RFR: 8342393: Promote commutative vector IR node sharing [v17]

[Jatin Bhateja]

On Mon, 27 Jan 2025 07:29:00 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Jatin Bhateja has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:
>> 
>>   Modifed scheme not based over fragile node level flags base solution.
>
> src/hotspot/share/opto/vectornode.cpp line 1056:
> 
>> 1054:   //   i.e. RES = VEC1.lanewise(OPER, VEC2, MASK) is semantically equivalent to
>> 1055:   //        RES = VEC1.BLEND(VEC1.lanewise(OPER, VEC2), MASK)
>> 1056:   // Here, first operand "VEC1" represents both source and destination vector.
> 
> Sorry @jatin-bhateja . But this still does not make sense to me. I thought the `RES` was the destination vector for the `BLEND`? Does `BLEND` not have 3 inputs (2 vectors + 1 mask vector), and one output vector?
> 
> So I would expect a `BLEND` to have a form like this:
> `RES = BLEND(V1, V2, M)`

Reframed for clarity.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22863#discussion_r1930334538