RFR: fix aarch64 membar elision with shenandoah

[Roman Kennke]

Am 12.07.2018 um 18:11 schrieb Roland Westrelin:
> 
>> Oh wait, I just got this from a test:
>>
>> #  Internal Error
>> (/home/rkennke/src/shenandoah-jdk/src/hotspot/cpu/aarch64/aarch64.ad:2873),
>> pid=27969, tid=28271
>> #  guarantee(mbar != NULL) failed: CAS not embedded in normal graph!
> 
> What test it it? Do you have a replay file? Is it with traversal
> enabled?
> 
> Roland.
> 

That was gc/shenandoah/TestSelectiveBarrierFlags.java

If you have access to merino, the replay and hs_err are here:

/tmp/replay_pid27969.log
/tmp/hs_err_pid27969.log

It happened with usual test run:
make run-test TEST=tier3_gc_shenandoah

Thanks, Roman