RFR: 8265132 : C2 compilation fails with assert "missing precedence edge" [v4]

[Dean Long]

On Thu, 27 May 2021 21:05:33 GMT, Jamsheed Mohammed C M <jcm at openjdk.org> wrote:

>> Issue is similar to https://bugs.openjdk.java.net/browse/JDK-8261730
>> but happens at next https://github.com/jamsheedcm/jdk/blob/master/src/hotspot/share/opto/gcm.cpp#L830
>> 
>> Request for review
>
> Jamsheed Mohammed C M has updated the pull request incrementally with one additional commit since the last revision:
> 
>   improving the fix for raise_LCA_above_marks

Please explain your changes better for those of us like me who are not experts with this code.  I have added code comments where I had questions.

src/hotspot/share/opto/gcm.cpp line 652:

> 650:   // raise_LCA_above_marks in inconsistent state, so always reset the
> 651:   // visited blocks after use.
> 652:   Block_List raise_LCA_visited_list;

I'm not an expert, but this sounds like a risky change to me.  Could you explain the problem in more detail, and why resetting these values is safe?

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PR: https://git.openjdk.java.net/jdk/pull/4200