Intel AVX : Why is there no 256-bits version of dot product for double precision floating point variables?
avx, c++, performance, simd
Solution
The underlying reason for this and various other AVX limitations is that architecturally AVX is little more than two SSE execution units side by side - you will notice that virtually no AVX instructions operate horizontally across the boundary between the two 128 bit halves of a vector (which is particularly annoying in the case of `vpalignr`). In general you effectively just get two 128 bit SSE operations in parallel, which is useful for the majority of instructions which just operate in an element-wise fashion, but not as useful as a proper 256 bit SIMD implementation.
Problem
In another question on SO we tried (and succeeded) to find a way to replace the AVX missing instruction: ``` __m256d _mm256_dp_pd(__m256d m1, __m256d m2, const int mask); ``` Anyone knows the reason why this instruction is missing ? Partial answer here.