RFR: 8351994: Enable Extended EVEX to REX2/REX demotion when src and dst are the same [v35]

[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 three additional commits since the last revision:

 - Update src/hotspot/cpu/x86/assembler_x86.cpp
   
   Co-authored-by: Jatin Bhateja <jatin.bhateja at intel.com>
 - Update src/hotspot/cpu/x86/assembler_x86.cpp
   
   Co-authored-by: Jatin Bhateja <jatin.bhateja at intel.com>
 - Update src/hotspot/cpu/x86/assembler_x86.cpp
   
   coding style
   
   Co-authored-by: Jatin Bhateja <jatin.bhateja at intel.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/24431/files
  - new: https://git.openjdk.org/jdk/pull/24431/files/110db142..c6718a15

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24431&range=34
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24431&range=33-34

  Stats: 6 lines in 1 file changed: 0 ins; 3 del; 3 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