Rewrites reshapes that are adding 1-sized dims and are followed by a tile on the one-sized dim to a tile on the original shape followed by a reshape.

[jorickert]

This is done to reduce the rank of tile ops to make downstream consumption easier

[ljfitz]

Is the core canonicalization to minimize the dimensions needed to express the tile operation? If so it would be better to do so regardless of a directly connected reshape or not and instead insert reshape before and after as appropriate.

If this is not the core goal then I question having this as a canonicalization as matching tile will still have a guarantee that the tile op is in canonicalized form.

[jorickert]

I do not think its a good idea to always do the tile rank reduction, as the inserted reshapes may prevent other patterns from matching.

I originally wrote this to target a specific case:

reshape 1x2x3 to 1x2x1x3
tile 1x2x1x3 to 1x2x4x3
reshape to 1x2x12

this could be canonicalized to :
tile 1x2x3 to 1x2x12

In this case the rank of the tile would be reduced and the reshapes completely canceled.

I marked this Pr as draft, as I think it generally needs more investigation when it makes sense to do this and when not