[llvm] [AMDGPU] Force the third source operand of the MAI instructions to VGPR if no AGPRs are used. (PR #69720)

[Stanislav Mekhanoshin via llvm-commits]

================
@@ -14169,18 +14176,19 @@ void SITargetLowering::AdjustInstrPostInstrSelection(MachineInstr &MI,
         MRI.setRegClass(Op.getReg(), NewRC);
       }
 
-      // Resolve the rest of AV operands to AGPRs.
-      if (auto *Src2 = TII->getNamedOperand(MI, AMDGPU::OpName::src2)) {
-        if (Src2->isReg() && Src2->getReg().isVirtual()) {
-          auto *RC = TRI->getRegClassForReg(MRI, Src2->getReg());
-          if (TRI->isVectorSuperClass(RC)) {
-            auto *NewRC = TRI->getEquivalentAGPRClass(RC);
-            MRI.setRegClass(Src2->getReg(), NewRC);
-            if (Src2->isTied())
-              MRI.setRegClass(MI.getOperand(0).getReg(), NewRC);
+      if (!NoAGPRs)
----------------
rampitec wrote:

You can do this instead:
```
if (NoAGPRs)
  return;
```

https://github.com/llvm/llvm-project/pull/69720