RFR: 8287087: C2: perform SLP reduction analysis on-demand [v2]

[Roberto Castañeda Lozano]

On Sun, 2 Apr 2023 05:14:37 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 incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 28 additional commits since the last revision:
>> 
>>  - 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
>>  - Add negative vectorization test
>>  - Update copyright headers
>>  - Add two more reduction vectorization microbenchmarks
>>  - ... and 18 more: https://git.openjdk.org/jdk/compare/dd0f65e9...95f6cc33
>
> src/hotspot/share/opto/superword.cpp line 539:
> 
>> 537:       pred = current;
>> 538:       current = original_input(current, reduction_input);
>> 539:     }
> 
> If we bookkeep the nodes in the reduction chain path during initial backward traversal we may simplify this checking and also another call to _original_input_ while populating _loop_reductions set on [#L547 ](https://github.com/openjdk/jdk/pull/13120/files#diff-8f29dd005a0f949d108687dabb7379c73dfd85cd782da453509dc9b6cb8c9f81R547)

Thanks, will consider this together with your earlier comments.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/13120#discussion_r1158248611