Reland "Replace slots buffer with remembered set. (patchset #14 id:250001 of https://codereview.chr…

src/heap/slots-buffer.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_HEAP_SLOTS_BUFFER_H_
-#define V8_HEAP_SLOTS_BUFFER_H_
-
-#include "src/objects.h"
-
-namespace v8 {
-namespace internal {
-
-// Forward declarations.
-class SlotsBuffer;
-
-
-// SlotsBufferAllocator manages the allocation and deallocation of slots buffer
-// chunks and links them together. Slots buffer chunks are always created by the
-// SlotsBufferAllocator.
-class SlotsBufferAllocator {
- public:
-  SlotsBuffer* AllocateBuffer(SlotsBuffer* next_buffer);
-  void DeallocateBuffer(SlotsBuffer* buffer);
-
-  void DeallocateChain(SlotsBuffer** buffer_address);
-};
-
-
-// SlotsBuffer records a sequence of slots that has to be updated
-// after live objects were relocated from evacuation candidates.
-// All slots are either untyped or typed:
-//    - Untyped slots are expected to contain a tagged object pointer.
-//      They are recorded by an address.
-//    - Typed slots are expected to contain an encoded pointer to a heap
-//      object where the way of encoding depends on the type of the slot.
-//      They are recorded as a pair (SlotType, slot address).
-// We assume that zero-page is never mapped this allows us to distinguish
-// untyped slots from typed slots during iteration by a simple comparison:
-// if element of slots buffer is less than NUMBER_OF_SLOT_TYPES then it
-// is the first element of typed slot's pair.
-class SlotsBuffer {
- public:
-  typedef Object** ObjectSlot;
-
-  explicit SlotsBuffer(SlotsBuffer* next_buffer)
-      : idx_(0), chain_length_(1), next_(next_buffer) {
-    if (next_ != NULL) {
-      chain_length_ = next_->chain_length_ + 1;
-    }
-  }
-
-  ~SlotsBuffer() {}
-
-  void Add(ObjectSlot slot) {
-    DCHECK(0 <= idx_ && idx_ < kNumberOfElements);
-#ifdef DEBUG
-    if (slot >= reinterpret_cast<ObjectSlot>(NUMBER_OF_SLOT_TYPES)) {
-      DCHECK_NOT_NULL(*slot);
-    }
-#endif
-    slots_[idx_++] = slot;
-  }
-
-  ObjectSlot Get(intptr_t i) {
-    DCHECK(i >= 0 && i < kNumberOfElements);
-    return slots_[i];
-  }
-
-  size_t Size() {
-    DCHECK(idx_ <= kNumberOfElements);
-    return idx_;
-  }
-
-  enum SlotType {
-    EMBEDDED_OBJECT_SLOT,
-    OBJECT_SLOT,
-    RELOCATED_CODE_OBJECT,
-    CELL_TARGET_SLOT,
-    CODE_TARGET_SLOT,
-    CODE_ENTRY_SLOT,
-    DEBUG_TARGET_SLOT,
-    NUMBER_OF_SLOT_TYPES
-  };
-
-  static const char* SlotTypeToString(SlotType type) {
-    switch (type) {
-      case EMBEDDED_OBJECT_SLOT:
-        return "EMBEDDED_OBJECT_SLOT";
-      case OBJECT_SLOT:
-        return "OBJECT_SLOT";
-      case RELOCATED_CODE_OBJECT:
-        return "RELOCATED_CODE_OBJECT";
-      case CELL_TARGET_SLOT:
-        return "CELL_TARGET_SLOT";
-      case CODE_TARGET_SLOT:
-        return "CODE_TARGET_SLOT";
-      case CODE_ENTRY_SLOT:
-        return "CODE_ENTRY_SLOT";
-      case DEBUG_TARGET_SLOT:
-        return "DEBUG_TARGET_SLOT";
-      case NUMBER_OF_SLOT_TYPES:
-        return "NUMBER_OF_SLOT_TYPES";
-    }
-    return "UNKNOWN SlotType";
-  }
-
-  SlotsBuffer* next() { return next_; }
-
-  static int SizeOfChain(SlotsBuffer* buffer) {
-    if (buffer == NULL) return 0;
-    return static_cast<int>(buffer->idx_ +
-                            (buffer->chain_length_ - 1) * kNumberOfElements);
-  }
-
-  inline bool IsFull() { return idx_ == kNumberOfElements; }
-
-  inline bool HasSpaceForTypedSlot() { return idx_ < kNumberOfElements - 1; }
-
-  enum AdditionMode { FAIL_ON_OVERFLOW, IGNORE_OVERFLOW };
-
-  static bool ChainLengthThresholdReached(SlotsBuffer* buffer) {
-    return buffer != NULL && buffer->chain_length_ >= kChainLengthThreshold;
-  }
-
-  INLINE(static bool AddTo(SlotsBufferAllocator* allocator,
-                           SlotsBuffer** buffer_address, ObjectSlot slot,
-                           AdditionMode mode)) {
-    SlotsBuffer* buffer = *buffer_address;
-    if (buffer == NULL || buffer->IsFull()) {
-      if (mode == FAIL_ON_OVERFLOW && ChainLengthThresholdReached(buffer)) {
-        allocator->DeallocateChain(buffer_address);
-        return false;
-      }
-      buffer = allocator->AllocateBuffer(buffer);
-      *buffer_address = buffer;
-    }
-    buffer->Add(slot);
-    return true;
-  }
-
-  static bool IsTypedSlot(ObjectSlot slot);
-
-  static bool AddTo(SlotsBufferAllocator* allocator,
-                    SlotsBuffer** buffer_address, SlotType type, Address addr,
-                    AdditionMode mode);
-
-  // Eliminates all stale entries from the slots buffer, 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 RemoveInvalidSlots(Heap* heap, SlotsBuffer* buffer);
-
-  // Eliminate all slots that are within the given address range.
-  static void RemoveObjectSlots(Heap* heap, SlotsBuffer* buffer,
-                                Address start_slot, Address end_slot);
-
-  // Ensures that there are no invalid slots in the chain of slots buffers.
-  static void VerifySlots(Heap* heap, SlotsBuffer* buffer);
-
-  static const int kNumberOfElements = 1021;
-
- private:
-  static const int kChainLengthThreshold = 15;
-
-  intptr_t idx_;
-  intptr_t chain_length_;
-  SlotsBuffer* next_;
-  ObjectSlot slots_[kNumberOfElements];
-};
-
-
-}  // namespace internal
-}  // namespace v8
-
-#endif  // V8_HEAP_SLOTS_BUFFER_H_