[llvm] Introducing a new ISD::POISON SDNode to represent the poison value in the IR. (PR #125883)

[Matt Arsenault via llvm-commits]

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@@ -6259,6 +6262,7 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     if (N1.isUndef())
       // sext(undef) = 0, because the top bits will all be the same.
       return getConstant(0, DL, VT);
+
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arsenm wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/125883