[ThinLTO] Show preserved symbols in DOT files

Differential revision: https://reviews.llvm.org/D71608

llvm/include/llvm/IR/ModuleSummaryIndex.h

@@ -1376,7 +1376,9 @@ public:
   void dump() const;
 
   /// Export summary to dot file for GraphViz.
-  void exportToDot(raw_ostream& OS) const;
+  void
+  exportToDot(raw_ostream &OS,
+              const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) const;
 
   /// Print out strongly connected components for debugging.
   void dumpSCCs(raw_ostream &OS);

llvm/include/llvm/LTO/Config.h

@@ -183,8 +183,9 @@ struct Config {
   ///
   /// It is called regardless of whether the backend is in-process, although it
   /// is not called from individual backend processes.
-  using CombinedIndexHookFn =
-      std::function<bool(const ModuleSummaryIndex &Index)>;
+  using CombinedIndexHookFn = std::function<bool(
+      const ModuleSummaryIndex &Index,
+      const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols)>;
   CombinedIndexHookFn CombinedIndexHook;
 
   /// This is a convenience function that configures this Config object to write

llvm/lib/Analysis/ModuleSummaryAnalysis.cpp

@@ -820,7 +820,7 @@ ModuleSummaryIndex llvm::buildModuleSummaryIndex(
     if (EC)
       report_fatal_error(Twine("Failed to open dot file ") +
                          ModuleSummaryDotFile + ": " + EC.message() + "\n");
-    Index.exportToDot(OSDot);
+    Index.exportToDot(OSDot, {});
   }
 
   return Index;

llvm/lib/IR/ModuleSummaryIndex.cpp

@@ -405,7 +405,9 @@ static bool hasWriteOnlyFlag(const GlobalValueSummary *S) {
   return false;
 }
 
-void ModuleSummaryIndex::exportToDot(raw_ostream &OS) const {
+void ModuleSummaryIndex::exportToDot(
+    raw_ostream &OS,
+    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) const {
   std::vector<Edge> CrossModuleEdges;
   DenseMap<GlobalValue::GUID, std::vector<uint64_t>> NodeMap;
   using GVSOrderedMapTy = std::map<GlobalValue::GUID, GlobalValueSummary *>;
@@ -485,6 +487,8 @@ void ModuleSummaryIndex::exportToDot(raw_ostream &OS) const {
         A.addComment("dsoLocal");
       if (Flags.CanAutoHide)
         A.addComment("canAutoHide");
+      if (GUIDPreservedSymbols.count(SummaryIt.first))
+        A.addComment("preserved");
 
       auto VI = getValueInfo(SummaryIt.first);
       A.add("label", getNodeLabel(VI, SummaryIt.second));

llvm/lib/LTO/LTO.cpp

@@ -1264,7 +1264,8 @@ Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
   if (ThinLTO.ModuleMap.empty())
     return Error::success();
 
-  if (Conf.CombinedIndexHook && !Conf.CombinedIndexHook(ThinLTO.CombinedIndex))
+  if (Conf.CombinedIndexHook &&
+      !Conf.CombinedIndexHook(ThinLTO.CombinedIndex, GUIDPreservedSymbols))
     return Error::success();
 
   // Collect for each module the list of function it defines (GUID ->

llvm/lib/LTO/LTOBackend.cpp

@@ -102,23 +102,25 @@ Error Config::addSaveTemps(std::string OutputFileName,
   setHook("4.opt", PostOptModuleHook);
   setHook("5.precodegen", PreCodeGenModuleHook);
 
-  CombinedIndexHook = [=](const ModuleSummaryIndex &Index) {
-    std::string Path = OutputFileName + "index.bc";
-    std::error_code EC;
-    raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::OF_None);
-    // Because -save-temps is a debugging feature, we report the error
-    // directly and exit.
-    if (EC)
-      reportOpenError(Path, EC.message());
-    WriteIndexToFile(Index, OS);
+  CombinedIndexHook =
+      [=](const ModuleSummaryIndex &Index,
+          const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
+        std::string Path = OutputFileName + "index.bc";
+        std::error_code EC;
+        raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::OF_None);
+        // Because -save-temps is a debugging feature, we report the error
+        // directly and exit.
+        if (EC)
+          reportOpenError(Path, EC.message());
+        WriteIndexToFile(Index, OS);
 
-    Path = OutputFileName + "index.dot";
-    raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::OF_None);
-    if (EC)
-      reportOpenError(Path, EC.message());
-    Index.exportToDot(OSDot);
-    return true;
-  };
+        Path = OutputFileName + "index.dot";
+        raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::OF_None);
+        if (EC)
+          reportOpenError(Path, EC.message());
+        Index.exportToDot(OSDot, GUIDPreservedSymbols);
+        return true;
+      };
 
   return Error::success();
 }

llvm/test/ThinLTO/X86/dot-dumper.ll

@@ -40,7 +40,7 @@
 ; COMBINED-NEXT:    label = "dot-dumper{{.*}}1.bc";
 ; COMBINED-NEXT:    node [style=filled,fillcolor=lightblue];
 ; COMBINED-NEXT:    M0_[[MAIN_ALIAS:[0-9]+]] [style="dotted,filled",shape="box",label="main_alias",fillcolor="red"]; // alias, dead
-; COMBINED-NEXT:    M0_[[MAIN:[0-9]+]] [shape="record",label="main|extern (inst: 4, ffl: 000000)}"]; // function
+; COMBINED-NEXT:    M0_[[MAIN:[0-9]+]] [shape="record",label="main|extern (inst: 4, ffl: 000000)}"]; // function, preserved
 ; COMBINED-NEXT:    // Edges:
 ; COMBINED-NEXT:    M0_[[MAIN_ALIAS]] -> M0_[[MAIN]] [style=dotted]; // alias
 ; COMBINED-NEXT:  }