RFR: 8347645: C2: XOR bounded value handling blocks constant folding [v45]

[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.

Johannes Graham has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 61 commits:

 - Merge branch 'openjdk:master' into xor_const
 - move code into a header file that can be shared with GTEST
 - Undo accidental changes to Int tests
 - Add random range tests for Long
 - 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
 - ... and 51 more: https://git.openjdk.org/jdk/compare/3d2c3cd4...ce17608b

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Changes: https://git.openjdk.org/jdk/pull/23089/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23089&range=44
  Stats: 624 lines in 6 files changed: 572 ins; 26 del; 26 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