Object's body descriptors refactoring.

src/objects-body-descriptors.h

+// 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(HeapObject* obj, int offset);
+//
+//
+// 2) Iterate object's body using stateful object visitor.
+//
+//   template <typename ObjectVisitor>
+//   static inline void IterateBody(HeapObject* obj, int object_size,
+//                                  ObjectVisitor* v);
+//
+//
+// 3) Iterate object's body using stateless object visitor.
+//
+//   template <typename StaticVisitor>
+//   static inline void IterateBody(HeapObject* obj, int object_size);
+//
+class BodyDescriptorBase BASE_EMBEDDED {
+ public:
+  template <typename ObjectVisitor>
+  static inline void IteratePointers(HeapObject* obj, int start_offset,
+                                     int end_offset, ObjectVisitor* v);
+
+  template <typename StaticVisitor>
+  static inline void IteratePointers(Heap* heap, HeapObject* obj,
+                                     int start_offset, int end_offset);
+
+  template <typename ObjectVisitor>
+  static inline void IteratePointer(HeapObject* obj, int offset,
+                                    ObjectVisitor* v);
+
+  template <typename StaticVisitor>
+  static inline void IteratePointer(Heap* heap, HeapObject* obj, int offset);
+
+ protected:
+  // Returns true for all header fields.
+  static inline bool IsValidSlotImpl(HeapObject* obj, int offset);
+
+  template <typename ObjectVisitor>
+  static inline void IterateBodyImpl(HeapObject* obj, int start_offset,
+                                     int end_offset, ObjectVisitor* v);
+
+  template <typename StaticVisitor>
+  static inline void IterateBodyImpl(Heap* heap, HeapObject* obj,
+                                     int start_offset, int end_offset);
+};
+
+
+// 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(HeapObject* obj, int offset) {
+    return offset >= kStartOffset && offset < kEndOffset;
+  }
+
+  template <typename ObjectVisitor>
+  static inline void IterateBody(HeapObject* obj, ObjectVisitor* v) {
+    IterateBodyImpl(obj, start_offset, end_offset, v);
+  }
+
+  template <typename ObjectVisitor>
+  static inline void IterateBody(HeapObject* obj, int object_size,
+                                 ObjectVisitor* v) {
+    IterateBody(obj, v);
+  }
+
+  template <typename StaticVisitor>
+  static inline void IterateBody(HeapObject* obj) {
+    Heap* heap = obj->GetHeap();
+    IterateBodyImpl<StaticVisitor>(heap, obj, start_offset, end_offset);
+  }
+
+  template <typename StaticVisitor>
+  static inline void IterateBody(HeapObject* obj, int object_size) {
+    IterateBody(obj);
+  }
+};
+
+
+// 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(HeapObject* obj, int offset) {
+    if (offset < kStartOffset) return false;
+    return IsValidSlotImpl(obj, offset);
+  }
+
+  template <typename ObjectVisitor>
+  static inline void IterateBody(HeapObject* obj, int object_size,
+                                 ObjectVisitor* v) {
+    IterateBodyImpl(obj, start_offset, object_size, v);
+  }
+
+  template <typename StaticVisitor>
+  static inline void IterateBody(HeapObject* obj, int object_size) {
+    Heap* heap = obj->GetHeap();
+    IterateBodyImpl<StaticVisitor>(heap, obj, start_offset, object_size);
+  }
+
+  static inline int SizeOf(Map* map, HeapObject* object);
+};
+
+
+typedef FlexibleBodyDescriptor<HeapObject::kHeaderSize> StructBodyDescriptor;
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_OBJECTS_BODY_DESCRIPTORS_H_