RFR: 8351994: Enable Extended EVEX to REX2/REX demotion when src and dst are the same [v6]

[Jatin Bhateja]

On Thu, 17 Apr 2025 00:53:27 GMT, Srinivas Vamsi Parasa <sparasa at openjdk.org> wrote:

>> The current scheme for Intel APX NDD code generation favors the emission of NDD instruction on APX-enabled targets, even if destination and source registers are the same. To prevent this, this PR extends the assembler layer to demote EEVEX to REX encoding if dst matches with source operands.
>
> Srinivas Vamsi Parasa has updated the pull request incrementally with one additional commit since the last revision:
> 
>   RRM refactorted to use a unified evex_ndd_and_int8 function

Hi Vamsi,
We should extend following peephole optimization rules for LEA detection to cover new NDD patterns.

https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86_64.ad#L14590
https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86_64.ad#L14599
https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/x86_64.ad#L14608

I have created a follow up JBS for this
https://bugs.openjdk.org/browse/JDK-8354939

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

PR Comment: https://git.openjdk.org/jdk/pull/24431#issuecomment-2812635082