RFR(S): 8231988: Unexpected test result caused by C2 IdealLoopTree::do_remove_empty_loop

[Yangfei (Felix)]

Hi,

  After some more try, I finally came up with a test case which does not depend on 8u javac to trigger the problem.  

public class Test8231988 {

    public void mainTest() {
        int i = 34;
        for (; i > 0; i -= 11);
        if (i < 0) {
            // Test passed
        } else {
            throw new RuntimeException("Test failed");
        }
    }

    public static void main(String[] args) {
        Test8231988 _instance = new Test8231988();
        for (int i = 0; i < 50000; i++) {
            _instance.mainTest();
        }
        System.out.println("Test passed.");
    }

}

$ java -version
openjdk version "14-internal" 2020-03-17
OpenJDK Runtime Environment (build 14-internal+0-adhoc.yangfei.openjdk-jdk)
OpenJDK 64-Bit Server VM (build 14-internal+0-adhoc.yangfei.openjdk-jdk, mixed mode, sharing)

$ javac Test8231988.java

$ java -Xint Test8231988
Test passed.

$ java -XX:-BackgroundCompilation -XX:-TieredCompilation Test8231988
Exception in thread "main" java.lang.RuntimeException: Test failed
        at Test8231988.mainTest(Test8231988.java:44)
        at Test8231988.main(Test8231988.java:51)

I am going to add this under test/hotspot/jtreg/compiler/c2 directory. 

Thanks,
Felix


> 
> Hmm...
> Looks like the reduced test case on the bugzilla is not suitable for us.
> It needs to be compiled by a 8u javac in order to triggers this problem.
> The bug will not trigger if we compile the test case by 11u javac or higher
> versions.
> I don't have other test cases to trigger this bug for now.
> 
> Thanks,
> Felix
> 
> >
> > Hi Nils,
> >
> >   Thanks for performing the test.
> >   Sure, let me add one based on the reduced test case on the bugzilla.
> >
> > Felix
> >
> > >
> > > Hi Felix,
> > >
> > > Do you have a test case that triggers this problem? Could you add
> > > that as a jtreg test?
> > >
> > > I have run your patch through testing tier1-3 and the results look good.
> > >