[CMake] FindCUDA Separable Compilation and cublas_device

[Jamil Appa]

Hi Robert

   I will put a minimal case together using one of the CUDA samples and
sent it through for testing with the new cmake support.

   On your second point, CUDA_CUBLAS_LIBRARIES should be empty if no cublas
libraries are present so that use case should be automatically handled
unless I am missing something.

   I will create a fork and topic branch with the change and submit it for
review.

 Thanks

  Jamil

On Fri, 3 Nov 2017 at 18:08 Robert Maynard <robert.maynard at kitware.com>
wrote:

> HI Jamil,
>
> If you are interested in submitting a fix I can review, but I would like
> to also make sure that this issue doesn't exist inside the new cmake
> support for CUDA as a first class language. Can you produce a minimal test
> case that we can rework to use the new support and add to CMake's test
> suite.
>
> You will also need to track down what version of CUDA first added cublas_device
> so that we properly guard the inclusion.
>
> On Fri, Nov 3, 2017 at 7:39 AM, Jamil Appa <jamil.appa at zenotech.com>
> wrote:
>
>> Hi Robert
>>
>>   I am using CUDA_ADD_CUBLAS_TO_TARGET but the error happens during the
>> prelink phase when using separable compilation. (nvcc -dlink phase)
>>
>>    My guess is that Nvidia have not included cublas_device.a in their
>> dlink phase as you don't have to provide any other libraries. I have asked
>> the Nvidia team if that is the case, but no reply yet.
>>
>>    The general fix seems to be to modify lines 1759/1772 of
>> FindCUDA.cmake (in gitlab master) to include CUBLAS_LIBRARIES
>>
>>  COMMAND ${CUDA_NVCC_EXECUTABLE} ${nvcc_flags} -dlink ${object_files}
>> ${CUDA_CUBLAS_LIBRARIES} -o ${output_file}
>>
>>  This will have no impact if the cublas symbols are not used in the
>> object files.
>>
>>   If you are happy with this I can submit the change for review.
>>
>>  Jamil
>>
>>
>> On Thu, 2 Nov 2017 at 13:53 Robert Maynard <robert.maynard at kitware.com>
>> wrote:
>>
>>> Hi,
>>>
>>> Have you tried using the 'CUDA_ADD_CUBLAS_TO_TARGET' command on the
>>> target that has FindCUDA separable compilation enabled?
>>>
>>> On Wed, Nov 1, 2017 at 11:16 AM, Jamil Appa <jamil.appa at zenotech.com>
>>> wrote:
>>>
>>>> Hi
>>>>
>>>>    When using FindCUDA with separable compilation combined with device
>>>> code that uses cublas_device I get missing symbols when linking the
>>>> intermediate file at line 1758
>>>> <https://gitlab.kitware.com/cmake/cmake/blob/release/Modules/FindCUDA.cmake#L1758>
>>>>  FindCUDA.cmake
>>>>
>>>>    If I  change line 1758 to include the cublas_device library the
>>>> symbols are resolved correctly.
>>>>
>>>>    COMMAND ${CUDA_NVCC_EXECUTABLE} ${nvcc_flags} -dlink ${object_files}
>>>> -o ${output_file} -lcublas_device
>>>>
>>>>    Is there a way to pass through a library to
>>>> the CUDA_LINK_SEPARABLE_COMPILATION_OBJECTS function that I am missing?
>>>>
>>>>    Thanks
>>>>
>>>>  Jamil
>>>>
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