title: 【UILabel】"set text" is too slow
body: <p>When setting <code>UILabel.text</code> to a string with many line breaks, it takes too much time.</p>
  <p>Why is this?</p>
  <p>Is there a solution?</p>
  <pre><code>@IBOutlet weak var textArea: UITextView!
  @IBOutlet weak var label: UILabel!
  
  @IBAction func tap(_ sender: Any) {
      var longTextWithLineBreaks = &quot;&quot;;
      for _ in 0 ..&lt; 50000 {
          longTextWithLineBreaks += &quot;1\n&quot;
      }
      
      var longText = &quot;&quot;;
      for _ in 0 ..&lt; 50000 {
          longText += &quot;12&quot;
      }
  
      //  UITextView
      self.textArea.text = longTextWithLineBreaks;    //  fast
      self.textArea.text = longText;      //  fast
      
      //  UILabel
      self.label.text = longTextWithLineBreaks;    //  too slow!!!!!! why???? processing time has minute over, CPU 100%
      self.label.text = longText;      //  fast ^^
  }
  </code></pre>