USA-Shanghai (1 day)-Japan Cruise (7 days)-Shanghai (8 hours)-Singapore

Yes, you will be eligible for a visa free transit policy. Anyway, to be precise, here are several conditiosn your itinerary has to fulfill:

- Your flight from US is not allowed to have any additional landing within mainland China and Japan of any kind
- Your cruise is not allowed to have its first port of call, immediately after Shanghai, in mainland Chian port
- Your cruise is not allowed to have its last port of call, immediately before Shanghai, in mainland China port
- Your flight from Shanghai to Singapore is not allowed to have any additional landing within mainland China and Japan of any kind

I assume that your itinerary fulfills those conditions, but I advise you to check it for a couple of minutes just to be 100% certain.

By the way, during your first stop in Shanghai, you will be eligible for 144 hour visa free transit and during your second stop for 24 hour visa free transit because your stay in Shanghai will be less than 24 hours long. In any case, you will travel absolutely without a visa.