I am using Xcode Version 6.1 (6A1052d), it is working well except the only problem is auto complete and code sense is broken for swift projects.
I can fix it by deleting derived data and the folder ~/Library/Caches/com.apple.dt.Xcode, which is described here, or changing the deployment target of the project from 8.1 to 8.0.
However, the first solution only last me for 1 or 2 days, out of no where it doesn't work again, I don't want to delete the folders every so often or change the target iOS versions all the time. Please help me.