This isn't a case of a missed optimization. The alternative loop they've used has different semantics: assumes 0 iterations never happen. It's equivalent of cha

This isn't a case of a missed optimization. The alternative loop they've used has different semantics: assumes 0 iterations never happen. It's equivalent of changing `while(){}` to `do {} while()`. It's not something an optimizer could safely do when the number of iterations isn't known.