[llvm] [SelectionDAG] Add and use SDNode::getAsAPIntVal() helper (PR #77455)

[Alex Bradbury via llvm-commits]

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@@ -932,6 +932,9 @@ END_TWO_BYTE_PACK()
   /// Helper method returns the APInt of a ConstantSDNode operand.
   inline const APInt &getConstantOperandAPInt(unsigned Num) const;
 
+  /// Helper method returns the APInt value of a ConstantSDNode.
+  inline const APInt &getAsAPIntVal() const;
+
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asb wrote:

The definition of ConstantSDNode doesn't come until later in the file, and this matches the approach used by the neighbouring getters.

https://github.com/llvm/llvm-project/pull/77455