[llvm] [AArch64][GlobalISel] Perfect Shuffles (PR #106446)

[Madhur Amilkanthwar via llvm-commits]

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@@ -504,6 +504,189 @@ void applyINS(MachineInstr &MI, MachineRegisterInfo &MRI,
   MI.eraseFromParent();
 }
 
+/// Match 4 elemental G_SHUFFLE_VECTOR
+bool matchPerfectShuffle(MachineInstr &MI, MachineRegisterInfo &MRI) {
+  assert(MI.getOpcode() == TargetOpcode::G_SHUFFLE_VECTOR);
+  return MRI.getType(MI.getOperand(0).getReg()).getNumElements() == 4;
+}
+
+static Register GeneratePerfectShuffle(unsigned ID, Register V1, Register V2,
+                                       unsigned PFEntry, Register LHS,
+                                       Register RHS, MachineIRBuilder &MIB,
+                                       MachineRegisterInfo &MRI) {
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madhur13490 wrote:

A comment please explaining the below calculations.

https://github.com/llvm/llvm-project/pull/106446