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Reserve room for a whole vector in VecWriter with simd - #387
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Hey @emschwartz 👋
Thanks for the contribution. However, you'll have to rebase over #385 👍
Have a nice week 🌵
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`visit_vector` appends all eight lanes and then truncates to the ones that matched, so a write near the end of the reserved space grows the Vec even though the output fits. Intersecting 500 values with a superset of 4000 reserves 500 and returns a Vec with capacity 1000, and `into_inner` does not shrink it. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Upstream made SIMD unconditional, so `#[cfg(feature = "simd")]` never matched and the extra capacity and its test were compiled out. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XGMzezWxjMNNrZCr1oDKCz
The vector algorithms only call `visit_vector` when both inputs hold a whole vector, so an output bound under 8 never needs the padding. Adding it anyway moves a 5-value result into a larger allocation size class, which made `ArrayStore -= &ArrayStore` on 5-value arrays take 105ns instead of 60ns. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XGMzezWxjMNNrZCr1oDKCz
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Stacked on #385: only the last commit is new.
With
simd,VecWriter::visit_vectorappends all eight lanes and then truncates to the ones that matched. A vector write within eight slots of the reserved capacity therefore grows the Vec even though the output fits, andinto_innerdoes not shrink it. Intersecting 500 values with a superset of 4000 reserves 500 and returns a Vec with capacity 1000.Reserving eight extra slots under
simdavoids the regrow. The added test fails without it. This is about memory, not speed: over 3 runs on the machines from #385, timings were within 1% of that PR.Authored with Claude (claude-opus-5-5).