Are you talking about C? In C it's not guaranteed whether a non existing function will result in an actual function call. As soon as an actual function call was generated by the compiler, a modern CPU is very likely to trap.
We are talking about an optimization of a language implementation here. This would be very much written in a ASM or another language were this is defined.
We are talking about an optimization of a language implementation here. This would be very much written in a ASM or another language were this is defined.