Index: ELF/LTO.h
===================================================================
--- ELF/LTO.h
+++ ELF/LTO.h
@@ -23,6 +23,7 @@
 
 #include "lld/Core/LLVM.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Linker/IRMover.h"
@@ -44,6 +45,7 @@
   llvm::IRMover Mover{Combined};
   SmallString<0> OwningData;
   std::unique_ptr<MemoryBuffer> MB;
+  llvm::StringSet<> Internalize;
 };
 }
 }
Index: ELF/LTO.cpp
===================================================================
--- ELF/LTO.cpp
+++ ELF/LTO.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Bitcode/ReaderWriter.h"
+#include "llvm/IR/AutoUpgrade.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/Linker/IRMover.h"
 #include "llvm/Support/StringSaver.h"
@@ -22,6 +23,7 @@
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
 
 using namespace llvm;
 using namespace llvm::object;
@@ -75,6 +77,13 @@
   unsigned BodyIndex = 0;
   ArrayRef<SymbolBody *> Bodies = F.getSymbols();
 
+  Module &M = Obj->getModule();
+  M.materializeMetadata();
+  UpgradeDebugInfo(M);
+
+  SmallPtrSet<GlobalValue *, 8> Used;
+  collectUsedGlobalVariables(M, Used, /* CompilerUsed */ false);
+
   for (const BasicSymbolRef &Sym : Obj->symbols()) {
     GlobalValue *GV = Obj->getSymbolGV(Sym.getRawDataRefImpl());
     assert(GV);
@@ -95,6 +104,12 @@
             GV->setLinkage(GlobalValue::WeakODRLinkage);
             break;
           }
+
+          // FIXME: Is the check for shared libraries correct?
+          if (!Config->Shared && !Used.count(GV) &&
+              !cast<DefinedBitcode>(B)->isReferencedFromOutside())
+            Internalize.insert(GV->getName());
+
           Keep.push_back(GV);
         }
     }
@@ -104,10 +119,22 @@
              [](GlobalValue &, IRMover::ValueAdder) {});
 }
 
+static void internalize(GlobalValue &GV) {
+  if (!GV.hasLocalLinkage())
+    GV.setLinkage(GlobalValue::InternalLinkage);
+}
+
 // Merge all the bitcode files we have seen, codegen the result
 // and return the resulting ObjectFile.
 template <class ELFT>
 std::unique_ptr<elf::ObjectFile<ELFT>> BitcodeCompiler::compile() {
+
+  for (const auto &Name : Internalize) {
+    GlobalValue *GV = Combined.getNamedValue(Name.first());
+    if (GV)
+      internalize(*GV);
+  }
+
   if (Config->SaveTemps)
     saveBCFile(Combined, ".lto.bc");
 
Index: ELF/SymbolTable.cpp
===================================================================
--- ELF/SymbolTable.cpp
+++ ELF/SymbolTable.cpp
@@ -214,6 +214,14 @@
 
   SymbolBody *Existing = Sym->Body;
 
+  // Needed for internalize step of symbols.
+  if (auto *BC = dyn_cast<DefinedBitcode>(Existing))
+    if (auto *U = dyn_cast<Undefined>(New))
+      BC->setReferencedFromOutside();
+  if (auto *U = dyn_cast<Undefined>(Existing))
+    if (auto *BC = dyn_cast<DefinedBitcode>(New))
+      BC->setReferencedFromOutside();
+
   if (Lazy *L = dyn_cast<Lazy>(Existing)) {
     if (auto *Undef = dyn_cast<Undefined>(New)) {
       addMemberFile(Undef, L);
Index: ELF/Symbols.h
===================================================================
--- ELF/Symbols.h
+++ ELF/Symbols.h
@@ -180,6 +180,12 @@
 public:
   DefinedBitcode(StringRef Name, bool IsWeak, uint8_t Visibility);
   static bool classof(const SymbolBody *S);
+
+  void setReferencedFromOutside() { RefFromOutside = true; }
+  bool isReferencedFromOutside() { return RefFromOutside; }
+
+private:
+  bool RefFromOutside;
 };
 
 class DefinedCommon : public Defined {
Index: ELF/Symbols.cpp
===================================================================
--- ELF/Symbols.cpp
+++ ELF/Symbols.cpp
@@ -16,6 +16,7 @@
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Config/config.h"
+#include "llvm/Support/raw_ostream.h"
 
 #ifdef HAVE_CXXABI_H
 #include <cxxabi.h>
Index: test/ELF/lto/internalize.ll
===================================================================
--- /dev/null
+++ test/ELF/lto/internalize.ll
@@ -0,0 +1,17 @@
+; REQUIRES: x86
+; RUN: llvm-as %s -o %t.o
+; RUN: ld.lld -m elf_x86_64 %t.o -o %t2 -save-temps
+; RUN: llvm-dis %t2 -o - | FileCheck %s
+
+; CHECK: blah
+
+target triple = "x86_64-unknown-linux-gnu"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @_start() {
+  ret void
+}
+
+define void @foo() {
+  ret void
+}