RFR: 8366444: Add support for add/mul reduction operations for Float16

[Emanuel Peter]

On Mon, 5 Jan 2026 12:40:21 GMT, Bhavana Kilambi <bkilambi at openjdk.org> wrote:

>> As for the IR verification failure, I've looked a bit and couldn't find such an issue already. Since it reproduces on master, I suggest you file a ticket, indeed. Thanks!
>
> Hi @marc-chevalier @eme64  Would you please be able to run some testing internally before I integrate this patch? Thanks!

@Bhavana-Kilambi This looks like a great addition!

I see that you have some new benchmarks and IR tests. I wonder if it would make sense to add `Float16` benchmarks to this existing test:
`test/hotspot/jtreg/compiler/loopopts/superword/TestReductions.java`
And also to this Benchmark:
`test/micro/org/openjdk/bench/vm/compiler/VectorReduction2.java`

It would be nice if we test `simple`, `dotProduct` and `Big` reductions. It can have an impact on profitability.

Your `ReductionAddFP16` and `ReductionMulFP16` are already "simple" reductions, so I'd suspect that the other reductions are also profitable.

For reference: https://github.com/openjdk/jdk/pull/27803 and https://github.com/openjdk/jdk/pull/25387

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PR Comment: https://git.openjdk.org/jdk/pull/27526#issuecomment-3724348378