gh-153568: Skip parser memo lookups that cannot match - #153571
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pablogsal
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warsaw
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July 11, 2026 13:57
Each token now carries a small filter of the rule types present in its memo list, so the common case of a miss no longer walks the list.
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Most memoization probes miss, and each one walked a linked list through arena memory to find out. A per-token filter of the memoized rule types answers definite misses with a single bit test.
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):