RFR (S): Replace ShHeapRegionSet::get with get_fast

[Roman Kennke]

Am 04.05.2017 um 18:50 schrieb Aleksey Shipilev:
> Hi,
>
> We knew from concmark performance work that the excess branch in get() costs us.
> It returns NULL if (idx < active). Today I reviewed all the places in Shenandoah
> where we call get(), and it seems almost everywhere NULL is not acceptable,
> leading straight to SEGV. It makes sense to use get_fast there then, or indeed
> rename get -> get_or_null, get_fast -> get.
>
> Fix:
>  http://cr.openjdk.java.net/~shade/shenandoah/hrs-get/webrev.01/
>
> Testing: hotspot_gc_shenandoah
>
> Thanks,
> -Aleksey
>
>
This sounds very reasonable. Yes!

Roman