Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35800
This PR includes the following changes:
* Introduce a new `Expr` type `Buf`: it plays a similar to `Var` role, but also has dimensions.
* Use the new `Buf` class in `Store` and `Load` instead of `Var` for specifying where to store to or load from. `Buf` contains the dimensions info of the buffer we're loading/storing to and hence we are able to keep N-d indexes without flattening them into a 1-d index ([x,y] vs [x+y*W]).
* Flattening of the indexes is now a separate pass that is executed in `LoopNest::prepareForCodegen` - backends still expect indexes to be flattened, and this PR preserves that.
* `Tensor` now contains a `Buf` instead of `Var`, and thus Tensor now has the dimensions info (previously it was a property of a `Function`, not a `Tensor`). This brings us closer to Tensor being a combination of Buffer + Function, where Buffer specifies iteration domain and the Function defines a computation.
TODOs:
* Consider merging `Buffer` with `Buf` or `BufHandle`. It seems that we don't need all of them.
* Harden the logic of how we create buffers in fuser pass. Currently it seems that sometimes we don't set dimensions.
* Use `Buf` in `Allocate` and `Free`.
* Make it clearer that `Function` doesn't "own" dimensions info and that dimensions are a property of a Tensor, not a Function.
Differential Revision: D20789005
Test Plan: Imported from OSS
Reviewed By: zheng-xq
Pulled By: ZolotukhinM
fbshipit-source-id: e04188d1d297f195f1c46669c614557d6bb6cde4
