diff --git a/llvm/include/llvm/Support/Casting.h b/llvm/include/llvm/Support/Casting.h
--- a/llvm/include/llvm/Support/Casting.h
+++ b/llvm/include/llvm/Support/Casting.h
@@ -525,6 +525,14 @@
   }
 };
 
+/// Provides a self-cast that simply returns whatever is given. This doesn't
+/// provide `castFailed` because a cast from T to T should never fail.
+template <typename T> struct CastInfo<T, T> {
+  static bool isPossible(const T &t) { return true; }
+  static decltype(auto) doCast(const T &t) { return t; }
+  static decltype(auto) doCastIfPossible(const T &t) { return t; }
+};
+
 //===----------------------------------------------------------------------===//
 // Pre-specialized CastInfo
 //===----------------------------------------------------------------------===//