[sh/8u] RFR 8229474: Shenandoah: Cleanup CM::update_roots()

[Roman Kennke]

Looks good to me!

(Has it already been backported to jdk11? This should happen before this.)

Thanks,
Roman

> I would like to backport this patch to shenandoah/8u.
> 
> The original patch does not apply cleanly, but conflicts are easy to 
> resolve. Also, there is no traversal GC, that part of patch is no longer 
> applicable.
> 
> The original bug: https://bugs.openjdk.java.net/browse/JDK-8229474
> The original patch: https://hg.openjdk.java.net/jdk/jdk/rev/23e13076e102
> 
> sh/8u webrev: 
> http://cr.openjdk.java.net/~zgu/shenandoah/JDK-8229474-8u/webrev.00/
> 
> Test:
>    hotspot_gc_shenandoah
> 
> 
> Thanks,
> 
> -Zhengyu
>