RFR(XXS) 8224525: Shenandoah: Eliminate shenandoah verifier's side-effects

[Roman Kennke]

Where exactly does verification interfere with evacuation-in-progress?
Because I don't see it. verify_before_evacuation() is done before
activating the flag, and verify_after_evacuation() is done after
clearing the flag.

Roman


> Since switching to LRB, verifier has side-effects of evacuating oops, if
> it is ran during evacuation phase.
> 
> The patch resets gc_state before LRB can be triggered by verifier, and
> restore gc_state when it is done.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8224525
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8224525/webrev.00/
> 
> Test:
>   hotspot_gc_shenandoah with -XX:+ShenandoahVerify (fastdebug and release)
> 
> 
> Thanks,
> 
> -Zhengyu