RFR: Refactor and improve ShenandoahCodeRoots strategies

[Aleksey Shipilev]

Ping.

On 05/24/2018 08:24 PM, Aleksey Shipilev wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/codecache-styles-rework/webrev.01/
> 
> This refactors our support for different code root styles, and improves style-2 a lot. Style-0 and
> style-1 are just general cleanups. We would try and switch to a more optimal style-2 later, as
> performance runs complete. But I would appreciate reviews for the code changes themselves meanwhile.
> 
> Testing: hotspot_gc_shenandoah with ShCodeRootsStyle={0,1,2}, benchmarks
> 
> Thanks,
> -Aleksey
>