8202377: Modularize C2 GC barriers

[Erik Österlund]

Hi Roland,

Thank you for having a look at these changes.

On 2018-05-17 14:58, Roland Westrelin wrote:
> Hi Erik,
>
>> http://cr.openjdk.java.net/~eosterlund/8202377/webrev.01/
> Overall, this looks good to me.
>
> I suppose:
>
> loop_optimize_gc_barrier()
> find_dominating_barriers()
>
> are there for ZGC and they don't feel generic enough to me to be
> included in this API. That is if I were to add another GC or let say
> change the G1 implementation so it's better suited for optimizations, I
> think it's quite unlikely I would reuse either hook. It would be better
> to remove them in my opinion.

Yes they are indeed hooks used only by ZGC at the moment, and I agree 
they might be an over-generalization at the moment. I am okay with 
removing those hooks now, and then we see what we might have in common 
with Shenandoah later when we have integrated them both.

Incremental webrev:
http://cr.openjdk.java.net/~eosterlund/8202377/webrev.01_02/

Full webrev:
http://cr.openjdk.java.net/~eosterlund/8202377/webrev.02/

Again, thanks a lot for looking at these changes.

Thanks,
/Erik

> Roland.