muxcover - cover trees of MUX cells with wider MUXes

yosys> help muxcover
muxcover [options] [selection]
Cover trees of $_MUX_ cells with $_MUX{4,8,16}_ cells
-mux4[=cost], -mux8[=cost], -mux16[=cost]
Cover $_MUX_ trees using the specified types of MUXes (with optional
integer costs). If none of these options are given, the effect is the
same as if all of them are.
Default costs: $_MUX4_ = 220, $_MUX8_ = 460,
               $_MUX16_ = 940
Use the specified cost for $_MUX_ cells when making covering decisions.
Default cost: $_MUX_ = 100
Use the specified cost for $_MUX_ cells used in decoders.
Default cost: 90
Do not insert decoder logic. This reduces the number of possible
substitutions, but guarantees that the resulting circuit is not
less efficient than the original circuit.
Do not consider mappings that use $_MUX<N>_ to select from less
than <N> different signals.