def alloc_timedelta_result(builder, name='ret'):
    """
    Allocate a NaT-initialized datetime64 (or timedelta64) result slot.
    """
    ret = cgutils.alloca_once(builder, TIMEDELTA64, name=name)
    builder.store(NAT, ret)
    return ret

    Allocate a NaT-initialized datetime64 (or timedelta64) result slot.
    
numba/np/npdatetime.py