So what's particularly hard on the compiler are hard coded sets of data that have mixed types. For example a dictionary that reflects a JSON response that also has nested dictionaries.
It helps if you test declare it like:
let json: [String: Any] = [ /** lots of fields here */ ]
String concatenation: could you give me a specific piece of code that fails? It could be that I really never write code that triggers the problem. Using the + operator to concatenate strings has some performance issues though.
I'm not telling you're crazy, I just noticed that things got so much faster in the past two years.