fix softmax input error check on float16 (#20273)

test=develop

python/paddle/fluid/layers/nn.py

@@ -2380,9 +2380,13 @@ def softmax(input, use_cudnn=False, name=None, axis=-1):
         raise TypeError(
             "The type of 'input' in softmax must be Variable, but received %s" %
             (type(input)))
-    if convert_dtype(input.dtype) not in ['float32', 'float64']:
+    if convert_dtype(input.dtype) in ['float16']:
+        warnings.warn(
+            "The data type of 'input' in softmax only support float16 in GPU now."
+        )
+    if convert_dtype(input.dtype) not in ['float16', 'float32', 'float64']:
         raise TypeError(
-            "The data type of 'input' in softmax must be float32 or float64, but received %s."
+            "The data type of 'input' in softmax must be float16, float32 or float64, but received %s."
             % (convert_dtype(input.dtype)))
 
     dtype = helper.input_dtype()

python/paddle/fluid/tests/unittests/test_softmax_op.py

@@ -83,9 +83,11 @@ class TestSoftmaxOpError(OpTest):
             x1 = fluid.create_lod_tensor(
                 np.array([[-1]]), [[1]], fluid.CPUPlace())
             self.assertRaises(TypeError, fluid.layers.softmax, x1)
-            # The input dtype of softmax_op must be float32 or float64.
+            # The input dtype of softmax_op must be float16, float32 or float64.
             x2 = fluid.layers.data(name='x2', shape=[4], dtype="int32")
             self.assertRaises(TypeError, fluid.layers.softmax, x2)
+            x3 = fluid.layers.data(name='x3', shape=[4], dtype="float16")
+            fluid.layers.softmax(x3)
 
 
 class TestSoftmaxOp2(TestSoftmaxOp):