Uh... the GPU drivers we're talking about in this subthread are precisely "compilers" for the shader architecture (and configuration generators for the texture units and framebuffer layouts, etc...). In fact for architectures other than NVIDIA's the hardware-facing part of the linux driver already is open source.

The only secrets left are the bits responsible for turning OpenGL (or Vulkan now, I guess) calls into programs to run on the GPU.

Wouldn't it be fair to say that GPU architectures (at least thus far) tend to change a helluva faster than CPU ones?

I can think of AMD adopting and then ditching VLIW for one.

OpenSPARC T1 and T2 are open source and don't have out-of-order execution.