Function core::arch::x86_64::_mm256_insertf128_pd

pub unsafe fn _mm256_insertf128_pd<const IMM1: i32>(
    a: __m256d, 
    b: __m128d
) -> __m256d

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

Copies a to result, then inserts 128 bits (composed of 2 packed double-precision (64-bit) floating-point elements) from b into result at the location specified by imm8.

Intel’s documentation