Developers want code that runs fast and users do too. However, it is easy to fall into the trap of early optimization; this story shows that even in non-trivial cases, modern compilers can do wonders. On the other hand, the myth of the “sufficiently smart compiler” is still very relevant. The best way is to look at what is actually generated for an example and that is what I’ll do in this article. Enter the SentinelInputRange.