An iterative approach to precondition inference using constrained Horn clauses

Bishoksan Kafle, John Patrick Gallagher, Graeme Gange, Peter Schachte, Harald Søndergaard, Peter J. Stuckey

Research output: Contribution to journalConference articleResearchpeer-review


We present a method for automatic inference of conditions on the initial states of a program that guarantee that the safety assertions in the program are not violated. Constrained Horn clauses (CHCs) are used to model the program and assertions in a uniform way, and we use standard abstract interpretations to derive an over-approximation of the set of unsafe initial states. The precondition then is the constraint corresponding to the complement of that set, under-approximating the set of safe initial states. This idea of complementation is not new, but previous attempts to exploit it have suffered from the loss of precision. Here we develop an iterative specialisation algorithm to give more precise, and in some cases optimal safety conditions. The algorithm combines existing transformations, namely constraint specialisation, partial evaluation and a trace elimination transformation. The last two of these transformations perform polyvariant specialisation, leading to disjunctive constraints which improve precision. The algorithm is implemented and tested on a benchmark suite of programs from the literature in precondition inference and software verification competitions.
Original languageEnglish
JournalTheory and Practice of Logic Programming
Issue number3-4
Pages (from-to)553-570
Publication statusPublished - Jul 2018
Event34th International Conference on Logic Programming - Oxford, United Kingdom
Duration: 14 Jul 201817 Jul 2018


Conference34th International Conference on Logic Programming
Country/TerritoryUnited Kingdom
Internet address


  • Logic programming
  • program analysis
  • program transformation
  • Program verification
  • precondition analysis

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