Fix the unloadable bprop mindir files

tests/ut/python/optimizer/test_bprop_mindir.py

@@ -23,6 +23,9 @@ import mindspore.ops as ops
 from mindspore.ops.operations import _inner_ops as inner
 import mindspore.common.dtype as mstype
 from mindspore.common.initializer import initializer
+from mindspore.ops.bprop_mindir import serializable_bprop_ops
+from mindspore._c_expression import load_mindir
+import mindspore.ops._grad as g
 
 
 class Net(nn.Cell):
@@ -54,6 +57,21 @@ class GradNet(nn.Cell):
         return gout
 
 
+def test_load_mindir_dir():
+    """
+    Feature: Bprop pre-compilation.
+    Description: Load all the mindir files of serializable bprop.
+    Expectation: All are loaded successfully.
+    """
+    bprop_path = g.__file__
+    bprop_installed_dir = bprop_path[: bprop_path.rindex('/')]
+    bprop_mindir_export_dir = bprop_installed_dir + "/../bprop_mindir"
+    for op in serializable_bprop_ops:
+        file_name = bprop_mindir_export_dir + "/" + op.name + "_bprop.mindir"
+        graph = load_mindir(file_name)
+        assert not graph is None
+
+
 def test_relu():
     x = Tensor(np.array([[[[-1, 1, 10],
                            [1, -1, 1],