[llvm] [X86] Avoid shl->mul lowbit-isolate fold on Zen when unprofitable (PR #217776)

[Simon Pilgrim via llvm-commits]

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@@ -50792,6 +50794,25 @@ static SDValue combineMul(SDNode *N, SelectionDAG &DAG,
   if (SDValue V = combineMulToPMADD52(N, DL, DAG, Subtarget))
     return V;
 
+  // #214517 folds shl X, cttz(Y) into mul(and(neg(Y), Y), X), which is
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RKSimon wrote:

Just say "InstCombine folds shl....."

https://github.com/llvm/llvm-project/pull/217776