Constant folding

Constant folding is the flip side of the DCE. If your calculation is based on constants and the result is often exactly the same, the JVM will detect this and replace the calculation with the result. To make sure this doesn't happen, we can move the computation outside the internal JMH loop. Constant folding can be prevented by always reading the inputs from non-final instance fields of a state object. In this case, the result will be based on fields of the state object:

@Benchmark
public int testMethod() {
    int a = 3;
    int b = 4;
    return a + b;
}

So, in the preceding code, the JVM can detect that the result value is based on two constants, a and b, and can replace our code with this:

public class MyBenchmark {
    @Benchmark
    public int testMethod() {
        int c = 3;
        return c;
    }
}

Or it can just return 3 or replace the invocation of this method with 3. To solve this problem, you should rewrite the code as follows:

public class MyBenchmark {

    @State(Scope.Thread)
    public static class MyState {
        int a = 3;
        int b = 4;
    }

    @Benchmark
    @BenchmarkMode(Mode.AverageTime)
    @OutputTimeUnit(TimeUnit.NANOSECONDS)
    public int testMethod(MyState state) {
        return state.a + state.b;
    }

}