[llvm] [SLP] Make getSameOpcode support interchangeable instructions. (PR #133888)

[Gaëtan Bossu via llvm-commits]

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@@ -839,9 +1126,27 @@ class InstructionsState {
   /// Some of the instructions in the list have alternate opcodes.
   bool isAltShuffle() const { return getMainOp() != getAltOp(); }
 
-  bool isOpcodeOrAlt(Instruction *I) const {
-    unsigned CheckedOpcode = I->getOpcode();
-    return getOpcode() == CheckedOpcode || getAltOpcode() == CheckedOpcode;
+  /// Checks if the instruction matches either the main or alternate opcode.
+  /// \returns
+  /// - MainOp if \param I matches MainOp's opcode directly or can be converted
+  /// to it
+  /// - AltOp if \param I matches AltOp's opcode directly or can be converted to
+  /// it
+  /// - nullptr if \param I cannot be matched or converted to either opcode
+  Instruction *isOpcodeOrAlt(Instruction *I) const {
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gbossu wrote:

Nit: The `isOpcodeOrAlt` name is a bit confusing, as this does not return a bool. Maybe name it something like `Instruction *getMatchingMainOrAltOp(Instruction *I)`?

https://github.com/llvm/llvm-project/pull/133888