This problem may occur if you are using ModelSim® version 6.2 (for example, 6.2a, 6.2b or 6.2<x>) while running the vsim command. ModelSim version 6.2 does not work correctly with Quartus® II simulation models. This is due to a problem in the ModelSim software version 6.2 and it is scheduled to be fixed in version 6.3.
Due to this problem, the Quartus II software does not officially support ModelSim version 6.2. For more information about the supported EDA tools for any particular version of the Quartus II software, refer to the Release Notes on the Quartus II Literature page.
To work around this issue, turn off the optimization flow by specifying the -novopt argument in the vsim command.
For example, you may use the following vsim command:
vsim -t ps work.test_tst
Modify the command by adding the -novopt argument as follows:
vsim -novopt -t ps work.test_tst