Index: lib/LTO/LTOCodeGenerator.cpp
===================================================================
--- lib/LTO/LTOCodeGenerator.cpp
+++ lib/LTO/LTOCodeGenerator.cpp
@@ -348,14 +348,74 @@
                                  RelocModel, CodeModel::Default, CGOptLevel));
 }
 
+// If a linkonce global is present in the MustPreserveSymbols, we need to make
+// sure we honor this. To force the compiler to not drop it, we add it to the
+// "llvm.used" global.
+static void preserveDiscardableGV(
+    Module &TheModule,
+    const std::function<bool(const GlobalValue &)> &MustPreserveGV) {
+  DenseSet<Constant *> UsedValuesSet;
+  if (GlobalVariable *LLVMUsed = TheModule.getGlobalVariable("llvm.used")) {
+    ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
+    for (auto &V : Inits->operands())
+      UsedValuesSet.insert(cast<Constant>(&V));
+    LLVMUsed->eraseFromParent();
+  }
+  llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(TheModule.getContext());
+  auto mayPreserveGlobal = [&](GlobalValue &GV) {
+    if (!GV.isDiscardableIfUnused() || GV.isDeclaration())
+      return;
+    if (!MustPreserveGV(GV))
+      return;
+    assert(!GV.hasAvailableExternallyLinkage() && !GV.hasInternalLinkage());
+    UsedValuesSet.insert(ConstantExpr::getBitCast(&GV, i8PTy));
+  };
+  for (auto &GV : TheModule)
+    mayPreserveGlobal(GV);
+  for (auto &GV : TheModule.globals())
+    mayPreserveGlobal(GV);
+  for (auto &GV : TheModule.aliases())
+    mayPreserveGlobal(GV);
+
+  if (UsedValuesSet.empty())
+    return;
+  std::vector<Constant *> UsedValuesList(UsedValuesSet.begin(),
+                                         UsedValuesSet.end());
+
+  llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, UsedValuesList.size());
+  auto *LLVMUsed = new llvm::GlobalVariable(
+      TheModule, ATy, false, llvm::GlobalValue::AppendingLinkage,
+      llvm::ConstantArray::get(ATy, UsedValuesList), "llvm.used");
+  LLVMUsed->setSection("llvm.metadata");
+}
+
 void LTOCodeGenerator::applyScopeRestrictions() {
-  if (ScopeRestrictionsDone || !ShouldInternalize)
+  if (ScopeRestrictionsDone)
+    return;
+
+  // Declare a callback for the internalize pass that will ask for every
+  // candidate GlobalValue if it can be internalized or not.
+  SmallString<64> MangledName;
+  auto MustPreserveGV = [&](const GlobalValue &GV) -> bool {
+    // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled
+    // with the linker supplied name, which on Darwin includes a leading
+    // underscore.
+    MangledName.clear();
+    MangledName.reserve(GV.getName().size() + 1);
+    Mangler::getNameWithPrefix(MangledName, GV.getName(),
+                               MergedModule->getDataLayout());
+    return MustPreserveSymbols.count(MangledName);
+  };
+
+  // Preserve linkonce value on linker request
+  preserveDiscardableGV(*MergedModule, MustPreserveGV);
+
+  if (!ShouldInternalize)
     return;
 
   if (ShouldRestoreGlobalsLinkage) {
     // Record the linkage type of non-local symbols so they can be restored
-    // prior
-    // to module splitting.
+    // prior to module splitting.
     auto RecordLinkage = [&](const GlobalValue &GV) {
       if (!GV.hasAvailableExternallyLinkage() && !GV.hasLocalLinkage() &&
           GV.hasName())
@@ -373,21 +433,6 @@
   // symbols referenced from asm
   UpdateCompilerUsed(*MergedModule, *TargetMach, AsmUndefinedRefs);
 
-  // Declare a callback for the internalize pass that will ask for every
-  // candidate GlobalValue if it can be internalized or not.
-  Mangler Mangler;
-  SmallString<64> MangledName;
-  auto MustPreserveGV = [&](const GlobalValue &GV) -> bool {
-    // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled
-    // with the linker supplied name, which on Darwin includes a leading
-    // underscore.
-    MangledName.clear();
-    MangledName.reserve(GV.getName().size() + 1);
-    Mangler::getNameWithPrefix(MangledName, GV.getName(),
-                               MergedModule->getDataLayout());
-    return MustPreserveSymbols.count(MangledName);
-  };
-
   internalizeModule(*MergedModule, MustPreserveGV);
 
   ScopeRestrictionsDone = true;
Index: test/tools/lto/hide-linkonce-odr.ll
===================================================================
--- test/tools/lto/hide-linkonce-odr.ll
+++ test/tools/lto/hide-linkonce-odr.ll
@@ -1,9 +1,11 @@
 ; RUN: llvm-as %s -o %t.o
-; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -dylib -arch x86_64 -macosx_version_min 10.10.0 -lSystem -o %t.dylib %t.o -save-temps  -undefined dynamic_lookup
+; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -dylib -arch x86_64 -macosx_version_min 10.10.0 -lSystem -o %t.dylib %t.o -save-temps  -undefined dynamic_lookup -exported_symbol _c -exported_symbol _b
 
 ; RUN: llvm-dis %t.dylib.lto.opt.bc -o - | FileCheck --check-prefix=IR %s
-; check that @a is still a linkonce_odr definition
-; IR: define linkonce_odr void @a()
+; check that @a is no longer a linkonce_odr definition
+; IR-NOT: define linkonce_odr void @a()
+; check that @b is appended in llvm.used
+; IR: @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @b to i8*)], section "llvm.metadata"
 
 ; RUN: llvm-nm %t.dylib | FileCheck --check-prefix=NM %s
 ; check that the linker can hide @a but not @b