The case analysis command describes a functional design mode by setting constants in the logic, similar to configuration registers. It can be applied to input ports, nets, hierarchical pins, or leaf cell input pins. The constant value propagates through the logic and turns off the analysis on any path that can never be active. The effect is similar to how the false path exception works.
The most common example is to set a multiplexer select pin to 0 or 1. This allows
only one of the two multiplexer inputs to propagate through. The following example turns
off the analysis on the paths through the mux/S and
mux/I1 pins:
set_case_analysis 0 [get_pins mux/S]