Compiling CUDA with clang on math functions - c++

Question

Compiling the following CUDA code helloWorld.cu with clang-11,
int main() {
return max(1.0f, 2.0f);
}
, using command clang++-11 -o helloWorld helloWorld.cu --cuda-gpu-arch=sm_75 -ldl -lrt -lcudart_static -pthread -L/usr/local/cuda/lib64, encountered the error:
helloWorld.cu:2:12: error: no matching function for call to 'max'
return max(1.0f, 2.0f);
^~~
/usr/lib/llvm-11/lib/clang/11.0.0/include/__clang_cuda_math.h:194:16: note: candidate function not viable: call to __device__ function from __host__ function
__DEVICE__ int max(int __a, int __b) { return __nv_max(__a, __b); }
...
/usr/local/cuda-10.2/include/crt/math_functions.hpp:1079:31: note: candidate function not viable: call to __device__ function from __host__ function
__MATH_FUNCTIONS_DECL__ float max(float a, float b)
...
Note that the matching function was actually located correctly by the compiler (ie, "math_functions.hpp:1079:31"), but was mistakenly inferred as a "_device_" function.
Thanks for any help in advance.

Answer 1

The code you have written is host code and it is not syntactically valid C++. That code should not compile, and the compiler behaviour is correct. The code should look like this in order to compile:
#include <algorithm>
int main() {
return std::max(1.0f, 2.0f);
}
i.e. you have to actually include the standard library header which defines the max function, and you have to use the correct namespace. C++ has no built-in max function. CUDA does. All you are seeing is an artifact of the clang CUDA compilation trajectory.