The CLOCK_REGION assignment must be associated to a specific clock signal.
For example:
set_instance_assignment -name CLOCK_REGION "REGIONAL CLOCK REGION 0" -to <clock>
If you wish to make a CLOCK_REGION assignment to a specific level of hierarchy in your design then you need to specify both the clock and the entity:
set_instance_assignment -name CLOCK_REGION "REGIONAL CLOCK REGION 0" -from <clock> -to <entity>
If you don\'t specify the clock as shown in the example below then the assignment may be ignored:
set_instance_assignment -name CLOCK_REGION "REGIONAL CLOCK REGION 0" -to <entity>
Support for entity only assignments will be evaluated for a future release of the Quartus® II software.