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Experiment: Enable SLP vectorizer for faster codegen#73957

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rschu1ze:faster-codegen
Dec 30, 2024
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Experiment: Enable SLP vectorizer for faster codegen#73957
rschu1ze merged 2 commits intoClickHouse:masterfrom
rschu1ze:faster-codegen

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@rschu1ze rschu1ze commented Dec 29, 2024

After the recent upgrades to LLVM 16 and 18, folks started to complain about slower codegen: #66053 (comment)

Prior to the LLVM 16 upgrade, CHJIT force-enabled the SLP vectorizer (see https://github.com/ClickHouse/ClickHouse/pull/69654/files#diff-897102eb40b3e08e4997b80459a83b97ac7d555e4534942cd30581e4f92cefe2). This PR now does the same using the new LLVM pass manager. Let's see if it helps with performance.

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@rschu1ze rschu1ze mentioned this pull request Dec 29, 2024
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@robot-clickhouse robot-clickhouse added the pr-not-for-changelog This PR should not be mentioned in the changelog label Dec 29, 2024
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robot-ch-test-poll2 commented Dec 29, 2024 •
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This is an automated comment for commit f6ba191 with description of existing statuses. It's updated for the latest CI running

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@alexey-milovidov alexey-milovidov self-assigned this Dec 29, 2024
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rschu1ze commented Dec 30, 2024

--> 1.5x speedup for JIT tests: https://s3.amazonaws.com/clickhouse-test-reports/73957/f6ba19106d95a512ab68df9a9a2850eeea506887/performance_comparison__release__[2_4]/report.html

@rschu1ze rschu1ze added this pull request to the merge queue Dec 30, 2024
Merged via the queue into ClickHouse:master with commit e89364b Dec 30, 2024
@rschu1ze rschu1ze deleted the faster-codegen branch December 30, 2024 13:27
@robot-ch-test-poll robot-ch-test-poll added the pr-synced-to-cloud The PR is synced to the cloud repo label Dec 30, 2024
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zhanglistar commented Jan 2, 2025

--> 1.5x speedup for JIT tests: https://s3.amazonaws.com/clickhouse-test-reports/73957/f6ba19106d95a512ab68df9a9a2850eeea506887/performance_comparison__release__[2_4]/report.html

https://s3.amazonaws.com/clickhouse-test-reports/66053/b0941e6a7967c1f410e473a98101a76532c9e00c/performance_comparison__release__%5B2_4%5D/report.html
Still ~20% slower?

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rschu1ze commented Jan 2, 2025

Yes that's still 20% slower than before LLVM 16 but nobody said that this PR was going to fix all performance issues 😄

The most reasonable explanation for the slowdown is the transition to the new pass manager: https://github.com/ClickHouse/ClickHouse/pull/69654/files#diff-897102eb40b3e08e4997b80459a83b97ac7d555e4534942cd30581e4f92cefe2

The missing SLP vectorizer enablement (this PR) was obvious but I couldn't find equivalents for

    pass_manager_builder.LoopVectorize = true;
    pass_manager_builder.RerollLoops = true;

in the new infrastructure. But I am not an expert in this, the code is actually copy-paste from https://llvm.org/docs/NewPassManager.html.

Further thoughts and inputs highly welcome ...

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