RFC/RFR: Cherry-pick 8221735: Shenandoah fails ctw/modules/jdk_management_agent.java with Traversal

[Roman Kennke]

OK

> Let's cherry pick the fix for CTW failure in sh/jdk:
>    https://bugs.openjdk.java.net/browse/JDK-8221735
>    http://hg.openjdk.java.net/jdk/jdk/rev/dfaa9daab43c
> 
> It would take a while until it gets to sh/jdk with merges.
> 
> -- diff -r 092d783d359e src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp
> --- a/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp  Tue Apr 02 13:22:56 2019 +0200
> +++ b/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp  Tue Apr 02 13:25:17 2019 +0200
> @@ -2097,10 +2097,11 @@
>   }
> 
>   int ShenandoahEnqueueBarrierNode::needed(Node* n) {
>     if (n == NULL ||
>         n->is_Allocate() ||
> +      n->Opcode() == Op_ShenandoahEnqueueBarrier ||
>         n->bottom_type() == TypePtr::NULL_PTR ||
>         (n->bottom_type()->make_oopptr() != NULL && n->bottom_type()->make_oopptr()->const_oop() !=
> NULL)) {
>       return NotNeeded;
>     }
>     if (n->is_Phi() ||
> 
> Testing: hotspot_gc_shenandoah, CTW tests
> 
> Thanks,
> -Aleksey
> 
>