Function core::arch::x86_64::_mm256_insertf128_si256

pub unsafe fn _mm256_insertf128_si256<const IMM1: i32>(
    a: __m256i, 
    b: __m128i
) -> __m256i

This is supported on x86-64 and target feature avx only.

Copies a to result, then inserts 128 bits from b into result at the location specified by imm8.

Intel’s documentation