[vector] RFR 8218750: Vectorized ChaCha20 Benchmark

[Adam Petcher]

New webrev: https://cr.openjdk.java.net/~apetcher/8218750/webrev.01/

On 2/11/2019 8:23 PM, Vladimir Ivanov wrote:
>
> A couple of minor suggestions:
>
>   - I'd prefer to see the benchmark condensed into a single file.

I moved the implementation into ChaChaBench as a nested class.

>
>   - IMO it's better to declare a dedicated @Benchmark method per 
> vector shape instead:
>
>   35     @Param({"128", "256", "512"})
>   36     private int vectorWidth;

I accomplished this (in the latest webrev) by making a subclass for each 
shape. This organization allows the shape-specific setup to happen 
outside of the benchmark method. There is no subclass for 64-bit, 
because the implementation needs a minimum of 128 bits by design.