--- a/graal/com.oracle.graal.debug.test/src/com/oracle/graal/debug/test/DebugHistogramTest.java	Fri Sep 06 18:11:30 2013 +0200
+++ b/graal/com.oracle.graal.debug.test/src/com/oracle/graal/debug/test/DebugHistogramTest.java	Mon Sep 09 13:57:53 2013 +0200
@@ -27,6 +27,7 @@
 import org.junit.*;
 
 import com.oracle.graal.debug.*;
+import com.oracle.graal.debug.internal.*;
 
 public class DebugHistogramTest {
 
@@ -34,7 +35,7 @@
     public void testEmptyHistogram() {
         DebugHistogram histogram = Debug.createHistogram("TestHistogram");
         ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
-        histogram.print(new PrintStream(outputStream));
+        new DebugHistogramAsciiPrinter(new PrintStream(outputStream)).print(histogram);
         Assert.assertEquals("TestHistogram is empty.\n", outputStream.toString());
     }
 
@@ -44,7 +45,7 @@
         ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
         histogram.add(new Integer(1));
         histogram.add(new Integer(1));
-        histogram.print(new PrintStream(outputStream));
+        new DebugHistogramAsciiPrinter(new PrintStream(outputStream)).print(histogram);
         String[] lines = outputStream.toString().split("\n");
         Assert.assertEquals(4, lines.length);
         Assert.assertEquals("TestHistogram has 1 unique elements and 2 total elements:", lines[0]);
@@ -66,7 +67,7 @@
         histogram.add(new Integer(1));
         histogram.add(new Integer(2));
         histogram.add(new Integer(2));
-        histogram.print(new PrintStream(outputStream));
+        new DebugHistogramAsciiPrinter(new PrintStream(outputStream)).print(histogram);
         String[] lines = outputStream.toString().split("\n");
         Assert.assertEquals(5, lines.length);
         Assert.assertEquals("TestHistogram has 2 unique elements and 3 total elements:", lines[0]);
@@ -89,7 +90,7 @@
         DebugHistogram histogram = Debug.createHistogram("TestHistogram");
         ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
         histogram.add("MyCustomValue");
-        histogram.print(new PrintStream(outputStream), Integer.MAX_VALUE, 10, 10);
+        new DebugHistogramAsciiPrinter(new PrintStream(outputStream), Integer.MAX_VALUE, 10, 10).print(histogram);
         String[] lines = outputStream.toString().split("\n");
         Assert.assertEquals(4, lines.length);
         Assert.assertEquals("TestHistogram has 1 unique elements and 1 total elements:", lines[0]);

--- a/graal/com.oracle.graal.debug/src/com/oracle/graal/debug/Debug.java	Fri Sep 06 18:11:30 2013 +0200
+++ b/graal/com.oracle.graal.debug/src/com/oracle/graal/debug/Debug.java	Mon Sep 09 13:57:53 2013 +0200
@@ -342,6 +342,9 @@
         }
     }
 
+    /**
+     * Creates an object for counting value frequencies.
+     */
     public static DebugHistogram createHistogram(String name) {
         return new DebugHistogramImpl(name);
     }

--- a/graal/com.oracle.graal.debug/src/com/oracle/graal/debug/DebugHistogram.java	Fri Sep 06 18:11:30 2013 +0200
+++ b/graal/com.oracle.graal.debug/src/com/oracle/graal/debug/DebugHistogram.java	Mon Sep 09 13:57:53 2013 +0200
@@ -22,15 +22,75 @@
  */
 package com.oracle.graal.debug;
 
-import java.io.*;
+import java.util.*;
 
+/**
+ * Facility for recording value frequencies.
+ */
 public interface DebugHistogram {
 
+    /**
+     * Gets the name specified when this objected was {@linkplain Debug#createHistogram(String)
+     * created}.
+     */
     String getName();
 
+    /**
+     * Increments the count for a given value.
+     */
     void add(Object value);
 
-    void print(PrintStream os);
+    /**
+     * A value and a frequency. The ordering imposed by {@link #compareTo(CountedValue)} places
+     * values with higher frequencies first.
+     */
+    public class CountedValue implements Comparable<CountedValue> {
+
+        private int count;
+        private final Object value;
+
+        public CountedValue(int count, Object value) {
+            this.count = count;
+            this.value = value;
+        }
+
+        public int compareTo(CountedValue o) {
+            if (count < o.count) {
+                return 1;
+            } else if (count > o.count) {
+                return -1;
+            }
+            return 0;
+        }
 
-    void print(PrintStream os, int limit, int nameSize, int barSize);
+        @Override
+        public String toString() {
+            return count + " -> " + value;
+        }
+
+        public void inc() {
+            count++;
+        }
+
+        public int getCount() {
+            return count;
+        }
+
+        public Object getValue() {
+            return value;
+        }
+    }
+
+    /**
+     * Gets a list of the counted values, sorted in descending order of frequency.
+     */
+    List<CountedValue> getValues();
+
+    /**
+     * Interface for a service that can render a visualization of a histogram.
+     */
+    public interface Printer {
+
+        void print(DebugHistogram histogram);
+    }
 }

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.graal.debug/src/com/oracle/graal/debug/internal/DebugHistogramAsciiPrinter.java	Mon Sep 09 13:57:53 2013 +0200
@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2013, 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 com.oracle.graal.debug.internal;
+
+import java.io.*;
+import java.util.*;
+
+import com.oracle.graal.debug.*;
+import com.oracle.graal.debug.DebugHistogram.*;
+
+/**
+ * Renders a textual representation of a histogram to a given print stream.
+ */
+public class DebugHistogramAsciiPrinter implements Printer {
+
+    public static final int NumberSize = 10;
+    public static final int DefaultNameSize = 50;
+    public static final int DefaultBarSize = 100;
+
+    private PrintStream os;
+    private int limit;
+    private int nameSize;
+    private int barSize;
+
+    public DebugHistogramAsciiPrinter(PrintStream os) {
+        this(os, Integer.MAX_VALUE, DefaultNameSize, DefaultBarSize);
+    }
+
+    /**
+     * @param os where to print
+     * @param limit limits printing to the {@code limit} most frequent values
+     * @param nameSize the width of the value names column
+     * @param barSize the width of the value frequency column
+     */
+    public DebugHistogramAsciiPrinter(PrintStream os, int limit, int nameSize, int barSize) {
+        this.os = os;
+        this.limit = limit;
+        this.nameSize = nameSize;
+        this.barSize = barSize;
+    }
+
+    public void print(DebugHistogram histogram) {
+        List<CountedValue> list = histogram.getValues();
+        if (list.isEmpty()) {
+            os.printf("%s is empty.\n", histogram.getName());
+            return;
+        }
+
+        // Sum up the total number of elements.
+        int total = 0;
+        for (CountedValue cv : list) {
+            total += cv.getCount();
+        }
+
+        // Print header.
+        os.printf("%s has %d unique elements and %d total elements:\n", histogram.getName(), list.size(), total);
+
+        int max = list.get(0).getCount();
+        final int lineSize = nameSize + NumberSize + barSize + 10;
+        printLine(os, '-', lineSize);
+        String formatString = "| %-" + nameSize + "s | %-" + NumberSize + "d | %-" + barSize + "s |\n";
+        for (int i = 0; i < list.size() && i < limit; ++i) {
+            CountedValue cv = list.get(i);
+            int value = cv.getCount();
+            char[] bar = new char[(int) (((double) value / (double) max) * barSize)];
+            Arrays.fill(bar, '=');
+            String objectString = String.valueOf(cv.getValue());
+            if (objectString.length() > nameSize) {
+                objectString = objectString.substring(0, nameSize - 3) + "...";
+            }
+            os.printf(formatString, objectString, value, new String(bar));
+        }
+        printLine(os, '-', lineSize);
+    }
+
+    private static void printLine(PrintStream printStream, char c, int lineSize) {
+        char[] charArr = new char[lineSize];
+        Arrays.fill(charArr, c);
+        printStream.printf("%s\n", new String(charArr));
+    }
+}

--- a/graal/com.oracle.graal.debug/src/com/oracle/graal/debug/internal/DebugHistogramImpl.java	Fri Sep 06 18:11:30 2013 +0200
+++ b/graal/com.oracle.graal.debug/src/com/oracle/graal/debug/internal/DebugHistogramImpl.java	Mon Sep 09 13:57:53 2013 +0200
@@ -22,28 +22,25 @@
  */
 package com.oracle.graal.debug.internal;
 
-import java.io.*;
 import java.util.*;
 
 import com.oracle.graal.debug.*;
 
 public class DebugHistogramImpl implements DebugHistogram {
 
-    public static final int NumberSize = 10;
-    public static final int DefaultNameSize = 50;
-    public static final int DefaultBarSize = 100;
     private final String name;
-    private HashMap<Object, Integer> map = new HashMap<>();
+    private HashMap<Object, CountedValue> map = new HashMap<>();
 
     public DebugHistogramImpl(String name) {
         this.name = name;
     }
 
     public void add(Object value) {
-        if (!map.containsKey(value)) {
-            map.put(value, 1);
+        CountedValue cv = map.get(value);
+        if (cv == null) {
+            map.put(value, new CountedValue(1, value));
         } else {
-            map.put(value, map.get(value) + 1);
+            cv.inc();
         }
     }
 
@@ -52,59 +49,9 @@
         return name;
     }
 
-    @Override
-    public void print(PrintStream os) {
-        print(os, Integer.MAX_VALUE, DefaultNameSize, DefaultBarSize);
-    }
-
-    public void print(PrintStream os, int limit, int nameSize, int barSize) {
-
-        List<Object> list = new ArrayList<>(map.keySet());
-        if (list.size() == 0) {
-            // No elements in the histogram.
-            os.printf("%s is empty.\n", name);
-            return;
-        }
-
-        // Sort from highest to smallest.
-        Collections.sort(list, new Comparator<Object>() {
-
-            @Override
-            public int compare(Object o1, Object o2) {
-                return map.get(o2) - map.get(o1);
-            }
-        });
-
-        // Sum up the total number of elements.
-        int total = 0;
-        for (Object o : list) {
-            total += map.get(o);
-        }
-
-        // Print header.
-        os.printf("%s has %d unique elements and %d total elements:\n", name, list.size(), total);
-
-        int max = map.get(list.get(0));
-        final int lineSize = nameSize + NumberSize + barSize + 10;
-        printLine(os, '-', lineSize);
-        String formatString = "| %-" + nameSize + "s | %-" + NumberSize + "d | %-" + barSize + "s |\n";
-        for (int i = 0; i < list.size() && i < limit; ++i) {
-            Object o = list.get(i);
-            int value = map.get(o);
-            char[] bar = new char[(int) (((double) value / (double) max) * barSize)];
-            Arrays.fill(bar, '=');
-            String objectString = o.toString();
-            if (objectString.length() > nameSize) {
-                objectString = objectString.substring(0, nameSize - 3) + "...";
-            }
-            os.printf(formatString, objectString, value, new String(bar));
-        }
-        printLine(os, '-', lineSize);
-    }
-
-    private static void printLine(PrintStream printStream, char c, int lineSize) {
-        char[] charArr = new char[lineSize];
-        Arrays.fill(charArr, c);
-        printStream.printf("%s\n", new String(charArr));
+    public List<CountedValue> getValues() {
+        ArrayList<CountedValue> res = new ArrayList<>(map.values());
+        Collections.sort(res);
+        return res;
     }
 }

--- a/graal/com.oracle.graal.truffle/src/com/oracle/graal/truffle/PartialEvaluator.java	Fri Sep 06 18:11:30 2013 +0200
+++ b/graal/com.oracle.graal.truffle/src/com/oracle/graal/truffle/PartialEvaluator.java	Mon Sep 09 13:57:53 2013 +0200
@@ -31,6 +31,7 @@
 import com.oracle.graal.api.code.*;
 import com.oracle.graal.api.meta.*;
 import com.oracle.graal.debug.*;
+import com.oracle.graal.debug.internal.*;
 import com.oracle.graal.graph.*;
 import com.oracle.graal.graph.Node;
 import com.oracle.graal.hotspot.*;
@@ -148,7 +149,7 @@
                     for (Constant c : constantReceivers) {
                         histogram.add(c.asObject().getClass().getSimpleName());
                     }
-                    histogram.print(TTY.out().out());
+                    new DebugHistogramAsciiPrinter(TTY.out().out()).print(histogram);
                 }
 
                 // Additional inlining.