On Fri, 22 Feb 2019, Björn Töpel wrote:

> > The problem is that the register needs to be referenced by the amo
> > instruction. Can amoadd increment an address relative to a scratch
> > register?
> >
>
> It cannot. So, we'll end up with (at least) a preempt disabled region...

If we need to do that then we already have so much overhead due to that
processing that it may not be worthwhile. lc/sc overhead is minor compared
to switching preempt on and off I think.