[all-commits] [llvm/llvm-project] 9b06e2: [mlir][vector] Add mask elimination transform (#99...

[Benjamin Maxwell via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 9b06e25e73470612d14f0e1e18fde82f62266216
      https://github.com/llvm/llvm-project/commit/9b06e25e73470612d14f0e1e18fde82f62266216
  Author: Benjamin Maxwell <benjamin.maxwell at arm.com>
  Date:   2024-08-09 (Fri, 09 Aug 2024)

  Changed paths:
    M mlir/include/mlir/Dialect/Vector/IR/VectorOps.h
    M mlir/include/mlir/Dialect/Vector/IR/VectorOps.td
    M mlir/include/mlir/Dialect/Vector/Transforms/VectorTransforms.h
    M mlir/lib/Dialect/Vector/IR/VectorOps.cpp
    M mlir/lib/Dialect/Vector/Transforms/CMakeLists.txt
    A mlir/lib/Dialect/Vector/Transforms/VectorMaskElimination.cpp
    A mlir/test/Dialect/Vector/eliminate-masks.mlir
    M mlir/test/lib/Dialect/Vector/TestVectorTransforms.cpp

  Log Message:
  -----------
  [mlir][vector] Add mask elimination transform (#99314)

This adds a new transform `eliminateVectorMasks()` which aims at
removing scalable `vector.create_masks` that will be all-true at
runtime. It attempts to do this by simply pattern-matching the mask
operands (similar to some canonicalizations), if that does not lead to
an answer (is all-true? yes/no), then value bounds analysis will be used
to find the lower bound of the unknown operands. If the lower bound is
>= to the corresponding mask vector type dim, then that dimension of the
mask is all true.

Note that the pattern matching prevents expensive value-bounds analysis
in cases where the mask won't be all true.

For example:
```mlir
%mask = vector.create_mask %dynamicValue, %c2 : vector<8x4xi1>
```
>From looking at `%c2` we can tell this is not going to be an all-true
mask, so we don't need to run the value-bounds analysis for
`%dynamicValue` (and can exit the transform early).

Note: Eliminating create_masks here means replacing them with all-true
constants (which will then lead to the masks folding away).



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