[CMake] Prevent libraries from linking twice during LLVM build

[Sanjay Srivallabh Singapuram]

Thanks a lot for the context Michael !

On Thu, 20 Apr 2017 at 22:03 Michael Kruse <meinersbur at googlemail.com>
wrote:

>  The cmake mailing list may not have sufficient context, so let me add
> some details.
>
> Polly is an extension library for LLVM. Both can be configured in
> multiple configurations:
>
> LLVM can be
> - A bunch of libLLVM*.a files
> - A bunch of libLLVM*.so files
> - A single libLLVM.so
>
> Polly can be
> - LLVMPolly.so to be loaded dynamically into the LLVM host application
> using an LD_PRELOAD-like mechanism (e.g. clang or opt)
> - Linked directly into the LLVM host application (target_link_library)
>   - as dynamic library libPolly.so
>   - as static library libPolly.a
>
> and it should work with all combinations of these.
>
> The issue is not all host applications always have all LLVM components
> linked into it. In the example below, there is the Julia compiler
> which does not have the the NVPTX backend in it, but it is required by
> (some configuration of) Polly.
>
> Hence if we have an LLVMPolly.so we don't know whether the host
> program has the LLVMNVPTX* libraries in it. If we do not depend on
> these libraries, the linker will complain about missing symbols if the
> host doesn't have these either. If we do depend on these libraries,
> and the host has them as well, we risk having the same library
> multiple times in the address space (e.g. LLVMNVPTX* is statically
> linked into libLLVM.so, but LLVMPolly.so contains them as well).
>
> This is not really a cmake-specific question, and the solution I
> proposed to Sanjay to require the host application to have all
> required components already linked into it. We can do this for clang,
> opt (and bugpoint), but the Julia compiler guys do not like to depend
> of the NVPTX backend, which they usually do not use.
>
> Michael
>
>
>
> 2017-04-20 17:56 GMT+02:00 Sanjay Srivallabh Singapuram
> <singapuram.sanjay at gmail.com>:
> > Hello,
> >
> > I'm proposing a patch to the Polly/LLVM project that involves linking
> > libPolly.a or libPolly.so to NVPTX back-end libraries. I'm currently
> using,
> > target_link_libraries(Polly
> >       LLVMNVPTXCodeGen
> >       LLVMNVPTXInfo
> >       LLVMNVPTXDesc
> >       LLVMNVPTXAsmPrinter
> >       )
> >
> > The opt binary links to both Polly and NVPTX back-end libraries,
> therefore
> > including the back-end libraries twice which causes problems. Can linking
> > the libraries as an INTERFACE to Polly solve the problem ?
> >
> > target_link_libraries(Polly INTERFACE
> >       LLVMNVPTXCodeGen
> >       LLVMNVPTXInfo
> >       LLVMNVPTXDesc
> >       LLVMNVPTXAsmPrinter
> >       )
> >
> > Thank You,
> > Sanjay
>
>
>
> --
> Tardyzentrismus verboten!
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/cmake/attachments/20170421/e246a0aa/attachment.html>