RFR: Implement flag to generate write-barriers without membars

[Roman Kennke]

Am 19.01.2018 um 17:59 schrieb Aleksey Shipilev:
> On 01/19/2018 05:53 PM, Roman Kennke wrote:
>> I extracted this from Traversal GC because it may be useful for other situations too. It introduces
>> a flag ShenandoahWBWithMembar which enables to avoid generation of the load-load-membar in the
>> write-barrier. This membar is not needed when evacuation is always turned off at safepoints (e.g.
>> partial).
>>
>> http://cr.openjdk.java.net/~rkennke/wbwithmembar/webrev.00/
> 
> Looks good to me, assuming nothing changed since Traversal GC code that Roland reviewed :)
> 
> Minor nit: can we make the option name consistent with other selective options. E.g. we have
> ShenandoahWriteBarrierRB. So this one seems to be ShenandoahWriteBarrierMembar?
> 
> Thanks,
> -Aleksey
> 

Nothing should have changed since Roland's review.

http://cr.openjdk.java.net/~rkennke/wbwithmembar/webrev.01/

Ok to go?

Roman