Update the build system to support Cuda.

[csukuangfj]

Now Cub is supported and the cuda branch is paritially compilable.

I've added a naive implementation for context and a test for ExclusivePrefixSum.

A google colab notebook is also added in case someone wants to try it out but does not have a GPU.

---

Note that CMake 3.8 is required. C++ 14 is used to remove the warnings reported by Cub.

@danpovey @qindazhu
please have a review.

[qindazhu]

maybe we should create a new branch (e.g. cuda), as Dan may push to cuda_draft directly.

[csukuangfj]

I've disabled the GitHub workflow for the CUDA branch since it requires CUDA and won't compile, which always fails.

[csukuangfj]

Once this pullrequest is merged, we can create a new branch from cuda_draft and leave cuda_draft for Dan.

[qindazhu]

Fantastic work! Only a few comments, +2!

[csukuangfj]

thanks, I will resolve the comments tonight.

[danpovey]

Great, thanks!

[danpovey]

@csukuangfj why did you upgrade the build to c++14 from c++11, and what file did you edit to do that?
It's causing me problems building it, as the version of gcc here doesn't support that. I don't like to use any newer
version of c++ than we need to.

[csukuangfj]

To use c++11, you can change
https://github.com/danpovey/k2/blob/a662f9bfea895ad5eef09abcb8a02b6657d7c1f8/CMakeLists.txt#L42

to

set(CMAKE_CXX_STANDARD 11 CACHE STRING "The C++ version to be used.") 

---

The reason to switch to c++14 is that the following code from CUB: https://github.com/NVlabs/cub/blob/master/cub/util_cpp_dialect.cuh#129

#if !defined(CUB_IGNORE_DEPRECATED_CPP_DIALECT) && CUB_CPP_DIALECT < 2014 && \
    (CUB_CPP_DIALECT != 2011 || !defined(CUB_IGNORE_DEPRECATED_CPP_11))
  CUB_COMPILER_DEPRECATION(C++14, pass -std=c++14 to your compiler);
#endif

issues warnings during the compilation if you are not using c++14.

[csukuangfj]

I can suppress the CUB warnings by deleting CUB_COMPILER_DEPRECATION(C++14, pass -std=c++14 to your compiler);
if you like.

[danpovey]

OK thanks... yeah suppress the warning for now. I guess it's more efficient with c++14, but I'd like to make sure our code works with c++11, so we can support a wider range of compilers.

…

On Thu, Jul 30, 2020 at 3:46 PM Fangjun Kuang ***@***.***> wrote: I can suppress the CUB warnings by deleting CUB_COMPILER_DEPRECATION(C++14, pass -std=c++14 to your compiler); if you like. — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <https://github.com/danpovey/k2/pull/75#issuecomment-666197935>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAZFLOZZNRHFHYWZGBGMORTR6EQMXANCNFSM4PI63YNA> .

[csukuangfj]

I will make a change this night.

You can use

cd build
cmake -DCMAKE_CXX_STANDARD=11 ..

to switch to c++11 without changing the CMakeLists.txt

[danpovey]

thanks

…

On Thu, Jul 30, 2020 at 3:54 PM Fangjun Kuang ***@***.***> wrote: I will make a change this night. You can use cd build cmake -DCMAKE_CXX_STANDARD=11 .. to switch to c++11 without changing the CMakeLists.txt — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <https://github.com/danpovey/k2/pull/75#issuecomment-666203003>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAZFLO5HZ5L5R7V64KOIVC3R6ERMFANCNFSM4PI63YNA> .