[llvm] [AArch64] Utilize `XAR` for certain vector rotates (PR #137629)

[David Green via llvm-commits]

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@@ -4558,9 +4558,27 @@ bool AArch64DAGToDAGISel::trySelectXAR(SDNode *N) {
         !TLI->isAllActivePredicate(*CurDAG, N1.getOperand(0)))
       return false;
 
-    SDValue XOR = N0.getOperand(1);
-    if (XOR.getOpcode() != ISD::XOR || XOR != N1.getOperand(1))
-      return false;
+    SDValue R1, R2;
+    if (N0.getOperand(1).getOpcode() != ISD::XOR) {
+      if (N0.getOperand(1) != N1.getOperand(1))
+        return false;
+      SDLoc DL(N1->getOperand(0));
+      EVT VT = N1->getOperand(0).getValueType();
+
+      SDValue Zero = CurDAG->getTargetConstant(0, DL, MVT::i64);
+      SDNode *MOV = CurDAG->getMachineNode(AArch64::MOVIv2d_ns, DL, VT, Zero);
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davemgreen wrote:

It is best to create nodes only if we know that the final result will be used (after the last `return false`). Is it possible to move the creation of these nodes later?

https://github.com/llvm/llvm-project/pull/137629