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// Copyright 2015 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_OBJECTS_BODY_DESCRIPTORS_H_
#define V8_OBJECTS_BODY_DESCRIPTORS_H_
#include "src/objects.h"
namespace v8 {
namespace internal {
// This is the base class for object's body descriptors.
//
// Each BodyDescriptor subclass must provide the following methods:
//
// 1) Returns true if the object contains a tagged value at given offset.
// It is used for invalid slots filtering. If the offset points outside
// of the object or to the map word, the result is UNDEFINED (!!!).
//
// static bool IsValidSlot(Map* map, HeapObject* obj, int offset);
//
//
// 2) Iterate object's body using stateful object visitor.
//
// template <typename ObjectVisitor>
// static inline void IterateBody(Map* map, HeapObject* obj, int object_size,
// ObjectVisitor* v);
class BodyDescriptorBase {
public:
template <typename ObjectVisitor>
static inline void IteratePointers(HeapObject* obj, int start_offset,
int end_offset, ObjectVisitor* v);
template <typename ObjectVisitor>
static inline void IteratePointer(HeapObject* obj, int offset,
ObjectVisitor* v);
template <typename ObjectVisitor>
static inline void IterateCustomWeakPointers(HeapObject* obj,
int start_offset, int end_offset,
ObjectVisitor* v);
template <typename ObjectVisitor>
static inline void IterateCustomWeakPointer(HeapObject* obj, int offset,
ObjectVisitor* v);
template <typename ObjectVisitor>
static inline void IterateMaybeWeakPointers(HeapObject* obj, int start_offset,
int end_offset, ObjectVisitor* v);
template <typename ObjectVisitor>
static inline void IterateMaybeWeakPointer(HeapObject* obj, int offset,
ObjectVisitor* v);
protected:
// Returns true for all header and embedder fields.
static inline bool IsValidSlotImpl(Map* map, HeapObject* obj, int offset);
// Treats all header and embedder fields in the range as tagged.
template <typename ObjectVisitor>
static inline void IterateBodyImpl(Map* map, HeapObject* obj,
int start_offset, int end_offset,
ObjectVisitor* v);
};
// This class describes a body of an object of a fixed size
// in which all pointer fields are located in the [start_offset, end_offset)
// interval.
template <int start_offset, int end_offset, int size>
class FixedBodyDescriptor final : public BodyDescriptorBase {
public:
static const int kStartOffset = start_offset;
static const int kEndOffset = end_offset;
static const int kSize = size;
static bool IsValidSlot(Map* map, HeapObject* obj, int offset) {
return offset >= kStartOffset && offset < kEndOffset;
}
template <typename ObjectVisitor>
static inline void IterateBody(Map* map, HeapObject* obj, ObjectVisitor* v) {
IteratePointers(obj, start_offset, end_offset, v);
}
template <typename ObjectVisitor>
static inline void IterateBody(Map* map, HeapObject* obj, int object_size,
ObjectVisitor* v) {
IterateBody(map, obj, v);
}
static inline int SizeOf(Map* map, HeapObject* object) { return kSize; }
};
// This class describes a body of an object of a variable size
// in which all pointer fields are located in the [start_offset, object_size)
// interval.
template <int start_offset>
class FlexibleBodyDescriptor final : public BodyDescriptorBase {
public:
static const int kStartOffset = start_offset;
static bool IsValidSlot(Map* map, HeapObject* obj, int offset) {
return (offset >= kStartOffset);
}
template <typename ObjectVisitor>
static inline void IterateBody(Map* map, HeapObject* obj, int object_size,
ObjectVisitor* v) {
IteratePointers(obj, start_offset, object_size, v);
}
static inline int SizeOf(Map* map, HeapObject* object);
};
typedef FlexibleBodyDescriptor<HeapObject::kHeaderSize> StructBodyDescriptor;
// This class describes a body of an object which has a parent class that also
// has a body descriptor. This represents a union of the parent's body
// descriptor, and a new descriptor for the child -- so, both parent and child's
// slots are iterated. The parent must be fixed size, and its slots be disjoint
// with the child's.
template <class ParentBodyDescriptor, class ChildBodyDescriptor>
class SubclassBodyDescriptor final : public BodyDescriptorBase {
public:
// The parent must end be before the child's start offset, to make sure that
// their slots are disjoint.
STATIC_ASSERT(ParentBodyDescriptor::kSize <=
ChildBodyDescriptor::kStartOffset);
static bool IsValidSlot(Map* map, HeapObject* obj, int offset) {
return ParentBodyDescriptor::IsValidSlot(map, obj, offset) ||
ChildBodyDescriptor::IsValidSlot(map, obj, offset);
}
template <typename ObjectVisitor>
static inline void IterateBody(Map* map, HeapObject* obj, ObjectVisitor* v) {
ParentBodyDescriptor::IterateBody(map, obj, v);
ChildBodyDescriptor::IterateBody(map, obj, v);
}
template <typename ObjectVisitor>
static inline void IterateBody(Map* map, HeapObject* obj, int object_size,
ObjectVisitor* v) {
ParentBodyDescriptor::IterateBody(map, obj, object_size, v);
ChildBodyDescriptor::IterateBody(map, obj, object_size, v);
}
static inline int SizeOf(Map* map, HeapObject* object) {
// The child should know its full size.
return ChildBodyDescriptor::SizeOf(map, object);
}
};
} // namespace internal
} // namespace v8
#endif // V8_OBJECTS_BODY_DESCRIPTORS_H_
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