RFR: 8302780: Add support for vectorized arraycopy GC barriers [v2]

[Albert Mingkun Yang]

On Fri, 24 Feb 2023 10:40:42 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> 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`?
>
> It won't (yet). I was just structuring it like setup_arg_regs, where it similarly checks if nargs >= 4. But I can change both to an assert that it isn't > 4.

An assert sounds good. This method (linux-part) gives me the impression that it's ensuring _four_ args are OK.

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