Function check_named_return 

fn check_named_return<'tcx>(
    tcx: TyCtxt<'tcx>,
    caller: DefId,
    producer: AliveProducer,
    signature: &SignatureInfo,
    lifetime: &str,
    pointer_origin_param: Option<usize>,
) -> SmtCheckResult

Checks whether an explicit return lifetime is tied to the pointer source.