1 files changed, 41 insertions, 0 deletions
diff --git a/include/llvm/IR/DerivedUser.h b/include/llvm/IR/DerivedUser.h
new file mode 100644
index 000000000000..4d681e0db611
--- /dev/null
+++ b/include/llvm/IR/DerivedUser.h
@@ -0,0 +1,41 @@
+//===-- DerivedUser.h - Base for non-IR Users -------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_IR_DERIVEDUSER_H
+#define LLVM_IR_DERIVEDUSER_H
+
+#include "llvm/IR/User.h"
+
+namespace llvm {
+
+/// Extension point for the Value hierarchy. All classes outside of lib/IR
+/// that wish to inherit from User should instead inherit from DerivedUser
+/// instead. Inheriting from this class is discouraged.
+///
+/// Generally speaking, Value is the base of a closed class hierarchy
+/// that can't be extended by code outside of lib/IR. This class creates a
+/// loophole that allows classes outside of lib/IR to extend User to leverage
+/// its use/def list machinery.
+class DerivedUser : public User {
+protected:
+  typedef void (*DeleteValueTy)(DerivedUser *);
+
+private:
+  friend Value;
+  DeleteValueTy DeleteValue;
+
+public:
+  DerivedUser(Type *Ty, unsigned VK, Use *U, unsigned NumOps,
+              DeleteValueTy DeleteValue)
+      : User(Ty, VK, U, NumOps), DeleteValue(DeleteValue) {}
+};
+
+} // namespace llvm
+
+#endif // LLVM_IR_DERIVEDUSER_H