read_liberty - read cells from liberty file

yosys> help read_liberty
read_liberty [filename]
Read cells from liberty file as modules into current design.
only create empty blackbox modules
mark imported cells as whiteboxes
ignore re-definitions of modules. (the default behavior is to
create an error message if the existing module is not a blackbox
module, and overwrite the existing module if it is  a blackbox module.)
overwrite existing modules with the same name
ignore cells with missing function specification of outputs
ignore cells with a missing or invalid direction
specification on a pin
ignore latches with missing data and/or enable pins
-setattr <attribute_name>
set the specified attribute (to the value 1) on all loaded modules