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 value. The function is

__m256i _mm256_set_m128i (__m128i hi, __m128i lo)

However, when I use it, like so:

__m256i as[2]; __m128i s[4]; as[0] = _mm256_setr_m128i(s[0], s[1]);

I get a compilation error:

error: incompatible types when assigning to type ‘__m256i’ from type ‘int’

I don't really understand why this happens. Any help is greatly appreciated!

Answer 1

Not all compilers seem to have _mm256_setr_m128i, or even _mm256_set_m128i, defined in immintrin.h. So I usually just define macros as needed, bracketed with suitable #ifdefs which test for compiler and version:

#define _mm256_set_m128i(v0, v1)  _mm256_insertf128_si256(_mm256_castsi128_si256(v1), (v0), 1)

#define _mm256_setr_m128i(v0, v1) _mm256_set_m128i((v1), (v0))

• Intel ICC 11.1 and later has both _mm256_set_m128i and _mm256_setr_m128i.

• MSVC 2012 and later has just _mm256_set_m128i.

• gcc/clang don't seem to have either, although I haven't checked recent versions to see if this has been fixed yet.