It is worth verifying that you can check your luggage through to SIN. There are some occasions when this is possible especially if you use the same airline on the same booking, but it by no means certain otherwise. If you cannot check your luggage through then you will have to go through Chinese immigration, collect your bags and re-check them. This will mean having a visa, or TWOV if Chengdu offer this. I've not done an INT-INT transfer through Chengdu but I have done through Guangzhou and it was pretty painless. However, that was with China Southern (both flights, same booking) and Guangzhou is their home airport.