RFR: 8293198: [vectorapi] Improve the implementation of VectorMask.indexInRange() [v2]

[Xiaohong Gong]

On Mon, 6 Feb 2023 17:39:42 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

>> Xiaohong Gong has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add smaller array size for benchmark tests
>
> I think it would be useful to adjust the naming and comments of some methods to make it clearer the method parameter constraints.
> 
> `indexInRange0Helper` is now called if the index is partially or totally out of range at the lower or upper ends and `indexInRange0` is called if partially or totally out of range at the upper end.
> e.g. a more literal naming could be:
> `AbstractMask::indexInRange0Helper` -> `AbstractMask::indexPartiallyInRangeHelper`
> `VectorSupport::indexInRange` -> VectorSupport::indexPartiallyInUpperRange`
> ?
> 
> IIUC the performance numbers show that when the array is not a multiple of the vector size there is still quite an impact overall to calling `VectorSupport::indexInRange` for the last loop iteration. I am guessing the overall loop shape is different which impacts other optimizations?
> 
> To do this more optimally likely requires a loop transformation where the last loop iteration is peeled off, but that's a harder transformation in one of the more complicated areas of C2 (although it already supports pre/post loop, so maybe its possible to leverage that?).

Thanks for the review @PaulSandoz !

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PR: https://git.openjdk.org/jdk/pull/12064