> 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.