[llvm] r264341 - [Support] Add ErrorInfo::ID static member definition.

[Reid Kleckner via llvm-commits]

Lang, see this thread where I tried to explain to Chandler why this pattern
basically doesn't work if you expect this template to instantiated this
template in multiple DLLs:
https://groups.google.com/d/topic/llvm-dev/Bo-I7aRS3CA/discussion

You're trying to ask the loader to coalesce a weak global symbol across
DSOs, and that's not something the Windows loader will do for you.

Also, it's bad for startup performance on other platforms. I've heard Chris
Bieneman go on about how this kind of symbol is banned in some contexts at
Apple.

I think you can solve the problem the same way I suggested that Chandler do
it: make the derived error classes responsible for providing this symbol,
and have classID() return &ThisErrT::ID.

On Thu, Mar 24, 2016 at 4:08 PM, NAKAMURA Takumi via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Lang, sorry for the issue. r264293 missed useful descriptions.
>
> A static member's definition cannot be unified among DLLs in Win32 DLL
> model, that has just "dllexport" and "dllimport".
>
> Although Chandler is proposing to drop supporting Win32 DLL configuration,
> I would like to watch and support it.
> I am still seeking how to get "class ID" in better way on that
> configuration.
>
>
> On Fri, Mar 25, 2016 at 7:16 AM Alexey Samsonov <vonosmas at gmail.com>
> wrote:
>
>> Some confusion is going on here. See r264293 which deleted these
>> definitions. As a result, I now have "multiple definitions" error while
>> trying to link ErrorTest
>>
>> On Thu, Mar 24, 2016 at 2:17 PM, Lang Hames via llvm-commits <
>> llvm-commits at lists.llvm.org> wrote:
>>
>>> Author: lhames
>>> Date: Thu Mar 24 16:17:50 2016
>>> New Revision: 264341
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=264341&view=rev
>>> Log:
>>> [Support] Add ErrorInfo::ID static member definition.
>>>
>>> Somehow this got dropped in an earlier patch.
>>>
>>>
>>> Modified:
>>>     llvm/trunk/include/llvm/Support/Error.h
>>>
>>> Modified: llvm/trunk/include/llvm/Support/Error.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Error.h?rev=264341&r1=264340&r2=264341&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/include/llvm/Support/Error.h (original)
>>> +++ llvm/trunk/include/llvm/Support/Error.h Thu Mar 24 16:17:50 2016
>>> @@ -291,6 +291,9 @@ private:
>>>    static char ID;
>>>  };
>>>
>>> +template <typename ThisErrT, typename ParentErrT>
>>> +char ErrorInfo<ThisErrT, ParentErrT>::ID = 0;
>>> +
>>>  /// Special ErrorInfo subclass representing a list of ErrorInfos.
>>>  /// Instances of this class are constructed by joinError.
>>>  class ErrorList final : public ErrorInfo<ErrorList> {
>>>
>>>
>>> _______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>>
>>
>>
>>
>> --
>> Alexey Samsonov
>> vonosmas at gmail.com
>>
>
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