perf: defer Position alloc in exprSuffix2 to the matching branch#877
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perf: defer Position alloc in exprSuffix2 to the matching branch#877He-Pin wants to merge 1 commit into
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Motivation:
exprSuffix2 was `Pos.flatMapX { i => CharIn(".[({")... }`, which allocated a
Position on EVERY attempt — including the failing attempt that terminates
`exprSuffix2.rep` after each expression. Most subexpressions have no suffix, so
that trailing failed attempt (one per expression) allocated a Position that was
immediately discarded.
Modification:
- Match the suffix char first; allocate `new Position(fileScope, ctx.index - 1)`
only inside the matching branch. No suffix -> CharIn fails fast, no Position.
Also drops the `.map(_(0))` Char step. Parse output (positions/errors) is
unchanged.
Result:
JMH ParserBenchmark (-f0, same-session): 1.560 -> 1.530 ms/op (+1.9%). Native
parse_time on kube-prometheus: non-regressing, min/p25 ~2% lower (noise-limited
on a loaded machine). Output byte-identical. 517/517 tests pass.
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Motivation
exprSuffix2wasPos.flatMapX { i => CharIn(".[({") ... }, which allocated aPositionon every attempt — including the failing attempt that terminatesexprSuffix2.repafter each expression. Most subexpressions have no suffix, so that trailing failed attempt allocates aPositionthat is immediately discarded.Modification
new Position(fileScope, ctx.index - 1)only inside the matching branch. No suffix →CharInfails fast, noPosition. Also drops the intermediate.map(_(0))step. Parse output (positions / error offsets) is unchanged.Result
ParserBenchmark(JVM, over the test suite): 1.560 → 1.530 ms/op (+1.9%, non-overlapping bands).--debug-stats parse_timeon kube-prometheus (interleaved, cooled): neutral-to-slightly-faster (min 89.1 vs 95.9 ms; mean 107.7 vs 110.0 ms — within noise on this loaded run, no regression).Test plan
./mill __.reformat./mill 'sjsonnet.jvm[3.3.7]'.test— 518/518 pass