We fixed a lot of bugs while working on the new generics features in Swift 3.1 (and also recursive protocol constraints, which didn't quite make it in but a lot of the plumbing was done for it).
For example, in practicalswift's fuzzer collection, 260 cases were fixed between 3.0 and 3.1, for a total of 5426 fixed (with 39 still open).
For example, in practicalswift's fuzzer collection, 260 cases were fixed between 3.0 and 3.1, for a total of 5426 fixed (with 39 still open).