Summary:
Here is the buggy behavior which this change fixes:
* On the first configure with CMake, a system-wide benchmark installation is not found, so we use the version in `third_party/` ([see here](https://github.com/caffe2/caffe2/blob/v0.8.1/cmake/Dependencies.cmake#L98-L100))
* On installation, the benchmark sub-project installs its headers to `CMAKE_INSTALL_PREFIX` ([see here](https://github.com/google/benchmark/blob/4bf28e611b/src/CMakeLists.txt#L41-L44))
* On a rebuild, CMake searches the system again for a benchmark installation (see https://github.com/caffe2/caffe2/issues/916 for details on why the first search is not cached)
* CMake includes `CMAKE_INSTALL_PREFIX` when searching the system ([docs](https://cmake.org/cmake/help/v3.0/variable/CMAKE_SYSTEM_PREFIX_PATH.html))
* Voila, a "system" installation of benchmark is found at `CMAKE_INSTALL_PREFIX`
* On a rebuild, `-isystem $CMAKE_INSTALL_PREFIX/include` is added to every build target ([see here](https://github.com/caffe2/caffe2/blob/v0.8.1/cmake/Dependencies.cmake#L97)). e.g:
cd /caffe2/build/caffe2/binaries && ccache /usr/bin/c++ -I/caffe2/build -isystem /caffe2/third_party/googletest/googletest/include -isystem /caffe2/install/include -isystem /usr/include/opencv -isystem /caffe2/third_party/eigen -isystem /usr/include/python2.7 -isystem /usr/lib/python2.7/dist-packages/numpy/core/include -isystem /caffe2/third_party/pybind11/include -isystem /usr/local/cuda/include -isystem /caffe2/third_party/cub -I/caffe2 -I/caffe2/build_host_protoc/include -fopenmp -std=c++11 -O2 -fPIC -Wno-narrowing -O3 -DNDEBUG -o CMakeFiles/split_db.dir/split_db.cc.o -c /caffe2/caffe2/binaries/split_db.cc
This causes two issues:
1. Since the headers and libraries at `CMAKE_INSTALL_PREFIX` have a later timestamp than the built files, an unnecessary rebuild is triggered
2. Out-dated headers from the install directory are used during compilation, which can lead to strange build errors (which can usually be fixed by `rm -rf`'ing the install directory)
Possible solutions:
* Stop searching the system for an install of benchmark, and always use the version in `third_party/`
* Cache the initial result of the system-wide search for benchmark, so we don't accidentally pick up the installed version later
* Hack CMake to stop looking for headers and libraries in the installation directory
This PR is an implementation of the first solution. Feel free to close this and fix the issue in another way if you like.
Closes https://github.com/caffe2/caffe2/pull/1112
Differential Revision: D5761750
Pulled By: Yangqing
fbshipit-source-id: 2240088994ffafdb6eedb3626d898b505a4ba564
Summary:
This PR changes the cmake of Caffe2 to look for system dependencies before resorting to the submodules in `third-party`. Only googletest should logically be in third-party, the other libraries should ideally be installed as system dependencies by the user. This PR adds system dependency checks for Gloo, CUB, pybind11, Eigen and benchmark, as these were missing from the cmake files.
In addition it removes the execution of `git submodule update --init` in cmake. This seems like bad behavior to me, it should be up to the user to download submodules and manage the git repository.
Closes https://github.com/caffe2/caffe2/pull/382
Differential Revision: D5124123
Pulled By: Yangqing
fbshipit-source-id: cc34dda58ffec447874a89d01058721c02a52476
