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

[Ruben]

On Thu, 5 Feb 2026 08:27:14 GMT, Andrew Haley <aph at openjdk.org> wrote:

> So let's do something really simple now. We don't need the with_barrier stuff. Keep the barrier in the non-LSE code, take it out for LSE. We can elaborate next release.

Sure, I have updated the PR - now the only changes are:
- Removal of `membar` from `LIR_Assembler::casw` and `LIR_Assembler::casl`
- Removal of non-LSE `membar` from `LIR_Assembler::atomic_op`
- Adding `membar` to non-LSE branches of `MacroAssembler::cmpxchg`, `MacroAssembler::atomic_##NAME` for `add*` and `MacroAssembler::atomic_##OP` for `xchg*`

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PR Comment: https://git.openjdk.org/jdk/pull/29287#issuecomment-3891908590