No, but these channels can be used to complement each other. CPF is mandatory, but SRS is not. Do not make the mistake of thinking that your CPF is enough for your future needs, only to find out you are short on cash when you are in your golden years.
One way to maximise your retirement income is to open an SRS account. When you do this, you can contribute to your retirement needs and enjoy tax relief at the same time. This is important considering many Singaporeans and PRs utilise their CPF Ordinary Account for home and mortgage payments and are left with meager interest earnings during retirement age.