[llvm] [DAGCombine] Count leading ones: refine post DAG/Type Legalisation if promotion (PR #102877)

[Min-Yih Hsu via llvm-commits]

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@@ -3755,6 +3755,50 @@ SDValue DAGCombiner::foldSubToUSubSat(EVT DstVT, SDNode *N, const SDLoc &DL) {
   return SDValue();
 }
 
+template <class MatchContextClass>
+static SDValue foldSubCtlzNot(SDNode *N, SelectionDAG &DAG) {
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mshockwave wrote:

could you add a brief comment explaining what this function does, primarily the pattern?

https://github.com/llvm/llvm-project/pull/102877