[pytorch] improve code analyzer to dump ops called from c++ functions (#35941)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35941
The key step of mobile custom build is to find out ops used by specific
model, with which it can produce a tailored build of optimal size.
However, ops can not only be called from TorchScript model but can also
be called from C++ code directly, e.g.: via torch::jit:: APIs. With
static dispatch, ops called this way will be statically linked into client
code. With dynamic dispatch, we need obtain & keep these ops explicitly.
This PR improves static code analyzer to dump ops that are called from
visible c++ symbols matching specific regex. This provides a mechanism
to solve the custom build problem with dynamic dispatch.
It starts with dumping ops that are callable from functions in torch::jit
namespace and include them in custom build with dynamic dispatch. We can
extend it to analyze custom code / to refine the set of JIT APIs that
are relevant, and etc. This is just a preliminary version. We need
improve its usability for more general purpose.
Test Plan: Imported from OSS
Differential Revision: D20835166
Pulled By: ljk53
fbshipit-source-id: a87cfb22b34f89545edd0674a5dfca6b7cff2b0c
