RFR: 8166583: Add oopDesc::klass_or_null_acquire()

[Thomas Schatzl]

Hi Kim,

On Thu, 2016-09-22 at 16:51 -0400, Kim Barrett wrote:
> Please review this addition of a new function to oopDesc.  This is a
> variant of an existing function; the new function provides acquire
> semantics to the access.
> 
> This is a subtask of JDK-8160369, providing additional infrastructure
> needed to fix that bug.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8166583
> 
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8166583/webrev.00/
> 
> Testing:
> Ran nightly tests with this being used by an in-development fix for
> part of JDK-8160369.
> 

  looks good.

Is there a bug filed for fixing the "// Workaround for non-const
load_acquire parameter." comment? I.e. it seems that actually more
infrastructure changes are required that have been deferred for now.

Thanks,
  Thomas