RFR: Add flag to switch between WB and RB-based acmp

[Aleksey Shipilev]

On 08/31/2018 09:37 PM, Roman Kennke wrote:
> This adds a flag to switch between WB- and RB-based acmp in C2. We'd
> like to see if there's a measurable difference.
> 
> http://cr.openjdk.java.net/~rkennke/acmpswitch/webrev.00/

I'd say it is "ShenandoahAcmpWBBarrier", "Acmp" first. Otherwise good!

-Aleksey