RFR: 8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier [v2]

[kuaiwei]

> The 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.

kuaiwei has updated the pull request incrementally with two additional commits since the last revision:

 - Move fsm to CodeBuffer
 - Add fsm for merging

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18467/files
  - new: https://git.openjdk.org/jdk/pull/18467/files/29e39bf0..8ae4496e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18467&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18467&range=00-01

  Stats: 355 lines in 17 files changed: 337 ins; 1 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/18467.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18467/head:pull/18467

PR: https://git.openjdk.org/jdk/pull/18467