RFR: 8315024: Vector API FP reduction tests should not test for exact equality [v2]

[Emanuel Peter]

On Thu, 12 Oct 2023 09:28:55 GMT, Gergö Barany <gbarany at openjdk.org> wrote:

>> Generally looks good, thanks for looking into this.
>> I left a few comments below.
>> 
>> Another concern I have, which I ran into by writing tests for the auto-vectorizer:
>> Are we making sure the float/double reductions do not degenerate to either zero or infinity? Because if they do degenerate, then we have only a very weak test.
>> I'm especially worried about all the values that depend on `i`, and then get multiplied. Don't the multiplications hit the maximal float value very quickly?
>
> @eme64 would you have time to take another look at the changes I have made to this PR?

@gergo- I just looked at it again. It looks better.

Still, I have a concern about `cornerCaseValues`: Does the result not always degenerate to zero / NaN now?
Every 17th value is a corner-case. And there, we mix in all of the special cases deterministically (zero, infty, min/max, NaN), depending on INT/FP type. But it seems that way we always have a NaN in the FP array - and therefore the reduction would always be NaN. Similar things happen with int-multiplication and zero.

I wonder if it would not be better to generate some data randomly, and throw in the special-cases with a very low probability. Maybe 50% that any show up, and then randomly pick one or more special case values. That way you can test the different special-cases separately. And their position could also be random.

BTW: is there any wiki about the template file format, and how to "compile" it to java? I might want to use it in the future myself :)

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PR Comment: https://git.openjdk.org/jdk/pull/16024#issuecomment-1761282558