[llvm] [DAG] isKnownNeverNaN - add DemandedElts element mask to isKnownNeverNaN calls (PR #135952)

[via llvm-commits]

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@@ -5615,6 +5630,9 @@ bool SelectionDAG::isKnownNeverNaN(SDValue Op, bool SNaN, unsigned Depth) const
            (SNaN && !C->getValueAPF().isSignaling());
   }
 
+  if (!DemandedElts)
+    return false; // No demanded elts, better to assume we don't know anything.
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LU-JOHN wrote:

Should this be an assertion?  Since there is no legacy code with this parameter, can we just require this to be correct?

https://github.com/llvm/llvm-project/pull/135952