That code doesn't make any sense. Either halts() itself is a function that solves the halting problem or the else branch is a dead branch because in order to be selected halts() must have never returned.

Dynamic code is where the GC can't know if something simply has a stale reference or if the codepath that calls it simply doesn't exist yet. It's be interesting to need to tag such data appropriately as that opens up a lot of leak protection.