!599 fix clipbynorm op run error in pynative mode

Merge pull request !599 from dinghao/master

mindspore/nn/layer/basic.py

@@ -23,6 +23,7 @@ from mindspore.ops import functional as F
 from mindspore.ops.functional import identity
 from mindspore.common.parameter import Parameter
 from mindspore._extends import cell_attr_register
+from mindspore.common.api import ms_function
 from ..cell import Cell
 from .activation import get_activation
 from ..._checkparam import Validator as validator
@@ -261,7 +262,9 @@ class ClipByNorm(Cell):
         self.expand_dims = P.ExpandDims()
         self.dtype = P.DType()
 
+    @ms_function
     def construct(self, x, clip_norm):
+        """add ms_function decorator for pynative mode"""
         mul_x = F.square(x)
         l2sum = self.cast(self.reduce_sum(mul_x, self.axis), mstype.float32)
         cond = self.greater_(l2sum, self.zero)