const char* const kXlaCompileTimeConstantInputsAttr =
    "_XlaCompileTimeConstantInputs";

namespace {
// Returns a string describing how an edge from src to dst would
// create a cycle.
string DescribeCycle(const GraphCycles* cycles, const Graph& graph, int src,
                     int dst) {
  int32_t max_path_size = graph.num_node_ids() + 1;
  std::vector<int32> path(max_path_size);