[llvm] Update amdgpu_gfx functions to use s0-s3 for inreg SGPR arguments on targets using scratch instructions for stack (PR #78553)

[Matt Arsenault via llvm-commits]

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@@ -633,7 +633,7 @@ bool AMDGPUCallLowering::lowerFormalArguments(
     const bool InReg = Arg.hasAttribute(Attribute::InReg);
 
     // SGPR arguments to functions not implemented.
-    if (!IsGraphics && InReg)
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arsenm wrote:

This is the wrong change for this particular patch. You want the AllocateReg above determineAssignments 

https://github.com/llvm/llvm-project/pull/78553