So your tests got much faster and does very well compared to C?
I also checked my original test case and could not reproduce the previous error, so I suppose for this simple use case the "issue" is fixed 
(I added a comment at the Swift bug entry).
There was a note by @Joe_Groff pointing at a concept for some general solution (?) and note by @drexin, and I would be interested to know how far the current solution goes / how much further one would like to go. Thanks.