CODEWITHSUNDEEP
javaoptimizationbenchmarkingjavac
vach
vach

Reputation: 11397

Possible unwanted compiler optimization on benchmark test

I've developed a small library that enables declarative argument validation using annotations, something like this:

@Validate({"not null | number"})
public static Integer notNullAnnotated(Integer number) {
    return number++;
}

now I'm benchmarking this against pure java code version:

public static Integer notNullInline(Integer number) {
    if (number != null) {
        return number++;
    } else {
        throw new IllegalArgumentException("argument should not be null");
    }
}

and here is the test:

@Test
public void performanceTest() {
    long time = System.nanoTime();
    for (int i = 0; i < iterationCount; i++) {
        notNullAnnotated(i);
    }
    System.out.println("time annotated : " + (System.nanoTime() - time));

    time = System.nanoTime();
    for (int i = 0; i < iterationCount; i++) {
        notNullInline(i); // TODO does compiler do any optimization here?
    }
    System.out.println("time inline : " + (System.nanoTime() - time));
}

I know that this is not the intended way to do benchmark tests. Right now I'd rather avoid adding any utility libraries for this simple test (as even this way results are good), but I'd like to know if compiler does any optimization here?

Upvotes: 0

Views: 183

Answers (2)

meriton
meriton

Reputation: 70584

Of course the just in time compiler will optimize your code (assuming a reasonably high iteration count), just as it would in an actual programm running that code. Optimization, by itself, is therefore desireable in a benchmark. Of course you'll have a problem if the artificial nature of your code permits optimizations not available to the real code. In your case, the compiler may conclude that notNullInline will never throw, therefore have no effect, and choose to remove the entire loop.

Writing a correct benchmark is already discussed at How do I write a correct micro-benchmark in Java?

Upvotes: 1

David Ehrmann
David Ehrmann

Reputation: 7576

Since you're already this far down the premature optimization path, look into the PrintAssembly and CompileThreshold flags for Hotspot. The first option lets you inspect the assembly Hotspot generates. The second lets you set a threshold for when the JIT kicks in.

Upvotes: 2

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