[PATCH] libstdc++: Correct export checks for _GLIBCXX_EXTERN_TEMPLATE

[Tomasz Kaminski]

On Tue, Jun 23, 2026 at 7:52 PM Tomasz Kamiński <tkaminsk@redhat.com> wrote:

> Replace a basic_string specific _GLIBCXX_EXTERN_TEMPLATE > 0 with
> simple check for _GLIBCXX_EXTERN_TEMPLATE. This make sure that
> extern definition is also use for -O0 (default).
> Exported declarations are also important for future extensibility,
> as they always pick latest implementation.
>
> libstdc++-v3/ChangeLog:
>
>         * include/std/format (__do_vformat_to): Change the preprocessor
>         check for __do_vformat_to.
> ---
> I haven't noticed the issue, because I was testing the build times
> with -O2.
>
For the file compiled with -O0 now I see:
 U
_ZNSt8__format15__do_vformat_toIcLj1EEENS_10_Sink_iterIT_EES3_St17basic_string_viewIS2_St11char_traitsIS2_EERSt20basic_format_contextIS3_S2_E

>
> Testing on x86_64-linux. OK for trunk and 16 when all test passes?
>
>  libstdc++-v3/include/std/format | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/include/std/format
> b/libstdc++-v3/include/std/format
> index 4a517b70889..db226ecb0c8 100644
> --- a/libstdc++-v3/include/std/format
> +++ b/libstdc++-v3/include/std/format
> @@ -5381,7 +5381,7 @@ namespace __format
>  // instantiates formatters for types stored in basic_format_arg, we can
>  // support only single encoding, in this case unicode. This should cover
>  // most common use cases.
> -#if __cplusplus <= 202002L && _GLIBCXX_EXTERN_TEMPLATE > 0
> +#if __cplusplus <= 202002L && _GLIBCXX_EXTERN_TEMPLATE
>      extern template _Sink_iter<char>
>        __do_vformat_to<char, 1>(_Sink_iter<char>, string_view,
>                                format_context&);
> --
> 2.54.0
>
>
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