Memlets propagated incorrectly out of nested SDFGs

[phschaad]

If a nested SDFG accesses a data container passed to it not starting from a 0 offset, the outside memlets are propagated incorrectly, leading to incorrect code being generated.

[Edit: It is not actually memlet propagation, but the Python frontend that is at fault here. Propagation works as intended. See the discussion in #1738]

For instance, take the following code:

N = dace.symbol('N')
M = dace.symbol('M')

@dace.program
def nested_conditional_in_loop_in_map(A: dace.float64[M, N]):
    for i in dace.map[0:M]:
        for j in range(2, N, 1):
            if A[0][0]:
                A[i, j] = 1
            else:
                A[i, j] = 2
            A[i, j] = A[i, j] * A[i, j]

It is clear that inside the nested SDFG, A is only accessed in the index range A[:, 2:N-1]. However, the memlet being propagated to the outside of the nested SDFG inside the map is on the subset A[i, 0:N-3]. This leads to the index expression A[i, j - 2] being generated in the corresponding C++, consequently producing wrong results.

A failing test was added in #1738.