As discussed in JBS all platforms (some tweaks to Zero are in progress) actually do support `cx8` i.e. 64-bit compare-and-exchange, so we can strip out the locked-based alternatives to using it and just add a guarantee that it is true at runtime. And all platforms except some ARM variants set `SUPPORTS_NATIVE_CX8`, so we can greatly simplify things. Summary of changes: - `_supports_cx8` field is only needed when `SUPPORTS_NATIVE_CX8` is not defined - Assertions for `supports_cx8()` are removed - Access backend is greatly simplified without the need for lock-based alternative - `java.util.concurrent.AtomicLongFieldUpdater` is simplified without the need for a lock-based alternative
I did consider moving all the ARM `kuser_helper` related code to be only defined when `SUPPORTS_NATIVE_CX8` is not defined, but there was a theoretical risk this could change the behaviour if ARMv7 binaries were run on other ARM CPU's. I added a note to that effect in vm_version_linux_arm32.cpp so the ARM port maintainers could clean this up further if desired. Testing: - All Oracle tiers 1-5 builds (which includes an ARMv7 build) - GHA builds/tests - Oracle tiers 1-3 sanity testing Zero changes coming in via [JDK-8319777](https://bugs.openjdk.org/browse/JDK-8319777) will be merged when they arrive. Thanks. ------------- Commit messages: - 8318776: Require supports_cx8 to always be true Changes: https://git.openjdk.org/jdk/pull/16625/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16625&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8318776 Stats: 386 lines in 35 files changed: 14 ins; 359 del; 13 mod Patch: https://git.openjdk.org/jdk/pull/16625.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/16625/head:pull/16625 PR: https://git.openjdk.org/jdk/pull/16625
