[13] 8221592: C2 compilation failed with assert(!q->is_MergeMem())

[Tobias Hartmann]

Thanks Nils.

Best regards,
Tobias

On 28.04.19 11:11, Nils Eliasson wrote:
> +1
> 
> // Nils
> 
>>
>> Thanks,
>> Vladimir
>>
>> On 4/26/19 5:14 AM, Tobias Hartmann wrote:
>>> Hi,
>>>
>>> please review the following patch:
>>> https://bugs.openjdk.java.net/browse/JDK-8221592
>>> http://cr.openjdk.java.net/~thartmann/8221592/webrev.00/
>>>
>>> We hit an assert during parsing with incremental inlining when merging memory edges into a target
>>> block because of a MergeMem that has another MergeMem as input. I've traced the MergeMem back to
>>> this code:
>>> http://hg.openjdk.java.net/jdk/jdk/file/47a8fdf84424/src/hotspot/share/opto/parse1.cpp#l1028
>>>
>>> The memory input of the _exit map is a MergeMem with a useless Phi input that has another MergeMem
>>> as input (see bug comments for details). After calling transform on this slice, the Phi is removed
>>> and we end up with a MergeMem that is then set as input to the original MergeMem. This later
>>> triggers the assert.
>>>
>>> The proposed fix is to transform the original MergeMem after transforming the slices to get rid of
>>> MergeMem inputs.
>>>
>>> The problem only shows up with the fix for JDK-8059241 [1] which reduced the number of times
>>> PhaseRemoveUseless is executed with incremental inlining. I don't think it's related though but just
>>> triggers the bug.
>>>
>>> Tested with multiple runs of the microbenchmark that triggered the assert and
>>> hs-tier1,hs-tier2,hs-tier3,hs-precheckin-comp,jdk-tier1,jdk-tier2,jdk-tier3 (running).
>>>
>>> Thanks,
>>> Tobias
>>>
>>> [1] https://bugs.openjdk.java.net/browse/JDK-8059241
>>>