Function _mm256_zeroupper 

pub fn _mm256_zeroupper()

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

Zeroes the upper 128 bits of all YMM registers; the lower 128-bits of the registers are unmodified.

This operation is purely a performance hint for the CPU and has no effect on the Abstract Machine state.

Intel’s documentation