message: Document merging of remote buffers when they're used in elementwise clusters
  Summary: Ref T45972.
  Test Plan: CI, no functional changes
  Reviewers: #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, hakons
  Maniphest Tasks: T45972
diff: @@ -520,7 +520,11 @@ StatusOr<GroupedInstructions> ChooseCreatorsToMerge(
  // cluster rearranged with CBR. Number of the elements in the buffer
  // will not be available until CBR instance created. If remote
  // buffer merge candidate is rearranged, allow only buffers from the
  - // same clusters, so they will have the same number of the elements.
  + // identical clusters, so they will have the same number of the
  + // elements. Provide partitioned cluster visitor with indicies of
  + // the merged parameters, so it can adjust number of the elements
  + // and host_rearrangement_id for all RemoteParameterInfo structures
  + // affected.
  TF_ASSIGN_OR_RETURN(bool is_rearranged,
  IsInsideElementwiseCluster(user, call_graph));
  if (is_rearranged) {
  @@ -571,8 +575,7 @@ Status AddMergedInfo(const GroupedInstructions& creators_to_merge,
  << buffer_name << "'";
  std::vector<int64> merged_params;
  - for (std::size_t i = 0; i < creators.size(); ++i) {
  - auto* inst = creators[i];
  + for (const HloInstruction* inst : creators) {
  if (IsRemoteParameter(inst, annotations)) {
  merged_params.push_back(inst->parameter_number());
  }
  