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GeezerVison is showing github.com — gh-153568: Skip parser memo lookups that cannot match by pablogsal · Pull Request #153571 · python/cpython

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@pablogsal

@pablogsal pablogsal commented Jul 11, 2026 •
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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):

build time per run speedup
main 1.82 s
this PR 1.72 s 1.06x faster

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@pablogsal
pablogsal requested review from FFY00, brettcannon, ericsnowcurrently, lysnikolaou, ncoghlan and warsaw as code owners July 11, 2026 13:57
@bedevere-app bedevere-app Bot mentioned this pull request Jul 11, 2026
Speed up the parser #153568
Open
@bedevere-app bedevere-app Bot added the awaiting core review label Jul 11, 2026
@pablogsal
pythongh-153568: Skip parser memo lookups that cannot match
a638dad 
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.
@pablogsal
pablogsal force-pushed the gh-153568-memo-filter branch from f6d8abf to a638dad Compare July 11, 2026 13:58
@pablogsal pablogsal mentioned this pull request Jul 11, 2026
gh-153568: Stop re-walking memo lists when growing left-recursive rules #153574
Merged
@brettcannon
brettcannon removed their request for review July 13, 2026 17:16
@pablogsal
pablogsal merged commit d49e76b into python:main Jul 18, 2026
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@pablogsal
pablogsal deleted the gh-153568-memo-filter branch July 18, 2026 16:12
@bedevere-app bedevere-app Bot removed the awaiting core review label Jul 18, 2026
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@lysnikolaou lysnikolaou Awaiting requested review from lysnikolaou lysnikolaou is a code owner
@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently
@ncoghlan ncoghlan Awaiting requested review from ncoghlan
@warsaw warsaw Awaiting requested review from warsaw
@FFY00 FFY00 Awaiting requested review from FFY00

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@pablogsal
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