How to track down all the registers connected to a specific downstream register? (for set_max_delay's --from)
If dest_reg is the full hierarchial name of the destination register, then you can add two constraints to your SDC:
To constraint ALL paths from different input ports to your destination register:
set_max_delay -from [get_ports in [*]] -to [get_cells dest_reg] &lt;delay&gt;

To constraint ALL paths from different registers to your destination register:
set_max_delay -from [get_cells [*]] -to [get_cells dest_reg] &lt;delay&gt;

EDIT:
As in Vivado the above second command generates warnings as the wildcard generates unsupported paths as well, so registers have to be explicitly mentioned for get_cells . In Altera, get_registers can be used, in Vivado it is not supported, so a work around is needed for get_cells. Since registers follow the naming convention _reg in the netlist :
set_max_delay -from [get_cells *_reg*] -to [get_cells dest_reg] &lt;delay&gt;