Function split_simd_to_128bit_chunks 

fn split_simd_to_128bit_chunks<'tcx, P: Projectable<'tcx, Provenance>>(
    ecx: &mut MiriInterpCx<'tcx>,
    op: &P,
) -> InterpResult<'tcx, (u64, u64, P)>

Splits op (which must be a SIMD vector) into 128-bit chunks.

Returns a tuple where:

• The first element is the number of 128-bit chunks (let’s call it N).
• The second element is the number of elements per chunk (let’s call it M).
• The third element is the op vector split into chunks, i.e, it’s type is [[T; M]; N] where T is the element type of op.