[libc++][atomic_ref] Use __atomic_fetch_{add,sub} builtins on floating-points whenever possible #135685
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…g-points whenever possible Fix llvm#135109 Clang is able to emit an `atomicrmw` instruction from the `__atomic_fetch_add` and `__atomic_fetch_sub` builtins on floating-point types.
kc9jud
reviewed
Apr 15, 2025
libcxx/include/__atomic/atomic_ref.h
Outdated
| @@ -322,20 +322,28 @@ struct atomic_ref<_Tp> : public __atomic_ref_base<_Tp> { | |||
| atomic_ref& operator=(const atomic_ref&) = delete; | |||
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| _LIBCPP_HIDE_FROM_ABI _Tp fetch_add(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept { | |||
| # ifdef _LIBCPP_COMPILER_CLANG_BASED | |||
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Does this need this fp80 workaround for #68602?
llvm-project/libcxx/include/__atomic/atomic.h
Lines 340 to 357 in d0c973a
huixie90
requested changes
Apr 18, 2025
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I would make atomic_ref and atomic share the similar logic (or just share the implantation) for these rmw operations. The reason why atomic has special branch for fp80 long double is that , the clang builtin that emit the llvm ir, has serious bug that affects all types whose data size is not power of 2. ( I think I have a patch but I never got a chance to finalise the tests. )
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Fix #135109
Clang is able to emit an
atomicrmwinstruction from the__atomic_fetch_addand__atomic_fetch_subbuiltins on floating-point types.