Re: [PATCH] c++: Predefine __STDCPP_THREADS__ in the compiler if thread model is not single

[Jason Merrill <jason@redhat.com>]

On 11/13/20 4:46 PM, Jakub Jelinek wrote:
> On Fri, Nov 13, 2020 at 04:39:25PM -0500, Jason Merrill wrote:
>> On 11/13/20 2:20 PM, Tom Tromey wrote:
>>>>>>>> "Jakub" == Jakub Jelinek via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
>>>
>>> Jakub> 2020-11-13  Jakub Jelinek  <jakub@redhat.com>
>>>
>>> Jakub> 	* c-cppbuiltin.c: Include configargs.h.
>>> Jakub> 	(c_cpp_builtins): For C++11 and later if THREAD_MODEL_SPEC is not
>>> Jakub> 	defined, predefine __STDCPP_THREADS__ to 1 unless thread_model is
>>> Jakub> 	"single".
>>>
>>> Note this is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63287
>>
>> Any opinions about the relative advantage of doing this in the compiler vs.
>> doing it in the library, as in Jonathan's patch in the PR?
> 
> If it is done in the library, it will be defined only if any of the library
> headers are included.
> The https://eel.is/c++draft/cpp.predefined wording doesn't look like it
> would allow defining it only if certain headers are included
> (unlike e.g. the __cpp_lib_* macros which have associated list of headers
> that should define those).

Then the patch is OK.

Jason