Property irrelevant predicates

1 Property-irrelevant predicates Loops (and recursions) are major hurdles in scalability of property verification tools (verifiers). Although slicing removes loops which have no bearing on assert statement in terms of its value and reachability, sliced programs still have loops challenging scale up of the verifiers. If we can transform a program by eliminating some of such loops, it is more likely that a given verifier succeeds on transformed program. Of course the transformation will be useful only if results on transformed program can be used to get results on original program. Loops existing in a (backward) sliced program, may compute value of some variables that impact outcome of assert expression in following ways: 1. Impact on value of assert expression, possibly through a chain of assignments. 2. Impact on value of some predicates, possibly through a chain of assignments, that (a) Value impact the assert statement (b) Influence the reachability of assert statement Obviously, loops of type (1) can not be eliminated, as they directly impact the value of assert expression. However, loops of type (2) can be eliminated if property can be checked even after abstracting the predicates which these loops are impacting. Since we want the transformed program to be useful in deciding the outcome on original program, ideally we would like the transformed program to be property equivalent to original program. So we focus on what kind of predicates can be abstracted so that loops and computations contributing to value of such predicates can be eliminated. Let C be a predicate in a given program P in which a property is encoded through an assert statement A. Let P be an abstract program obtained from P by replacing right hand side of reaching definitions used for C, with a non deterministic value, denoted by '*'. Following observations are obvious: 1. If predicate C is loop invariant in concrete program P then so it will be in abstract program P too.