>Look, GCC (what I have here: 7.3.0) is doing this even for the following trivial function: You're absolutely right that in this case, it's wasteful. In fact,

>Look, GCC (what I have here: 7.3.0) is doing this even for the following trivial function: You're absolutely right that in this case, it's wasteful. In fact, if you try Clang you will see that it only emits a ret. Maybe GCC is doing you a courtesy (or maybe nobody taught it to completely omit an Undef return value, so it just picks zero!). Either way, it's unconditionally UB, GCC can do whatever it likes. >do we still know until run-time that this has UB? Well, there is no branch here, is there? I'm clearly not going to disagree with you on this one =] To be clear: UB is still a property of the execution of the program, but here it's not hard to statically determine that all executions of this program are Undefined Behavior.