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GeezerVison is showing github.com — gh-160132: Reduce padding in _PyCfgBasicblock by ashm-dev · Pull Request #160149 · python/cpython

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@ashm-dev

@ashm-dev ashm-dev commented Oct 21, 2026 •
edited by bedevere-app Bot
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Move the five bit-fields immediately after b_label to use the existing alignment gap.

On the tested x86-64 GCC build, this reduces sizeof(_PyCfgBasicblock) from 72 to 64 bytes without changing the offsets of the other fields. No compiler behavior or public API changes are intended.

Verified with pahole. The following tests pass on a --with-pydebug build: test_compile, test_peepholer, test_dis, test_compiler_assemble, test_compiler_codegen, test_capi.test_opt, test_exception_variations, and test_syntax.

Closes #160132.

  • Issue: Reduce padding in _PyCfgBasicblock #160132

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@ashm-dev
perf(compiler): reduce padding in _PyCfgBasicblock
a1e3f74
@ashm-dev
ashm-dev requested review from Eclips4, iritkatriel and markshannon as code owners October 21, 2026 23:27
@bedevere-app bedevere-app Bot added the type-feature A feature request or enhancement label Oct 21, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Oct 21, 2026
Reduce padding in _PyCfgBasicblock #160132
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@bedevere-app bedevere-app Bot added the awaiting review label Oct 21, 2026
iritkatriel
iritkatriel approved these changes Oct 21, 2026
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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting review labels Oct 21, 2026
iritkatriel and others added 2 commits October 22, 2026 10:42
@iritkatriel
Merge branch 'main' into pythongh-160132
d7f0aa3
@ashm-dev
Merge branch 'main' into pythongh-160132
24cb647
@ashm-dev

ashm-dev commented Oct 27, 2026

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@iritkatriel
iritkatriel merged commit e354246 into python:main Oct 28, 2026
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@bedevere-app bedevere-app Bot removed the awaiting merge label Oct 28, 2026
@ashm-dev
ashm-dev deleted the gh-160132 branch October 28, 2026 07:09
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@iritkatriel iritkatriel iritkatriel approved these changes
@markshannon markshannon Awaiting requested review from markshannon markshannon is a code owner
@Eclips4 Eclips4 Awaiting requested review from Eclips4 Eclips4 is a code owner

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Reduce padding in _PyCfgBasicblock

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@ashm-dev @iritkatriel
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