[heap] Process live weak cells directly in the marking visitor.

src/heap/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_
 
 #include "src/heap/array-buffer-tracker.h"
 #include "src/heap/objects-visiting.h"
 #include "src/ic/ic-state.h"
@@ skipping 336 matching lines @@
 
 template <typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitWeakCell(Map* map,
                                                         HeapObject* object) {
   Heap* heap = map->GetHeap();
   WeakCell* weak_cell = reinterpret_cast<WeakCell*>(object);
   // Enqueue weak cell in linked list of encountered weak collections.
   // We can ignore weak cells with cleared values because they will always
   // contain smi zero.
   if (weak_cell->next_cleared() && !weak_cell->cleared()) {
-    weak_cell->set_next(heap->encountered_weak_cells(),
-                        UPDATE_WEAK_WRITE_BARRIER);
-    heap->set_encountered_weak_cells(weak_cell);
+    HeapObject* value = HeapObject::cast(weak_cell->value());
+    if (MarkCompactCollector::IsMarked(value)) {

[ulan, 2015/09/22 11:30:46]

Please add a comment explaining that this is done for performance and the
general case is processed in the "else" branch.

[Hannes Payer (out of office), 2015/09/22 13:22:57]

Done.

+      Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
+      map->GetHeap()->mark_compact_collector()->RecordSlot(weak_cell, slot,
+                                                           *slot);
+    } else {
+      weak_cell->set_next(heap->encountered_weak_cells(),
+                          UPDATE_WEAK_WRITE_BARRIER);
+      heap->set_encountered_weak_cells(weak_cell);
+    }
   }
 }
 
 
 template <typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitAllocationSite(
     Map* map, HeapObject* object) {
   Heap* heap = map->GetHeap();
 
   StaticVisitor::VisitPointers(
@@ skipping 517 matching lines @@
 
   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_