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diff --git a/build/clang-plugin/RecurseGuard.h b/build/clang-plugin/RecurseGuard.h
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+++ b/build/clang-plugin/RecurseGuard.h
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef RecurseGuard_h__
+#define RecurseGuard_h__
+
+#include "Utils.h"
+
+// This class acts as a tracker for avoiding infinite recursion when traversing
+// chains in CFGs etc.
+//
+// Constructing a RecurseGuard sets up a shared backing store which tracks the
+// currently observed objects. Whenever recursing, use RecurseGuard.recurse(T)
+// to construct another RecurseGuard with the same backing store.
+//
+// The RecurseGuard object will unregister its object when it is destroyed, and
+// has a method `isRepeat()` which will return `true` if the item was already
+// seen.
+template <typename T> class RecurseGuard {
+public:
+  RecurseGuard(T Thing) : Thing(Thing), Set(new DenseSet<T>()), Repeat(false) {
+    Set->insert(Thing);
+  }
+  RecurseGuard(T Thing, std::shared_ptr<DenseSet<T>> &Set)
+      : Thing(Thing), Set(Set), Repeat(false) {
+    Repeat = !Set->insert(Thing).second;
+  }
+  RecurseGuard(const RecurseGuard &) = delete;
+  RecurseGuard(RecurseGuard &&Other)
+      : Thing(Other.Thing), Set(Other.Set), Repeat(Other.Repeat) {
+    Other.Repeat = true;
+  }
+  ~RecurseGuard() {
+    if (!Repeat) {
+      Set->erase(Thing);
+    }
+  }
+
+  bool isRepeat() { return Repeat; }
+
+  T get() { return Thing; }
+
+  operator T() { return Thing; }
+
+  T operator->() { return Thing; }
+
+  RecurseGuard recurse(T NewThing) { return RecurseGuard(NewThing, Set); }
+
+private:
+  T Thing;
+  std::shared_ptr<DenseSet<T>> Set;
+  bool Repeat;
+};
+
+#endif // RecurseGuard_h__