While assigning signals to global resources, Designer considers this information in the following priority:
The set_global and set_io statements (instances of those global cells, which cannot be demoted)
Nets with the highest potential fanout above 32 (after removal of all buffers and inverters)
Global cell instantiation in a netlist (global cells which can be demoted)
Note: By default, a net with a fanout of less than 32 will not be promoted to global automatically unless the set_global or set_io constraint statements is used for this net. You can override this threshold of 32 by using the set_auto_global_fanout constraint statement.