RFR: Uses keep_alive_barrier to keep deduped char array alive

[Aleksey Shipilev]

On 10/11/2017 08:41 PM, Zhengyu Gu wrote:
> We need to use newly introduced keep_alive_barrier to ensure deduped string's char array alive, as
> required by new concurrent partial GC.
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/strdedup_keep_alive/webrev.00/e

Shouldn't the read barrier be on some common path, and not here, at least not under UseShenandoahGC?
Why do we need it here?

-Aleksey