Priority order for global promotion

While assigning signals to global resources, Designer considers this information in the following priority:

1. The set_global and set_io statements (instances of those global cells, which cannot be demoted)

2. Nets with the highest potential fanout above 32 (after removal of all buffers and inverters)

3. 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.