> There has always been undefined behavior in C, but back in the day, compilers were nowhere near as aggressive in taking advantage of it to make your code fast

> There has always been undefined behavior in C, but back in the day, compilers were nowhere near as aggressive in taking advantage of it to make your code faster. That much is true. If you put the derefence of a pointer and the null check in the wrong order both those statements would have code emitted for them. Now, it is almost certain that one of those statements would not be emitted. OTOH, compiling with -O0 still leaves most code to be emitted and fewer dead-code elimination places.