Hi TaCheng, this is Chris Balcom, good to be talking with you again!
Here's some info I dug up on this question:
.SUBCKT statements in the hierarchical Spice layout netlist are each followed with a comment line containing statistics about the respective layout cell. For example:
.SUBCKT PVDD2 1 2 ** N=452 EP=2 IP=516 FDC=249
N is the number of nets in the cell. EP is the number of external pins in the cell (pins of the cell).
IP is the number of internal pins in the cell (placement pins in the cell). Note that N and IP may not be identical to what is actually present in the netlist, because not all layout nets and placement pins are represented in the netlist. For example, the netlist normally does not contain floating nets or placements of cells that have no devices.
FDC is the flat device count in the cell. This is the number of all primitive devices in the cell, including the sub-hierarchy of the cell, counted flat. In this context, primitive devices are objects formed with rule file Device operations. LVS Box cells are treated as normal cells. The FDC number is a good measure of cell size.
Note that this data is provided for information only. It is not used or interpreted by the LVS circuit comparison module and it is not an integral part of the netlist.