On Fri, Jan 08, 2021 at 12:48:51AM +0000, Paul Fee via Gcc-patches wrote:
> Derived from the changes that added C++2a support in 2017.
> https://gcc.gnu.org/g:026a79f70cf33f836ea5275eda72d4870a3041e5
>
> No C++2b features are added here.
> Use of -std=c++2b sets __cplusplus to 202101L.
What Jon wrote, plus:
>
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 5541e694bb3..3a0d452b62b 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,10 @@
> +2021-01-08 Paul Fee <paul.f....@gmail.com>
> +
> + Add support for -std=c++2b
> + * doc/cpp.texi (__cplusplus): Document value for -std=c++2b
> + or -std=gnu+2b.
One plus missing above.
> --- a/gcc/c-family/c-common.h
> +++ b/gcc/c-family/c-common.h
> @@ -738,7 +738,9 @@ enum cxx_dialect {
> /* C++17 */
> cxx17,
> /* C++20 */
> - cxx20
> + cxx20,
> + /* C++23? */
In the past we used
/* C++2a (C++20?) */
here, so perhaps
/* C++2b (C++23?) */
?
> + cxx2b
>
> +/* Set the C++ 2020 standard (without GNU extensions if ISO). */
2020 is wrong. In the past we used
/* Set the C++ 202a draft standard (without GNU extensions if ISO). */
so perhaps
/* Set the C++ 202b draft standard (without GNU extensions if ISO). */
> +static void
> +set_std_cxx2b (int iso)
> +{
> + cpp_set_lang (parse_in, iso ? CLK_CXX2B: CLK_GNUCXX2B);
Wrong formatting, only 2 char indentation for the whole function body.
> + flag_no_gnu_keywords = iso;
> + flag_no_nonansi_builtin = iso;
> + flag_iso = iso;
> + /* C++2b includes the C11 standard library. */
> + flag_isoc94 = 1;
> + flag_isoc99 = 1;
> + flag_isoc11 = 1;
> + /* C++2b includes coroutines. */
> + flag_coroutines = true;
> + cxx_dialect = cxx2b;
> + lang_hooks.name = "GNU C++20"; /* Pretend C++20 until standardization.
> */
> +}
> +
> /* Args to -d specify what to dump. Silently ignore
> unrecognized options; they may be aimed at toplev.c. */
> static void
> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> index 1766364806e..3464d72591b 100644
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -2214,6 +2214,11 @@ std=c++20
> C++ ObjC++
> Conform to the ISO 2020 C++ draft standard (experimental and
> incomplete support).
>
> +std=c++2b
> +C++ ObjC++
> +Conform to the ISO 2023 (?) C++ draft standard (experimental and
> +incomplete support).
Perhaps no space before (?) ?
And to be consistent with other similar entries, there was no line wrapping in
the description.
> +
> std=c11
> C ObjC
> Conform to the ISO 2011 C standard.
> @@ -2292,6 +2297,11 @@ std=gnu++20
> C++ ObjC++
> Conform to the ISO 2020 C++ draft standard with GNU extensions
> (experimental and incomplete support).
>
> +std=gnu++2b
> +C++ ObjC++
> +Conform to the ISO 2023 (?) C++ draft standard with GNU extensions
Likewise.
> (experimental
> +and incomplete support).
> + * lib/target-supports.exp: (check_effective_target_c++2a_only)
> + rename to check_effective_target_c++20_only.
The : belongs after ), and description after : should start with capital
letter. So
* lib/target-supports.exp (check_effective_target_c++2a_only):
Rename to ...
(check_effective_target_c++20_only): ... this.
Though, what you are really doing is swapping the names of the two.
Also, while your patch keeps lang_name as GNU C++20 even for -std=c++2b,
I think it would be better to adjust dwarf2out.c too:
else if (strcmp (language_string, "GNU C++17") == 0
|| strcmp (language_string, "GNU C++20") == 0)
/* For now. */
language = DW_LANG_C_plus_plus_14;
and add there || strcmp (language_string, "GNU C++23") == 0
so that we don't forget.
Jakub
