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

[Shilei Tian via llvm-commits]

shiltian 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.

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