Use modern __atomic builtins in atomic.c #111
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Replace legacy __sync_fetch_and_* builtins with their modern __atomic_fetch_* equivalents. This simplifies the code significantly, particularly for the nand operation which previously required extensive workarounds for compiler compatibility issues.
Changes:
- Replace __sync_fetch_and_{add,sub,and,or,xor} with __atomic_fetch_*
- Replace __sync_fetch_and_nand with __atomic_fetch_nand
- Remove CAS-based fallback for nand operations
- Remove compiler-specific warning suppressions for -Wsync-nand
- Remove volatile qualifiers (not needed with __atomic builtins)
- Update comments to reflect modern atomics usage
All operations maintain __ATOMIC_SEQ_CST memory ordering for sequential consistency, matching the original behavior.
hsyl20
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Nov 12, 2025
hsyl20
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LGTM. We should upstream this if it works on all supported platforms.
I was put off by the Note [__sync_fetch_and_nand usage] but I think the note is wrong (see inline comment).
| #pragma GCC diagnostic ignored "-Wsync-nand" | ||
| #endif | ||
| // The modern __atomic_fetch_nand has well-defined semantics: | ||
| // it atomically replaces *ptr with ~(*ptr & val) and returns the old value. |
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Isn't the original note bogus? I think it has the semantics change reversed, no?
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Replace legacy _sync_fetch_and* builtins with their modern _atomic_fetch* equivalents. This simplifies the code significantly, particularly for the nand operation which previously required extensive workarounds for compiler compatibility issues.
Changes:
Replace _sync_fetch_and{add,sub,and,or,xor} with _atomic_fetch*
Replace __sync_fetch_and_nand with __atomic_fetch_nand
Remove CAS-based fallback for nand operations
Remove compiler-specific warning suppressions for -Wsync-nand
Remove volatile qualifiers (not needed with __atomic builtins)
Update comments to reflect modern atomics usage
All operations maintain __ATOMIC_SEQ_CST memory ordering for sequential consistency, matching the original behavior.