RFR: 8347645: C2: XOR bounded value handling blocks constant folding [v29]

[Johannes Graham]

On Thu, 13 Feb 2025 20:28:51 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))
>> 
>> ### Reviewing
>> <details><summary>Using <code>git</code></summary>
>> 
>> Checkout this PR locally: \
>> `$ git fetch https://git.openjdk.org/jdk.git pull/23089/head:pull/23089` \
>> `$ git checkout pull/23089`
>> 
>> Update a local copy of the PR: \
>> `$ git checkout pull/23089` \
>> `$ git pull https://git.openjdk.org/jdk.git pull/23089/head`
>> 
>> </details>
>> <details><summary>Using Skara CLI tools</summary>
>> 
>> Checkout this PR locally: \
>> `$ git pr checkout 23089`
>> 
>> View PR using the GUI difftool: \
>> `$ git pr show -t 23089`
>> 
>> </details>
>> <details><summary>Using diff file</summary>
>> 
>> Download this PR as a diff file: \
>> <a href="https://git.openjdk.org/jdk/pull/23089.diff">https://git.openjdk.org/jdk/pull/23089.diff</a>
>> 
>> </details>
>> <details><summary>Using Webrev</summary>
>> 
>> [Link to Webrev Comment](https://git.openjdk.org/jdk/pull/23089#issuecomment-25939...
>
> Johannes Graham has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update test

I have updated the summary to be more informative. I believe the related optimizations are now covered in tests.

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

PR Comment: https://git.openjdk.org/jdk/pull/23089#issuecomment-2657707937