[llvm] [GISel][AMDGPU] Expand ShuffleVector (PR #124527)

[Matt Arsenault via llvm-commits]

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@@ -384,6 +384,45 @@ void CombinerHelper::applyCombineConcatVectors(
   MI.eraseFromParent();
 }
 
+bool CombinerHelper::matchCombineShuffle(MachineInstr &MI) const {
+  assert(MI.getOpcode() == TargetOpcode::G_SHUFFLE_VECTOR &&
+         "Invalid instruction");
+  auto &Shuffle = cast<GShuffleVector>(MI);
+
+  auto SrcVec1 = Shuffle.getSrc1Reg();
+  int SrcVec2 = Shuffle.getSrc2Reg();
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arsenm wrote:

mixed auto, and int. But the correct type is Register for both 

https://github.com/llvm/llvm-project/pull/124527