RFR: 8280126: C2: detect and remove dead irreducible loops [v2]

[Emanuel Peter]

On Thu, 12 Jan 2023 09:22:39 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:
>> 
>>  - Merge branch 'master' into JDK-8280126
>>  - 8280126: C2: detect and remove dead irreducible loops
>
> src/hotspot/share/opto/loopnode.cpp line 5311:
> 
>> 5309:     l = l->_parent;
>> 5310:   } while (l != nullptr);
>> 5311:   // Infinite loops are not always properly attached to the loop-tree. Infinite
> 
> @vnkozlov Should I change this too, just as in `ciTypeFlow::Block::is_in_irreducible_loop`?

I now  did it for both, let me know if that is ok.

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PR: https://git.openjdk.org/jdk/pull/11764