RFR: 8328998: Encoding support for Intel APX extended general-purpose registers [v28]

[Steve Dohrmann]

On Tue, 21 May 2024 06:12:16 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> @steveatgh I think it could make sense to add a simple "hello world" JTREG test that enables the `UseAPX` flag, just to test if it is handled correctly, even on platforms that do not have the feature enabled.
>
>> Thank you @eme64 for the comments. The functionality of the UseAPX flag is, as you point out, incomplete in this pull request. A subsequent PR (see JDK-8329030) will tie the logic of the flag in with a query of the hardware features. It was added in this PR thinking it could be useful for testing or debugging the encoding functionality.
> 
> Wait. Does this mean that if I enable the `UseAPX` flag on my `AVX512` machine with `UseAVX=3`, that we will start encoding instructions using APX? Can that lead to wrong results?

Hi @eme64, just wanted to check on the status of testing.  Thanks.

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PR Comment: https://git.openjdk.org/jdk/pull/18476#issuecomment-2127572193