RFR: Use PLAB for evacuations instead of TLAB

[Aleksey Shipilev]

On 05/11/2018 10:31 PM, Roman Kennke wrote:
> Differential patch:
> http://cr.openjdk.java.net/~rkennke/plab-gclab/webrev.04.diff/
> Full patch:
> http://cr.openjdk.java.net/~rkennke/plab-gclab/webrev.04/
> 
> Ok?

OK. "obj1" might use a better name, e.g. "head_obj"?

A bit sad we need to call post-alloc setup for fillers. We should maybe revisit this places some
time later, and split the paths with UseShenandoahGC.

-Aleksey