compute_array_dim_size: recompute explicit representations for divs
compute_array_dim_size: recompute explicit representations for divs

Explicit representations are already computed in can_tile_for_shared_memory,
but check_stride may apply a shift, which in turn may result in new
unknown existentially quantified variables.
These are not allowed because we will convert the constraints into isl_affs.

Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

nicolasvasilache/ppcg,Meinersbur/ppcg,nicolasvasilache/ppcg,Meinersbur/ppcg