llvm dev - Mar 2015 - [LLVMdev] LLVM 3.6: problems building on Windows using MSVC 2013

Ok, I have just found the cause of the error messages I am getting, and it
now makes sense to me why the 'normal' build works fine on Windows,
Linux
and OS X, and why my personal build works on Linux and OS X, but not on
Windows. However, I still don't understand why I am getting the error
messages I am getting.

 

Anyway, it has to do with wanting to export some classes and function,
including clang::driver::Compilation. Now, since the export/import of
classes/function is not supported by the LLVM+Clang project (incidentally, I
really wish it was!), I had to modify the definition of the classes and
functions that I need in order to have something like:

 

class LLVM_EXPORT Compilation { . };

 

rather than

 

class Compilation { . };

 

with LLVM_EXPORT being defined as:

 

#ifdef _WIN32

    #ifdef BUILD_LLVM

        #define LLVM_EXPORT __declspec(dllexport)

    #else

        #define LLVM_EXPORT __declspec(dllimport)

    #endif

#else

    #define LLVM_EXPORT

#endif

 

Now, as I mentioned before, that approach works fine up to LLVM+Clang 3.5.1,
but it fails with LLVM+Clang 3.6. Not for all the classes/functions that I
need to export/import though, only some of them (in Clang, it would seem).

 

To convince myself, I set up a very simple CMake+Ninja project to build
tools/clang/lib/Driver/Compilation.cpp (and nothing else since it's just for
checking) and it builds fine if I have:

 

class Compilation { . };

 

but not if I have:

 

class declspec(dllexport) Compilation { . };

 

So. my question is: why?! More importantly: what do I need to do to be able
to export/import a class such as clang::driver::Compilation?

 

Cheers, Alan.

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On Tue, Mar 10, 2015 at 5:20 AM, Alan Garny <agarny at hellix.com>
wrote:
> Ok, I have just found the cause of the error messages I am getting, and it
> now makes sense to me why the ‘normal’ build works fine on Windows, Linux
> and OS X, and why my personal build works on Linux and OS X, but not on
> Windows. However, I still don’t understand why I am getting the error
> messages I am getting.
>
>
>
> Anyway, it has to do with wanting to export some classes and function,
> including clang::driver::Compilation. Now, since the export/import of
> classes/function is not supported by the LLVM+Clang project (incidentally,
I
> really wish it was!), I had to modify the definition of the classes and
> functions that I need in order to have something like:
>
>
>
> class LLVM_EXPORT Compilation { … };
>
>
>
> rather than
>
>
>
> class Compilation { … };
>
>
>
> with LLVM_EXPORT being defined as:
>
>
>
> #ifdef _WIN32
>
>     #ifdef BUILD_LLVM
>
>         #define LLVM_EXPORT __declspec(dllexport)
>
>     #else
>
>         #define LLVM_EXPORT __declspec(dllimport)
>
>     #endif
>
> #else
>
>     #define LLVM_EXPORT
>
> #endif
>
>
>
> Now, as I mentioned before, that approach works fine up to LLVM+Clang
3.5.1,
> but it fails with LLVM+Clang 3.6. Not for all the classes/functions that I
> need to export/import though, only some of them (in Clang, it would seem).
>
>
>
> To convince myself, I set up a very simple CMake+Ninja project to build
> tools/clang/lib/Driver/Compilation.cpp (and nothing else since it’s just
for
> checking) and it builds fine if I have:
>
>
>
> class Compilation { … };
>
>
>
> but not if I have:
>
>
>
> class declspec(dllexport) Compilation { … };
>
>
>
> So… my question is: why?! More importantly: what do I need to do to be able
> to export/import a class such as clang::driver::Compilation?
It looks like MSVC is trying to synthesize and export the copy
assignment operator and copy constructur. This is interesting, as I
thought it wouldn't do that if the class turns out not to be
non-copyable.

Does adding the following to the class (and similarly for others that
are failing) work?

  Compilation& operator=(Compilation&) = delete;
  Compilation(Compilation&) = delete

 - Hans

> > So… my question is: why?! More importantly: what do I need to do to be
> > able to export/import a class such as clang::driver::Compilation?
> 
> It looks like MSVC is trying to synthesize and export the copy assignment
> operator and copy constructur. This is interesting, as I thought it
wouldn't do
> that if the class turns out not to be non-copyable.
> 
> Does adding the following to the class (and similarly for others that are
> failing) work?
> 
>   Compilation& operator=(Compilation&) = delete;
>   Compilation(Compilation&) = delete
Good timing. This is the conclusion and solution to which I came too. I have
tried it on my test case and it is working fine. I am now going to try it on my
project and see how it goes, but at least that seems promising.

Alan