UILabel is not auto-shrinking text to fit label size

Question

I have this strange issue, and im dealing with it for more than 8 hours now.. Depending on situation i have to calculate UILabels size dynamically,
e.g

Answer 1

In iOS 9 I just had to:

1. Add constraints from the left and right of the label to the superview.
2. Set the line break mode to clipping in IB.
3. Set the number of lines to 1 in IB.

Someone recommended setting number of lines to 0, but for me this just made the label go to multiple lines...