RFR: 8314488: Compile the JDK as C++17 [v5]

[Martin Doerr]

On Thu, 11 Jan 2024 12:36:31 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Regarding https://github.com/TheShermanTanker/jdk/actions/runs/7070564987/job/19247370401, could it be that the adlc build didn't get the correct C++ version flags? It doesn't look like a clang 13 specific problem.
>
>> @TheRealMDoerr
>> 
>> > The only issue I see is requiring clang 14.0 on MacOS is not in sync with "Other JDK 22 build platforms" (https://wiki.openjdk.org/display/Build/Supported+Build+Platforms).
>> 
>> That page is suppose to document what we actually do, not be a binding contract; so if we change stuff, we update the page to reflect it, rather than the other way around.
>> 
>> Or maybe I misunderstood your comment?
> 
> Correct, but raising requirements requires extra effort to change the build environments, updating docs, etc. (It may even cause incompatibilities. Probably not in this case.) While it may be better to use a newer Xcode on Mac, I can't see sufficient reason for forcing the whole world to build with clang 14.

> @TheRealMDoerr The adlc build is notoriously problematic, since it does not share the common flags set for JVM or JDK native compilation. :( So your suggestion sounds highly likely to me. Running with LOG=cmdlines will confirm this.
> 
> (This can be done on GHA by manually starting a run, and setting the value of "Additional make arguments" to `LOG=cmdlines` or possibly `LOG=info,cmdlines`)

Thanks for the hint! The command line is also shown here: make-support/failure-logs/hotspot_variant-server_tools_adlc_objs_adlparse.o.cmdline
The -std option is not passed. That seems to be the issue. So, this is not a clang 13 vs 14 thing.

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PR Comment: https://git.openjdk.org/jdk/pull/14988#issuecomment-1887095112