RFR: 8347645: C2: XOR bounded value handling blocks constant folding [v39]

[Johannes Graham]

> 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.
> 
> ---------
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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 incrementally with one additional commit since the last revision:

  update bug numbers and summary

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23089/files
  - new: https://git.openjdk.org/jdk/pull/23089/files/7658fc9a..f5674420

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23089&range=38
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23089&range=37-38

  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/23089.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23089/head:pull/23089

PR: https://git.openjdk.org/jdk/pull/23089