[heap] Do not clear mark bits of black large objects on right trim.

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/context-slot-cache.h"
 #include "src/base/bits.h"
@@ skipping 3220 matching lines @@
   Address new_end = old_end - 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.
   // We do not create a filler for objects in large object space.
   // TODO(hpayer): We should shrink the large object page if the size
   // of the object changed significantly.
   if (!lo_space()->Contains(object)) {
     CreateFillerObjectAt(new_end, bytes_to_trim, ClearRecordedSlots::kYes);
-  }
-
-  // Clear the mark bits of the black area that belongs now to the filler.
-  // This is an optimization. The sweeper will release black fillers anyway.
-  if (incremental_marking()->black_allocation() &&
-      Marking::IsBlackOrGrey(ObjectMarking::MarkBitFrom(new_end))) {
-    Page* page = Page::FromAddress(new_end);
-    page->markbits()->ClearRange(
-        page->AddressToMarkbitIndex(new_end),
-        page->AddressToMarkbitIndex(new_end + bytes_to_trim));
+    // Clear the mark bits of the black area that belongs now to the filler.
+    // This is an optimization. The sweeper will release black fillers anyway.
+    if (incremental_marking()->black_allocation() &&
+        Marking::IsBlackOrGrey(ObjectMarking::MarkBitFrom(new_end))) {
+      Page* page = Page::FromAddress(new_end);
+      page->markbits()->ClearRange(
+          page->AddressToMarkbitIndex(new_end),
+          page->AddressToMarkbitIndex(new_end + bytes_to_trim));
+    }
   }
 
   // Initialize header of the trimmed array. We are storing the new length
   // using release store after creating a filler for the left-over space to
   // avoid races with the sweeper thread.
   object->synchronized_set_length(len - elements_to_trim);
 
   // Maintain consistency of live bytes during incremental marking
   AdjustLiveBytes(object, -bytes_to_trim);
 
@@ skipping 3254 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8