Landing: deb5f74feeaf

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Project / Subsystem

gcc / c-family

Date

2026-07-14

Author

Jakub Jelinek

Commit

deb5f74feeaf3a43f6d4008a1e01fc4d23c1efdf

Source

github

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project: gcc
subsystem: c-family
patch_id: —
commit_hash: deb5f74feeaf3a43f6d4008a1e01fc4d23c1efdf
source_type: github
headline: c-family: Use CAS loop for small _BitInt atomics with padding.
tldr: Uses CAS loop instead of RMW atomics for small _BitInt types with padding on certain architectures.
author: Jakub Jelinek
outcome: committed
performance_win: false
breaking_change: false
series_id: —
series_parts: []
tags: • c
• c++
• atomic
• bitint
• bugfix
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/deb5f74feeaf3a43f6d4008a1e01fc4d23c1efdf
date: 2026-07-14T00:00:00.000Z

For small _BitInt types with padding, some atomic/sync builtins that operate on TYPE * arguments do not correctly sign or zero-extend the values. This commit changes the implementation to use a Compare-And-Swap (CAS) loop instead of Read-Modify-Write (RMW) atomics for these specific cases. This ensures correct behavior when the target architecture requires extension into the padding bits, addressing PR124948.