<atomic>: clang-cl reports undeclared identifier '_InterlockedCompareExchange128_nf' for ARM64

[zufuliu]

Describe the bug
clang-cl (LLVM-11.0.0-win64.exe from https://github.com/llvm/llvm-project/releases/tag/llvmorg-11.0.0) reports undeclared identifier _InterlockedCompareExchange128_nf at atomic(484,12) for ARM64 with -std:c++latest, no errors with -std:c++17 or -std:c++14 or without C++ language standard option.

STL/stl/inc/atomic

Lines 483 to 485 in 19c683d

	#else // ^^^ _M_X64 / ARM64 vvv
	return _InterlockedCompareExchange128_nf(_Dest, _Tmp[1], _Tmp[0], _Tmp) != 0;
	#endif // ^^^ ARM64 ^^^

Command-line test case

C:\Temp>type repro.cpp
#include <atomic>

C:\Temp>clang-cl -c --target=aarch64-pc-windows-msvc .\repro.cpp

C:\Temp>clang-cl -c --target=aarch64-pc-windows-msvc -std:c++14 .\repro.cpp

C:\Temp>clang-cl -c --target=aarch64-pc-windows-msvc -std:c++17 .\repro.cpp

C:\Temp>clang-cl -c --target=aarch64-pc-windows-msvc -std:c++latest .\repro.cpp
In file included from .\repro.cpp:1:
D:\Program Files\Microsoft Visual Studio\2019\VC\Tools\MSVC\14.28.29333\include\atomic(484,12): error: use of undeclared identifier '_InterlockedCompareExchange128_nf'
    return _InterlockedCompareExchange128_nf(_Dest, _Tmp[1], _Tmp[0], _Tmp) != 0;
           ^
1 error generated.

Expected behavior
No errors like other architectures.

STL version
Visual Studio 2019 14.28.29333

Additional context
My failed GitHub Actions job Build with LLVM (Visual C++) for LLVMRelease configuration at
https://github.com/zufuliu/notepad2/runs/1424448830?check_suite_focus=true#step:7:7
It use LLVM_v142 toolchain from https://github.com/zufuliu/llvm-utils, also reproducible with LLVM (clang-cl) toolchain.

   In file included from ..\..\scintilla\src\AutoComplete.cxx:19:
  In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.28.29333\include\memory:18:
C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.28.29333\include\atomic(484,12): error : use of undeclared identifier '_InterlockedCompareExchange128_nf' [D:\a\notepad2\notepad2\build\VS2017\Notepad2.vcxproj]
C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.28.29333\include\atomic(484,12): error :     return _InterlockedCompareExchange128_nf(_Dest, _Tmp[1], _Tmp[0], _Tmp) != 0; [D:\a\notepad2\notepad2\build\VS2017\Notepad2.vcxproj]

[StephanTLavavej]

Thanks for reporting this. I see (at least) 3 issues here:

• Clang should implement the same intrinsics that the MSVC compiler implements; this should be reported as an LLVM bug
• The STL should work around this, temporarily, by using the sequentially consistent intrinsic (assuming it works)
• The STL should have coverage for Clang targeting ARM64 (tracked by Run tests for ARM64 #820)

[zufuliu]

_InterlockedCompareExchange128_nf is declared at line 171 of VC\Tools\MSVC\14.28.29333\include\intrin0.h, but for some reason not visible to Clang.

#ifdef __clang__
// This looks like a circular include but it is not because clang overrides <intrin.h> with their specific version.
// See further discussion in LLVM-47099.
#include <intrin.h>
#else /* ^^^ __clang__ // !__clang__ vvv */

// other definitions and declarations
// line 171 for _InterlockedCompareExchange128_nf
#endif /* ^^^ !__clang__ */

https://bugs.llvm.org/show_bug.cgi?id=47099

[cbezault]

We could start building all the tests for ARM64 even if we don't run them. That would have caught this problem.

[AlexGuteniev]

Is there non- _nf function available? If so, could use it

[zufuliu]

None are available in Clang 11 or bellow for ARM64, see https://reviews.llvm.org/D92062, but Clang has some atomic builtins http://clang.llvm.org/docs/LanguageExtensions.html#c11-atomic-builtins

[AlexGuteniev]

Probably can also use inline assembly for Clang.
Unlike MSVC in Clang it works in x64 and it allows specifying clobbering, so it is not expected to be problematic.