When reading the map from a live object, use a barrier load

src/heap/mark-compact.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/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 3225 matching lines @@
         freed_bytes = Free<parallelism>(space, free_list, free_start, size);
         max_freed_bytes = Max(freed_bytes, max_freed_bytes);
 #ifdef ENABLE_GDB_JIT_INTERFACE
         if (FLAG_gdbjit && space->identity() == CODE_SPACE) {
           GDBJITInterface::RemoveCodeRange(free_start, free_end);
         }
 #endif
       }
       HeapObject* live_object = HeapObject::FromAddress(free_end);
       DCHECK(Marking::IsBlack(Marking::MarkBitFrom(live_object)));
-      Map* map = live_object->map();
+      Map* map = live_object->synchronized_map();
       int size = live_object->SizeFromMap(map);
       if (sweeping_mode == SWEEP_AND_VISIT_LIVE_OBJECTS) {
         live_object->IterateBody(map->instance_type(), size, v);
       }
       if ((skip_list_mode == REBUILD_SKIP_LIST) && skip_list != NULL) {
         int new_region_start = SkipList::RegionNumber(free_end);
         int new_region_end =
             SkipList::RegionNumber(free_end + size - kPointerSize);
         if (new_region_start != curr_region || new_region_end != curr_region) {
           skip_list->AddObject(free_end, size);
@@ skipping 1183 matching lines @@
   SlotsBuffer* buffer = *buffer_address;
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 }
 }  // namespace v8::internal