JDK7 do escape analysis by default

During the JVM Summit, I was doing some tests for
my presentation with the latest
jdk7 binaries
when I've seen some *BIG* performance improvement between jdk7 b71 and jdk7 b72.


A quick look to the summary of changes, hum,
Escape Analysis is now enabled by default.


On my tests, I got a 3x improvement, Wow !

With a quick micro-benchmark, it's even better, as always :)

  class DoubleSlot {
    final int value1;
    final int value2;
    
    public DoubleSlot(int value1, int value2) {
      this.value1 = value1;
      this.value2 = value2;
    }
  }
  
  static int slotValue(DoubleSlot slot) {
    return slot.value1 + slot.value2;
  }
  
  static int sum(int[] values) {
    int sum = 0;
    int length = values.length;
    for(int i=1; i<length; i++) {
      DoubleSlot slot = new DoubleSlot(values[i-1], values[i]);
      sum += slotValue(slot);
    }
    return sum;
  }

  static void test(int[] values) {
    long start = System.nanoTime();
    int value = sum(values);
    long end = System.nanoTime();
    System.out.println("time "+(end-start)+" "+value);
  }
  
  public static void main(String[] args) {
    int[] values = new int[1000000];
    for(int i=0; i<values.length; i++) {
      values[i] = i;
    }
    
    for(int i=0; i<100; i++)
      sum(values);
    
    for(int i=0; i<100; i++)
      test(values);
  }

With Escape Analysis, the allocation of DoubleSlot is not done anymore.

  $ /usr/jdk/jdk1.7.0b71/bin/java -server EscapeAnalysisTest
  time 8889261

  $ /usr/jdk/jdk1.7.0b73/bin/java -server EscapeAnalysisTest
  time 1408140

I love this kind of optimisation, you don't change your program,
just use a newer VM, and got a 3x improvement :)


cheers,


Rémi