[llvm] [AMDGPU] S_SET_GPR_IDX_ON can be passed an immediate index (PR #125086)

[Jon Chesterfield via llvm-commits]

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@@ -2366,11 +2366,10 @@ bool SIInstrInfo::expandPostRAPseudo(MachineInstr &MI) const {
     assert(ST.useVGPRIndexMode());
     Register VecReg = MI.getOperand(0).getReg();
     bool IsUndef = MI.getOperand(1).isUndef();
-    Register Idx = MI.getOperand(3).getReg();
     Register SubReg = MI.getOperand(4).getImm();
 
     MachineInstr *SetOn = BuildMI(MBB, MI, DL, get(AMDGPU::S_SET_GPR_IDX_ON))
-                              .addReg(Idx)
+                              .add(MI.getOperand(3)) // Index
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JonChesterfield wrote:

Sure, that's equivalent and makes the diff smaller. Done.

https://github.com/llvm/llvm-project/pull/125086