text: // 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/assembler.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 };
  
  // TODO(ulan): Investigate performance of de-templatizing this class.
  template <PointerDirection direction>
  class RememberedSet : public AllStatic {
   public:
    // Given a page and a slot in that page, this function adds the slot to the
    // remembered set.
    static void Insert(MemoryChunk* chunk, Address slot_addr) {
      DCHECK(chunk->Contains(slot_addr));
      SlotSet* slot_set = GetSlotSet(chunk);
      if (slot_set == nullptr) {
        slot_set = AllocateSlotSet(chunk);
      }
      uintptr_t offset = slot_addr - chunk->address();
      slot_set[offset / Page::kPageSize].Insert(offset % Page::kPageSize);
    }
  
    // Given a page and a slot in that page, this function returns true if
    // the remembered set contains the slot.
    static bool Contains(MemoryChunk* chunk, Address slot_addr) {
      DCHECK(chunk->Contains(slot_addr));
      SlotSet* slot_set = GetSlotSet(chunk);
      if (slot_set == nullptr) {
        return false;
      }
      uintptr_t offset = slot_addr - chunk->address();
      return slot_set[offset / Page::kPageSize].Contains(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(MemoryChunk* chunk, Address slot_addr) {
      DCHECK(chunk->Contains(slot_addr));
      SlotSet* slot_set = GetSlotSet(chunk);
      if (slot_set != nullptr) {
        uintptr_t offset = slot_addr - chunk->address();
        slot_set[offset / Page::kPageSize].Remove(offset % Page::kPageSize);
      }
    }
  
    // Given a page and a range of slots in that page, this function removes the
    // slots from the remembered set.
    static void RemoveRange(MemoryChunk* chunk, Address start, Address end,
                            SlotSet::EmptyBucketMode mode) {
      SlotSet* slot_set = GetSlotSet(chunk);
      if (slot_set != nullptr) {
        uintptr_t start_offset = start - chunk->address();
        uintptr_t end_offset = end - chunk->address();
        DCHECK_LT(start_offset, end_offset);
        if (end_offset < static_cast<uintptr_t>(Page::kPageSize)) {
          slot_set->RemoveRange(static_cast<int>(start_offset),
                                static_cast<int>(end_offset), mode);
        } else {
          // The large page has multiple slot sets.
          // Compute slot set indicies for the range [start_offset, end_offset).
          int start_chunk = static_cast<int>(start_offset / Page::kPageSize);
          int end_chunk = static_cast<int>((end_offset - 1) / Page::kPageSize);
          int offset_in_start_chunk =
              static_cast<int>(start_offset % Page::kPageSize);
          // Note that using end_offset % Page::kPageSize would be incorrect
          // because end_offset is one beyond the last slot to clear.
          int offset_in_end_chunk = static_cast<int>(
              end_offset - static_cast<uintptr_t>(end_chunk) * Page::kPageSize);
          if (start_chunk == end_chunk) {
            slot_set[start_chunk].RemoveRange(offset_in_start_chunk,
                                              offset_in_end_chunk, mode);
          } else {
            // Clear all slots from start_offset to the end of first chunk.
            slot_set[start_chunk].RemoveRange(offset_in_start_chunk,
                                              Page::kPageSize, mode);
            // Clear all slots in intermediate chunks.
            for (int i = start_chunk + 1; i < end_chunk; i++) {
              slot_set[i].RemoveRange(0, Page::kPageSize, mode);
            }
            // Clear slots from the beginning of the last page to end_offset.
            slot_set[end_chunk].RemoveRange(0, offset_in_end_chunk, mode);
          }
        }
      }
    }
  
    // Iterates and filters the remembered set with the given callback.
    // The callback should take (Address slot) and return SlotCallbackResult.
    template <typename Callback>
    static void Iterate(Heap* heap, Callback callback) {
      IterateMemoryChunks(
          heap, [callback](MemoryChunk* chunk) { Iterate(chunk, callback); });
    }
  
    // Iterates over all memory chunks that contains non-empty slot sets.
    // The callback should take (MemoryChunk* chunk) and return void.
    template <typename Callback>
    static void IterateMemoryChunks(Heap* heap, Callback callback) {
      MemoryChunkIterator it(heap);
      MemoryChunk* chunk;
      while ((chunk = it.next()) != nullptr) {
        SlotSet* slots = GetSlotSet(chunk);
        TypedSlotSet* typed_slots = GetTypedSlotSet(chunk);
        if (slots != nullptr || typed_slots != nullptr) {
          callback(chunk);
        }
      }
    }
  
    // Iterates and filters the remembered set in the given memory chunk with
    // the given callback. The callback should take (Address slot) and return
    // SlotCallbackResult.
    template <typename Callback>
    static void Iterate(MemoryChunk* chunk, Callback callback) {
      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, SlotSet::PREFREE_EMPTY_BUCKETS);
        }
        // Only old-to-old slot sets are released eagerly. Old-new-slot sets are
        // released by the sweeper threads.
        if (direction == OLD_TO_OLD && new_count == 0) {
          chunk->ReleaseOldToOldSlots();
        }
      }
    }
  
    // Given a page and a typed slot in that page, this function adds the slot
    // to the remembered set.
    static void InsertTyped(Page* page, Address host_addr, SlotType slot_type,
                            Address slot_addr) {
      TypedSlotSet* slot_set = GetTypedSlotSet(page);
      if (slot_set == nullptr) {
        AllocateTypedSlotSet(page);
        slot_set = GetTypedSlotSet(page);
      }
      if (host_addr == nullptr) {
        host_addr = page->address();
      }
      uintptr_t offset = slot_addr - page->address();
      uintptr_t host_offset = host_addr - page->address();
      DCHECK_LT(offset, static_cast<uintptr_t>(TypedSlotSet::kMaxOffset));
      DCHECK_LT(host_offset, static_cast<uintptr_t>(TypedSlotSet::kMaxOffset));
      slot_set->Insert(slot_type, static_cast<uint32_t>(host_offset),
                       static_cast<uint32_t>(offset));
    }
  
    // Given a page and a range of typed slots in that page, this function removes
    // the slots from the remembered set.
    static void RemoveRangeTyped(MemoryChunk* page, Address start, Address end) {
      TypedSlotSet* slots = GetTypedSlotSet(page);
      if (slots != nullptr) {
        slots->Iterate(
            [start, end](SlotType slot_type, Address host_addr,
                         Address slot_addr) {
              return start <= slot_addr && slot_addr < end ? REMOVE_SLOT
                                                           : KEEP_SLOT;
            },
            TypedSlotSet::PREFREE_EMPTY_CHUNKS);
      }
    }
  
    // Iterates and filters the remembered set with the given callback.
    // The callback should take (SlotType slot_type, SlotAddress slot) and return
    // SlotCallbackResult.
    template <typename Callback>
    static void IterateTyped(Heap* heap, Callback callback) {
      IterateMemoryChunks(heap, [callback](MemoryChunk* chunk) {
        IterateTyped(chunk, callback);
      });
    }
  
    // Iterates and filters typed old to old pointers in the given memory chunk
    // with the given callback. The callback should take (SlotType slot_type,
    // Address slot_addr) and return SlotCallbackResult.
    template <typename Callback>
    static void IterateTyped(MemoryChunk* chunk, Callback callback) {
      TypedSlotSet* slots = GetTypedSlotSet(chunk);
      if (slots != nullptr) {
        int new_count = slots->Iterate(callback, TypedSlotSet::KEEP_EMPTY_CHUNKS);
        if (new_count == 0) {
          ReleaseTypedSlotSet(chunk);
        }
      }
    }
  
    // Clear all old to old slots from the remembered set.
    static void ClearAll(Heap* heap) {
      STATIC_ASSERT(direction == OLD_TO_OLD);
      MemoryChunkIterator it(heap);
      MemoryChunk* chunk;
      while ((chunk = it.next()) != nullptr) {
        chunk->ReleaseOldToOldSlots();
        chunk->ReleaseTypedOldToOldSlots();
      }
    }
  
    // 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 ClearInvalidTypedSlots(Heap* heap, MemoryChunk* chunk);
  
   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 TypedSlotSet* GetTypedSlotSet(MemoryChunk* chunk) {
      if (direction == OLD_TO_OLD) {
        return chunk->typed_old_to_old_slots();
      } else {
        return chunk->typed_old_to_new_slots();
      }
    }
  
    static void ReleaseTypedSlotSet(MemoryChunk* chunk) {
      if (direction == OLD_TO_OLD) {
        chunk->ReleaseTypedOldToOldSlots();
      }
    }
  
    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();
      }
    }
  
    static TypedSlotSet* AllocateTypedSlotSet(MemoryChunk* chunk) {
      if (direction == OLD_TO_OLD) {
        chunk->AllocateTypedOldToOldSlots();
        return chunk->typed_old_to_old_slots();
      } else {
        chunk->AllocateTypedOldToNewSlots();
        return chunk->typed_old_to_new_slots();
      }
    }
  
    static bool IsValidSlot(Heap* heap, MemoryChunk* chunk, Object** slot);
  };
  
  class UpdateTypedSlotHelper {
   public:
    // Updates a cell slot using an untyped slot callback.
    // The callback accepts Object** and returns SlotCallbackResult.
    template <typename Callback>
    static SlotCallbackResult UpdateCell(RelocInfo* rinfo, Callback callback) {
      DCHECK(rinfo->rmode() == RelocInfo::CELL);
      Object* cell = rinfo->target_cell();
      Object* old_cell = cell;
      SlotCallbackResult result = callback(&cell);
      if (cell != old_cell) {
        rinfo->set_target_cell(reinterpret_cast<Cell*>(cell));
      }
      return result;
    }
  
    // Updates a code entry slot using an untyped slot callback.
    // The callback accepts Object** and returns SlotCallbackResult.
    template <typename Callback>
    static SlotCallbackResult UpdateCodeEntry(Address entry_address,
                                              Callback callback) {
      Object* code = Code::GetObjectFromEntryAddress(entry_address);
      Object* old_code = code;
      SlotCallbackResult result = callback(&code);
      if (code != old_code) {
        Memory::Address_at(entry_address) =
            reinterpret_cast<Code*>(code)->entry();
      }
      return result;
    }
  
    // Updates a code target slot using an untyped slot callback.
    // The callback accepts Object** and returns SlotCallbackResult.
    template <typename Callback>
    static SlotCallbackResult UpdateCodeTarget(RelocInfo* rinfo,
                                               Callback callback) {
      DCHECK(RelocInfo::IsCodeTarget(rinfo->rmode()));
      Object* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
      Object* old_target = target;
      SlotCallbackResult result = callback(&target);
      if (target != old_target) {
        rinfo->set_target_address(Code::cast(target)->instruction_start());
      }
      return result;
    }
  
    // Updates an embedded pointer slot using an untyped slot callback.
    // The callback accepts Object** and returns SlotCallbackResult.
    template <typename Callback>
    static SlotCallbackResult UpdateEmbeddedPointer(RelocInfo* rinfo,
                                                    Callback callback) {
      DCHECK(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
      HeapObject* old_target = rinfo->target_object();
      Object* new_target = old_target;
      SlotCallbackResult result = callback(&new_target);
      if (new_target != old_target) {
        rinfo->set_target_object(HeapObject::cast(new_target));
      }
      return result;
    }
  
    // Updates a debug target slot using an untyped slot callback.
    // The callback accepts Object** and returns SlotCallbackResult.
    template <typename Callback>
    static SlotCallbackResult UpdateDebugTarget(RelocInfo* rinfo,
                                                Callback callback) {
      DCHECK(RelocInfo::IsDebugBreakSlot(rinfo->rmode()) &&
             rinfo->IsPatchedDebugBreakSlotSequence());
      Object* target =
          Code::GetCodeFromTargetAddress(rinfo->debug_call_address());
      SlotCallbackResult result = callback(&target);
      rinfo->set_debug_call_address(Code::cast(target)->instruction_start());
      return result;
    }
  
    // Updates a typed slot using an untyped slot callback.
    // The callback accepts Object** and returns SlotCallbackResult.
    template <typename Callback>
    static SlotCallbackResult UpdateTypedSlot(Isolate* isolate,
                                              SlotType slot_type, Address addr,
                                              Callback callback) {
      switch (slot_type) {
        case CODE_TARGET_SLOT: {
          RelocInfo rinfo(isolate, addr, RelocInfo::CODE_TARGET, 0, NULL);
          return UpdateCodeTarget(&rinfo, callback);
        }
        case CELL_TARGET_SLOT: {
          RelocInfo rinfo(isolate, addr, RelocInfo::CELL, 0, NULL);
          return UpdateCell(&rinfo, callback);
        }
        case CODE_ENTRY_SLOT: {
          return UpdateCodeEntry(addr, callback);
        }
        case DEBUG_TARGET_SLOT: {
          RelocInfo rinfo(isolate, addr, RelocInfo::DEBUG_BREAK_SLOT_AT_POSITION,
                          0, NULL);
          if (rinfo.IsPatchedDebugBreakSlotSequence()) {
            return UpdateDebugTarget(&rinfo, callback);
          }
          return REMOVE_SLOT;
        }
        case EMBEDDED_OBJECT_SLOT: {
          RelocInfo rinfo(isolate, addr, RelocInfo::EMBEDDED_OBJECT, 0, NULL);
          return UpdateEmbeddedPointer(&rinfo, callback);
        }
        case OBJECT_SLOT: {
          return callback(reinterpret_cast<Object**>(addr));
        }
        case CLEARED_SLOT:
          break;
      }
      UNREACHABLE();
      return REMOVE_SLOT;
    }
  };
  
  inline SlotType SlotTypeForRelocInfoMode(RelocInfo::Mode rmode) {
    if (RelocInfo::IsCodeTarget(rmode)) {
      return CODE_TARGET_SLOT;
    } else if (RelocInfo::IsCell(rmode)) {
      return CELL_TARGET_SLOT;
    } else if (RelocInfo::IsEmbeddedObject(rmode)) {
      return EMBEDDED_OBJECT_SLOT;
    } else if (RelocInfo::IsDebugBreakSlot(rmode)) {
      return DEBUG_TARGET_SLOT;
    }
    UNREACHABLE();
    return CLEARED_SLOT;
  }
  
  }  // namespace internal
  }  // namespace v8
  
  #endif  // V8_REMEMBERED_SET_H
  