Function _mm_cmpeq_epu64_mask 

pub fn _mm_cmpeq_epu64_mask(a: __m128i, b: __m128i) -> __mmask8

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

Compare packed unsigned 64-bit integers in a and b for equality, and store the results in mask vector k.

Intel’s documentation