RFR: 8261008: Optimize Xor

[Eric Liu]

On Mon, 1 Mar 2021 20:42:49 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> `x - x` is already optimized: https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/subnode.cpp#L96
> `x | x` - here: https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/addnode.cpp#L781
> 
> For `x ^ x` Value() method should be used as for SubNode.

Thanks for your review. I removed those code into `Value()` and will update after some tests finished.

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PR: https://git.openjdk.java.net/jdk/pull/2776