RFR: Improve/trim register saving/restoring around WB slowpath call in stub

[Roman Kennke]

http://cr.openjdk.java.net/~rkennke/improve-wb-stub/webrev.01/

Roman

> On 11/21/18 12:56 PM, Roman Kennke wrote:
>>>> http://cr.openjdk.java.net/~rkennke/improve-wb-stub/webrev.00/
>>>
>>> Can you rebase it to current Shenandoah, please?
>>
>> It is already based on current Shenandoah.
> 
> I meant, please rebase the patch against current sh/jdk, which now includes the "redo" of WB change.
> 
> -Aleksey
>