RFR: 8367611: Enable vblendvp[sd] on Future ECore [v2]

[Manuel Hässig]

On Thu, 18 Sep 2025 23:28:07 GMT, Mohamed Issa <missa at openjdk.org> wrote:

>> The upcoming ECore platforms will benefit from using `vblendvps` and `vblendvpd` instructions when the destination register is the same as the source register. This change takes that situation into account.
>> 
>> The JTREG test shown below was used to verify correctness against the [OpenJDK v26-b15](https://github.com/openjdk/jdk/releases/tag/jdk-26%2B15) baseline build.
>> 
>> 1. `jtreg:test/hotspot/jtreg/compiler/intrinsics/math/TestSignumIntrinsic.java`
>
> Mohamed Issa has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use function to identify Darkmont cores instead of global flag

Thank you for this improvement, @missa-prime! The change looks good to me, but I have a question.

> The JTREG test shown below was used to verify correctness against the [OpenJDK v26-b15](https://github.com/openjdk/jdk/releases/tag/jdk-26%2B15) baseline build.
> -  jtreg:test/hotspot/jtreg/compiler/intrinsics/math/TestSignumIntrinsic.java

Can you elaborate, what this verification entails? Why this test?

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Changes requested by mhaessig (Committer).

PR Review: https://git.openjdk.org/jdk/pull/27354#pullrequestreview-3243446726