RFR: Pre-filter oops before enqueing them in SBS slowpaths

[Roman Kennke]

Am 19.06.2018 um 10:27 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/sbs-prefilter/webrev.01/
> 
> The comment says it all:
> 
>   // Filter marked objects before hitting the SATB queues. The same predicate would
>   // be used by SATBMQ::filter to eliminate already marked objects downstream, but
>   // filtering here helps to avoid wasteful SATB queueing work to begin with.
>   if (!_heap->requires_marking(obj)) return;
> 
> This cuts down ref_array_pre lags around 3x on specjbb.
> 
> Testing: tier3_gc_shenandoah, eyeballing SBS lags on specjbb.
> 
> Thanks,
> -Aleksey
> 

Very good! Go!

Thanks,
Roman