RFR: 8238190 : [JVMCI] Fix single implementor speculation for diamond shapes.

[Vladimir Kozlov]

CCing to Runtime group since it is runtime code. Coleen already looked on this fix but we need 
official review here.

David, it seems you did not pull latest fixes from JDK. Most of failures in your testing should be 
fixed already. There are testing infra "red" failures which are nothing to do with changes.
I would suggest to pull latest changes before push (after reviews) and run tier1-2 again.

In short, I don't see new failures in tier1-2 testing and tier3-graal. Fix looks good to me.

Thanks,
Vladimir

On 1/31/20 12:49 AM, David Leopoldseder wrote:
> Hi,
> 
> Please review this tiny change (+ a new test case exercising the pattern) to
> fix the single implementor logic in instanceKlass for diamond shaped class hierarchies.
> 
> This bug was revealed in Graal where we use the single implementor logic for invokeinterface 
> devirtualization.
> 
> https://bugs.openjdk.java.net/browse/JDK-8238190
> http://cr.openjdk.java.net/~davleopo/JDK-8238190/webrev.001/
> 
> Thank you.
> 
> - david
>