RFR (S): Optimize partial GC preparation

[Roman Kennke]

Am 04.05.2017 um 11:07 schrieb Aleksey Shipilev:
> Hi,
>
> We can massage partial GC preparation code to be more efficient. Matrix scans
> take the longest time there, so we want to scan the matix once, not twice. Plus
> other optimizations:
>   http://cr.openjdk.java.net/~shade/shenandoah/partial-prepare-perf-2/webrev.01/
>
> Improves performance a lot:
>   http://cr.openjdk.java.net/~shade/shenandoah/partial-prepare-perf-2/perf.txt
>
> Testing: hotspot_gc_shenandoah
>
> Thanks,
> -Aleksey
>
>
Looks good to me.

Roman