ClangCodeModel confused by IMM intrinsics

With MSVC as the compiler, when ClangCodeModel is enabled, it gets confused by IMM intrinsics (at least), but unfortunately I cannot give a fully accurate and concrete description.

I first noticed it in this code snippet, where it failed to recognize anything from <immintrin.h>, despite the code compiling (and running) with no issues:

Then, when attempting to narrow it down for a bug report, the issue manifested itself differently and I was unable to construct a test case that showed the exact same behavior. In this case, it recognize the intrinsics but failed to recognize the Microsoft-specific form of __m256, which has some member fields:

As with the first observation, the above code compiles with no issues.

Here is that second test in text form:

using uint = unsigned;
#define USE_IMM 1
#if USE_IMM
#include <immintrin.h>
#endif

int main () {

    const auto xcoef = [] (const float *a, const float *b, uint len) {
#if USE_IMM
        __m256 sum = { 0, 0, 0, 0 };
        for (uint k = 0; k < len; k += 4) {
            __m256 avals = _mm256_load_ps(a + k);
            __m256 bvals = _mm256_load_ps(b + k);
            sum = _mm256_fmadd_ps(avals, bvals, sum);
        }
        return sum.m256_f32[0] + sum.m256_f32[1] + sum.m256_f32[2] + sum.m256_f32[3];
#else
        double sum = 0;
        while (len) { sum += *(a++) * *(b++); -- len; }
        return sum;
#endif
    };

}

It seems like it is perhaps assuming gcc's form of immintrin.h? But I am not sure.

I'm sorry that I do not have more to offer here.