We could also add more general rewriting, but
- these new special cases catch something like
  95% of the cases that we weren't rewriting
- these special cases are faster than doing the generic
  nonzerno mechanism (looking up the attribute, etc)

It'd be nice if we could get to the point that the generic
rewrites we'd create would be as good as the hand-crafted ones,
but that would require knowing that we don't need to guard on
constant classes, and then inlining within rewrites.