Build minimal PyTorch using setup.py

This CMakeLists.txt manages the building of a minimal PyTorch library from PyTorch 1.7.0 by setting environment variables and calling pytorch/setup.py

Prerequisites

1. Clone PyTorch 1.7.0 and adjust the CMakeLists.txt variable PYTORCH_SRC_DIR to point to the local repository, for example set(PYTORCH_SRC_DIR ../pytorch)
2. Install the PyTorch prerequisites

Equivalent bash script inspired by C++ development tips

cd pytorch
export DEBUG=1
export BUILD_TEST=0
export USE_CUDA=0
export USE_DISTRIBUTED=0
export USE_MKLDNN=0
export USE_FBGEMM=0
export USE_NNPACK=0
export USE_QNNPACK=0
export USE_XNNPACK=0
export BUILD_CAFFE2_OPS=0
[see below for minor edits to PyTorch tree]
python setup.py build --cmake-only
cmake --build build

Usage

Generate the project buildsystem

cmake -S . -B build

CMakeLists.txt adjusts the following in ${PYTORCH_SRC_DIR}/CMakeLists.txt

GCC

-Og enables optimizations that do not interfere with debugging. This replaces -O2 in CMAKE_CXX_FLAGS

CMakeLists.txt adjusts the following in ${PYTORCH_SRC_DIR}/cmake/Dependencies.cmake

Remove deprecated find_package(PythonLibs 3.0)

This avoids the following error -

CMake Error at cmake/Dependencies.cmake:926 (if):
  if given arguments:

    "VERSION_LESS" "3"

  Unknown arguments specified

Optionally adjust ${PYTORCH_SRC_DIR}/build/CMakeCache.txt

CMAKE_BUILD_TYPE

The environmental variable DEBUG=1, sets CMAKE_BUILD_TYPE=Debug to build libraries with debug symbols

BUILD_SHARED_LIBS

The build generates shared libraries by default. This can be disabled by setting BUILD_SHARED_LIBS=OFF

Build the PyTorch project

cmake --build ${PYTORCH_SRC_DIR}/build

Example

cmake ---S . -B build
cmake --build ../pytorch/build

Location of built libraries

pytorch/build/lib

Cleaning / trouble-shooting

Linux

rm build/CMakeCache.txt
rm -rf build

Windows

del build/CMakeCache.txt
rmdir /s /q build
mklink /d build d:\build

Clean PyTorch source without using standard ignore rules

git clean -dfx