Example3_3.java

Example3_3.java

// java -ea -Xms16m -Xmx16M -XX:+UnlockExperimentalVMOptions -XX:-UseOnStackReplacement -XX:+PrintEscapeAnalysis -XX:+PrintEliminateAllocations -XX:+UseEpsilonGC -XX:-UseTLAB -XX:+DoPartialEscapeAnalysis -XX:CompileCommand=compileonly,Example3_3::foo -XX:CompileCommand=dontinline,Example3_3::blackhole -XX:CompileCommand=quiet -Xbatch Example3_3
class Example3_3 {
    // use volatile to force c2 to load it again
    volatile int value;

    Example3_3(int value) {
        this.value = value;
    }

    void blackhole(int field) {
        assert field  == 42 :" wrong answer";
    }
  
    public static void foo(int value) {
        var x = new Example3_3(value);
        x.blackhole(x.value);
        return;
    }

    public static void main(String[] args)  {
        long iterations = 0;
        try {
            while (true) {
                foo(42);
                iterations++;
            }
        } finally {
            System.err.println("Epsilon Test: " + iterations);
        }
    }
}

There are two key factors in this example

1. Example3_3::value is volatile, so c2 will use MemBarAcquire for the argument of blackhole(int)
2. Example3_3::blackhole is not inlined. it triggers the materialization of x at function call.

I have a patch to handle this, but I need more time to polish it.
put aside it because it's not a blocker.