[clang] Record mainfile name in the Frontend time trace (PR #99866)

[Ilya Biryukov via cfe-commits]

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@@ -152,7 +152,13 @@ void clang::ParseAST(Sema &S, bool PrintStats, bool SkipFunctionBodies) {
   bool HaveLexer = S.getPreprocessor().getCurrentLexer();
 
   if (HaveLexer) {
-    llvm::TimeTraceScope TimeScope("Frontend");
+    llvm::TimeTraceScope TimeScope("Frontend", [&]() {
+      llvm::TimeTraceMetadata M;
+      const SourceManager &SM = S.getSourceManager();
+      if (const auto *FE = SM.getFileEntryForID(SM.getMainFileID()))
+        M.File = FE->tryGetRealPathName();
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ilya-biryukov wrote:

Could we still put it under a flag for consistency?

I agree performance concerns are not an issue here, but we are outputting data in a different format now and the name of the main file is actually quite easy to get in most cases because it's passed as a command line argument.

https://github.com/llvm/llvm-project/pull/99866