[mypyc] Enable SIMD for librt.base64 on x86-64 #20244
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p-sawicki
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Nov 17, 2025
JukkaL
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…uild flags (#20253) Fixes the current SSE4.2 requirement added in 1b6ebb1 / #20244 This PR fully enables the existing x86-64 CPU detection and dispatch code for SSSE3, SSE4.1, SSE4.2, AVX, and AVX2 in the base64 module. To use the existing CPU dispatch from the [upstream base64 code](https://github.com/aklomp/base64), one needs to compile the sources in each of the CPU specific codec directories with a specific compiler flag; alas this is difficult to do with setuptools, but I found a solution inspired by https://stackoverflow.com/a/68508804 Note that I did not enable the AVX512 path with this PR, as many intel CPUs that support AVX512 can come with a performance hit if AVX512 is sporadically used; the performance of the AVX512 (encoding) path need to be evaluated in the context of how mypyc uses base64 in various realistic scenarios. (There is no AVX512 accelerated decoding path in the upstream base64 codebase, it falls back to the avx2 decoder). If there are additional performance concerns, then I suggest benchmarking with the openmp feature of base64 turned on, for multi-core processing.
p-sawicki
pushed a commit
that referenced
this pull request
Nov 28, 2025
…uild flags (#20253) Fixes the current SSE4.2 requirement added in 1b6ebb1 / #20244 This PR fully enables the existing x86-64 CPU detection and dispatch code for SSSE3, SSE4.1, SSE4.2, AVX, and AVX2 in the base64 module. To use the existing CPU dispatch from the [upstream base64 code](https://github.com/aklomp/base64), one needs to compile the sources in each of the CPU specific codec directories with a specific compiler flag; alas this is difficult to do with setuptools, but I found a solution inspired by https://stackoverflow.com/a/68508804 Note that I did not enable the AVX512 path with this PR, as many intel CPUs that support AVX512 can come with a performance hit if AVX512 is sporadically used; the performance of the AVX512 (encoding) path need to be evaluated in the context of how mypyc uses base64 in various realistic scenarios. (There is no AVX512 accelerated decoding path in the upstream base64 codebase, it falls back to the avx2 decoder). If there are additional performance concerns, then I suggest benchmarking with the openmp feature of base64 turned on, for multi-core processing.
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Also generally enable SSE4.2 instructions when targeting x86-64. These have been supported by hardware since ~2010, so it seems fine to require them now.
This speeds up
b64encodeby up to 100% on Linux running on a recent AMD CPU.Some fairly recent hardware doesn't support AVX2, so it's not enabled. We'd probably need to rely on hardware capability checking for AVX2 support, and we'd need compile different files with different architecture flags probably, and I didn't want to go there (at least not yet).