ConSUS: a light-weight program conditioner

Program conditioning consists of identifying and removing a set of statements which cannot be executed when a condition of interest holds at some point in a program. It has been applied to problems in maintenance, testing, re–use and re–engineering. Program conditioning relies upon both symbolic execution and reasoning about symbolic predicates. Automation of the process therefore requires some form of automated theorem proving. However, the use of a full-power ‘heavyweight’ theorem prover would impose unrealistic performance constraints. This paper reports on a lightweight approach to theorem proving using the FermaT simplify decision procedure. This is used as a component to ConSUS, a program conditioning system for the Wide Spectrum Language WSL. The paper describes the symbolic execution algorithm used by ConSUS, which prunes as it conditions. The paper also provides empirical evidence that conditioning produces a significant reduction in program size and, although exponential in the worst case, the conditioning system has low degree polynomial behaviour in many cases, thereby making it scalable to unit level applications of program conditioning.