RFR: 8287087: C2: perform SLP reduction analysis on-demand [v3]

[Roberto Castañeda Lozano]

On Mon, 24 Apr 2023 09:02:47 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Roberto Castañeda Lozano has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 31 commits:
>> 
>>  - Use is_marked_reduction() in new SLP code
>>  - Merge master
>>  - Emit Node::Flag_has_swapped_edges in IGV graphs
>>  - Merge master
>>  - Relax the reduction cycle search bound
>>  - Remove redundant IR check precondition
>>  - Use SuperWord members in reduction marking
>>  - Remove redundant opcode checks
>>  - Do not run test in x86-32
>>  - Update existing test instead of removing it
>>  - ... and 21 more: https://git.openjdk.org/jdk/compare/a3137c75...d9fc7b22
>
> src/hotspot/share/opto/superword.cpp line 518:
> 
>> 516:     }
>> 517:     // Test that reduction nodes do not have any users in the loop besides their
>> 518:     // reduction cycle predecessors.
> 
> Slight nomenclature confusion in comment, I think you meant successor in above comment, phi is a successor of first node, we are using fast_outs in following loop to check for unique successors.

Good catch, thanks! My confusion stemmed from thinking about the traversal order rather than the direction of the edges in the Ideal graph. I have updated the comment and the variable name.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13120#discussion_r1175431599