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 SIMD — r/cpp
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Record
| Original publisher | Chaitanya Kumar's Blog |
| Canonical URL | https://loonatick-src.github.io/posts/vectorized-copy-if-analysis/ |
| Publication time | Tue, 26 May 2026 06:14:02 +0000 |
| Retrieval time | 2026-05-26T06:37:45.433Z |
| Last seen | 2026-05-26T06:37:45.433Z |
| Headline source | Publisher (no WeSearch rewrite) |
| Excerpt source | publisher body |
| Excerpt method | First ~120 words (~800 chars) of extracted publisher body, fair-use limited. |
| Summary | WeSearch · cerebras-chat (WeSearch summarizer) |
| Summary source text | contentText |
| Citation coverage | Summary is a WeSearch-generated derivative; primary citation is the original publisher URL. |
| Cluster | lIxvzW83Hikr · 2 stories |
| Cluster logic | Grouped by semantic title/content similarity across sources within a rolling window. Same-publisher template collisions are excluded from coverage comparison. |
| Ranking reason | Story pages are not engagement-ranked. Hub feeds use recency, with optional source-diversified chronological ordering (cap consecutive stories per source). No personalized ranking. |
| Publisher visit | Yes — open original |
| Substitutes article? | No — link-out required for full text |
Rights status (four layers)
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| Indexing | May the item be indexed (stored, ranked, made findable)? | Allowed |
| Snippet | May a short excerpt of the publisher's text be shown? | Allowed |
| AI summary | May WeSearch generate its own short summary of the article? | Limited |
| Retrieval / RAG | May the content be exposed for third-party retrieval-augmented generation? | Not asserted |
| Model training | May the content be used to train AI models? | Not asserted |
| Commercial reuse | May the content be reused commercially? | Not permitted |
Basis: Derived from the published RSS/Atom feed. Contact: [email protected]. Reviewed: 2026-07-24.
Opening excerpt (first ~120 words) tap to expand
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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