<intrin0.h>: needs some stuff for `_M_ARM64`

[fsb4000]

For #2127 I need

1. __uint64ToN64_v
2. neon_cnt
3. neon_addv8
4. __n64

from <arm64_neon.h>

https://godbolt.org/z/MbEqfshGG

[fsb4000]

clang generates only 2 errors.

#include <intrin0.h>

_NODISCARD int _Arm64_popcount(const unsigned long long _Val) noexcept {
    const __n64 _Result = neon_cnt(__uint64ToN64_v(_Val));
    return neon_addv8(_Result).n8_u8[0];
}

int main() {
    return _Arm64_popcount(0xFFFF);
}

$ clang++ --target=aarch64-windows-msvc -O3 -S test.cpp
test.cpp:4:11: error: unknown type name '__n64'
    const __n64 _Result = neon_cnt(__uint64ToN64_v(_Val));
          ^
test.cpp:4:36: error: use of undeclared identifier '__uint64ToN64_v'
    const __n64 _Result = neon_cnt(__uint64ToN64_v(_Val));
                                   ^
2 errors generated.

So does clang use different <intrin0.h>?
If so should I create a bug report at LLVM bugzilla?

[AlexGuteniev]

Want also neon_cntq, neon_addvq8, __n128 to optimize bitset::count further than with 64-bit versions

[StephanTLavavej]

Igor Zhukov (@fsb4000) Yes, according to my understanding, Clang has their own <intrin0.h> that they use instead of ours.