Add missing barrier in C1 NIOCheckIndex intrinsic

[Aleksey Shipilev]

On 12/21/2017 04:13 PM, Roman Kennke wrote:
> Am 21.12.2017 um 16:13 schrieb 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?
>>
> 
> Oh yes, that would be perfect!

Coming up with a regression test for this proves much more difficult than I anticipated: we seem to
be needing a particular sequence of ByteBuffer calls to arrive to the bug. I'll figure it out
eventually. Meanwhile, I tested if this fixes the Jetty issue, and indeed it does. Push the fix! We
can add the regression test later.

Thanks,
-Aleksey