialized(Map* map, HeapObject* object) {
251 DCHECK(BodyDescriptor::SizeOf(map, object) == object_size);
252 BodyVisitorBase<StaticVisitor>::IteratePointers(
253 map->GetHeap(), object, BodyDescriptor::kStartOffset, object_size);
254 return static_cast<ReturnType>(object_size);
259 template <typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
260 class FixedBodyVisitor : public BodyVisitorBase<StaticVisitor> {
262 INLINE(static ReturnType Visit(Map* map, HeapObject* object)) {
263 BodyVisitorBase<StaticVisitor>::IterateBody(map->GetHeap(), object,
264 BodyDescriptor::kStartOffset,
265 BodyDescriptor::kEndOffset);
266 return static_cast<ReturnType>(BodyDescriptor::kSize);
271 // Base class for visitors used for a linear new space iteration.
272 // IterateBody returns size of visited object.
273 // Certain types of objects (i.e. Code objects) are not handled
274 // by dispatch table of this visitor because they cannot appear
277 // This class is intended to be used in the following way:
279 // class SomeVisitor : public StaticNewSpaceVisitor<SomeVisitor> {
283 // This is an example of Curiously recurring template pattern
284 // (see http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern).
285 // We use CRTP to guarantee aggressive compile time optimizations (i.e.
286 // inlining and specialization of StaticVisitor::VisitPointers methods).
287 template <typename StaticVisitor>
288 class StaticNewSpaceVisitor : public StaticVisitorBase {
290 static void Initialize();
292 INLINE(static int IterateBody(Map* map, HeapObject* obj)) {
293 return table_.GetVisitor(map)(map, obj);
296 INLINE(static void VisitPointers(Heap* heap, HeapObject* object,
297 Object** start, Object** end)) {
298 for (Object** p = start; p < end; p++) StaticVisitor::VisitPointer(heap, p);
302 INLINE(static int VisitJSFunction(Map* map, HeapObject* object)) {
303 Heap* heap = map->GetHeap();
304 VisitPointers(heap, object,
305 HeapObject::RawField(object, JSFunction::kPropertiesOffset),
306 HeapObject::RawField(object, JSFunction::kCodeEntryOffset));
308 // Don't visit code entry. We are using this visitor only during scavenges.
311 heap, object, HeapObject::RawField(
312 object, JSFunction::kCodeEntryOffset + kPointerSize),
313 HeapObject::RawField(object, JSFunction::kNonWeakFieldsEndOffset));
314 return JSFunction::kSize;
317 INLINE(static int VisitByteArray(Map* map, HeapObject* object)) {
318 return reinterpret_cast<ByteArray*>(object)->ByteArraySize();
321 INLINE(static int VisitBytecodeArray(Map* map, HeapObject* object)) {
322 return reinterpret_cast<BytecodeArray*>(object)->BytecodeArraySize();
325 INLINE(static int VisitFixedDoubleArray(Map* map, HeapObject* object)) {
326 int length = reinterpret_cast<FixedDoubleArray*>(object)->length();
327 return FixedDoubleArray::SizeFor(length);
330 INLINE(static int VisitFixedTypedArray(Map* map, HeapObject* object)) {
331 return reinterpret_cast<FixedTypedArrayBase*>(object)->size();
334 INLINE(static int VisitJSObject(Map* map, HeapObject* object)) {
335 return JSObjectVisitor::Visit(map, object);
338 INLINE(static int VisitSeqOneByteString(Map* map, HeapObject* object)) {
339 return SeqOneByteString::cast(object)
340 ->SeqOneByteStringSize(map->instance_type());
343 INLINE(static int VisitSeqTwoByteString(Map* map, HeapObject* object)) {
344 return SeqTwoByteString::cast(object)
345 ->SeqTwoByteStringSize(map->instance_type());
348 INLINE(static int VisitFreeSpace(Map* map, HeapObject* object)) {
349 return FreeSpace::cast(object)->Size();
352 INLINE(static int VisitJSArrayBuffer(Map* map, HeapObject* object));
353 INLINE(static int VisitJSTypedArray(Map* map, HeapObject* object));
354 INLINE(static int VisitJSDataView(Map* map, HeapObject* object));
356 class DataObjectVisitor {
358 template <int object_size>
359 static inline int VisitSpecialized(Map* map, HeapObject* object) {
363 INLINE(static int Visit(Map* map, HeapObject* object)) {
364 return map->instance_size();
368 typedef FlexibleBodyVisitor<StaticVisitor, StructBodyDescriptor, int>
371 typedef FlexibleBodyVisitor<StaticVisitor, JSObject::BodyDescriptor, int>
374 typedef int (*Callback)(Map* map, HeapObject* object);
376 static VisitorDispatchTable<Callback> table_;
380 template <typename StaticVisitor>
381 VisitorDispatchTable<typename StaticNewSpaceVisitor<StaticVisitor>::Callback>
382 StaticNewSpaceVisitor<StaticVisitor>::table_;
385 // Base class for visitors used to transitively mark the entire heap.
386 // IterateBody returns nothing.
387 // Certain types of objects might not be handled by this base class and
388 // no visitor function is registered by the generic initialization. A
389 // specialized visitor function needs to be provided by the inheriting
390 // class itself for those cases.
392 // This class is intended to be used in the following way:
394 // class SomeVisitor : public StaticMarkingVisitor<SomeVisitor> {
398 // This is an example of Curiously recurring template pattern.
399 template <typename StaticVisitor>
400 class StaticMarkingVisitor : public StaticVisitorBase {
402 static void Initialize();
404 INLINE(static void IterateBody(Map* map, HeapObject* obj)) {
405 table_.GetVisitor(map)(map, obj);
408 INLINE(static void VisitPropertyCell(Map* map, HeapObject* object));
409 INLINE(static void VisitWeakCell(Map* map, HeapObject* object));
410 INLINE(static void VisitCodeEntry(Heap* heap, HeapObject* object,
411 Address entry_address));
412 INLINE(static void VisitEmbeddedPointer(Heap* heap, RelocInfo* rinfo));
413 INLINE(static void VisitCell(Heap* heap, RelocInfo* rinfo));
414 INLINE(static void VisitDebugTarget(Heap* heap, RelocInfo* rinfo));
415 INLINE(static void VisitCodeTarget(Heap* heap, RelocInfo* rinfo));
416 INLINE(static void VisitCodeAgeSequence(Heap* heap, RelocInfo* rinfo));
417 INLINE(static void VisitExternalReference(RelocInfo* rinfo)) {}
418 INLINE(static void VisitInternalReference(RelocInfo* rinfo)) {}
419 INLINE(static void VisitRuntimeEntry(RelocInfo* rinfo)) {}
420 // Skip the weak next code link in a code object.
421 INLINE(static void VisitNextCodeLink(Heap* heap, Object** slot)) {}
423 // Mark non-optimize code for functions inlined into the given optimized
424 // code. This will prevent it from being flushed.
425 static void MarkInlinedFunctionsCode(Heap* heap, Code* code);
428 INLINE(static void VisitMap(Map* map, HeapObject* object));
429 INLINE(static void VisitCode(Map* map, HeapObject* object));
430 INLINE(static void VisitSharedFunctionInfo(Map* map, HeapObject* object));
431 INLINE(static void VisitAllocationSite(Map* map, HeapObject* object));
432 INLINE(static void VisitWeakCollection(Map* map, HeapObject* object));
433 INLINE(static void VisitJSFunction(Map* map, HeapObject* object));
434 INLINE(static void VisitJSRegExp(Map* map, HeapObject* object));
435 INLINE(static void VisitJSArrayBuffer(Map* map, HeapObject* object));
436 INLINE(static void VisitJSTypedArray(Map* map, HeapObject* object));
437 INLINE(static void VisitJSDataView(Map* map, HeapObject* object));
438 INLINE(static void VisitNativeContext(Map* map, HeapObject* object));
440 // Mark pointers in a Map and its TransitionArray together, possibly
441 // treating transitions or back pointers weak.
442 static void MarkMapContents(Heap* heap, Map* map);
443 static void MarkTransitionArray(Heap* heap, TransitionArray* transitions);
445 // Mark pointers in the optimized code map that should act as strong
446 // references, possibly treating some entries weak.
447 static void MarkOptimizedCodeMap(Heap* heap, FixedArray* code_map);
449 // Code flushing support.
450 INLINE(static bool IsFlushable(Heap* heap, JSFunction* function));
451 INLINE(static bool IsFlushable(Heap* heap, SharedFunctionInfo* shared_info));
453 // Helpers used by code flushing support that visit pointer fields and treat
454 // references to code objects either strongly or weakly.
455 static void VisitSharedFunctionInfoStrongCode(Heap* heap, HeapObject* object);
456 static void VisitSharedFunctionInfoWeakCode(Heap* heap, HeapObject* object);
457 static void VisitJSFunctionStrongCode(Heap* heap, HeapObject* object);
458 static void VisitJSFunctionWeakCode(Heap* heap, HeapObject* object);
460 class DataObjectVisitor {
463 static inline void VisitSpecialized(Map* map, HeapObject* object) {}
465 INLINE(static void Visit(Map* map, HeapObject* object)) {}
468 typedef FlexibleBodyVisitor<StaticVisitor, FixedArray::BodyDescriptor, void>
471 typedef FlexibleBodyVisitor<StaticVisitor, JSObject::BodyDescriptor, void>
474 typedef FlexibleBodyVisitor<StaticVisitor, StructBodyDescriptor, void>
477 typedef void (*Callback)(Map* map, HeapObject* object);
479 static VisitorDispatchTable<Callback> table_;
483 template <typename StaticVisitor>
484 VisitorDispatchTable<typename StaticMarkingVisitor<StaticVisitor>::Callback>
485 StaticMarkingVisitor<StaticVisitor>::table_;
488 class WeakObjectRetainer;
491 // A weak list is single linked list where each element has a weak pointer to
492 // the next element. Given the head of the list, this function removes dead
493 // elements from the list and if requested records slots for next-element
494 // pointers. The template parameter T is a WeakListVisitor that defines how to
495 // access the next-element pointers.
497 Object* VisitWeakList(Heap* heap, Object* list, WeakObjectRetainer* retainer);
499 } // namespace v8::internal
501 #endif // V8_OBJECTS_VISITING_H_