RFR(sh/jdk8): [backport] 8231087: Shenandoah: Self-fixing load reference barriers for C1/C2

[Roman Kennke]

I made a mistake in the aarch64 parts. Please review this webrev instead:

http://cr.openjdk.java.net/~rkennke/JDK-8231087-jdk8/webrev.02/

> 2nd attempt:
> 
> Issue:
> https://bugs.openjdk.java.net/browse/JDK-8231087
> 
> Backport:
> http://cr.openjdk.java.net/~rkennke/JDK-8231087-jdk8/webrev.01/
> 
> This time includes the actual C1 stuff (depended on JDK-8228369).
> 
> Let's include a few follow-ups:
> 
> https://bugs.openjdk.java.net/browse/JDK-8233165
> http://cr.openjdk.java.net/~rkennke/JDK-8233165-jdk8/webrev.00/
> 
> and
> 
> https://bugs.openjdk.java.net/browse/JDK-8233021
> http://cr.openjdk.java.net/~rkennke/JDK-8233021-jdk8/webrev.00/
> 
> and
> 
> https://bugs.openjdk.java.net/browse/JDK-8238153
> http://cr.openjdk.java.net/~rkennke/JDK-8238153-jdk8/webrev.00/
> 
> Can I please get a review?
> 
> Thanks,
> Roman