Unnecessary code is one thing, exploiting the presence of undefined behavior to compile something that the programmer likely didn't want is another. It doesn't

Unnecessary code is one thing, exploiting the presence of undefined behavior to compile something that the programmer likely didn't want is another. It doesn't matter much if it's fast if it's wrong. A good compiler shouldn't try to read the mind of the programmer, it should complain loudly and stop. It should be free to do so, given tha leeway it has with undefined behavior. And of course, the standards committee should get off their asses and define some behaviors.