RFR: 8251925: C2: RenaissanceStressTest fails with assert(!had_error): bad dominance [v2]

[Christian Hagedorn]

On Tue, 3 Nov 2020 18:30:10 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Christian Hagedorn has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Check dominance with pre loop head instead of tail
>
> src/hotspot/share/opto/superword.cpp line 3989:
> 
>> 3987:     }
>> 3988:   }
>> 3989:   if (!is_main_loop_member(n)) {
> 
> Please, add comment here explaining why !is_main_loop_member() is used in this case instead of invariant().
> Other places looks good.

I updated it and also moved the following `invariant()` check into the if block as it can only hold if `!is_main_loop_member()` is true.

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PR: https://git.openjdk.java.net/jdk/pull/954