llvm-xray: Broken chrome trace event format output

[chris3k]

Summary

Missing comma separator for EXIT and TAIL_EXIT RecordTypes emit invalid
JSON output for Chrome Trace Event Format.

[dberris]

LGTM -- good catch, @chris3k.

@kpw, we probably should have tests to cover some more of these cases, now that @sammccall has landed the JSON parser/writer (and also probably move to using that instead of our own ad hoc implementation here).

[dberris]

@chris3k -- do you already have commit access, or do you need someone else to land this for you?

[chris3k]

Hi @dberris, I don't have commit access. Please land this change for me. Thank you and best regards.

llvm/trunk/tools/llvm-xray/xray-converter.cpp

for (const auto &R : Records) {
     case RecordTypes::TAIL_EXIT:
       // No entries to record end for.
       if (StackCursor == nullptr)
         break;
       // Should we emit an END record anyway or account this condition?
       // (And/Or in loop termination below)
       StackTrieNode *PreviousCursor = nullptr;
       do {
+        if (PreviousCursor != nullptr) {
+          OS << ",\n";
+        }
         writeTraceViewerRecord(Version, OS, StackCursor->FuncId, R.TId, R.PId,
                                Symbolize, FuncIdHelper, EventTimestampUs,
                                *StackCursor, "E");
         PreviousCursor = StackCursor;
         StackCursor = StackCursor->Parent;
       } while (PreviousCursor->FuncId != R.FuncId && StackCursor != nullptr);
       break;
     }