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

[Manish Kausik H via llvm-commits]

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@@ -642,21 +642,43 @@ SDValue DAGTypeLegalizer::PromoteIntRes_CTLZ(SDNode *N) {
     }
   }
 
-  // Zero extend to the promoted type and do the count there.
-  SDValue Op = ZExtPromotedInteger(N->getOperand(0));
+  unsigned CtlzOpcode = N->getOpcode();
+  if (CtlzOpcode == ISD::CTLZ) {
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Nirhar wrote:

Have accomodated it as well!

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