Function codegen_autodiff 

fn codegen_autodiff<'ll, 'tcx>(
    bx: &mut GenericBuilder<'_, 'll, FullCx<'ll, 'tcx>>,
    tcx: TyCtxt<'tcx>,
    instance: Instance<'tcx>,
    args: &[OperandRef<'tcx, &'ll Value>],
    result: PlaceRef<'tcx, &'ll Value>,
)