Preprocessing directives GPU

Question

I have a C/C++ package where I make use of some GPU acceleration methods, CUDA for Nvidia hardware and using OpenCL for non-Nvidia hardware. I also have SIMD functions specific to Intel CPUs and some specific for ARM. I want to be able to install these different acceleration methods based on the install flags passed in when building with CMake but I am unsure how to also structure my header file.

The two things I am trying to tackle with preprocessor directives and the optional installation piece with CMake is:

1. Check if the headers were installed from the optional CMake flags (is this possible?)
2. Check if the given host machine matches one of the compatible platforms I wrote code for (OpenCL compatible platforms and CUDA) AND include the optional header files based on that

I am thinking of the header file for this project looking something like this but am unsure of the directives themselves

#ifdef Intel/Apple... OpenCL compatible GPUs
    // include GPU code that uses OpenCL
#endif

#ifdef Nvidia GPU
    // include GPU code that uses CUDA
#endif

#ifdef Intel CPUs
   // include SIMD code that uses Intel intrinsics 
#endif

#ifdef ARM CPUs
   // include SIMD code that uses ARM intrinsics
#endif

Is this the proper way to go about creating code to run on multiple platforms? I am curious how projects do something similar like OpenCV being compatible with CUDA and OpenCL.

Answer 1

Check if the headers were installed from the optional CMake flags (is this possible?)

Compile a sample program with that header, and check if it compiles. https://cmake.org/cmake/help/latest/module/CheckIncludeFile.html or https://cmake.org/cmake/help/latest/command/try_compile.html

Check if the given host machine matches one of the compatible platforms I wrote code for (OpenCL compatible platforms and CUDA)

How to identify platform/compiler from preprocessor macros? and https://github.com/Kitware/CMake/blob/master/Modules/CMakePlatformId.h.in etc.

s this the proper way to go about creating code to run on multiple platforms?

There is no "proper" way. It is one of the ways, and it's fine.

how projects do something similar like OpenCV being compatible with CUDA and OpenCL.

OpenCV is an open source project. https://github.com/opencv/opencv/blob/a4a9f56c8bbb11fd4a017d3c1819b89f43160474/cmake/OpenCVDetectCUDA.cmake#L82 https://github.com/opencv/opencv/blob/a4a9f56c8bbb11fd4a017d3c1819b89f43160474/modules/core/src/matrix_wrap.cpp#L319 etc.