RFR: 8293007: riscv: optimize nmethod entry barrier

[Fei Yang]

On Sat, 27 Aug 2022 14:54:18 GMT, Yadong Wang <yadongwang at openjdk.org> wrote:

> https://bugs.openjdk.org/browse/JDK-8290700 introduced a faster nmethod entry barrier: a out-of-line stub to the entry barriers of C2 methods, and also a concurrent-data-and instruction-patching barrier.
> Porting loom and generational ZGC are both under development in progress in riscv port project, and we brought the similar modification to make things smooth. 
> 
> Tier1 passed on unmatched.

The riscv-specific code changes look fine. And I see the changes made to hotspot shared code are small and are guarded with #if defined(RISCV), which is the same as how aarch64 does, this should be safe and won't affect other platforms.

BTW: I also performed tier2 hotspot & jdk test on riscv64-linux unmatched machine, result looks good.

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Marked as reviewed by fyang (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10056