This change adds a new AffineDelinearizeIndexOp to the affine dialect.
The operation accepts an index type as well as a basis (array of index
values) representing how the index should be decomposed into a
multi-index. The decomposition obeys a canonical semantic that treats
the final basis element as "fastest varying" and the first basis element
as "slowest varying". A naive lowering of the operation using a sequence
of AffineApplyOps is given.
RFC was discussed on discourse here: https://discourse.llvm.org/t/rfc-tensor-extracting-slices-from-tensor-collapse-shape/64034