RFR(M): 8212243: More gc interface tweaks for arraycopy and some other smaller changes in preparation for Shenandoah

[Roland Westrelin]

Thanks for re-reviewing this

> I think this 'bs' is not used in arraycopynode.cpp:
>
> +  BarrierSetC2* bs = BarrierSet::barrier_set()->barrier_set_c2();
>     for (int i = 0; i < count; i++) {
>
> It seems you wanted to pass it to new load() and store() methods. May be do that instead of loading it inside  these 
> methods especially since in some placed they are called in loop.

Here is a new webrev that implements this suggestion:

http://cr.openjdk.java.net/~roland/8212243/webrev.03/

Roland.