Invalid code generated by C2 compiler in OpenJDK 21

[David Holmes]

Please ignore. These are old emails that likely just got released by the 
mailing list owner.

David

On 26/02/2024 2:39 pm, David Holmes wrote:
> Hi,
> 
> <snip>
>> On 15/12/23 3:42 pm, Antoine DESSAIGNE wrote:
>>> Hello everyone,
>>>
>>> I've found an issue while migrating to OpenJDK 21. A valued local 
>>> variable (effectively final) has its value removed and it throws a 
>>> NullPointerException. Unfortunately, I cannot provide the source code 
>>> and the data to reproduce the issue, and I couldn't create a smaller 
>>> code snippet to show the issue. That said, I'll happily show the code 
>>> and perform many tests during calls.
>>>
>>> Here's what I did so far to diagnose the issue.
>>>
>>> I bisected the repository to find where the regression comes from. I 
>>> found this commit 3696711efa5 [1] but it's a merge so I bisected the 
>>> branch and found 10737e168c9 [2]. Looking at this commit, I have no 
>>> idea how it could introduce this kind of regression.
> 
> It is likely because that commit has a bug in it, fixed recently by
> 
> https://bugs.openjdk.org/browse/JDK-8322282
> 
> The fix is in 21.0.3
> 
> Cheers,
> David
> -----
> 
>>>
>>> Then, thanks to the guidance from Aleksey Shipilëv, I tested many things
>>> * Issue does *not* happen with the following 
>>> flags: -Xint, -XX:-TieredCompilation, -XX:TieredStopAtLevel=1, -XX:TieredStopAtLevel=2, -XX:TieredStopAtLevel=3
>>> * Issue also happens with fastdebug builds of OpenJDK, without 
>>> crashing due to assertions
>>> * Issue still happens in the latest version of the code 
>>> (commit b31454e3623)
>>> * Issue happens no matter which GC is used, I tried SerialGC, 
>>> ParallelGC, G1GC, and ShenandoahGC
>>>
>>> The tests were performed in Docker containers running on 4 different 
>>> hosts.
>>>
>>> Therefore it looks like C2 is generating an invalid assembly code. 
>>> Unfortunately, I'm not great with assembly and the generated assembly 
>>> is quite big (main code is around 20k).
>>>
>>> Do you have an idea of why this is happening? Do you know what test I 
>>> can run? If one of you is available, we can schedule calls for me to 
>>> show you the code and my tests. Thank you very much for your assistance.
>>>
>>> Have a nice day,
>>>
>>> Antoine DESSAIGNE
>>>
>>> [1] 
>>> https://github.com/openjdk/jdk/commit/3696711efa566fb776d6923da86e17b0e1e22964
>>> [2] 
>>> https://github.com/openjdk/jdk/commit/10737e168c967a08e257927251861bf2c14795ab
>>>
>>>