Sparse matrix multiplication is generally considered to be a different problem. Sparse matrices need to be represented differently (See https://en.wikipedia.org/wiki/Sparse_matrix for an introduction). There has been recently a lot of research on how to do sparse matrix multiplication efficiently on manycore architectures. See this 2018 paper for example: https://arxiv.org/pdf/1804.01698.pdf. Note that sparse matrix-vector multiplication is also a different problem.