[11] RFR: Fix ShenandoahBarrierSetC2::enqueue_useful_gc_barrier (part of JDK-8212611)

[Aleksey Shipilev]

On 2/21/20 1:46 PM, Roman Kennke wrote:
>> I am thinking to re-push this to sh/jdk11. The downside: it increases our upstream exposure until
>> JDK-8212611 and dependent issues are in 11u. Thoughts?
> 
> Yes, I think we should do that, and also start working on backporting
> JDK-8212611.

Re-pushed to sh/jdk11.

-- 
Thanks,
-Aleksey