MemRegion MemRegion::intersection(const MemRegion mr2) const {
  MemRegion res;
  HeapWord* res_start = MAX2(start(), mr2.start());
  HeapWord* res_end   = MIN2(end(),   mr2.end());
  if (res_start < res_end) {
    res.set_start(res_start);
    res.set_end(res_end);
  }
  return res;
}
MemRegion MemRegion::_union(const MemRegion mr2) const {
  // If one region is empty, return the other
  if (is_empty()) return mr2;
  if (mr2.is_empty()) return MemRegion(start(), end());

  // Otherwise, regions must overlap or be adjacent
  assert(((start() <= mr2.start()) && (end() >= mr2.start())) ||
         ((mr2.start() <= start()) && (mr2.end() >= start())),
             "non-adjacent or overlapping regions");
  MemRegion res;
  HeapWord* res_start = MIN2(start(), mr2.start());
  HeapWord* res_end   = MAX2(end(),   mr2.end());
  res.set_start(res_start);
  res.set_end(res_end);
  return res;
}