RFR: JDK-8226695: Shenandoah: Wire C1 and C2 IN_NATIVE barrier

[Roman Kennke]

Ping?

Roman

> IN_NATIVE accesses in compiled code should go to runtime, in order to be
> able to check reachability of accessed objects, and possibly offer NULL
> for unreachable objects.
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8226695
> Webrev:
> http://cr.openjdk.java.net/~rkennke/JDK-8226695/webrev.00/
> 
> Testing: hotspot_gc_dev
> 
> Ok?
> 
> Roman
>