I’m not entirely convinced that stages 2 & 3 are
  necessary, maybe we stop at stage 1.  It all depends on
  what optimizations we’d like to do that can’t be done
  because the IR is in the wrong form.  Proceeding with
  stages 2 and 3 might gain some efficiency in the compiler
  itself because then we don’t have to generate the old IR
  at all.  I suspect that effect will be small, however.