Accelerating Copy_if Using SIMD
The article discusses the implementation of the std::copy_if algorithm using SIMD on a Zen 4 CPU. It highlights the challenges faced in vectorizing the algorithm due to loop-carried dependencies and the performance analysis conducted to optimize it. Various performance measurement tools and methods are employed to evaluate the implementation's efficiency.
- ▪The author aimed to implement an algorithm that cannot be vectorized by an optimizing compiler.
- ▪The std::copy_if algorithm was chosen for its simplicity but posed challenges in vectorization due to dependencies.
- ▪Performance analysis was conducted using tools like Google benchmark and likwid-bench to measure the implementation's efficiency.
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Accelerating copy_if using SIMDMay 25, 2026Table of ContentsIntroductionFirst SIMD AttemptFirst Moment of (Bitter) TruthA Crash Course on CPU Microarchitecture and PMCsThe Top-Down Analysis using Performance CountersLevel 1Level 2Retiring MicrocodeProfiling with AMD IBSThe Fix and Final Moment of TruthWhat’s LeftConclusionAppendixBenchmark SetupSources of varianceDisabling SMTSetting Thread AffinityIncreasing scheduling priority of the benchmark threadPutting it all togetherllvm-mcaIntroduction#I have a Zen 4 CPU with a bunch of AVX512 feature flags. So I thought - let’s try and use it to implement something, even if it’s in the realm of wheel-reinvention.
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Excerpt limited to ~120 words for fair-use compliance. The full article is at Chaitanya Kumar's Blog.
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