Index: include/llvm/LinkAllPasses.h
===================================================================
--- include/llvm/LinkAllPasses.h
+++ include/llvm/LinkAllPasses.h
@@ -86,6 +86,7 @@
       (void) llvm::createDomViewerPass();
       (void) llvm::createGCOVProfilerPass();
       (void) llvm::createInstrProfilingPass();
+      (void) llvm::createFunctionImportPass();
       (void) llvm::createFunctionInliningPass();
       (void) llvm::createAlwaysInlinerPass();
       (void) llvm::createGlobalDCEPass();
Index: include/llvm/Linker/Linker.h
===================================================================
--- include/llvm/Linker/Linker.h
+++ include/llvm/Linker/Linker.h
@@ -104,6 +104,13 @@
   DiagnosticHandlerFunction DiagnosticHandler;
 };
 
+/// Create a new module with exported local functions renamed and promoted
+/// for ThinLTO.
+std::unique_ptr<Module>
+renameModuleForThinLTO(std::unique_ptr<Module> &M,
+                       const FunctionInfoIndex *Index,
+                       DiagnosticHandlerFunction DiagnosticHandler);
+
 } // End llvm namespace
 
 #endif
Index: include/llvm/Transforms/IPO.h
===================================================================
--- include/llvm/Transforms/IPO.h
+++ include/llvm/Transforms/IPO.h
@@ -20,6 +20,7 @@
 
 namespace llvm {
 
+class FunctionInfoIndex;
 class ModulePass;
 class Pass;
 class Function;
@@ -86,6 +87,10 @@
                                    deleteFn = false);
 
 //===----------------------------------------------------------------------===//
+/// This pass performs iterative function importing from other modules.
+ModulePass *createFunctionImportPass(FunctionInfoIndex *Index = nullptr);
+
+//===----------------------------------------------------------------------===//
 /// createFunctionInliningPass - Return a new pass object that uses a heuristic
 /// to inline direct function calls to small functions.
 ///
Index: include/llvm/Transforms/IPO/PassManagerBuilder.h
===================================================================
--- include/llvm/Transforms/IPO/PassManagerBuilder.h
+++ include/llvm/Transforms/IPO/PassManagerBuilder.h
@@ -15,9 +15,11 @@
 #ifndef LLVM_TRANSFORMS_IPO_PASSMANAGERBUILDER_H
 #define LLVM_TRANSFORMS_IPO_PASSMANAGERBUILDER_H
 
+#include <memory>
 #include <vector>
 
 namespace llvm {
+class FunctionInfoIndex;
 class Pass;
 class TargetLibraryInfoImpl;
 class TargetMachine;
@@ -114,6 +116,9 @@
   /// added to the per-module passes.
   Pass *Inliner;
 
+  /// The function summary index to use for function importing.
+  std::unique_ptr<FunctionInfoIndex> FunctionIndex;
+
   bool DisableTailCalls;
   bool DisableUnitAtATime;
   bool DisableUnrollLoops;
Index: lib/Linker/LinkModules.cpp
===================================================================
--- lib/Linker/LinkModules.cpp
+++ lib/Linker/LinkModules.cpp
@@ -2123,6 +2123,18 @@
   return L.linkInModule(Src, Flags);
 }
 
+std::unique_ptr<Module>
+llvm::renameModuleForThinLTO(std::unique_ptr<Module> &M,
+                             const FunctionInfoIndex *Index,
+                             DiagnosticHandlerFunction DiagnosticHandler) {
+  std::unique_ptr<llvm::Module> RenamedModule(
+      new llvm::Module(M->getModuleIdentifier(), M->getContext()));
+  Linker L(RenamedModule.get(), DiagnosticHandler);
+  if (L.linkInModule(M.get(), llvm::Linker::Flags::None, Index))
+    return nullptr;
+  return RenamedModule;
+}
+
 //===----------------------------------------------------------------------===//
 // C API.
 //===----------------------------------------------------------------------===//
Index: lib/Transforms/IPO/FunctionImport.cpp
===================================================================
--- lib/Transforms/IPO/FunctionImport.cpp
+++ lib/Transforms/IPO/FunctionImport.cpp
@@ -239,23 +239,37 @@
 
 /// Pass that performs cross-module function import provided a summary file.
 class FunctionImportPass : public ModulePass {
+  /// Function summary index to use for importing
+  FunctionInfoIndex *Index;
 
 public:
   /// Pass identification, replacement for typeid
   static char ID;
 
-  explicit FunctionImportPass() : ModulePass(ID) {}
+  /// Specify pass name for debug output
+  const char *getPassName() const override {
+    return "Function Importing";
+  }
+
+  explicit FunctionImportPass(FunctionInfoIndex *Index = nullptr)
+      : ModulePass(ID), Index(Index) {}
 
   bool runOnModule(Module &M) override {
-    if (SummaryFile.empty()) {
-      report_fatal_error("error: -function-import requires -summary-file\n");
-    }
-    std::string Error;
-    std::unique_ptr<FunctionInfoIndex> Index =
-        getFunctionIndexForFile(SummaryFile, Error, diagnosticHandler);
-    if (!Index) {
-      errs() << "Error loading file '" << SummaryFile << "': " << Error << "\n";
-      return false;
+    if (SummaryFile.empty() && !Index)
+      report_fatal_error("error: -function-import requires -summary-file or "
+                         "file from frontend\n");
+    std::unique_ptr<FunctionInfoIndex> IndexPtr;
+    if (!SummaryFile.empty()) {
+      if (Index)
+        report_fatal_error("error: -summary-file and index from frontend\n");
+      std::string Error;
+      IndexPtr = getFunctionIndexForFile(SummaryFile, Error, diagnosticHandler);
+      if (!IndexPtr) {
+        errs() << "Error loading file '" << SummaryFile << "': " << Error
+               << "\n";
+        return false;
+      }
+      Index = IndexPtr.get();
     }
 
     // Perform the import now.
@@ -273,5 +287,7 @@
                     "Summary Based Function Import", false, false)
 
 namespace llvm {
-Pass *createFunctionImportPass() { return new FunctionImportPass(); }
+Pass *createFunctionImportPass(FunctionInfoIndex *Index = nullptr) {
+  return new FunctionImportPass(Index);
+}
 }
Index: lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- lib/Transforms/IPO/PassManagerBuilder.cpp
+++ lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -18,6 +18,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Analysis/Passes.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/FunctionInfo.h"
 #include "llvm/IR/Verifier.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/Support/CommandLine.h"
@@ -476,6 +477,9 @@
   // Provide AliasAnalysis services for optimizations.
   addInitialAliasAnalysisPasses(PM);
 
+  if (FunctionIndex)
+    PM.add(createFunctionImportPass(FunctionIndex.get()));
+
   // Propagate constants at call sites into the functions they call.  This
   // opens opportunities for globalopt (and inlining) by substituting function
   // pointers passed as arguments to direct uses of functions.