[ros-users] Question about cmake and SSE optimizations

[Rosen Diankov]

i'm pasting cmake code i use for sse checks. it checks for both sse1
and sse2, although similar checks can be used for sse3-5, there's also
a check for msvc

# check for SSE extensions
include(CheckCXXSourceRuns)
if( CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX )
  set(SSE_FLAGS)

  set(CMAKE_REQUIRED_FLAGS "-msse2")
  check_cxx_source_runs("
    #include <emmintrin.h>

    int main()
    {
        __m128d a, b;
        double vals[2] = {0};
        a = _mm_loadu_pd(vals);
        b = _mm_add_pd(a,a);
        _mm_storeu_pd(vals,b);
        return 0;
     }"
     HAS_SSE2_EXTENSIONS)

  set(CMAKE_REQUIRED_FLAGS "-msse")
  check_cxx_source_runs("
    #include <xmmintrin.h>
    int main()
    {
        __m128 a, b;
        float vals[4] = {0};
        a = _mm_loadu_ps(vals);
        b = a;
        b = _mm_add_ps(a,b);
        _mm_storeu_ps(vals,b);
        return 0;
    }"
    HAS_SSE_EXTENSIONS)

  set(CMAKE_REQUIRED_FLAGS)

  if(HAS_SSE2_EXTENSIONS)
    message(STATUS "Using SSE2 extensions")
    set(SSE_FLAGS "-msse2 -mfpmath=sse")
  elseif(HAS_SSE_EXTENSIONS)
    message(STATUS "Using SSE extensions")
    set(SSE_FLAGS "-msse -mfpmath=sse")
  endif()

  add_definitions(${SSE_FLAGS})
elseif(MSVC)
  check_cxx_source_runs("
    #include <emmintrin.h>

    int main()
    {
        __m128d a, b;
        double vals[2] = {0};
        a = _mm_loadu_pd(vals);
        b = _mm_add_pd(a,a);
        _mm_storeu_pd(vals,b);
        return 0;
     }"
     HAS_SSE2_EXTENSIONS)
  if( HAS_SSE2_EXTENSIONS )
    message(STATUS "Using SSE2 extensions")
    add_definitions( "/arch:SSE2 /fp:fast -D__SSE__ -D__SSE2__" )
  endif()
endif()





2010/3/24 Jose Gonzalez <de0a100 at gmail.com>:
> Thanks for the comments?
>
> What about  check_cxx_compiler_flag("-msse2" COMPILER_SUPPORT_SSE2)?
> Have you ever tried it?
>
> On Tue, Mar 23, 2010 at 12:16 PM, Radu Bogdan Rusu
> <rusu at willowgarage.com> wrote:
>> Depending on what compiler and cpu you use, some of these flags might be already turned on by default. You can check
>> that using:
>>
>> $ gcc -Q -O3 --help=target
>>
>> for example.
>>
>> Other than that, we don't have a proper way to enable/disable different SSE optimizations for now. Most ROS packages
>> cram a add_definitions ("-msse... etc") in their CMakeLists.txt.
>>
>> Patches to make this more standard across multiple platforms and enable/disable SSE1-5 automatically would be great!
>>
>> Cheers,
>> Radu.
>>
>> Jose Gonzalez wrote:
>>> Hi,
>>>
>>> Doing some experiments in the past with OpenCV (linux/g++) I realized
>>> that there is a significant performance difference between the
>>> versions compiled with autoconf and cmake. Digging in the compilation
>>> scripts I came to the conclusion that the only extra flags that were
>>> added by the autoconf scripts were the SSE optimizations (and openMP).
>>>
>>> Talking about the SSE optimizations, I can see how ROS sets the flags
>>> in a similar way. When the detected platform is i686, all the SSE
>>> optimizations are disabled by default (there is a comment "SSE/SSE2
>>> might probably be not available for some old AMD or VIA processors").
>>> Before finding out a solution by myself I'd like to ask the list if
>>> somebody knows a standard way of testing for SSE optimizations in
>>> cmake.
>>>
>>> Thanks,
>>> Jose
>>>
>>> ------------------------------------------------------------------------------
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>>
>> --
>> | Radu Bogdan Rusu | http://rbrusu.com/
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