[llvm] [X86] Narrow BT/BTC/BTR/BTS compare + RMW patterns on very large integers (PR #165540)

[Simon Pilgrim via llvm-commits]

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@@ -56516,6 +56594,37 @@ static SDValue combineSetCC(SDNode *N, SelectionDAG &DAG,
       if (SDValue AndN = MatchAndCmpEq(RHS, LHS))
         return DAG.getSetCC(DL, VT, AndN, DAG.getConstant(0, DL, OpVT), CC);
 
+      // If we're performing a bit test on a larger than legal type, attempt
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RKSimon wrote:

I'm happy to split this into separate BT and BTC/BTR/BTS patches - however there are some codegen regressions, but given the size of the current codegen is that a problem?

https://github.com/llvm/llvm-project/pull/165540