read_liberty - read cells from liberty file

    read_liberty [filename]

Read cells from liberty file as modules into current design.

        only create empty blackbox modules

        ignore re-definitions of modules. (the default behavior is to
        create an error message.)

        ignore cells with missing function specification of outputs

        ignore cells with a missing or invalid direction
        specification on a pin

    -setattr <attribute_name>
        set the specified attribute (to the value 1) on all loaded modules