> To clarify, what I am interested in here is the interaction of C-standard UB with any guarantee this compiler may give with regard to semantics preservation u

> To clarify, what I am interested in here is the interaction of C-standard UB with any guarantee this compiler may give with regard to semantics preservation under optimization. To clarify my point: undefined behaviour has any semantics you might want it to have. Anything and everything is semantically correct even under optimization. Even if the compiler says it will do one thing and then does another: it's correct either way. The computer may "do something" with division by zero. Or the compiler might completely elide the code and replace it with a picture of a teapot before it even gets as far as hitting a register in anger. It's still valid, semantically, because you're dividing by zero from which you can prove anything and everything.