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diff --git a/include/llvm/ADT/SmallSet.h b/include/llvm/ADT/SmallSet.h
new file mode 100644
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+++ b/include/llvm/ADT/SmallSet.h
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+//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the SmallSet class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_SMALLSET_H
+#define LLVM_ADT_SMALLSET_H
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include <set>
+
+namespace llvm {
+
+/// SmallSet - This maintains a set of unique values, optimizing for the case
+/// when the set is small (less than N).  In this case, the set can be
+/// maintained with no mallocs.  If the set gets large, we expand to using an
+/// std::set to maintain reasonable lookup times.
+///
+/// Note that this set does not provide a way to iterate over members in the
+/// set.
+template <typename T, unsigned N>
+class SmallSet {
+  /// Use a SmallVector to hold the elements here (even though it will never
+  /// reach it's 'large' stage) to avoid calling the default ctors of elements
+  /// we will never use.
+  SmallVector<T, N> Vector;
+  std::set<T> Set;
+  typedef typename SmallVector<T, N>::const_iterator VIterator;
+  typedef typename SmallVector<T, N>::iterator mutable_iterator;
+public:
+  SmallSet() {}
+
+  bool empty() const { return Vector.empty() && Set.empty(); }
+  unsigned size() const {
+    return isSmall() ? Vector.size() : Set.size();
+  }
+
+  /// count - Return true if the element is in the set.
+  bool count(const T &V) const {
+    if (isSmall()) {
+      // Since the collection is small, just do a linear search.
+      return vfind(V) != Vector.end();
+    } else {
+      return Set.count(V);
+    }
+  }
+
+  /// insert - Insert an element into the set if it isn't already there.
+  bool insert(const T &V) {
+    if (!isSmall())
+      return Set.insert(V).second;
+
+    VIterator I = vfind(V);
+    if (I != Vector.end())    // Don't reinsert if it already exists.
+      return false;
+    if (Vector.size() < N) {
+      Vector.push_back(V);
+      return true;
+    }
+
+    // Otherwise, grow from vector to set.
+    while (!Vector.empty()) {
+      Set.insert(Vector.back());
+      Vector.pop_back();
+    }
+    Set.insert(V);
+    return true;
+  }
+
+  template <typename IterT>
+  void insert(IterT I, IterT E) {
+    for (; I != E; ++I)
+      insert(*I);
+  }
+  
+  bool erase(const T &V) {
+    if (!isSmall())
+      return Set.erase(V);
+    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
+      if (*I == V) {
+        Vector.erase(I);
+        return true;
+      }
+    return false;
+  }
+
+  void clear() {
+    Vector.clear();
+    Set.clear();
+  }
+private:
+  bool isSmall() const { return Set.empty(); }
+
+  VIterator vfind(const T &V) const {
+    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
+      if (*I == V)
+        return I;
+    return Vector.end();
+  }
+};
+
+/// If this set is of pointer values, transparently switch over to using
+/// SmallPtrSet for performance.
+template <typename PointeeType, unsigned N>
+class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
+
+} // end namespace llvm
+
+#endif