[fix] Support nullop in transpose

src/operator/tensor/matrix_op-inl.h

@@ -324,6 +324,9 @@ void Transpose(const nnvm::NodeAttrs& attrs,
                const std::vector<TBlob>& inputs,
                const std::vector<OpReqType>& req,
                const std::vector<TBlob>& outputs) {
+  if (req[0] == kNullOp) {
+    return;
+  }
   const TransposeParam& param = nnvm::get<TransposeParam>(attrs.parsed);
   CHECK_EQ(req[0], kWriteTo) << "Transpose does not support inplace";
   if (param.axes.ndim() == 0) {

src/operator/tensor/matrix_op.cc

@@ -321,6 +321,9 @@ static void TransposeComputeExCPU(const nnvm::NodeAttrs& attrs,
                                   const std::vector<NDArray>& inputs,
                                   const std::vector<OpReqType>& req,
                                   const std::vector<NDArray>& outputs) {
+  if (req[0] == kNullOp) {
+    return;
+  }
   const TransposeParam& param = nnvm::get<TransposeParam>(attrs.parsed);
   CHECK_EQ(req[0], kWriteTo) << "Transpose does not support inplace";
   CHECK_EQ(inputs.size(), 1U);

tests/python/unittest/test_symbol.py

@@ -389,6 +389,22 @@ def test_children_same_name():
     for c in b.get_children():
         pass
 
+
+def test_transpose_nullop():
+    for dim in range(1, 7):
+        a = mx.sym.Variable('a')
+        b = mx.sym.transpose(a, axes=tuple(np.random.permutation(dim)))
+        c = mx.sym.zeros_like(b)
+
+        shape = rand_shape_nd(dim)
+        nd_a = mx.nd.random.normal(shape=shape)
+        c_out = c.eval(ctx=mx.cpu(), a=nd_a)
+        b_out = b.eval(ctx=mx.cpu(), a=nd_a)
+
+        assert mx.test_utils.same(c_out[0].asnumpy(),
+                                  np.zeros_like(b_out[0].asnumpy()))
+
+
 if __name__ == '__main__':
     import nose
     nose.runmodule()