pytorch

b2520ab3 - Add a demo backend with compiler (#52603)

Add a demo backend with compiler (#52603) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/52603 This PR introduced a backend with minimum compilation capability to the to_<backend> flow. The targets are: - Demonstrate the end-to-end flow with adding a backend -> compilation -> runtime - How the backend compilation errors be surfaced to the user, with the original model's source code information. (C++ only in this PR. Python APIs will be demonstrated in a following PR.) Changes: - Compilation 1. A backend with minimum compilation features, "backend_with_compiler_demo" is added. 2. The compilation happens AOT in the ```pre_process``` function registered to this backend. 3. Compiled results are stored in a string blob for each method. They are serialized to the lowered module with ```__get_state__``` function. 4. Error message with model source code is thrown, for features not handled by the backend compiler. - Runtime 1. The compiled blob is loaded in ```__set_state__``` method. 2. The ```compile``` function of the backend pass through the AOT compiled blob. (TODO: parsing the blob to the format that the backend can understand can happen here.) 3. The ```execute``` function of the backend executes the specified method (handle). Test Plan: - ```BackendTest.TestCompiler```: the C++ end-to-end demonstration on a supported model. After compilation and running, the lowered model produces the same result as the original torchscript model. - ```BackendTest.TestCompilerNotSupport```: Demonstrate the error message from the AOT compilation for a feature not supported from the input module. The error message looks like: ``` "The node of aten::mul is not supported in this compiler. Source code: File "<string>", line 3 def forward(self, x, h): return x * h ~~~~~ <--- HERE ``` Reviewed By: raziel Differential Revision: D26593968 Pulled By: iseeyuan fbshipit-source-id: 8f264f60a0470e9f07e36fdeccbf17da6c1d7cd7