Abstract. Precise dynamic race detectors report an error if and only if an observed program trace exhibits a data race. They must typically check for races on all memory accesses to ensure that they catch all races and generate no spurious warnings. However, a race check for a particular memory access is guaranteed to be redundant if the accessing thread has already accessed that location within the same release-free span. A release-free span is any sequence of instructions containing no lock releases or other “release-like ” synchronization operations, such as notify or fork. We present a static analysis to identify redundant race checks by reasoning about memory accesses within release-free spans. In contrast to prior whole program analyses for identifying accesses that are always race-free, our redundant check analysis is span-local and can also be made methodlocal without any major loss in effectiveness. RedCard, our prototype implementation for the Java language, enables dynamic race detectors to reduce the number of run-time checks by close to 40 % with no loss in precision. We also present a complementary shadow proxy analysis for identifying when multiple memory locations can be treated as a single location by a dynamic race detector, again with no loss in precision. Combined, our analyses reduce the number of memory accesses requiring checks by roughly 50%.
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