RFR: 8261649: AArch64: Optimize LSE atomics in C++ code

[Andrew Dinn]

On Wed, 17 Feb 2021 17:14:46 GMT, Andrew Haley <aph at openjdk.org> wrote:

> Now that we have support for LSE atomics in C++ HotSpot source, we can generate much better code for them. In particular, the sequence we generate for CMPXCHG with a full two-way barrier using two DMBs is way suboptimal.
> 
> This patch:
> 
> Moves memory barriers from the atomic_linux_aarch64 file into the stubs.
> Rewrites the LSE versions of the stubs to be more efficient.
> Fixes a race condition in stub generation.
> Mostly leaves the pre-LSE stubs alone, except that I added a PRFM which according to kernel engineers improves performance.

Ok, this looks good enough to me.

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Marked as reviewed by adinn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/2611