6A-2 Facilitating Unreachable Code Diagnosis and Debugging

Abstract — 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 unreachability problem, which can further facilitate debugging. Our experimental results show that this technique can greatly reduce an engineer’s effort in analyzing unreachable code. I