[heap] Remove recorded slots in fixed array header area on left trimming.

src/heap/heap.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/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/scopeinfo.h"
 #include "src/base/bits.h"
@@ skipping 3119 matching lines @@
   DCHECK(elements_to_trim <= len);
 
   // Calculate location of new array start.
   Address new_start = object->address() + bytes_to_trim;
 
   // Technically in new space this write might be omitted (except for
   // debug mode which iterates through the heap), but to play safer
   // we still do it.
   CreateFillerObjectAt(object->address(), bytes_to_trim,
                        ClearRecordedSlots::kYes);
-
   // Initialize header of the trimmed array. Since left trimming is only
   // performed on pages which are not concurrently swept creating a filler
   // object does not require synchronization.
   DCHECK(CanMoveObjectStart(object));
   Object** former_start = HeapObject::RawField(object, 0);
   int new_start_index = elements_to_trim * (element_size / kPointerSize);
   former_start[new_start_index] = map;
   former_start[new_start_index + 1] = Smi::FromInt(len - elements_to_trim);
   FixedArrayBase* new_object =
       FixedArrayBase::cast(HeapObject::FromAddress(new_start));
 
+  // Remove recorded slots for the new map and length offset.
+  ClearRecordedSlot(new_object, HeapObject::RawField(object, 0));
+  ClearRecordedSlot(
+      new_object, HeapObject::RawField(object, FixedArrayBase::kLengthOffset));
+
   // Maintain consistency of live bytes during incremental marking
   Marking::TransferMark(this, object->address(), new_start);
   AdjustLiveBytes(new_object, -bytes_to_trim, Heap::CONCURRENT_TO_SWEEPER);
 
   // Notify the heap profiler of change in object layout.
   OnMoveEvent(new_object, object, new_object->Size());
   return new_object;
 }
 
 
@@ skipping 3268 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8