[llvm] [X86] fold AND(X,SEXT(SETCC())) -> SELECT(SETCC(),X,0) to support AVX512 predicated {k}{z} masks (PR #131788)

[Simon Pilgrim via llvm-commits]

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@@ -51481,6 +51483,22 @@ static SDValue combineAnd(SDNode *N, SelectionDAG &DAG,
     }
   }
 
+  // On AVX512 targets, attempt to reverse foldVSelectToSignBitSplatMask.
+  // to make use of predicated selects.
+  // AND(X,SEXT(SETCC())) -> SELECT(SETCC(),X,0)
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RKSimon wrote:

The legality checks should protect us from that - I'll leave it for now and will experiment for a future patch for review

https://github.com/llvm/llvm-project/pull/131788