[ros-users] Question about cmake and SSE optimizations

[Brian Gerkey]

It would be great to see this functionality wrapped up in a single
CMake macro, something like:
  rosbuild_add_sse_flags(target)
It would do checks, compute flags, then call
rosbuild_add_compile_flags(target ...).  Of course, this assumes that
you want the highest / best level of SSE available; I'm not familiar
enough with these optimizations to know if that's appropriate, or if
you'd rather have finer-grained control.

I'd happily add such a macro to rosbuild, for general reuse.  Come to
think of it, this would be a nice module to contribute to CMake
itself.

	brian.

On Tue, Mar 23, 2010 at 11:14 AM, Radu Bogdan Rusu
<rusu at willowgarage.com> wrote:
> Great job Rosen! That's exactly what I had in mind.
>
> We should add SSE3 and SSE4. Gotta love that dot product :)
>
> Cheers,
> Radu.
>
> Rosen Diankov wrote:
>> 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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>
> --
> | Radu Bogdan Rusu | http://rbrusu.com/
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