Merge pull request #13494 from peterrum/use_src_inplace

GC: enable inplace operation for coarse side

diff --cc include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
index b1ffe7c3d46f61ece811c613895317642fdfbf32,6f251fee8b0412b4d282d7eb8f74fe5d77a0a3f5..88fc24d4263eb5c1eef232f4324b0f720605d84e
--- 1/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
--- 2/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
+++ b/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
@@@ -2861,8 -2775,9 +2890,8 @@@ MGTwoLevelTransfer<dim, LinearAlgebra::
              {
                for (unsigned int i = 0; i < scheme.n_dofs_per_cell_coarse; ++i)
                  evaluation_data_coarse[i][v] =
-                   read_dof_values(indices_coarse[i], this->vec_coarse);
+                   read_dof_values(indices_coarse[i], *vec_coarse_ptr);
                indices_coarse += scheme.n_dofs_per_cell_coarse;
 -              indices_coarse_plain += scheme.n_dofs_per_cell_coarse;
              }
  
            // ... fast hanging-node-constraints algorithm
@@@ -3089,8 -3017,9 +3129,8 @@@ MGTwoLevelTransfer<dim, LinearAlgebra::
                for (unsigned int i = 0; i < scheme.n_dofs_per_cell_coarse; ++i)
                  distribute_local_to_global(indices_coarse[i],
                                             evaluation_data_coarse[i][v],
-                                            this->vec_coarse);
+                                            *vec_coarse_ptr);
                indices_coarse += scheme.n_dofs_per_cell_coarse;
 -              indices_coarse_plain += scheme.n_dofs_per_cell_coarse;
              }
          }
      }