[CMake] Specifying different compilers for subsets of a project

[George Zagaris]

Hi Marcel,

Thanks for your e-mail. I am not sure if your approach wil fully satisfy my
use case. I need to compile on both the back-end and front-end.

My question really boils down to whether it's possible to use two different
compilers for the same language within the same configuration.

I was hoping there would be a way to set properties on individual files or
directories and specify a different compiler (as one could specify
different compilers flags). Is that possible?

Perhaps, another alternative is to define a FRONTEND_C, FRONTEND_CXX and
FRONTEND_F90 languages, as well as, define associated
"add_frontend_executable()" and "add_frontend_library()", which would work
with the frontend compiler when we are cross-compiling, or call
"add_executable()" and "add_library" otherwise. This may be a bit of
overkill though (but very useful), given that only a relative small subset
of the project needs to be compiled for the front-end.

Is there a good guide on how would one could define a different language in
CMake?

I am curious if there are any other known alternatives?

Cheers,
George

On Wed, Oct 15, 2014 at 1:54 AM, Marcel Loose <loose at astron.nl> wrote:

>  Hi George,
>
> You could (ab)use the "assembler plugin" system for that. Define your own
> CMake-ASM-BGQ*.cmake files and use the assembler to compile the sources.
>
> Here's how I did this a couple of years ago for the BG/P.
>
> In the CMakeLists.txt file for the files that need to be compiled with the
> BG/P compiler I have:
>
> ## ---------------------------------------------------------------------------
> ## Enable BGP specific assembler.
> ## Use the BGP assembler also for linking C/C++ programs.
> ## ---------------------------------------------------------------------------
> enable_language(ASM-BGP)
> set(CMAKE_C_LINK_EXECUTABLE ${CMAKE_ASM-BGP_LINK_EXECUTABLE})
> set(CMAKE_CXX_LINK_EXECUTABLE ${CMAKE_ASM-BGP_LINK_EXECUTABLE})
>
>
> CMakeASM-BGPInformation.cmake:
>
> set(ASM_DIALECT "-BGP")
> set(CMAKE_ASM${ASM_DIALECT}_SOURCE_FILE_EXTENSIONS S)
> set(CMAKE_ASM${ASM_DIALECT}_COMPILE_OBJECT "<CMAKE_ASM${ASM_DIALECT}_COMPILER> <DEFINES> <FLAGS> -c -o <OBJECT> <SOURCE>")
> set(CMAKE_ASM${ASM_DIALECT}_LINK_EXECUTABLE "<CMAKE_ASM${ASM_DIALECT}_COMPILER> <FLAGS> <LINK_FLAGS> <OBJECTS>  -o <TARGET> <LINK_LIBRARIES>")
> include(CMakeASMInformation)
> set(ASM_DIALECT)
>
>
> CMakeDetermineASM-BGPCompiler.cmake:
>
> set(ASM_DIALECT "-BGP")
> set(CMAKE_ASM${ASM_DIALECT}_COMPILER_INIT ${CMAKE_ASM_COMPILER})
> include(CMakeDetermineASMCompiler)
> set(ASM_DIALECT)
>
>
> CMakeTestASM-BGPCompiler.cmake:
>
> set(ASM_DIALECT "-BGP")
> include(CMakeTestASMCompiler)
> set(ASM_DIALECT)
>
>
> Hope this helps.
>
> Regards,
> Marcel Loose.
>
>
> On 15/10/14 04:23, George Zagaris wrote:
>
> Dear all,
>
>  I am working on a project where on certain platforms, namely, on a BG/Q
> or Cray, we have to cross-compile the code, but still, there are parts of
> the code that should only be compiled for the front end, login nodes.
>
>  Typically, we have a toolchain file, which among other things sets:
> - CMAKE_CXX_COMPILER
> - CMAKE_C_COMPILER
> - CMAKE_FORTRAN_COMPILER
>
>  to the respective cross-compilers available on the target platform.
>
>  This compiles everything for the back-end.
>
>  The obvious way to compile front-end tools is to create another
> directory, e.g., "front-end-build" and run cmake therein to re-configure
> and build with a front-end compiler.
>
>  However, since only a relatively small subset of the files needs to be
> compiled for the front-end, it is desirable to do this within the same
> build, which leads to my question:
>
>  Is it possible to tell CMake to build certain files with a different
> compiler? I know there is a way to set file properties to control the
> compiler flags of certain files. Is there a "blessed" approach to control
> the compiler for certain files and/or directories (and avoid things like
> set(CMAKE_CXX_COMPILER...) within a CMakeLists file)?
>
>  Thank you very much for all your help.
>
>  Best,
> George
>
>
>
>
>
>
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