RFR: 8328998: Encoding support for Intel APX extended general-purpose registers [v22]

[Jatin Bhateja]

On Thu, 16 May 2024 19:03:18 GMT, Steve Dohrmann <duke at openjdk.org> wrote:

>> Add instruction encoding support for Intel APX extended general-purpose registers:
>> 
>> Intel Advanced Performance Extensions (APX) doubles the number of general-purpose registers, from 16 to 32. For more information about APX, see https://www.intel.com/content/www/us/en/developer/articles/technical/advanced-performance-extensions-apx.html.
>> 
>> By specification, instruction encoding remains unchanged for instructions using only the lower 16 GPRs. For cases where one or more instruction operands reference extended GPRs (Egprs), encoding targets either REX2, an extension of REX encoding, or an extended version of EVEX encoding. These new encoding schemes extend or modify existing instruction prefixes only when Egprs are used.
>
> Steve Dohrmann has updated the pull request incrementally with one additional commit since the last revision:
> 
>   simplify test in new asserts to just assert UseAPX

src/hotspot/cpu/x86/vm_version_x86.cpp line 1005:

> 1003:   }
> 1004: 
> 1005:   if (UseAPX && (UseAVX < 3)) {

A comment here will be helpful stating the need to disable APX functionality for non AVX512 targets, please note UseAVX is set to level 3 based on existence of CPUID (EAX=07, EBX[16] = AVX512F) bit, and future AVX10 targets may support APX.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18476#discussion_r1604657235