RFR: 8302780: Add support for vectorized arraycopy GC barriers

[Albert Mingkun Yang]

On Mon, 20 Feb 2023 15:23:04 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

> So far, the arraycopy stubs have performed some kind of bulk pre/post barriers for arraycopy, which have been good enough, and allowed the copying itself to be done with plain loads and stores. For generational ZGC, this approach is not good enough, and we need barriers for the actual copying, but instead don't need the pre/post barriers. To prepare the JVM for generational ZGC, we need to add an API for arraycopy barriers.

src/hotspot/cpu/x86/gc/shared/barrierSetAssembler_x86.cpp line 218:

> 216:     fatal("No support for 8 bytes copy");
> 217: #endif
> 218:   }

I believe the intent would be clearer using `switch`.

src/hotspot/cpu/x86/stubGenerator_x86_64.cpp line 1198:

> 1196:   const Register saved_r15 = r9;
> 1197: #ifdef _WIN64
> 1198:   if (nargs >= 4) {

When would `nargs` ever be `> 4`?

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PR: https://git.openjdk.org/jdk/pull/12670