Report Number: CSL-TR-97-724
Institution: Stanford University, Computer Systems Laboratory
Title: State Reduction Methods for Automatic Formal Verification
Author: Ip, C. Norris
Date: December 1996
Abstract: Validation of industrial designs is becoming more challenging as technology advances. One of the most suitable debugging aids is automatic formal verification. This thesis presents several techniques for reducing the state explosion problem, that is, reducing the number of states that are examined. A major contribution of this thesis is the design of simple extensions to the Murphi description language, which enable us to convert two existing abstraction strategies into two fully automatic algorithms, making these strategies easy to use and safe to apply. These two algorithms rely on two facts about high-level designs: they frequently exhibit structural symmetry, and their behavior is often independent of the exact number of replicated components they contain. Another contribution is the design of a new state reduction algorithm, which relies on reversible rules (transitions that do not lose information) in a system description. This new reduction algorithm can be used simultaneously with the other two algorithms. These techniques, implemented in the Murphi verification system, have been applied to many applications, such as cache coherence protocols and distributed algorithms. In the cases of two important classes of infinite systems, infinite state graphs can be automatically converted to small finite state graphs.