RFR[XS] JDK-8178543 - Optimize Klass::is_shared()

[Jiangli Zhou]

Hi Ioi,

Could you please explain the change in klassVtable.cpp?

Thanks,
Jiangli

> On Apr 13, 2017, at 2:30 AM, Ioi Lam <ioi.lam at oracle.com> wrote:
> 
> Hi, please review this small start-up enhancement:
> 
> https://bugs.openjdk.java.net/browse/JDK-8178543
> http://cr.openjdk.java.net/~iklam/jdk10/8178543-klass-is-shared.v01/
> 
> We have a benchmark that shows Klass::is_shared() is called very frequently during InstanceKlass::link_class_impl, and costs about 2% of the start-up time.
> 
> The fix is simple -- instead of walking the list of CDS shared regions, use a new bit in Klass::_access_flags
> 
> Thanks
> - Ioi