Function addresses 

pub fn addresses(
    func: &mut Func,
    insts: &FrameInsts,
    names: &mut Interner,
    waiting: &HashSet<Inst>,
) -> usize

Folds every address computation that one memory operand reads, and gives back how many.

waiting is the instructions whose displacement crate::finish has still to write, which are the ones this must not touch.

Run after lowering and before allocation. Running it twice can find more than running it once, because folding a lea into a second lea leaves that second one foldable in turn, and the walk below takes those in the one pass since it goes forwards.