[llvm] [LegalizeDAG] Optimize CodeGen for `ISD::CTLZ_ZERO_UNDEF` (PR #83039)

[Matt Arsenault via llvm-commits]

================
@@ -5115,6 +5114,22 @@ void SelectionDAGLegalize::PromoteNode(SDNode *Node) {
     Results.push_back(DAG.getNode(ISD::TRUNCATE, dl, OVT, Tmp1));
     break;
   }
+  case ISD::CTLZ_ZERO_UNDEF:
+    // We know that the argument is unlikely to be zero, hence we can take a
+    // different approach as compared to ISD::CTLZ
+
+    // Any Extend the argument
+    Tmp1 = DAG.getNode(ISD::ANY_EXTEND, dl, NVT, Node->getOperand(0));
----------------
arsenm wrote:

Nicer to use locally defined, better named temporary variables 

https://github.com/llvm/llvm-project/pull/83039