Combining range and inequality information for pointer disambiguation

Pentagons is an abstract domain invented by Logozzo and Fahndrich to validate array accesses in low-level programming languages. This algebraic structure provides a cheap “less-than check”, which builds a partial order between the integer variables used in a program. In this paper, we show how we have used the ideas available in Pentagons to design and implement a novel alias analysis. This new algorithm lets us disambiguate pointers with offsets, so common in C-style pointer arithmetics, in a precise and efficient way. Together with this new abstract domain we describe several implementation decisions that lets us produce a practical pointer disambiguation algorithm on top of the LLVM compiler. Our alias analysis is able to handle programs as large as SPEC’s gcc in a few minutes. Furthermore, we have been able to improve the percentage of pairs of pointers disambiguated, when compared to LLVM’s built-in analyses, by a four-fold factor in some benchmarks.