message: Move the poplar graph into `compileGraph`.
  Summary: Ref T50427
  Test Plan: CI tests
  Reviewers: #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, vladimirm
  Maniphest Tasks: T50427
diff: @@ -1821,6 +1821,9 @@ StatusOr<std::unique_ptr<PoplarExecutableCore>> CompileEngine(
  main_graph.outputVertexGraph(stream, progs);
  }
  + const std::string map_json =
  + GetTensorMappingJson(module->name(), main_graph, resources.tensor_maps);
  +
  try {
  Tracepoint tracepoint("PoplarEngineConstruction");
  VLOG(1) << "Begin compiling Poplar engine " << module->name();
  @@ -1849,8 +1852,8 @@ StatusOr<std::unique_ptr<PoplarExecutableCore>> CompileEngine(
  poplar_executor->GetModuleReportDirectory(module->name());
  poplar::Executable exec =
  - poplar::compileGraph(main_graph, progs, opt_flags, progress_logging,
  - executable_debug_name);
  + poplar::compileGraph(std::move(main_graph), progs, opt_flags,
  + progress_logging, executable_debug_name);
  if (is_cacheable) {
  // If we have the lock, serialize the result to the executable cache.
  @@ -1933,9 +1936,6 @@ StatusOr<std::unique_ptr<PoplarExecutableCore>> CompileEngine(
  TF_ASSIGN_OR_RETURN(auto inst_info,
  GetInstructionCompilationInfo(module, resources));
  - std::string map_json = GetTensorMappingJson(module->name(), main_graph,
  - resources.tensor_maps);
  -
  poplar_executor->AddCompileEndEventRecord(module->name(), map_json,
  inst_info, duration);
  }
  