[llvm] [AArch64][GloablISel] Refactor Combine G_CONCAT_VECTOR (PR #80866)

[Matt Arsenault via llvm-commits]

================
@@ -224,22 +224,22 @@ class CombinerHelper {
   /// - concat_vector(undef, undef) => undef
   /// - concat_vector(build_vector(A, B), build_vector(C, D)) =>
   ///   build_vector(A, B, C, D)
-  ///
-  /// \pre MI.getOpcode() == G_CONCAT_VECTORS.
-  bool tryCombineConcatVectors(MachineInstr &MI);
+  /// ==========================================================
   /// Check if the G_CONCAT_VECTORS \p MI is undef or if it
   /// can be flattened into a build_vector.
-  /// In the first case \p IsUndef will be true.
-  /// In the second case \p Ops will contain the operands needed
-  /// to produce the flattened build_vector.
+  /// In the first case \p bool will be true.
+  /// In the second case \p SmallVector<Register> will contain the operands
+  /// needed to produce the flattened build_vector.
   ///
   /// \pre MI.getOpcode() == G_CONCAT_VECTORS.
-  bool matchCombineConcatVectors(MachineInstr &MI, bool &IsUndef,
-                                 SmallVectorImpl<Register> &Ops);
-  /// Replace \p MI with a flattened build_vector with \p Ops or an
-  /// implicit_def if IsUndef is true.
-  void applyCombineConcatVectors(MachineInstr &MI, bool IsUndef,
-                                 const ArrayRef<Register> Ops);
+  bool
+  matchCombineConcatVectors(MachineInstr &MI,
+                            std::pair<bool, SmallVector<Register>> &matchinfo);
+  /// Replace \p MI with a flattened build_vector with \p SmallVector<Register>
+  /// or an implicit_def if \p bool is true.
----------------
arsenm wrote:

Probably should refer to the pair fields as first/second rather than the type. Don't know what doxygen will do with \p on just the type 

https://github.com/llvm/llvm-project/pull/80866