Iteratively parse nested parentheses in PrattParser - #1245
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Replace the lookahead-based grouping parentheses counter (`countGroupingParentheses`) with a bottom-up iterative approach in `PrattParser.parsePrimary()` to eliminate quadratic $O(N^2)$ lookahead scans while keeping $O(1)$ call-stack frames on deeply nested parenthesized expressions. ### Benchmarks (`CelParserBenchmark`, `-c opt`, `parserType=PRATT`, `parseOnly`) | Benchmark Case | Before (Mean) | After (Mean) | Change / Speedup | | :--- | ---: | ---: | ---: | | `NESTED_PARENS` (N=200) | 8,528.69 ns | 5,119.12 ns | -40.0% (1.67x faster) | | `NESTED_LEFT_PARENS_CALC` (N=200) | 951,027.39 ns | 27,998.44 ns | -97.1% (34.0x faster) | | Benchmark Case (Allocations) | Before (Bytes / Objs) | After (Bytes / Objs) | Change | | :--- | ---: | ---: | ---: | | `NESTED_PARENS` (N=200) | 29,200 B / 855 objs | 16,336 B / 453 objs | -44.1% B / -47.0% objs | | `NESTED_LEFT_PARENS_CALC` (N=200) | ~2,690,000 B / ~84,500 objs | 127,016 B / 4,577 objs | -95.3% B / -94.6% objs | PiperOrigin-RevId: 984184714
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Iteratively parse nested parentheses in PrattParser
Replace the lookahead-based grouping parentheses counter ($O(N^2)$ lookahead scans while keeping $O(1)$ call-stack frames on deeply nested parenthesized expressions.
countGroupingParentheses) with a bottom-up iterative approach inPrattParser.parsePrimary()to eliminate quadraticBenchmarks (
CelParserBenchmark,-c opt,parserType=PRATT,parseOnly)NESTED_PARENS(N=200)NESTED_LEFT_PARENS_CALC(N=200)NESTED_PARENS(N=200)NESTED_LEFT_PARENS_CALC(N=200)