The `split_axes` attribute is defined as "array attribute of array
attributes". Following the definition, empty `split_axes` values should
not be allowed, since that would break the definition and would lead to
invalid IR. In such scenario, passes leveraging the mesh dialect can
observe:
* crashes in sharding-propagation;
* creation of null MeshShardingAttrs in spmdization;
* non roundtrippable IR.
The patch prevents `split_axes` to become empty by modifying the
`removeTrailingEmptySubArray` such that a minimum size of one is
guaranteed when constructing the attribute, and adds a test that would
crash without the change.
2f664f2bdf