Facilitating unreachable code diagnosis and debugging

Code coverage is a popular method to find design bugs and verification loopholes. However, once a piece of code is determined to be unreachable, diagnosing the cause of the problem can be challenging: since the code is unreachable, no counterexample can be returned for debugging. Therefore, engineers need to analyze the legality of nonexistent execution paths, which can be difficult. To address such a problem, we analyzed the cause of unreachability in several industrial designs and proposed a diagnosis technique that can explain the cause of unreachability. In addition, our method provides suggestions on how to solve the un-reachability problem, which can further facilitate debugging. Our experimental results show that this technique can greatly reduce an engineer's effort in analyzing unreachable code.