Combining Range and Inequality Information for Pointer Disambiguation
Résumé
Pentagons is an abstract domain invented by Logozzo and Fähndrich 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.
With this new algorithm, we are able to disambiguate pointers with off- sets, that commonly occur in C programs, in a precise and efficient way. Together with this new abstract domain we describe several implementation decisions that let 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 CPU2006’s gcc in a few minutes. Furthermore, it improves on LLVM’s industrial quality analyses. As an extreme example, we have observed a 4x improvement when analyzing SPEC’s lbm.
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