Implement map collection for incremental marking.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 0aa119219adfaad70c22460973ca125b3aa21086..c455564b41a736d268db2e81a9259fec07b261bd 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -64,13 +64,13 @@ MarkCompactCollector::MarkCompactCollector() :  // NOLINT
       abort_incremental_marking_(false),
       compacting_(false),
       was_marked_incrementally_(false),
-      collect_maps_(FLAG_collect_maps),
       flush_monomorphic_ics_(false),
       tracer_(NULL),
       migration_slots_buffer_(NULL),
       heap_(NULL),
       code_flusher_(NULL),
-      encountered_weak_maps_(NULL) { }
+      encountered_weak_maps_(NULL),
+      marker_(this, this) { }
 
 
 #ifdef DEBUG
@@ -282,7 +282,7 @@ void MarkCompactCollector::CollectGarbage() {
   MarkLiveObjects();
   ASSERT(heap_->incremental_marking()->IsStopped());
 
-  if (collect_maps_) ClearNonLiveTransitions();
+  if (FLAG_collect_maps) ClearNonLiveTransitions();
 
   ClearWeakMaps();
 
@@ -294,7 +294,7 @@ void MarkCompactCollector::CollectGarbage() {
 
   SweepSpaces();
 
-  if (!collect_maps_) ReattachInitialMaps();
+  if (!FLAG_collect_maps) ReattachInitialMaps();
 
   Finish();
 
@@ -658,11 +658,6 @@ void MarkCompactCollector::AbortCompaction() {
 void MarkCompactCollector::Prepare(GCTracer* tracer) {
   was_marked_incrementally_ = heap()->incremental_marking()->IsMarking();
 
-  // Disable collection of maps if incremental marking is enabled.
-  // Map collection algorithm relies on a special map transition tree traversal
-  // order which is not implemented for incremental marking.
-  collect_maps_ = FLAG_collect_maps && !was_marked_incrementally_;
-
   // 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.
@@ -1798,11 +1793,11 @@ void MarkCompactCollector::ProcessNewlyMarkedObject(HeapObject* object) {
     heap_->ClearCacheOnMap(map);
 
     // When map collection is enabled we have to mark through map's transitions
-    // in a special way to make transition links weak.
-    // Only maps for subclasses of JSReceiver can have transitions.
+    // in a special way to make transition links weak. Only maps for subclasses
+    // of JSReceiver can have transitions.
     STATIC_ASSERT(LAST_TYPE == LAST_JS_RECEIVER_TYPE);
-    if (collect_maps_ && map->instance_type() >= FIRST_JS_RECEIVER_TYPE) {
-      MarkMapContents(map);
+    if (FLAG_collect_maps && map->instance_type() >= FIRST_JS_RECEIVER_TYPE) {
+      marker_.MarkMapContents(map);
     } else {
       marking_deque_.PushBlack(map);
     }
@@ -1812,85 +1807,86 @@ void MarkCompactCollector::ProcessNewlyMarkedObject(HeapObject* object) {
 }
 
 
-void MarkCompactCollector::MarkMapContents(Map* map) {
+// Force instantiation of template instances.
+template void Marker<IncrementalMarking>::MarkMapContents(Map* map);
+template void Marker<MarkCompactCollector>::MarkMapContents(Map* map);
+
+
+template <class T>
+void Marker<T>::MarkMapContents(Map* map) {
   // Mark prototype transitions array but don't push it into marking stack.
   // This will make references from it weak. We will clean dead prototype
-  // transitions in ClearNonLiveTransitions. But make sure that back pointers
-  // stored inside prototype transitions arrays are marked.
-  Object* raw_proto_transitions = map->unchecked_prototype_transitions();
-  if (raw_proto_transitions->IsFixedArray()) {
-    FixedArray* prototype_transitions = FixedArray::cast(raw_proto_transitions);
+  // transitions in ClearNonLiveTransitions.
+  Object** proto_trans_slot =
+      HeapObject::RawField(map, Map::kPrototypeTransitionsOrBackPointerOffset);
+  HeapObject* prototype_transitions = HeapObject::cast(*proto_trans_slot);
+  if (prototype_transitions->IsFixedArray()) {
+    mark_compact_collector()->RecordSlot(proto_trans_slot,
+                                         proto_trans_slot,
+                                         prototype_transitions);
     MarkBit mark = Marking::MarkBitFrom(prototype_transitions);
     if (!mark.Get()) {
       mark.Set();
       MemoryChunk::IncrementLiveBytesFromGC(prototype_transitions->address(),
                                             prototype_transitions->Size());
-      MarkObjectAndPush(HeapObject::cast(
-          prototype_transitions->get(Map::kProtoTransitionBackPointerOffset)));
     }
   }
 
-  Object** raw_descriptor_array_slot =
+  // Make sure that the back pointer stored either in the map itself or inside
+  // its prototype transitions array is marked. Treat pointers in the descriptor
+  // array as weak and also mark that array to prevent visiting it later.
+  base_marker()->MarkObjectAndPush(HeapObject::cast(map->GetBackPointer()));
+
+  Object** descriptor_array_slot =
       HeapObject::RawField(map, Map::kInstanceDescriptorsOrBitField3Offset);
-  Object* raw_descriptor_array = *raw_descriptor_array_slot;
-  if (!raw_descriptor_array->IsSmi()) {
-    MarkDescriptorArray(
-        reinterpret_cast<DescriptorArray*>(raw_descriptor_array));
+  Object* descriptor_array = *descriptor_array_slot;
+  if (!descriptor_array->IsSmi()) {
+    MarkDescriptorArray(reinterpret_cast<DescriptorArray*>(descriptor_array));
+  }
+
+  // Mark the Object* fields of the Map. Since the descriptor array has been
+  // marked already, it is fine that one of these fields contains a pointer
+  // to it. But make sure to skip back pointer and prototype transitions.
+  STATIC_ASSERT(Map::kPointerFieldsEndOffset ==
+      Map::kPrototypeTransitionsOrBackPointerOffset + kPointerSize);
+  Object** start_slot = HeapObject::RawField(
+      map, Map::kPointerFieldsBeginOffset);
+  Object** end_slot = HeapObject::RawField(
+      map, Map::kPrototypeTransitionsOrBackPointerOffset);
+  for (Object** slot = start_slot; slot < end_slot; slot++) {
+    Object* obj = *slot;
+    if (!obj->NonFailureIsHeapObject()) continue;
+    mark_compact_collector()->RecordSlot(start_slot, slot, obj);
+    base_marker()->MarkObjectAndPush(reinterpret_cast<HeapObject*>(obj));
   }
-
-  // Mark the Object* fields of the Map.
-  // Since the descriptor array has been marked already, it is fine
-  // that one of these fields contains a pointer to it.
-  Object** start_slot = HeapObject::RawField(map,
-                                             Map::kPointerFieldsBeginOffset);
-
-  Object** end_slot = HeapObject::RawField(map, Map::kPointerFieldsEndOffset);
-
-  StaticMarkingVisitor::VisitPointers(map->GetHeap(), start_slot, end_slot);
 }
 
 
-void MarkCompactCollector::MarkAccessorPairSlot(HeapObject* accessors,
-                                                int offset) {
-  Object** slot = HeapObject::RawField(accessors, offset);
-  HeapObject* accessor = HeapObject::cast(*slot);
-  if (accessor->IsMap()) return;
-  RecordSlot(slot, slot, accessor);
-  MarkObjectAndPush(accessor);
-}
-
-
-void MarkCompactCollector::MarkDescriptorArray(
-    DescriptorArray* descriptors) {
-  MarkBit descriptors_mark = Marking::MarkBitFrom(descriptors);
-  if (descriptors_mark.Get()) return;
+template <class T>
+void Marker<T>::MarkDescriptorArray(DescriptorArray* descriptors) {
   // Empty descriptor array is marked as a root before any maps are marked.
-  ASSERT(descriptors != heap()->empty_descriptor_array());
-  SetMark(descriptors, descriptors_mark);
+  ASSERT(descriptors != descriptors->GetHeap()->empty_descriptor_array());
 
-  FixedArray* contents = reinterpret_cast<FixedArray*>(
+  // The DescriptorArray contains a pointer to its contents array, but the
+  // contents array will be marked black and hence not be visited again.
+  if (!base_marker()->MarkObjectAndPush(descriptors)) return;
+  FixedArray* contents = FixedArray::cast(
       descriptors->get(DescriptorArray::kContentArrayIndex));
-  ASSERT(contents->IsHeapObject());
-  ASSERT(!IsMarked(contents));
-  ASSERT(contents->IsFixedArray());
   ASSERT(contents->length() >= 2);
-  MarkBit contents_mark = Marking::MarkBitFrom(contents);
-  SetMark(contents, contents_mark);
-  // Contents contains (value, details) pairs.  If the details say that the type
-  // of descriptor is MAP_TRANSITION, CONSTANT_TRANSITION,
-  // EXTERNAL_ARRAY_TRANSITION or NULL_DESCRIPTOR, we don't mark the value as
-  // live.  Only for MAP_TRANSITION, EXTERNAL_ARRAY_TRANSITION and
-  // CONSTANT_TRANSITION is the value an Object* (a Map*).
+  ASSERT(Marking::IsWhite(Marking::MarkBitFrom(contents)));
+  base_marker()->MarkObjectWithoutPush(contents);
+
+  // Contents contains (value, details) pairs.  If the descriptor contains a
+  // transition (value is a Map), we don't mark the value as live.  It might
+  // be set to the NULL_DESCRIPTOR in ClearNonLiveTransitions later.
   for (int i = 0; i < contents->length(); i += 2) {
-    // If the pair (value, details) at index i, i+1 is not
-    // a transition or null descriptor, mark the value.
     PropertyDetails details(Smi::cast(contents->get(i + 1)));
 
     Object** slot = contents->data_start() + i;
     if (!(*slot)->IsHeapObject()) continue;
     HeapObject* value = HeapObject::cast(*slot);
 
-    RecordSlot(slot, slot, *slot);
+    mark_compact_collector()->RecordSlot(slot, slot, *slot);
 
     switch (details.type()) {
       case NORMAL:
@@ -1898,21 +1894,22 @@ void MarkCompactCollector::MarkDescriptorArray(
       case CONSTANT_FUNCTION:
       case HANDLER:
       case INTERCEPTOR:
-        MarkObjectAndPush(value);
+        base_marker()->MarkObjectAndPush(value);
         break;
       case CALLBACKS:
         if (!value->IsAccessorPair()) {
-          MarkObjectAndPush(value);
-        } else if (!MarkObjectWithoutPush(value)) {
-          MarkAccessorPairSlot(value, AccessorPair::kGetterOffset);
-          MarkAccessorPairSlot(value, AccessorPair::kSetterOffset);
+          base_marker()->MarkObjectAndPush(value);
+        } else if (base_marker()->MarkObjectWithoutPush(value)) {
+          AccessorPair* accessors = AccessorPair::cast(value);
+          MarkAccessorPairSlot(accessors, AccessorPair::kGetterOffset);
+          MarkAccessorPairSlot(accessors, AccessorPair::kSetterOffset);
         }
         break;
       case ELEMENTS_TRANSITION:
         // For maps with multiple elements transitions, the transition maps are
         // stored in a FixedArray. Keep the fixed array alive but not the maps
         // that it refers to.
-        if (value->IsFixedArray()) MarkObjectWithoutPush(value);
+        if (value->IsFixedArray()) base_marker()->MarkObjectWithoutPush(value);
         break;
       case MAP_TRANSITION:
       case CONSTANT_TRANSITION:
@@ -1920,9 +1917,16 @@ void MarkCompactCollector::MarkDescriptorArray(
         break;
     }
   }
-  // The DescriptorArray descriptors contains a pointer to its contents array,
-  // but the contents array is already marked.
-  marking_deque_.PushBlack(descriptors);
+}
+
+
+template <class T>
+void Marker<T>::MarkAccessorPairSlot(AccessorPair* accessors, int offset) {
+  Object** slot = HeapObject::RawField(accessors, offset);
+  HeapObject* accessor = HeapObject::cast(*slot);
+  if (accessor->IsMap()) return;
+  mark_compact_collector()->RecordSlot(slot, slot, accessor);
+  base_marker()->MarkObjectAndPush(accessor);
 }