fn codegen_autodiff<'ll, 'tcx>(
bx: &mut GenericBuilder<'_, 'll, FullCx<'ll, 'tcx>>,
tcx: TyCtxt<'tcx>,
instance: Instance<'tcx>,
args: &[OperandRef<'tcx, &'ll Value>],
result_layout: TyAndLayout<'tcx>,
result_place: Option<PlaceValue<&'ll Value>>,
) -> IntrinsicResult<'tcx, &'ll Value>