[cmake] CMake script for choosing CCs

[griwodz]

The idea is to have a CMake function that can be re-used and extended to get an up-to-date list of default CCs for compilation as CUDA develops further.

[griwodz]

@simogasp Could you take a look at this attempt? It is not hooked into CMakeLists.txt yet, just to discuss the idea and link it to the bug report.

[griwodz]

Would it be possible to upgrade to cmake 3.11 also in PopSift (and discard the commit "replace >=")?
I see that we use 3.11 in AliceVision, but not sure how to make it happen.

[simogasp]

I changed the destination base to dev/cleaning for the time being so we can see just the related diffs

[simogasp]

So I guess we want to give the possibility to the user to provide a -DPopSift_CUDA_CC_LIST=30;70 at cmake stage, am I correct?
In that case:

1. we should document it in the README in the build section

2. more importantly, we should check that those provided are good/supported. One way to go it could be something like:

# we always need to know which are all the supported CC
chooseCudaCC(PopSift_CUDA_CC_LIST_BASIC 
            PopSift_CUDA_GENCODE_FLAGS
            MIN_CC 30
            MIN_CUDA_VERSION 7.0)
# if PopSift_CUDA_CC_LIST is provided
if(DEFINED PopSift_CUDA_CC_LIST)
    # check each provided element is supported
    # ideally this function checks the provided cc are in the list generating an error if not
    check_if_supported(PopSift_CUDA_CC_LIST  PopSift_CUDA_CC_LIST_BASIC)
    getFlagsForCudaCCList(PopSift_CUDA_CC_LIST PopSift_CUDA_GENCODE_FLAGS)
else()
    set(PopSift_CUDA_CC_LIST ${PopSift_CUDA_CC_LIST_BASIC} CACHE STRING "CUDA CC versions to compile")
endif()
list(APPEND CUDA_NVCC_FLAGS "${PopSift_CUDA_GENCODE_FLAGS}")

and

function(check_if_supported PROVIDED_CC  SUPPORTED_CC)
    foreach(cc IN LISTS PROVIDED_CC)
        if(NOT ${cc} IN_LIST SUPPORTED_CC)
            message(FATAL_ERROR "Compute capability ${cc} not supported. Supported CC are ${SUPPORTED_CC}")
    endforeach()
endfunction()

What do you think?

[griwodz]

Is that a really good thing? Without that check, a user can configure for a brand new CC that we haven't put into the ChooseCudaCC.cmake file yet.

[simogasp]

Well, you have a point!
We can then leave it like that and assume that it is an advanced feature and the user knows what is doing.

[simogasp]

I was thinking, since we are going to use it in all the other projects, shall we rather create a repository with these sorts of help functions and import them as git submodules? @fabiencastan