Reland of [heap] Remove live weak cells from weak cell list when finalizing incremental marking.

src/heap/incremental-marking.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/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/conversions.h"
 #include "src/heap/gc-idle-time-handler.h"
@@ skipping 629 matching lines @@
 
   IncrementalMarkingRootMarkingVisitor visitor(this);
   heap_->mark_compact_collector()->MarkImplicitRefGroups(&MarkObject);
   heap_->isolate()->global_handles()->IterateObjectGroups(
       &visitor, &MarkCompactCollector::IsUnmarkedHeapObjectWithHeap);
   heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
   heap_->isolate()->global_handles()->RemoveObjectGroups();
 }
 
 
+void IncrementalMarking::ProcessWeakCells() {
+  DCHECK(FLAG_finalize_marking_incrementally);
+  DCHECK(!finalize_marking_completed_);
+  DCHECK(IsMarking());
+
+  Object* weak_cell_obj = heap()->encountered_weak_cells();
+  Object* weak_cell_head = Smi::FromInt(0);
+  WeakCell* prev_weak_cell_obj = NULL;
+  while (weak_cell_obj != Smi::FromInt(0)) {
+    WeakCell* weak_cell = reinterpret_cast<WeakCell*>(weak_cell_obj);
+    // We do not insert cleared weak cells into the list, so the value
+    // cannot be a Smi here.
+    HeapObject* value = HeapObject::cast(weak_cell->value());
+    // Remove weak cells with live objects from the list, they do not need
+    // clearing.
+    if (MarkCompactCollector::IsMarked(value)) {
+      // Record slot, if value is pointing to an evacuation candidate.
+      Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
+      heap_->mark_compact_collector()->RecordSlot(weak_cell, slot, *slot);
+      // Remove entry somewhere after top.
+      if (prev_weak_cell_obj != NULL) {
+        prev_weak_cell_obj->set_next(weak_cell->next());
+      }
+      weak_cell_obj = weak_cell->next();
+      weak_cell->clear_next(heap());
+    } else {
+      if (weak_cell_head == Smi::FromInt(0)) {
+        weak_cell_head = weak_cell;
+      }
+      prev_weak_cell_obj = weak_cell;
+      weak_cell_obj = weak_cell->next();
+    }
+  }
+  // Top may have changed.
+  heap()->set_encountered_weak_cells(weak_cell_head);
+}
+
+
 void IncrementalMarking::FinalizeIncrementally() {
   DCHECK(FLAG_finalize_marking_incrementally);
   DCHECK(!finalize_marking_completed_);
   DCHECK(IsMarking());
 
   int old_marking_deque_top =
       heap_->mark_compact_collector()->marking_deque()->top();
 
   // After finishing incremental marking, we try to discover all unmarked
   // objects to reduce the marking load in the final pause.
   // 1) We scan and mark the roots again to find all changes to the root set.
   // 2) We mark the object groups.
+  // 3) Remove weak cell with live values from the list of weak cells, they
+  // do not need processing during GC.
   MarkRoots();
   MarkObjectGroups();
+  ProcessWeakCells();
 
   int marking_progress =
       abs(old_marking_deque_top -
           heap_->mark_compact_collector()->marking_deque()->top());
 
   ++incremental_marking_finalization_rounds_;
   if ((incremental_marking_finalization_rounds_ >=
        FLAG_max_incremental_marking_finalization_rounds) ||
       (marking_progress <
        FLAG_min_progress_during_incremental_marking_finalization)) {
@@ skipping 480 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }  // namespace internal
 }  // namespace v8