RFC: C2 LRB self-fixup for testing to sh/jdk

[Roman Kennke]

This looks good to me.

As discussed on IRC, we need to clarify (post-push) with Roland:
- What's up with EA there. Why it fails without the change, and why the
change fixes it, and if it's correct.
- If we can ditch the whole implicit-null-checking fluff, because the
load of mark-word is gone, which was -afaik- the whole reason why we
needed it to begin with. That would be a nice simplification and one
lesser pain in the ...

Go for it!
Cheers,
Roman

> Hi,
> 
> I want to push these patches to sh/jdk for testing:
>   http://cr.openjdk.java.net/~shade/8225357/webrev.01/
>   http://cr.openjdk.java.net/~shade/8225441/webrev.01/
>   http://cr.openjdk.java.net/~shade/shenandoah/lrb-sfx.patch
> 
> This is the bulk change I am going to push:
>   http://cr.openjdk.java.net/~shade/shenandoah/lrb-c2-fixup/webrev.01/
> 
> Testing: hotspot_gc_shenandoah
>