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

[Vladimir Kozlov]

On Fri, 30 Oct 2020 17:13:41 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
>
> I would also suggest to run locally next jtreg command and compare number of created vector nodes to make sure your changes did not affect common cases:
> 
> `$ jtreg -testjdk:/my_jdk/ -va -javaoptions:'-server  -Xbatch -XX:-TieredCompilation -XX:CICompilerCount=1 -XX:+TraceNewVectors' -J-Djavatest.maxOutputSize=1000000 compiler/c2/cr6340864/ compiler/codegen/ compiler/loopopts/superword/ compiler/vectorization >new_vects.log`
> 
> `$ grep "new Vector node:" new_vects.log|wc`

> @vnkozlov Thanks for your review!
> 
> > $ jtreg -testjdk:/my_jdk/ -va -javaoptions:'-server -Xbatch -XX:-TieredCompilation -XX:CICompilerCount=1 -XX:+TraceNewVectors' -J-Djavatest.maxOutputSize=1000000 compiler/c2/cr6340864/ compiler/codegen/ compiler/loopopts/superword/ compiler/vectorization >new_vects.log
> > $ grep "new Vector node:" new_vects.log|wc
> 
> I ran that with the new commit - there is no difference between the fix and base without fix:
> $ grep "new Vector node:" new_vects_fix.log | wc
> 9439 227498 1941126
> $ grep "new Vector node:" new_vects_base.log | wc
> 9437 227521 1941437

You have 2 more new vectors with fix! 9439 vs 9437
It is actually more than I tested last time: 9421

Good - no regression.

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