The CompilerToVM::Data::initialize() member function of JVMCI identifies barrier sets with cards by taking the current BarrierSet and in a switch statement enumerating if it is in the set of all BarrierSets.
This switch statement includes both concrete barrier sets and abstract barrier sets.
This seems like the wrong way of doing things, and FakeRTTI should be used instead to see if the current barrier set is-a CardTableModRefBS.