[clang] [CIR] Skip trivially-recursive available_externally function bodies (PR #198363)

[Erich Keane via cfe-commits]

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@@ -2648,6 +2649,12 @@ class FunctionDecl : public DeclaratorDecl,
   /// Determine if this function provides an inline implementation of a builtin.
   bool isInlineBuiltinDeclaration() const;
 
+  /// Return true if this function's body contains only a direct call back to
+  /// the same symbol via an asm label or a __builtin_* alias.  Such
+  /// available_externally bodies are not valid stand-ins for the real
+  /// implementation (PR9614) and should be dropped before codegen.
+  bool isTriviallyRecursive(MangleContext &MC) const;
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erichkeane wrote:

We probably shouldn't be doing mangle-contexts inside of our declarations here, thats a bit of a layering violation.  Perhaps this is a valuable function to put in the `MangleContext` itself?

https://github.com/llvm/llvm-project/pull/198363