RFR: 8341260: Add Float16 to jdk.incubator.vector

[John R Rose]

On Thu, 17 Oct 2024 23:11:07 GMT, Joe Darcy <darcy at openjdk.org> wrote:

> Port of Float16 from java.lang in the lworld+fp16 branch to jdk.incubabor.vector.

Comparing with https://github.com/openjdk/jdk/pull/21490 we can see that there are more than minimum number of intrinsics I recommended above, but (crucially) the intrinsics are decoupled from the box type, and refactored into `Float16Math.java`.

https://github.com/openjdk/jdk/pull/21490/files#diff-105a2bf4929174c594b5bcc54f749e93d9fca1b5371ca301fff02badd0e8da5a

For example, see the max intrinsics line 53.  These intrinsics are better structured for the JIT, because there is no extraneous boxing to deal with.  (Boxes involve null checks and heap allocation and other details which are just extra overhead.)

Apart from intrinsic classification, a simpler thing to do that may help the box methods to fold up correctly would be a `@ForceInline` annotation.  But for the simple methods in this PR that is usually overkill.

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PR Comment: https://git.openjdk.org/jdk/pull/21574#issuecomment-2424347511