TestLogSum.java

/*
 * Copyright (c) 2014, 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.
 *
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 */

/*
 * @test
 * @bug 8046516
 * @summary Segmentation fault in JVM (easily reproducible)
 *
 * @run main/othervm -XX:-TieredCompilation -Xbatch compiler.loopopts.TestLogSum
 * @author [email protected]
 */

package compiler.loopopts;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class TestLogSum {
  public static void main(String[] args) {
    double sum;

    for (int i = 0; i < 6; i++) {
        for (int n = 2; n < 30; n++) {
           for (int j = 1; j <= n; j++) {
              for (int k = 1; k <= j; k++) {
                // System.out.println(computeSum(k, j));
                sum = computeSum(k, j);
              }
           }
        }
      }
   }

   private static Map<List<Integer>, Double> cache = new HashMap<List<Integer>, Double>();
   public static double computeSum(int x, int y) {
      List<Integer> key = Arrays.asList(new Integer[] {x, y});

      if (!cache.containsKey(key)) {

        // explicitly creating/updating a double[] array, instead of using the LogSumArray wrapper object, will prevent the error
        LogSumArray toReturn = new LogSumArray(x);

        // changing loop indices will prevent the error
        // in particular, for(z=0; z<x-1; z++), and then using z+1 in place of z, will not produce error
        for (int z = 1; z < x+1; z++) {
           double logSummand = Math.log(z + x + y);
           toReturn.addLogSummand(logSummand);
        }

        // returning the value here without cacheing it will prevent the segfault
        cache.put(key, toReturn.retrieveLogSum());
      }
      return cache.get(key);
   }

   /*
    * Given a bunch of logarithms log(X),log(Y),log(Z),...
    * This class is used to compute the log of the sum, log(X+Y+Z+...)
    */
   private static class LogSumArray {
      private double[] logSummandArray;
      private int currSize;

      private double maxLogSummand;

      public LogSumArray(int maxEntries) {
        this.logSummandArray = new double[maxEntries];

        this.currSize = 0;
        this.maxLogSummand = Double.NEGATIVE_INFINITY;
      }

      public void addLogSummand(double logSummand) {
        logSummandArray[currSize] = logSummand;
        currSize++;
        // removing this line will prevent the error
        maxLogSummand = Math.max(maxLogSummand, logSummand);
      }

      public double retrieveLogSum() {
        if (maxLogSummand == Double.NEGATIVE_INFINITY) return Double.NEGATIVE_INFINITY;

        assert currSize <= logSummandArray.length;

        double factorSum = 0;
        for (int i = 0; i < currSize; i++) {
           factorSum += Math.exp(logSummandArray[i] - maxLogSummand);
        }

        return Math.log(factorSum) + maxLogSummand;
      }
   }
}