[Bugfix] Fix duplicate edges in Coauthor Dataset #2553 (#2569)

* fix

* address comment

python/dgl/data/gnn_benckmark.py

@@ -7,6 +7,7 @@ from .dgl_dataset import DGLBuiltinDataset
 from .utils import save_graphs, load_graphs, _get_dgl_url, deprecate_property, deprecate_class
 from ..convert import graph as dgl_graph
 from .. import backend as F
+from .. import transform
 
 __all__ = ["AmazonCoBuyComputerDataset", "AmazonCoBuyPhotoDataset", "CoauthorPhysicsDataset", "CoauthorCSDataset",
            "CoraFullDataset", "AmazonCoBuy", "Coauthor", "CoraFull"]
@@ -42,17 +43,17 @@ class GNNBenchmarkDataset(DGLBuiltinDataset):
         self._print_info()
 
     def has_cache(self):
-        graph_path = os.path.join(self.save_path, 'dgl_graph.bin')
+        graph_path = os.path.join(self.save_path, 'dgl_graph_v1.bin')
         if os.path.exists(graph_path):
             return True
         return False
 
     def save(self):
-        graph_path = os.path.join(self.save_path, 'dgl_graph.bin')
+        graph_path = os.path.join(self.save_path, 'dgl_graph_v1.bin')
         save_graphs(graph_path, self._graph)
 
     def load(self):
-        graph_path = os.path.join(self.save_path, 'dgl_graph.bin')
+        graph_path = os.path.join(self.save_path, 'dgl_graph_v1.bin')
         graphs, _ = load_graphs(graph_path)
         self._graph = graphs[0]
         self._data = [graphs[0]]
@@ -91,9 +92,8 @@ class GNNBenchmarkDataset(DGLBuiltinDataset):
                 labels = loader['labels']
             else:
                 labels = None
-        row = np.hstack([adj_matrix.row, adj_matrix.col])
-        col = np.hstack([adj_matrix.col, adj_matrix.row])
-        g = dgl_graph((row, col))
+        g = dgl_graph((adj_matrix.row, adj_matrix.col))
+        g = transform.to_bidirected(g)
         g.ndata['feat'] = F.tensor(attr_matrix, F.data_type_dict['float32'])
         g.ndata['label'] = F.tensor(labels, F.data_type_dict['int64'])
         return g