RFR: fix aarch64 membar elision with shenandoah

[Aleksey Shipilev]

On 07/12/2018 05:05 PM, Roman Kennke wrote:
> Am 12.07.2018 um 15:51 schrieb Roland Westrelin:
>>
>> http://cr.openjdk.java.net/~roland/shenandoah/aarch64-membars-elision/webrev.02/
>>
>> This fixes membar elision on aarch64 with shenandoah. Thanks to Andrew
>> Dinn for verifying the change and fixing the traversal gc case.
>>
>> Roland.
>>
> 
> 
> The patch looks good.
> 
> I verified that it builds + passes tests.
> 
> I'll check the predicates in x86. They should be equivalent.

If there are predicate changes that make sense on their own, they should be pushed as separate
changesets, so they arrive to backports.

-Aleksey