[mlir][vector] Canonicalize/fold 'order preserving' transposes (#135841)

Handles special case where transpose doesn't permute any non-1
dimensions (and so is effectively a shape_cast) and is adjacent to a
shape_cast that it can fold into. For example

```
%1 = vector.transpose %0, [1, 0, 3, 2] : vector<4x1x1x6xf32> to vector<1x4x6x1xf32>
```

can be folded into an adjacent shape_cast. An alternative to this PR
would be to canonicalize such transposes to shape_casts directly, but I
think it'll be difficult getting consensus that shape_cast is 'more
canonical' than transpose, so this PR compromises with the less
opinionated claim that

1) shape_cast is more canonical than shape_cast(transpose)
2) shape_cast is more canonical than transpose(shape_cast)

The pattern `ConvertIllegalShapeCastOpsToTransposes` that is specific to
transposes with scalable dimensions reverses the canonicalization added
here, so I've I've disabled this canonicalization for scalable vectors

0 files changed, 0 insertions, 0 deletions