[llvm] Update amdgpu_gfx functions to use s0-s3 for inreg SGPR arguments on targets using scratch instructions for stack #78226 (PR #81394)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @arsenm, why are some test updates crashing with this output: Assertion failed: (Reg != AMDGPU::NoRegister), function allocateFixedSGPRInputImpl, file /Users/sahilpatidar/Desktop/llvm/llvm-project/llvm/lib/Target/AMDGPU/SIISelLowering.cpp, line 2292.

That indicates a free register wasn't found available for an input. What do the function signatures look like for the cases that hit this?

https://github.com/llvm/llvm-project/pull/81394