[q-big]

kllrnohj already wrote that Vulkan has no predefined source code language for shaders. I can imagine that the SPIR-V code of these shaders could have been hand-optimized by some team at AMD, so a textual reprsentation of this binary code is the version that the engineers at AMD work on.

Also: the license of the repository is MIT license, so you are free to reverse-engineer these shaders and port them to a high-level language of your choice.