Add libtorch

[abirbasak]

It will be nice to have libtorch (c++ library from PyTorch ) on vcpkg,
The github repo https://github.com/pytorch/pytorch

[Fleischner]

Currently I'm blocked by the fact that during cmake configure step it needs an python installation with yaml package. How do you handle those cases normally?
Is it up to the user to install an suitable python setup?

[Fleischner]

Will start an pull request for cooperate work soon. Some updates so far:

• Trying to build with cuda and cudadnn, otherwise it's deadly slow. cudadnn needs to be installed by hand.

• Currently used Eigen Version 3.3.4 has incompatibilites with GPU __half types. The current compatible Eigen branch is d41dc4dd74. There would be an option to build with hidden dependency

• Protobuf needs patches. There are problems with nvcc in the generated files with "constexpr kIndexInFileMessages" static variables. pytorch has options DBUILD_CUSTOM_PROTOBUF and DCAFFE2_LINK_LOCAL_PROTOBUF to use hidden dependency protobuf and link statically against it.

• I fear pytorch has incompatibility with caffe2 port. It uses caffe2 internally and is strongly coupled to this. There seems to be no option to use an system installed caffe2

[Fleischner]

From 1.0 release pytorch seems to be a fusion of torch+pytorch+caffe2+onnx in a single package.
Caffe2_PyTorch_1_0

So I suggest to discontinue caffe2 port and continue only with libtorch (c++ frontend of pytorch)

Edit:
libtorch build includes caffe2 build.
Currently no vcpkg ports depend on caffe2

[Fleischner]

If build without python, libtorch shouldn't depend on pybind11. But still it tries to include some pybind headers.

Building with pybind11 now. However libtorch build process requires python.exe. If set to the python executable in tools directory, pybind11 complains that this executable is 32bit...

Since I'm not sure if downloading and installing an x64 portable python will result in linking to the wrong libraries, I will change the python3 port to build with the python3.exe as tools

[Fleischner]

pytorch build needs an python.exe to be set. But then pybind11 cmake targets wrongly search libraries relative to this exe instead of using the correct libraries from the python3 port.

I got it to build with an very ugly port file, many hacks and some hidden deps....
But eigen3, protobuf and pybind need patches. No way around.

[jasjuang]

@Fleischner could you share what you have so far? I am interested in this too. Is it easy to build it without python?

[JackBoosY]

We can’t reopen this issue until a PR is opened, unfortunately, consider making a pull request!

[soroshsabz]

I need this, please consider again.

[zhaofeng-shu33]

Need this also

[Bzz2745]

I want to know if libtorch could build with CUDA and CUDNN on vcpkg now ?I didn't see any dependencies about that when I run 'vcpkg search libtorch'.