[CMake] How to use CMake with icc via configuration options when needing interprocedural optimization?

[janitor 048]

Thank you so much for the hint. Setting the environment variable CXX from
within my CMakeLists.txt via
SET(ENV{CXX} "icpc")
but before any call to project() or enable_language() seems indeed to do
the trick.

Setting CMAKE_CXX_FLAGS_RELEASE or CMAKE_CXX_FLAGS_DEBUG at this stage
however does not work. This apparently needs to go after the project()
statement.
I could of course set the environment cxx-flags in the same way as above.
This would somewhat sacrifice the nice RELEASE / DEBUG distinction but
maybe this can be done by some if-statements (there certainly is a way to
query the CMAKE_BUILD_TYPE variable, right?).

Cheers,
Oliver


2012/2/9 Michael Hertling <mhertling at online.de>

> On 02/07/2012 02:43 PM, janitor 048 wrote:
> > Hello,
> >
> > this is a question I recently asked on stackoverflow (
> >
> http://stackoverflow.com/questions/9129233/recommended-ways-to-use-cmake-with-icc-via-configuration-options
> )
> > but that has not received any response since then. Maybe this mailing
> list
> > is a better place to ask... Here goes
> >
> > I would like to use the Intel compiler icc (or icpc) with a CMake-based
> > project (on Linux for what it's worth). I can of course export the CXX
> > variable when calling cmake, e.g. like
> >
> > CXX=icpc cmake ../
> >
> > and this works fine. I would however like to make this choice available
> via
> > a custom option. For this I parse custom option, e.g.
> >
> > cmake -DMY_COMPILER_OPTION=Intel ..
> >
> > as
> >
> > IF (MY_COMPILER_OPTION STREQUAL "Intel")
> >   MESSAGE(STATUS "** Compiling with Intel settings **")
> >   SET(CMAKE_CXX_COMPILER "icpc")
> >   SET(CMAKE_CXX_FLAGS_RELEASE "-O3 -w")
> >   SET(CMAKE_CXX_FLAGS_DEBUG "-g")
> > ENDIF ()
> >
> > and set CMAKE_CXX_COMPILER together with some compiler flags. This also
> > works, however there is an important "but".
> >
> > I would also like to use the option -ipo (interprocedural optimization)
> for
> > my code when compiling with icc plus I need to compile a static library
> > within the build process. For this to work, I need to use Intel's xiar
> (and
> > also xilink I guess).
> >
> > cmake actually offers a special property for this
> >
> > set_property(TARGET mytarget PROPERTY INTERPROCEDURAL_OPTIMIZATION 1)
> >
> > however this only seems to works properly when the compiler has been set
> > via the environment variable (then xiar is used). When setting the
> compiler
> > via CMAKE_CXX_COMPILER this property is ignored.
> >
> > Is there another way to do this?. Some recommended way? Or at least a
> > work-around?
>
> If it actually works well when the compiler is specified via the
> respective environment variable, you might try the following:
>
> IF (MY_COMPILER_OPTION STREQUAL "Intel")
>  MESSAGE(STATUS "** Compiling with Intel settings **")
>   SET(ENV{CXX} "icpc")
>   SET(CMAKE_CXX_FLAGS_RELEASE "-O3 -w")
>  SET(CMAKE_CXX_FLAGS_DEBUG "-g")
> ENDIF ()
>
> However, note that you must do this *before* the language is enabled,
> i.e. before the PROJECT() or ENABLE_LANGUAGE() commands. Note further
> that this can be done only for the *initial* configuration of a build
> tree; afterwards, the compiler can't be changed anymore. In order to
> make that approach more robust, you might consider some refinements:
>
> IF (MY_COMPILER_OPTION STREQUAL "Intel")
>   FIND_PROGRAM(ICPC_PROGRAM icpc ...)
>  IF(ICPC_PROGRAM)
>     MESSAGE(STATUS "** Compiling with Intel settings **")
>     IF(ENV{CXX})
>      MESSAGE(WARNING "Overwriting CXX envvar")
>    ENDIF()
>    SET(ENV{CXX} "${ICPC_PROGRAM}")
>     SET(CMAKE_CXX_FLAGS_RELEASE "-O3 -w")
>    SET(CMAKE_CXX_FLAGS_DEBUG "-g")
>   ELSE()
>    MESSAGE(FATAL_ERROR "Intel compiler not found")
>  ENDIF()
> ENDIF ()
>
> Regards,
>
> Michael
> --
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