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…m on Every parse registered each node it might later reuse in a dictionary keyed by node identity, which is a hash insertion per node. Only an incremental reparse reads those ranges, and it reads them from the result of the parse before it, so a parse whose ranges nobody will receive is doing the work for nothing — which is every `Parser.parse(source:)`. `Parser` now takes `collectsLookaheadRanges`. The `parseIncrementally` entry points, which return the ranges to the caller, pass true; the ones that return only a tree leave it false. A parse given a `parseTransition` records regardless of what the caller asked, because the ranges it hands on are what the reparse after it decides reuse from, and a node with no recorded range is not reused at all — so a caller driving `Parser` directly would otherwise lose reuse for everything that parse produced, silently and with no diagnostic. `testLookaheadRangesAreRecordedForAnIncrementalParseWithoutAsking` pins that: it fails with the gate on the argument alone, reporting that nothing was reusable. A parse that does collect reserves the table against the byte count first, since a node is registered roughly every 90 bytes of source and the table would otherwise grow and rehash through the parse. Reserving is skipped for an incremental parse, whose table is replaced by the one it inherits.
rintaro
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September 18, 2026 18:11
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@swift-ci Please test |
rintaro
marked this pull request as draft
September 22, 2026 05:42
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Every parse used to register each node that might later be reused in a dictionary keyed by node identity, which is a hash insertion per node. In
Parser.parse(source:), nothing reads the dictionary and it was wasted.Parsernow takescollectsLookaheadRanges. TheparseIncrementallyentry points, which return the ranges, pass true; the entry points that return only a tree leave it false. A parse given aparseTransitionrecords regardless of what the caller asked, because what it hands on is what the next reparse decides reuse from, andIncrementalParseLookupwill not reuse a node it has no range for — so a caller drivingParserdirectly would otherwise lose reuse for everything that parse produced, with a correct tree and no diagnostic to show for it.A parse that does collect reserves the table against the source's byte count first, since a node is registered roughly every 90 bytes and the table would otherwise grow and rehash through the parse; an incremental parse skips the reserve, because the table it inherits replaces it.
Measured against
main(1f995c7), 2.5-2.9% instruction reduction, but 0.1% for deliberately corrupted sample source, which spends its parse recovering rather than registering nodes.One behavior change:
Parser.lookaheadRangesispublic internal(set), and a caller drivingParserdirectly for a full parse now finds it empty unless it passescollectsLookaheadRanges: true. An incremental parse is not affected.