[PATCH] D143747: [mlir][MemRef][Transform] Don't apply multibuffer on "useless" allocs

[Quentin Colombet via Phabricator via llvm-commits]

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`alloc`s that have users outside of loops are guaranteed to fail in
`multibuffer`.

Instead of exposing ourselves to that failure in the transform dialect,
filter out the `alloc`s that fall in this category.

To be able to do this filtering we have to change the `multibuffer`
transform op from `TransformEachOpTrait` to a plain `TransformOp`. This is
because `TransformEachOpTrait` expects that every successful `applyToOne`
returns a non-empty result.

Couple of notes:

- I changed the assembly syntax to make sure we only get `alloc` ops as input. (And added a test case to make sure we reject invalid inputs.)
- `multibuffer` can still fail pretty easily when you know its limitations. See the updated `op failed to multibuffer` test case for instance. Longer term, instead of leaking/coupling the actual implementation (in this case the checks normally done in `memref::multiBuffer`) with the transform dialect (the added check in `::apply`), we may want to refactor how we structure the underlying implementation. E.g., we could imagine a `canApply` method for all the implementations that we want to hook up in the transform dialect. This has some implications on how not to duplicate work between `canApply` and the actual implementation but I thought I throw that here to have us think about it :).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D143747

Files:
  mlir/include/mlir/Dialect/MemRef/TransformOps/MemRefTransformOps.td
  mlir/lib/Dialect/MemRef/TransformOps/MemRefTransformOps.cpp
  mlir/test/Dialect/MemRef/transform-ops.mlir

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