In reply to Rahulkumar Patel:
Thank you for your check. Just in case, here is error log by Xcelium(Cadence).
I understood this is a sort of limitation in Xcelium.
xrun(64): 19.06-v001: (c) Copyright 1995-2019 Cadence Design Systems, Inc.
cg = new();
xmvlog: *E,UNDIDN (tb01.sv,4|7): 'cg': undeclared identifier [12.5(IEEE)].
xmvlog: *W,NOTOPL: no top-level unit found, must have recursive instances.
Total errors/warnings found outside modules and primitives:
errors: 1, warnings: 1
xrun: *E,VLGERR: An error occurred during parsing. Review the log file for errors with the code *E and fix those identified problems to proceed. Exiting with code (status 1).
TOOL: xrun(64) 19.06-v001: Exiting on Jan 08, 2020 at 22:59:52 PST (total: 00:00:00)