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

[Jamsheed Mohammed C M]

On Thu, 17 Jun 2021 03:25:53 GMT, Dean Long <dlong at openjdk.org> wrote:

>> 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
>
> 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?

AFAIU reinit is ok. it is not reinitialized as it holds unique value.
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/block.hpp#L214

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