RFR: 8350988: Consolidate Identity of self-inverse operations

[Chen Liang]

On Sat, 1 Mar 2025 13:34:30 GMT, Hannes Greule <hgreule at openjdk.org> wrote:

> subnode has multiple nodes that are self-inverse but lacking the respective optimization. ReverseINode and ReverseLNode already have the optimization, but we can deduplicate the code for all those operations.
> 
> For most nodes, the optimization is obvious. The NegF/DNodes however are worth to look at in detail imo:
> - `Float.NaN` has the same bits set as `-Float.NaN`. That means, it this specific case, the operation is a no-op anyway
> - For other values, the msb is flipped, flipping twice results in the original value again.
> 
> Similar changes could be made to the corresponding vector nodes. If you want, I can do that in a follow-up RFE.
> 
> One note: During benchmarking those changes, I ran into https://bugs.openjdk.org/browse/JDK-8307516. That means code like
> 
>         int v = 0;
>         for (int datum : data) {
>             v ^= Integer.reverseBytes(Integer.reverseBytes(datum));
>         }
>         return v;
> 
> was vectorized before but is considered "not profitable" with the changes here, causing slowdowns in such cases.

Per my understanding this should be an issue with autovectorization, and it should be fixed by fixing autovectorization instead of by blocking valid and sound simplifications.

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PR Comment: https://git.openjdk.org/jdk/pull/23851#issuecomment-2694495187