[CMake] Replacing compiler flags for certain project subdirectories

[Verweij, Arjen]

Tim,

I don't think cmake can facilitate this out of the box (to my knowledge). The problem is that some compilers and fortran code just don't mix with +O3 (blas, lapack).

We have worked around it by reimplementing a mechanism from our old build system, where optimization for fortran c and cxx were parameterized, e.g. MDFC_OPT_LVLX (0-3 (up to 7 for Altix I think)). We have a wrapper function that sets COMPILE_FLAGS to this value with set_source_files_properties().

The catch is that at top level you have to strip CMAKE_<LANG>_FLAGS from any optimization instruction:

HPUX-IA64: set (CMAKE_C_LINK_FLAGS "+DSitanium2 +DD64 +DO11.23 -Aa -Ae -D_HPUX_SOURCE +Z")

Note: you may also have to redefine the default link flags.

Hope this helps,
Arjen

>-----Original Message-----
>From: cmake-bounces at cmake.org [mailto:cmake-bounces at cmake.org] On Behalf
>Of Whitcomb, Mr. Tim
>Sent: woensdag 30 maart 2011 20:00
>To: 'cmake at cmake.org'
>Subject: Re: [CMake] Replacing compiler flags for certain project
>subdirectories
>
>Shortening to reduce wall-of-text:
>
>I have a Fortran project with a top-level CMakeLists.txt file with 47
>add_subdirectory calls.  Three of the subdirectories require a different
>set of preprocessor definitions and compiler flags than the other 47.  I
>can add the preprocessor definitions, but am having trouble with the
>compiler flags.  I need to have a completely different set in those
>subdirectories, so COMPILE_FLAGS target property won't work as it
>augments what's already there.
>
>How can I replace (not extend) the compiler flags for these few
>subdirectories?
>
>Tim
>
>> -----Original Message-----
>> From: cmake-bounces at cmake.org
>> [mailto:cmake-bounces at cmake.org] On Behalf Of Whitcomb, Mr. Tim
>> Sent: Friday, March 25, 2011 3:18 PM
>> To: 'cmake at cmake.org'
>> Subject: [CMake] Replacing compiler flags for certain project
>> subdirectories
>>
>> I'm in the process of adding Cmake-build capability to a
>> Fortran project that currently follows a traditional
>> recursive-make build structure.  I've converted all the
>> makefiles to CMakeLists.txt files and can now produce all the
>> target libraries and executables with their dependencies
>> correctly recognized.  These dependencies have made a huge
>> difference in allowing us to perform parallel builds and have
>> the project ready to go *much* faster than before.  I have a
>> top-level CMakeLists.txt file that contains a few library
>> searches (e.g. LAPACK, BLAS) and then an add_subdirectory
>> call for each subdirectory in the project.  Each subdirectory
>> corresponds to a library and/or an executable.
>>
>> Now that the listing files contain all the sources files they
>> need, my current task is to go through and set the proper
>> compiler/preprocessor flags to match the original makefiles.
>> We have several directories in our source tree that are
>> auxiliary libraries that we store in our Subversion
>> repository and build as part of our regular build process.
>> The libraries that are built in these directories are
>> compiled with different compiler flags and different
>> preprocessor definitions than the rest of the project.  I've
>> been able to handle the preprocessor definitions by using
>> add_definitions in the CMakeLists.txt files in the
>> lower-level directories.  I see based on reading through some
>> past threads (including the recent "Different CMAKE_CXX_FLAGS
>> for different executables") on this list and on some
>> StackOverflow questions that the COMPILE_FLAGS target
>> property is very close to what I need (and actually *was*
>> what I needed in several cases) but only appends flags to
>> those currently  in use.  What I need is to be able to define
>> a new set of compile flags (i.e. "forget everything you were
>> using before and use THIS set in this directory").
>>
>> I've started going through the documentation for Building
>> External Projects[*] but the first line states that "[a]n
>> "external project" is one that you can get the source code
>> for, but does not readily build with a simple
>> ADD_SUBDIRECTORY call in your CMakeLists.txt file."  This
>> feels like it's designed to solve a slightly different
>> problem than what I'm trying to do - I have an
>> add_subdirectory call in my CMakeLists.txt file - is the
>> proper fix for this issue to make the pieces that require
>> different flags external projects?  Will making some of these
>> libraries external projects mess with the dependency calculation?
>>
>> I'm just getting started and trying to wrap my head around
>> the options available.  What is the standard way of dealing
>> with this issue?  Is there anything I'm missing?  Thank you
>> for your assistance!
>>
>> Tim
>> [w]
>>
>> [*]
>> http://www.kitware.com/products/html/BuildingExternalProjectsW
>> ithCMake2.8.html
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