RFR: 8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier [v8]

[kuaiwei]

> he origin patch for https://bugs.openjdk.org/browse/JDK-8324186 has 2 issues:
> 1 It show regression in some platform, like Apple silicon in mac os
> 2 Can not handle instruction sequence like "dmb.ishld; dmb.ishst; dmb.ishld; dmb.ishld"
> 
> It can be fixed by:
> 1 Enable AlwaysMergeDMB by default, only disable it in architecture we can see performance improvement (N1 or N2)
> 2 Check the special pattern and merge the subsequent dmb.
> 
> It also fix a bug when code buffer is expanding, st/ld/dmb can not be merged. I added unit tests for these.
> 
> This patch still has a unhandled case. Insts like "dmb.ishld; dmb.ishst; dmb.ish", it will merge the last 2 instructions and can not merge all three. Because when emitting dmb.ish, if merge all previous dmbs, the code buffer will shrink the size. I think it may break some resumption and think it's not a common pattern.
> 
> In previous PR https://github.com/openjdk/jdk/pull/18467 , I tried an implementation to use state machine for merging. But it looks risky to pending instruction during emitting.

kuaiwei 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 master
 - Use constexpr for test encoding
 - Add comment in aarch64.ad
 - Remove tailing white space
 - Refine merge dmb test cases
 - Add more unit tests
 - Make MacroAssembler::merge more clear
 - 8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier

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

Changes: https://git.openjdk.org/jdk/pull/19278/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19278&range=07
  Stats: 523 lines in 9 files changed: 510 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/19278.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19278/head:pull/19278

PR: https://git.openjdk.org/jdk/pull/19278