Load reference barriers and safepoints

[Florian Weimer]

* Liang Mao:

> No. Load reference barriers don't have oopmap.  And the slow path
> runtime call of LRB is a leaf call which doesn't have oopmap and
> cannot suspend in safepoint.

Thanks.

What happens on evacuation failure?  Is that impossible for mutator
threads, or will the thread throw a pre-allocated exception?