Add missing barrier in C1 NIOCheckIndex intrinsic

[Aleksey Shipilev]

On 12/21/2017 05:28 PM, Aleksey Shipilev wrote:
> 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.

...and maybe backport it right away to sh/jdk9 and sh/jdk8u? The fix is trivial, and the impact for
it is potentially huge.

Thanks,
-Aleksey