[llvm] [AMDGPU] Account for existing SDWA selections (PR #123221)

[Matt Arsenault via llvm-commits]

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@@ -164,12 +164,34 @@ class SDWASrcOperand : public SDWAOperand {
   bool Neg;
   bool Sext;
 
-public:
+protected:
   SDWASrcOperand(MachineOperand *TargetOp, MachineOperand *ReplacedOp,
                  SdwaSel SrcSel_ = DWORD, bool Abs_ = false, bool Neg_ = false,
                  bool Sext_ = false)
-      : SDWAOperand(TargetOp, ReplacedOp),
-        SrcSel(SrcSel_), Abs(Abs_), Neg(Neg_), Sext(Sext_) {}
+      : SDWAOperand(TargetOp, ReplacedOp), SrcSel(SrcSel_), Abs(Abs_),
+        Neg(Neg_), Sext(Sext_) {}
+public:
+  /// Create an SDWASrcOperand as an operand for \p MI from the given arguments
+  /// if \p SrcSel_ and the src_sel0 and src_sel1 operands of \p MI are
+  /// compatible.
+  static std::unique_ptr<SDWAOperand>
+  create(const SIInstrInfo *TII, const MachineInstr &MI,
+         MachineOperand *TargetOp, MachineOperand *ReplacedOp,
+         SdwaSel SrcSel_ = DWORD, bool Abs_ = false, bool Neg_ = false,
+         bool Sext_ = false) {
+    if (TII->isSDWA(MI.getOpcode())) {
+      for (auto SelOpName :
+           {AMDGPU::OpName::src0_sel, AMDGPU::OpName::src1_sel}) {
+        const MachineOperand *NamedOp = TII->getNamedOperand(MI, SelOpName);
+        if (NamedOp && !compatibleSelections(
+                           static_cast<SdwaSel>(NamedOp->getImm()), SrcSel_))
+          return std::unique_ptr<SDWAOperand>(nullptr);
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arsenm wrote:

can just return nullptr directly? 

https://github.com/llvm/llvm-project/pull/123221