[vector] RFR: Rematerialization support for vector masks

[Paul Sandoz]

> On Mar 5, 2018, at 4:08 PM, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
> 
> http://cr.openjdk.java.net/~vlivanov/panama/vector/mask_rematerialization/webrev.00/
> 
> Vector masks need special treatment in JVM to support rematerialization at safepoints.
> 
> Also, temporarily converted Vector.Mask and Vector.Shuffle from interfaces to abstract classes to overcome limitations of vector box elimination implementation. Once the analysis is enhanced to cover interfaces, they should be converted back.
> 
> Contributed-by: vlivanov, rlupusoru
> 

+1 on Java bits.

Paul.