[GSoC][C++: Implement compiler built-in traits for the standard library traits]

[GSoC][C++: Implement compiler built-in traits for the standard library traits]

[Berke Yavas]

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Hi,

I am Berke. I am interested in the project C++: Implement compiler built-in
traits for the standard library traits for the upcoming GSoC. I am a
Software Engineer with a year of experience. I am very excited to have a
chance to work on gcc.

So far, I have built gcc from source, runned tests. Have a few follow up
questions.

1. Project is related with C++ frontend and library development, so during
the development there should be no issue configuring with
--disable-bootstrap --disable-multilib --disablelibstdcxx-pch(Thanks to irc
folks who suggested the latter 2, I just wanted to confirm) right?
2. Is there any other built-in compiler traits that are not in the file
`gcc/cp/cp-trait.def`?
3. __is_same built in is already used in a couple of places in libstdc++.

File: libstdc++-v3/include/bits/c++config
   840 #if _GLIBCXX_HAS_BUILTIN(__is_same)
    841 #  define _GLIBCXX_HAVE_BUILTIN_IS_SAME 1
    842 #endif

Is this the file where gcc checks if the compiler built in is available? So
other compiler built-ins should be checked here too?

I will prepare a draft of the proposal and send it here for review as soon
as possible.

Best regards,
Berke

Re: [GSoC][C++: Implement compiler built-in traits for the standard library traits]

[Jonathan Wakely]

On Tue, 28 Feb 2023 at 10:58, Berke Yavas via Gcc <gcc@gcc.gnu.org> wrote:
>
> Hi,
>
> I am Berke. I am interested in the project C++: Implement compiler built-in
> traits for the standard library traits for the upcoming GSoC. I am a
> Software Engineer with a year of experience. I am very excited to have a
> chance to work on gcc.

Great, thanks for your interest in the project.

> So far, I have built gcc from source, runned tests. Have a few follow up
> questions.
>
> 1. Project is related with C++ frontend and library development, so during
> the development there should be no issue configuring with
> --disable-bootstrap --disable-multilib --disablelibstdcxx-pch(Thanks to irc
> folks who suggested the latter 2, I just wanted to confirm) right?

That's fine.

> 2. Is there any other built-in compiler traits that are not in the file
> `gcc/cp/cp-trait.def`?
> 3. __is_same built in is already used in a couple of places in libstdc++.
>
> File: libstdc++-v3/include/bits/c++config
>    840 #if _GLIBCXX_HAS_BUILTIN(__is_same)
>     841 #  define _GLIBCXX_HAVE_BUILTIN_IS_SAME 1
>     842 #endif
>
> Is this the file where gcc checks if the compiler built in is available? So
> other compiler built-ins should be checked here too?

No, that's old code that's done differently for historical reasons.
For new built-ins you can just use __has_builtin instead. There are
lots of examples of using that in <type_traits>.