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

[Vladimir Kozlov]

On Mon, 15 Apr 2024 17:41:14 GMT, Vladimir Kozlov <kvn 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.
>
> src/hotspot/cpu/x86/globals_x86.hpp line 236:
> 
>> 234:              "mitigations for the Intel JCC erratum")                       \
>> 235:                                                                             \
>> 236:   product(bool, UseAPX, false, EXPERIMENTAL,                                              \
> 
> Spacing to ``

@steveatgh, do you plan to add code to `vm_version_x86.*` to check for presence of AVX and setting this flag accordingly?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18476#discussion_r1566220173