//      non-NULL, in which case it must point to an empty, freshly allocated
//      `TF_Buffer` that may be updated to contain the serialized representation
//      of a `RunMetadata` protocol buffer.
//
// The caller retains ownership of `input_values` (which can be deleted using
// TF_DeleteTensor). The caller also retains ownership of `run_options` and/or

  TFE_DeleteOp(matmul);
  TFE_DeleteTensorHandle(m);
  TF_Buffer* b = TF_NewBuffer();
  TFE_ContextExportRunMetadata(ctx, b, status);
  ASSERT_EQ(TF_OK, TF_GetCode(status)) << TF_Message(status);
  tensorflow::RunMetadata rm;
  EXPECT_TRUE(
      rm.ParseFromString({reinterpret_cast<const char*>(b->data), b->length}));
  TF_DeleteBuffer(b);
  ASSERT_EQ(TF_OK, TF_GetCode(status)) << TF_Message(status);
  ASSERT_EQ(1, num_retvals);