dff2dffe - transform $dff cells to $dffe cells

    dff2dffe [options] [selection]

This pass transforms $dff cells driven by a tree of multiplexers with one or
more feedback paths to $dffe cells. It also works on gate-level cells such as
$_DFF_P_, $_DFF_N_ and $_MUX_.

        operate in the opposite direction: replace $dffe cells with combinations
        of $dff and $mux cells. the options below are ignore in unmap mode.

    -direct <internal_gate_type> <external_gate_type>
        map directly to external gate type. <internal_gate_type> can
        be any internal gate-level FF cell (except $_DFFE_??_). the
        <external_gate_type> is the cell type name for a cell with an
        identical interface to the <internal_gate_type>, except it
        also has an high-active enable port 'E'.
          Usually <external_gate_type> is an intermediate cell type
        that is then translated to the final type using 'techmap'.

    -direct-match <pattern>
        like -direct for all DFF cell types matching the expression.
        this will use $__DFFE_* as <external_gate_type> matching the
        internal gate type $_DFF_*_, except for $_DFF_[NP]_, which is
        converted to $_DFFE_[NP]_.