std::string ShapeDebugString(TF_Tensor* tensor) {
  // A TF_Tensor cannot have an unknown rank.
  CHECK_GE(TF_NumDims(tensor), 0);
  tensorflow::string s = "[";
  for (int i = 0; i < TF_NumDims(tensor); ++i) {
    if (i > 0) tensorflow::strings::StrAppend(&s, ",");
    int64_t dim = TF_Dim(tensor, i);
    // A TF_Tensor cannot have an unknown dimension.
    CHECK_GE(dim, 0);
    tensorflow::strings::StrAppend(&s, dim);
  }

#include "tensorflow/core/lib/hash/hash.h"

namespace tensorflow {

Operation::Operation(Node* n) : inputs_(GetInputs(n)), node_(n) {}

Output Operation::input(int32_t i) const {
  CHECK_NOTNULL(node_);
  CHECK_GE(i, 0);
  CHECK_LT(i, node_->num_inputs());
  // Handle the case where the input was unknown at the time this
  // Operation was constructed.
  if (inputs_[i].first == nullptr && inputs_[i].second == -1) {