When an nmethod is compiled, it's registered with the heap if ScavengeRootsInCode is non-zero (which it always is). However, during code patching in C1 we re-register the nmethod with the heap only if it also has scavengable oops. This additional requirement is only valid for calls to CodeCache::add_scavenge_root_nmethod(), and not for CollectedHeap::register_nmethod(). This happens to work today since G1's is_scavengable() basically always returns true.