RFR: 8227085: ZGC: Add on_weak load barrier verification

[Erik Österlund]

Hi Stefan,

Looks good.

Thanks,
/Erik

On 2019-07-02 15:47, Stefan Karlsson wrote:
> Hi all,
>
> Please review this patch to add some verification to our on_weak load 
> barriers.
>
> http://cr.openjdk.java.net/~stefank/8227085/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8227085
>
> We've had a few bugs where on_weak load barriers have been generated 
> instead of the normal, on_strong, load barriers. The on_weak barriers 
> should only be used to read the referent fields of WeakReferences and 
> SoftReferences. The given oop* is used to calculate the address of the 
> containing object and check that it is a valid Reference object.
>
> This code was tested against the bugs in JDK-8225770 and JDK-8227083.
>
> Tested with tier 1-7
>
> Thanks,
> StefanK