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

[Björn Pettersson via llvm-commits]

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@@ -690,8 +690,17 @@ END_TWO_BYTE_PACK()
   /// \<target\>ISD namespace).
   bool isTargetOpcode() const { return NodeType >= ISD::BUILTIN_OP_END; }
 
-  /// Return true if the type of the node type undefined.
-  bool isUndef() const { return NodeType == ISD::UNDEF; }
+  /// Returns true if the node type is UNDEF or, when UndefOnly is false,
+  /// POISON.
+  /// - When UndefOnly is true, returns true only for UNDEF.
+  /// - When UndefOnly is false, returns true for both UNDEF and POISON.
+  /// @param UndefOnly Determines whether to check only for UNDEF.
+  bool isUndef(bool UndefOnly = false) const {
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bjope wrote:

Should this be called something else?
Since we have ISD::UNDEF it would be easy to think that isUndef() checks if the type is ISD::UNDEF. Just like isPoison() checks for ISD::POISON.

Would be clearer to have an isUndefOrPoison helper (or something totally generic not mapping to an ISD type, such as isUndefinedType()) when it isn't a 1-1 mapping to the ISD type name.

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