RFR: 8360654: AArch64: Remove redundant dmb from C1 compareAndSet [v2]

[Ruben]

> This is duplicate of the PR #26000 which was originally created by @spchee.
> 
> ===========
> 
> AtomicLong.CompareAndSet has the following assembly dump snippet which gets emitted from the intermediary LIRGenerator::atomic_cmpxchg:
> 
> 
> ;; cmpxchg {
>   0x0000e708d144cf60:   mov	x8, x2
>   0x0000e708d144cf64:   casal	x8, x3, [x0]
>   0x0000e708d144cf68:   cmp	x8, x2
>  ;; 0x1F1F1F1F1F1F1F1F
>   0x0000e708d144cf6c:   mov	x8, #0x1f1f1f1f1f1f1f1f
>  ;; } cmpxchg
>   0x0000e708d144cf70:   cset	x8, ne  // ne = any
>   0x0000e708d144cf74:   dmb	ish
> 
> According to the Oracle Java Specification, AtomicLong.CompareAndSet [1] has the same memory effects as specified by VarHandle.compareAndSet which has the following effects: [2]
> 
>> Atomically sets the value of a variable to the
>> newValue with the memory semantics of setVolatile if
>> the variable's current value, referred to as the witness
>> value, == the expectedValue, as accessed with the memory
>> semantics of getVolatile.
> 
> Hence the release on the store due to setVolatile only occurs if the compare is successful. Since casal already satisfies these requirements, the dmb does not need to occur to ensure memory ordering in case the compare fails and a release does not happen.
> 
> Hence we remove the dmb from both casl and casw (same logic applies to the non-long variant)
> 
> This is also reflected by C2 not having a dmb for the same respective method.
> 
> [1] https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/util/concurrent/atomic/AtomicLong.html#compareAndSet(long,long)
> [2] https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/lang/invoke/VarHandle.html#compareAndSet(java.lang.Object...)

Ruben has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:

 - Address review comments
 - Revert "Add cmpxchg_barrier helper"
   
   This reverts commit 092c92e904d3862b2772e8b229782b940e4dcbd1.
 - Revert "Address review comments. Refine."
   
   This reverts commit 135123cb238ed2b603260cca4aa1280dab47c8d7.
 - Revert "Add "/*with_barrier*/" comments"
   
   This reverts commit 6d9030d3181215de6240798d8a6254242ea29926.
 - Merge from mainline
 - Add "/*with_barrier*/" comments
 - Address review comments. Refine.
 - Merge from the main branch
 - Add cmpxchg_barrier helper
   
   Change-Id: I17acf999140f0c1decb256de8291361c568a4ff8
 - Add comment
   
   Signed-off-by: Samuel Chee <samche01 at arm.com>
   Change-Id: I9793ed6ffdff6c044552d069af23620d178f2284
 - ... and 2 more: https://git.openjdk.org/jdk/compare/e236126e...08ace3ee

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29287/files
  - new: https://git.openjdk.org/jdk/pull/29287/files/6d9030d3..08ace3ee

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29287&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29287&range=00-01

  Stats: 564834 lines in 7538 files changed: 338524 ins; 136964 del; 89346 mod
  Patch: https://git.openjdk.org/jdk/pull/29287.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29287/head:pull/29287

PR: https://git.openjdk.org/jdk/pull/29287