Add a generic remembered set class.

src/heap/remembered-set.h

+// Copyright 2016 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_REMEMBERED_SET_H
+#define V8_REMEMBERED_SET_H
+
+#include "src/heap/heap.h"
+#include "src/heap/slot-set.h"
+#include "src/heap/spaces.h"
+
+namespace v8 {
+namespace internal {
+
+enum PointerDirection { OLD_TO_OLD, OLD_TO_NEW };
+
+template <PointerDirection direction>
+class RememberedSet {
+ public:
+  // Given a page and a slot in that page, this function adds the slot to the
+  // remembered set.
+  static void Insert(Page* page, Address slot_addr) {
+    DCHECK(page->Contains(slot_addr));

[Hannes Payer (out of office), 2016/02/15 16:53:39]

You can drop the DCHECK if you move the page lookup to this function.

+    SlotSet* slot_set = GetSlotSet(page);
+    if (slot_set == nullptr) {
+      slot_set = AllocateSlotSet(page);
+    }
+    uintptr_t offset = slot_addr - page->address();
+    slot_set[offset / Page::kPageSize].Insert(offset % Page::kPageSize);
+  }
+
+  // Given a page and a slot in that page, this function removes the slot from
+  // the remembered set.
+  // If the slot was never added, then the function does nothing.
+  static void Remove(Page* page, Address slot_addr) {
+    DCHECK(page->Contains(slot_addr));

[Hannes Payer (out of office), 2016/02/15 16:53:38]

You can drop the DCHECK if you move the page lookup to this function.

+    SlotSet* slot_set = GetSlotSet(page);
+    if (slot_set != nullptr) {
+      uintptr_t offset = slot_addr - page->address();
+      slot_set[offset / Page::kPageSize].Remove(offset % Page::kPageSize);
+    }
+  }
+
+  // Iterates and filters the remembered set with the given callback.
+  // The callback should take (Address slot) and return SlotSet::CallbackResult.
+  template <typename Callback>
+  static void Iterate(Heap* heap, Callback callback) {
+    PointerChunkIterator it(heap);
+    MemoryChunk* chunk;
+    while ((chunk = it.next()) != nullptr) {
+      SlotSet* slots = GetSlotSet(chunk);
+      if (slots != nullptr) {
+        size_t pages = (chunk->size() + Page::kPageSize - 1) / Page::kPageSize;
+        int new_count = 0;
+        for (size_t page = 0; page < pages; page++) {
+          new_count += slots[page].Iterate(callback);
+        }
+        if (new_count == 0) {
+          ReleaseSlotSet(chunk);
+        }
+      }
+    }
+  }
+
+  // Iterates and filters the remembered set with the given callback.
+  // The callback should take (HeapObject** slot, HeapObject* target) and
+  // update the slot.
+  // A special wrapper takes care of filtering the slots based on their values.
+  // For OLD_TO_NEW case: slots that do not point to the ToSpace after
+  // callback invocation will be removed from the set.
+  template <typename Callback>
+  static void IterateWithWrapper(Heap* heap, Callback callback) {
+    Iterate(heap, [heap, callback](Address addr) {
+      return Wrapper(heap, addr, callback);
+    });
+  }
+
+  // Eliminates all stale slots from the remembered set, i.e.
+  // slots that are not part of live objects anymore. This method must be
+  // called after marking, when the whole transitive closure is known and
+  // must be called before sweeping when mark bits are still intact.
+  static void ClearInvalidSlots(Heap* heap);
+
+  static void VerifyValidSlots(Heap* heap);
+
+ private:
+  static SlotSet* GetSlotSet(MemoryChunk* chunk) {
+    if (direction == OLD_TO_OLD) {
+      return chunk->old_to_old_slots();
+    } else {
+      return chunk->old_to_new_slots();
+    }
+  }
+
+  static void ReleaseSlotSet(MemoryChunk* chunk) {
+    if (direction == OLD_TO_OLD) {
+      chunk->ReleaseOldToOldSlots();
+    } else {
+      chunk->ReleaseOldToNewSlots();
+    }
+  }
+
+  static SlotSet* AllocateSlotSet(MemoryChunk* chunk) {
+    if (direction == OLD_TO_OLD) {
+      chunk->AllocateOldToOldSlots();
+      return chunk->old_to_old_slots();
+    } else {
+      chunk->AllocateOldToNewSlots();
+      return chunk->old_to_new_slots();
+    }
+  }
+
+  template <typename Callback>
+  static SlotSet::CallbackResult Wrapper(Heap* heap, Address slot_address,
+                                         Callback slot_callback) {
+    STATIC_ASSERT(direction == OLD_TO_NEW);
+    Object** slot = reinterpret_cast<Object**>(slot_address);
+    Object* object = *slot;
+    if (heap->InFromSpace(object)) {
+      HeapObject* heap_object = reinterpret_cast<HeapObject*>(object);
+      DCHECK(heap_object->IsHeapObject());
+      slot_callback(reinterpret_cast<HeapObject**>(slot), heap_object);
+      object = *slot;
+      // If the object was in from space before and is after executing the
+      // callback in to space, the object is still live.
+      // Unfortunately, we do not know about the slot. It could be in a
+      // just freed free space object.
+      if (heap->InToSpace(object)) {
+        return SlotSet::KEEP_SLOT;
+      }
+    } else {
+      DCHECK(!heap->InNewSpace(object));
+    }
+    return SlotSet::REMOVE_SLOT;
+  }
+
+  static bool IsValidSlot(Heap* heap, Object** slot);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_REMEMBERED_SET_H