RFR: 8184181: Use oopDesc::cas_set_mark() instead of raw CAS when accessing oop header

[Kim Barrett]

> On Jul 14, 2017, at 7:31 AM, Roman Kennke <rkennke at redhat.com> wrote:
> 
> BiasedLocking and ObjectSynchronizer both use raw Atomic::cmpxchg_ptr()
> calls to CAS the header word of an oop. It's cleaner to use
> oopDesc::cas_set_mark() instead. Besides this being a cleanup, in the
> future (Shenandoah) we will also require GC barriers to do the right
> thing there.
> 
> Webrev:
> http://cr.openjdk.java.net/~rkennke/8184181/webrev.00/
> <http://cr.openjdk.java.net/%7Erkennke/8184181/webrev.00/>
> 
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8184181
> 
> Ok?
> 
> Tested by running hotspot_runtime tests.
> 
> Roman

Looks good.