src/objects-visiting-inl.h

// 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.

#ifndef V8_OBJECTS_VISITING_INL_H_
#define V8_OBJECTS_VISITING_INL_H_


namespace v8 {
namespace internal {

template<typename StaticVisitor>
void StaticNewSpaceVisitor<StaticVisitor>::Initialize() {
  table_.Register(kVisitShortcutCandidate,
                  &FixedBodyVisitor<StaticVisitor,
                  ConsString::BodyDescriptor,
                  int>::Visit);

  table_.Register(kVisitConsString,
                  &FixedBodyVisitor<StaticVisitor,
                  ConsString::BodyDescriptor,
                  int>::Visit);

  table_.Register(kVisitSlicedString,
                  &FixedBodyVisitor<StaticVisitor,
                  SlicedString::BodyDescriptor,
                  int>::Visit);

  table_.Register(kVisitSymbol,
                  &FixedBodyVisitor<StaticVisitor,
                  Symbol::BodyDescriptor,
                  int>::Visit);

  table_.Register(kVisitFixedArray,
                  &FlexibleBodyVisitor<StaticVisitor,
                  FixedArray::BodyDescriptor,
                  int>::Visit);

  table_.Register(kVisitFixedDoubleArray, &VisitFixedDoubleArray);
  table_.Register(kVisitFixedTypedArray, &VisitFixedTypedArray);
  table_.Register(kVisitFixedFloat64Array, &VisitFixedTypedArray);

  table_.Register(kVisitNativeContext,
                  &FixedBodyVisitor<StaticVisitor,
                  Context::ScavengeBodyDescriptor,
                  int>::Visit);

  table_.Register(kVisitByteArray, &VisitByteArray);

  table_.Register(kVisitSharedFunctionInfo,
                  &FixedBodyVisitor<StaticVisitor,
                  SharedFunctionInfo::BodyDescriptor,
                  int>::Visit);

  table_.Register(kVisitSeqOneByteString, &VisitSeqOneByteString);

  table_.Register(kVisitSeqTwoByteString, &VisitSeqTwoByteString);

  table_.Register(kVisitJSFunction, &VisitJSFunction);

  table_.Register(kVisitJSArrayBuffer, &VisitJSArrayBuffer);

  table_.Register(kVisitJSTypedArray, &VisitJSTypedArray);

  table_.Register(kVisitJSDataView, &VisitJSDataView);

  table_.Register(kVisitFreeSpace, &VisitFreeSpace);

  table_.Register(kVisitJSWeakMap, &JSObjectVisitor::Visit);

  table_.Register(kVisitJSWeakSet, &JSObjectVisitor::Visit);

  table_.Register(kVisitJSRegExp, &JSObjectVisitor::Visit);

  table_.template RegisterSpecializations<DataObjectVisitor,
                                          kVisitDataObject,
                                          kVisitDataObjectGeneric>();

  table_.template RegisterSpecializations<JSObjectVisitor,
                                          kVisitJSObject,
                                          kVisitJSObjectGeneric>();
  table_.template RegisterSpecializations<StructVisitor,
                                          kVisitStruct,
                                          kVisitStructGeneric>();
}


template<typename StaticVisitor>
int StaticNewSpaceVisitor<StaticVisitor>::VisitJSArrayBuffer(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();

  STATIC_ASSERT(
      JSArrayBuffer::kWeakFirstViewOffset ==
      JSArrayBuffer::kWeakNextOffset + kPointerSize);
  VisitPointers(
      heap,
      HeapObject::RawField(object, JSArrayBuffer::BodyDescriptor::kStartOffset),
      HeapObject::RawField(object, JSArrayBuffer::kWeakNextOffset));
  VisitPointers(
      heap,
      HeapObject::RawField(object,
          JSArrayBuffer::kWeakNextOffset + 2 * kPointerSize),
      HeapObject::RawField(object, JSArrayBuffer::kSizeWithInternalFields));
  return JSArrayBuffer::kSizeWithInternalFields;
}


template<typename StaticVisitor>
int StaticNewSpaceVisitor<StaticVisitor>::VisitJSTypedArray(
    Map* map, HeapObject* object) {
  VisitPointers(
      map->GetHeap(),
      HeapObject::RawField(object, JSTypedArray::BodyDescriptor::kStartOffset),
      HeapObject::RawField(object, JSTypedArray::kWeakNextOffset));
  VisitPointers(
      map->GetHeap(),
      HeapObject::RawField(object,
          JSTypedArray::kWeakNextOffset + kPointerSize),
      HeapObject::RawField(object, JSTypedArray::kSizeWithInternalFields));
  return JSTypedArray::kSizeWithInternalFields;
}


template<typename StaticVisitor>
int StaticNewSpaceVisitor<StaticVisitor>::VisitJSDataView(
    Map* map, HeapObject* object) {
  VisitPointers(
      map->GetHeap(),
      HeapObject::RawField(object, JSDataView::BodyDescriptor::kStartOffset),
      HeapObject::RawField(object, JSDataView::kWeakNextOffset));
  VisitPointers(
      map->GetHeap(),
      HeapObject::RawField(object,
          JSDataView::kWeakNextOffset + kPointerSize),
      HeapObject::RawField(object, JSDataView::kSizeWithInternalFields));
  return JSDataView::kSizeWithInternalFields;
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::Initialize() {
  table_.Register(kVisitShortcutCandidate,
                  &FixedBodyVisitor<StaticVisitor,
                  ConsString::BodyDescriptor,
                  void>::Visit);

  table_.Register(kVisitConsString,
                  &FixedBodyVisitor<StaticVisitor,
                  ConsString::BodyDescriptor,
                  void>::Visit);

  table_.Register(kVisitSlicedString,
                  &FixedBodyVisitor<StaticVisitor,
                  SlicedString::BodyDescriptor,
                  void>::Visit);

  table_.Register(kVisitSymbol,
                  &FixedBodyVisitor<StaticVisitor,
                  Symbol::BodyDescriptor,
                  void>::Visit);

  table_.Register(kVisitFixedArray, &FixedArrayVisitor::Visit);

  table_.Register(kVisitFixedDoubleArray, &DataObjectVisitor::Visit);

  table_.Register(kVisitFixedTypedArray, &DataObjectVisitor::Visit);

  table_.Register(kVisitFixedFloat64Array, &DataObjectVisitor::Visit);

  table_.Register(kVisitConstantPoolArray, &VisitConstantPoolArray);

  table_.Register(kVisitNativeContext, &VisitNativeContext);

  table_.Register(kVisitAllocationSite, &VisitAllocationSite);

  table_.Register(kVisitByteArray, &DataObjectVisitor::Visit);

  table_.Register(kVisitFreeSpace, &DataObjectVisitor::Visit);

  table_.Register(kVisitSeqOneByteString, &DataObjectVisitor::Visit);

  table_.Register(kVisitSeqTwoByteString, &DataObjectVisitor::Visit);

  table_.Register(kVisitJSWeakMap, &StaticVisitor::VisitWeakCollection);

  table_.Register(kVisitJSWeakSet, &StaticVisitor::VisitWeakCollection);

  table_.Register(kVisitOddball,
                  &FixedBodyVisitor<StaticVisitor,
                  Oddball::BodyDescriptor,
                  void>::Visit);

  table_.Register(kVisitMap, &VisitMap);

  table_.Register(kVisitCode, &VisitCode);

  table_.Register(kVisitSharedFunctionInfo, &VisitSharedFunctionInfo);

  table_.Register(kVisitJSFunction, &VisitJSFunction);

  table_.Register(kVisitJSArrayBuffer, &VisitJSArrayBuffer);

  table_.Register(kVisitJSTypedArray, &VisitJSTypedArray);

  table_.Register(kVisitJSDataView, &VisitJSDataView);

  // Registration for kVisitJSRegExp is done by StaticVisitor.

  table_.Register(kVisitCell,
                  &FixedBodyVisitor<StaticVisitor,
                  Cell::BodyDescriptor,
                  void>::Visit);

  table_.Register(kVisitPropertyCell, &VisitPropertyCell);

  table_.template RegisterSpecializations<DataObjectVisitor,
                                          kVisitDataObject,
                                          kVisitDataObjectGeneric>();

  table_.template RegisterSpecializations<JSObjectVisitor,
                                          kVisitJSObject,
                                          kVisitJSObjectGeneric>();

  table_.template RegisterSpecializations<StructObjectVisitor,
                                          kVisitStruct,
                                          kVisitStructGeneric>();
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitCodeEntry(
    Heap* heap, Address entry_address) {
  Code* code = Code::cast(Code::GetObjectFromEntryAddress(entry_address));
  heap->mark_compact_collector()->RecordCodeEntrySlot(entry_address, code);
  StaticVisitor::MarkObject(heap, code);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitEmbeddedPointer(
    Heap* heap, RelocInfo* rinfo) {
  ASSERT(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
  ASSERT(!rinfo->target_object()->IsConsString());
  HeapObject* object = HeapObject::cast(rinfo->target_object());
  heap->mark_compact_collector()->RecordRelocSlot(rinfo, object);
  // TODO(ulan): It could be better to record slots only for strongly embedded
  // objects here and record slots for weakly embedded object during clearing
  // of non-live references in mark-compact.
  if (!rinfo->host()->IsWeakObject(object)) {
    StaticVisitor::MarkObject(heap, object);
  }
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitCell(
    Heap* heap, RelocInfo* rinfo) {
  ASSERT(rinfo->rmode() == RelocInfo::CELL);
  Cell* cell = rinfo->target_cell();
  // No need to record slots because the cell space is not compacted during GC.
  if (!rinfo->host()->IsWeakObject(cell)) {
    StaticVisitor::MarkObject(heap, cell);
  }
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitDebugTarget(
    Heap* heap, RelocInfo* rinfo) {
  ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) &&
          rinfo->IsPatchedReturnSequence()) ||
         (RelocInfo::IsDebugBreakSlot(rinfo->rmode()) &&
          rinfo->IsPatchedDebugBreakSlotSequence()));
  Code* target = Code::GetCodeFromTargetAddress(rinfo->call_address());
  heap->mark_compact_collector()->RecordRelocSlot(rinfo, target);
  StaticVisitor::MarkObject(heap, target);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitCodeTarget(
    Heap* heap, RelocInfo* rinfo) {
  ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode()));
  Code* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
  // Monomorphic ICs are preserved when possible, but need to be flushed
  // when they might be keeping a Context alive, or when the heap is about
  // to be serialized.
  if (FLAG_cleanup_code_caches_at_gc && target->is_inline_cache_stub()
      && (target->ic_state() == MEGAMORPHIC || target->ic_state() == GENERIC ||
          target->ic_state() == POLYMORPHIC || heap->flush_monomorphic_ics() ||
          Serializer::enabled() || target->ic_age() != heap->global_ic_age() ||
          target->is_invalidated_weak_stub())) {
    IC::Clear(target->GetIsolate(), rinfo->pc(),
              rinfo->host()->constant_pool());
    target = Code::GetCodeFromTargetAddress(rinfo->target_address());
  }
  heap->mark_compact_collector()->RecordRelocSlot(rinfo, target);
  StaticVisitor::MarkObject(heap, target);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitCodeAgeSequence(
    Heap* heap, RelocInfo* rinfo) {
  ASSERT(RelocInfo::IsCodeAgeSequence(rinfo->rmode()));
  Code* target = rinfo->code_age_stub();
  ASSERT(target != NULL);
  heap->mark_compact_collector()->RecordRelocSlot(rinfo, target);
  StaticVisitor::MarkObject(heap, target);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitNativeContext(
    Map* map, HeapObject* object) {
  FixedBodyVisitor<StaticVisitor,
                   Context::MarkCompactBodyDescriptor,
                   void>::Visit(map, object);

  MarkCompactCollector* collector = map->GetHeap()->mark_compact_collector();
  for (int idx = Context::FIRST_WEAK_SLOT;
       idx < Context::NATIVE_CONTEXT_SLOTS;
       ++idx) {
    Object** slot = Context::cast(object)->RawFieldOfElementAt(idx);
    collector->RecordSlot(slot, slot, *slot);
  }
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitMap(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();
  Map* map_object = Map::cast(object);

  // Clears the cache of ICs related to this map.
  if (FLAG_cleanup_code_caches_at_gc) {
    map_object->ClearCodeCache(heap);
  }

  // When map collection is enabled we have to mark through map's transitions
  // and back pointers in a special way to make these links weak.
  if (FLAG_collect_maps && map_object->CanTransition()) {
    MarkMapContents(heap, map_object);
  } else {
    StaticVisitor::VisitPointers(heap,
        HeapObject::RawField(object, Map::kPointerFieldsBeginOffset),
        HeapObject::RawField(object, Map::kPointerFieldsEndOffset));
  }
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitPropertyCell(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();

  Object** slot =
      HeapObject::RawField(object, PropertyCell::kDependentCodeOffset);
  if (FLAG_collect_maps) {
    // Mark property cell dependent codes array but do not push it onto marking
    // stack, this will make references from it weak. We will clean dead
    // codes when we iterate over property cells in ClearNonLiveReferences.
    HeapObject* obj = HeapObject::cast(*slot);
    heap->mark_compact_collector()->RecordSlot(slot, slot, obj);
    StaticVisitor::MarkObjectWithoutPush(heap, obj);
  } else {
    StaticVisitor::VisitPointer(heap, slot);
  }

  StaticVisitor::VisitPointers(heap,
      HeapObject::RawField(object, PropertyCell::kPointerFieldsBeginOffset),
      HeapObject::RawField(object, PropertyCell::kPointerFieldsEndOffset));
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitAllocationSite(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();

  Object** slot =
      HeapObject::RawField(object, AllocationSite::kDependentCodeOffset);
  if (FLAG_collect_maps) {
    // Mark allocation site dependent codes array but do not push it onto
    // marking stack, this will make references from it weak. We will clean
    // dead codes when we iterate over allocation sites in
    // ClearNonLiveReferences.
    HeapObject* obj = HeapObject::cast(*slot);
    heap->mark_compact_collector()->RecordSlot(slot, slot, obj);
    StaticVisitor::MarkObjectWithoutPush(heap, obj);
  } else {
    StaticVisitor::VisitPointer(heap, slot);
  }

  StaticVisitor::VisitPointers(heap,
      HeapObject::RawField(object, AllocationSite::kPointerFieldsBeginOffset),
      HeapObject::RawField(object, AllocationSite::kPointerFieldsEndOffset));
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitCode(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();
  Code* code = Code::cast(object);
  if (FLAG_cleanup_code_caches_at_gc) {
    code->ClearTypeFeedbackInfo(heap);
  }
  if (FLAG_age_code && !Serializer::enabled()) {
    code->MakeOlder(heap->mark_compact_collector()->marking_parity());
  }
  code->CodeIterateBody<StaticVisitor>(heap);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitSharedFunctionInfo(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();
  SharedFunctionInfo* shared = SharedFunctionInfo::cast(object);
  if (shared->ic_age() != heap->global_ic_age()) {
    shared->ResetForNewContext(heap->global_ic_age());
  }
  if (FLAG_cache_optimized_code &&
      FLAG_flush_optimized_code_cache &&
      !shared->optimized_code_map()->IsSmi()) {
    // Always flush the optimized code map if requested by flag.
    shared->ClearOptimizedCodeMap();
  }
  MarkCompactCollector* collector = heap->mark_compact_collector();
  if (collector->is_code_flushing_enabled()) {
    if (FLAG_cache_optimized_code && !shared->optimized_code_map()->IsSmi()) {
      // Add the shared function info holding an optimized code map to
      // the code flusher for processing of code maps after marking.
      collector->code_flusher()->AddOptimizedCodeMap(shared);
      // Treat all references within the code map weakly by marking the
      // code map itself but not pushing it onto the marking deque.
      FixedArray* code_map = FixedArray::cast(shared->optimized_code_map());
      StaticVisitor::MarkObjectWithoutPush(heap, code_map);
    }
    if (IsFlushable(heap, shared)) {
      // This function's code looks flushable. But we have to postpone
      // the decision until we see all functions that point to the same
      // SharedFunctionInfo because some of them might be optimized.
      // That would also make the non-optimized version of the code
      // non-flushable, because it is required for bailing out from
      // optimized code.
      collector->code_flusher()->AddCandidate(shared);
      // Treat the reference to the code object weakly.
      VisitSharedFunctionInfoWeakCode(heap, object);
      return;
    }
  } else {
    if (FLAG_cache_optimized_code && !shared->optimized_code_map()->IsSmi()) {
      // Flush optimized code map on major GCs without code flushing,
      // needed because cached code doesn't contain breakpoints.
      shared->ClearOptimizedCodeMap();
    }
  }
  VisitSharedFunctionInfoStrongCode(heap, object);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitConstantPoolArray(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();
  ConstantPoolArray* constant_pool = ConstantPoolArray::cast(object);
  for (int i = 0; i < constant_pool->count_of_code_ptr_entries(); i++) {
    int index = constant_pool->first_code_ptr_index() + i;
    Address code_entry =
        reinterpret_cast<Address>(constant_pool->RawFieldOfElementAt(index));
    StaticVisitor::VisitCodeEntry(heap, code_entry);
  }
  for (int i = 0; i < constant_pool->count_of_heap_ptr_entries(); i++) {
    int index = constant_pool->first_heap_ptr_index() + i;
    Object** slot = constant_pool->RawFieldOfElementAt(index);
    HeapObject* object = HeapObject::cast(*slot);
    heap->mark_compact_collector()->RecordSlot(slot, slot, object);
    bool is_weak_object =
        (constant_pool->get_weak_object_state() ==
              ConstantPoolArray::WEAK_OBJECTS_IN_OPTIMIZED_CODE &&
         Code::IsWeakObjectInOptimizedCode(object)) ||
        (constant_pool->get_weak_object_state() ==
              ConstantPoolArray::WEAK_OBJECTS_IN_IC &&
         Code::IsWeakObjectInIC(object));
    if (!is_weak_object) {
      StaticVisitor::MarkObject(heap, object);
    }
  }
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitJSFunction(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();
  JSFunction* function = JSFunction::cast(object);
  MarkCompactCollector* collector = heap->mark_compact_collector();
  if (collector->is_code_flushing_enabled()) {
    if (IsFlushable(heap, function)) {
      // This function's code looks flushable. But we have to postpone
      // the decision until we see all functions that point to the same
      // SharedFunctionInfo because some of them might be optimized.
      // That would also make the non-optimized version of the code
      // non-flushable, because it is required for bailing out from
      // optimized code.
      collector->code_flusher()->AddCandidate(function);
      // Visit shared function info immediately to avoid double checking
      // of its flushability later. This is just an optimization because
      // the shared function info would eventually be visited.
      SharedFunctionInfo* shared = function->shared();
      if (StaticVisitor::MarkObjectWithoutPush(heap, shared)) {
        StaticVisitor::MarkObject(heap, shared->map());
        VisitSharedFunctionInfoWeakCode(heap, shared);
      }
      // Treat the reference to the code object weakly.
      VisitJSFunctionWeakCode(heap, object);
      return;
    } else {
      // Visit all unoptimized code objects to prevent flushing them.
      StaticVisitor::MarkObject(heap, function->shared()->code());
      if (function->code()->kind() == Code::OPTIMIZED_FUNCTION) {
        MarkInlinedFunctionsCode(heap, function->code());
      }
    }
  }
  VisitJSFunctionStrongCode(heap, object);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitJSRegExp(
    Map* map, HeapObject* object) {
  int last_property_offset =
      JSRegExp::kSize + kPointerSize * map->inobject_properties();
  StaticVisitor::VisitPointers(map->GetHeap(),
      HeapObject::RawField(object, JSRegExp::kPropertiesOffset),
      HeapObject::RawField(object, last_property_offset));
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitJSArrayBuffer(
    Map* map, HeapObject* object) {
  Heap* heap = map->GetHeap();

  STATIC_ASSERT(
      JSArrayBuffer::kWeakFirstViewOffset ==
      JSArrayBuffer::kWeakNextOffset + kPointerSize);
  StaticVisitor::VisitPointers(
      heap,
      HeapObject::RawField(object, JSArrayBuffer::BodyDescriptor::kStartOffset),
      HeapObject::RawField(object, JSArrayBuffer::kWeakNextOffset));
  StaticVisitor::VisitPointers(
      heap,
      HeapObject::RawField(object,
          JSArrayBuffer::kWeakNextOffset + 2 * kPointerSize),
      HeapObject::RawField(object, JSArrayBuffer::kSizeWithInternalFields));
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitJSTypedArray(
    Map* map, HeapObject* object) {
  StaticVisitor::VisitPointers(
      map->GetHeap(),
      HeapObject::RawField(object, JSTypedArray::BodyDescriptor::kStartOffset),
      HeapObject::RawField(object, JSTypedArray::kWeakNextOffset));
  StaticVisitor::VisitPointers(
      map->GetHeap(),
      HeapObject::RawField(object,
        JSTypedArray::kWeakNextOffset + kPointerSize),
      HeapObject::RawField(object, JSTypedArray::kSizeWithInternalFields));
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitJSDataView(
    Map* map, HeapObject* object) {
  StaticVisitor::VisitPointers(
      map->GetHeap(),
      HeapObject::RawField(object, JSDataView::BodyDescriptor::kStartOffset),
      HeapObject::RawField(object, JSDataView::kWeakNextOffset));
  StaticVisitor::VisitPointers(
      map->GetHeap(),
      HeapObject::RawField(object,
        JSDataView::kWeakNextOffset + kPointerSize),
      HeapObject::RawField(object, JSDataView::kSizeWithInternalFields));
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::MarkMapContents(
    Heap* heap, Map* map) {
  // Make sure that the back pointer stored either in the map itself or
  // inside its transitions array is marked. Skip recording the back
  // pointer slot since map space is not compacted.
  StaticVisitor::MarkObject(heap, HeapObject::cast(map->GetBackPointer()));

  // Treat pointers in the transitions array as weak and also mark that
  // array to prevent visiting it later. Skip recording the transition
  // array slot, since it will be implicitly recorded when the pointer
  // fields of this map are visited.
  if (map->HasTransitionArray()) {
    TransitionArray* transitions = map->transitions();
    MarkTransitionArray(heap, transitions);
  }

  // Since descriptor arrays are potentially shared, ensure that only the
  // descriptors that belong to this map are marked. The first time a
  // non-empty descriptor array is marked, its header is also visited. The slot
  // holding the descriptor array will be implicitly recorded when the pointer
  // fields of this map are visited.
  DescriptorArray* descriptors = map->instance_descriptors();
  if (StaticVisitor::MarkObjectWithoutPush(heap, descriptors) &&
      descriptors->length() > 0) {
    StaticVisitor::VisitPointers(heap,
        descriptors->GetFirstElementAddress(),
        descriptors->GetDescriptorEndSlot(0));
  }
  int start = 0;
  int end = map->NumberOfOwnDescriptors();
  if (start < end) {
    StaticVisitor::VisitPointers(heap,
        descriptors->GetDescriptorStartSlot(start),
        descriptors->GetDescriptorEndSlot(end));
  }

  // Mark prototype dependent codes array but do not push it onto marking
  // stack, this will make references from it weak. We will clean dead
  // codes when we iterate over maps in ClearNonLiveTransitions.
  Object** slot = HeapObject::RawField(map, Map::kDependentCodeOffset);
  HeapObject* obj = HeapObject::cast(*slot);
  heap->mark_compact_collector()->RecordSlot(slot, slot, obj);
  StaticVisitor::MarkObjectWithoutPush(heap, obj);

  // Mark the pointer fields of the Map. Since the transitions array has
  // been marked already, it is fine that one of these fields contains a
  // pointer to it.
  StaticVisitor::VisitPointers(heap,
      HeapObject::RawField(map, Map::kPointerFieldsBeginOffset),
      HeapObject::RawField(map, Map::kPointerFieldsEndOffset));
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::MarkTransitionArray(
    Heap* heap, TransitionArray* transitions) {
  if (!StaticVisitor::MarkObjectWithoutPush(heap, transitions)) return;

  // Simple transitions do not have keys nor prototype transitions.
  if (transitions->IsSimpleTransition()) return;

  if (transitions->HasPrototypeTransitions()) {
    // Mark prototype transitions array but do not push it onto marking
    // stack, this will make references from it weak. We will clean dead
    // prototype transitions in ClearNonLiveTransitions.
    Object** slot = transitions->GetPrototypeTransitionsSlot();
    HeapObject* obj = HeapObject::cast(*slot);
    heap->mark_compact_collector()->RecordSlot(slot, slot, obj);
    StaticVisitor::MarkObjectWithoutPush(heap, obj);
  }

  for (int i = 0; i < transitions->number_of_transitions(); ++i) {
    StaticVisitor::VisitPointer(heap, transitions->GetKeySlot(i));
  }
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::MarkInlinedFunctionsCode(
    Heap* heap, Code* code) {
  // For optimized functions we should retain both non-optimized version
  // of its code and non-optimized version of all inlined functions.
  // This is required to support bailing out from inlined code.
  DeoptimizationInputData* data =
      DeoptimizationInputData::cast(code->deoptimization_data());
  FixedArray* literals = data->LiteralArray();
  for (int i = 0, count = data->InlinedFunctionCount()->value();
       i < count;
       i++) {
    JSFunction* inlined = JSFunction::cast(literals->get(i));
    StaticVisitor::MarkObject(heap, inlined->shared()->code());
  }
}


inline static bool IsValidNonBuiltinContext(Object* context) {
  return context->IsContext() &&
      !Context::cast(context)->global_object()->IsJSBuiltinsObject();
}


inline static bool HasSourceCode(Heap* heap, SharedFunctionInfo* info) {
  Object* undefined = heap->undefined_value();
  return (info->script() != undefined) &&
      (reinterpret_cast<Script*>(info->script())->source() != undefined);
}


template<typename StaticVisitor>
bool StaticMarkingVisitor<StaticVisitor>::IsFlushable(
    Heap* heap, JSFunction* function) {
  SharedFunctionInfo* shared_info = function->shared();

  // Code is either on stack, in compilation cache or referenced
  // by optimized version of function.
  MarkBit code_mark = Marking::MarkBitFrom(function->code());
  if (code_mark.Get()) {
    return false;
  }

  // The function must have a valid context and not be a builtin.
  if (!IsValidNonBuiltinContext(function->context())) {
    return false;
  }

  // We do not (yet) flush code for optimized functions.
  if (function->code() != shared_info->code()) {
    return false;
  }

  // Check age of optimized code.
  if (FLAG_age_code && !function->code()->IsOld()) {
    return false;
  }

  return IsFlushable(heap, shared_info);
}


template<typename StaticVisitor>
bool StaticMarkingVisitor<StaticVisitor>::IsFlushable(
    Heap* heap, SharedFunctionInfo* shared_info) {
  // Code is either on stack, in compilation cache or referenced
  // by optimized version of function.
  MarkBit code_mark = Marking::MarkBitFrom(shared_info->code());
  if (code_mark.Get()) {
    return false;
  }

  // The function must be compiled and have the source code available,
  // to be able to recompile it in case we need the function again.
  if (!(shared_info->is_compiled() && HasSourceCode(heap, shared_info))) {
    return false;
  }

  // We never flush code for API functions.
  Object* function_data = shared_info->function_data();
  if (function_data->IsFunctionTemplateInfo()) {
    return false;
  }

  // Only flush code for functions.
  if (shared_info->code()->kind() != Code::FUNCTION) {
    return false;
  }

  // Function must be lazy compilable.
  if (!shared_info->allows_lazy_compilation()) {
    return false;
  }

  // We do not (yet?) flush code for generator functions, because we don't know
  // if there are still live activations (generator objects) on the heap.
  if (shared_info->is_generator()) {
    return false;
  }

  // If this is a full script wrapped in a function we do not flush the code.
  if (shared_info->is_toplevel()) {
    return false;
  }

  // If this is a function initialized with %SetCode then the one-to-one
  // relation between SharedFunctionInfo and Code is broken.
  if (shared_info->dont_flush()) {
    return false;
  }

  // Check age of code. If code aging is disabled we never flush.
  if (!FLAG_age_code || !shared_info->code()->IsOld()) {
    return false;
  }

  return true;
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitSharedFunctionInfoStrongCode(
    Heap* heap, HeapObject* object) {
  StaticVisitor::BeforeVisitingSharedFunctionInfo(object);
  Object** start_slot =
      HeapObject::RawField(object,
                           SharedFunctionInfo::BodyDescriptor::kStartOffset);
  Object** end_slot =
      HeapObject::RawField(object,
                           SharedFunctionInfo::BodyDescriptor::kEndOffset);
  StaticVisitor::VisitPointers(heap, start_slot, end_slot);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitSharedFunctionInfoWeakCode(
    Heap* heap, HeapObject* object) {
  StaticVisitor::BeforeVisitingSharedFunctionInfo(object);
  Object** name_slot =
      HeapObject::RawField(object, SharedFunctionInfo::kNameOffset);
  StaticVisitor::VisitPointer(heap, name_slot);

  // Skip visiting kCodeOffset as it is treated weakly here.
  STATIC_ASSERT(SharedFunctionInfo::kNameOffset + kPointerSize ==
      SharedFunctionInfo::kCodeOffset);
  STATIC_ASSERT(SharedFunctionInfo::kCodeOffset + kPointerSize ==
      SharedFunctionInfo::kOptimizedCodeMapOffset);

  Object** start_slot =
      HeapObject::RawField(object,
                           SharedFunctionInfo::kOptimizedCodeMapOffset);
  Object** end_slot =
      HeapObject::RawField(object,
                           SharedFunctionInfo::BodyDescriptor::kEndOffset);
  StaticVisitor::VisitPointers(heap, start_slot, end_slot);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitJSFunctionStrongCode(
    Heap* heap, HeapObject* object) {
  Object** start_slot =
      HeapObject::RawField(object, JSFunction::kPropertiesOffset);
  Object** end_slot =
      HeapObject::RawField(object, JSFunction::kCodeEntryOffset);
  StaticVisitor::VisitPointers(heap, start_slot, end_slot);

  VisitCodeEntry(heap, object->address() + JSFunction::kCodeEntryOffset);
  STATIC_ASSERT(JSFunction::kCodeEntryOffset + kPointerSize ==
      JSFunction::kPrototypeOrInitialMapOffset);

  start_slot =
      HeapObject::RawField(object, JSFunction::kPrototypeOrInitialMapOffset);
  end_slot =
      HeapObject::RawField(object, JSFunction::kNonWeakFieldsEndOffset);
  StaticVisitor::VisitPointers(heap, start_slot, end_slot);
}


template<typename StaticVisitor>
void StaticMarkingVisitor<StaticVisitor>::VisitJSFunctionWeakCode(
    Heap* heap, HeapObject* object) {
  Object** start_slot =
      HeapObject::RawField(object, JSFunction::kPropertiesOffset);
  Object** end_slot =
      HeapObject::RawField(object, JSFunction::kCodeEntryOffset);
  StaticVisitor::VisitPointers(heap, start_slot, end_slot);

  // Skip visiting kCodeEntryOffset as it is treated weakly here.
  STATIC_ASSERT(JSFunction::kCodeEntryOffset + kPointerSize ==
      JSFunction::kPrototypeOrInitialMapOffset);

  start_slot =
      HeapObject::RawField(object, JSFunction::kPrototypeOrInitialMapOffset);
  end_slot =
      HeapObject::RawField(object, JSFunction::kNonWeakFieldsEndOffset);
  StaticVisitor::VisitPointers(heap, start_slot, end_slot);
}


void Code::CodeIterateBody(ObjectVisitor* v) {
  int mode_mask = RelocInfo::kCodeTargetMask |
                  RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT) |
                  RelocInfo::ModeMask(RelocInfo::CELL) |
                  RelocInfo::ModeMask(RelocInfo::EXTERNAL_REFERENCE) |
                  RelocInfo::ModeMask(RelocInfo::JS_RETURN) |
                  RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT) |
                  RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY);

  // There are two places where we iterate code bodies: here and the
  // templated CodeIterateBody (below). They should be kept in sync.
  IteratePointer(v, kRelocationInfoOffset);
  IteratePointer(v, kHandlerTableOffset);
  IteratePointer(v, kDeoptimizationDataOffset);
  IteratePointer(v, kTypeFeedbackInfoOffset);
  IterateNextCodeLink(v, kNextCodeLinkOffset);
  IteratePointer(v, kConstantPoolOffset);

  RelocIterator it(this, mode_mask);
  Isolate* isolate = this->GetIsolate();
  for (; !it.done(); it.next()) {
    it.rinfo()->Visit(isolate, v);
  }
}


template<typename StaticVisitor>
void Code::CodeIterateBody(Heap* heap) {
  int mode_mask = RelocInfo::kCodeTargetMask |
                  RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT) |
                  RelocInfo::ModeMask(RelocInfo::CELL) |
                  RelocInfo::ModeMask(RelocInfo::EXTERNAL_REFERENCE) |
                  RelocInfo::ModeMask(RelocInfo::JS_RETURN) |
                  RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT) |
                  RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY);

  // There are two places where we iterate code bodies: here and the non-
  // templated CodeIterateBody (above). They should be kept in sync.
  StaticVisitor::VisitPointer(
      heap,
      reinterpret_cast<Object**>(this->address() + kRelocationInfoOffset));
  StaticVisitor::VisitPointer(
      heap,
      reinterpret_cast<Object**>(this->address() + kHandlerTableOffset));
  StaticVisitor::VisitPointer(
      heap,
      reinterpret_cast<Object**>(this->address() + kDeoptimizationDataOffset));
  StaticVisitor::VisitPointer(
      heap,
      reinterpret_cast<Object**>(this->address() + kTypeFeedbackInfoOffset));
  StaticVisitor::VisitNextCodeLink(
      heap,
      reinterpret_cast<Object**>(this->address() + kNextCodeLinkOffset));
  StaticVisitor::VisitPointer(
      heap,
      reinterpret_cast<Object**>(this->address() + kConstantPoolOffset));


  RelocIterator it(this, mode_mask);
  for (; !it.done(); it.next()) {
    it.rinfo()->template Visit<StaticVisitor>(heap);
  }
}


} }  // namespace v8::internal

#endif  // V8_OBJECTS_VISITING_INL_H_