How to compile Cuda within Clang when included by main c++ file? - cmake

Question

I am currently working on a project, where I want to execute some code in Cuda, which should be called from the main c++ file. When I am compiling with Clang only the .cpp files are compiled and the compiler tells me "expected exprission" on the <<<>>> Kernel call notation. Any Idea how I can fix this?
I have a .cuh files with the definition which I am including and a .cu source file. I am using CMake to configure the project and building it with Ninja.
I am using ccached clang++ and supplying "--cuda-path=/usr/local/cuda-10.1 --cuda-gpu-arch=sm_61 -L/usr/local/cuda-10.1/lib64 -lcudart_static -ldl -lrt -pthread -std=c++17" to clang args.
When I add the -x cuda flag, the error does not appear, but instead it tells me that a library that I am linking against is not allowed to overwrite some host function, but I think this is because it wants to compile everything as cuda, which is not intended.
I am passing all files inside my source folder to add_executable in CMake via a GLOB ${APP_PATH}/src/*, which should add all files.
main.cpp
#include "ParticleEngine.cuh"
...
int main(){
simulation_timestep(&this->particles[0], this->gravity, 1, delta_frame,
this->particles.size());
}
ParticleEngine.cuh
#pragma once
#include "cuda_runtime.h"
#include "device_launch_parameters.h"
void simulation_timestep(Particle *particles, ci::vec3 gravity, double mass,
double time_delta, unsigned long long n_particles);
ParticleEngine.cu
#include "ParticleEngine.cuh"
__global__ void particle_kernel(Particle *particles, ci::vec3 *gravity,
double *mass, double *time_delta) {
...
}
void simulation_timestep(Particle *particles, ci::vec3 gravity, double mass,
double time_delta, unsigned long long n_particles) {
... //memcpy stuff
particle_kernel<<<dimgrid, dimblock>>>(cuda_particles, cuda_gravity,
cuda_mass, cuda_time_delta);
...
}
edit:
Full error message:
[build] In file included from ../src/main.cpp:1:
[build] ../src/ParticleEngine.cu:43:20: error: expected expression
[build] particle_kernel<<<dimgrid, dimblock>>>(cuda_particles, cuda_gravity,
[build] ^
edit:
Error message when executing clang with -x cuda:
[build] /home/mebenstein/Cinder/include/glm/gtx/io.inl:97:32: error: __host__ __device__ function 'get_facet' cannot overload __host__ function 'get_facet'
[build] GLM_FUNC_QUALIFIER FTy const& get_facet(std::basic_ios<CTy, CTr>& ios)
[build] ^
[build] /home/mebenstein/Cinder/include/glm/gtx/io.hpp:145:14: note: previous declaration is here
[build] FTy const& get_facet(std::basic_ios<CTy,CTr>&);
[build] ^
I am including the c++ library cinder in main.cpp and this error appears.

Answer 1

#include in C++ works by literally replacing that statement with the contents of the included file. As a consequence, the included file is also parsed as C++ code.
To compile a file as CUDA code, the file needs to be a separate compilation unit, i.e. given as an argument to the clang invocation. It also either needs to have a name ending in .cu, or the -x cuda flag needs to be given to clang.
Update after error messages have been included in the question:
It appears that Cinder does not support compilation of the CUDA part with clang++ because of a difference in how __host__/__device__ attributes are treated.
At this point your options are the following:
You can modify Cinder to also support clang++, it's open source.
You can ask the Cinder authors or third parties whether they are willing to make the necessary changes. A cash incentive may or may not increase willingness.
You can use nvcc to compile the code.