[BE] Abstract out strings to top of file (pytorch#125640)

Summary:
Move const strings to top of file. This is in preparation of tooling to
make use of shared constants (e.g. version string). A non-functional change.
Ideally we want these const strings to be available from both C++ and Python - but I haven't figured out how to correctly share things in PyTorch. I'll do this in a subsequent change.

Test Plan:
python test/distributed/test_c10d_nccl.py NCCLTraceTest

Pull Request resolved: pytorch#125640
Approved by: https://github.com/wconstab

torch/csrc/distributed/c10d/TraceUtils.h

@@ -15,6 +15,34 @@
 #include <vector>
 namespace c10d {
 
+static c10::IValue entries_key = "entries";
+static c10::IValue nccl_comm_key = "nccl_comm_state";
+static c10::IValue version_key = "version";
+// Update whenever changing contents or formatting of the dump
+// (minor when adding fields, major when changing existing fields)
+static c10::IValue version_val = "1.5";
+static c10::IValue pg_config_key = "pg_config";
+static c10::IValue record_id_key = "record_id";
+static c10::IValue pg_id_key = "pg_id";
+static c10::IValue pg_name_key = "process_group";
+static c10::IValue seq_id_key = "seq_id";
+static c10::IValue op_id_key = "op_id";
+static c10::IValue profiling_name_key = "profiling_name";
+static c10::IValue input_sizes_key = "input_sizes";
+static c10::IValue output_sizes_key = "output_sizes";
+static c10::IValue time_created_key = "time_created_ns";
+static c10::IValue duration_key = "duration_ms";
+
+static c10::IValue frames_key = "frames";
+static c10::IValue state_key = "state";
+static c10::IValue line_key = "line";
+static c10::IValue name_key = "name";
+static c10::IValue filename_key = "filename";
+static c10::IValue retired_key = "retired";
+static c10::IValue time_discovered_started_key = "time_discovered_started_ns";
+static c10::IValue time_discovered_completed_key =
+    "time_discovered_completed_ns";
+
 /* Trace Utils Related to TORCH_NCCL_DESYNC_DEBUG */
 
 inline std::string getTraceStartKey(const std::string& pgName, int rank) {
@@ -606,32 +634,6 @@ struct NCCLTraceBuffer {
           std::unordered_map<std::string, std::string>>>& ncclDumpMap) {
     auto result = dump_entries();
     auto entries = new_list();
-    c10::IValue entries_key = "entries";
-    c10::IValue nccl_comm_key = "nccl_comm_state";
-    c10::IValue version_key = "version";
-    // Update whenever changing contents or formatting of the dump
-    // (minor when adding fields, major when changing existing fields)
-    c10::IValue version_val = "1.5";
-    c10::IValue pg_config_key = "pg_config";
-    c10::IValue record_id_key = "record_id";
-    c10::IValue pg_id_key = "pg_id";
-    c10::IValue pg_name_key = "process_group";
-    c10::IValue seq_id_key = "seq_id";
-    c10::IValue op_id_key = "op_id";
-    c10::IValue profiling_name_key = "profiling_name";
-    c10::IValue input_sizes_key = "input_sizes";
-    c10::IValue output_sizes_key = "output_sizes";
-    c10::IValue time_created_key = "time_created_ns";
-    c10::IValue duration_key = "duration_ms";
-
-    c10::IValue frames_key = "frames";
-    c10::IValue state_key = "state";
-    c10::IValue line_key = "line";
-    c10::IValue name_key = "name";
-    c10::IValue filename_key = "filename";
-    c10::IValue retired_key = "retired";
-    c10::IValue time_discovered_started_key = "time_discovered_started_ns";
-    c10::IValue time_discovered_completed_key = "time_discovered_completed_ns";
 
     std::vector<torch::CapturedTraceback*> tracebacks;
     for (auto& e : result) {