remove element_unordered_atomic intrinsics #789
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tgross35
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Mar 18, 2025
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SGTM. It seems like these are emitted from https://llvm.org/docs/LangRef.html#element-wise-atomic-memory-intrinsics, but if we aren't using that and C++ also has no way to represent these operations, doesn't seem likely that anybody can actually be expecting them to be available.
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Includes the following changes related to unordered atomics: * Remove element_unordered_atomic intrinsics [1] * Remove use of `atomic_load_unordered` and undefined behaviour [2] There are a handful of other small changes, but nothing else user-visible. [1]: rust-lang/compiler-builtins#789 [2]: rust-lang/compiler-builtins#790
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It is not clear how these "unordered" operations are supposed to fit the memory model. The intrinsics used here are labeled with "DO NOT USE" in the docs. The plan in rust-lang/rfcs#3301 and for C++, as I understand it, is to have "bytewise atomic memcpy" with the usual orderings: SeqCst, Release, Acquire, Relaxed. These "unordered" intrinsics seem to be a dead end.
These intrinsics are also unused as far as I can tell; rust-lang/rust#59155 which planned to use them never landed.
Part of #788.