Footprint Optimization

What's footprint?

Footprint is a attribute of library cells. It's provide by by vendors.
See following library cell information (log of report_lib):

  Cell                Footprint    Vth group     Attributes
  ------------------------------------------------------------
  ADDFCINX1HXP        "addfcinx1"                r, udp
  ADDFCINX2HXP        "addfcinx2"                r, udp
  ADDFCINX4HXP        "addfcinx4"                r, udp
  ADDFCINX05HXP       "addfcinx05"               r, udp  

Footprint Optimization

  Footprint optimization is special size method, cells only can be sized to other cells with the same footprint.