Dynamic data race detectors are successful at flagging concurrency bugs, but their high runtime overhead limits adoption. This overhead stems primarily from pervasive instrumentation of memory accesses -- a significant fraction of which is for safe accesses. We address this inefficiency through a compiler-integrated approach that identifies safe accesses using static analysis and eliminates instrumentation for these. We strike a careful balance between analysis precision and cost, to ensure applicability to real-world applications. We show that our optimizations never cause ThreadSanitizer to miss races it would otherwise detect. We further observe that many checks are redundant: They only flag a race if a preceding check has already flagged an equivalent race for the same memory location. We show that, when reporting one representative per class is sufficient, even more instrumentation can be eliminated. Lastly, we introduce a dynamic technique that skips instrumentation when there is only one thread at runtime, even when this could not be determined statically. We integrate these static analyses and program transformations into the ThreadSanitizer race detector based on LLVM. Our experiments on a diverse suite of real-world applications, including Memcached, Redis, SQLite, MySQL, and Chromium, demonstrate that our optimizations reduce the number of instrumentation calls at runtime by up to 91% and yield application-level speedups of up to 1.91x, a geometric-mean Chromium speedup of 1.25x on Blink and 1.14x on Speedometer 3.0, and peak speedups reaching 2.28x on Memcached with two server threads. Our optimizations are in the process of being upstreamed into ThreadSanitizer.

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