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

[Nils Eliasson]

+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
>>