Summary:
Separating CUDA fuser from CPU fuser.
1. New node in IR - prim::CudaFusionGroup:
This enables the cuda fuser to co-exist along side the old fuser. Allows us
to incrementally build and expand cuda fuser.
2. copied FuseGraph optimization passes to CudaFuserGraph:
We will re-factor & reuse Chunk/Concat in the old fuser logic, which is
handled in the optimization pass at this moment. Unfortunately many code in
the pass is tightly binded with the legacy fuser, which makes code sharing
difficult.
The CudaFusionGraph will support only a subset of operations comparing to
legacy fuser (CUDA only). It is registered as a custom pass post fusion via
```torch._C._jit_register_cuda_fuser()```
To have it in effect, you should also turn off fusion on GPU via
```torch._C._jit_override_can_fuse_on_gpu(False)```
3. We don't have codegen in this PR yet (WIP). Currently we just fall back to
the old fuser.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33527
Differential Revision: D20171598
Pulled By: ZolotukhinM
fbshipit-source-id: 9a3c0f06f46da7eaa80ae7551c04869f5b03ef71
