gh-153568: Make the parser's per-rule stack check an inline comparison - #153573
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maurycy
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eendebakpt
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Sep 14, 2026
…parison The parser now caches the thread state and stack limit up front and only falls back to the full check when the stack is nearly exhausted.
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Every rule entry paid a thread-state fetch plus an out-of-line call just to ask whether the C stack is about to overflow. Caching the thread state and soft stack limit in the parser turns that into one inline pointer comparison, and the overflow guard still fires exactly as before.
Benchmark (parsing 8 of the largest stdlib files, 1.3 MB, 20 times per run with
_PyParser_ASTFromString— parser only, no AST-to-Python conversion; pyperf, interleaved runs):