[15] RFR(XS): 8239852:java/util/concurrent tests fail with +VerifyGraphEdges: assert(!VerifyGraphEdges) failed: verification should have failed

[Christian Hagedorn]

Hi Nils

Thank you for your review!

Best regards,
Christian

On 28.02.20 14:44, Nils Eliasson wrote:
> +1
> 
> // Nils
> 
> On 2020-02-28 12:30, Tobias Hartmann wrote:
>> Hi Christian,
>>
>> looks reasonable to me.
>>
>> Best regards,
>> Tobias
>>
>> On 26.02.20 12:49, Christian Hagedorn wrote:
>>> Hi
>>>
>>> Please review the following patch:
>>> https://bugs.openjdk.java.net/browse/JDK-8239852
>>> http://cr.openjdk.java.net/~chagedorn/8239852/webrev.00/
>>>
>>> The failing assert is too strong in some cases where the IR is valid 
>>> but PhaseCFG::schedule_late()
>>> bails out at [1] and the recompilation with subsume_loads == false 
>>> does not bail out anymore.
>>>
>>> One such case occurs during the compilation of
>>> java.util.concurrent.locks.AbstractQueuedLongSynchronizer::hasQueuedPredecessors 
>>> when running, for
>>> example, [2] with -XX:+VerifyGraphEdges. Before calling 
>>> PhaseCFG::insert_anti_dependences(), LCA and
>>> early both point to block A with _dom_depth x for some node. However, 
>>> the early block is temporarily
>>> changed inside insert_anti_dependences() by memory_early_block() to 
>>> point to an earlier block B with
>>> _dom_depth y < x. The LCA is updated to point to block B and is 
>>> returned. As a result, the assert
>>> fails because early->_dom_depth (x) > LCA->_dom_depth (y). The 
>>> recompilation of the method with
>>> subsume_loads == false does not bail out anymore.
>>>
>>> The assert can be completely remove since we already have this assert 
>>> [3] which catches an
>>> unschedulable graph of a compilation with subsume_loads == false and 
>>> there are no other bailouts in
>>> PhaseCFG::schedule_late().
>>>
>>>
>>> Thank you!
>>>
>>> Best regards,
>>> Christian
>>>
>>>
>>> [1] 
>>> http://hg.openjdk.java.net/jdk/jdk/file/61ee15b9a1ac/src/hotspot/share/opto/gcm.cpp#l1349 
>>>
>>> [2]
>>> http://hg.openjdk.java.net/jdk/jdk/file/61ee15b9a1ac/test/jdk/java/util/concurrent/Semaphore/RacingReleases.java 
>>>
>>>
>>> [3] 
>>> http://hg.openjdk.java.net/jdk/jdk/file/61ee15b9a1ac/src/hotspot/share/opto/gcm.cpp#l1352 
>>>
>