fn copy_intrinsic<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
    bx: &mut Bx,
    allow_overlap: bool,
    volatile: bool,
    ty: Ty<'tcx>,
    dst: Bx::Value,
    src: Bx::Value,
    count: Bx::Value
)