Add missing barrier in C1 NIOCheckIndex intrinsic

[Aleksey Shipilev]

On 12/21/2017 04:09 PM, Roman Kennke wrote:
> We're missing a read-barrier in a C1 intrinsic for NIO checkIndex.
> 
> This is the root cause for:
> http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-December/004495.html
> 
> This is the fix:
> http://cr.openjdk.java.net/~rkennke/c1-missing-barrier/webrev.00/

This makes sense.

I just got home, and was meaning to write the regression test for it. Give me an hour?

-Aleksey