[llvm] [AArch64] Avoid creating a new generic constant in SelectSMETileSlice (PR #203344)

[Sander de Smalen via llvm-commits]

================
@@ -5032,6 +5032,15 @@ bool AArch64DAGToDAGISel::trySelectXAR(SDNode *N) {
   return true;
 }
 
+/// Returns a copy from WZR or XZR. This can be used during instruction
+/// selection (it does not require any further selection/legalization).
+static SDValue getZeroRegister(SelectionDAG &DAG, SDLoc DL, EVT VT) {
+  if (VT == MVT::i32)
+    return DAG.getCopyFromReg(DAG.getEntryNode(), DL, AArch64::WZR, MVT::i32);
+  assert(VT == MVT::i64);
+  return DAG.getCopyFromReg(DAG.getEntryNode(), DL, AArch64::XZR, MVT::i64);
----------------
sdesmalen-arm wrote:

very minor nit:
```suggestion
  assert(VT == MVT::i32 || VT == MVT::i64);
  return DAG.getCopyFromReg(DAG.getEntryNode(), DL,
                            VT == MVT::i32 ? AArch64::WZR : AArch64::XZR, VT);
```

https://github.com/llvm/llvm-project/pull/203344