RFR: 8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier [v5]

[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 incrementally with one additional commit since the last revision:

  Remove tailing white space

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19278/files
  - new: https://git.openjdk.org/jdk/pull/19278/files/00262c4c..8ef3e037

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19278&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19278&range=03-04

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 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