Enable optimization of arraycopy as loads/stores with Shenandoah

[Roman Kennke]

Am Donnerstag, den 08.12.2016, 16:55 +0100 schrieb Roland Westrelin:
> > This removes the call to SharedRuntime::shenandoah_clone_barrier().
> 
> It doesn't remove it. It moves it around. It's now only added to
> those
> clones that were not converted to loads/stores. Clone when it's not
> converted to loads/stores uses bulk copies. So it's not obvious to me
> that we can do better than using the
> SharedRuntime::shenandoah_clone_barrier() call.

Now that you say it, I wonder what's done for other GCs. They must be
doing something here, to update the card tables. Other arraycopy
routines call a special barrier in
BarrierSet::static_write_ref_array_post(), this is not suitable for
clones, but do they call any barrier for clone too? Or can other GCs
ignore it because it's basically initializing stores?

Roman