Fuse dense bitmap intersection output and popcount - #541
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Summary
Use a cardinality lower bound to identify bitmap intersections that cannot become array containers. On the AVX2 path, the new helper writes the AND result and accumulates its popcount in one traversal instead of counting the operands and then recomputing the AND. Intersections that may produce arrays retain the existing path, avoiding a sparse-result allocation tradeoff. Add a parallel dense-container benchmark for this path.
Performance
On workload
128-container dense parallel bitmap intersection, median metricns/opchanged from 526751 to 450119; paired median delta -96460 (-18.3% of baseline; at least 19/20 confidence interval -110167 to -32439 from 10 pairs).Testing
Ran the full Go test suite, appengine-tagged tests, the unconvert check, and an arm64 cross-compilation check. Added representation-boundary coverage and AVX2 differential tests for the fused helper.
All 4 declared correctness checks passed.
Full verification record: https://app.perfloop.ai/t/oss/case_qsx98z9dsk