--- /dev/null	2016-05-31 09:42:47.975716356 -0700
+++ new/src/jdk.vm.compiler/share/classes/org.graalvm.compiler.core.common/src/org/graalvm/compiler/core/common/util/FrequencyEncoder.java	2016-12-09 00:47:19.175577258 -0800
@@ -0,0 +1,134 @@
+/*
+ * Copyright (c) 2015, 2015, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.graalvm.compiler.core.common.util;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Creates an array of T objects order by the occurrence frequency of each object. The most
+ * frequently used object is the first one, the least frequently used the last one. If {@code null}
+ * is added, it is always the first element.
+ *
+ * Either object {@link #createIdentityEncoder() identity} or object {@link #createEqualityEncoder()
+ * equality} can be used to build the array and count the frequency.
+ */
+public class FrequencyEncoder<T> {
+
+    static class Entry<T> {
+        protected final T object;
+        protected int frequency;
+        protected int index;
+
+        protected Entry(T object) {
+            this.object = object;
+            this.index = -1;
+        }
+    }
+
+    protected final Map<T, Entry<T>> map;
+    protected boolean containsNull;
+
+    /**
+     * Creates an encoder that uses object identity.
+     */
+    public static <T> FrequencyEncoder<T> createIdentityEncoder() {
+        return new FrequencyEncoder<>(new IdentityHashMap<>());
+    }
+
+    /**
+     * Creates an encoder that uses {@link Object#equals(Object) object equality}.
+     */
+    public static <T> FrequencyEncoder<T> createEqualityEncoder() {
+        return new FrequencyEncoder<>(new HashMap<>());
+    }
+
+    protected FrequencyEncoder(Map<T, Entry<T>> map) {
+        this.map = map;
+    }
+
+    /**
+     * Adds an object to the array.
+     */
+    public void addObject(T object) {
+        if (object == null) {
+            containsNull = true;
+            return;
+        }
+
+        Entry<T> entry = map.get(object);
+        if (entry == null) {
+            entry = new Entry<>(object);
+            map.put(object, entry);
+        }
+        entry.frequency++;
+    }
+
+    /**
+     * Returns the index of an object in the array. The object must have been
+     * {@link #addObject(Object) added} before.
+     */
+    public int getIndex(Object object) {
+        if (object == null) {
+            assert containsNull;
+            return 0;
+        }
+        Entry<T> entry = map.get(object);
+        assert entry != null && entry.index >= 0;
+        return entry.index;
+    }
+
+    /**
+     * Returns the number of distinct objects that have been added, i.e., the length of the array.
+     */
+    public int getLength() {
+        return map.size() + (containsNull ? 1 : 0);
+    }
+
+    /**
+     * Fills the provided array with the added objects. The array must have the {@link #getLength()
+     * correct length}.
+     */
+    public T[] encodeAll(T[] allObjects) {
+        assert allObjects.length == getLength();
+        List<Entry<T>> sortedEntries = new ArrayList<>(map.values());
+        sortedEntries.sort((e1, e2) -> -Integer.compare(e1.frequency, e2.frequency));
+
+        int offset = 0;
+        if (containsNull) {
+            allObjects[0] = null;
+            offset = 1;
+        }
+        for (int i = 0; i < sortedEntries.size(); i++) {
+            Entry<T> entry = sortedEntries.get(i);
+            int index = i + offset;
+            entry.index = index;
+            allObjects[index] = entry.object;
+            assert entry.object != null;
+        }
+        return allObjects;
+    }
+}