[bitm0de]

The misleading thing here is that in most cases while debugging, IDA for instance will replace instances of memcpy with rep movsb, but I'm pretty sure that is a conditional replacement if found that the memory regions do not contain addresses and offsets that interfere with each other. For the most part it's an optimization thing. Things like memmove do support overlapping memory blocks and won't invoke undefined behavior like memcpy will.