I don't see anything directly relevant to this in the archives, and I haven't prepared a detailed proposal. But I'm raising the general idea because I recently criticized Swift 3 for allowing unreachable code in a blog post: https://blogs.synopsys.com/software-integrity/2017/03/24/swift-programming-language-design-part-2/ (search for "unreachable code"). And I want you to have every opportunity to rectify this, even though I'm in the business of finding defects the compiler doesn't.
Part of my argument is that people commonly ignore compiler warnings. We see lots of defective code that would be (or is) caught by compiler warnings but people don't pay attention.
If you would like to see more defect examples from open-source software (other languages for the moment), I am able to dig up such things.
Peter Dillinger, Ph.D.
Software Engineering Manager, Coverity Analysis, Software Integrity Group | Synopsys