[LLVMdev] LLVM 3.6: problems building on Windows using MSVC 2013

Alan Garny agarny at hellix.com
Tue Mar 10 05:20:35 PDT 2015

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)


        #define LLVM_EXPORT __declspec(dllimport)



    #define LLVM_EXPORT



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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