Olivier Giroux

Detecting increases in feature coupling using regression tests

Repeated changes to a software system can introduce small weaknesses such as unplanned dependencies between different parts of the system. While such problems usually go undetected, their cumulative effect can result in a noticeable decrease in the quality of a system. We present an approach to warn developers about increased coupling between the (potentially scattered) implementation of different features. Our automated approach can detect sections of the source code contributing to the increased coupling as soon as software changes are tested. Developers can then inspect the results to assess whether the quality of their changes is adequate. We have implemented our approach for C++ and integrated it with the development process of a proprietary 3D graphics software. We report on our evaluation of the approach in the field, and on a study showing that, for files in the target system, causing increases in feature coupling is a significant predictor of future modifications due to bug fixes.

Automated Synthesis of Comprehensive Memory Model Litmus Test Suites

The memory consistency model is a fundamental part of any shared memory architecture or programming model. Modern weak memory models are notoriously difficult to define and to implement correctly. Most real-world programming languages, compilers, and (micro)architectures therefore rely heavily on black-box testing methodologies. The success of such techniques requires that the suite of litmus tests used to perform the testing be comprehensive--it should ideally stress all obscure corner cases of the model and of its implementation. Most litmus test suites today are generated from some combination of manual effort and randomization; however, the complex and subtle nature of contemporary memory models means that manual effort is both error-prone and subject to incomplete coverage. This paper presents a methodology for synthesizing comprehensive litmus test suites directly from a memory model specification. By construction, these suites contain all tests satisfying a minimality criterion: that no synchronization mechanism in the test can be weakened without causing new behaviors to become observable. We formalize this notion using the Alloy modeling language, and we apply it to a number of existing and newly-proposed memory models. Our results show not only that this synthesis technique can automatically reproduce all manually-generated tests from existing suites, but also that it discovers new tests that are not as well studied.