Optimize matching MPI send/receive a bit more

src/debug/traces/starpu_fxt_mpi.c

@@ -116,7 +116,7 @@ unsigned mpi_recvs_used[MAX_MPI_NODES] = {0};
 /* number of slots already matched at the beginning of the list. This permits
  * going through the lists from the beginning to match each and every
  * transfer, thus avoiding a quadratic complexity. */
-unsigned mpi_recvs_matched[MAX_MPI_NODES] = {0};
+unsigned mpi_recvs_matched[MAX_MPI_NODES][MAX_MPI_NODES] = {0};
 
 void _starpu_fxt_mpi_add_send_transfer(int src, int dst STARPU_ATTRIBUTE_UNUSED, int mpi_tag, size_t size, float date)
 {
@@ -176,7 +176,7 @@ static
 struct mpi_transfer *try_to_match_send_transfer(int src STARPU_ATTRIBUTE_UNUSED, int dst, int mpi_tag)
 {
 	unsigned slot;
-	unsigned firstslot = mpi_recvs_matched[dst];
+	unsigned firstslot = mpi_recvs_matched[src][dst];
 
 	unsigned all_previous_were_matched = 1;
 
@@ -199,7 +199,7 @@ struct mpi_transfer *try_to_match_send_transfer(int src STARPU_ATTRIBUTE_UNUSED,
 			{
 				/* All previous transfers are already matched,
 				 * we need not consider them anymore */
-				mpi_recvs_matched[dst] = slot;
+				mpi_recvs_matched[src][dst] = slot;
 			}
 		}
 	}