>if those cliffs are unreachable for a given ISA, they don't matter By rice's theorem, for any ISA that has a jmp or mov, there is no way to know/prove/predict

>if those cliffs are unreachable for a given ISA, they don't matter By rice's theorem, for any ISA that has a jmp or mov, there is no way to know/prove/predict this. So you're still not saying anything useful.