pytorch

38986e1d - Split libtorch.so back into libtorch_{cpu,cuda,hip} (#30315)

Split libtorch.so back into libtorch_{cpu,cuda,hip} (#30315) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/30315 The new structure is that libtorch_cpu contains the bulk of our code, and libtorch depends on libtorch_cpu and libtorch_cuda. This is a reland of https://github.com/pytorch/pytorch/pull/29731 but I've extracted all of the prep work into separate PRs which can be landed before this one. Some things of note: * torch/csrc/cuda/nccl.cpp was added to the wrong list of SRCS, now fixed (this didn't matter before because previously they were all in the same library) * The dummy file for libtorch was brought back from the dead; it was previously deleted in #20774 In an initial version of the patch, I forgot to make torch_cuda explicitly depend on torch_cpu. This lead to some very odd errors, most notably "bin/blob_test: hidden symbol `_ZNK6google8protobuf5Arena17OnArenaAllocationEPKSt9type_infom' in lib/libprotobuf.a(arena.cc.o) is referenced by DSO" * A number of places in Android/iOS builds have to add torch_cuda explicitly as a library, as they do not have transitive dependency calculation working correctly * I had to torch_cpu/torch_cuda caffe2_interface_library so that they get whole-archived linked into torch when you statically link. And I had to do this in an *exported* fashion because torch needs to depend on torch_cpu_library. In the end I exported everything and removed the redefinition in the Caffe2Config.cmake. However, I am not too sure why the old code did it in this way in the first place; however, it doesn't seem to have broken anything to switch it this way. * There's some uses of `__HIP_PLATFORM_HCC__` still in `torch_cpu` code, so I had to apply it to that library too (UGH). This manifests as a failer when trying to run the CUDA fuser. This doesn't really matter substantively right now because we still in-place HIPify, but it would be good to fix eventually. This was a bit difficult to debug because of an unrelated HIP bug, see https://github.com/ROCm-Developer-Tools/HIP/issues/1706 Fixes #27215 (as our libraries are smaller), and executes on part of the plan in #29235. Signed-off-by: Edward Z. Yang <ezyang@fb.com> Test Plan: Imported from OSS Differential Revision: D18790941 Pulled By: ezyang fbshipit-source-id: 01296f6089d3de5e8365251b490c51e694f2d6c7