message: Use DCE to post-process SSA round-trip tests
  The current state of the SSA examples can leave references to an
  intentionally undefined variable (`__undefined`) in situations where it
  thinks the value will never be used. So we allow ourselves to run
  trivial DCE to clean up these assignments before attempting to run the
  code.
diff: -command = "bril2json < {filename} | python ../../to_ssa.py | python ../../from_ssa.py | brili {args}"
  +command = "bril2json < {filename} | python ../../to_ssa.py | python ../../from_ssa.py | python ../../tdce.py | brili {args}"
  