RFR: 8347555: [REDO] C2: implement optimization for series of Add of unique value [v7]

[Kangcheng Xu]

On Mon, 2 Jun 2025 11:50:38 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Ping @eme64 again for awareness. :)
>
> @tabjy
> 
>> I could, at very least, try to swap LHS and RHS if no match is found
> 
> I think that would be a good idea, and not very hard. You can just have a function `add_pattern(lhs, rhs)`, and then run it also with `add_pattern(rhs, lhs)` for **swapping**.
> 
> Personally, I would have preferred a recursive algorithm, but that could have some compile time overhead. @chhagedorn Was a little more skeptical about the recursive algorithm.
> 
> It seems the motivation for this change is the benchmark from here:
> ArithmeticCanonicalizationBenchmark
> https://ionutbalosin.com/2024/02/jvm-performance-comparison-for-jdk-21/#jit-compiler
> 
> This benchmark is of course somewhat arbitrary, and so are now all of your added patterns. Having a most general solution would be nice, but maybe the recursive algorithm is too much, I'm not 100% sure. Of course we now still have cases that do not optimize/canonicalize, and so someone could write a benchmark for those cases still.. oh well.
> 
> What I would like to see for **testing**: add some more patterns with IR rules. More that now optimize, and also a few that do not optimize, just so we have a bit of a sense what we are still missing.
> 
> @rwestrel Filed this issue. I wonder: what do you think we should do here? How general should the optimization/canonicalization be?

@eme64 Thank you for reviewing! Those are very valid suggestion, especially on naming as this PR evolves. I've done the following:

- updated naming (mostly with "serial addition" to "collapsable addition (into multiplication)")
- updated comments
- moved test file
- merged in master

Please enjoy your time off!

Once GHA passes, @rwestrel could you please give this a quick review if you have some time? Thank you very much!

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PR Comment: https://git.openjdk.org/jdk/pull/23506#issuecomment-3354754246