By contrast, many more people are updating optimizations to GCC or clang for arm, more frequently and over a longer timeframe.
GCC and Clang are very nice compilers, but they are a different thing than the std lib. glibc, musl, the Windows C Runtime, iOS, Android, all have different implementations, sometimes outdated.
Same is true of MSVC.
It's been that way on most modern compilers for about 20 years.
That's why I'm saying rolling your own may be futile. Compilers, not just libc, have paid a lot of attention to getting those things fast.
But testing is always there to the rescue, and these days we have Godbolt.
But I have not published those benchmarks, if this is what you're asking, the Nintendo thing I am afraid I cannot reproduce easily as I no longer have this devkit on hand.
About the strlen benchmark, this is something I've done a few years ago, that could be easy to run again, but I am not sure this is worth the effort just to convince a random dude on the internet...
Yes. Share the data or you're spreading FUD.
I got the prefetching trick from Intel source code, except that I replaced the PLD instruction by a simple dummy load.
And about strlen, you'd be surprised, some implems are very good, and some are not, depends on the compiler and the library. I've ran benchmarks, I was surprised too.
To be honest, I don't really need super fast strlen, but I was curious and also learning to write fast SIMD code, basic string handling is a nice exercise.