1804 RNN fix

apex/amp/wrap.py

@@ -138,7 +138,7 @@ def rnn_cast(backend, fn, verbose=False):
             # autograd graph correctly backprops from the wgrads computed
             # inside cuDNN (on fp16 weights) into the fp32 weights.
             assert utils.type_string(flat_weight) == 'FloatTensor'
-            if compat.tensor_is_float_tensor():
+            if compat.tensor_is_float_tensor() or compat.tensor_is_variable():
                 # Pre-0.4. A little slower, since it zeros out memory.
                 flat_weight_fp16 = flat_weight.new().half().resize_(flat_weight.shape)
             else: