[mlir][linalg] Extend DecomposeOuterUnitDimsPackOpPattern (linalg.pack) (#162666)

Similarly to #152960, this PR fixes `getTiledOuterDims` for `linalg.pack` by
ensuring that the `outer_dims_perm` attributeis properly taken into account.

This enables the main change in this PR: relaxing the constraints in
  * `DecomposeOuterUnitDimsPackOpPattern`.

Specifically, the pattern is extended to allow non-unit untiled outer
dimensions. For example:
```mlir
func.func @example(
    %src: tensor<2x32x16x8xf32>,
    %dest: tensor<2x1x16x8x32xf32>) ->  tensor<2x1x16x8x32xf32> {

  %pack = linalg.pack %src
    inner_dims_pos = [1]
    inner_tiles = [32] into %dest
    : tensor<2x32x16x8xf32> -> tensor<2x1x16x8x32xf32>

  return %pack : tensor<2x1x16x8x32xf32>
}
```
decomposes as:
```mlir
func.func @example(
      %src: tensor<2x32x16x8xf32>,
      %dest: tensor<2x1x16x8x32xf32>) -> tensor<2x1x16x8x32xf32> {

  %0 = tensor.empty() : tensor<2x16x8x32xf32>
  %transposed = linalg.transpose
    ins(%src : tensor<2x32x16x8xf32>)
    outs(%init : tensor<2x16x8x32xf32>)
    permutation = [0, 2, 3, 1]
  %inserted_slice = tensor.insert_slice %transposed
    into %dest[0, 0, 0, 0, 0] [2, 1, 16, 8, 32] [1, 1, 1, 1, 1]
    : tensor<2x16x8x32xf32> into tensor<2x1x16x8x32xf32>

  return %inserted_slice : tensor<2x1x16x8x32xf32>
  }
```
Importantly, this change makes `DecomposeOuterUnitDimsPackOpPattern` (the
decomposition pattern for `linalg.pack`) consistent with the corresponding
pattern for `linalg.unpack`:
  * `DecomposeOuterUnitDimsUnPackOpPattern`.

One notable assumption remains: untiled outer dimensions are not permuted. This
was already the case but is now explicitly documented.

Co-authored by: Max Bartel <bartel@roofline.ai>

0 files changed, 0 insertions, 0 deletions