Indeed, those two statements are the same thing. If you want a correct compiler it has to be correct according to a model, which means it can't handle things o

Indeed, those two statements are the same thing. If you want a correct compiler it has to be correct according to a model, which means it can't handle things outside that model, and now you have "undefined behavior". People want compilers to limit how much they transform UB, but that's not possible unless it gets defined. Which you can do, of course, but it's more limiting than it looks.