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diff --git a/include/llvm/ADT/IndexedMap.h b/include/llvm/ADT/IndexedMap.h
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+//===- llvm/ADT/IndexedMap.h - An index map implementation ------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements an indexed map. The index map template takes two
+// types. The first is the mapped type and the second is a functor
+// that maps its argument to a size_t. On instantiation a "null" value
+// can be provided to be used as a "does not exist" indicator in the
+// map. A member function grow() is provided that given the value of
+// the maximally indexed key (the argument of the functor) makes sure
+// the map has enough space for it.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_INDEXEDMAP_H
+#define LLVM_ADT_INDEXEDMAP_H
+
+#include <cassert>
+#include <functional>
+#include <vector>
+
+namespace llvm {
+
+  struct IdentityFunctor : std::unary_function<unsigned, unsigned> {
+    unsigned operator()(unsigned Index) const {
+      return Index;
+    }
+  };
+
+  template <typename T, typename ToIndexT = IdentityFunctor>
+  class IndexedMap {
+    typedef typename ToIndexT::argument_type IndexT;
+    typedef std::vector<T> StorageT;
+    StorageT storage_;
+    T nullVal_;
+    ToIndexT toIndex_;
+
+  public:
+    IndexedMap() : nullVal_(T()) { }
+
+    explicit IndexedMap(const T& val) : nullVal_(val) { }
+
+    typename StorageT::reference operator[](IndexT n) {
+      assert(toIndex_(n) < storage_.size() && "index out of bounds!");
+      return storage_[toIndex_(n)];
+    }
+
+    typename StorageT::const_reference operator[](IndexT n) const {
+      assert(toIndex_(n) < storage_.size() && "index out of bounds!");
+      return storage_[toIndex_(n)];
+    }
+
+    void clear() {
+      storage_.clear();
+    }
+
+    void grow(IndexT n) {
+      unsigned NewSize = toIndex_(n) + 1;
+      if (NewSize > storage_.size())
+        storage_.resize(NewSize, nullVal_);
+    }
+
+    typename StorageT::size_type size() const {
+      return storage_.size();
+    }
+  };
+
+} // End llvm namespace
+
+#endif