RFR: 8351016: RA support for EVEX to REX/REX2 demotion to optimize NDD instructions [v6]

[Jatin Bhateja]

On Tue, 21 Oct 2025 16:38:07 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains eight commits:
>> 
>>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8351016
>>  - Limiting register biasing to NDD specific demotable instructions
>>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8351016
>>  - Fix jtreg, one less spill
>>  - Updating as per reivew suggestions
>>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8351016
>>  - Some refactoring
>>  - 8351016: RA support for EVEX to REX/REX2 demotion to optimize NDD instructions
>
> src/hotspot/cpu/x86/x86_64.ad line 440:
> 
>> 438:   switch(mopc) {
>> 439:     default:
>> 440:       return false;
> 
> What happens if we wrongly `return false` here? Is that a missed optimization or a correctness issue?

It will never result in a correctness issue; we will simply ditch register biasing.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26283#discussion_r2449123448