RFR(S): 8212611: Small collection of simple changes from shenandoah

[Erik Österlund]

Hi Roland,

 From a GC interface perspective, this looks good.

Thanks,
/Erik

On 2018-10-18 09:30, Roland Westrelin wrote:
> http://cr.openjdk.java.net/~roland/8212611/webrev.00/
>
> - Signature of enqueue_useful_gc_barrier(),
>    eliminate_useless_gc_barriers() is modified.
>
> - Call set_req_X() in some places so disconnected input has a chance to
>   be reprocessed
>
> - Add calls to step_over_gc_barrier() in places where peeking through a
>    barrier helps local optimizations.
>
> In isa_java_mirror_load(), I dropped the call is_gc_barrier_node()
> because for zgc (the only gc for which it is implemented), it duplicates
> the logic of step_over_gc_barrier() so it's more efficient to simply
> call step_over_gc_barrier().
>
> Roland.