RFR(M): Shenandoah string dedup support

[Aleksey Shipilev]

On 08/23/2017 07:07 PM, Roman Kennke wrote:
> 
>>  *) Trying to understand the logic for dedup during evacuation. Why do we need to have the block
>> before the fwdptr CAS? Why can't we increment the copy_val age after successful copy?
> As far as I can tell, that would race with other mods of the header
> field (esp. locking) and become really complicated.

Ah, makes sense. Needs comment saying that then.

-Aleksey