[llvm] [AMDGPU] Change SGPR layout to striped caller/callee saved (PR #127353)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > Striping SGPRs serves no purpose on GFX10+ where all waves get the full allocation of SGPRs. But hopefully it doesn't do any harm either.
> 
> This doesn't serve as a performance improvement anyway. I'll request a performance cycle.

The only reason for doing striping is to get roughly the same ratio of callee-saves / non-callee-saves at different occupancies. Why would you want to keep that ratio constant, if not for performance?

Anyway that reason does not apply on GFX10+.

https://github.com/llvm/llvm-project/pull/127353