RFR: 8347645: C2: XOR bounded value handling blocks constant folding [v33]

[Jasmine Karthikeyan]

On Thu, 20 Feb 2025 16:25:48 GMT, Johannes Graham <duke at openjdk.org> wrote:

>> An interaction between xor bounds optimization and constant folding resulted in xor over constants not being optimized. This has a noticeable effect on `Long.expand` with a constant mask, on architectures that don't have instructions equivalent  to `PDEP` to be used in an intrinsic.
>> 
>> This change moves logic from the `Xor(L|I)Node::Value` methods into the `add_ring` methods, and gives priority to constant-folding. A static method was separated out to facilitate direct unit-testing. It also (subjectively) simplified the  calculation of the upper bound and added an explanation of the reasoning behind it.
>> 
>> In addition to testing for constant folding over xor, IR tests were added to `XorINodeIdealizationTests` and `XorLNodeIdealizationTests` to cover these related items:
>>  - Bounds optimization of xor
>>  - A check for  `x ^ x = 0`
>>  - Explicit testing of xor over booleans.
>> 
>> Also `test_xor_node.cpp` was added to more extensively test the correctness of the bounds optimization. It exhaustively tests ranges of 4-bit numbers as well as at the high and low end of the affected types.
>> 
>> ---------
>> ### Progress
>> - [x] Change must not contain extraneous whitespace
>> - [x] Commit message must refer to an issue
>> - [ ] Change must be properly reviewed (2 reviews required, with at least 2 [Reviewers](https://openjdk.org/bylaws#reviewer))
>> 
>> 
>> 
>> ### Reviewers
>>  * [Quan Anh Mai](https://openjdk.org/census#qamai) (@merykitty - Committer) 🔄 Re-review required (review applies to [cf779497](https://git.openjdk.org/jdk/pull/23089/files/cf77949776f7a4601268c7291a5743c2eb164186))
>> 
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>
> Johannes Graham has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update tests

Thanks for the update! It looks good to me.

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Marked as reviewed by jkarthikeyan (Committer).

PR Review: https://git.openjdk.org/jdk/pull/23089#pullrequestreview-2631705601