[llvm] [DAG] ISD::matchUnaryPredicate / matchUnaryFpPredicate / matchBinaryPredicate - add DemandedElts variant (PR #183013)

[Simon Pilgrim via llvm-commits]

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@@ -4675,26 +4683,11 @@ bool SelectionDAG::isKnownToBeAPowerOfTwo(SDValue Val,
   };
 
   // Is the constant a known power of 2 or zero?
-  if (ISD::matchUnaryPredicate(Val, IsPowerOfTwoOrZero))
+  if (ISD::matchUnaryPredicate(Val, DemandedElts, IsPowerOfTwoOrZero,
+                               /*AllowUndefs=*/false, /*AllowTruncation=*/true))
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RKSimon wrote:

in which case we should probably do that part as a separate follow up PR 

https://github.com/llvm/llvm-project/pull/183013