RFR: Skip pre-evac verification and pacing on shortcut cycle path

[Zhengyu Gu]

On 10/21/2018 02:58 PM, Aleksey Shipilev wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/verifier-shortcut/webrev.01/
> 
> This cleans up a corner case in our verification and pacing bindings: we don't need to call pacer on
> shortcut path, and there is no need to do double verification on non-shortcut path. This also
> naturally handles VerifyAfterGC on shortcut path.

For piggyback ref-update cycle, should op_final_mark()'s 
trash_cset_regions() also signal the end of GC cycle?

Thanks,

-Zhengyu

> 
> Testing: tier3_gc_shenandoah {fastdebug|release}
> 
> Thanks,
> -Aleksey
>