RFR: 8293007: riscv: optimize nmethod entry barrier

[Yadong Wang]

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, and also full jtreg tests tested on qemu user mode without new failures.

Better have another review, maybe @shipilev please?

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