[jdk17u-dev] RFR: 8316645: RISC-V: Remove dependency on libatomic by adding cmpxchg 1b

[Ludovic Henry]

On Sat, 18 Nov 2023 10:15:59 GMT, Gui Cao <gcao at openjdk.org> wrote:

> Hi, I would like to backport this riscv-specific change to remove dependency on latomic libraries.
> latomic is used for non native atomic operation which causes problems with extra dependency. This have been fixed in recent gcc, so latomic is no longer needed. this backport will work for older gcc versions as well,  it uses assembly code.
> The backport is not clean because jdk17u-dev has no [JDK-8307806](https://bugs.openjdk.org/browse/JDK-8307806), and the original patch modified a test case(test/hotspot/gtest/runtime/test_atomic.cpp), but there is no corresponding test case in the jdk17u-dev.
> 
> ### Testing:
> qemu 8.1.50 with UseRVV:
> - [x] Tier1 tests (release)
> - [x] Tier2 tests (release)
> - [x] Tier3 tests (release)

Marked as reviewed by luhenry (no project role).

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PR Review: https://git.openjdk.org/jdk17u-dev/pull/1970#pullrequestreview-1738686186