编译和链接 Cuda 和 Clang 以在主机代码上支持 c++20

Question

I am trying to compile, link and execute a simple Cuda example using Clang instead of Gcc. The general idea behind using Clang is to allow c++20 in Host Code and more compiler optimizations using the llvm/clang stack.

I looked at the following sources: llvm docs google paper about gpucc This example is from the llvm documents about compiling cuda with clang

     #include <iostream>

      __global__ void axpy(float a, float* x, float* y) {
     y[threadIdx.x] = a * x[threadIdx.x];
     }

     int main(int argc, char* argv[]) {
    const int kDataLen = 4;

    float a = 2.0f;
    float host_x[kDataLen] = {1.0f, 2.0f, 3.0f, 4.0f};
    float host_y[kDataLen];

    // Copy input data to device.
   float* device_x;
   float* device_y;
   cudaMalloc(&device_x, kDataLen * sizeof(float));
   cudaMalloc(&device_y, kDataLen * sizeof(float));
   cudaMemcpy(device_x, host_x, kDataLen * sizeof(float),
         cudaMemcpyHostToDevice);

   // Launch the kernel.
   axpy<<<1, kDataLen>>>(a, device_x, device_y);

   // Copy output data to host.
   cudaDeviceSynchronize();
   cudaMemcpy(host_y, device_y, kDataLen * sizeof(float),
         cudaMemcpyDeviceToHost);

  // Print the results.
  for (int i = 0; i < kDataLen; ++i) {
  std::cout << "y[" << i << "] = " << host_y[i] << "\n";
  }

 cudaDeviceReset();
  return 0;
  }

The Command to compile and link used is:

clang++-12 axpy.cu -o axpy --cuda-gpu-arch=sm_72     
-L/usr/local/cuda-11.4/lib64 -lcudart -ldl -lrt -pthread axpy.cu 
--cuda-path=/usr/local/cuda-11 --no-cuda-version-check

The output indicates that it successfully compiles but fails to link:

clang: warning: Unknown CUDA version. cuda.h: CUDA_VERSION=11040. Assuming the l                                                                                              atest supported version 10.1 [-Wunknown-cuda-version]
/usr/bin/ld: /tmp/axpy-35c781.o: in function `__device_stub__axpy(float, float*,                                                                                            float*)':
axpy.cu:(.text+0x0): multiple definition of `__device_stub__axpy(float, float*,                                                                                          float*)'; /tmp/axpy-c82a7d.o:axpy.cu:(.text+0x0): first defined here
/usr/bin/ld: /tmp/axpy-35c781.o: in function `main':
axpy.cu:(.text+0xa0): multiple definition of `main'; /tmp/axpy-c82a7d.o:axpy.cu:                                                                                          (.text+0xa0): first defined here
clang: error: linker command failed with exit code 1 (use -v to see invocation)

The error seems to indicate that clang is doing multiple passes over the code to link and wrongfully includes main twice.

OS: Ubuntu 20.04 Kernel 5.40 Cuda: 11.4 Clang (tried 11/12/13)

I would be grateful for any hints how to get CUDA and Clang working together. Things I have tried so far: Different Clang versions 11/12/13. Different Cuda Versions 11.2/11.4.

Answer 1

The output indicates that it successfully compiles but fails to link:

axpy.cu:(.text+0xa0): multiple definition of `main';

This seems to have been sorted in the comments:

Maybe the only problem is that you pass axpy.cu twice in your compile command.

clang++-12 axpy.cu -o axpy --cuda-gpu-arch=sm_72 -L/usr/local/cuda-11.4/lib64 -lcudart -ldl -lrt -pthread axpy.cu --cuda-path=/usr/local/cuda-11 --no-cuda-version-check
           ^^^^^^^                                                                                        ^^^^^^^

That was it. thank you.