RFR: 8347645: C2: XOR bounded value handling blocks constant folding [v42]

[Emanuel Peter]

On Mon, 24 Mar 2025 14:28:52 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
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>> 
>> 
>> 
>> ### 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 with a new target base due to a merge or a rebase. The pull request now contains 57 commits:
> 
>  - Merge branch 'openjdk:master' into xor_const
>  - Merge branch 'openjdk:master' into xor_const
>  - invert comparison in tests
>  - update bug numbers and summary
>  - add test of random ranges
>  - consistency
>  - Merge branch 'openjdk:master' into xor_const
>  - widen range of test values; add missing comment
>  - a few more tests
>  - add comments
>    
>    Co-authored-by: Emanuel Peter <emanuel.peter at oracle.com>
>  - ... and 47 more: https://git.openjdk.org/jdk/compare/02a4ce23...06537f21

Thanks for the updates @j3graham !

Could we have the same tests for long as for int? I see that the `testRandomLimits` only exists for int right now.

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

Changes requested by epeter (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23089#pullrequestreview-2710852134