This is a single header (only) library that does vertex cache optimization, as described by Tom Forsyth: https://tomforsyth1000.github.io/papers/fast_vert_cache_opt.html
It is released on a public domain license. You can find the license in the header file.
Please note that I have only tested that is compiles with the compilers availble through godbolt.org so far. It should compile without any warnings or errors.
If you successfully or unsuccesfully are able to use it with anything other than clang, please let me know and I'll keep a list of compilers it works with and ensure that we fix it for the compilers that chokes.
Contributions are welcome!