Programming Languages and Systems

Volume 3924 of the series Lecture Notes in Computer Science pp 279-293

Assertion Checking over Combined Abstraction of Linear Arithmetic and Uninterpreted Functions

  • Sumit GulwaniAffiliated withMicrosoft Research
  • , Ashish TiwariAffiliated withSRI International


This paper presents results on the problem of checking equality assertions in programs whose expressions have been abstracted using combination of linear arithmetic and uninterpreted functions, and whose conditionals are treated as non-deterministic.

We first show that the problem of assertion checking for this combined abstraction is coNP-hard, even for loop-free programs. This result is quite surprising since assertion checking for the individual abstractions of linear arithmetic and uninterpreted functions can be performed efficiently in polynomial time.

Next, we give an assertion checking algorithm for this combined abstraction, thereby proving decidability of this problem despite the underlying lattice having infinite height. Our algorithm is based on an important connection between unification theory and program analysis. Specifically, we show that weakest preconditions can be strengthened by replacing equalities by their unifiers, without losing any precision, during backward analysis of programs.