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author | Noah Goldstein <goldstein.w.n@gmail.com> | 2022-04-15 12:28:00 -0500 |
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committer | Noah Goldstein <goldstein.w.n@gmail.com> | 2022-04-15 13:08:42 -0500 |
commit | 7cbc03d03091d5664060924789afe46d30a5477e (patch) | |
tree | 470f2da631bec6a058a5e4e53680106efdd1abbd /sysdeps/x86_64/dl-procinfo.c | |
parent | 8804157ad9da39631703b92315460808eac86b0c (diff) | |
download | glibc-7cbc03d03091d5664060924789afe46d30a5477e.tar.gz glibc-7cbc03d03091d5664060924789afe46d30a5477e.tar.xz glibc-7cbc03d03091d5664060924789afe46d30a5477e.zip |
x86: Remove memcmp-sse4.S
Code didn't actually use any sse4 instructions since `ptest` was removed in: commit 2f9062d7171850451e6044ef78d91ff8c017b9c0 Author: Noah Goldstein <goldstein.w.n@gmail.com> Date: Wed Nov 10 16:18:56 2021 -0600 x86: Shrink memcmp-sse4.S code size The new memcmp-sse2 implementation is also faster. geometric_mean(N=20) of page cross cases SSE2 / SSE4: 0.905 Note there are two regressions preferring SSE2 for Size = 1 and Size = 65. Size = 1: size, align0, align1, ret, New Time/Old Time 1, 1, 1, 0, 1.2 1, 1, 1, 1, 1.197 1, 1, 1, -1, 1.2 This is intentional. Size == 1 is significantly less hot based on profiles of GCC11 and Python3 than sizes [4, 8] (which is made hotter). Python3 Size = 1 -> 13.64% Python3 Size = [4, 8] -> 60.92% GCC11 Size = 1 -> 1.29% GCC11 Size = [4, 8] -> 33.86% size, align0, align1, ret, New Time/Old Time 4, 4, 4, 0, 0.622 4, 4, 4, 1, 0.797 4, 4, 4, -1, 0.805 5, 5, 5, 0, 0.623 5, 5, 5, 1, 0.777 5, 5, 5, -1, 0.802 6, 6, 6, 0, 0.625 6, 6, 6, 1, 0.813 6, 6, 6, -1, 0.788 7, 7, 7, 0, 0.625 7, 7, 7, 1, 0.799 7, 7, 7, -1, 0.795 8, 8, 8, 0, 0.625 8, 8, 8, 1, 0.848 8, 8, 8, -1, 0.914 9, 9, 9, 0, 0.625 Size = 65: size, align0, align1, ret, New Time/Old Time 65, 0, 0, 0, 1.103 65, 0, 0, 1, 1.216 65, 0, 0, -1, 1.227 65, 65, 0, 0, 1.091 65, 0, 65, 1, 1.19 65, 65, 65, -1, 1.215 This is because A) the checks in range [65, 96] are now unrolled 2x and B) because smaller values <= 16 are now given a hotter path. By contrast the SSE4 version has a branch for Size = 80. The unrolled version has get better performance for returns which need both comparisons. size, align0, align1, ret, New Time/Old Time 128, 4, 8, 0, 0.858 128, 4, 8, 1, 0.879 128, 4, 8, -1, 0.888 As well, out of microbenchmark environments that are not full predictable the branch will have a real-cost. Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Diffstat (limited to 'sysdeps/x86_64/dl-procinfo.c')
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