RFR: JDK-8316991: Reduce nullable allocation merges [v9]

[Cesar Soares Lucas]

On Wed, 27 Mar 2024 17:33:29 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Cesar Soares Lucas has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 13 commits:
>> 
>>  - Merge remote-tracking branch 'origin/master' into ram-nullables
>>  - Catching up with master
>>  - Fix broken build.
>>  - Merge with origin/master
>>  - Update test/micro/org/openjdk/bench/vm/compiler/AllocationMerges.java
>>    
>>    Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>
>>  - Ammend previous fix & add repro tests.
>>  - Fix to prevent reducing already reduced Phi
>>  - Fix to prevent creating NULL ConNKlass constants.
>>  - Refrain from RAM of arrays and Phis controlled by Loop nodes.
>>  - Fix typo in test.
>>  - ... and 3 more: https://git.openjdk.org/jdk/compare/89e0889a...3129378f
>
> src/hotspot/share/opto/memnode.cpp line 1552:
> 
>> 1550: // by 'split_through_phi'. The first use of this method was in EA code as part
>> 1551: // of simplification of allocation merges.
>> 1552: // Some differences from original method:
> 
> What "original method" do you refer to here?

The current method, `can_split_through_phi_base`, is just a helper that contains a copy of the validations performed by `split_through_phi`. The original method is `split_through_phi`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15825#discussion_r1543564696