RFR [11] 2018-11-20: Bulk backports to sh/jdk11

[Roman Kennke]

Looks good. Thanks!

Roman


> http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20181120/webrev.01/
> 
> This backports recent work to sh/jdk11. I skipped some C2 patches that are irrelevant in 11, because
> GC API is different. This also backports up to last unproblematic change, as far as Gotland sees it.
> List of changes:
> 
>  [backport] undo useless ifnode.cpp change
>  [backport] ShenandoahMemoryPool should support usage threshold
>  [backport] Shenandoah filter for gc/TestFullGCCount.java test
>  [backport] Move save/restore vector registers into ShenandoahBarrierSetAssembler
>  [backport] Compact heuristics adjustments
>  [backport] Cherry-pick bulk MarkBitMap clearing methods
>  [backport] Shenandoah filter for vmTestbase/nsk/jvmti/scenarios/general_functions/GF08/gf08t001
>  [backport] is_gc_barrier_node should accept barriers called with both CallLeaf and CallLeafNoFP
>  [backport] Remove ShenandoahWriteBarrierCsetTestInIR flag
>  [backport] Trivial C2 cleanups
> 
> Testing: tier3_gc_shenandoah {fastdebug|release}
> 
> Thanks,
> -Aleksey
>