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PLCOPEN-CP2: All code shall be used in the application

Unreachable code reflects a logic mistake and should be removed.

Why is it bad?​

Code that the program can never execute is dead weight: it inflates the binary, adds maintenance burden, and almost always reflects a logic mistake the author did not notice. Statements that follow an unconditional RETURN, EXIT or CONTINUE are unreachable and should be removed.

This rule walks the control-flow graph of every POU and reports basic blocks that are not reachable from the entry block.

Example​

FUNCTION dead_code_after_return : INT
  VAR
    counter : INT := 0;
    some_var : INT;
  END_VAR
  counter := counter + 1;
  RETURN;
  some_var := SQRT(16#42);  (* unreachable *)
END_FUNCTION

Use instead:

FUNCTION live_code : INT
  VAR
    counter : INT := 0;
    some_var : INT;
  END_VAR
  counter := counter + 1;
  some_var := SQRT(16#42);
  RETURN;
END_FUNCTION

Resources​

  1. PLCOpen Software Construction Guidelines