opt_lut - optimize LUT cells

yosys> help opt_lut

opt_lut [options] [selection]
This pass combines cascaded $lut cells with unused inputs.
-dlogic <type>:<cell-port>=<LUT-input>[:<cell-port>=<LUT-input>...]
preserve connections to dedicated logic cell <type> that has ports
<cell-port> connected to LUT inputs <LUT-input>. this includes
the case where both LUT and dedicated logic input are connected to
the same constant.
-limit N
only perform the first N combines, then stop. useful for debugging.