Function _mm256_alignr_epi64 

pub fn _mm256_alignr_epi64(a: __m256i, b: __m256i, const IMM8: i32) -> __m256i

Available on x86-64 and target feature avx512f and target feature avx512vl only.

Concatenate a and b into a 64-byte immediate result, shift the result right by imm8 64-bit elements, and store the low 32 bytes (4 elements) in dst.

Only lowest 2 bits are used from the mask (shift at maximum by 24 bytes)!

Intel’s documentation