The following pattern is fairly common in the GC code:

ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

Code for a specific collector should use its heap() function to avoid casting and asserting. The example above should be replaced by:

ParallelScavengeHeap* heap = ParallelScavengeHeap::heap();

There are also other places where Universe::heap() is used, even when it's clear what we are inside, e.g. ParallelScavenge-related code. We should be using ParallelScavengeHeap::heap() here instead. Universe::heap() should (for clarity) only be used by code that doesn't know/care which collector we are currently using.