

A slightly better metric to train it on would be chances of survival/years of life saved thanks to the transplant. However those also suffer from human bias due to the past decisions that influenced who got a transpant and thus what data we were able to gather.
It is not guaranteed to do that. It could also use a register or be optimized out completly (like in the example you posted in the other comment).
The stack pointer is also not changed for each local variable, but instead for each function call, so it wouldn’t make a difference anyway.