[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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@@ -9244,6 +9248,11 @@ SDValue SelectionDAG::getLoad(ISD::MemIndexedMode AM, ISD::LoadExtType ExtType,
 
   SDVTList VTs = Indexed ?
     getVTList(VT, Ptr.getValueType(), MVT::Other) : getVTList(VT, MVT::Other);
+
+  // Lower poison to undef.
+  if (Ptr.getNode()->isPoison())
+    Ptr = getUNDEF(Ptr.getValueType());
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arsenm wrote:

Can you fix the lack of CSE and drop the special case? Or switch getLoad to preserve the poison? 

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