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

[Jay Foad via llvm-commits]

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@@ -5003,6 +5002,22 @@ void SelectionDAGLegalize::PromoteNode(SDNode *Node) {
     }
     Results.push_back(DAG.getNode(ISD::TRUNCATE, dl, OVT, Tmp1));
     break;
+  case ISD::CTLZ_ZERO_UNDEF:
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jayfoad wrote:

Remove the check for `Node->getOpcode() == ISD::CTLZ_ZERO_UNDEF` on line 4997 above?

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