RetroGaming

I recently came across a rust book on how pointers aren't just ints, because of UB.

fn main() {
    a = &1
    b = &2
    a++
    if a == b {
        *a = 3
        print(b)
    }
}

This may either: not print anything, print 3 or print 2.

Depending on the compiler, since b isn't changed at all, it might optimize the print for print(2) instead of print(b). Even though everyone can agree that it should either not print anything or 3, but never 2.

I hope you are not argueing that using assembly is an improvement over using C in that regard....

A compiler making assumptions like that about undefined behaviour sounds just like a bug. Maybe the bug is in the spec rather than the compiler, but I can't think of any time it would be better to optimize that code out entirely because UB is detected rather than just throwing an error or warning and otherwise ignoring the edge cases where the behaviour might break. It sounds like the worst possible option exactly for the reasons listed in that blog.