HeapRegion::note_self_forwarding_removal_start, I would expect tams == bottom already with the single bitmap changes JDK-8210708

I.e.:

  if (during_concurrent_start) {
    ...
  } else if (during_conc_mark) {
    // During concurrent mark, all objects in the CSet (including
    // the ones we find to be self-forwarded) are implicitly live.
    // So all objects need to be above TAMS.
    _top_at_mark_start = bottom();
  }

should be

  if (during_concurrent_start) {
    ...
  } else {
    assert(_top_at_mark_start == bottom(), "inv);
  }

The reason is that during evacuation failure
  * the young regions must always have TAMS==bottom