RFR: 8351140: RISC-V: Intrinsify Unsafe::setMemory

[Anjian-Wen]

On Wed, 26 Mar 2025 16:34:58 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> From [JDK-8329331](https://bugs.openjdk.org/browse/JDK-8329331), add riscv unsafe::setMemory intrinsic’s generator generate_unsafe_setmemory. This intrinsic optimizes about 15%-20% unsafe setmemory time
>
> You may want to use `UnsafeMemoryAccessMark` as on x86.

@TheRealMDoerr 
Thanks for your kindly reply. 
I found that the main logic on the x86 is in 'generate_unsafe_setmemory' function, while the main logic on the riscv and aarch64 is in generate_fill. I have not found 'UnsafeMemoryAccess' on aarch64 in generate_fill, I will check whether we need to add it and where to insert it if needed on riscv.

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PR Comment: https://git.openjdk.org/jdk/pull/23890#issuecomment-2756440074