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

[Emanuel Peter]

On Wed, 1 Oct 2025 05:03:27 GMT, Kangcheng Xu <kxu at openjdk.org> wrote:

>> @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!

@tabjy The code now looks good to me. I ran some internal testing, should take about 24h.

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PR Comment: https://git.openjdk.org/jdk/pull/23506#issuecomment-3385705024