unresolved external symbol __mm256_setr_epi64x

问题

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 external symbol __mm256_setr_epi64x referenced in function "private: union __m256i __thiscall avx_matrix::avx_bit_mask(unsigned int)const " (?avx_bit_mask@avx_matrix@@ABE?AT__m256i@@I@Z)

The referenced piece of code is

...

#include <immintrin.h>

...

    /* All zeros except for pos-th position (0..255) */
    __m256i avx_matrix::avx_bit_mask(const std::size_t pos) const
    {
        int64_t a = (pos >= 0 && pos < 64) ? 1LL << (pos - 0) : 0;
        int64_t b = (pos >= 64 && pos < 128) ? 1LL << (pos - 64) : 0;
        int64_t c = (pos >= 128 && pos < 192) ? 1LL << (pos - 128) : 0;
        int64_t d = (pos >= 192 && pos < 256) ? 1LL << (pos - 256) : 0;
        return _mm256_setr_epi64x(a, b, c, d);
    }
...

I have enabled /arch:AVX, but it doesn't make any difference.
My machine definitely supports AVX - it is the same one I used for the original Linux project.
Also, http://msdn.microsoft.com/en-us/library/hh977022.aspx lists _mm256_setr_epi64x among the available intrinsics.

Any help would be much appreciated.

回答1:

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.

回答2:

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.

来源：https://stackoverflow.com/questions/27258261/unresolved-external-symbol-mm256-setr-epi64x

标签

c++

visual-studio-2012

intrinsics

avx

msvc12