hg: shenandoah/jdk11: Shenandoah: Isolate changes around BarrierSetC2::enqueue_useful_gc_barrier()

[rkennke at redhat.com]

Changeset: 804dc32ba262
Author:    rkennke
Date:      2020-07-08 12:54 +0200
URL:       https://hg.openjdk.java.net/shenandoah/jdk11/rev/804dc32ba262

Shenandoah: Isolate changes around BarrierSetC2::enqueue_useful_gc_barrier()
Reviewed-by: roland

! src/hotspot/share/gc/shared/c2/barrierSetC2.hpp
! src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp
! src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.hpp
! src/hotspot/share/gc/z/c2/zBarrierSetC2.cpp
! src/hotspot/share/gc/z/c2/zBarrierSetC2.hpp
! src/hotspot/share/opto/node.cpp
! src/hotspot/share/opto/phaseX.cpp