Maybe the biggest issue is optimizing register allocation while providing the information for all roots for the garbage collection... For non-GC languages you d

Maybe the biggest issue is optimizing register allocation while providing the information for all roots for the garbage collection... For non-GC languages you don't need to care about it and just agressively optimize register allocation. For GC languages you have to be careful, because the GC must know 1) which registers are holding references and which not 2) which of those registers are "alive" and which are not in use anymore (and therefore ready for garbage collection)...