Function core::arch::x86::_mm256_inserti128_si256

pub unsafe fn _mm256_inserti128_si256(
    a: __m256i, 
    b: __m128i, 
    const IMM1: i32
) -> __m256i

This is supported on x86 and target feature avx2 only.

Copies a to dst, then insert 128 bits (of integer data) from b at the location specified by IMM1.

Intel’s documentation