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

[Nikita Popov via llvm-commits]

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@@ -773,7 +773,10 @@ enum NodeType {
   /// into new bits.
   SIGN_EXTEND,
 
-  /// ZERO_EXTEND - Used for integer types, zeroing the new bits.
+  /// ZERO_EXTEND - Used for integer types, zeroing the new bits. Can carry
+  /// the NonNeg SDNodeFlag to indicate that the input is known to be
+  /// non-negative. If the flag is present and the input is negative, the reuslt
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nikic wrote:

```suggestion
  /// non-negative. If the flag is present and the input is negative, the result
```

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