> The set of things you are worrying about it actually precisely the set of things CLZ solves :) I think the set of things I worry about is slightly different,

> The set of things you are worrying about it actually precisely the set of things CLZ solves :) I think the set of things I worry about is slightly different, because they operate in a static environment and I operate in a dynamic one. For example, they don't seem to be worried about the transformation from: loop { if (pred) { // o and o.f are loop invariants Guard(o is X); v = Load(o.f); Use(v) } } to Guard(o is X); v = Load(o.f); loop { if (pred) { Use(v) } } this tranformation might or might not be "beneficial" depending on relation between predicate and the guard - e.g. it can lead to a code which will just deoptimize on the guard before entering the loop. There is no way of knowing this statically, so you just have to take a bet (unless you have clear indications that guard will fail when hoisted) and then undo your decision later.