[heap] Drop filler objects on marking deque.

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 870 matching lines @@
 }
 
 
 void IncrementalMarking::MarkObject(Heap* heap, HeapObject* obj) {
   MarkBit mark_bit = ObjectMarking::MarkBitFrom(obj);
   if (Marking::IsWhite(mark_bit)) {
     heap->incremental_marking()->WhiteToGreyAndPush(obj, mark_bit);
   }
 }
 
-
-intptr_t IncrementalMarking::ProcessMarkingDeque(intptr_t bytes_to_process) {
+intptr_t IncrementalMarking::ProcessMarkingDeque(
+    intptr_t bytes_to_process, ForceCompletionAction completion) {
   intptr_t bytes_processed = 0;
-  Map* one_pointer_filler_map = heap_->one_pointer_filler_map();
-  Map* two_pointer_filler_map = heap_->two_pointer_filler_map();
   MarkingDeque* marking_deque =
       heap_->mark_compact_collector()->marking_deque();
-  while (!marking_deque->IsEmpty() && bytes_processed < bytes_to_process) {
+  while (!marking_deque->IsEmpty() && (bytes_processed < bytes_to_process ||
+                                       completion == FORCE_COMPLETION)) {
     HeapObject* obj = marking_deque->Pop();
 
-    // Explicitly skip one and two word fillers. Incremental markbit patterns
-    // are correct only for objects that occupy at least two words.
-    // Moreover, slots filtering for left-trimmed arrays works only when
-    // the distance between the old array start and the new array start
-    // is greater than two if both starts are marked.
+    // Left trimming may result in white filler objects on the marking deque.
+    // Ignore these objects.
+    if (obj->IsFiller()) {
+      DCHECK(Marking::IsImpossible(ObjectMarking::MarkBitFrom(obj)) ||
+             Marking::IsWhite(ObjectMarking::MarkBitFrom(obj)));
+      continue;
+    }
+
     Map* map = obj->map();
-    if (map == one_pointer_filler_map || map == two_pointer_filler_map)
-      continue;
-
     int size = obj->SizeFromMap(map);
     unscanned_bytes_of_large_object_ = 0;
     VisitObject(map, obj, size);
     bytes_processed += size - unscanned_bytes_of_large_object_;
   }
   return bytes_processed;
 }
 
 
-void IncrementalMarking::ProcessMarkingDeque() {
-  Map* filler_map = heap_->one_pointer_filler_map();
-  MarkingDeque* marking_deque =
-      heap_->mark_compact_collector()->marking_deque();
-  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();
-    if (map == filler_map) continue;
-
-    VisitObject(map, obj, obj->SizeFromMap(map));
-  }
-}
-
-
 void IncrementalMarking::Hurry() {
   // A scavenge may have pushed new objects on the marking deque (due to black
   // allocation) even in COMPLETE state. This may happen if scavenges are
   // forced e.g. in tests. It should not happen when COMPLETE was set when
   // incremental marking finished and a regular GC was triggered after that
   // because should_hurry_ will force a full GC.
   if (!heap_->mark_compact_collector()->marking_deque()->IsEmpty()) {
     double start = 0.0;
     if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
       start = heap_->MonotonicallyIncreasingTimeInMs();
       if (FLAG_trace_incremental_marking) {
         PrintF("[IncrementalMarking] Hurry\n");
       }
     }
     // TODO(gc) hurry can mark objects it encounters black as mutator
     // was stopped.
-    ProcessMarkingDeque();
+    ProcessMarkingDeque(0, FORCE_COMPLETION);
     state_ = COMPLETE;
     if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
       double end = heap_->MonotonicallyIncreasingTimeInMs();
       double delta = end - start;
       heap_->tracer()->AddMarkingTime(delta);
       if (FLAG_trace_incremental_marking) {
         PrintF("[IncrementalMarking] Complete (hurry), spent %d ms.\n",
                static_cast<int>(delta));
       }
     }
@@ skipping 315 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }  // namespace internal
 }  // namespace v8