RFR: 8314488: Compiling the JDK with C++17

[Kim Barrett]

On Sat, 16 Aug 2025 09:44:22 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> I'm hijacking the PR mechanism as a way to discuss new C++17 features that can
>> be more easily structured and captured than bare email. Once discussion
>> settles down I'll turn the results into HotSpot Style Guide changes. I don't
>> intend to integrate any version of this document to the OpenJDK repository.
>
> doc/cpp17-features.md line 740:
> 
>> 738: ##### 35.1.2. Keyword `register`
>> 739: 
>> 740: We don't use the `register` keyword in the OpenJDK anymore?
> 
> It's essential in some uses of GCC extended asm. See `atomic_linux_aarch64.hpp` for a good example.

`register` is not used as a storage class specifier in the JDK. That use for
gcc extended asm is a gcc extension, with a different meaning and syntax. (It
has some similarities in appearance, but is really pretty different.) C++17
still retains `register` as a reserved word, so one still can't start using it
for other purposes.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25992#discussion_r2280393882