Improve VectorUtil::xorBitCount perf on ARM #13545
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jimczi
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Jul 8, 2024
ChrisHegarty
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Jul 8, 2024
This commit improves the performance of VectorUtil::xorBitCount on ARM by ~4x. This change is effectively a workaround for the lack of vectorization of Long::bitCount on ARM. On x64 there is no issue, the long variant of xorBitCount outperforms the int variant by ~15%.
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Hi, |
uschindler
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Jul 8, 2024
| * For xorBitCount we stride over the values as either 64-bits (long) or 32-bits (int) at a time. | ||
| * On ARM Long::bitCount is not vectorized, and therefore produces less than optimal code, when | ||
| * compared to Integer::bitCount. While Long::bitCount is optimal on x64. TODO: include the | ||
| * OpenJDK JIRA url |
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Oops. I just added it in 4baaeda
asfgit
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I reverted the addition of the file to 9.x branch: 86d080a |
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@uschindler Apologies, I didn't notice this when cherrypicking. Thanks for reverting (while I was sleeping ;-) ) |
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This commit improves the performance of
VectorUtil::xorBitCounton ARM by ~4x.This change is effectively a workaround for the lack of vectorization of
Long::bitCounton ARM, see https://github.com/ChrisHegarty/hammingBench/. I'll get an issue filed against Hotspot for this. ( JDK bug tracking this issue: https://bugs.openjdk.org/browse/JDK-8336000 )On x64 there is no issue, the long variant of xorBitCount outperforms the int variant by ~15%.
Before (measures throughput in seconds, so bigger numbers are better)
After