Significant Performance Discrepancy Between OpenJ9 and Hotspot JVMs for Simple Java Loop

[xwqmary]

Problem Overview: When executing the following Java program with a loop condition that never meets the exit condition, the OpenJ9 JVM exhibits significantly higher execution time compared to the Hotspot JVM. This behavior suggests that OpenJ9 use the sub-optimal optimization on this program.

Java Code Example:

class B59062_0 {
       static int a = 0;

      public static void main(String[] args) {
          while (a != 14) {
             a += 9;
      }
  }
}

Execution Times:
Hotspot JVM:
time /root/hotspot/jdk-21.0.5/bin/java B59062_0

 real    0m0.341s
 user    0m0.333s
 sys     0m0.021s

Hotspot JVM: The program terminates quickly in approximately 0.34 seconds, suggesting that Hotspot JVM may be optimizing or detecting the infinite loop and exiting early.

OpenJ9 JVM:
time /root/openj9/jdk-21.0.5+11/bin/java B59062_0

real    0m28.353s
user    0m28.483s
sys     0m0.121s

OpenJ9 JVM: The program runs for approximately 28.35 seconds, indicating a prolonged execution likely due to the infinite loop.

Additional Description: I have attempted multiple optimization methods（-Xjit:count=1；-Xaot ；-Xjit:optlevel=scorching ） to improve the performance of the OpenJ9 JVM when executing this code. However, the execution time remains excessively long.

[pshipton]

@hzongaro fyi