Dead code is code that doesn’t have any effect in your simulation or synthesis. Examples of dead code are signals that are never used, or conditions that are never triggered.
Dead code does not bother the simulator nor the synthesis tool. However, it consumes mental energy of anybody reading the code. People will try to figure the puropose of a given statement and it may take a while before they realize that they are dealing with dead code. This makes it more expensive to review code and to reuse code. In general, dead code is a form of technological debt that should be avoided.
Sigasi Studio flags some kinds of dead code:
- unused declarations (signals, constants, …) (rule 55): a Quick Fix is available to help you remove unused declarations fast.
- unused ports (rule 67) and generics (rule 68)
- unreachable statements (rule 79): if the Sigasi Studio analyzer can determine that a condition is always false, it will mark the if-statement because it contains dead code.
if true then v := v + 1; else v := v - 1; end if;
- dead states in a state machine: a state is considered dead if it has no outgoing transitions (rule 71)
type t_state is (IDLE, START, RUN, DONE); signal state: t_state; -- [some code omitted] case state is when IDLE => -- do something state <= RUN; when RUN => -- do something state <= DONE; when DONE => -- do something state <= IDLE; when others => -- do nothing end case;
These rules can be disabled for your project, or its severity can be modified in the project linting settings.
Manual configuration in