Integrated: 8347645: C2: XOR bounded value handling blocks constant folding

[Johannes Graham]

On Mon, 13 Jan 2025 22:16:20 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.

This pull request has now been integrated.

Changeset: 37f8e419
Author:    Johannes Graham <j3graham at gmail.com>
URL:       https://git.openjdk.org/jdk/commit/37f8e419f9661ba30b3c34bd9fecef71ab1eddb1
Stats:     620 lines in 5 files changed: 568 ins; 27 del; 25 mod

8347645: C2: XOR bounded value handling blocks constant folding

Reviewed-by: epeter, vlivanov, qamai, jkarthikeyan

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