unresolved external symbol __mm256_setr_epi64x

Question

I have written and debugged some AVX code with g++ and now I\'m trying to get it to work with MSVC, but I keep getting

error LNK2019: unresolved exte

Answer 1

In 32-bit mode MSVC does not support

• _mm_set_epi64x
• _mm_setr_epi64x
• _mm_set1_epi64x
• _mm256_set_epi64x
• _mm256_setr_epi64x
• _mm256_set1_epi64x

In your case in 32-bit mode you can do this:

    union {
        int64_t q[4];
        int32_t r[8];
    } u;
    u.q[0] = a; u.q[1] = b; u.q[2] = c; u.q[3] = d;
    return _mm256_setr_epi32(u.r[0], u.r[1], u.r[2], u.r[3], u.r[4], u.r[5], u.r[6], u.r[7]);

---

Since Visual Studio 2015 (_MSC_VER 1900) these intrinsics are supported in 32-bit mode.

Answer 2

It looks this might actually be a known bug - certain AVX intrinsics are apparently not available in 32-bit mode. Try building for 64 bit and/or upgrading to Visual Studio 2013 Update 2, where this has supposedly now been fixed.

Alternatively, if you just have the one instance above where you are using this intrinsic, then you could change your function to:

__m256i avx_matrix::avx_bit_mask(const std::size_t pos) const
{
    int64_t a[4] = { (pos >=   0 && pos <  64) ? 1LL << (pos -   0) : 0,
                     (pos >=  64 && pos < 128) ? 1LL << (pos -  64) : 0,
                     (pos >= 128 && pos < 192) ? 1LL << (pos - 128) : 0,
                     (pos >= 192 && pos < 256) ? 1LL << (pos - 256) : 0 };
    return _mm256_loadu_si256((__m256i *)a);
}

or perhaps even:

__m256i avx_matrix::avx_bit_mask(const std::size_t pos) const
{
    int64_t a[4] = { 0 };
    a[pos >> 6] = 1LL << (pos & 63ULL);
    return _mm256_loadu_si256((__m256i *)a);
}

which might be a little more efficient.