Implement map collection for incremental marking.

src/incremental-marking.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 639 matching lines @@
     // TODO(gc) hurry can mark objects it encounters black as mutator
     // was stopped.
     Map* filler_map = heap_->one_pointer_filler_map();
     Map* global_context_map = heap_->global_context_map();
     IncrementalMarkingMarkingVisitor marking_visitor(heap_, this);
     while (!marking_deque_.IsEmpty()) {
       HeapObject* obj = marking_deque_.Pop();
 
       // Explicitly skip one word fillers. Incremental markbit patterns are
       // correct only for objects that occupy at least two words.
       Map* map = obj->map();

[Vyacheslav Egorov (Chromium), 2012/05/11 12:58:35]

Hurry should also treat maps in a special way.

[Michael Starzinger, 2012/05/11 14:51:53]

Done.

       if (map == filler_map) {
         continue;
       } else if (map == global_context_map) {
         // Global contexts have weak fields.
         VisitGlobalContext(Context::cast(obj), &marking_visitor);
       } else {
         obj->Iterate(&marking_visitor);
       }
 
       MarkBit mark_bit = Marking::MarkBitFrom(obj);
@@ skipping 129 matching lines @@
     Map* global_context_map = heap_->global_context_map();
     IncrementalMarkingMarkingVisitor marking_visitor(heap_, this);
     while (!marking_deque_.IsEmpty() && bytes_to_process > 0) {
       HeapObject* obj = marking_deque_.Pop();
 
       // Explicitly skip one word fillers. Incremental markbit patterns are
       // correct only for objects that occupy at least two words.
       Map* map = obj->map();
       if (map == filler_map) continue;
 
-      if (obj->IsMap()) {
-        Map* map = Map::cast(obj);
-        heap_->ClearCacheOnMap(map);
-      }
-
-
       int size = obj->SizeFromMap(map);
       bytes_to_process -= size;
       MarkBit map_mark_bit = Marking::MarkBitFrom(map);
       if (Marking::IsWhite(map_mark_bit)) {
         WhiteToGreyAndPush(map, map_mark_bit);
       }
 
       // TODO(gc) switch to static visitor instead of normal visitor.
       if (map == global_context_map) {
         // Global contexts have weak fields.
         Context* ctx = Context::cast(obj);
 
         // We will mark cache black with a separate pass
         // when we finish marking.
         MarkObjectGreyDoNotEnqueue(ctx->normalized_map_cache());
 
         VisitGlobalContext(ctx, &marking_visitor);
+      } else if (map->instance_type() == JS_MAP_TYPE) {

[Vyacheslav Egorov (Chromium), 2012/05/11 12:58:35]

s/JS_MAP_TYPE/MAP_TYPE/

[Michael Starzinger, 2012/05/11 14:51:53]

Already fixed in second patch set.

+        Map* map = Map::cast(obj);
+        heap_->ClearCacheOnMap(map);
+
+        // 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.  Only maps for subclasses of JSReceiver can have transitions.
+        STATIC_ASSERT(LAST_TYPE == LAST_JS_RECEIVER_TYPE);
+        if (FLAG_collect_maps && map->instance_type() >= FIRST_JS_RECEIVER_TYPE) {
+          heap_->mark_compact_collector()->MarkWeakMapContents(map);
+
+          // 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);
+          marking_visitor.VisitPointers(
+              HeapObject::RawField(map, Map::kPointerFieldsBeginOffset),
+              HeapObject::RawField(
+                  map, Map::kPrototypeTransitionsOrBackPointerOffset));
+        } else {
+          marking_visitor.VisitPointers(
+              HeapObject::RawField(map, Map::kPointerFieldsBeginOffset),
+              HeapObject::RawField(map, Map::kPointerFieldsEndOffset));
+        }
       } else if (map->instance_type() == JS_FUNCTION_TYPE) {
         marking_visitor.VisitPointers(
             HeapObject::RawField(obj, JSFunction::kPropertiesOffset),
             HeapObject::RawField(obj, JSFunction::kCodeEntryOffset));
 
         marking_visitor.VisitCodeEntry(
             obj->address() + JSFunction::kCodeEntryOffset);
 
         marking_visitor.VisitPointers(
             HeapObject::RawField(obj,
@@ skipping 105 matching lines @@
   allocation_marking_factor_ = kInitialAllocationMarkingFactor;
   bytes_scanned_ = 0;
 }
 
 
 int64_t IncrementalMarking::SpaceLeftInOldSpace() {
   return heap_->MaxOldGenerationSize() - heap_->PromotedSpaceSizeOfObjects();
 }
 
 } }  // namespace v8::internal