What does AggressiveOpts do with my timings?

[Regina Anger]

Hi,

When I run the code attached belog with -XX:+AggressiveOpts I get weird timings.


  1       BugTest::fillRect (27 bytes)
  2       java.lang.Math::abs (11 bytes)
  1%      BugTest::main @ 9 (50 bytes)
  1%  made not entrant  (2)  BugTest::main @ 9 (50 bytes)
Run: 677
  2%      BugTest::main @ 9 (50 bytes)
Run: 780
Run: 623
Run: 676
Run: 676
Run: 624
Run: 104  <----- Why so low?
Run: 1193<------ Why so high?
Run: 624

Without -XX:+AggressiveOpts the timings are stable at ~630ms after initial warm-up.
I am using JDK7b20 on Linux.
Although its really unimporntant, I am quite curious, whats going on here?

Regi

public class SpeedTest {
	static int[] opcodes = new int[30];
	static int cnt = 0;
	static int dummy=0;
	
	public static void main(String[] args) {
		while (true)
		{			
			long start = System.currentTimeMillis();
			
			for (int i = 0; i < 100000000; i++)
			{
				test();
			}
			System.out.println("Run: " + (System.currentTimeMillis() - start));
		}
	}
	
	public static final void test() {
			dummy += opcodes[Math.abs(++cnt % 30)];
	}
}
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