RFR: Factor out storeval barrier from read barriers

[Aleksey Shipilev]

On 08/25/2017 08:37 PM, Roman Kennke wrote:
> I also added a flag ShenandoahStoreValBarriers that does the same as the
> other ShenandoahXXXBarriers flag, turn generation of the barriers off on
> request. The way it's currently done, the storeval barrier is also
> controlled by ShenandoahReadBarriers, dunno if we want to change that?
> I.e. -ShReadBarrier not affect ShStoreValBarrier ?

Making a separate ShStoreValBarrier is good with me. Having it separate from ShReadBarrier is good
with me too, because I wondered what the impact on storeval barriers was.

> http://cr.openjdk.java.net/~rkennke/storevalbarrier/webrev.00/

This looks good.

Thanks,
-Aleksey