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

[Simon Pilgrim 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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RKSimon wrote:

We could, I've mainly matched what we've done in the past. IIRC it's helped in strange edge cases but ideally we'd catch these in the caller.

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