RFR: 8351994: Enable Extended EVEX to REX2/REX demotion when src and dst are the same [v28]

[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:

  Update src/hotspot/cpu/x86/assembler_x86.cpp
  
  Change int b1 to int opcode_byte
  
  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/b2e8fd2a..c3e8f9ec

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24431&range=27
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24431&range=26-27

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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