[llvm] [SelectionDAG] Add initial support for nneg flag on ISD::ZERO_EXTEND. (PR #70872)

[Nikita Popov via llvm-commits]

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@@ -5037,6 +5036,10 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   case ISD::BUILD_PAIR:
     return false;
 
+  // Matches hasPoisonGeneratingFlags().
+  case ISD::ZERO_EXTEND:
+    return ConsiderFlags && Op->getFlags().hasNonneg();
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nikic wrote:

```suggestion
    return ConsiderFlags && Op->getFlags().hasNonNeg();
```

https://github.com/llvm/llvm-project/pull/70872