Use atomic operation to read the length of a fixed array.

src/runtime/runtime-regexp.cc

 // Copyright 2014 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/v8.h"
 
 #include "src/arguments.h"
 #include "src/jsregexp-inl.h"
 #include "src/jsregexp.h"
 #include "src/runtime/runtime-utils.h"
@@ skipping 620 matching lines @@
   if (delta == 0) return *answer;
 
   Address end_of_string = answer->address() + string_size;
   Heap* heap = isolate->heap();
 
   // The trimming is performed on a newly allocated object, which is on a
   // fresly allocated page or on an already swept page. Hence, the sweeper
   // thread can not get confused with the filler creation. No synchronization
   // needed.
   heap->CreateFillerObjectAt(end_of_string, delta);
-  heap->AdjustLiveBytes(answer->address(), -delta, Heap::FROM_MUTATOR);
+  heap->AdjustLiveBytes(answer->address(), -delta, Heap::SWEEPING_STARTED);
   return *answer;
 }
 
 
 RUNTIME_FUNCTION(Runtime_StringReplaceGlobalRegExpWithString) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 4);
 
   CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
   CONVERT_ARG_HANDLE_CHECKED(String, replacement, 2);
@@ skipping 468 matching lines @@
 
 
 RUNTIME_FUNCTION(Runtime_IsRegExp) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_CHECKED(Object, obj, 0);
   return isolate->heap()->ToBoolean(obj->IsJSRegExp());
 }
 }
 }  // namespace v8::internal