Setting __m256i to the value of two __m128i values

Question

So, AVX has a function from immintrin.h, which should allow to store the concatenation of two __m128i values into a single __m256i val

Answer 1

We had the same problem and used a macro to work around it.

#ifdef __GNUC__ 
#if __GNUC__ < 8
#define _mm256_set_m128i(xmm1, xmm2) _mm256_permute2f128_si256(_mm256_castsi128_si256(xmm1), _mm256_castsi128_si256(xmm2), 2)
#define _mm256_set_m128f(xmm1, xmm2) _mm256_permute2f128_ps(_mm256_castps128_ps256(xmm1), _mm256_castps128_ps256(xmm2), 2)
#endif
#endif