title: Swift type-check takes long time
body: <p>I've added the flag <code>-Xfrontend -warn-long-expression-type-checking=50</code> to my Swift project to see what is taking too long. I've the following 
  expression:</p>
  
  <pre><code>let s: String = "1234"
  let t: Int? = Int(s)
  </code></pre>
  
  <p>On the <code>Int(s)</code> I get the warning <code>Expression took 52ms to type-check (limit: 50ms)</code>. I'm just wondering why this takes more than 50ms to figure out since I specified all types.</p>