[MLIR][Shape] Allow for `shape_of` to return extent tensors

Authored by frgossen on Jul 24 2020, 1:39 AM.


[MLIR][Shape] Allow for shape_of to return extent tensors

The operation shape.shape_of now returns an extent tensor tensor<?xindex> in
cases when no error are possible. All consuming operation will eventually accept
both, shapes and extent tensors.

Differential Revision: https://reviews.llvm.org/D84160