The following comment within G1BarrierSetC2::post_barrier():

    // We can skip marks on a freshly-allocated object in Eden.
    // Keep this code in sync with new_deferred_store_barrier() in runtime.cpp.
    // That routine informs GC to take appropriate compensating steps,
    // upon a slow-path allocation, so as to make this card-mark
    // elision safe.

refers to a function new_deferred_store_barrier() that does not exist anymore. The correct reference should be CardTableBarrierSet::on_slowpath_allocation_exit.