New CUDA Fuser code lowering refactor (#36199)
Summary:
This PR completely refactors the code lowering process from our IR to CUDA. Before we had one giant step that would go from a relatively high level IR straight to CUDA, now we're lowering this first into concepts like ForLoop, IfThenElse, TensorIndex, Allocate. This lowering will allow us to do more complex code lowering like reductions and unrolling. Unrolling will quickly follow this PR.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36199
Reviewed By: dzhulgakov
Differential Revision: D20925220
Pulled By: soumith
fbshipit-source-id: 8f621c694c68a1aad8653e625d7287fe2d8b35dc
