Yes. Surprisingly, many naive implementations you might assume would be identified aren't. You are far more likely to write a naive implementation that is not identified than one that is. I've spent a few weekends testing many different implementations to better understand the limitations of the compiler at identifying bit-twiddling instructions and it still doesn't work nearly as well as you might hope.

Also, not every compiler will identify a specific bit-twiddling implementation, Clang seems to identify more of these idiomatic implementations than GCC in my experience, but that is anecdotal. The set of code patterns they can identify is not documented anywhere that I've seen, though it must be in the compiler source code somewhere.