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GeezerVison is showing github.com — gh-153568: Make the parser's per-rule stack check an inline comparison by pablogsal · Pull Request #153573 · python/cpython

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@pablogsal

@pablogsal pablogsal commented Jul 11, 2026 •
edited by bedevere-app Bot
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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):

build time per run speedup
main 1.86 s
this PR 1.65 s 1.13x faster
  • Issue: Speed up the parser #153568

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@pablogsal
pablogsal requested a review from lysnikolaou as a code owner July 11, 2026 13:58
@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
maurycy
maurycy reviewed Jul 17, 2026
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Comment thread Parser/pegen.c Resolved

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@pablogsal pablogsal mentioned this pull request Sep 13, 2026
gh-153568: Parse arithmetic with operator loops #157413
Open
eendebakpt
eendebakpt reviewed Sep 14, 2026
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Comment thread Parser/pegen.c Resolved

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Comment thread Parser/pegen.h Resolved

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pablogsal and others added 3 commits September 14, 2026 16:31
@pablogsal
pythongh-153568: Make the parser's per-rule stack check an inline com…
e0b6d7d 
…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.
@pablogsal
fixup! pythongh-153568: Make the parser's per-rule stack check an inl…
b78ead8 
…ine comparison
@pablogsal
fixup! pythongh-153568: Make the parser's per-rule stack check an inl…
fad63c3 
…ine comparison
@pablogsal
pablogsal force-pushed the gh-153568-stack-check branch from f684750 to fad63c3 Compare September 14, 2026 15:34
@pablogsal
pablogsal enabled auto-merge (squash) September 14, 2026 15:41
@pablogsal
pablogsal merged commit f88d668 into python:main Sep 14, 2026
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@pablogsal
pablogsal deleted the gh-153568-stack-check branch September 14, 2026 16:09
@bedevere-app bedevere-app Bot removed the awaiting core review label Sep 14, 2026
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@eendebakpt eendebakpt eendebakpt left review comments
@lysnikolaou lysnikolaou Awaiting requested review from lysnikolaou lysnikolaou is a code owner
+1 more reviewer
@maurycy maurycy maurycy left review comments
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3 participants

@pablogsal @maurycy @eendebakpt
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