[vector] Fix variable shift count amount

[Paul Sandoz]

> On May 21, 2018, at 3:50 PM, Lupusoru, Razvan A <razvan.a.lupusoru at intel.com> wrote:
> 
> Hi everyone,
>  
> This is a fix to follow up on an issue that Paul’s comments led to its discovery. Namely that scalar implementation of shift implicitly truncates the shift count while the vector instructions actually saturate on the shift count. This patch fixes this issue. We will be working on adding a few tests soon so stay posted - they will be done as a follow up change.
> http://cr.openjdk.java.net/~rlupusoru/panama/webrev_varshiftcountfix_00/index.html
>  

Thanks for doing this, and for thinking about the tests.

You can use the SPECIES constant rather than the method call, as is used in other places.

It makes me wonder whether we should declare these 0x1f/0x3f vectors in the same manner as ZERO. WDYT?

Paul.

> Thanks,
> Razvan