#include "tensorflow/core/platform/macros.h"

namespace tensorflow {
namespace {

struct OutputHash {
  uint64 operator()(const Output& x) const { return x.hash(); }
};

struct OutputEq {
  bool operator()(const Output& x, const Output& y) const {
    return (x.node() == y.node()) && (x.index() == y.index());
  }
};

class SymbolicGradientBuilder {
 public: