[mlir][tensor] Update `GeneralizeOuterUnitDimsPackOpPattern` (#115312)

Avoid generating spurious tensor.extract_slice, follow-on for #114315.

This is best to demonstrate with an example. Here's input for
`GeneralizeOuterUnitDimsPackOpPattern`:
```mlir
%pack = tensor.pack %input
  padding_value(%pad : f32)
  inner_dims_pos = [1, 0]
  inner_tiles = [2, %tile_dim_1]
  into %output : tensor<5x1xf32> -> tensor<1x1x2x?xf32>
```

Output _before_:
```mlir
%padded = tensor.pad %arg0 low[0, 0] high[%0, 1] {
^bb0(%arg4: index, %arg5: index):
  tensor.yield %arg2 : f32
} : tensor<5x1xf32> to tensor<?x2xf32>
// NOTE: skipped in the output _after_
%extracted_slice = tensor.extract_slice
  %padded[0, 0] [%arg3, 2] [1, 1] :
  tensor<?x2xf32> to tensor<?x2xf32>
%empty = tensor.empty(%arg3) : tensor<2x?xf32>
%transposed = linalg.transpose
  ins(%extracted_slice : tensor<?x2xf32>)
  outs(%empty : tensor<2x?xf32>)
  permutation = [1, 0]
%inserted_slice = tensor.insert_slice %transposed=
  into %arg1[0, 0, 0, 0] [1, 1, 2, %arg3] [1, 1, 1, 1] :
  tensor<2x?xf32> into tensor<1x1x2x?xf32>
```

Output _after_:
```mlir
%padded = tensor.pad %arg0 low[0, 0] high[%0, 1] {
^bb0(%arg4: index, %arg5: index):
  tensor.yield %arg2 : f32
} : tensor<5x1xf32> to tensor<?x2xf32>
%empty = tensor.empty(%arg3) : tensor<2x?xf32>
%transposed = linalg.transpose
  ins(%padded : tensor<?x2xf32>)
  outs(%empty : tensor<2x?xf32>) permutation = [1, 0]
%inserted_slice = tensor.insert_slice %transposed
  into %arg1[0, 0, 0, 0] [1, 1, 2, %arg3] [1, 1, 1, 1] :
  tensor<2x?xf32> into tensor<1x1x2x?xf32>
```

This PR also adds a check to verify that only the last N trailing
dimensions are tiled (for some value of N). Based on the PR
discussion, this restriction seems reasonable - especially as there
are no in-tree tests requiring otherwise. For now, it also simplifies
the computation of permutations for linalg.transpose. This
restriction can be relaxed in the future if needed.

0 files changed, 0 insertions, 0 deletions