Move a bunch of GC related files to heap/ subdirectory

src/mark-compact.cc

-// Copyright 2012 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.
-
-#include "src/v8.h"
-
-#include "src/base/atomicops.h"
-#include "src/code-stubs.h"
-#include "src/compilation-cache.h"
-#include "src/cpu-profiler.h"
-#include "src/deoptimizer.h"
-#include "src/execution.h"
-#include "src/gdb-jit.h"
-#include "src/global-handles.h"
-#include "src/heap-profiler.h"
-#include "src/ic-inl.h"
-#include "src/incremental-marking.h"
-#include "src/mark-compact.h"
-#include "src/objects-visiting.h"
-#include "src/objects-visiting-inl.h"
-#include "src/spaces-inl.h"
-#include "src/stub-cache.h"
-#include "src/sweeper-thread.h"
-
-namespace v8 {
-namespace internal {
-
-
-const char* Marking::kWhiteBitPattern = "00";
-const char* Marking::kBlackBitPattern = "10";
-const char* Marking::kGreyBitPattern = "11";
-const char* Marking::kImpossibleBitPattern = "01";
-
-
-// -------------------------------------------------------------------------
-// MarkCompactCollector
-
-MarkCompactCollector::MarkCompactCollector(Heap* heap) :  // NOLINT
-#ifdef DEBUG
-      state_(IDLE),
-#endif
-      sweep_precisely_(false),
-      reduce_memory_footprint_(false),
-      abort_incremental_marking_(false),
-      marking_parity_(ODD_MARKING_PARITY),
-      compacting_(false),
-      was_marked_incrementally_(false),
-      sweeping_in_progress_(false),
-      pending_sweeper_jobs_semaphore_(0),
-      sequential_sweeping_(false),
-      migration_slots_buffer_(NULL),
-      heap_(heap),
-      code_flusher_(NULL),
-      have_code_to_deoptimize_(false) { }
-
-#ifdef VERIFY_HEAP
-class VerifyMarkingVisitor: public ObjectVisitor {
- public:
-  explicit VerifyMarkingVisitor(Heap* heap) : heap_(heap) {}
-
-  void VisitPointers(Object** start, Object** end) {
-    for (Object** current = start; current < end; current++) {
-      if ((*current)->IsHeapObject()) {
-        HeapObject* object = HeapObject::cast(*current);
-        CHECK(heap_->mark_compact_collector()->IsMarked(object));
-      }
-    }
-  }
-
-  void VisitEmbeddedPointer(RelocInfo* rinfo) {
-    DCHECK(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
-    if (!rinfo->host()->IsWeakObject(rinfo->target_object())) {
-      Object* p = rinfo->target_object();
-      VisitPointer(&p);
-    }
-  }
-
-  void VisitCell(RelocInfo* rinfo) {
-    Code* code = rinfo->host();
-    DCHECK(rinfo->rmode() == RelocInfo::CELL);
-    if (!code->IsWeakObject(rinfo->target_cell())) {
-      ObjectVisitor::VisitCell(rinfo);
-    }
-  }
-
- private:
-  Heap* heap_;
-};
-
-
-static void VerifyMarking(Heap* heap, Address bottom, Address top) {
-  VerifyMarkingVisitor visitor(heap);
-  HeapObject* object;
-  Address next_object_must_be_here_or_later = bottom;
-
-  for (Address current = bottom;
-       current < top;
-       current += kPointerSize) {
-    object = HeapObject::FromAddress(current);
-    if (MarkCompactCollector::IsMarked(object)) {
-      CHECK(current >= next_object_must_be_here_or_later);
-      object->Iterate(&visitor);
-      next_object_must_be_here_or_later = current + object->Size();
-    }
-  }
-}
-
-
-static void VerifyMarking(NewSpace* space) {
-  Address end = space->top();
-  NewSpacePageIterator it(space->bottom(), end);
-  // The bottom position is at the start of its page. Allows us to use
-  // page->area_start() as start of range on all pages.
-  CHECK_EQ(space->bottom(),
-           NewSpacePage::FromAddress(space->bottom())->area_start());
-  while (it.has_next()) {
-    NewSpacePage* page = it.next();
-    Address limit = it.has_next() ? page->area_end() : end;
-    CHECK(limit == end || !page->Contains(end));
-    VerifyMarking(space->heap(), page->area_start(), limit);
-  }
-}
-
-
-static void VerifyMarking(PagedSpace* space) {
-  PageIterator it(space);
-
-  while (it.has_next()) {
-    Page* p = it.next();
-    VerifyMarking(space->heap(), p->area_start(), p->area_end());
-  }
-}
-
-
-static void VerifyMarking(Heap* heap) {
-  VerifyMarking(heap->old_pointer_space());
-  VerifyMarking(heap->old_data_space());
-  VerifyMarking(heap->code_space());
-  VerifyMarking(heap->cell_space());
-  VerifyMarking(heap->property_cell_space());
-  VerifyMarking(heap->map_space());
-  VerifyMarking(heap->new_space());
-
-  VerifyMarkingVisitor visitor(heap);
-
-  LargeObjectIterator it(heap->lo_space());
-  for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
-    if (MarkCompactCollector::IsMarked(obj)) {
-      obj->Iterate(&visitor);
-    }
-  }
-
-  heap->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
-}
-
-
-class VerifyEvacuationVisitor: public ObjectVisitor {
- public:
-  void VisitPointers(Object** start, Object** end) {
-    for (Object** current = start; current < end; current++) {
-      if ((*current)->IsHeapObject()) {
-        HeapObject* object = HeapObject::cast(*current);
-        CHECK(!MarkCompactCollector::IsOnEvacuationCandidate(object));
-      }
-    }
-  }
-};
-
-
-static void VerifyEvacuation(Page* page) {
-  VerifyEvacuationVisitor visitor;
-  HeapObjectIterator iterator(page, NULL);
-  for (HeapObject* heap_object = iterator.Next(); heap_object != NULL;
-      heap_object = iterator.Next()) {
-    // We skip free space objects.
-    if (!heap_object->IsFiller()) {
-      heap_object->Iterate(&visitor);
-    }
-  }
-}
-
-
-static void VerifyEvacuation(NewSpace* space) {
-  NewSpacePageIterator it(space->bottom(), space->top());
-  VerifyEvacuationVisitor visitor;
-
-  while (it.has_next()) {
-    NewSpacePage* page = it.next();
-    Address current = page->area_start();
-    Address limit = it.has_next() ? page->area_end() : space->top();
-    CHECK(limit == space->top() || !page->Contains(space->top()));
-    while (current < limit) {
-      HeapObject* object = HeapObject::FromAddress(current);
-      object->Iterate(&visitor);
-      current += object->Size();
-    }
-  }
-}
-
-
-static void VerifyEvacuation(Heap* heap, PagedSpace* space) {
-  if (!space->swept_precisely()) return;
-  if (FLAG_use_allocation_folding &&
-      (space == heap->old_pointer_space() || space == heap->old_data_space())) {
-    return;
-  }
-  PageIterator it(space);
-
-  while (it.has_next()) {
-    Page* p = it.next();
-    if (p->IsEvacuationCandidate()) continue;
-    VerifyEvacuation(p);
-  }
-}
-
-
-static void VerifyEvacuation(Heap* heap) {
-  VerifyEvacuation(heap, heap->old_pointer_space());
-  VerifyEvacuation(heap, heap->old_data_space());
-  VerifyEvacuation(heap, heap->code_space());
-  VerifyEvacuation(heap, heap->cell_space());
-  VerifyEvacuation(heap, heap->property_cell_space());
-  VerifyEvacuation(heap, heap->map_space());
-  VerifyEvacuation(heap->new_space());
-
-  VerifyEvacuationVisitor visitor;
-  heap->IterateStrongRoots(&visitor, VISIT_ALL);
-}
-#endif  // VERIFY_HEAP
-
-
-#ifdef DEBUG
-class VerifyNativeContextSeparationVisitor: public ObjectVisitor {
- public:
-  VerifyNativeContextSeparationVisitor() : current_native_context_(NULL) {}
-
-  void VisitPointers(Object** start, Object** end) {
-    for (Object** current = start; current < end; current++) {
-      if ((*current)->IsHeapObject()) {
-        HeapObject* object = HeapObject::cast(*current);
-        if (object->IsString()) continue;
-        switch (object->map()->instance_type()) {
-          case JS_FUNCTION_TYPE:
-            CheckContext(JSFunction::cast(object)->context());
-            break;
-          case JS_GLOBAL_PROXY_TYPE:
-            CheckContext(JSGlobalProxy::cast(object)->native_context());
-            break;
-          case JS_GLOBAL_OBJECT_TYPE:
-          case JS_BUILTINS_OBJECT_TYPE:
-            CheckContext(GlobalObject::cast(object)->native_context());
-            break;
-          case JS_ARRAY_TYPE:
-          case JS_DATE_TYPE:
-          case JS_OBJECT_TYPE:
-          case JS_REGEXP_TYPE:
-            VisitPointer(HeapObject::RawField(object, JSObject::kMapOffset));
-            break;
-          case MAP_TYPE:
-            VisitPointer(HeapObject::RawField(object, Map::kPrototypeOffset));
-            VisitPointer(HeapObject::RawField(object, Map::kConstructorOffset));
-            break;
-          case FIXED_ARRAY_TYPE:
-            if (object->IsContext()) {
-              CheckContext(object);
-            } else {
-              FixedArray* array = FixedArray::cast(object);
-              int length = array->length();
-              // Set array length to zero to prevent cycles while iterating
-              // over array bodies, this is easier than intrusive marking.
-              array->set_length(0);
-              array->IterateBody(
-                  FIXED_ARRAY_TYPE, FixedArray::SizeFor(length), this);
-              array->set_length(length);
-            }
-            break;
-          case CELL_TYPE:
-          case JS_PROXY_TYPE:
-          case JS_VALUE_TYPE:
-          case TYPE_FEEDBACK_INFO_TYPE:
-            object->Iterate(this);
-            break;
-          case DECLARED_ACCESSOR_INFO_TYPE:
-          case EXECUTABLE_ACCESSOR_INFO_TYPE:
-          case BYTE_ARRAY_TYPE:
-          case CALL_HANDLER_INFO_TYPE:
-          case CODE_TYPE:
-          case FIXED_DOUBLE_ARRAY_TYPE:
-          case HEAP_NUMBER_TYPE:
-          case MUTABLE_HEAP_NUMBER_TYPE:
-          case INTERCEPTOR_INFO_TYPE:
-          case ODDBALL_TYPE:
-          case SCRIPT_TYPE:
-          case SHARED_FUNCTION_INFO_TYPE:
-            break;
-          default:
-            UNREACHABLE();
-        }
-      }
-    }
-  }
-
- private:
-  void CheckContext(Object* context) {
-    if (!context->IsContext()) return;
-    Context* native_context = Context::cast(context)->native_context();
-    if (current_native_context_ == NULL) {
-      current_native_context_ = native_context;
-    } else {
-      CHECK_EQ(current_native_context_, native_context);
-    }
-  }
-
-  Context* current_native_context_;
-};
-
-
-static void VerifyNativeContextSeparation(Heap* heap) {
-  HeapObjectIterator it(heap->code_space());
-
-  for (Object* object = it.Next(); object != NULL; object = it.Next()) {
-    VerifyNativeContextSeparationVisitor visitor;
-    Code::cast(object)->CodeIterateBody(&visitor);
-  }
-}
-#endif
-
-
-void MarkCompactCollector::SetUp() {
-  free_list_old_data_space_.Reset(new FreeList(heap_->old_data_space()));
-  free_list_old_pointer_space_.Reset(new FreeList(heap_->old_pointer_space()));
-}
-
-
-void MarkCompactCollector::TearDown() {
-  AbortCompaction();
-}
-
-
-void MarkCompactCollector::AddEvacuationCandidate(Page* p) {
-  p->MarkEvacuationCandidate();
-  evacuation_candidates_.Add(p);
-}
-
-
-static void TraceFragmentation(PagedSpace* space) {
-  int number_of_pages = space->CountTotalPages();
-  intptr_t reserved = (number_of_pages * space->AreaSize());
-  intptr_t free = reserved - space->SizeOfObjects();
-  PrintF("[%s]: %d pages, %d (%.1f%%) free\n",
-         AllocationSpaceName(space->identity()),
-         number_of_pages,
-         static_cast<int>(free),
-         static_cast<double>(free) * 100 / reserved);
-}
-
-
-bool MarkCompactCollector::StartCompaction(CompactionMode mode) {
-  if (!compacting_) {
-    DCHECK(evacuation_candidates_.length() == 0);
-
-#ifdef ENABLE_GDB_JIT_INTERFACE
-    // If GDBJIT interface is active disable compaction.
-    if (FLAG_gdbjit) return false;
-#endif
-
-    CollectEvacuationCandidates(heap()->old_pointer_space());
-    CollectEvacuationCandidates(heap()->old_data_space());
-
-    if (FLAG_compact_code_space &&
-        (mode == NON_INCREMENTAL_COMPACTION ||
-         FLAG_incremental_code_compaction)) {
-      CollectEvacuationCandidates(heap()->code_space());
-    } else if (FLAG_trace_fragmentation) {
-      TraceFragmentation(heap()->code_space());
-    }
-
-    if (FLAG_trace_fragmentation) {
-      TraceFragmentation(heap()->map_space());
-      TraceFragmentation(heap()->cell_space());
-      TraceFragmentation(heap()->property_cell_space());
-    }
-
-    heap()->old_pointer_space()->EvictEvacuationCandidatesFromFreeLists();
-    heap()->old_data_space()->EvictEvacuationCandidatesFromFreeLists();
-    heap()->code_space()->EvictEvacuationCandidatesFromFreeLists();
-
-    compacting_ = evacuation_candidates_.length() > 0;
-  }
-
-  return compacting_;
-}
-
-
-void MarkCompactCollector::CollectGarbage() {
-  // Make sure that Prepare() has been called. The individual steps below will
-  // update the state as they proceed.
-  DCHECK(state_ == PREPARE_GC);
-
-  MarkLiveObjects();
-  DCHECK(heap_->incremental_marking()->IsStopped());
-
-  if (FLAG_collect_maps) ClearNonLiveReferences();
-
-  ClearWeakCollections();
-
-#ifdef VERIFY_HEAP
-  if (FLAG_verify_heap) {
-    VerifyMarking(heap_);
-  }
-#endif
-
-  SweepSpaces();
-
-#ifdef DEBUG
-  if (FLAG_verify_native_context_separation) {
-    VerifyNativeContextSeparation(heap_);
-  }
-#endif
-
-#ifdef VERIFY_HEAP
-  if (heap()->weak_embedded_objects_verification_enabled()) {
-    VerifyWeakEmbeddedObjectsInCode();
-  }
-  if (FLAG_collect_maps && FLAG_omit_map_checks_for_leaf_maps) {
-    VerifyOmittedMapChecks();
-  }
-#endif
-
-  Finish();
-
-  if (marking_parity_ == EVEN_MARKING_PARITY) {
-    marking_parity_ = ODD_MARKING_PARITY;
-  } else {
-    DCHECK(marking_parity_ == ODD_MARKING_PARITY);
-    marking_parity_ = EVEN_MARKING_PARITY;
-  }
-}
-
-
-#ifdef VERIFY_HEAP
-void MarkCompactCollector::VerifyMarkbitsAreClean(PagedSpace* space) {
-  PageIterator it(space);
-
-  while (it.has_next()) {
-    Page* p = it.next();
-    CHECK(p->markbits()->IsClean());
-    CHECK_EQ(0, p->LiveBytes());
-  }
-}
-
-
-void MarkCompactCollector::VerifyMarkbitsAreClean(NewSpace* space) {
-  NewSpacePageIterator it(space->bottom(), space->top());
-
-  while (it.has_next()) {
-    NewSpacePage* p = it.next();
-    CHECK(p->markbits()->IsClean());
-    CHECK_EQ(0, p->LiveBytes());
-  }
-}
-
-
-void MarkCompactCollector::VerifyMarkbitsAreClean() {
-  VerifyMarkbitsAreClean(heap_->old_pointer_space());
-  VerifyMarkbitsAreClean(heap_->old_data_space());
-  VerifyMarkbitsAreClean(heap_->code_space());
-  VerifyMarkbitsAreClean(heap_->cell_space());
-  VerifyMarkbitsAreClean(heap_->property_cell_space());
-  VerifyMarkbitsAreClean(heap_->map_space());
-  VerifyMarkbitsAreClean(heap_->new_space());
-
-  LargeObjectIterator it(heap_->lo_space());
-  for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
-    MarkBit mark_bit = Marking::MarkBitFrom(obj);
-    CHECK(Marking::IsWhite(mark_bit));
-    CHECK_EQ(0, Page::FromAddress(obj->address())->LiveBytes());
-  }
-}
-
-
-void MarkCompactCollector::VerifyWeakEmbeddedObjectsInCode() {
-  HeapObjectIterator code_iterator(heap()->code_space());
-  for (HeapObject* obj = code_iterator.Next();
-       obj != NULL;
-       obj = code_iterator.Next()) {
-    Code* code = Code::cast(obj);
-    if (!code->is_optimized_code() && !code->is_weak_stub()) continue;
-    if (WillBeDeoptimized(code)) continue;
-    code->VerifyEmbeddedObjectsDependency();
-  }
-}
-
-
-void MarkCompactCollector::VerifyOmittedMapChecks() {
-  HeapObjectIterator iterator(heap()->map_space());
-  for (HeapObject* obj = iterator.Next();
-       obj != NULL;
-       obj = iterator.Next()) {
-    Map* map = Map::cast(obj);
-    map->VerifyOmittedMapChecks();
-  }
-}
-#endif  // VERIFY_HEAP
-
-
-static void ClearMarkbitsInPagedSpace(PagedSpace* space) {
-  PageIterator it(space);
-
-  while (it.has_next()) {
-    Bitmap::Clear(it.next());
-  }
-}
-
-
-static void ClearMarkbitsInNewSpace(NewSpace* space) {
-  NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());
-
-  while (it.has_next()) {
-    Bitmap::Clear(it.next());
-  }
-}
-
-
-void MarkCompactCollector::ClearMarkbits() {
-  ClearMarkbitsInPagedSpace(heap_->code_space());
-  ClearMarkbitsInPagedSpace(heap_->map_space());
-  ClearMarkbitsInPagedSpace(heap_->old_pointer_space());
-  ClearMarkbitsInPagedSpace(heap_->old_data_space());
-  ClearMarkbitsInPagedSpace(heap_->cell_space());
-  ClearMarkbitsInPagedSpace(heap_->property_cell_space());
-  ClearMarkbitsInNewSpace(heap_->new_space());
-
-  LargeObjectIterator it(heap_->lo_space());
-  for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
-    MarkBit mark_bit = Marking::MarkBitFrom(obj);
-    mark_bit.Clear();
-    mark_bit.Next().Clear();
-    Page::FromAddress(obj->address())->ResetProgressBar();
-    Page::FromAddress(obj->address())->ResetLiveBytes();
-  }
-}
-
-
-class MarkCompactCollector::SweeperTask : public v8::Task {
- public:
-  SweeperTask(Heap* heap, PagedSpace* space)
-    : heap_(heap), space_(space) {}
-
-  virtual ~SweeperTask() {}
-
- private:
-  // v8::Task overrides.
-  virtual void Run() V8_OVERRIDE {
-    heap_->mark_compact_collector()->SweepInParallel(space_, 0);
-    heap_->mark_compact_collector()->pending_sweeper_jobs_semaphore_.Signal();
-  }
-
-  Heap* heap_;
-  PagedSpace* space_;
-
-  DISALLOW_COPY_AND_ASSIGN(SweeperTask);
-};
-
-
-void MarkCompactCollector::StartSweeperThreads() {
-  DCHECK(free_list_old_pointer_space_.get()->IsEmpty());
-  DCHECK(free_list_old_data_space_.get()->IsEmpty());
-  sweeping_in_progress_ = true;
-  for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
-    isolate()->sweeper_threads()[i]->StartSweeping();
-  }
-  if (FLAG_job_based_sweeping) {
-    V8::GetCurrentPlatform()->CallOnBackgroundThread(
-        new SweeperTask(heap(), heap()->old_data_space()),
-        v8::Platform::kShortRunningTask);
-    V8::GetCurrentPlatform()->CallOnBackgroundThread(
-        new SweeperTask(heap(), heap()->old_pointer_space()),
-        v8::Platform::kShortRunningTask);
-  }
-}
-
-
-void MarkCompactCollector::EnsureSweepingCompleted() {
-  DCHECK(sweeping_in_progress_ == true);
-
-  // If sweeping is not completed, we try to complete it here. If we do not
-  // have sweeper threads we have to complete since we do not have a good
-  // indicator for a swept space in that case.
-  if (!AreSweeperThreadsActivated() || !IsSweepingCompleted()) {
-    SweepInParallel(heap()->paged_space(OLD_DATA_SPACE), 0);
-    SweepInParallel(heap()->paged_space(OLD_POINTER_SPACE), 0);
-  }
-
-  for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
-    isolate()->sweeper_threads()[i]->WaitForSweeperThread();
-  }
-  if (FLAG_job_based_sweeping) {
-    // Wait twice for both jobs.
-    pending_sweeper_jobs_semaphore_.Wait();
-    pending_sweeper_jobs_semaphore_.Wait();
-  }
-  ParallelSweepSpacesComplete();
-  sweeping_in_progress_ = false;
-  RefillFreeList(heap()->paged_space(OLD_DATA_SPACE));
-  RefillFreeList(heap()->paged_space(OLD_POINTER_SPACE));
-  heap()->paged_space(OLD_DATA_SPACE)->ResetUnsweptFreeBytes();
-  heap()->paged_space(OLD_POINTER_SPACE)->ResetUnsweptFreeBytes();
-
-#ifdef VERIFY_HEAP
-  if (FLAG_verify_heap) {
-    VerifyEvacuation(heap_);
-  }
-#endif
-}
-
-
-bool MarkCompactCollector::IsSweepingCompleted() {
-  for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
-    if (!isolate()->sweeper_threads()[i]->SweepingCompleted()) {
-      return false;
-    }
-  }
-
-  if (FLAG_job_based_sweeping) {
-    if (!pending_sweeper_jobs_semaphore_.WaitFor(
-            base::TimeDelta::FromSeconds(0))) {
-      return false;
-    }
-    pending_sweeper_jobs_semaphore_.Signal();
-  }
-
-  return true;
-}
-
-
-void MarkCompactCollector::RefillFreeList(PagedSpace* space) {
-  FreeList* free_list;
-
-  if (space == heap()->old_pointer_space()) {
-    free_list = free_list_old_pointer_space_.get();
-  } else if (space == heap()->old_data_space()) {
-    free_list = free_list_old_data_space_.get();
-  } else {
-    // Any PagedSpace might invoke RefillFreeLists, so we need to make sure
-    // to only refill them for old data and pointer spaces.
-    return;
-  }
-
-  intptr_t freed_bytes = space->free_list()->Concatenate(free_list);
-  space->AddToAccountingStats(freed_bytes);
-  space->DecrementUnsweptFreeBytes(freed_bytes);
-}
-
-
-bool MarkCompactCollector::AreSweeperThreadsActivated() {
-  return isolate()->sweeper_threads() != NULL || FLAG_job_based_sweeping;
-}
-
-
-void Marking::TransferMark(Address old_start, Address new_start) {
-  // This is only used when resizing an object.
-  DCHECK(MemoryChunk::FromAddress(old_start) ==
-         MemoryChunk::FromAddress(new_start));
-
-  if (!heap_->incremental_marking()->IsMarking()) return;
-
-  // If the mark doesn't move, we don't check the color of the object.
-  // It doesn't matter whether the object is black, since it hasn't changed
-  // size, so the adjustment to the live data count will be zero anyway.
-  if (old_start == new_start) return;
-
-  MarkBit new_mark_bit = MarkBitFrom(new_start);
-  MarkBit old_mark_bit = MarkBitFrom(old_start);
-
-#ifdef DEBUG
-  ObjectColor old_color = Color(old_mark_bit);
-#endif
-
-  if (Marking::IsBlack(old_mark_bit)) {
-    old_mark_bit.Clear();
-    DCHECK(IsWhite(old_mark_bit));
-    Marking::MarkBlack(new_mark_bit);
-    return;
-  } else if (Marking::IsGrey(old_mark_bit)) {
-    old_mark_bit.Clear();
-    old_mark_bit.Next().Clear();
-    DCHECK(IsWhite(old_mark_bit));
-    heap_->incremental_marking()->WhiteToGreyAndPush(
-        HeapObject::FromAddress(new_start), new_mark_bit);
-    heap_->incremental_marking()->RestartIfNotMarking();
-  }
-
-#ifdef DEBUG
-  ObjectColor new_color = Color(new_mark_bit);
-  DCHECK(new_color == old_color);
-#endif
-}
-
-
-const char* AllocationSpaceName(AllocationSpace space) {
-  switch (space) {
-    case NEW_SPACE: return "NEW_SPACE";
-    case OLD_POINTER_SPACE: return "OLD_POINTER_SPACE";
-    case OLD_DATA_SPACE: return "OLD_DATA_SPACE";
-    case CODE_SPACE: return "CODE_SPACE";
-    case MAP_SPACE: return "MAP_SPACE";
-    case CELL_SPACE: return "CELL_SPACE";
-    case PROPERTY_CELL_SPACE:
-      return "PROPERTY_CELL_SPACE";
-    case LO_SPACE: return "LO_SPACE";
-    default:
-      UNREACHABLE();
-  }
-
-  return NULL;
-}
-
-
-// Returns zero for pages that have so little fragmentation that it is not
-// worth defragmenting them.  Otherwise a positive integer that gives an
-// estimate of fragmentation on an arbitrary scale.
-static int FreeListFragmentation(PagedSpace* space, Page* p) {
-  // If page was not swept then there are no free list items on it.
-  if (!p->WasSwept()) {
-    if (FLAG_trace_fragmentation) {
-      PrintF("%p [%s]: %d bytes live (unswept)\n",
-             reinterpret_cast<void*>(p),
-             AllocationSpaceName(space->identity()),
-             p->LiveBytes());
-    }
-    return 0;
-  }
-
-  PagedSpace::SizeStats sizes;
-  space->ObtainFreeListStatistics(p, &sizes);
-
-  intptr_t ratio;
-  intptr_t ratio_threshold;
-  intptr_t area_size = space->AreaSize();
-  if (space->identity() == CODE_SPACE) {
-    ratio = (sizes.medium_size_ * 10 + sizes.large_size_ * 2) * 100 /
-        area_size;
-    ratio_threshold = 10;
-  } else {
-    ratio = (sizes.small_size_ * 5 + sizes.medium_size_) * 100 /
-        area_size;
-    ratio_threshold = 15;
-  }
-
-  if (FLAG_trace_fragmentation) {
-    PrintF("%p [%s]: %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %s\n",
-           reinterpret_cast<void*>(p),
-           AllocationSpaceName(space->identity()),
-           static_cast<int>(sizes.small_size_),
-           static_cast<double>(sizes.small_size_ * 100) /
-           area_size,
-           static_cast<int>(sizes.medium_size_),
-           static_cast<double>(sizes.medium_size_ * 100) /
-           area_size,
-           static_cast<int>(sizes.large_size_),
-           static_cast<double>(sizes.large_size_ * 100) /
-           area_size,
-           static_cast<int>(sizes.huge_size_),
-           static_cast<double>(sizes.huge_size_ * 100) /
-           area_size,
-           (ratio > ratio_threshold) ? "[fragmented]" : "");
-  }
-
-  if (FLAG_always_compact && sizes.Total() != area_size) {
-    return 1;
-  }
-
-  if (ratio <= ratio_threshold) return 0;  // Not fragmented.
-
-  return static_cast<int>(ratio - ratio_threshold);
-}
-
-
-void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
-  DCHECK(space->identity() == OLD_POINTER_SPACE ||
-         space->identity() == OLD_DATA_SPACE ||
-         space->identity() == CODE_SPACE);
-
-  static const int kMaxMaxEvacuationCandidates = 1000;
-  int number_of_pages = space->CountTotalPages();
-  int max_evacuation_candidates =
-      static_cast<int>(std::sqrt(number_of_pages / 2.0) + 1);
-
-  if (FLAG_stress_compaction || FLAG_always_compact) {
-    max_evacuation_candidates = kMaxMaxEvacuationCandidates;
-  }
-
-  class Candidate {
-   public:
-    Candidate() : fragmentation_(0), page_(NULL) { }
-    Candidate(int f, Page* p) : fragmentation_(f), page_(p) { }
-
-    int fragmentation() { return fragmentation_; }
-    Page* page() { return page_; }
-
-   private:
-    int fragmentation_;
-    Page* page_;
-  };
-
-  enum CompactionMode {
-    COMPACT_FREE_LISTS,
-    REDUCE_MEMORY_FOOTPRINT
-  };
-
-  CompactionMode mode = COMPACT_FREE_LISTS;
-
-  intptr_t reserved = number_of_pages * space->AreaSize();
-  intptr_t over_reserved = reserved - space->SizeOfObjects();
-  static const intptr_t kFreenessThreshold = 50;
-
-  if (reduce_memory_footprint_ && over_reserved >= space->AreaSize()) {
-    // If reduction of memory footprint was requested, we are aggressive
-    // about choosing pages to free.  We expect that half-empty pages
-    // are easier to compact so slightly bump the limit.
-    mode = REDUCE_MEMORY_FOOTPRINT;
-    max_evacuation_candidates += 2;
-  }
-
-
-  if (over_reserved > reserved / 3 && over_reserved >= 2 * space->AreaSize()) {
-    // If over-usage is very high (more than a third of the space), we
-    // try to free all mostly empty pages.  We expect that almost empty
-    // pages are even easier to compact so bump the limit even more.
-    mode = REDUCE_MEMORY_FOOTPRINT;
-    max_evacuation_candidates *= 2;
-  }
-
-  if (FLAG_trace_fragmentation && mode == REDUCE_MEMORY_FOOTPRINT) {
-    PrintF("Estimated over reserved memory: %.1f / %.1f MB (threshold %d), "
-           "evacuation candidate limit: %d\n",
-           static_cast<double>(over_reserved) / MB,
-           static_cast<double>(reserved) / MB,
-           static_cast<int>(kFreenessThreshold),
-           max_evacuation_candidates);
-  }
-
-  intptr_t estimated_release = 0;
-
-  Candidate candidates[kMaxMaxEvacuationCandidates];
-
-  max_evacuation_candidates =
-      Min(kMaxMaxEvacuationCandidates, max_evacuation_candidates);
-
-  int count = 0;
-  int fragmentation = 0;
-  Candidate* least = NULL;
-
-  PageIterator it(space);
-  if (it.has_next()) it.next();  // Never compact the first page.
-
-  while (it.has_next()) {
-    Page* p = it.next();
-    p->ClearEvacuationCandidate();
-
-    if (FLAG_stress_compaction) {
-      unsigned int counter = space->heap()->ms_count();
-      uintptr_t page_number = reinterpret_cast<uintptr_t>(p) >> kPageSizeBits;
-      if ((counter & 1) == (page_number & 1)) fragmentation = 1;
-    } else if (mode == REDUCE_MEMORY_FOOTPRINT) {
-      // Don't try to release too many pages.
-      if (estimated_release >= over_reserved) {
-        continue;
-      }
-
-      intptr_t free_bytes = 0;
-
-      if (!p->WasSwept()) {
-        free_bytes = (p->area_size() - p->LiveBytes());
-      } else {
-        PagedSpace::SizeStats sizes;
-        space->ObtainFreeListStatistics(p, &sizes);
-        free_bytes = sizes.Total();
-      }
-
-      int free_pct = static_cast<int>(free_bytes * 100) / p->area_size();
-
-      if (free_pct >= kFreenessThreshold) {
-        estimated_release += free_bytes;
-        fragmentation = free_pct;
-      } else {
-        fragmentation = 0;
-      }
-
-      if (FLAG_trace_fragmentation) {
-        PrintF("%p [%s]: %d (%.2f%%) free %s\n",
-               reinterpret_cast<void*>(p),
-               AllocationSpaceName(space->identity()),
-               static_cast<int>(free_bytes),
-               static_cast<double>(free_bytes * 100) / p->area_size(),
-               (fragmentation > 0) ? "[fragmented]" : "");
-      }
-    } else {
-      fragmentation = FreeListFragmentation(space, p);
-    }
-
-    if (fragmentation != 0) {
-      if (count < max_evacuation_candidates) {
-        candidates[count++] = Candidate(fragmentation, p);
-      } else {
-        if (least == NULL) {
-          for (int i = 0; i < max_evacuation_candidates; i++) {
-            if (least == NULL ||
-                candidates[i].fragmentation() < least->fragmentation()) {
-              least = candidates + i;
-            }
-          }
-        }
-        if (least->fragmentation() < fragmentation) {
-          *least = Candidate(fragmentation, p);
-          least = NULL;
-        }
-      }
-    }
-  }
-
-  for (int i = 0; i < count; i++) {
-    AddEvacuationCandidate(candidates[i].page());
-  }
-
-  if (count > 0 && FLAG_trace_fragmentation) {
-    PrintF("Collected %d evacuation candidates for space %s\n",
-           count,
-           AllocationSpaceName(space->identity()));
-  }
-}
-
-
-void MarkCompactCollector::AbortCompaction() {
-  if (compacting_) {
-    int npages = evacuation_candidates_.length();
-    for (int i = 0; i < npages; i++) {
-      Page* p = evacuation_candidates_[i];
-      slots_buffer_allocator_.DeallocateChain(p->slots_buffer_address());
-      p->ClearEvacuationCandidate();
-      p->ClearFlag(MemoryChunk::RESCAN_ON_EVACUATION);
-    }
-    compacting_ = false;
-    evacuation_candidates_.Rewind(0);
-    invalidated_code_.Rewind(0);
-  }
-  DCHECK_EQ(0, evacuation_candidates_.length());
-}
-
-
-void MarkCompactCollector::Prepare() {
-  was_marked_incrementally_ = heap()->incremental_marking()->IsMarking();
-
-#ifdef DEBUG
-  DCHECK(state_ == IDLE);
-  state_ = PREPARE_GC;
-#endif
-
-  DCHECK(!FLAG_never_compact || !FLAG_always_compact);
-
-  if (sweeping_in_progress()) {
-    // Instead of waiting we could also abort the sweeper threads here.
-    EnsureSweepingCompleted();
-  }
-
-  // Clear marking bits if incremental marking is aborted.
-  if (was_marked_incrementally_ && abort_incremental_marking_) {
-    heap()->incremental_marking()->Abort();
-    ClearMarkbits();
-    AbortCompaction();
-    was_marked_incrementally_ = false;
-  }
-
-  // Don't start compaction if we are in the middle of incremental
-  // marking cycle. We did not collect any slots.
-  if (!FLAG_never_compact && !was_marked_incrementally_) {
-    StartCompaction(NON_INCREMENTAL_COMPACTION);
-  }
-
-  PagedSpaces spaces(heap());
-  for (PagedSpace* space = spaces.next();
-       space != NULL;
-       space = spaces.next()) {
-    space->PrepareForMarkCompact();
-  }
-
-#ifdef VERIFY_HEAP
-  if (!was_marked_incrementally_ && FLAG_verify_heap) {
-    VerifyMarkbitsAreClean();
-  }
-#endif
-}
-
-
-void MarkCompactCollector::Finish() {
-#ifdef DEBUG
-  DCHECK(state_ == SWEEP_SPACES || state_ == RELOCATE_OBJECTS);
-  state_ = IDLE;
-#endif
-  // The stub cache is not traversed during GC; clear the cache to
-  // force lazy re-initialization of it. This must be done after the
-  // GC, because it relies on the new address of certain old space
-  // objects (empty string, illegal builtin).
-  isolate()->stub_cache()->Clear();
-
-  if (have_code_to_deoptimize_) {
-    // Some code objects were marked for deoptimization during the GC.
-    Deoptimizer::DeoptimizeMarkedCode(isolate());
-    have_code_to_deoptimize_ = false;
-  }
-}
-
-
-// -------------------------------------------------------------------------
-// Phase 1: tracing and marking live objects.
-//   before: all objects are in normal state.
-//   after: a live object's map pointer is marked as '00'.
-
-// Marking all live objects in the heap as part of mark-sweep or mark-compact
-// collection.  Before marking, all objects are in their normal state.  After
-// marking, live objects' map pointers are marked indicating that the object
-// has been found reachable.
-//
-// The marking algorithm is a (mostly) depth-first (because of possible stack
-// overflow) traversal of the graph of objects reachable from the roots.  It
-// uses an explicit stack of pointers rather than recursion.  The young
-// generation's inactive ('from') space is used as a marking stack.  The
-// objects in the marking stack are the ones that have been reached and marked
-// but their children have not yet been visited.
-//
-// The marking stack can overflow during traversal.  In that case, we set an
-// overflow flag.  When the overflow flag is set, we continue marking objects
-// reachable from the objects on the marking stack, but no longer push them on
-// the marking stack.  Instead, we mark them as both marked and overflowed.
-// When the stack is in the overflowed state, objects marked as overflowed
-// have been reached and marked but their children have not been visited yet.
-// After emptying the marking stack, we clear the overflow flag and traverse
-// the heap looking for objects marked as overflowed, push them on the stack,
-// and continue with marking.  This process repeats until all reachable
-// objects have been marked.
-
-void CodeFlusher::ProcessJSFunctionCandidates() {
-  Code* lazy_compile =
-      isolate_->builtins()->builtin(Builtins::kCompileUnoptimized);
-  Object* undefined = isolate_->heap()->undefined_value();
-
-  JSFunction* candidate = jsfunction_candidates_head_;
-  JSFunction* next_candidate;
-  while (candidate != NULL) {
-    next_candidate = GetNextCandidate(candidate);
-    ClearNextCandidate(candidate, undefined);
-
-    SharedFunctionInfo* shared = candidate->shared();
-
-    Code* code = shared->code();
-    MarkBit code_mark = Marking::MarkBitFrom(code);
-    if (!code_mark.Get()) {
-      if (FLAG_trace_code_flushing && shared->is_compiled()) {
-        PrintF("[code-flushing clears: ");
-        shared->ShortPrint();
-        PrintF(" - age: %d]\n", code->GetAge());
-      }
-      shared->set_code(lazy_compile);
-      candidate->set_code(lazy_compile);
-    } else {
-      candidate->set_code(code);
-    }
-
-    // We are in the middle of a GC cycle so the write barrier in the code
-    // setter did not record the slot update and we have to do that manually.
-    Address slot = candidate->address() + JSFunction::kCodeEntryOffset;
-    Code* target = Code::cast(Code::GetObjectFromEntryAddress(slot));
-    isolate_->heap()->mark_compact_collector()->
-        RecordCodeEntrySlot(slot, target);
-
-    Object** shared_code_slot =
-        HeapObject::RawField(shared, SharedFunctionInfo::kCodeOffset);
-    isolate_->heap()->mark_compact_collector()->
-        RecordSlot(shared_code_slot, shared_code_slot, *shared_code_slot);
-
-    candidate = next_candidate;
-  }
-
-  jsfunction_candidates_head_ = NULL;
-}
-
-
-void CodeFlusher::ProcessSharedFunctionInfoCandidates() {
-  Code* lazy_compile =
-      isolate_->builtins()->builtin(Builtins::kCompileUnoptimized);
-
-  SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
-  SharedFunctionInfo* next_candidate;
-  while (candidate != NULL) {
-    next_candidate = GetNextCandidate(candidate);
-    ClearNextCandidate(candidate);
-
-    Code* code = candidate->code();
-    MarkBit code_mark = Marking::MarkBitFrom(code);
-    if (!code_mark.Get()) {
-      if (FLAG_trace_code_flushing && candidate->is_compiled()) {
-        PrintF("[code-flushing clears: ");
-        candidate->ShortPrint();
-        PrintF(" - age: %d]\n", code->GetAge());
-      }
-      candidate->set_code(lazy_compile);
-    }
-
-    Object** code_slot =
-        HeapObject::RawField(candidate, SharedFunctionInfo::kCodeOffset);
-    isolate_->heap()->mark_compact_collector()->
-        RecordSlot(code_slot, code_slot, *code_slot);
-
-    candidate = next_candidate;
-  }
-
-  shared_function_info_candidates_head_ = NULL;
-}
-
-
-void CodeFlusher::ProcessOptimizedCodeMaps() {
-  STATIC_ASSERT(SharedFunctionInfo::kEntryLength == 4);
-
-  SharedFunctionInfo* holder = optimized_code_map_holder_head_;
-  SharedFunctionInfo* next_holder;
-
-  while (holder != NULL) {
-    next_holder = GetNextCodeMap(holder);
-    ClearNextCodeMap(holder);
-
-    FixedArray* code_map = FixedArray::cast(holder->optimized_code_map());
-    int new_length = SharedFunctionInfo::kEntriesStart;
-    int old_length = code_map->length();
-    for (int i = SharedFunctionInfo::kEntriesStart;
-         i < old_length;
-         i += SharedFunctionInfo::kEntryLength) {
-      Code* code =
-          Code::cast(code_map->get(i + SharedFunctionInfo::kCachedCodeOffset));
-      if (!Marking::MarkBitFrom(code).Get()) continue;
-
-      // Move every slot in the entry.
-      for (int j = 0; j < SharedFunctionInfo::kEntryLength; j++) {
-        int dst_index = new_length++;
-        Object** slot = code_map->RawFieldOfElementAt(dst_index);
-        Object* object = code_map->get(i + j);
-        code_map->set(dst_index, object);
-        if (j == SharedFunctionInfo::kOsrAstIdOffset) {
-          DCHECK(object->IsSmi());
-        } else {
-          DCHECK(Marking::IsBlack(
-              Marking::MarkBitFrom(HeapObject::cast(*slot))));
-          isolate_->heap()->mark_compact_collector()->
-              RecordSlot(slot, slot, *slot);
-        }
-      }
-    }
-
-    // Trim the optimized code map if entries have been removed.
-    if (new_length < old_length) {
-      holder->TrimOptimizedCodeMap(old_length - new_length);
-    }
-
-    holder = next_holder;
-  }
-
-  optimized_code_map_holder_head_ = NULL;
-}
-
-
-void CodeFlusher::EvictCandidate(SharedFunctionInfo* shared_info) {
-  // Make sure previous flushing decisions are revisited.
-  isolate_->heap()->incremental_marking()->RecordWrites(shared_info);
-
-  if (FLAG_trace_code_flushing) {
-    PrintF("[code-flushing abandons function-info: ");
-    shared_info->ShortPrint();
-    PrintF("]\n");
-  }
-
-  SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
-  SharedFunctionInfo* next_candidate;
-  if (candidate == shared_info) {
-    next_candidate = GetNextCandidate(shared_info);
-    shared_function_info_candidates_head_ = next_candidate;
-    ClearNextCandidate(shared_info);
-  } else {
-    while (candidate != NULL) {
-      next_candidate = GetNextCandidate(candidate);
-
-      if (next_candidate == shared_info) {
-        next_candidate = GetNextCandidate(shared_info);
-        SetNextCandidate(candidate, next_candidate);
-        ClearNextCandidate(shared_info);
-        break;
-      }
-
-      candidate = next_candidate;
-    }
-  }
-}
-
-
-void CodeFlusher::EvictCandidate(JSFunction* function) {
-  DCHECK(!function->next_function_link()->IsUndefined());
-  Object* undefined = isolate_->heap()->undefined_value();
-
-  // Make sure previous flushing decisions are revisited.
-  isolate_->heap()->incremental_marking()->RecordWrites(function);
-  isolate_->heap()->incremental_marking()->RecordWrites(function->shared());
-
-  if (FLAG_trace_code_flushing) {
-    PrintF("[code-flushing abandons closure: ");
-    function->shared()->ShortPrint();
-    PrintF("]\n");
-  }
-
-  JSFunction* candidate = jsfunction_candidates_head_;
-  JSFunction* next_candidate;
-  if (candidate == function) {
-    next_candidate = GetNextCandidate(function);
-    jsfunction_candidates_head_ = next_candidate;
-    ClearNextCandidate(function, undefined);
-  } else {
-    while (candidate != NULL) {
-      next_candidate = GetNextCandidate(candidate);
-
-      if (next_candidate == function) {
-        next_candidate = GetNextCandidate(function);
-        SetNextCandidate(candidate, next_candidate);
-        ClearNextCandidate(function, undefined);
-        break;
-      }
-
-      candidate = next_candidate;
-    }
-  }
-}
-
-
-void CodeFlusher::EvictOptimizedCodeMap(SharedFunctionInfo* code_map_holder) {
-  DCHECK(!FixedArray::cast(code_map_holder->optimized_code_map())->
-         get(SharedFunctionInfo::kNextMapIndex)->IsUndefined());
-
-  // Make sure previous flushing decisions are revisited.
-  isolate_->heap()->incremental_marking()->RecordWrites(code_map_holder);
-
-  if (FLAG_trace_code_flushing) {
-    PrintF("[code-flushing abandons code-map: ");
-    code_map_holder->ShortPrint();
-    PrintF("]\n");
-  }
-
-  SharedFunctionInfo* holder = optimized_code_map_holder_head_;
-  SharedFunctionInfo* next_holder;
-  if (holder == code_map_holder) {
-    next_holder = GetNextCodeMap(code_map_holder);
-    optimized_code_map_holder_head_ = next_holder;
-    ClearNextCodeMap(code_map_holder);
-  } else {
-    while (holder != NULL) {
-      next_holder = GetNextCodeMap(holder);
-
-      if (next_holder == code_map_holder) {
-        next_holder = GetNextCodeMap(code_map_holder);
-        SetNextCodeMap(holder, next_holder);
-        ClearNextCodeMap(code_map_holder);
-        break;
-      }
-
-      holder = next_holder;
-    }
-  }
-}
-
-
-void CodeFlusher::EvictJSFunctionCandidates() {
-  JSFunction* candidate = jsfunction_candidates_head_;
-  JSFunction* next_candidate;
-  while (candidate != NULL) {
-    next_candidate = GetNextCandidate(candidate);
-    EvictCandidate(candidate);
-    candidate = next_candidate;
-  }
-  DCHECK(jsfunction_candidates_head_ == NULL);
-}
-
-
-void CodeFlusher::EvictSharedFunctionInfoCandidates() {
-  SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
-  SharedFunctionInfo* next_candidate;
-  while (candidate != NULL) {
-    next_candidate = GetNextCandidate(candidate);
-    EvictCandidate(candidate);
-    candidate = next_candidate;
-  }
-  DCHECK(shared_function_info_candidates_head_ == NULL);
-}
-
-
-void CodeFlusher::EvictOptimizedCodeMaps() {
-  SharedFunctionInfo* holder = optimized_code_map_holder_head_;
-  SharedFunctionInfo* next_holder;
-  while (holder != NULL) {
-    next_holder = GetNextCodeMap(holder);
-    EvictOptimizedCodeMap(holder);
-    holder = next_holder;
-  }
-  DCHECK(optimized_code_map_holder_head_ == NULL);
-}
-
-
-void CodeFlusher::IteratePointersToFromSpace(ObjectVisitor* v) {
-  Heap* heap = isolate_->heap();
-
-  JSFunction** slot = &jsfunction_candidates_head_;
-  JSFunction* candidate = jsfunction_candidates_head_;
-  while (candidate != NULL) {
-    if (heap->InFromSpace(candidate)) {
-      v->VisitPointer(reinterpret_cast<Object**>(slot));
-    }
-    candidate = GetNextCandidate(*slot);
-    slot = GetNextCandidateSlot(*slot);
-  }
-}
-
-
-MarkCompactCollector::~MarkCompactCollector() {
-  if (code_flusher_ != NULL) {
-    delete code_flusher_;
-    code_flusher_ = NULL;
-  }
-}
-
-
-static inline HeapObject* ShortCircuitConsString(Object** p) {
-  // Optimization: If the heap object pointed to by p is a non-internalized
-  // cons string whose right substring is HEAP->empty_string, update
-  // it in place to its left substring.  Return the updated value.
-  //
-  // Here we assume that if we change *p, we replace it with a heap object
-  // (i.e., the left substring of a cons string is always a heap object).
-  //
-  // The check performed is:
-  //   object->IsConsString() && !object->IsInternalizedString() &&
-  //   (ConsString::cast(object)->second() == HEAP->empty_string())
-  // except the maps for the object and its possible substrings might be
-  // marked.
-  HeapObject* object = HeapObject::cast(*p);
-  if (!FLAG_clever_optimizations) return object;
-  Map* map = object->map();
-  InstanceType type = map->instance_type();
-  if (!IsShortcutCandidate(type)) return object;
-
-  Object* second = reinterpret_cast<ConsString*>(object)->second();
-  Heap* heap = map->GetHeap();
-  if (second != heap->empty_string()) {
-    return object;
-  }
-
-  // Since we don't have the object's start, it is impossible to update the
-  // page dirty marks. Therefore, we only replace the string with its left
-  // substring when page dirty marks do not change.
-  Object* first = reinterpret_cast<ConsString*>(object)->first();
-  if (!heap->InNewSpace(object) && heap->InNewSpace(first)) return object;
-
-  *p = first;
-  return HeapObject::cast(first);
-}
-
-
-class MarkCompactMarkingVisitor
-    : public StaticMarkingVisitor<MarkCompactMarkingVisitor> {
- public:
-  static void ObjectStatsVisitBase(StaticVisitorBase::VisitorId id,
-                                   Map* map, HeapObject* obj);
-
-  static void ObjectStatsCountFixedArray(
-      FixedArrayBase* fixed_array,
-      FixedArraySubInstanceType fast_type,
-      FixedArraySubInstanceType dictionary_type);
-
-  template<MarkCompactMarkingVisitor::VisitorId id>
-  class ObjectStatsTracker {
-   public:
-    static inline void Visit(Map* map, HeapObject* obj);
-  };
-
-  static void Initialize();
-
-  INLINE(static void VisitPointer(Heap* heap, Object** p)) {
-    MarkObjectByPointer(heap->mark_compact_collector(), p, p);
-  }
-
-  INLINE(static void VisitPointers(Heap* heap, Object** start, Object** end)) {
-    // Mark all objects pointed to in [start, end).
-    const int kMinRangeForMarkingRecursion = 64;
-    if (end - start >= kMinRangeForMarkingRecursion) {
-      if (VisitUnmarkedObjects(heap, start, end)) return;
-      // We are close to a stack overflow, so just mark the objects.
-    }
-    MarkCompactCollector* collector = heap->mark_compact_collector();
-    for (Object** p = start; p < end; p++) {
-      MarkObjectByPointer(collector, start, p);
-    }
-  }
-
-  // Marks the object black and pushes it on the marking stack.
-  INLINE(static void MarkObject(Heap* heap, HeapObject* object)) {
-    MarkBit mark = Marking::MarkBitFrom(object);
-    heap->mark_compact_collector()->MarkObject(object, mark);
-  }
-
-  // Marks the object black without pushing it on the marking stack.
-  // Returns true if object needed marking and false otherwise.
-  INLINE(static bool MarkObjectWithoutPush(Heap* heap, HeapObject* object)) {
-    MarkBit mark_bit = Marking::MarkBitFrom(object);
-    if (!mark_bit.Get()) {
-      heap->mark_compact_collector()->SetMark(object, mark_bit);
-      return true;
-    }
-    return false;
-  }
-
-  // Mark object pointed to by p.
-  INLINE(static void MarkObjectByPointer(MarkCompactCollector* collector,
-                                         Object** anchor_slot,
-                                         Object** p)) {
-    if (!(*p)->IsHeapObject()) return;
-    HeapObject* object = ShortCircuitConsString(p);
-    collector->RecordSlot(anchor_slot, p, object);
-    MarkBit mark = Marking::MarkBitFrom(object);
-    collector->MarkObject(object, mark);
-  }
-
-
-  // Visit an unmarked object.
-  INLINE(static void VisitUnmarkedObject(MarkCompactCollector* collector,
-                                         HeapObject* obj)) {
-#ifdef DEBUG
-    DCHECK(collector->heap()->Contains(obj));
-    DCHECK(!collector->heap()->mark_compact_collector()->IsMarked(obj));
-#endif
-    Map* map = obj->map();
-    Heap* heap = obj->GetHeap();
-    MarkBit mark = Marking::MarkBitFrom(obj);
-    heap->mark_compact_collector()->SetMark(obj, mark);
-    // Mark the map pointer and the body.
-    MarkBit map_mark = Marking::MarkBitFrom(map);
-    heap->mark_compact_collector()->MarkObject(map, map_mark);
-    IterateBody(map, obj);
-  }
-
-  // Visit all unmarked objects pointed to by [start, end).
-  // Returns false if the operation fails (lack of stack space).
-  INLINE(static bool VisitUnmarkedObjects(Heap* heap,
-                                          Object** start,
-                                          Object** end)) {
-    // Return false is we are close to the stack limit.
-    StackLimitCheck check(heap->isolate());
-    if (check.HasOverflowed()) return false;
-
-    MarkCompactCollector* collector = heap->mark_compact_collector();
-    // Visit the unmarked objects.
-    for (Object** p = start; p < end; p++) {
-      Object* o = *p;
-      if (!o->IsHeapObject()) continue;
-      collector->RecordSlot(start, p, o);
-      HeapObject* obj = HeapObject::cast(o);
-      MarkBit mark = Marking::MarkBitFrom(obj);
-      if (mark.Get()) continue;
-      VisitUnmarkedObject(collector, obj);
-    }
-    return true;
-  }
-
- private:
-  template<int id>
-  static inline void TrackObjectStatsAndVisit(Map* map, HeapObject* obj);
-
-  // Code flushing support.
-
-  static const int kRegExpCodeThreshold = 5;
-
-  static void UpdateRegExpCodeAgeAndFlush(Heap* heap,
-                                          JSRegExp* re,
-                                          bool is_ascii) {
-    // Make sure that the fixed array is in fact initialized on the RegExp.
-    // We could potentially trigger a GC when initializing the RegExp.
-    if (HeapObject::cast(re->data())->map()->instance_type() !=
-            FIXED_ARRAY_TYPE) return;
-
-    // Make sure this is a RegExp that actually contains code.
-    if (re->TypeTag() != JSRegExp::IRREGEXP) return;
-
-    Object* code = re->DataAt(JSRegExp::code_index(is_ascii));
-    if (!code->IsSmi() &&
-        HeapObject::cast(code)->map()->instance_type() == CODE_TYPE) {
-      // Save a copy that can be reinstated if we need the code again.
-      re->SetDataAt(JSRegExp::saved_code_index(is_ascii), code);
-
-      // Saving a copy might create a pointer into compaction candidate
-      // that was not observed by marker.  This might happen if JSRegExp data
-      // was marked through the compilation cache before marker reached JSRegExp
-      // object.
-      FixedArray* data = FixedArray::cast(re->data());
-      Object** slot = data->data_start() + JSRegExp::saved_code_index(is_ascii);
-      heap->mark_compact_collector()->
-          RecordSlot(slot, slot, code);
-
-      // Set a number in the 0-255 range to guarantee no smi overflow.
-      re->SetDataAt(JSRegExp::code_index(is_ascii),
-                    Smi::FromInt(heap->sweep_generation() & 0xff));
-    } else if (code->IsSmi()) {
-      int value = Smi::cast(code)->value();
-      // The regexp has not been compiled yet or there was a compilation error.
-      if (value == JSRegExp::kUninitializedValue ||
-          value == JSRegExp::kCompilationErrorValue) {
-        return;
-      }
-
-      // Check if we should flush now.
-      if (value == ((heap->sweep_generation() - kRegExpCodeThreshold) & 0xff)) {
-        re->SetDataAt(JSRegExp::code_index(is_ascii),
-                      Smi::FromInt(JSRegExp::kUninitializedValue));
-        re->SetDataAt(JSRegExp::saved_code_index(is_ascii),
-                      Smi::FromInt(JSRegExp::kUninitializedValue));
-      }
-    }
-  }
-
-
-  // Works by setting the current sweep_generation (as a smi) in the
-  // code object place in the data array of the RegExp and keeps a copy
-  // around that can be reinstated if we reuse the RegExp before flushing.
-  // If we did not use the code for kRegExpCodeThreshold mark sweep GCs
-  // we flush the code.
-  static void VisitRegExpAndFlushCode(Map* map, HeapObject* object) {
-    Heap* heap = map->GetHeap();
-    MarkCompactCollector* collector = heap->mark_compact_collector();
-    if (!collector->is_code_flushing_enabled()) {
-      VisitJSRegExp(map, object);
-      return;
-    }
-    JSRegExp* re = reinterpret_cast<JSRegExp*>(object);
-    // Flush code or set age on both ASCII and two byte code.
-    UpdateRegExpCodeAgeAndFlush(heap, re, true);
-    UpdateRegExpCodeAgeAndFlush(heap, re, false);
-    // Visit the fields of the RegExp, including the updated FixedArray.
-    VisitJSRegExp(map, object);
-  }
-
-  static VisitorDispatchTable<Callback> non_count_table_;
-};
-
-
-void MarkCompactMarkingVisitor::ObjectStatsCountFixedArray(
-    FixedArrayBase* fixed_array,
-    FixedArraySubInstanceType fast_type,
-    FixedArraySubInstanceType dictionary_type) {
-  Heap* heap = fixed_array->map()->GetHeap();
-  if (fixed_array->map() != heap->fixed_cow_array_map() &&
-      fixed_array->map() != heap->fixed_double_array_map() &&
-      fixed_array != heap->empty_fixed_array()) {
-    if (fixed_array->IsDictionary()) {
-      heap->RecordFixedArraySubTypeStats(dictionary_type,
-                                         fixed_array->Size());
-    } else {
-      heap->RecordFixedArraySubTypeStats(fast_type,
-                                         fixed_array->Size());
-    }
-  }
-}
-
-
-void MarkCompactMarkingVisitor::ObjectStatsVisitBase(
-    MarkCompactMarkingVisitor::VisitorId id, Map* map, HeapObject* obj) {
-  Heap* heap = map->GetHeap();
-  int object_size = obj->Size();
-  heap->RecordObjectStats(map->instance_type(), object_size);
-  non_count_table_.GetVisitorById(id)(map, obj);
-  if (obj->IsJSObject()) {
-    JSObject* object = JSObject::cast(obj);
-    ObjectStatsCountFixedArray(object->elements(),
-                               DICTIONARY_ELEMENTS_SUB_TYPE,
-                               FAST_ELEMENTS_SUB_TYPE);
-    ObjectStatsCountFixedArray(object->properties(),
-                               DICTIONARY_PROPERTIES_SUB_TYPE,
-                               FAST_PROPERTIES_SUB_TYPE);
-  }
-}
-
-
-template<MarkCompactMarkingVisitor::VisitorId id>
-void MarkCompactMarkingVisitor::ObjectStatsTracker<id>::Visit(
-    Map* map, HeapObject* obj) {
-  ObjectStatsVisitBase(id, map, obj);
-}
-
-
-template<>
-class MarkCompactMarkingVisitor::ObjectStatsTracker<
-    MarkCompactMarkingVisitor::kVisitMap> {
- public:
-  static inline void Visit(Map* map, HeapObject* obj) {
-    Heap* heap = map->GetHeap();
-    Map* map_obj = Map::cast(obj);
-    DCHECK(map->instance_type() == MAP_TYPE);
-    DescriptorArray* array = map_obj->instance_descriptors();
-    if (map_obj->owns_descriptors() &&
-        array != heap->empty_descriptor_array()) {
-      int fixed_array_size = array->Size();
-      heap->RecordFixedArraySubTypeStats(DESCRIPTOR_ARRAY_SUB_TYPE,
-                                         fixed_array_size);
-    }
-    if (map_obj->HasTransitionArray()) {
-      int fixed_array_size = map_obj->transitions()->Size();
-      heap->RecordFixedArraySubTypeStats(TRANSITION_ARRAY_SUB_TYPE,
-                                         fixed_array_size);
-    }
-    if (map_obj->has_code_cache()) {
-      CodeCache* cache = CodeCache::cast(map_obj->code_cache());
-      heap->RecordFixedArraySubTypeStats(MAP_CODE_CACHE_SUB_TYPE,
-                                         cache->default_cache()->Size());
-      if (!cache->normal_type_cache()->IsUndefined()) {
-        heap->RecordFixedArraySubTypeStats(
-            MAP_CODE_CACHE_SUB_TYPE,
-            FixedArray::cast(cache->normal_type_cache())->Size());
-      }
-    }
-    ObjectStatsVisitBase(kVisitMap, map, obj);
-  }
-};
-
-
-template<>
-class MarkCompactMarkingVisitor::ObjectStatsTracker<
-    MarkCompactMarkingVisitor::kVisitCode> {
- public:
-  static inline void Visit(Map* map, HeapObject* obj) {
-    Heap* heap = map->GetHeap();
-    int object_size = obj->Size();
-    DCHECK(map->instance_type() == CODE_TYPE);
-    Code* code_obj = Code::cast(obj);
-    heap->RecordCodeSubTypeStats(code_obj->kind(), code_obj->GetRawAge(),
-                                 object_size);
-    ObjectStatsVisitBase(kVisitCode, map, obj);
-  }
-};
-
-
-template<>
-class MarkCompactMarkingVisitor::ObjectStatsTracker<
-    MarkCompactMarkingVisitor::kVisitSharedFunctionInfo> {
- public:
-  static inline void Visit(Map* map, HeapObject* obj) {
-    Heap* heap = map->GetHeap();
-    SharedFunctionInfo* sfi = SharedFunctionInfo::cast(obj);
-    if (sfi->scope_info() != heap->empty_fixed_array()) {
-      heap->RecordFixedArraySubTypeStats(
-          SCOPE_INFO_SUB_TYPE,
-          FixedArray::cast(sfi->scope_info())->Size());
-    }
-    ObjectStatsVisitBase(kVisitSharedFunctionInfo, map, obj);
-  }
-};
-
-
-template<>
-class MarkCompactMarkingVisitor::ObjectStatsTracker<
-    MarkCompactMarkingVisitor::kVisitFixedArray> {
- public:
-  static inline void Visit(Map* map, HeapObject* obj) {
-    Heap* heap = map->GetHeap();
-    FixedArray* fixed_array = FixedArray::cast(obj);
-    if (fixed_array == heap->string_table()) {
-      heap->RecordFixedArraySubTypeStats(
-          STRING_TABLE_SUB_TYPE,
-          fixed_array->Size());
-    }
-    ObjectStatsVisitBase(kVisitFixedArray, map, obj);
-  }
-};
-
-
-void MarkCompactMarkingVisitor::Initialize() {
-  StaticMarkingVisitor<MarkCompactMarkingVisitor>::Initialize();
-
-  table_.Register(kVisitJSRegExp,
-                  &VisitRegExpAndFlushCode);
-
-  if (FLAG_track_gc_object_stats) {
-    // Copy the visitor table to make call-through possible.
-    non_count_table_.CopyFrom(&table_);
-#define VISITOR_ID_COUNT_FUNCTION(id)                                   \
-    table_.Register(kVisit##id, ObjectStatsTracker<kVisit##id>::Visit);
-    VISITOR_ID_LIST(VISITOR_ID_COUNT_FUNCTION)
-#undef VISITOR_ID_COUNT_FUNCTION
-  }
-}
-
-
-VisitorDispatchTable<MarkCompactMarkingVisitor::Callback>
-    MarkCompactMarkingVisitor::non_count_table_;
-
-
-class CodeMarkingVisitor : public ThreadVisitor {
- public:
-  explicit CodeMarkingVisitor(MarkCompactCollector* collector)
-      : collector_(collector) {}
-
-  void VisitThread(Isolate* isolate, ThreadLocalTop* top) {
-    collector_->PrepareThreadForCodeFlushing(isolate, top);
-  }
-
- private:
-  MarkCompactCollector* collector_;
-};
-
-
-class SharedFunctionInfoMarkingVisitor : public ObjectVisitor {
- public:
-  explicit SharedFunctionInfoMarkingVisitor(MarkCompactCollector* collector)
-      : collector_(collector) {}
-
-  void VisitPointers(Object** start, Object** end) {
-    for (Object** p = start; p < end; p++) VisitPointer(p);
-  }
-
-  void VisitPointer(Object** slot) {
-    Object* obj = *slot;
-    if (obj->IsSharedFunctionInfo()) {
-      SharedFunctionInfo* shared = reinterpret_cast<SharedFunctionInfo*>(obj);
-      MarkBit shared_mark = Marking::MarkBitFrom(shared);
-      MarkBit code_mark = Marking::MarkBitFrom(shared->code());
-      collector_->MarkObject(shared->code(), code_mark);
-      collector_->MarkObject(shared, shared_mark);
-    }
-  }
-
- private:
-  MarkCompactCollector* collector_;
-};
-
-
-void MarkCompactCollector::PrepareThreadForCodeFlushing(Isolate* isolate,
-                                                        ThreadLocalTop* top) {
-  for (StackFrameIterator it(isolate, top); !it.done(); it.Advance()) {
-    // Note: for the frame that has a pending lazy deoptimization
-    // StackFrame::unchecked_code will return a non-optimized code object for
-    // the outermost function and StackFrame::LookupCode will return
-    // actual optimized code object.
-    StackFrame* frame = it.frame();
-    Code* code = frame->unchecked_code();
-    MarkBit code_mark = Marking::MarkBitFrom(code);
-    MarkObject(code, code_mark);
-    if (frame->is_optimized()) {
-      MarkCompactMarkingVisitor::MarkInlinedFunctionsCode(heap(),
-                                                          frame->LookupCode());
-    }
-  }
-}
-
-
-void MarkCompactCollector::PrepareForCodeFlushing() {
-  // Enable code flushing for non-incremental cycles.
-  if (FLAG_flush_code && !FLAG_flush_code_incrementally) {
-    EnableCodeFlushing(!was_marked_incrementally_);
-  }
-
-  // If code flushing is disabled, there is no need to prepare for it.
-  if (!is_code_flushing_enabled()) return;
-
-  // Ensure that empty descriptor array is marked. Method MarkDescriptorArray
-  // relies on it being marked before any other descriptor array.
-  HeapObject* descriptor_array = heap()->empty_descriptor_array();
-  MarkBit descriptor_array_mark = Marking::MarkBitFrom(descriptor_array);
-  MarkObject(descriptor_array, descriptor_array_mark);
-
-  // Make sure we are not referencing the code from the stack.
-  DCHECK(this == heap()->mark_compact_collector());
-  PrepareThreadForCodeFlushing(heap()->isolate(),
-                               heap()->isolate()->thread_local_top());
-
-  // Iterate the archived stacks in all threads to check if
-  // the code is referenced.
-  CodeMarkingVisitor code_marking_visitor(this);
-  heap()->isolate()->thread_manager()->IterateArchivedThreads(
-      &code_marking_visitor);
-
-  SharedFunctionInfoMarkingVisitor visitor(this);
-  heap()->isolate()->compilation_cache()->IterateFunctions(&visitor);
-  heap()->isolate()->handle_scope_implementer()->Iterate(&visitor);
-
-  ProcessMarkingDeque();
-}
-
-
-// Visitor class for marking heap roots.
-class RootMarkingVisitor : public ObjectVisitor {
- public:
-  explicit RootMarkingVisitor(Heap* heap)
-    : collector_(heap->mark_compact_collector()) { }
-
-  void VisitPointer(Object** p) {
-    MarkObjectByPointer(p);
-  }
-
-  void VisitPointers(Object** start, Object** end) {
-    for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
-  }
-
-  // Skip the weak next code link in a code object, which is visited in
-  // ProcessTopOptimizedFrame.
-  void VisitNextCodeLink(Object** p) { }
-
- private:
-  void MarkObjectByPointer(Object** p) {
-    if (!(*p)->IsHeapObject()) return;
-
-    // Replace flat cons strings in place.
-    HeapObject* object = ShortCircuitConsString(p);
-    MarkBit mark_bit = Marking::MarkBitFrom(object);
-    if (mark_bit.Get()) return;
-
-    Map* map = object->map();
-    // Mark the object.
-    collector_->SetMark(object, mark_bit);
-
-    // Mark the map pointer and body, and push them on the marking stack.
-    MarkBit map_mark = Marking::MarkBitFrom(map);
-    collector_->MarkObject(map, map_mark);
-    MarkCompactMarkingVisitor::IterateBody(map, object);
-
-    // Mark all the objects reachable from the map and body.  May leave
-    // overflowed objects in the heap.
-    collector_->EmptyMarkingDeque();
-  }
-
-  MarkCompactCollector* collector_;
-};
-
-
-// Helper class for pruning the string table.
-template<bool finalize_external_strings>
-class StringTableCleaner : public ObjectVisitor {
- public:
-  explicit StringTableCleaner(Heap* heap)
-    : heap_(heap), pointers_removed_(0) { }
-
-  virtual void VisitPointers(Object** start, Object** end) {
-    // Visit all HeapObject pointers in [start, end).
-    for (Object** p = start; p < end; p++) {
-      Object* o = *p;
-      if (o->IsHeapObject() &&
-          !Marking::MarkBitFrom(HeapObject::cast(o)).Get()) {
-        if (finalize_external_strings) {
-          DCHECK(o->IsExternalString());
-          heap_->FinalizeExternalString(String::cast(*p));
-        } else {
-          pointers_removed_++;
-        }
-        // Set the entry to the_hole_value (as deleted).
-        *p = heap_->the_hole_value();
-      }
-    }
-  }
-
-  int PointersRemoved() {
-    DCHECK(!finalize_external_strings);
-    return pointers_removed_;
-  }
-
- private:
-  Heap* heap_;
-  int pointers_removed_;
-};
-
-
-typedef StringTableCleaner<false> InternalizedStringTableCleaner;
-typedef StringTableCleaner<true> ExternalStringTableCleaner;
-
-
-// Implementation of WeakObjectRetainer for mark compact GCs. All marked objects
-// are retained.
-class MarkCompactWeakObjectRetainer : public WeakObjectRetainer {
- public:
-  virtual Object* RetainAs(Object* object) {
-    if (Marking::MarkBitFrom(HeapObject::cast(object)).Get()) {
-      return object;
-    } else if (object->IsAllocationSite() &&
-               !(AllocationSite::cast(object)->IsZombie())) {
-      // "dead" AllocationSites need to live long enough for a traversal of new
-      // space. These sites get a one-time reprieve.
-      AllocationSite* site = AllocationSite::cast(object);
-      site->MarkZombie();
-      site->GetHeap()->mark_compact_collector()->MarkAllocationSite(site);
-      return object;
-    } else {
-      return NULL;
-    }
-  }
-};
-
-
-// Fill the marking stack with overflowed objects returned by the given
-// iterator.  Stop when the marking stack is filled or the end of the space
-// is reached, whichever comes first.
-template<class T>
-static void DiscoverGreyObjectsWithIterator(Heap* heap,
-                                            MarkingDeque* marking_deque,
-                                            T* it) {
-  // The caller should ensure that the marking stack is initially not full,
-  // so that we don't waste effort pointlessly scanning for objects.
-  DCHECK(!marking_deque->IsFull());
-
-  Map* filler_map = heap->one_pointer_filler_map();
-  for (HeapObject* object = it->Next();
-       object != NULL;
-       object = it->Next()) {
-    MarkBit markbit = Marking::MarkBitFrom(object);
-    if ((object->map() != filler_map) && Marking::IsGrey(markbit)) {
-      Marking::GreyToBlack(markbit);
-      MemoryChunk::IncrementLiveBytesFromGC(object->address(), object->Size());
-      marking_deque->PushBlack(object);
-      if (marking_deque->IsFull()) return;
-    }
-  }
-}
-
-
-static inline int MarkWordToObjectStarts(uint32_t mark_bits, int* starts);
-
-
-static void DiscoverGreyObjectsOnPage(MarkingDeque* marking_deque,
-                                      MemoryChunk* p) {
-  DCHECK(!marking_deque->IsFull());
-  DCHECK(strcmp(Marking::kWhiteBitPattern, "00") == 0);
-  DCHECK(strcmp(Marking::kBlackBitPattern, "10") == 0);
-  DCHECK(strcmp(Marking::kGreyBitPattern, "11") == 0);
-  DCHECK(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
-
-  for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
-    Address cell_base = it.CurrentCellBase();
-    MarkBit::CellType* cell = it.CurrentCell();
-
-    const MarkBit::CellType current_cell = *cell;
-    if (current_cell == 0) continue;
-
-    MarkBit::CellType grey_objects;
-    if (it.HasNext()) {
-      const MarkBit::CellType next_cell = *(cell+1);
-      grey_objects = current_cell &
-          ((current_cell >> 1) | (next_cell << (Bitmap::kBitsPerCell - 1)));
-    } else {
-      grey_objects = current_cell & (current_cell >> 1);
-    }
-
-    int offset = 0;
-    while (grey_objects != 0) {
-      int trailing_zeros = CompilerIntrinsics::CountTrailingZeros(grey_objects);
-      grey_objects >>= trailing_zeros;
-      offset += trailing_zeros;
-      MarkBit markbit(cell, 1 << offset, false);
-      DCHECK(Marking::IsGrey(markbit));
-      Marking::GreyToBlack(markbit);
-      Address addr = cell_base + offset * kPointerSize;
-      HeapObject* object = HeapObject::FromAddress(addr);
-      MemoryChunk::IncrementLiveBytesFromGC(object->address(), object->Size());
-      marking_deque->PushBlack(object);
-      if (marking_deque->IsFull()) return;
-      offset += 2;
-      grey_objects >>= 2;
-    }
-
-    grey_objects >>= (Bitmap::kBitsPerCell - 1);
-  }
-}
-
-
-int MarkCompactCollector::DiscoverAndEvacuateBlackObjectsOnPage(
-    NewSpace* new_space,
-    NewSpacePage* p) {
-  DCHECK(strcmp(Marking::kWhiteBitPattern, "00") == 0);
-  DCHECK(strcmp(Marking::kBlackBitPattern, "10") == 0);
-  DCHECK(strcmp(Marking::kGreyBitPattern, "11") == 0);
-  DCHECK(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
-
-  MarkBit::CellType* cells = p->markbits()->cells();
-  int survivors_size = 0;
-
-  for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
-    Address cell_base = it.CurrentCellBase();
-    MarkBit::CellType* cell = it.CurrentCell();
-
-    MarkBit::CellType current_cell = *cell;
-    if (current_cell == 0) continue;
-
-    int offset = 0;
-    while (current_cell != 0) {
-      int trailing_zeros = CompilerIntrinsics::CountTrailingZeros(current_cell);
-      current_cell >>= trailing_zeros;
-      offset += trailing_zeros;
-      Address address = cell_base + offset * kPointerSize;
-      HeapObject* object = HeapObject::FromAddress(address);
-
-      int size = object->Size();
-      survivors_size += size;
-
-      Heap::UpdateAllocationSiteFeedback(object, Heap::RECORD_SCRATCHPAD_SLOT);
-
-      offset++;
-      current_cell >>= 1;
-
-      // TODO(hpayer): Refactor EvacuateObject and call this function instead.
-      if (heap()->ShouldBePromoted(object->address(), size) &&
-          TryPromoteObject(object, size)) {
-        continue;
-      }
-
-      AllocationResult allocation = new_space->AllocateRaw(size);
-      if (allocation.IsRetry()) {
-        if (!new_space->AddFreshPage()) {
-          // Shouldn't happen. We are sweeping linearly, and to-space
-          // has the same number of pages as from-space, so there is
-          // always room.
-          UNREACHABLE();
-        }
-        allocation = new_space->AllocateRaw(size);
-        DCHECK(!allocation.IsRetry());
-      }
-      Object* target = allocation.ToObjectChecked();
-
-      MigrateObject(HeapObject::cast(target),
-                    object,
-                    size,
-                    NEW_SPACE);
-      heap()->IncrementSemiSpaceCopiedObjectSize(size);
-    }
-    *cells = 0;
-  }
-  return survivors_size;
-}
-
-
-static void DiscoverGreyObjectsInSpace(Heap* heap,
-                                       MarkingDeque* marking_deque,
-                                       PagedSpace* space) {
-  if (space->swept_precisely()) {
-    HeapObjectIterator it(space);
-    DiscoverGreyObjectsWithIterator(heap, marking_deque, &it);
-  } else {
-    PageIterator it(space);
-    while (it.has_next()) {
-      Page* p = it.next();
-      DiscoverGreyObjectsOnPage(marking_deque, p);
-      if (marking_deque->IsFull()) return;
-    }
-  }
-}
-
-
-static void DiscoverGreyObjectsInNewSpace(Heap* heap,
-                                          MarkingDeque* marking_deque) {
-  NewSpace* space = heap->new_space();
-  NewSpacePageIterator it(space->bottom(), space->top());
-  while (it.has_next()) {
-    NewSpacePage* page = it.next();
-    DiscoverGreyObjectsOnPage(marking_deque, page);
-    if (marking_deque->IsFull()) return;
-  }
-}
-
-
-bool MarkCompactCollector::IsUnmarkedHeapObject(Object** p) {
-  Object* o = *p;
-  if (!o->IsHeapObject()) return false;
-  HeapObject* heap_object = HeapObject::cast(o);
-  MarkBit mark = Marking::MarkBitFrom(heap_object);
-  return !mark.Get();
-}
-
-
-bool MarkCompactCollector::IsUnmarkedHeapObjectWithHeap(Heap* heap,
-                                                        Object** p) {
-  Object* o = *p;
-  DCHECK(o->IsHeapObject());
-  HeapObject* heap_object = HeapObject::cast(o);
-  MarkBit mark = Marking::MarkBitFrom(heap_object);
-  return !mark.Get();
-}
-
-
-void MarkCompactCollector::MarkStringTable(RootMarkingVisitor* visitor) {
-  StringTable* string_table = heap()->string_table();
-  // Mark the string table itself.
-  MarkBit string_table_mark = Marking::MarkBitFrom(string_table);
-  if (!string_table_mark.Get()) {
-    // String table could have already been marked by visiting the handles list.
-    SetMark(string_table, string_table_mark);
-  }
-  // Explicitly mark the prefix.
-  string_table->IteratePrefix(visitor);
-  ProcessMarkingDeque();
-}
-
-
-void MarkCompactCollector::MarkAllocationSite(AllocationSite* site) {
-  MarkBit mark_bit = Marking::MarkBitFrom(site);
-  SetMark(site, mark_bit);
-}
-
-
-void MarkCompactCollector::MarkRoots(RootMarkingVisitor* visitor) {
-  // Mark the heap roots including global variables, stack variables,
-  // etc., and all objects reachable from them.
-  heap()->IterateStrongRoots(visitor, VISIT_ONLY_STRONG);
-
-  // Handle the string table specially.
-  MarkStringTable(visitor);
-
-  MarkWeakObjectToCodeTable();
-
-  // There may be overflowed objects in the heap.  Visit them now.
-  while (marking_deque_.overflowed()) {
-    RefillMarkingDeque();
-    EmptyMarkingDeque();
-  }
-}
-
-
-void MarkCompactCollector::MarkImplicitRefGroups() {
-  List<ImplicitRefGroup*>* ref_groups =
-      isolate()->global_handles()->implicit_ref_groups();
-
-  int last = 0;
-  for (int i = 0; i < ref_groups->length(); i++) {
-    ImplicitRefGroup* entry = ref_groups->at(i);
-    DCHECK(entry != NULL);
-
-    if (!IsMarked(*entry->parent)) {
-      (*ref_groups)[last++] = entry;
-      continue;
-    }
-
-    Object*** children = entry->children;
-    // A parent object is marked, so mark all child heap objects.
-    for (size_t j = 0; j < entry->length; ++j) {
-      if ((*children[j])->IsHeapObject()) {
-        HeapObject* child = HeapObject::cast(*children[j]);
-        MarkBit mark = Marking::MarkBitFrom(child);
-        MarkObject(child, mark);
-      }
-    }
-
-    // Once the entire group has been marked, dispose it because it's
-    // not needed anymore.
-    delete entry;
-  }
-  ref_groups->Rewind(last);
-}
-
-
-void MarkCompactCollector::MarkWeakObjectToCodeTable() {
-  HeapObject* weak_object_to_code_table =
-      HeapObject::cast(heap()->weak_object_to_code_table());
-  if (!IsMarked(weak_object_to_code_table)) {
-    MarkBit mark = Marking::MarkBitFrom(weak_object_to_code_table);
-    SetMark(weak_object_to_code_table, mark);
-  }
-}
-
-
-// Mark all objects reachable from the objects on the marking stack.
-// Before: the marking stack contains zero or more heap object pointers.
-// After: the marking stack is empty, and all objects reachable from the
-// marking stack have been marked, or are overflowed in the heap.
-void MarkCompactCollector::EmptyMarkingDeque() {
-  while (!marking_deque_.IsEmpty()) {
-    HeapObject* object = marking_deque_.Pop();
-    DCHECK(object->IsHeapObject());
-    DCHECK(heap()->Contains(object));
-    DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
-
-    Map* map = object->map();
-    MarkBit map_mark = Marking::MarkBitFrom(map);
-    MarkObject(map, map_mark);
-
-    MarkCompactMarkingVisitor::IterateBody(map, object);
-  }
-}
-
-
-// Sweep the heap for overflowed objects, clear their overflow bits, and
-// push them on the marking stack.  Stop early if the marking stack fills
-// before sweeping completes.  If sweeping completes, there are no remaining
-// overflowed objects in the heap so the overflow flag on the markings stack
-// is cleared.
-void MarkCompactCollector::RefillMarkingDeque() {
-  DCHECK(marking_deque_.overflowed());
-
-  DiscoverGreyObjectsInNewSpace(heap(), &marking_deque_);
-  if (marking_deque_.IsFull()) return;
-
-  DiscoverGreyObjectsInSpace(heap(),
-                             &marking_deque_,
-                             heap()->old_pointer_space());
-  if (marking_deque_.IsFull()) return;
-
-  DiscoverGreyObjectsInSpace(heap(),
-                             &marking_deque_,
-                             heap()->old_data_space());
-  if (marking_deque_.IsFull()) return;
-
-  DiscoverGreyObjectsInSpace(heap(),
-                             &marking_deque_,
-                             heap()->code_space());
-  if (marking_deque_.IsFull()) return;
-
-  DiscoverGreyObjectsInSpace(heap(),
-                             &marking_deque_,
-                             heap()->map_space());
-  if (marking_deque_.IsFull()) return;
-
-  DiscoverGreyObjectsInSpace(heap(),
-                             &marking_deque_,
-                             heap()->cell_space());
-  if (marking_deque_.IsFull()) return;
-
-  DiscoverGreyObjectsInSpace(heap(),
-                             &marking_deque_,
-                             heap()->property_cell_space());
-  if (marking_deque_.IsFull()) return;
-
-  LargeObjectIterator lo_it(heap()->lo_space());
-  DiscoverGreyObjectsWithIterator(heap(),
-                                  &marking_deque_,
-                                  &lo_it);
-  if (marking_deque_.IsFull()) return;
-
-  marking_deque_.ClearOverflowed();
-}
-
-
-// Mark all objects reachable (transitively) from objects on the marking
-// stack.  Before: the marking stack contains zero or more heap object
-// pointers.  After: the marking stack is empty and there are no overflowed
-// objects in the heap.
-void MarkCompactCollector::ProcessMarkingDeque() {
-  EmptyMarkingDeque();
-  while (marking_deque_.overflowed()) {
-    RefillMarkingDeque();
-    EmptyMarkingDeque();
-  }
-}
-
-
-// Mark all objects reachable (transitively) from objects on the marking
-// stack including references only considered in the atomic marking pause.
-void MarkCompactCollector::ProcessEphemeralMarking(ObjectVisitor* visitor) {
-  bool work_to_do = true;
-  DCHECK(marking_deque_.IsEmpty());
-  while (work_to_do) {
-    isolate()->global_handles()->IterateObjectGroups(
-        visitor, &IsUnmarkedHeapObjectWithHeap);
-    MarkImplicitRefGroups();
-    ProcessWeakCollections();
-    work_to_do = !marking_deque_.IsEmpty();
-    ProcessMarkingDeque();
-  }
-}
-
-
-void MarkCompactCollector::ProcessTopOptimizedFrame(ObjectVisitor* visitor) {
-  for (StackFrameIterator it(isolate(), isolate()->thread_local_top());
-       !it.done(); it.Advance()) {
-    if (it.frame()->type() == StackFrame::JAVA_SCRIPT) {
-      return;
-    }
-    if (it.frame()->type() == StackFrame::OPTIMIZED) {
-      Code* code = it.frame()->LookupCode();
-      if (!code->CanDeoptAt(it.frame()->pc())) {
-        code->CodeIterateBody(visitor);
-      }
-      ProcessMarkingDeque();
-      return;
-    }
-  }
-}
-
-
-void MarkCompactCollector::MarkLiveObjects() {
-  GCTracer::Scope gc_scope(heap()->tracer(), GCTracer::Scope::MC_MARK);
-  double start_time = 0.0;
-  if (FLAG_print_cumulative_gc_stat) {
-    start_time = base::OS::TimeCurrentMillis();
-  }
-  // The recursive GC marker detects when it is nearing stack overflow,
-  // and switches to a different marking system.  JS interrupts interfere
-  // with the C stack limit check.
-  PostponeInterruptsScope postpone(isolate());
-
-  bool incremental_marking_overflowed = false;
-  IncrementalMarking* incremental_marking = heap_->incremental_marking();
-  if (was_marked_incrementally_) {
-    // Finalize the incremental marking and check whether we had an overflow.
-    // Both markers use grey color to mark overflowed objects so
-    // non-incremental marker can deal with them as if overflow
-    // occured during normal marking.
-    // But incremental marker uses a separate marking deque
-    // so we have to explicitly copy its overflow state.
-    incremental_marking->Finalize();
-    incremental_marking_overflowed =
-        incremental_marking->marking_deque()->overflowed();
-    incremental_marking->marking_deque()->ClearOverflowed();
-  } else {
-    // Abort any pending incremental activities e.g. incremental sweeping.
-    incremental_marking->Abort();
-  }
-
-#ifdef DEBUG
-  DCHECK(state_ == PREPARE_GC);
-  state_ = MARK_LIVE_OBJECTS;
-#endif
-  // The to space contains live objects, a page in from space is used as a
-  // marking stack.
-  Address marking_deque_start = heap()->new_space()->FromSpacePageLow();
-  Address marking_deque_end = heap()->new_space()->FromSpacePageHigh();
-  if (FLAG_force_marking_deque_overflows) {
-    marking_deque_end = marking_deque_start + 64 * kPointerSize;
-  }
-  marking_deque_.Initialize(marking_deque_start,
-                            marking_deque_end);
-  DCHECK(!marking_deque_.overflowed());
-
-  if (incremental_marking_overflowed) {
-    // There are overflowed objects left in the heap after incremental marking.
-    marking_deque_.SetOverflowed();
-  }
-
-  PrepareForCodeFlushing();
-
-  if (was_marked_incrementally_) {
-    // There is no write barrier on cells so we have to scan them now at the end
-    // of the incremental marking.
-    {
-      HeapObjectIterator cell_iterator(heap()->cell_space());
-      HeapObject* cell;
-      while ((cell = cell_iterator.Next()) != NULL) {
-        DCHECK(cell->IsCell());
-        if (IsMarked(cell)) {
-          int offset = Cell::kValueOffset;
-          MarkCompactMarkingVisitor::VisitPointer(
-              heap(),
-              reinterpret_cast<Object**>(cell->address() + offset));
-        }
-      }
-    }
-    {
-      HeapObjectIterator js_global_property_cell_iterator(
-          heap()->property_cell_space());
-      HeapObject* cell;
-      while ((cell = js_global_property_cell_iterator.Next()) != NULL) {
-        DCHECK(cell->IsPropertyCell());
-        if (IsMarked(cell)) {
-          MarkCompactMarkingVisitor::VisitPropertyCell(cell->map(), cell);
-        }
-      }
-    }
-  }
-
-  RootMarkingVisitor root_visitor(heap());
-  MarkRoots(&root_visitor);
-
-  ProcessTopOptimizedFrame(&root_visitor);
-
-  // The objects reachable from the roots are marked, yet unreachable
-  // objects are unmarked.  Mark objects reachable due to host
-  // application specific logic or through Harmony weak maps.
-  ProcessEphemeralMarking(&root_visitor);
-
-  // The objects reachable from the roots, weak maps or object groups
-  // are marked, yet unreachable objects are unmarked.  Mark objects
-  // reachable only from weak global handles.
-  //
-  // First we identify nonlive weak handles and mark them as pending
-  // destruction.
-  heap()->isolate()->global_handles()->IdentifyWeakHandles(
-      &IsUnmarkedHeapObject);
-  // Then we mark the objects and process the transitive closure.
-  heap()->isolate()->global_handles()->IterateWeakRoots(&root_visitor);
-  while (marking_deque_.overflowed()) {
-    RefillMarkingDeque();
-    EmptyMarkingDeque();
-  }
-
-  // Repeat host application specific and Harmony weak maps marking to
-  // mark unmarked objects reachable from the weak roots.
-  ProcessEphemeralMarking(&root_visitor);
-
-  AfterMarking();
-
-  if (FLAG_print_cumulative_gc_stat) {
-    heap_->tracer()->AddMarkingTime(base::OS::TimeCurrentMillis() - start_time);
-  }
-}
-
-
-void MarkCompactCollector::AfterMarking() {
-  // Object literal map caches reference strings (cache keys) and maps
-  // (cache values). At this point still useful maps have already been
-  // marked. Mark the keys for the alive values before we process the
-  // string table.
-  ProcessMapCaches();
-
-  // Prune the string table removing all strings only pointed to by the
-  // string table.  Cannot use string_table() here because the string
-  // table is marked.
-  StringTable* string_table = heap()->string_table();
-  InternalizedStringTableCleaner internalized_visitor(heap());
-  string_table->IterateElements(&internalized_visitor);
-  string_table->ElementsRemoved(internalized_visitor.PointersRemoved());
-
-  ExternalStringTableCleaner external_visitor(heap());
-  heap()->external_string_table_.Iterate(&external_visitor);
-  heap()->external_string_table_.CleanUp();
-
-  // Process the weak references.
-  MarkCompactWeakObjectRetainer mark_compact_object_retainer;
-  heap()->ProcessWeakReferences(&mark_compact_object_retainer);
-
-  // Remove object groups after marking phase.
-  heap()->isolate()->global_handles()->RemoveObjectGroups();
-  heap()->isolate()->global_handles()->RemoveImplicitRefGroups();
-
-  // Flush code from collected candidates.
-  if (is_code_flushing_enabled()) {
-    code_flusher_->ProcessCandidates();
-    // If incremental marker does not support code flushing, we need to
-    // disable it before incremental marking steps for next cycle.
-    if (FLAG_flush_code && !FLAG_flush_code_incrementally) {
-      EnableCodeFlushing(false);
-    }
-  }
-
-  if (FLAG_track_gc_object_stats) {
-    heap()->CheckpointObjectStats();
-  }
-}
-
-
-void MarkCompactCollector::ProcessMapCaches() {
-  Object* raw_context = heap()->native_contexts_list();
-  while (raw_context != heap()->undefined_value()) {
-    Context* context = reinterpret_cast<Context*>(raw_context);
-    if (IsMarked(context)) {
-      HeapObject* raw_map_cache =
-          HeapObject::cast(context->get(Context::MAP_CACHE_INDEX));
-      // A map cache may be reachable from the stack. In this case
-      // it's already transitively marked and it's too late to clean
-      // up its parts.
-      if (!IsMarked(raw_map_cache) &&
-          raw_map_cache != heap()->undefined_value()) {
-        MapCache* map_cache = reinterpret_cast<MapCache*>(raw_map_cache);
-        int existing_elements = map_cache->NumberOfElements();
-        int used_elements = 0;
-        for (int i = MapCache::kElementsStartIndex;
-             i < map_cache->length();
-             i += MapCache::kEntrySize) {
-          Object* raw_key = map_cache->get(i);
-          if (raw_key == heap()->undefined_value() ||
-              raw_key == heap()->the_hole_value()) continue;
-          STATIC_ASSERT(MapCache::kEntrySize == 2);
-          Object* raw_map = map_cache->get(i + 1);
-          if (raw_map->IsHeapObject() && IsMarked(raw_map)) {
-            ++used_elements;
-          } else {
-            // Delete useless entries with unmarked maps.
-            DCHECK(raw_map->IsMap());
-            map_cache->set_the_hole(i);
-            map_cache->set_the_hole(i + 1);
-          }
-        }
-        if (used_elements == 0) {
-          context->set(Context::MAP_CACHE_INDEX, heap()->undefined_value());
-        } else {
-          // Note: we don't actually shrink the cache here to avoid
-          // extra complexity during GC. We rely on subsequent cache
-          // usages (EnsureCapacity) to do this.
-          map_cache->ElementsRemoved(existing_elements - used_elements);
-          MarkBit map_cache_markbit = Marking::MarkBitFrom(map_cache);
-          MarkObject(map_cache, map_cache_markbit);
-        }
-      }
-    }
-    // Move to next element in the list.
-    raw_context = context->get(Context::NEXT_CONTEXT_LINK);
-  }
-  ProcessMarkingDeque();
-}
-
-
-void MarkCompactCollector::ClearNonLiveReferences() {
-  // Iterate over the map space, setting map transitions that go from
-  // a marked map to an unmarked map to null transitions.  This action
-  // is carried out only on maps of JSObjects and related subtypes.
-  HeapObjectIterator map_iterator(heap()->map_space());
-  for (HeapObject* obj = map_iterator.Next();
-       obj != NULL;
-       obj = map_iterator.Next()) {
-    Map* map = Map::cast(obj);
-
-    if (!map->CanTransition()) continue;
-
-    MarkBit map_mark = Marking::MarkBitFrom(map);
-    ClearNonLivePrototypeTransitions(map);
-    ClearNonLiveMapTransitions(map, map_mark);
-
-    if (map_mark.Get()) {
-      ClearNonLiveDependentCode(map->dependent_code());
-    } else {
-      ClearDependentCode(map->dependent_code());
-      map->set_dependent_code(DependentCode::cast(heap()->empty_fixed_array()));
-    }
-  }
-
-  // Iterate over property cell space, removing dependent code that is not
-  // otherwise kept alive by strong references.
-  HeapObjectIterator cell_iterator(heap_->property_cell_space());
-  for (HeapObject* cell = cell_iterator.Next();
-       cell != NULL;
-       cell = cell_iterator.Next()) {
-    if (IsMarked(cell)) {
-      ClearNonLiveDependentCode(PropertyCell::cast(cell)->dependent_code());
-    }
-  }
-
-  // Iterate over allocation sites, removing dependent code that is not
-  // otherwise kept alive by strong references.
-  Object* undefined = heap()->undefined_value();
-  for (Object* site = heap()->allocation_sites_list();
-       site != undefined;
-       site = AllocationSite::cast(site)->weak_next()) {
-    if (IsMarked(site)) {
-      ClearNonLiveDependentCode(AllocationSite::cast(site)->dependent_code());
-    }
-  }
-
-  if (heap_->weak_object_to_code_table()->IsHashTable()) {
-    WeakHashTable* table =
-        WeakHashTable::cast(heap_->weak_object_to_code_table());
-    uint32_t capacity = table->Capacity();
-    for (uint32_t i = 0; i < capacity; i++) {
-      uint32_t key_index = table->EntryToIndex(i);
-      Object* key = table->get(key_index);
-      if (!table->IsKey(key)) continue;
-      uint32_t value_index = table->EntryToValueIndex(i);
-      Object* value = table->get(value_index);
-      if (key->IsCell() && !IsMarked(key)) {
-        Cell* cell = Cell::cast(key);
-        Object* object = cell->value();
-        if (IsMarked(object)) {
-          MarkBit mark = Marking::MarkBitFrom(cell);
-          SetMark(cell, mark);
-          Object** value_slot = HeapObject::RawField(cell, Cell::kValueOffset);
-          RecordSlot(value_slot, value_slot, *value_slot);
-        }
-      }
-      if (IsMarked(key)) {
-        if (!IsMarked(value)) {
-          HeapObject* obj = HeapObject::cast(value);
-          MarkBit mark = Marking::MarkBitFrom(obj);
-          SetMark(obj, mark);
-        }
-        ClearNonLiveDependentCode(DependentCode::cast(value));
-      } else {
-        ClearDependentCode(DependentCode::cast(value));
-        table->set(key_index, heap_->the_hole_value());
-        table->set(value_index, heap_->the_hole_value());
-        table->ElementRemoved();
-      }
-    }
-  }
-}
-
-
-void MarkCompactCollector::ClearNonLivePrototypeTransitions(Map* map) {
-  int number_of_transitions = map->NumberOfProtoTransitions();
-  FixedArray* prototype_transitions = map->GetPrototypeTransitions();
-
-  int new_number_of_transitions = 0;
-  const int header = Map::kProtoTransitionHeaderSize;
-  const int proto_offset = header + Map::kProtoTransitionPrototypeOffset;
-  const int map_offset = header + Map::kProtoTransitionMapOffset;
-  const int step = Map::kProtoTransitionElementsPerEntry;
-  for (int i = 0; i < number_of_transitions; i++) {
-    Object* prototype = prototype_transitions->get(proto_offset + i * step);
-    Object* cached_map = prototype_transitions->get(map_offset + i * step);
-    if (IsMarked(prototype) && IsMarked(cached_map)) {
-      DCHECK(!prototype->IsUndefined());
-      int proto_index = proto_offset + new_number_of_transitions * step;
-      int map_index = map_offset + new_number_of_transitions * step;
-      if (new_number_of_transitions != i) {
-        prototype_transitions->set(
-            proto_index,
-            prototype,
-            UPDATE_WRITE_BARRIER);
-        prototype_transitions->set(
-            map_index,
-            cached_map,
-            SKIP_WRITE_BARRIER);
-      }
-      Object** slot = prototype_transitions->RawFieldOfElementAt(proto_index);
-      RecordSlot(slot, slot, prototype);
-      new_number_of_transitions++;
-    }
-  }
-
-  if (new_number_of_transitions != number_of_transitions) {
-    map->SetNumberOfProtoTransitions(new_number_of_transitions);
-  }
-
-  // Fill slots that became free with undefined value.
-  for (int i = new_number_of_transitions * step;
-       i < number_of_transitions * step;
-       i++) {
-    prototype_transitions->set_undefined(header + i);
-  }
-}
-
-
-void MarkCompactCollector::ClearNonLiveMapTransitions(Map* map,
-                                                      MarkBit map_mark) {
-  Object* potential_parent = map->GetBackPointer();
-  if (!potential_parent->IsMap()) return;
-  Map* parent = Map::cast(potential_parent);
-
-  // Follow back pointer, check whether we are dealing with a map transition
-  // from a live map to a dead path and in case clear transitions of parent.
-  bool current_is_alive = map_mark.Get();
-  bool parent_is_alive = Marking::MarkBitFrom(parent).Get();
-  if (!current_is_alive && parent_is_alive) {
-    parent->ClearNonLiveTransitions(heap());
-  }
-}
-
-
-void MarkCompactCollector::ClearDependentICList(Object* head) {
-  Object* current = head;
-  Object* undefined = heap()->undefined_value();
-  while (current != undefined) {
-    Code* code = Code::cast(current);
-    if (IsMarked(code)) {
-      DCHECK(code->is_weak_stub());
-      IC::InvalidateMaps(code);
-    }
-    current = code->next_code_link();
-    code->set_next_code_link(undefined);
-  }
-}
-
-
-void MarkCompactCollector::ClearDependentCode(
-    DependentCode* entries) {
-  DisallowHeapAllocation no_allocation;
-  DependentCode::GroupStartIndexes starts(entries);
-  int number_of_entries = starts.number_of_entries();
-  if (number_of_entries == 0) return;
-  int g = DependentCode::kWeakICGroup;
-  if (starts.at(g) != starts.at(g + 1)) {
-    int i = starts.at(g);
-    DCHECK(i + 1 == starts.at(g + 1));
-    Object* head = entries->object_at(i);
-    ClearDependentICList(head);
-  }
-  g = DependentCode::kWeakCodeGroup;
-  for (int i = starts.at(g); i < starts.at(g + 1); i++) {
-    // If the entry is compilation info then the map must be alive,
-    // and ClearDependentCode shouldn't be called.
-    DCHECK(entries->is_code_at(i));
-    Code* code = entries->code_at(i);
-    if (IsMarked(code) && !code->marked_for_deoptimization()) {
-      code->set_marked_for_deoptimization(true);
-      code->InvalidateEmbeddedObjects();
-      have_code_to_deoptimize_ = true;
-    }
-  }
-  for (int i = 0; i < number_of_entries; i++) {
-    entries->clear_at(i);
-  }
-}
-
-
-int MarkCompactCollector::ClearNonLiveDependentCodeInGroup(
-    DependentCode* entries, int group, int start, int end, int new_start) {
-  int survived = 0;
-  if (group == DependentCode::kWeakICGroup) {
-    // Dependent weak IC stubs form a linked list and only the head is stored
-    // in the dependent code array.
-    if (start != end) {
-      DCHECK(start + 1 == end);
-      Object* old_head = entries->object_at(start);
-      MarkCompactWeakObjectRetainer retainer;
-      Object* head = VisitWeakList<Code>(heap(), old_head, &retainer);
-      entries->set_object_at(new_start, head);
-      Object** slot = entries->slot_at(new_start);
-      RecordSlot(slot, slot, head);
-      // We do not compact this group even if the head is undefined,
-      // more dependent ICs are likely to be added later.
-      survived = 1;
-    }
-  } else {
-    for (int i = start; i < end; i++) {
-      Object* obj = entries->object_at(i);
-      DCHECK(obj->IsCode() || IsMarked(obj));
-      if (IsMarked(obj) &&
-          (!obj->IsCode() || !WillBeDeoptimized(Code::cast(obj)))) {
-        if (new_start + survived != i) {
-          entries->set_object_at(new_start + survived, obj);
-        }
-        Object** slot = entries->slot_at(new_start + survived);
-        RecordSlot(slot, slot, obj);
-        survived++;
-      }
-    }
-  }
-  entries->set_number_of_entries(
-      static_cast<DependentCode::DependencyGroup>(group), survived);
-  return survived;
-}
-
-
-void MarkCompactCollector::ClearNonLiveDependentCode(DependentCode* entries) {
-  DisallowHeapAllocation no_allocation;
-  DependentCode::GroupStartIndexes starts(entries);
-  int number_of_entries = starts.number_of_entries();
-  if (number_of_entries == 0) return;
-  int new_number_of_entries = 0;
-  // Go through all groups, remove dead codes and compact.
-  for (int g = 0; g < DependentCode::kGroupCount; g++) {
-    int survived = ClearNonLiveDependentCodeInGroup(
-        entries, g, starts.at(g), starts.at(g + 1), new_number_of_entries);
-    new_number_of_entries += survived;
-  }
-  for (int i = new_number_of_entries; i < number_of_entries; i++) {
-    entries->clear_at(i);
-  }
-}
-
-
-void MarkCompactCollector::ProcessWeakCollections() {
-  GCTracer::Scope gc_scope(heap()->tracer(),
-                           GCTracer::Scope::MC_WEAKCOLLECTION_PROCESS);
-  Object* weak_collection_obj = heap()->encountered_weak_collections();
-  while (weak_collection_obj != Smi::FromInt(0)) {
-    JSWeakCollection* weak_collection =
-        reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
-    DCHECK(MarkCompactCollector::IsMarked(weak_collection));
-    if (weak_collection->table()->IsHashTable()) {
-      ObjectHashTable* table = ObjectHashTable::cast(weak_collection->table());
-      Object** anchor = reinterpret_cast<Object**>(table->address());
-      for (int i = 0; i < table->Capacity(); i++) {
-        if (MarkCompactCollector::IsMarked(HeapObject::cast(table->KeyAt(i)))) {
-          Object** key_slot =
-              table->RawFieldOfElementAt(ObjectHashTable::EntryToIndex(i));
-          RecordSlot(anchor, key_slot, *key_slot);
-          Object** value_slot =
-              table->RawFieldOfElementAt(ObjectHashTable::EntryToValueIndex(i));
-          MarkCompactMarkingVisitor::MarkObjectByPointer(
-              this, anchor, value_slot);
-        }
-      }
-    }
-    weak_collection_obj = weak_collection->next();
-  }
-}
-
-
-void MarkCompactCollector::ClearWeakCollections() {
-  GCTracer::Scope gc_scope(heap()->tracer(),
-                           GCTracer::Scope::MC_WEAKCOLLECTION_CLEAR);
-  Object* weak_collection_obj = heap()->encountered_weak_collections();
-  while (weak_collection_obj != Smi::FromInt(0)) {
-    JSWeakCollection* weak_collection =
-        reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
-    DCHECK(MarkCompactCollector::IsMarked(weak_collection));
-    if (weak_collection->table()->IsHashTable()) {
-      ObjectHashTable* table = ObjectHashTable::cast(weak_collection->table());
-      for (int i = 0; i < table->Capacity(); i++) {
-        HeapObject* key = HeapObject::cast(table->KeyAt(i));
-        if (!MarkCompactCollector::IsMarked(key)) {
-          table->RemoveEntry(i);
-        }
-      }
-    }
-    weak_collection_obj = weak_collection->next();
-    weak_collection->set_next(heap()->undefined_value());
-  }
-  heap()->set_encountered_weak_collections(Smi::FromInt(0));
-}
-
-
-void MarkCompactCollector::RecordMigratedSlot(Object* value, Address slot) {
-  if (heap_->InNewSpace(value)) {
-    heap_->store_buffer()->Mark(slot);
-  } else if (value->IsHeapObject() && IsOnEvacuationCandidate(value)) {
-    SlotsBuffer::AddTo(&slots_buffer_allocator_,
-                       &migration_slots_buffer_,
-                       reinterpret_cast<Object**>(slot),
-                       SlotsBuffer::IGNORE_OVERFLOW);
-  }
-}
-
-
-
-// We scavange new space simultaneously with sweeping. This is done in two
-// passes.
-//
-// The first pass migrates all alive objects from one semispace to another or
-// promotes them to old space.  Forwarding address is written directly into
-// first word of object without any encoding.  If object is dead we write
-// NULL as a forwarding address.
-//
-// The second pass updates pointers to new space in all spaces.  It is possible
-// to encounter pointers to dead new space objects during traversal of pointers
-// to new space.  We should clear them to avoid encountering them during next
-// pointer iteration.  This is an issue if the store buffer overflows and we
-// have to scan the entire old space, including dead objects, looking for
-// pointers to new space.
-void MarkCompactCollector::MigrateObject(HeapObject* dst,
-                                         HeapObject* src,
-                                         int size,
-                                         AllocationSpace dest) {
-  Address dst_addr = dst->address();
-  Address src_addr = src->address();
-  DCHECK(heap()->AllowedToBeMigrated(src, dest));
-  DCHECK(dest != LO_SPACE && size <= Page::kMaxRegularHeapObjectSize);
-  if (dest == OLD_POINTER_SPACE) {
-    Address src_slot = src_addr;
-    Address dst_slot = dst_addr;
-    DCHECK(IsAligned(size, kPointerSize));
-
-    for (int remaining = size / kPointerSize; remaining > 0; remaining--) {
-      Object* value = Memory::Object_at(src_slot);
-
-      Memory::Object_at(dst_slot) = value;
-
-      // We special case ConstantPoolArrays below since they could contain
-      // integers value entries which look like tagged pointers.
-      // TODO(mstarzinger): restructure this code to avoid this special-casing.
-      if (!src->IsConstantPoolArray()) {
-        RecordMigratedSlot(value, dst_slot);
-      }
-
-      src_slot += kPointerSize;
-      dst_slot += kPointerSize;
-    }
-
-    if (compacting_ && dst->IsJSFunction()) {
-      Address code_entry_slot = dst_addr + JSFunction::kCodeEntryOffset;
-      Address code_entry = Memory::Address_at(code_entry_slot);
-
-      if (Page::FromAddress(code_entry)->IsEvacuationCandidate()) {
-        SlotsBuffer::AddTo(&slots_buffer_allocator_,
-                           &migration_slots_buffer_,
-                           SlotsBuffer::CODE_ENTRY_SLOT,
-                           code_entry_slot,
-                           SlotsBuffer::IGNORE_OVERFLOW);
-      }
-    } else if (dst->IsConstantPoolArray()) {
-      ConstantPoolArray* array = ConstantPoolArray::cast(dst);
-      ConstantPoolArray::Iterator code_iter(array, ConstantPoolArray::CODE_PTR);
-      while (!code_iter.is_finished()) {
-        Address code_entry_slot =
-            dst_addr + array->OffsetOfElementAt(code_iter.next_index());
-        Address code_entry = Memory::Address_at(code_entry_slot);
-
-        if (Page::FromAddress(code_entry)->IsEvacuationCandidate()) {
-          SlotsBuffer::AddTo(&slots_buffer_allocator_,
-                             &migration_slots_buffer_,
-                             SlotsBuffer::CODE_ENTRY_SLOT,
-                             code_entry_slot,
-                             SlotsBuffer::IGNORE_OVERFLOW);
-        }
-      }
-      ConstantPoolArray::Iterator heap_iter(array, ConstantPoolArray::HEAP_PTR);
-      while (!heap_iter.is_finished()) {
-        Address heap_slot =
-            dst_addr + array->OffsetOfElementAt(heap_iter.next_index());
-        Object* value = Memory::Object_at(heap_slot);
-        RecordMigratedSlot(value, heap_slot);
-      }
-    }
-  } else if (dest == CODE_SPACE) {
-    PROFILE(isolate(), CodeMoveEvent(src_addr, dst_addr));
-    heap()->MoveBlock(dst_addr, src_addr, size);
-    SlotsBuffer::AddTo(&slots_buffer_allocator_,
-                       &migration_slots_buffer_,
-                       SlotsBuffer::RELOCATED_CODE_OBJECT,
-                       dst_addr,
-                       SlotsBuffer::IGNORE_OVERFLOW);
-    Code::cast(dst)->Relocate(dst_addr - src_addr);
-  } else {
-    DCHECK(dest == OLD_DATA_SPACE || dest == NEW_SPACE);
-    heap()->MoveBlock(dst_addr, src_addr, size);
-  }
-  heap()->OnMoveEvent(dst, src, size);
-  Memory::Address_at(src_addr) = dst_addr;
-}
-
-
-// Visitor for updating pointers from live objects in old spaces to new space.
-// It does not expect to encounter pointers to dead objects.
-class PointersUpdatingVisitor: public ObjectVisitor {
- public:
-  explicit PointersUpdatingVisitor(Heap* heap) : heap_(heap) { }
-
-  void VisitPointer(Object** p) {
-    UpdatePointer(p);
-  }
-
-  void VisitPointers(Object** start, Object** end) {
-    for (Object** p = start; p < end; p++) UpdatePointer(p);
-  }
-
-  void VisitEmbeddedPointer(RelocInfo* rinfo) {
-    DCHECK(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
-    Object* target = rinfo->target_object();
-    Object* old_target = target;
-    VisitPointer(&target);
-    // Avoid unnecessary changes that might unnecessary flush the instruction
-    // cache.
-    if (target != old_target) {
-      rinfo->set_target_object(target);
-    }
-  }
-
-  void VisitCodeTarget(RelocInfo* rinfo) {
-    DCHECK(RelocInfo::IsCodeTarget(rinfo->rmode()));
-    Object* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
-    Object* old_target = target;
-    VisitPointer(&target);
-    if (target != old_target) {
-      rinfo->set_target_address(Code::cast(target)->instruction_start());
-    }
-  }
-
-  void VisitCodeAgeSequence(RelocInfo* rinfo) {
-    DCHECK(RelocInfo::IsCodeAgeSequence(rinfo->rmode()));
-    Object* stub = rinfo->code_age_stub();
-    DCHECK(stub != NULL);
-    VisitPointer(&stub);
-    if (stub != rinfo->code_age_stub()) {
-      rinfo->set_code_age_stub(Code::cast(stub));
-    }
-  }
-
-  void VisitDebugTarget(RelocInfo* rinfo) {
-    DCHECK((RelocInfo::IsJSReturn(rinfo->rmode()) &&
-            rinfo->IsPatchedReturnSequence()) ||
-           (RelocInfo::IsDebugBreakSlot(rinfo->rmode()) &&
-            rinfo->IsPatchedDebugBreakSlotSequence()));
-    Object* target = Code::GetCodeFromTargetAddress(rinfo->call_address());
-    VisitPointer(&target);
-    rinfo->set_call_address(Code::cast(target)->instruction_start());
-  }
-
-  static inline void UpdateSlot(Heap* heap, Object** slot) {
-    Object* obj = *slot;
-
-    if (!obj->IsHeapObject()) return;
-
-    HeapObject* heap_obj = HeapObject::cast(obj);
-
-    MapWord map_word = heap_obj->map_word();
-    if (map_word.IsForwardingAddress()) {
-      DCHECK(heap->InFromSpace(heap_obj) ||
-             MarkCompactCollector::IsOnEvacuationCandidate(heap_obj));
-      HeapObject* target = map_word.ToForwardingAddress();
-      *slot = target;
-      DCHECK(!heap->InFromSpace(target) &&
-             !MarkCompactCollector::IsOnEvacuationCandidate(target));
-    }
-  }
-
- private:
-  inline void UpdatePointer(Object** p) {
-    UpdateSlot(heap_, p);
-  }
-
-  Heap* heap_;
-};
-
-
-static void UpdatePointer(HeapObject** address, HeapObject* object) {
-  Address new_addr = Memory::Address_at(object->address());
-
-  // The new space sweep will overwrite the map word of dead objects
-  // with NULL. In this case we do not need to transfer this entry to
-  // the store buffer which we are rebuilding.
-  // We perform the pointer update with a no barrier compare-and-swap. The
-  // compare and swap may fail in the case where the pointer update tries to
-  // update garbage memory which was concurrently accessed by the sweeper.
-  if (new_addr != NULL) {
-    base::NoBarrier_CompareAndSwap(
-        reinterpret_cast<base::AtomicWord*>(address),
-        reinterpret_cast<base::AtomicWord>(object),
-        reinterpret_cast<base::AtomicWord>(HeapObject::FromAddress(new_addr)));
-  } else {
-    // We have to zap this pointer, because the store buffer may overflow later,
-    // and then we have to scan the entire heap and we don't want to find
-    // spurious newspace pointers in the old space.
-    // TODO(mstarzinger): This was changed to a sentinel value to track down
-    // rare crashes, change it back to Smi::FromInt(0) later.
-    base::NoBarrier_CompareAndSwap(
-        reinterpret_cast<base::AtomicWord*>(address),
-        reinterpret_cast<base::AtomicWord>(object),
-        reinterpret_cast<base::AtomicWord>(Smi::FromInt(0x0f100d00 >> 1)));
-  }
-}
-
-
-static String* UpdateReferenceInExternalStringTableEntry(Heap* heap,
-                                                         Object** p) {
-  MapWord map_word = HeapObject::cast(*p)->map_word();
-
-  if (map_word.IsForwardingAddress()) {
-    return String::cast(map_word.ToForwardingAddress());
-  }
-
-  return String::cast(*p);
-}
-
-
-bool MarkCompactCollector::TryPromoteObject(HeapObject* object,
-                                            int object_size) {
-  DCHECK(object_size <= Page::kMaxRegularHeapObjectSize);
-
-  OldSpace* target_space = heap()->TargetSpace(object);
-
-  DCHECK(target_space == heap()->old_pointer_space() ||
-         target_space == heap()->old_data_space());
-  HeapObject* target;
-  AllocationResult allocation = target_space->AllocateRaw(object_size);
-  if (allocation.To(&target)) {
-    MigrateObject(target,
-                  object,
-                  object_size,
-                  target_space->identity());
-    heap()->IncrementPromotedObjectsSize(object_size);
-    return true;
-  }
-
-  return false;
-}
-
-
-void MarkCompactCollector::EvacuateNewSpace() {
-  // There are soft limits in the allocation code, designed trigger a mark
-  // sweep collection by failing allocations.  But since we are already in
-  // a mark-sweep allocation, there is no sense in trying to trigger one.
-  AlwaysAllocateScope scope(isolate());
-
-  NewSpace* new_space = heap()->new_space();
-
-  // Store allocation range before flipping semispaces.
-  Address from_bottom = new_space->bottom();
-  Address from_top = new_space->top();
-
-  // Flip the semispaces.  After flipping, to space is empty, from space has
-  // live objects.
-  new_space->Flip();
-  new_space->ResetAllocationInfo();
-
-  int survivors_size = 0;
-
-  // First pass: traverse all objects in inactive semispace, remove marks,
-  // migrate live objects and write forwarding addresses.  This stage puts
-  // new entries in the store buffer and may cause some pages to be marked
-  // scan-on-scavenge.
-  NewSpacePageIterator it(from_bottom, from_top);
-  while (it.has_next()) {
-    NewSpacePage* p = it.next();
-    survivors_size += DiscoverAndEvacuateBlackObjectsOnPage(new_space, p);
-  }
-
-  heap_->IncrementYoungSurvivorsCounter(survivors_size);
-  new_space->set_age_mark(new_space->top());
-}
-
-
-void MarkCompactCollector::EvacuateLiveObjectsFromPage(Page* p) {
-  AlwaysAllocateScope always_allocate(isolate());
-  PagedSpace* space = static_cast<PagedSpace*>(p->owner());
-  DCHECK(p->IsEvacuationCandidate() && !p->WasSwept());
-  p->MarkSweptPrecisely();
-
-  int offsets[16];
-
-  for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
-    Address cell_base = it.CurrentCellBase();
-    MarkBit::CellType* cell = it.CurrentCell();
-
-    if (*cell == 0) continue;
-
-    int live_objects = MarkWordToObjectStarts(*cell, offsets);
-    for (int i = 0; i < live_objects; i++) {
-      Address object_addr = cell_base + offsets[i] * kPointerSize;
-      HeapObject* object = HeapObject::FromAddress(object_addr);
-      DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
-
-      int size = object->Size();
-
-      HeapObject* target_object;
-      AllocationResult allocation = space->AllocateRaw(size);
-      if (!allocation.To(&target_object)) {
-        // If allocation failed, use emergency memory and re-try allocation.
-        CHECK(space->HasEmergencyMemory());
-        space->UseEmergencyMemory();
-        allocation = space->AllocateRaw(size);
-      }
-      if (!allocation.To(&target_object)) {
-        // OS refused to give us memory.
-        V8::FatalProcessOutOfMemory("Evacuation");
-        return;
-      }
-
-      MigrateObject(target_object, object, size, space->identity());
-      DCHECK(object->map_word().IsForwardingAddress());
-    }
-
-    // Clear marking bits for current cell.
-    *cell = 0;
-  }
-  p->ResetLiveBytes();
-}
-
-
-void MarkCompactCollector::EvacuatePages() {
-  int npages = evacuation_candidates_.length();
-  for (int i = 0; i < npages; i++) {
-    Page* p = evacuation_candidates_[i];
-    DCHECK(p->IsEvacuationCandidate() ||
-           p->IsFlagSet(Page::RESCAN_ON_EVACUATION));
-    DCHECK(static_cast<int>(p->parallel_sweeping()) ==
-           MemoryChunk::SWEEPING_DONE);
-    PagedSpace* space = static_cast<PagedSpace*>(p->owner());
-    // Allocate emergency memory for the case when compaction fails due to out
-    // of memory.
-    if (!space->HasEmergencyMemory()) {
-      space->CreateEmergencyMemory();
-    }
-    if (p->IsEvacuationCandidate()) {
-      // During compaction we might have to request a new page. Check that we
-      // have an emergency page and the space still has room for that.
-      if (space->HasEmergencyMemory() && space->CanExpand()) {
-        EvacuateLiveObjectsFromPage(p);
-      } else {
-        // Without room for expansion evacuation is not guaranteed to succeed.
-        // Pessimistically abandon unevacuated pages.
-        for (int j = i; j < npages; j++) {
-          Page* page = evacuation_candidates_[j];
-          slots_buffer_allocator_.DeallocateChain(page->slots_buffer_address());
-          page->ClearEvacuationCandidate();
-          page->SetFlag(Page::RESCAN_ON_EVACUATION);
-        }
-        break;
-      }
-    }
-  }
-  if (npages > 0) {
-    // Release emergency memory.
-    PagedSpaces spaces(heap());
-    for (PagedSpace* space = spaces.next(); space != NULL;
-         space = spaces.next()) {
-      if (space->HasEmergencyMemory()) {
-        space->FreeEmergencyMemory();
-      }
-    }
-  }
-}
-
-
-class EvacuationWeakObjectRetainer : public WeakObjectRetainer {
- public:
-  virtual Object* RetainAs(Object* object) {
-    if (object->IsHeapObject()) {
-      HeapObject* heap_object = HeapObject::cast(object);
-      MapWord map_word = heap_object->map_word();
-      if (map_word.IsForwardingAddress()) {
-        return map_word.ToForwardingAddress();
-      }
-    }
-    return object;
-  }
-};
-
-
-static inline void UpdateSlot(Isolate* isolate,
-                              ObjectVisitor* v,
-                              SlotsBuffer::SlotType slot_type,
-                              Address addr) {
-  switch (slot_type) {
-    case SlotsBuffer::CODE_TARGET_SLOT: {
-      RelocInfo rinfo(addr, RelocInfo::CODE_TARGET, 0, NULL);
-      rinfo.Visit(isolate, v);
-      break;
-    }
-    case SlotsBuffer::CODE_ENTRY_SLOT: {
-      v->VisitCodeEntry(addr);
-      break;
-    }
-    case SlotsBuffer::RELOCATED_CODE_OBJECT: {
-      HeapObject* obj = HeapObject::FromAddress(addr);
-      Code::cast(obj)->CodeIterateBody(v);
-      break;
-    }
-    case SlotsBuffer::DEBUG_TARGET_SLOT: {
-      RelocInfo rinfo(addr, RelocInfo::DEBUG_BREAK_SLOT, 0, NULL);
-      if (rinfo.IsPatchedDebugBreakSlotSequence()) rinfo.Visit(isolate, v);
-      break;
-    }
-    case SlotsBuffer::JS_RETURN_SLOT: {
-      RelocInfo rinfo(addr, RelocInfo::JS_RETURN, 0, NULL);
-      if (rinfo.IsPatchedReturnSequence()) rinfo.Visit(isolate, v);
-      break;
-    }
-    case SlotsBuffer::EMBEDDED_OBJECT_SLOT: {
-      RelocInfo rinfo(addr, RelocInfo::EMBEDDED_OBJECT, 0, NULL);
-      rinfo.Visit(isolate, v);
-      break;
-    }
-    default:
-      UNREACHABLE();
-      break;
-  }
-}
-
-
-enum SweepingMode {
-  SWEEP_ONLY,
-  SWEEP_AND_VISIT_LIVE_OBJECTS
-};
-
-
-enum SkipListRebuildingMode {
-  REBUILD_SKIP_LIST,
-  IGNORE_SKIP_LIST
-};
-
-
-enum FreeSpaceTreatmentMode {
-  IGNORE_FREE_SPACE,
-  ZAP_FREE_SPACE
-};
-
-
-template<MarkCompactCollector::SweepingParallelism mode>
-static intptr_t Free(PagedSpace* space,
-                     FreeList* free_list,
-                     Address start,
-                     int size) {
-  if (mode == MarkCompactCollector::SWEEP_ON_MAIN_THREAD) {
-    DCHECK(free_list == NULL);
-    return space->Free(start, size);
-  } else {
-    // TODO(hpayer): account for wasted bytes in concurrent sweeping too.
-    return size - free_list->Free(start, size);
-  }
-}
-
-
-// Sweep a space precisely.  After this has been done the space can
-// be iterated precisely, hitting only the live objects.  Code space
-// is always swept precisely because we want to be able to iterate
-// over it.  Map space is swept precisely, because it is not compacted.
-// Slots in live objects pointing into evacuation candidates are updated
-// if requested.
-// Returns the size of the biggest continuous freed memory chunk in bytes.
-template<SweepingMode sweeping_mode,
-         MarkCompactCollector::SweepingParallelism parallelism,
-         SkipListRebuildingMode skip_list_mode,
-         FreeSpaceTreatmentMode free_space_mode>
-static int SweepPrecisely(PagedSpace* space,
-                           FreeList* free_list,
-                           Page* p,
-                           ObjectVisitor* v) {
-  DCHECK(!p->IsEvacuationCandidate() && !p->WasSwept());
-  DCHECK_EQ(skip_list_mode == REBUILD_SKIP_LIST,
-            space->identity() == CODE_SPACE);
-  DCHECK((p->skip_list() == NULL) || (skip_list_mode == REBUILD_SKIP_LIST));
-  DCHECK(parallelism == MarkCompactCollector::SWEEP_ON_MAIN_THREAD ||
-         sweeping_mode == SWEEP_ONLY);
-
-  Address free_start = p->area_start();
-  DCHECK(reinterpret_cast<intptr_t>(free_start) % (32 * kPointerSize) == 0);
-  int offsets[16];
-
-  SkipList* skip_list = p->skip_list();
-  int curr_region = -1;
-  if ((skip_list_mode == REBUILD_SKIP_LIST) && skip_list) {
-    skip_list->Clear();
-  }
-
-  intptr_t freed_bytes = 0;
-  intptr_t max_freed_bytes = 0;
-
-  for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
-    Address cell_base = it.CurrentCellBase();
-    MarkBit::CellType* cell = it.CurrentCell();
-    int live_objects = MarkWordToObjectStarts(*cell, offsets);
-    int live_index = 0;
-    for ( ; live_objects != 0; live_objects--) {
-      Address free_end = cell_base + offsets[live_index++] * kPointerSize;
-      if (free_end != free_start) {
-        int size = static_cast<int>(free_end - free_start);
-        if (free_space_mode == ZAP_FREE_SPACE) {
-          memset(free_start, 0xcc, size);
-        }
-        freed_bytes = Free<parallelism>(space, free_list, free_start, size);
-        max_freed_bytes = Max(freed_bytes, max_freed_bytes);
-#ifdef ENABLE_GDB_JIT_INTERFACE
-        if (FLAG_gdbjit && space->identity() == CODE_SPACE) {
-          GDBJITInterface::RemoveCodeRange(free_start, free_end);
-        }
-#endif
-      }
-      HeapObject* live_object = HeapObject::FromAddress(free_end);
-      DCHECK(Marking::IsBlack(Marking::MarkBitFrom(live_object)));
-      Map* map = live_object->map();
-      int size = live_object->SizeFromMap(map);
-      if (sweeping_mode == SWEEP_AND_VISIT_LIVE_OBJECTS) {
-        live_object->IterateBody(map->instance_type(), size, v);
-      }
-      if ((skip_list_mode == REBUILD_SKIP_LIST) && skip_list != NULL) {
-        int new_region_start =
-            SkipList::RegionNumber(free_end);
-        int new_region_end =
-            SkipList::RegionNumber(free_end + size - kPointerSize);
-        if (new_region_start != curr_region ||
-            new_region_end != curr_region) {
-          skip_list->AddObject(free_end, size);
-          curr_region = new_region_end;
-        }
-      }
-      free_start = free_end + size;
-    }
-    // Clear marking bits for current cell.
-    *cell = 0;
-  }
-  if (free_start != p->area_end()) {
-    int size = static_cast<int>(p->area_end() - free_start);
-    if (free_space_mode == ZAP_FREE_SPACE) {
-      memset(free_start, 0xcc, size);
-    }
-    freed_bytes = Free<parallelism>(space, free_list, free_start, size);
-    max_freed_bytes = Max(freed_bytes, max_freed_bytes);
-#ifdef ENABLE_GDB_JIT_INTERFACE
-    if (FLAG_gdbjit && space->identity() == CODE_SPACE) {
-      GDBJITInterface::RemoveCodeRange(free_start, p->area_end());
-    }
-#endif
-  }
-  p->ResetLiveBytes();
-
-  if (parallelism == MarkCompactCollector::SWEEP_IN_PARALLEL) {
-    // When concurrent sweeping is active, the page will be marked after
-    // sweeping by the main thread.
-    p->set_parallel_sweeping(MemoryChunk::SWEEPING_FINALIZE);
-  } else {
-    p->MarkSweptPrecisely();
-  }
-  return FreeList::GuaranteedAllocatable(static_cast<int>(max_freed_bytes));
-}
-
-
-static bool SetMarkBitsUnderInvalidatedCode(Code* code, bool value) {
-  Page* p = Page::FromAddress(code->address());
-
-  if (p->IsEvacuationCandidate() ||
-      p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
-    return false;
-  }
-
-  Address code_start = code->address();
-  Address code_end = code_start + code->Size();
-
-  uint32_t start_index = MemoryChunk::FastAddressToMarkbitIndex(code_start);
-  uint32_t end_index =
-      MemoryChunk::FastAddressToMarkbitIndex(code_end - kPointerSize);
-
-  Bitmap* b = p->markbits();
-
-  MarkBit start_mark_bit = b->MarkBitFromIndex(start_index);
-  MarkBit end_mark_bit = b->MarkBitFromIndex(end_index);
-
-  MarkBit::CellType* start_cell = start_mark_bit.cell();
-  MarkBit::CellType* end_cell = end_mark_bit.cell();
-
-  if (value) {
-    MarkBit::CellType start_mask = ~(start_mark_bit.mask() - 1);
-    MarkBit::CellType end_mask = (end_mark_bit.mask() << 1) - 1;
-
-    if (start_cell == end_cell) {
-      *start_cell |= start_mask & end_mask;
-    } else {
-      *start_cell |= start_mask;
-      for (MarkBit::CellType* cell = start_cell + 1; cell < end_cell; cell++) {
-        *cell = ~0;
-      }
-      *end_cell |= end_mask;
-    }
-  } else {
-    for (MarkBit::CellType* cell = start_cell ; cell <= end_cell; cell++) {
-      *cell = 0;
-    }
-  }
-
-  return true;
-}
-
-
-static bool IsOnInvalidatedCodeObject(Address addr) {
-  // We did not record any slots in large objects thus
-  // we can safely go to the page from the slot address.
-  Page* p = Page::FromAddress(addr);
-
-  // First check owner's identity because old pointer and old data spaces
-  // are swept lazily and might still have non-zero mark-bits on some
-  // pages.
-  if (p->owner()->identity() != CODE_SPACE) return false;
-
-  // In code space only bits on evacuation candidates (but we don't record
-  // any slots on them) and under invalidated code objects are non-zero.
-  MarkBit mark_bit =
-      p->markbits()->MarkBitFromIndex(Page::FastAddressToMarkbitIndex(addr));
-
-  return mark_bit.Get();
-}
-
-
-void MarkCompactCollector::InvalidateCode(Code* code) {
-  if (heap_->incremental_marking()->IsCompacting() &&
-      !ShouldSkipEvacuationSlotRecording(code)) {
-    DCHECK(compacting_);
-
-    // If the object is white than no slots were recorded on it yet.
-    MarkBit mark_bit = Marking::MarkBitFrom(code);
-    if (Marking::IsWhite(mark_bit)) return;
-
-    invalidated_code_.Add(code);
-  }
-}
-
-
-// Return true if the given code is deoptimized or will be deoptimized.
-bool MarkCompactCollector::WillBeDeoptimized(Code* code) {
-  return code->is_optimized_code() && code->marked_for_deoptimization();
-}
-
-
-bool MarkCompactCollector::MarkInvalidatedCode() {
-  bool code_marked = false;
-
-  int length = invalidated_code_.length();
-  for (int i = 0; i < length; i++) {
-    Code* code = invalidated_code_[i];
-
-    if (SetMarkBitsUnderInvalidatedCode(code, true)) {
-      code_marked = true;
-    }
-  }
-
-  return code_marked;
-}
-
-
-void MarkCompactCollector::RemoveDeadInvalidatedCode() {
-  int length = invalidated_code_.length();
-  for (int i = 0; i < length; i++) {
-    if (!IsMarked(invalidated_code_[i])) invalidated_code_[i] = NULL;
-  }
-}
-
-
-void MarkCompactCollector::ProcessInvalidatedCode(ObjectVisitor* visitor) {
-  int length = invalidated_code_.length();
-  for (int i = 0; i < length; i++) {
-    Code* code = invalidated_code_[i];
-    if (code != NULL) {
-      code->Iterate(visitor);
-      SetMarkBitsUnderInvalidatedCode(code, false);
-    }
-  }
-  invalidated_code_.Rewind(0);
-}
-
-
-void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
-  Heap::RelocationLock relocation_lock(heap());
-
-  bool code_slots_filtering_required;
-  { GCTracer::Scope gc_scope(heap()->tracer(),
-                             GCTracer::Scope::MC_SWEEP_NEWSPACE);
-    code_slots_filtering_required = MarkInvalidatedCode();
-    EvacuateNewSpace();
-  }
-
-  { GCTracer::Scope gc_scope(heap()->tracer(),
-                             GCTracer::Scope::MC_EVACUATE_PAGES);
-    EvacuatePages();
-  }
-
-  // Second pass: find pointers to new space and update them.
-  PointersUpdatingVisitor updating_visitor(heap());
-
-  { GCTracer::Scope gc_scope(heap()->tracer(),
-                             GCTracer::Scope::MC_UPDATE_NEW_TO_NEW_POINTERS);
-    // Update pointers in to space.
-    SemiSpaceIterator to_it(heap()->new_space()->bottom(),
-                            heap()->new_space()->top());
-    for (HeapObject* object = to_it.Next();
-         object != NULL;
-         object = to_it.Next()) {
-      Map* map = object->map();
-      object->IterateBody(map->instance_type(),
-                          object->SizeFromMap(map),
-                          &updating_visitor);
-    }
-  }
-
-  { GCTracer::Scope gc_scope(heap()->tracer(),
-                             GCTracer::Scope::MC_UPDATE_ROOT_TO_NEW_POINTERS);
-    // Update roots.
-    heap_->IterateRoots(&updating_visitor, VISIT_ALL_IN_SWEEP_NEWSPACE);
-  }
-
-  { GCTracer::Scope gc_scope(heap()->tracer(),
-                             GCTracer::Scope::MC_UPDATE_OLD_TO_NEW_POINTERS);
-    StoreBufferRebuildScope scope(heap_,
-                                  heap_->store_buffer(),
-                                  &Heap::ScavengeStoreBufferCallback);
-    heap_->store_buffer()->IteratePointersToNewSpaceAndClearMaps(
-        &UpdatePointer);
-  }
-
-  { GCTracer::Scope gc_scope(heap()->tracer(),
-                             GCTracer::Scope::MC_UPDATE_POINTERS_TO_EVACUATED);
-    SlotsBuffer::UpdateSlotsRecordedIn(heap_,
-                                       migration_slots_buffer_,
-                                       code_slots_filtering_required);
-    if (FLAG_trace_fragmentation) {
-      PrintF("  migration slots buffer: %d\n",
-             SlotsBuffer::SizeOfChain(migration_slots_buffer_));
-    }
-
-    if (compacting_ && was_marked_incrementally_) {
-      // It's difficult to filter out slots recorded for large objects.
-      LargeObjectIterator it(heap_->lo_space());
-      for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
-        // LargeObjectSpace is not swept yet thus we have to skip
-        // dead objects explicitly.
-        if (!IsMarked(obj)) continue;
-
-        Page* p = Page::FromAddress(obj->address());
-        if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
-          obj->Iterate(&updating_visitor);
-          p->ClearFlag(Page::RESCAN_ON_EVACUATION);
-        }
-      }
-    }
-  }
-
-  int npages = evacuation_candidates_.length();
-  { GCTracer::Scope gc_scope(
-      heap()->tracer(), GCTracer::Scope::MC_UPDATE_POINTERS_BETWEEN_EVACUATED);
-    for (int i = 0; i < npages; i++) {
-      Page* p = evacuation_candidates_[i];
-      DCHECK(p->IsEvacuationCandidate() ||
-             p->IsFlagSet(Page::RESCAN_ON_EVACUATION));
-
-      if (p->IsEvacuationCandidate()) {
-        SlotsBuffer::UpdateSlotsRecordedIn(heap_,
-                                           p->slots_buffer(),
-                                           code_slots_filtering_required);
-        if (FLAG_trace_fragmentation) {
-          PrintF("  page %p slots buffer: %d\n",
-                 reinterpret_cast<void*>(p),
-                 SlotsBuffer::SizeOfChain(p->slots_buffer()));
-        }
-
-        // Important: skip list should be cleared only after roots were updated
-        // because root iteration traverses the stack and might have to find
-        // code objects from non-updated pc pointing into evacuation candidate.
-        SkipList* list = p->skip_list();
-        if (list != NULL) list->Clear();
-      } else {
-        if (FLAG_gc_verbose) {
-          PrintF("Sweeping 0x%" V8PRIxPTR " during evacuation.\n",
-                 reinterpret_cast<intptr_t>(p));
-        }
-        PagedSpace* space = static_cast<PagedSpace*>(p->owner());
-        p->ClearFlag(MemoryChunk::RESCAN_ON_EVACUATION);
-
-        switch (space->identity()) {
-          case OLD_DATA_SPACE:
-            SweepConservatively<SWEEP_ON_MAIN_THREAD>(space, NULL, p);
-            break;
-          case OLD_POINTER_SPACE:
-            SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS,
-                           SWEEP_ON_MAIN_THREAD,
-                           IGNORE_SKIP_LIST,
-                           IGNORE_FREE_SPACE>(
-                space, NULL, p, &updating_visitor);
-            break;
-          case CODE_SPACE:
-            if (FLAG_zap_code_space) {
-              SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS,
-                             SWEEP_ON_MAIN_THREAD,
-                             REBUILD_SKIP_LIST,
-                             ZAP_FREE_SPACE>(
-                  space, NULL, p, &updating_visitor);
-            } else {
-              SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS,
-                             SWEEP_ON_MAIN_THREAD,
-                             REBUILD_SKIP_LIST,
-                             IGNORE_FREE_SPACE>(
-                  space, NULL, p, &updating_visitor);
-            }
-            break;
-          default:
-            UNREACHABLE();
-            break;
-        }
-      }
-    }
-  }
-
-  GCTracer::Scope gc_scope(heap()->tracer(),
-                           GCTracer::Scope::MC_UPDATE_MISC_POINTERS);
-
-  // Update pointers from cells.
-  HeapObjectIterator cell_iterator(heap_->cell_space());
-  for (HeapObject* cell = cell_iterator.Next();
-       cell != NULL;
-       cell = cell_iterator.Next()) {
-    if (cell->IsCell()) {
-      Cell::BodyDescriptor::IterateBody(cell, &updating_visitor);
-    }
-  }
-
-  HeapObjectIterator js_global_property_cell_iterator(
-      heap_->property_cell_space());
-  for (HeapObject* cell = js_global_property_cell_iterator.Next();
-       cell != NULL;
-       cell = js_global_property_cell_iterator.Next()) {
-    if (cell->IsPropertyCell()) {
-      PropertyCell::BodyDescriptor::IterateBody(cell, &updating_visitor);
-    }
-  }
-
-  heap_->string_table()->Iterate(&updating_visitor);
-  updating_visitor.VisitPointer(heap_->weak_object_to_code_table_address());
-  if (heap_->weak_object_to_code_table()->IsHashTable()) {
-    WeakHashTable* table =
-        WeakHashTable::cast(heap_->weak_object_to_code_table());
-    table->Iterate(&updating_visitor);
-    table->Rehash(heap_->isolate()->factory()->undefined_value());
-  }
-
-  // Update pointers from external string table.
-  heap_->UpdateReferencesInExternalStringTable(
-      &UpdateReferenceInExternalStringTableEntry);
-
-  EvacuationWeakObjectRetainer evacuation_object_retainer;
-  heap()->ProcessWeakReferences(&evacuation_object_retainer);
-
-  // Visit invalidated code (we ignored all slots on it) and clear mark-bits
-  // under it.
-  ProcessInvalidatedCode(&updating_visitor);
-
-  heap_->isolate()->inner_pointer_to_code_cache()->Flush();
-
-  slots_buffer_allocator_.DeallocateChain(&migration_slots_buffer_);
-  DCHECK(migration_slots_buffer_ == NULL);
-}
-
-
-void MarkCompactCollector::MoveEvacuationCandidatesToEndOfPagesList() {
-  int npages = evacuation_candidates_.length();
-  for (int i = 0; i < npages; i++) {
-    Page* p = evacuation_candidates_[i];
-    if (!p->IsEvacuationCandidate()) continue;
-    p->Unlink();
-    PagedSpace* space = static_cast<PagedSpace*>(p->owner());
-    p->InsertAfter(space->LastPage());
-  }
-}
-
-
-void MarkCompactCollector::ReleaseEvacuationCandidates() {
-  int npages = evacuation_candidates_.length();
-  for (int i = 0; i < npages; i++) {
-    Page* p = evacuation_candidates_[i];
-    if (!p->IsEvacuationCandidate()) continue;
-    PagedSpace* space = static_cast<PagedSpace*>(p->owner());
-    space->Free(p->area_start(), p->area_size());
-    p->set_scan_on_scavenge(false);
-    slots_buffer_allocator_.DeallocateChain(p->slots_buffer_address());
-    p->ResetLiveBytes();
-    space->ReleasePage(p);
-  }
-  evacuation_candidates_.Rewind(0);
-  compacting_ = false;
-  heap()->FreeQueuedChunks();
-}
-
-
-static const int kStartTableEntriesPerLine = 5;
-static const int kStartTableLines = 171;
-static const int kStartTableInvalidLine = 127;
-static const int kStartTableUnusedEntry = 126;
-
-#define _ kStartTableUnusedEntry
-#define X kStartTableInvalidLine
-// Mark-bit to object start offset table.
-//
-// The line is indexed by the mark bits in a byte.  The first number on
-// the line describes the number of live object starts for the line and the
-// other numbers on the line describe the offsets (in words) of the object
-// starts.
-//
-// Since objects are at least 2 words large we don't have entries for two
-// consecutive 1 bits.  All entries after 170 have at least 2 consecutive bits.
-char kStartTable[kStartTableLines * kStartTableEntriesPerLine] = {
-  0, _, _, _, _,  // 0
-  1, 0, _, _, _,  // 1
-  1, 1, _, _, _,  // 2
-  X, _, _, _, _,  // 3
-  1, 2, _, _, _,  // 4
-  2, 0, 2, _, _,  // 5
-  X, _, _, _, _,  // 6
-  X, _, _, _, _,  // 7
-  1, 3, _, _, _,  // 8
-  2, 0, 3, _, _,  // 9
-  2, 1, 3, _, _,  // 10
-  X, _, _, _, _,  // 11
-  X, _, _, _, _,  // 12
-  X, _, _, _, _,  // 13
-  X, _, _, _, _,  // 14
-  X, _, _, _, _,  // 15
-  1, 4, _, _, _,  // 16
-  2, 0, 4, _, _,  // 17
-  2, 1, 4, _, _,  // 18
-  X, _, _, _, _,  // 19
-  2, 2, 4, _, _,  // 20
-  3, 0, 2, 4, _,  // 21
-  X, _, _, _, _,  // 22
-  X, _, _, _, _,  // 23
-  X, _, _, _, _,  // 24
-  X, _, _, _, _,  // 25
-  X, _, _, _, _,  // 26
-  X, _, _, _, _,  // 27
-  X, _, _, _, _,  // 28
-  X, _, _, _, _,  // 29
-  X, _, _, _, _,  // 30
-  X, _, _, _, _,  // 31
-  1, 5, _, _, _,  // 32
-  2, 0, 5, _, _,  // 33
-  2, 1, 5, _, _,  // 34
-  X, _, _, _, _,  // 35
-  2, 2, 5, _, _,  // 36
-  3, 0, 2, 5, _,  // 37
-  X, _, _, _, _,  // 38
-  X, _, _, _, _,  // 39
-  2, 3, 5, _, _,  // 40
-  3, 0, 3, 5, _,  // 41
-  3, 1, 3, 5, _,  // 42
-  X, _, _, _, _,  // 43
-  X, _, _, _, _,  // 44
-  X, _, _, _, _,  // 45
-  X, _, _, _, _,  // 46
-  X, _, _, _, _,  // 47
-  X, _, _, _, _,  // 48
-  X, _, _, _, _,  // 49
-  X, _, _, _, _,  // 50
-  X, _, _, _, _,  // 51
-  X, _, _, _, _,  // 52
-  X, _, _, _, _,  // 53
-  X, _, _, _, _,  // 54
-  X, _, _, _, _,  // 55
-  X, _, _, _, _,  // 56
-  X, _, _, _, _,  // 57
-  X, _, _, _, _,  // 58
-  X, _, _, _, _,  // 59
-  X, _, _, _, _,  // 60
-  X, _, _, _, _,  // 61
-  X, _, _, _, _,  // 62
-  X, _, _, _, _,  // 63
-  1, 6, _, _, _,  // 64
-  2, 0, 6, _, _,  // 65
-  2, 1, 6, _, _,  // 66
-  X, _, _, _, _,  // 67
-  2, 2, 6, _, _,  // 68
-  3, 0, 2, 6, _,  // 69
-  X, _, _, _, _,  // 70
-  X, _, _, _, _,  // 71
-  2, 3, 6, _, _,  // 72
-  3, 0, 3, 6, _,  // 73
-  3, 1, 3, 6, _,  // 74
-  X, _, _, _, _,  // 75
-  X, _, _, _, _,  // 76
-  X, _, _, _, _,  // 77
-  X, _, _, _, _,  // 78
-  X, _, _, _, _,  // 79
-  2, 4, 6, _, _,  // 80
-  3, 0, 4, 6, _,  // 81
-  3, 1, 4, 6, _,  // 82
-  X, _, _, _, _,  // 83
-  3, 2, 4, 6, _,  // 84
-  4, 0, 2, 4, 6,  // 85
-  X, _, _, _, _,  // 86
-  X, _, _, _, _,  // 87
-  X, _, _, _, _,  // 88
-  X, _, _, _, _,  // 89
-  X, _, _, _, _,  // 90
-  X, _, _, _, _,  // 91
-  X, _, _, _, _,  // 92
-  X, _, _, _, _,  // 93
-  X, _, _, _, _,  // 94
-  X, _, _, _, _,  // 95
-  X, _, _, _, _,  // 96
-  X, _, _, _, _,  // 97
-  X, _, _, _, _,  // 98
-  X, _, _, _, _,  // 99
-  X, _, _, _, _,  // 100
-  X, _, _, _, _,  // 101
-  X, _, _, _, _,  // 102
-  X, _, _, _, _,  // 103
-  X, _, _, _, _,  // 104
-  X, _, _, _, _,  // 105
-  X, _, _, _, _,  // 106
-  X, _, _, _, _,  // 107
-  X, _, _, _, _,  // 108
-  X, _, _, _, _,  // 109
-  X, _, _, _, _,  // 110
-  X, _, _, _, _,  // 111
-  X, _, _, _, _,  // 112
-  X, _, _, _, _,  // 113
-  X, _, _, _, _,  // 114
-  X, _, _, _, _,  // 115
-  X, _, _, _, _,  // 116
-  X, _, _, _, _,  // 117
-  X, _, _, _, _,  // 118
-  X, _, _, _, _,  // 119
-  X, _, _, _, _,  // 120
-  X, _, _, _, _,  // 121
-  X, _, _, _, _,  // 122
-  X, _, _, _, _,  // 123
-  X, _, _, _, _,  // 124
-  X, _, _, _, _,  // 125
-  X, _, _, _, _,  // 126
-  X, _, _, _, _,  // 127
-  1, 7, _, _, _,  // 128
-  2, 0, 7, _, _,  // 129
-  2, 1, 7, _, _,  // 130
-  X, _, _, _, _,  // 131
-  2, 2, 7, _, _,  // 132
-  3, 0, 2, 7, _,  // 133
-  X, _, _, _, _,  // 134
-  X, _, _, _, _,  // 135
-  2, 3, 7, _, _,  // 136
-  3, 0, 3, 7, _,  // 137
-  3, 1, 3, 7, _,  // 138
-  X, _, _, _, _,  // 139
-  X, _, _, _, _,  // 140
-  X, _, _, _, _,  // 141
-  X, _, _, _, _,  // 142
-  X, _, _, _, _,  // 143
-  2, 4, 7, _, _,  // 144
-  3, 0, 4, 7, _,  // 145
-  3, 1, 4, 7, _,  // 146
-  X, _, _, _, _,  // 147
-  3, 2, 4, 7, _,  // 148
-  4, 0, 2, 4, 7,  // 149
-  X, _, _, _, _,  // 150
-  X, _, _, _, _,  // 151
-  X, _, _, _, _,  // 152
-  X, _, _, _, _,  // 153
-  X, _, _, _, _,  // 154
-  X, _, _, _, _,  // 155
-  X, _, _, _, _,  // 156
-  X, _, _, _, _,  // 157
-  X, _, _, _, _,  // 158
-  X, _, _, _, _,  // 159
-  2, 5, 7, _, _,  // 160
-  3, 0, 5, 7, _,  // 161
-  3, 1, 5, 7, _,  // 162
-  X, _, _, _, _,  // 163
-  3, 2, 5, 7, _,  // 164
-  4, 0, 2, 5, 7,  // 165
-  X, _, _, _, _,  // 166
-  X, _, _, _, _,  // 167
-  3, 3, 5, 7, _,  // 168
-  4, 0, 3, 5, 7,  // 169
-  4, 1, 3, 5, 7   // 170
-};
-#undef _
-#undef X
-
-
-// Takes a word of mark bits.  Returns the number of objects that start in the
-// range.  Puts the offsets of the words in the supplied array.
-static inline int MarkWordToObjectStarts(uint32_t mark_bits, int* starts) {
-  int objects = 0;
-  int offset = 0;
-
-  // No consecutive 1 bits.
-  DCHECK((mark_bits & 0x180) != 0x180);
-  DCHECK((mark_bits & 0x18000) != 0x18000);
-  DCHECK((mark_bits & 0x1800000) != 0x1800000);
-
-  while (mark_bits != 0) {
-    int byte = (mark_bits & 0xff);
-    mark_bits >>= 8;
-    if (byte != 0) {
-      DCHECK(byte < kStartTableLines);  // No consecutive 1 bits.
-      char* table = kStartTable + byte * kStartTableEntriesPerLine;
-      int objects_in_these_8_words = table[0];
-      DCHECK(objects_in_these_8_words != kStartTableInvalidLine);
-      DCHECK(objects_in_these_8_words < kStartTableEntriesPerLine);
-      for (int i = 0; i < objects_in_these_8_words; i++) {
-        starts[objects++] = offset + table[1 + i];
-      }
-    }
-    offset += 8;
-  }
-  return objects;
-}
-
-
-static inline Address DigestFreeStart(Address approximate_free_start,
-                                      uint32_t free_start_cell) {
-  DCHECK(free_start_cell != 0);
-
-  // No consecutive 1 bits.
-  DCHECK((free_start_cell & (free_start_cell << 1)) == 0);
-
-  int offsets[16];
-  uint32_t cell = free_start_cell;
-  int offset_of_last_live;
-  if ((cell & 0x80000000u) != 0) {
-    // This case would overflow below.
-    offset_of_last_live = 31;
-  } else {
-    // Remove all but one bit, the most significant.  This is an optimization
-    // that may or may not be worthwhile.
-    cell |= cell >> 16;
-    cell |= cell >> 8;
-    cell |= cell >> 4;
-    cell |= cell >> 2;
-    cell |= cell >> 1;
-    cell = (cell + 1) >> 1;
-    int live_objects = MarkWordToObjectStarts(cell, offsets);
-    DCHECK(live_objects == 1);
-    offset_of_last_live = offsets[live_objects - 1];
-  }
-  Address last_live_start =
-      approximate_free_start + offset_of_last_live * kPointerSize;
-  HeapObject* last_live = HeapObject::FromAddress(last_live_start);
-  Address free_start = last_live_start + last_live->Size();
-  return free_start;
-}
-
-
-static inline Address StartOfLiveObject(Address block_address, uint32_t cell) {
-  DCHECK(cell != 0);
-
-  // No consecutive 1 bits.
-  DCHECK((cell & (cell << 1)) == 0);
-
-  int offsets[16];
-  if (cell == 0x80000000u) {  // Avoid overflow below.
-    return block_address + 31 * kPointerSize;
-  }
-  uint32_t first_set_bit = ((cell ^ (cell - 1)) + 1) >> 1;
-  DCHECK((first_set_bit & cell) == first_set_bit);
-  int live_objects = MarkWordToObjectStarts(first_set_bit, offsets);
-  DCHECK(live_objects == 1);
-  USE(live_objects);
-  return block_address + offsets[0] * kPointerSize;
-}
-
-
-// Force instantiation of templatized SweepConservatively method for
-// SWEEP_ON_MAIN_THREAD mode.
-template int MarkCompactCollector::
-    SweepConservatively<MarkCompactCollector::SWEEP_ON_MAIN_THREAD>(
-        PagedSpace*, FreeList*, Page*);
-
-
-// Force instantiation of templatized SweepConservatively method for
-// SWEEP_IN_PARALLEL mode.
-template int MarkCompactCollector::
-    SweepConservatively<MarkCompactCollector::SWEEP_IN_PARALLEL>(
-        PagedSpace*, FreeList*, Page*);
-
-
-// Sweeps a space conservatively.  After this has been done the larger free
-// spaces have been put on the free list and the smaller ones have been
-// ignored and left untouched.  A free space is always either ignored or put
-// on the free list, never split up into two parts.  This is important
-// because it means that any FreeSpace maps left actually describe a region of
-// memory that can be ignored when scanning.  Dead objects other than free
-// spaces will not contain the free space map.
-template<MarkCompactCollector::SweepingParallelism mode>
-int MarkCompactCollector::SweepConservatively(PagedSpace* space,
-                                              FreeList* free_list,
-                                              Page* p) {
-  DCHECK(!p->IsEvacuationCandidate() && !p->WasSwept());
-  DCHECK((mode == MarkCompactCollector::SWEEP_IN_PARALLEL &&
-         free_list != NULL) ||
-         (mode == MarkCompactCollector::SWEEP_ON_MAIN_THREAD &&
-         free_list == NULL));
-
-  intptr_t freed_bytes = 0;
-  intptr_t max_freed_bytes = 0;
-  size_t size = 0;
-
-  // Skip over all the dead objects at the start of the page and mark them free.
-  Address cell_base = 0;
-  MarkBit::CellType* cell = NULL;
-  MarkBitCellIterator it(p);
-  for (; !it.Done(); it.Advance()) {
-    cell_base = it.CurrentCellBase();
-    cell = it.CurrentCell();
-    if (*cell != 0) break;
-  }
-
-  if (it.Done()) {
-    size = p->area_end() - p->area_start();
-    freed_bytes = Free<mode>(space, free_list, p->area_start(),
-                             static_cast<int>(size));
-    max_freed_bytes = Max(freed_bytes, max_freed_bytes);
-    DCHECK_EQ(0, p->LiveBytes());
-    if (mode == MarkCompactCollector::SWEEP_IN_PARALLEL) {
-      // When concurrent sweeping is active, the page will be marked after
-      // sweeping by the main thread.
-      p->set_parallel_sweeping(MemoryChunk::SWEEPING_FINALIZE);
-    } else {
-      p->MarkSweptConservatively();
-    }
-    return FreeList::GuaranteedAllocatable(static_cast<int>(max_freed_bytes));
-  }
-
-  // Grow the size of the start-of-page free space a little to get up to the
-  // first live object.
-  Address free_end = StartOfLiveObject(cell_base, *cell);
-  // Free the first free space.
-  size = free_end - p->area_start();
-  freed_bytes = Free<mode>(space, free_list, p->area_start(),
-                           static_cast<int>(size));
-  max_freed_bytes = Max(freed_bytes, max_freed_bytes);
-
-  // The start of the current free area is represented in undigested form by
-  // the address of the last 32-word section that contained a live object and
-  // the marking bitmap for that cell, which describes where the live object
-  // started.  Unless we find a large free space in the bitmap we will not
-  // digest this pair into a real address.  We start the iteration here at the
-  // first word in the marking bit map that indicates a live object.
-  Address free_start = cell_base;
-  MarkBit::CellType free_start_cell = *cell;
-
-  for (; !it.Done(); it.Advance()) {
-    cell_base = it.CurrentCellBase();
-    cell = it.CurrentCell();
-    if (*cell != 0) {
-      // We have a live object.  Check approximately whether it is more than 32
-      // words since the last live object.
-      if (cell_base - free_start > 32 * kPointerSize) {
-        free_start = DigestFreeStart(free_start, free_start_cell);
-        if (cell_base - free_start > 32 * kPointerSize) {
-          // Now that we know the exact start of the free space it still looks
-          // like we have a large enough free space to be worth bothering with.
-          // so now we need to find the start of the first live object at the
-          // end of the free space.
-          free_end = StartOfLiveObject(cell_base, *cell);
-          freed_bytes = Free<mode>(space, free_list, free_start,
-                                   static_cast<int>(free_end - free_start));
-          max_freed_bytes = Max(freed_bytes, max_freed_bytes);
-        }
-      }
-      // Update our undigested record of where the current free area started.
-      free_start = cell_base;
-      free_start_cell = *cell;
-      // Clear marking bits for current cell.
-      *cell = 0;
-    }
-  }
-
-  // Handle the free space at the end of the page.
-  if (cell_base - free_start > 32 * kPointerSize) {
-    free_start = DigestFreeStart(free_start, free_start_cell);
-    freed_bytes = Free<mode>(space, free_list, free_start,
-                             static_cast<int>(p->area_end() - free_start));
-    max_freed_bytes = Max(freed_bytes, max_freed_bytes);
-  }
-
-  p->ResetLiveBytes();
-  if (mode == MarkCompactCollector::SWEEP_IN_PARALLEL) {
-    // When concurrent sweeping is active, the page will be marked after
-    // sweeping by the main thread.
-    p->set_parallel_sweeping(MemoryChunk::SWEEPING_FINALIZE);
-  } else {
-    p->MarkSweptConservatively();
-  }
-  return FreeList::GuaranteedAllocatable(static_cast<int>(max_freed_bytes));
-}
-
-
-int MarkCompactCollector::SweepInParallel(PagedSpace* space,
-                                          int required_freed_bytes) {
-  int max_freed = 0;
-  int max_freed_overall = 0;
-  PageIterator it(space);
-  while (it.has_next()) {
-    Page* p = it.next();
-    max_freed = SweepInParallel(p, space);
-    DCHECK(max_freed >= 0);
-    if (required_freed_bytes > 0 && max_freed >= required_freed_bytes) {
-      return max_freed;
-    }
-    max_freed_overall = Max(max_freed, max_freed_overall);
-    if (p == space->end_of_unswept_pages()) break;
-  }
-  return max_freed_overall;
-}
-
-
-int MarkCompactCollector::SweepInParallel(Page* page, PagedSpace* space) {
-  int max_freed = 0;
-  if (page->TryParallelSweeping()) {
-    FreeList* free_list = space == heap()->old_pointer_space()
-                              ? free_list_old_pointer_space_.get()
-                              : free_list_old_data_space_.get();
-    FreeList private_free_list(space);
-    if (space->swept_precisely()) {
-      max_freed = SweepPrecisely<SWEEP_ONLY, SWEEP_IN_PARALLEL,
-                                 IGNORE_SKIP_LIST, IGNORE_FREE_SPACE>(
-          space, &private_free_list, page, NULL);
-    } else {
-      max_freed = SweepConservatively<SWEEP_IN_PARALLEL>(
-          space, &private_free_list, page);
-    }
-    free_list->Concatenate(&private_free_list);
-  }
-  return max_freed;
-}
-
-
-void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
-  space->set_swept_precisely(sweeper == PRECISE ||
-                             sweeper == CONCURRENT_PRECISE ||
-                             sweeper == PARALLEL_PRECISE);
-  space->ClearStats();
-
-  // We defensively initialize end_of_unswept_pages_ here with the first page
-  // of the pages list.
-  space->set_end_of_unswept_pages(space->FirstPage());
-
-  PageIterator it(space);
-
-  int pages_swept = 0;
-  bool unused_page_present = false;
-  bool parallel_sweeping_active = false;
-
-  while (it.has_next()) {
-    Page* p = it.next();
-    DCHECK(p->parallel_sweeping() == MemoryChunk::SWEEPING_DONE);
-
-    // Clear sweeping flags indicating that marking bits are still intact.
-    p->ClearSweptPrecisely();
-    p->ClearSweptConservatively();
-
-    if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION) ||
-        p->IsEvacuationCandidate()) {
-      // Will be processed in EvacuateNewSpaceAndCandidates.
-      DCHECK(evacuation_candidates_.length() > 0);
-      continue;
-    }
-
-    // One unused page is kept, all further are released before sweeping them.
-    if (p->LiveBytes() == 0) {
-      if (unused_page_present) {
-        if (FLAG_gc_verbose) {
-          PrintF("Sweeping 0x%" V8PRIxPTR " released page.\n",
-                 reinterpret_cast<intptr_t>(p));
-        }
-        // Adjust unswept free bytes because releasing a page expects said
-        // counter to be accurate for unswept pages.
-        space->IncreaseUnsweptFreeBytes(p);
-        space->ReleasePage(p);
-        continue;
-      }
-      unused_page_present = true;
-    }
-
-    switch (sweeper) {
-      case CONCURRENT_CONSERVATIVE:
-      case PARALLEL_CONSERVATIVE: {
-        if (!parallel_sweeping_active) {
-          if (FLAG_gc_verbose) {
-            PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
-                   reinterpret_cast<intptr_t>(p));
-          }
-          SweepConservatively<SWEEP_ON_MAIN_THREAD>(space, NULL, p);
-          pages_swept++;
-          parallel_sweeping_active = true;
-        } else {
-          if (FLAG_gc_verbose) {
-            PrintF("Sweeping 0x%" V8PRIxPTR " conservatively in parallel.\n",
-                   reinterpret_cast<intptr_t>(p));
-          }
-          p->set_parallel_sweeping(MemoryChunk::SWEEPING_PENDING);
-          space->IncreaseUnsweptFreeBytes(p);
-        }
-        space->set_end_of_unswept_pages(p);
-        break;
-      }
-      case CONCURRENT_PRECISE:
-      case PARALLEL_PRECISE:
-        if (!parallel_sweeping_active) {
-          if (FLAG_gc_verbose) {
-            PrintF("Sweeping 0x%" V8PRIxPTR " precisely.\n",
-                   reinterpret_cast<intptr_t>(p));
-          }
-          SweepPrecisely<SWEEP_ONLY,
-                         SWEEP_ON_MAIN_THREAD,
-                         IGNORE_SKIP_LIST,
-                         IGNORE_FREE_SPACE>(space, NULL, p, NULL);
-          pages_swept++;
-          parallel_sweeping_active = true;
-        } else {
-          if (FLAG_gc_verbose) {
-            PrintF("Sweeping 0x%" V8PRIxPTR " conservatively in parallel.\n",
-                   reinterpret_cast<intptr_t>(p));
-          }
-          p->set_parallel_sweeping(MemoryChunk::SWEEPING_PENDING);
-          space->IncreaseUnsweptFreeBytes(p);
-        }
-        space->set_end_of_unswept_pages(p);
-        break;
-      case PRECISE: {
-        if (FLAG_gc_verbose) {
-          PrintF("Sweeping 0x%" V8PRIxPTR " precisely.\n",
-                 reinterpret_cast<intptr_t>(p));
-        }
-        if (space->identity() == CODE_SPACE && FLAG_zap_code_space) {
-          SweepPrecisely<SWEEP_ONLY,
-                         SWEEP_ON_MAIN_THREAD,
-                         REBUILD_SKIP_LIST,
-                         ZAP_FREE_SPACE>(space, NULL, p, NULL);
-        } else if (space->identity() == CODE_SPACE) {
-          SweepPrecisely<SWEEP_ONLY,
-                         SWEEP_ON_MAIN_THREAD,
-                         REBUILD_SKIP_LIST,
-                         IGNORE_FREE_SPACE>(space, NULL, p, NULL);
-        } else {
-          SweepPrecisely<SWEEP_ONLY,
-                         SWEEP_ON_MAIN_THREAD,
-                         IGNORE_SKIP_LIST,
-                         IGNORE_FREE_SPACE>(space, NULL, p, NULL);
-        }
-        pages_swept++;
-        break;
-      }
-      default: {
-        UNREACHABLE();
-      }
-    }
-  }
-
-  if (FLAG_gc_verbose) {
-    PrintF("SweepSpace: %s (%d pages swept)\n",
-           AllocationSpaceName(space->identity()),
-           pages_swept);
-  }
-
-  // Give pages that are queued to be freed back to the OS.
-  heap()->FreeQueuedChunks();
-}
-
-
-static bool ShouldStartSweeperThreads(MarkCompactCollector::SweeperType type) {
-  return type == MarkCompactCollector::PARALLEL_CONSERVATIVE ||
-         type == MarkCompactCollector::CONCURRENT_CONSERVATIVE ||
-         type == MarkCompactCollector::PARALLEL_PRECISE ||
-         type == MarkCompactCollector::CONCURRENT_PRECISE;
-}
-
-
-static bool ShouldWaitForSweeperThreads(
-    MarkCompactCollector::SweeperType type) {
-  return type == MarkCompactCollector::PARALLEL_CONSERVATIVE ||
-         type == MarkCompactCollector::PARALLEL_PRECISE;
-}
-
-
-void MarkCompactCollector::SweepSpaces() {
-  GCTracer::Scope gc_scope(heap()->tracer(), GCTracer::Scope::MC_SWEEP);
-  double start_time = 0.0;
-  if (FLAG_print_cumulative_gc_stat) {
-    start_time = base::OS::TimeCurrentMillis();
-  }
-
-#ifdef DEBUG
-  state_ = SWEEP_SPACES;
-#endif
-  SweeperType how_to_sweep = CONCURRENT_CONSERVATIVE;
-  if (FLAG_parallel_sweeping) how_to_sweep = PARALLEL_CONSERVATIVE;
-  if (FLAG_concurrent_sweeping) how_to_sweep = CONCURRENT_CONSERVATIVE;
-  if (FLAG_always_precise_sweeping && FLAG_parallel_sweeping) {
-    how_to_sweep = PARALLEL_PRECISE;
-  }
-  if (FLAG_always_precise_sweeping && FLAG_concurrent_sweeping) {
-    how_to_sweep = CONCURRENT_PRECISE;
-  }
-  if (sweep_precisely_) how_to_sweep = PRECISE;
-
-  MoveEvacuationCandidatesToEndOfPagesList();
-
-  // Noncompacting collections simply sweep the spaces to clear the mark
-  // bits and free the nonlive blocks (for old and map spaces).  We sweep
-  // the map space last because freeing non-live maps overwrites them and
-  // the other spaces rely on possibly non-live maps to get the sizes for
-  // non-live objects.
-  { GCTracer::Scope sweep_scope(heap()->tracer(),
-                                GCTracer::Scope::MC_SWEEP_OLDSPACE);
-    { SequentialSweepingScope scope(this);
-      SweepSpace(heap()->old_pointer_space(), how_to_sweep);
-      SweepSpace(heap()->old_data_space(), how_to_sweep);
-    }
-
-    if (ShouldStartSweeperThreads(how_to_sweep)) {
-      StartSweeperThreads();
-    }
-
-    if (ShouldWaitForSweeperThreads(how_to_sweep)) {
-      EnsureSweepingCompleted();
-    }
-  }
-  RemoveDeadInvalidatedCode();
-
-  { GCTracer::Scope sweep_scope(heap()->tracer(),
-                                GCTracer::Scope::MC_SWEEP_CODE);
-    SweepSpace(heap()->code_space(), PRECISE);
-  }
-
-  { GCTracer::Scope sweep_scope(heap()->tracer(),
-                                GCTracer::Scope::MC_SWEEP_CELL);
-    SweepSpace(heap()->cell_space(), PRECISE);
-    SweepSpace(heap()->property_cell_space(), PRECISE);
-  }
-
-  EvacuateNewSpaceAndCandidates();
-
-  // ClearNonLiveTransitions depends on precise sweeping of map space to
-  // detect whether unmarked map became dead in this collection or in one
-  // of the previous ones.
-  { GCTracer::Scope sweep_scope(heap()->tracer(),
-                                GCTracer::Scope::MC_SWEEP_MAP);
-    SweepSpace(heap()->map_space(), PRECISE);
-  }
-
-  // Deallocate unmarked objects and clear marked bits for marked objects.
-  heap_->lo_space()->FreeUnmarkedObjects();
-
-  // Deallocate evacuated candidate pages.
-  ReleaseEvacuationCandidates();
-
-  if (FLAG_print_cumulative_gc_stat) {
-    heap_->tracer()->AddSweepingTime(base::OS::TimeCurrentMillis() -
-                                     start_time);
-  }
-}
-
-
-void MarkCompactCollector::ParallelSweepSpaceComplete(PagedSpace* space) {
-  PageIterator it(space);
-  while (it.has_next()) {
-    Page* p = it.next();
-    if (p->parallel_sweeping() == MemoryChunk::SWEEPING_FINALIZE) {
-      p->set_parallel_sweeping(MemoryChunk::SWEEPING_DONE);
-      if (space->swept_precisely()) {
-        p->MarkSweptPrecisely();
-      } else {
-        p->MarkSweptConservatively();
-      }
-    }
-    DCHECK(p->parallel_sweeping() == MemoryChunk::SWEEPING_DONE);
-  }
-}
-
-
-void MarkCompactCollector::ParallelSweepSpacesComplete() {
-  ParallelSweepSpaceComplete(heap()->old_pointer_space());
-  ParallelSweepSpaceComplete(heap()->old_data_space());
-}
-
-
-void MarkCompactCollector::EnableCodeFlushing(bool enable) {
-  if (isolate()->debug()->is_loaded() ||
-      isolate()->debug()->has_break_points()) {
-    enable = false;
-  }
-
-  if (enable) {
-    if (code_flusher_ != NULL) return;
-    code_flusher_ = new CodeFlusher(isolate());
-  } else {
-    if (code_flusher_ == NULL) return;
-    code_flusher_->EvictAllCandidates();
-    delete code_flusher_;
-    code_flusher_ = NULL;
-  }
-
-  if (FLAG_trace_code_flushing) {
-    PrintF("[code-flushing is now %s]\n", enable ? "on" : "off");
-  }
-}
-
-
-// TODO(1466) ReportDeleteIfNeeded is not called currently.
-// Our profiling tools do not expect intersections between
-// code objects. We should either reenable it or change our tools.
-void MarkCompactCollector::ReportDeleteIfNeeded(HeapObject* obj,
-                                                Isolate* isolate) {
-  if (obj->IsCode()) {
-    PROFILE(isolate, CodeDeleteEvent(obj->address()));
-  }
-}
-
-
-Isolate* MarkCompactCollector::isolate() const {
-  return heap_->isolate();
-}
-
-
-void MarkCompactCollector::Initialize() {
-  MarkCompactMarkingVisitor::Initialize();
-  IncrementalMarking::Initialize();
-}
-
-
-bool SlotsBuffer::IsTypedSlot(ObjectSlot slot) {
-  return reinterpret_cast<uintptr_t>(slot) < NUMBER_OF_SLOT_TYPES;
-}
-
-
-bool SlotsBuffer::AddTo(SlotsBufferAllocator* allocator,
-                        SlotsBuffer** buffer_address,
-                        SlotType type,
-                        Address addr,
-                        AdditionMode mode) {
-  SlotsBuffer* buffer = *buffer_address;
-  if (buffer == NULL || !buffer->HasSpaceForTypedSlot()) {
-    if (mode == FAIL_ON_OVERFLOW && ChainLengthThresholdReached(buffer)) {
-      allocator->DeallocateChain(buffer_address);
-      return false;
-    }
-    buffer = allocator->AllocateBuffer(buffer);
-    *buffer_address = buffer;
-  }
-  DCHECK(buffer->HasSpaceForTypedSlot());
-  buffer->Add(reinterpret_cast<ObjectSlot>(type));
-  buffer->Add(reinterpret_cast<ObjectSlot>(addr));
-  return true;
-}
-
-
-static inline SlotsBuffer::SlotType SlotTypeForRMode(RelocInfo::Mode rmode) {
-  if (RelocInfo::IsCodeTarget(rmode)) {
-    return SlotsBuffer::CODE_TARGET_SLOT;
-  } else if (RelocInfo::IsEmbeddedObject(rmode)) {
-    return SlotsBuffer::EMBEDDED_OBJECT_SLOT;
-  } else if (RelocInfo::IsDebugBreakSlot(rmode)) {
-    return SlotsBuffer::DEBUG_TARGET_SLOT;
-  } else if (RelocInfo::IsJSReturn(rmode)) {
-    return SlotsBuffer::JS_RETURN_SLOT;
-  }
-  UNREACHABLE();
-  return SlotsBuffer::NUMBER_OF_SLOT_TYPES;
-}
-
-
-void MarkCompactCollector::RecordRelocSlot(RelocInfo* rinfo, Object* target) {
-  Page* target_page = Page::FromAddress(reinterpret_cast<Address>(target));
-  RelocInfo::Mode rmode = rinfo->rmode();
-  if (target_page->IsEvacuationCandidate() &&
-      (rinfo->host() == NULL ||
-       !ShouldSkipEvacuationSlotRecording(rinfo->host()))) {
-    bool success;
-    if (RelocInfo::IsEmbeddedObject(rmode) && rinfo->IsInConstantPool()) {
-      // This doesn't need to be typed since it is just a normal heap pointer.
-      Object** target_pointer =
-          reinterpret_cast<Object**>(rinfo->constant_pool_entry_address());
-      success = SlotsBuffer::AddTo(&slots_buffer_allocator_,
-                                   target_page->slots_buffer_address(),
-                                   target_pointer,
-                                   SlotsBuffer::FAIL_ON_OVERFLOW);
-    } else if (RelocInfo::IsCodeTarget(rmode) && rinfo->IsInConstantPool()) {
-      success = SlotsBuffer::AddTo(&slots_buffer_allocator_,
-                                   target_page->slots_buffer_address(),
-                                   SlotsBuffer::CODE_ENTRY_SLOT,
-                                   rinfo->constant_pool_entry_address(),
-                                   SlotsBuffer::FAIL_ON_OVERFLOW);
-    } else {
-      success = SlotsBuffer::AddTo(&slots_buffer_allocator_,
-                                  target_page->slots_buffer_address(),
-                                  SlotTypeForRMode(rmode),
-                                  rinfo->pc(),
-                                  SlotsBuffer::FAIL_ON_OVERFLOW);
-    }
-    if (!success) {
-      EvictEvacuationCandidate(target_page);
-    }
-  }
-}
-
-
-void MarkCompactCollector::RecordCodeEntrySlot(Address slot, Code* target) {
-  Page* target_page = Page::FromAddress(reinterpret_cast<Address>(target));
-  if (target_page->IsEvacuationCandidate() &&
-      !ShouldSkipEvacuationSlotRecording(reinterpret_cast<Object**>(slot))) {
-    if (!SlotsBuffer::AddTo(&slots_buffer_allocator_,
-                            target_page->slots_buffer_address(),
-                            SlotsBuffer::CODE_ENTRY_SLOT,
-                            slot,
-                            SlotsBuffer::FAIL_ON_OVERFLOW)) {
-      EvictEvacuationCandidate(target_page);
-    }
-  }
-}
-
-
-void MarkCompactCollector::RecordCodeTargetPatch(Address pc, Code* target) {
-  DCHECK(heap()->gc_state() == Heap::MARK_COMPACT);
-  if (is_compacting()) {
-    Code* host = isolate()->inner_pointer_to_code_cache()->
-        GcSafeFindCodeForInnerPointer(pc);
-    MarkBit mark_bit = Marking::MarkBitFrom(host);
-    if (Marking::IsBlack(mark_bit)) {
-      RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
-      RecordRelocSlot(&rinfo, target);
-    }
-  }
-}
-
-
-static inline SlotsBuffer::SlotType DecodeSlotType(
-    SlotsBuffer::ObjectSlot slot) {
-  return static_cast<SlotsBuffer::SlotType>(reinterpret_cast<intptr_t>(slot));
-}
-
-
-void SlotsBuffer::UpdateSlots(Heap* heap) {
-  PointersUpdatingVisitor v(heap);
-
-  for (int slot_idx = 0; slot_idx < idx_; ++slot_idx) {
-    ObjectSlot slot = slots_[slot_idx];
-    if (!IsTypedSlot(slot)) {
-      PointersUpdatingVisitor::UpdateSlot(heap, slot);
-    } else {
-      ++slot_idx;
-      DCHECK(slot_idx < idx_);
-      UpdateSlot(heap->isolate(),
-                 &v,
-                 DecodeSlotType(slot),
-                 reinterpret_cast<Address>(slots_[slot_idx]));
-    }
-  }
-}
-
-
-void SlotsBuffer::UpdateSlotsWithFilter(Heap* heap) {
-  PointersUpdatingVisitor v(heap);
-
-  for (int slot_idx = 0; slot_idx < idx_; ++slot_idx) {
-    ObjectSlot slot = slots_[slot_idx];
-    if (!IsTypedSlot(slot)) {
-      if (!IsOnInvalidatedCodeObject(reinterpret_cast<Address>(slot))) {
-        PointersUpdatingVisitor::UpdateSlot(heap, slot);
-      }
-    } else {
-      ++slot_idx;
-      DCHECK(slot_idx < idx_);
-      Address pc = reinterpret_cast<Address>(slots_[slot_idx]);
-      if (!IsOnInvalidatedCodeObject(pc)) {
-        UpdateSlot(heap->isolate(),
-                   &v,
-                   DecodeSlotType(slot),
-                   reinterpret_cast<Address>(slots_[slot_idx]));
-      }
-    }
-  }
-}
-
-
-SlotsBuffer* SlotsBufferAllocator::AllocateBuffer(SlotsBuffer* next_buffer) {
-  return new SlotsBuffer(next_buffer);
-}
-
-
-void SlotsBufferAllocator::DeallocateBuffer(SlotsBuffer* buffer) {
-  delete buffer;
-}
-
-
-void SlotsBufferAllocator::DeallocateChain(SlotsBuffer** buffer_address) {
-  SlotsBuffer* buffer = *buffer_address;
-  while (buffer != NULL) {
-    SlotsBuffer* next_buffer = buffer->next();
-    DeallocateBuffer(buffer);
-    buffer = next_buffer;
-  }
-  *buffer_address = NULL;
-}
-
-
-} }  // namespace v8::internal