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gh-160247: Reduce padding in _PyInstructionSequence - #160271

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ashm-dev:gh-160247

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@ashm-dev ashm-dev commented Oct 22, 2026 •

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Move s_labelmap_size immediately before s_labelmap to eliminate the two alignment gaps in _PyInstructionSequence.

On the tested x86-64 GCC build, this reduces sizeof(_PyInstructionSequence) from 72 to 64 bytes without changing any field types. No compiler behavior or public API changes are intended.

Verified with a C layout check and the rebuilt interpreter. The following tests pass on a --with-pydebug build: test_compile, test_compiler_assemble, test_compiler_codegen, test_dis, test_peepholer, test_type_annotations, and test_grammar.

Closes #160247.

@bedevere-app bedevere-app Bot added the type-feature A feature request or enhancement label Oct 22, 2026
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Friendly ping

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Reduce padding in the instruction sequence structure

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