RFR [8] [backport] Move (Java)Thread::_gc_state to lower offset to optimize barrier fast-path encoding

[Aleksey Shipilev]

Ping. (realized I never pushed it)

On 06/14/2018 08:23 PM, Aleksey Shipilev wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/gcstate-low-8u/webrev.01/
> 
> This is the backport for the change we pushed to sh/jdk10 recently, and it seems to pass the tests
> there well.
> 
> Testing: hotspot_tier3_gc_shenandoah {fastdebug|release}, eyeballing assembly
> 
> Thanks,
> -Aleksey
>