RFR: 8303970: C2 can not merge homogeneous adjacent two If

[Yi Yang]

On Fri, 10 Mar 2023 16:08:23 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

> May I ask why is global value numbering not able to merge these 2? Can we modify `BoolNode::hash` and `BoolNode::cmp` to take these into consideration?
> Thanks a lot.

Hi @merykitty I do considered using GVN since it is a good candidate for that in theory. But I think they have [different input](https://github.com/openjdk/jdk/blob/c26e1d0148de27d0b257ec10380a5c50483fd3c0/src/hotspot/share/opto/phaseX.cpp#L119) and would collide eventually in practice. On the other hand, Identity is more common that GVN, so I try to find existing bool node by its Identity.

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PR: https://git.openjdk.org/jdk/pull/12978