RFR: 8294588: Auto vectorize half precision floating point conversion APIs [v7]

[Vladimir Kozlov]

On Wed, 7 Dec 2022 05:18:34 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Smita Kamath has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Updated test case
>
> New test failed when run with `-XX:UseAVX=1`. I added output to RFE in comment.
> 
> - counts: Graph contains wrong number of nodes:
> * Constraint 1: "(\\d+(\\s){2}(VectorCastH2F.*)+(\\s){2}===.*)" 
>            - Failed comparison: [found] 0 > 0 [given] 
>            - No nodes matched!

> @vnkozlov I have addressed comments from Fei Gao and Xiaohong Gong. I have limited vectorization to avx2 and higher. If the changes look good to you, could you kindly run the tests? Thanks for all your help.

@smita-kamath, can you explain why it does not work with AVX1? If it really requires AVX2 then you should just disable F16C for `(AVX < 2)` instead of current `(AVX < 1)` in `vm_version_x86.cpp`. And you would not need to modify `.ad` file and test.

-------------

PR: https://git.openjdk.org/jdk/pull/11471