[11] RFR jck test fails with C2: vm/jvmti/FollowReferences/fref001/fref00113/fref00113.html

[Vladimir Kozlov]

On 7/2/18 10:39 AM, Paul Sandoz wrote:
> Hi,
> 
> Please review this fix for 11:
> 
>    http://cr.openjdk.java.net/~psandoz/jdk/JDK-8202769-ci-stream-cp-tag/webrev/

Seems good to me. I will run testing with it.

> 
> This is a regression introduced by constant dynamic that causes a JCK test to fail when using "-Xcomp -XX:-TieredCompilation”.
> 
> The problem is due to a lossy mapping between a constant tag and basic type.
> 
> A constant tag of say JVM_CONSTANT_Class is mapped to a basic type of T_OBJECT. T_OBJECT is mapped to a constant tag of JVM_CONSTANT_String. So the round trip is lossy, and this for some reasons results in the JVMTI test failure under certain conditions. This also includes mapping JVM_CONSTANT_UnresolvedClass to T_OBJECT, which might be the source of the problem.
> 
> I verified all the JCK JVMTI tests pass with "-Xcomp -XX:-TieredCompilation”.

Thank you.

> 
> I am not familiar with the interactions between JVMTI,  -Xcomp, and C2. So i don’t fully understand why the failure occurred under certain conditions and not others.

-Xcomp -XX:-TieredCompilation combination means is compiled all called 
methods and only C2 JIT is used.

I think we may not running JCK testing with this combination of flags. 
The problem was reported by Goetz from SAP.

Thanks,
Vladimir

> 
> Thanks,
> Paul.
>