RFR: 8314488: Compile the JDK as C++17 [v6]

[Andrew Haley]

On Thu, 15 Feb 2024 17:11:34 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> > Sure, you can always install a newer GCC than the system one, but it's another thing that makes it harder for people to build OpenJDK. Having said that, C++17 is nice to have.
> 
> @theRealAph I am still just hearing hand-waving "perhaps someone somewhere will have a somewhat harder time building the JDK". 

I'm going to ignore that rather insulting language.

> Yes, perhaps that is so. But that is very uncertain, and I have still not heard a single concrete example of where this would apply. In contrast, going to gcc 10 will clearly bring a benefit to all other platforms, since it allows us to synchronize the code base at C++17.

Well, hold on. You're implying that going to C++17 allows us to synchronize the code base at C++17. Sure, it does, but it's important also to discuss the pitfalls. And one of those pitfalls is that the system I'm typing this message on — still in support — won't be able to build the JDK without my first finding or building gcc 10 for it.

> In light of this, I think we need to hear some really compelling evidence of problems that would ensue if we raise the minimum to gcc 10. If nobody can produce such evidence, then to me it is a sign that this fear is not well-grounded, and we should proceed with this PR.

As the proposer of this change, the onus is on you to show the benefit. Certainly there are C++17 advantages, such as hex float constants. better templates, and so on. I guess the discussion of such advantages must have taken place elsewhere because it's not on the https://bugs.openjdk.org/browse/JDK-8314488 either.

To be clear: I do not object to this PR. I would like to use C++17.

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PR Comment: https://git.openjdk.org/jdk/pull/14988#issuecomment-1947960141