RFR: 8351994: Enable Extended EVEX to REX2/REX demotion when src and dst are the same [v36]

[Srinivas Vamsi Parasa]

> Intel APX NDD instructions are encoded using EVEX encoding. The goal of this PR is to enable optimized instruction encoding for Intel APX NDD instructions when the non-destructive destination is same as the first source.
> 
> For example:
> 
> `eaddl r18, r18, r25` can be encoded as `addl r18, r25` using APX REX2 encoding
> `eaddl r2, r2, r7` can be encoded as `addl r2, r7` using non-APX legacy encoding

Srinivas Vamsi Parasa has updated the pull request incrementally with one additional commit since the last revision:

  refactor is_P6_or_later and remove cpu_family==18

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/24431/files
  - new: https://git.openjdk.org/jdk/pull/24431/files/c6718a15..3378eaee

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24431&range=35
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24431&range=34-35

  Stats: 8 lines in 2 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/24431.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24431/head:pull/24431

PR: https://git.openjdk.org/jdk/pull/24431