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[Clang] Fix __cpuidex conflict with CUDA #152556

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Merged
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Aug 7, 2025
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[Clang] Fix __cpuidex conflict with CUDA #152556

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5 changes: 5 additions & 0 deletions clang/lib/Headers/cpuid.h
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Original file line number Diff line number Diff line change
Expand Up @@ -345,10 +345,15 @@ static __inline int __get_cpuid_count (unsigned int __leaf,
// In some configurations, __cpuidex is defined as a builtin (primarily
// -fms-extensions) which will conflict with the __cpuidex definition below.
#if !(__has_builtin(__cpuidex))
// In some cases, offloading will set the host as the aux triple and define the
// builtin. Given __has_builtin does not detect builtins on aux triples, we need
// to explicitly check for some offloading cases.
#ifndef __NVPTX__
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@sarnex sarnex Aug 7, 2025 •
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Thanks so much for the quick investigation!

I'm not really familiar with CUDA offloading but if the cc1 command is cc1 -triple nvptx64-nvidia-cuda -aux-triple x86_64-unknown-linux-gnu, __has_builtin(__cpuidex) returning false seems correct, so I would think the actual root cause is that cpuidex is getting defined for CUDA with -triple nvptx64-nvidia-cuda -aux-triple x86_64-unknown-linux-gnu.

If so, I'm happy to have this workaround for now but we might want to file a tracker somewhere for the root cause to be investigated.

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Good point. I've filed #152558 to track this.

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Awesome, thanks again!

static __inline void __cpuidex(int __cpu_info[4], int __leaf, int __subleaf) {
__cpuid_count(__leaf, __subleaf, __cpu_info[0], __cpu_info[1], __cpu_info[2],
__cpu_info[3]);
}
#endif
#endif

#endif /* __CPUID_H */
1 change: 1 addition & 0 deletions clang/test/Headers/__cpuidex_conflict.c
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Expand Up @@ -5,6 +5,7 @@

// Ensure that we do not run into conflicts when offloading.
// RUN: %clang_cc1 %s -DIS_STATIC=static -ffreestanding -fopenmp -fopenmp-is-target-device -aux-triple x86_64-unknown-linux-gnu
// RUN: %clang_cc1 -DIS_STATIC="" -triple nvptx64-nvidia-cuda -aux-triple x86_64-unknown-linux-gnu -aux-target-cpu x86-64 -fcuda-is-device -internal-isystem /home/gha/llvm-project/build/lib/clang/22/include -x cuda %s -o -

typedef __SIZE_TYPE__ size_t;

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