RFR: 8347645: C2: XOR bounded value handling blocks constant folding [v46]

[Quan Anh Mai]

On Mon, 31 Mar 2025 22:28:49 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Johannes Graham has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   add missing import
>
> Thanks.
> 
>> The naming of that method evolved during the course of the review of this PR. I believe the thinking was that the check was not necessarily an overall upper bound, and a simpler name would imply it was more general.
> 
> There's usually a lot of invariants a function assumes and it's simply impractical to encode everything in the name. Speaking of this particular case (`calc_xor_upper_bound_of_non_neg`): 
>   * `calc_` is redundant and IMO only adds noise;
>   * `_non_neg` part is confusing; I'd stress instead that it works on **ranges**.
> 
> So, `xor_upper_bound_for_ranges` then? (And, please, explain in the comment what's the correspondense between `S` and `U` template type parameters.)
> 
>> `addnodeXorUtil.hpp`
> 
> I'm fine with placing it under `opto`. Please, rename the file into `src/hotspot/share/opto/utilities/xor.hpp`.

@iwanowww

> `_non_neg` part is confusing; I'd stress instead that it works on ranges.

I find it easier to think of it as calculating the upperbound of the xor of 2 non-negative integers whose upperbounds are given in the parameters.

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PR Comment: https://git.openjdk.org/jdk/pull/23089#issuecomment-2767875213