Index: include/llvm/IR/ModuleSummaryIndex.h
===================================================================
--- include/llvm/IR/ModuleSummaryIndex.h
+++ include/llvm/IR/ModuleSummaryIndex.h
@@ -807,6 +807,9 @@
   /// Summary).
   void collectDefinedGVSummariesPerModule(
       StringMap<GVSummaryMapTy> &ModuleToDefinedGVSummaries) const;
+
+  /// Export summary to dot file for GraphViz.
+  void exportToDot(raw_ostream& OS) const;
 };
 
 } // end namespace llvm
Index: lib/IR/ModuleSummaryIndex.cpp
===================================================================
--- lib/IR/ModuleSummaryIndex.cpp
+++ lib/IR/ModuleSummaryIndex.cpp
@@ -69,3 +69,214 @@
       return true;
   return false;
 }
+
+namespace {
+struct Attributes {
+  void add(const Twine &Name, const Twine &Value);
+  std::string getAsString() const;
+
+  std::vector<std::string> Attrs;
+};
+
+struct Edge {
+  int SrcMod;
+  int Hotness;
+  GlobalValue::GUID Src;
+  GlobalValue::GUID Dst;
+};
+}
+
+void Attributes::add(const Twine& Name, const Twine& Value) {
+  std::string A = Name.str();
+  A += "=\"";
+  A += Value.str();
+  A += "\"";
+  Attrs.push_back(A);
+}
+
+std::string Attributes::getAsString() const {
+  if (Attrs.empty())
+    return "";
+
+  std::string Ret = "[";
+  for (auto &A : Attrs)
+    Ret += A + ",";
+  Ret.pop_back();
+  Ret += "]";
+  return Ret;
+}
+
+static std::string linkageToString(GlobalValue::LinkageTypes LT) {
+  switch (LT) {
+  case GlobalValue::ExternalLinkage:
+    return "extern";
+  case GlobalValue::AvailableExternallyLinkage:
+    return "av_ext";
+  case GlobalValue::LinkOnceAnyLinkage:
+    return "linkonce";
+  case GlobalValue::LinkOnceODRLinkage:
+    return "linkonce_odr";
+  case GlobalValue::WeakAnyLinkage:
+    return "weak";
+  case GlobalValue::WeakODRLinkage:
+    return "weak_odr";
+  case GlobalValue::AppendingLinkage:
+    return "appending";
+  case GlobalValue::InternalLinkage:
+    return "internal";
+  case GlobalValue::PrivateLinkage:
+    return "private";
+  case GlobalValue::ExternalWeakLinkage:
+    return "extern_weak";
+  case GlobalValue::CommonLinkage:
+    return "common";
+  }
+
+  return "<unknown>";
+}
+
+static std::string fflagsToString(FunctionSummary::FFlags F) {
+  auto FlagValue = [](unsigned V) { return V ? '1' : '0'; };
+  char FlagRep[] = {FlagValue(F.ReadNone), FlagValue(F.ReadOnly),
+                    FlagValue(F.NoRecurse), FlagValue(F.ReturnDoesNotAlias), 0};
+
+  return FlagRep;
+}
+
+// Get string representation of function instruction count and flags.
+static std::string getSummaryAttributes(GlobalValueSummary* GVS) {
+  auto *FS = dyn_cast_or_null<FunctionSummary>(GVS);
+  if (!FS)
+    return "";
+
+  return std::string("inst: ") + std::to_string(FS->instCount()) +
+         ", ffl: " + fflagsToString(FS->fflags());
+}
+
+// Get node label in form MXXX_<GUID>. The MXXX prefix is required,
+// because we may have multiple linkonce functions summaries.
+static std::string getNodeLabel(GlobalValueSummary *GVS) {
+  if (isa<AliasSummary>(GVS))
+    return std::string("@") + std::to_string(GVS->getOriginalName());
+
+  std::string Attrs = getSummaryAttributes(GVS);
+  std::string Label = std::string("{@") +
+                      std::to_string(GVS->getOriginalName()) + "|" +
+                      linkageToString(GVS->linkage());
+  if (!Attrs.empty())
+    Label += std::string(" (") + Attrs + ")";
+  Label += "}";
+
+  return Label;
+}
+
+// Write definition of node without ValueInfo. This is typically
+// an external function or variable
+static void defineExternalNode(raw_ostream &OS, const char *Pfx,
+                               GlobalValue::GUID Id) {
+  auto StrId = std::to_string(Id);
+  OS << "  " << StrId << " [label=\"@" << StrId << "\"];\n";
+}
+
+void ModuleSummaryIndex::exportToDot(raw_ostream& OS) const {
+  std::vector<Edge> CrossModuleEdges;
+  DenseMap<GlobalValue::GUID, std::vector<int>> NodeMap;
+  StringMap<GVSummaryMapTy> ModuleToDefinedGVS;
+  collectDefinedGVSummariesPerModule(ModuleToDefinedGVS);
+
+  auto NodeId = [](int ModNum, GlobalValue::GUID Id) {
+    return ModNum < 0 ? std::to_string(Id)
+                      : std::string("M") + std::to_string(ModNum) + "_" +
+                            std::to_string(Id);
+  };
+
+  auto DrawEdge = [&](const char *Pfx, int SrcMod, GlobalValue::GUID SrcId,
+                      int DstMod, GlobalValue::GUID DstId, int Hotness) {
+    ++Hotness; // 0 corresponds to ref edge, 1 to call with unknown hotness, ...
+    static const char *EdgeAttrs[] = {
+        " [style=dashed]",         "", " [color=blue]", "", " [color=brown]",
+        " [style=bold,color=read]"};
+
+    assert(static_cast<size_t>(Hotness) <
+           sizeof(EdgeAttrs) / sizeof(EdgeAttrs[0]));
+    OS << Pfx << NodeId(SrcMod, SrcId) << " -> " << NodeId(DstMod, DstId)
+       << EdgeAttrs[Hotness] << "; // " << std::to_string(SrcId) << " -> "
+       << std::to_string(DstId) << "\n";
+  };
+
+  int ModNum = 0;
+  OS << "digraph Summary {\n";
+  for (auto &ModIt : ModuleToDefinedGVS) {
+    OS << "  subgraph cluster_" << std::to_string(ModNum) << " {\n";
+    OS << "    style = filled;\n";
+    OS << "    color = lightgrey;\n";
+    OS << "    label = \"" << ModIt.first() << "\";\n";
+    OS << "    node [style=filled,fillcolor=lightblue];\n";
+
+    auto &GVSMap = ModIt.second;
+    auto Draw = [&](GlobalValue::GUID IdFrom, GlobalValue::GUID IdTo, int Hotness) {
+      if (!GVSMap.count(IdTo)) {
+        CrossModuleEdges.push_back({ModNum, Hotness, IdFrom, IdTo});
+        return;
+      }
+      DrawEdge("    ", ModNum, IdFrom, ModNum, IdTo, Hotness);
+    };
+
+    for (auto &SummaryIt : GVSMap) {
+      NodeMap[SummaryIt.first].push_back(ModNum);
+      auto Flags = SummaryIt.second->flags();
+      Attributes A;
+      if (isa<FunctionSummary>(SummaryIt.second)) {
+        A.add("shape", "record");
+      } else if (isa<AliasSummary>(SummaryIt.second)) {
+        A.add("style", "dotted,filled");
+        A.add("shape", "box");
+      } else {
+        A.add("shape", "Mrecord");
+      }
+
+      A.add("label", getNodeLabel(SummaryIt.second));
+      if (!Flags.Live)
+        A.add("fillcolor", "red");
+      else if (Flags.NotEligibleToImport)
+        A.add("fillcolor", "yellow");
+
+      OS << "    " << NodeId(ModNum, SummaryIt.first) << " " << A.getAsString()
+         << ";\n";
+    }
+
+    for (auto &SummaryIt : GVSMap) {
+      auto *GVS = SummaryIt.second;
+      for (auto &R : GVS->refs())
+        Draw(SummaryIt.first, R.getGUID(), -1);
+
+      if (auto *AS = dyn_cast_or_null<AliasSummary>(SummaryIt.second)) {
+        auto AliaseeOrigId = AS->getAliasee().getOriginalName();
+        auto AliaseeId = getGUIDFromOriginalID(AliaseeOrigId);
+
+        Draw(SummaryIt.first, AliaseeId ? AliaseeId : AliaseeOrigId, -1);
+        continue;
+      }
+
+      if (auto *FS = dyn_cast_or_null<FunctionSummary>(SummaryIt.second))
+        for (auto &CGEdge : FS->calls())
+          Draw(SummaryIt.first, CGEdge.first.getGUID(),
+               static_cast<int>(CGEdge.second.Hotness));
+    }
+    OS << "  }\n";
+    ++ModNum;
+  }
+
+  for (auto &E : CrossModuleEdges) {
+    auto &ModList = NodeMap[E.Dst];
+    if (ModList.empty()) {
+      defineExternalNode(OS, "  ", E.Dst);
+      ModList.push_back(-1);
+    }
+    for (int DstMod : ModList)
+      if (DstMod != E.SrcMod)
+        DrawEdge("  ", E.SrcMod, E.Src, DstMod, E.Dst, E.Hotness);
+  }
+
+  OS << "}";
+}
Index: lib/LTO/LTOBackend.cpp
===================================================================
--- lib/LTO/LTOBackend.cpp
+++ lib/LTO/LTOBackend.cpp
@@ -103,6 +103,12 @@
     if (EC)
       reportOpenError(Path, EC.message());
     WriteIndexToFile(Index, OS);
+
+    Path = OutputFileName + "index.dot";
+    raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::F_None);
+    if (EC)
+      reportOpenError(Path, EC.message());
+    Index.exportToDot(OSDot);
     return true;
   };