Being able to automatically repair programs is at the same time a very compelling vision and an extremely challenging task. In this paper, we present MintHint, a novel technique for program repair that is a departure from most of today's approaches. Instead of trying to fully automate program repair, which is often an unachievable goal, MintHint performs statistical correlation analysis to identify expressions that are likely to occur in the repaired code and generates, using pattern-matching based synthesis, repair hints from these expressions. Intuitively, these hints suggest how to rectify a faulty statement and help developers find a complete, actual repair. MintHint can address a variety of common faults, including incorrect, spurious, and even missing expressions.We also present an empirical evaluation of MintHint that consists of two main parts. The first part is a user study that shows that, when debugging, developers' productivity can improve manyfold with the use of repair hints-compared to having only traditional fault localization information. The second part consists of applying MintHint to several faults of a widely used Unix utility program to further assess the effectiveness of the approach. Our results show that MintHint performs well even in situations, seen frequently in practice, where (1) the repair space searched does not contain the exact repair, and (2) the operational specification obtained from the test cases for repair is incomplete or even imprecise-which can be challenging for approaches aiming at fully automated repair.

With the growing complexity of modern day software, software model checking has become a critical technology for ensuring correctness of software. As is true with any promising technology, there are a number of tools for software model checking. However, their respective performance trade-offs are difficult to characterize accurately -making it difficult for practitioners to select a suitable tool for the task at hand. This paper proposes a technique called MUX that addresses the problem of selecting the most suitable software model checker for a given input instance. MUX performs machine learning on a repository of software verification instances. The algorithm selector, synthesized through machine learning, uses structural features from an input instance, comprising a program-property pair, at runtime and determines which tool to use.We have implemented MUX for Windows device drivers and evaluated it on a number of drivers and model checkers. Our results are promising in that the algorithm selector not only avoids a significant number of timeouts but also improves the total runtime by a large margin, compared to any individual model checker. It also outperforms a portfolio-based algorithm selector being used in Microsoft at present. Besides, MUX identifies structural features of programs that are key factors in determining performance of model checkers.

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