Don't duplicate ddt in `sufrevpass$add`.

[awf]

Don't duplicate ddt in sufrevpass$add.

rewriteSUFRevPass P_ts_add _ (Tuple [ddr, Tuple []])
  -- FIXME: This is bad because it duplicates the expression ddr.  CSE
  -- will probably resolve this problem, but we shouldn't create it in
  -- the first place.

It's OK to just introduce a classic let, because sufrevpass does not need to be SUF.

Originally posted by @awf in #766 (comment)