some changes to avoid compiler errors

* for -O3 gcc generated wrong code for these loops

src/grid_reg2d_common.c

@@ -106,15 +106,15 @@ struct basic_grid_data yac_generate_basic_grid_data_reg2d_common(
         (i + 1) * num_vertices_2d[0]};
       for (size_t j = 0; j < num_cells_2d[0]; ++j)
         for (size_t l = 0; l < 4; ++l, ++k)
-          cell_to_vertex[k] = temp_cell_to_vertex[l]++;
+          cell_to_vertex[k] = temp_cell_to_vertex[l] + j;
     }
   } else {
     size_t temp_cell_to_vertex[4] =
       {0, 1, num_vertices_2d[0] + 1, num_vertices_2d[0]};
-    for (size_t i = 0, k = 0; i < num_cells_2d[1]; ++i)
-      for (size_t j = 0; j < num_cells_2d[0]; ++j)
+    for (size_t i = 0, k = 0, m = 0; i < num_cells_2d[1]; ++i)
+      for (size_t j = 0; j < num_cells_2d[0]; ++j, ++m)
         for (int l = 0; l < 4; ++l, ++k)
-          cell_to_vertex[k] = temp_cell_to_vertex[l]++;
+          cell_to_vertex[k] = temp_cell_to_vertex[l] + m;
     for (size_t i = 0; i < num_cells_2d[1]; ++i) {
       cell_to_vertex[4*((i+1)*num_cells_2d[0]-1)+1] = i * num_cells_2d[0];
       cell_to_vertex[4*((i+1)*num_cells_2d[0]-1)+2] = (i + 1) * num_cells_2d[0];