Fix use-of-uninitialized-value in SVE accumulator operations#18
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alexey-milovidov merged 1 commit intoClickHouse/v6.5.15from Mar 30, 2026
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Use `_m` (merge) instead of `_x` (don't-care) for SVE multiply-accumulate operations on accumulator vectors. The `_x` variant leaves inactive lanes undefined, but the final `svaddv` with `svptrue` sums all lanes including those undefined ones, causing MemorySanitizer to report use-of-uninitialized-value when vector length is not a multiple of the SVE register width. The `_m` variant preserves the accumulator value for inactive lanes, keeping them at their initialized zero. Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
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Maybe we need to update library instead? |
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Summary
Use
_m(merge) instead of_x(don't-care) for SVE multiply-accumulate operations (svmla,svmls) on accumulator vectors inspatial.handdot.h.The
_xvariant leaves inactive lanes undefined, but the finalsvaddvwithsvptruesums all lanes — including those undefined ones. This causes MemorySanitizer to report use-of-uninitialized-value when the input vector length is not a multiple of the SVE register width. The_mvariant preserves the accumulator value for inactive lanes, keeping them at their initialized zero.Detected as
MemorySanitizer: use-of-uninitialized-value(STID: 1003-358c) insimsimd_cos_f32_sveduring ClickHouse CI stress tests on ARM with MSan: https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=100177&sha=a7031a78dd031fc0e90fbeebc0c95df386c5c1a7&name_0=PR&name_1=Stress%20test%20%28arm_msan%29Tracked as ClickHouse/ClickHouse#101232