Ooh now that is very interesting. I would really love to see how this speeds up the run-time of fpng as a whole, if you have any numbers. It looks like fjxl [0] and fpnge [1] (which also uses AVX2) are at the Pareto front for lossless image compression right now [2], but if this speeds things significantly then it's possible there'll be a huge shakeup!
[0] https://github.com/libjxl/libjxl/tree/main/experimental/fast...
[1] https://github.com/veluca93/fpnge
[2] https://twitter.com/richgel999/status/1485976101692358656