RFR: 8360654: AArch64: Remove redundant dmb from C1 compareAndSet

[Ruben]

This is duplicate of the PR #26000 which was originally created by @spchee.

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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...)

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Commit messages:
 - Add "/*with_barrier*/" comments
 - Address review comments. Refine.
 - Merge from the main branch
 - Add cmpxchg_barrier helper
 - Add comment
 - Add back in dmb membar for non-LSE
 - 8360654: AArch64: Remove redundant dmb from C1 compareAndSet

Changes: https://git.openjdk.org/jdk/pull/29287/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29287&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8360654
  Stats: 90 lines in 3 files changed: 60 ins; 5 del; 25 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