DO NOT MERGE — reduce-acc SROA regresses (defeats vec-reduce)

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Reduce-accumulator scalar replacement: lower (reduce (fn [acc x] body) (->Rec
inits) coll) with a non-escaping record accumulator to a loop carrying the acc
fields as scalar vars. Correct (run-reduce-sroa.ss 7/7, make test + shakesmoke
green) but a PERF REGRESSION: ray tracer hit-all 38.4s -> ~53s.

Root cause: jolt's reduce already iterates a vector with vec-reduce (seq.ss) — a
tight index loop over the backing store, zero per-element allocation. Lowering to
a (seq)/(first)/(next) loop allocates a seq node per element, trading hit-all's
CONDITIONAL ->HitAcc allocation for a per-element seq allocation. The targeted
accumulator allocation is also conditional (only on hit improvement), not the
dominant per-sphere cost. Kept on this branch for reference; not merged.

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Yogthos 2026-06-26 11:28:34 -04:00

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