RFR: 8328998: Encoding support for Intel APX extended general-purpose registers [v15]

[Steve Dohrmann]

On Thu, 9 May 2024 11:21:28 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Thanks @jatin-bhateja .  Do you mean a check such as:
>> 
>> `if ((UseAVX > 2 || UseAPX) && !attributes->is_legacy_mode())` ?
>
>> UseAPX
> 
> Yes, attaching a test depicting incorrectness with UseAVX=2 for SHLX which is a legacy map 2 instruction promotable to extended EVEX with EGPR operands.
> [shift_left_APX.txt](https://github.com/openjdk/jdk/files/15261495/shift_left_APX.txt)
> 
> It will not be appropriate to modify VM_Version::supports_evex for APX feature since its used for constraining dynamic register classes associated with vector operands.

Ok, thanks.  I've added the above change to the conditionals in the vex_prefix and vex_prefix_and_encode functions.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/18476#discussion_r1595713834