RFR: 8338023: Support two vector selectFrom API [v14]

[Jatin Bhateja]

On Tue, 1 Oct 2024 18:10:10 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Review comments resolutions.
>
> src/hotspot/share/opto/vectorIntrinsics.cpp line 2797:
> 
>> 2795: 
>> 2796:   Node* operation = lowerSelectFromOp ?
>> 2797:                       LowerSelectFromTwoVectorOperation(gvn(), opd1, opd2, opd3, vt) :
> 
> Thanks for bringing the lowering right here. It opens up an optimization opportunity: currently for float/double we have two casts for index (e.g. from float -> int at line 2786 and from int -> byte at line 2661 as part of LowerSelectFromTwoVectorOperation. Could this be done by one cast?

This is not sub-optimal, Float to sub-word cast is two step process where we first convert float value to integer following by integer down casting to sub-word. So resulting JIT code will still be same if we directly emit F2X or the way its handled currently. All existing targets support F2X take this route. But its good to be safe.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20508#discussion_r1785634731