RFR: Add missing case for CAE to ShLRB::needs_barrier_impl()

[Aleksey Shipilev]

On 2/22/19 12:23 PM, Roman Kennke wrote:
> We need a case for CompareAndExchangeP|N in
> ShenandoahLoadReferenceBarrierNode::needs_barrier_impl(), otherwise we
> crash in the ShouldNotReachHere() below (in debug builds). This happened
> in CI.
> 
> Testing: hotspot_gc_shenandoah
> 
> http://cr.openjdk.java.net/~rkennke/lrb-cae-2/webrev.00/

But wait, how do we even get these nodes with Shenandoah enabled? Isn't that basically a bug
somewhere else?

-Aleksey