Index: include/llvm/LTO/legacy/LTOCodeGenerator.h
===================================================================
--- include/llvm/LTO/legacy/LTOCodeGenerator.h
+++ include/llvm/LTO/legacy/LTOCodeGenerator.h
@@ -48,6 +48,9 @@
 #include <string>
 #include <vector>
 
+/// Enable global value internalization in LTO.
+extern llvm::cl::opt<bool> EnableLTOInternalization;
+
 namespace llvm {
 template <typename T> class ArrayRef;
   class LLVMContext;
@@ -233,7 +236,7 @@
   unsigned OptLevel = 2;
   lto_diagnostic_handler_t DiagHandler = nullptr;
   void *DiagContext = nullptr;
-  bool ShouldInternalize = true;
+  bool ShouldInternalize = EnableLTOInternalization;
   bool ShouldEmbedUselists = false;
   bool ShouldRestoreGlobalsLinkage = false;
   TargetMachine::CodeGenFileType FileType = TargetMachine::CGFT_ObjectFile;
Index: lib/LTO/LTO.cpp
===================================================================
--- lib/LTO/LTO.cpp
+++ lib/LTO/LTO.cpp
@@ -56,6 +56,11 @@
     DumpThinCGSCCs("dump-thin-cg-sccs", cl::init(false), cl::Hidden,
                    cl::desc("Dump the SCCs in the ThinLTO index's callgraph"));
 
+/// Enable global value internalization in LTO.
+cl::opt<bool> EnableLTOInternalization(
+    "enable-lto-internalization", cl::init(true), cl::Hidden,
+    cl::desc("Enable global value internalization in LTO"));
+
 // Returns a unique hash for the Module considering the current list of
 // export/import and other global analysis results.
 // The hash is produced in \p Key.
@@ -344,7 +349,8 @@
     if (isExported(S->modulePath(), GUID)) {
       if (GlobalValue::isLocalLinkage(S->linkage()))
         S->setLinkage(GlobalValue::ExternalLinkage);
-    } else if (!GlobalValue::isLocalLinkage(S->linkage()))
+    } else if (EnableLTOInternalization &&
+               !GlobalValue::isLocalLinkage(S->linkage()))
       S->setLinkage(GlobalValue::InternalLinkage);
   }
 }
@@ -876,7 +882,7 @@
         continue;
       GV->setUnnamedAddr(R.second.UnnamedAddr ? GlobalValue::UnnamedAddr::Global
                                               : GlobalValue::UnnamedAddr::None);
-      if (R.second.Partition == 0)
+      if (EnableLTOInternalization && R.second.Partition == 0)
         GV->setLinkage(GlobalValue::InternalLinkage);
     }
 
Index: test/LTO/X86/internalize.ll
===================================================================
--- /dev/null
+++ test/LTO/X86/internalize.ll
@@ -0,0 +1,42 @@
+; RUN: opt %s -o %t1.bc
+
+; RUN: llvm-lto %t1.bc -o %t1.save.opt  --exported-symbol=_foo -save-merged-module -O0
+; RUN: llvm-dis < %t1.save.opt.merged.bc | FileCheck %s --check-prefix=INTERNALIZE
+
+; Test the enable-lto-internalization option by setting it to false.
+; enable-lto-internalization makes sure internalization does not happen.
+; RUN: llvm-lto %t1.bc -enable-lto-internalization=false -o %t1.save.opt  \
+; RUN:                 --exported-symbol=_foo -save-merged-module -O0
+; RUN: llvm-dis < %t1.save.opt.merged.bc | FileCheck %s --check-prefix=INTERNALIZE-OPTION-DISABLE
+
+; RUN: llvm-lto2 run %t1.bc -o %t.o -save-temps \
+; RUN:     -r=%t1.bc,_foo,pxl \
+; RUN:     -r=%t1.bc,_bar,pl
+; RUN: llvm-dis < %t.o.0.2.internalize.bc | FileCheck  %s --check-prefix=INTERNALIZE2
+
+; Test the enable-lto-internalization option by setting it to false.
+; enable-lto-internalization=false makes sure internalization does not happen in runRegularLTO().
+; RUN: llvm-lto2 run %t1.bc -o %t.o -save-temps -enable-lto-internalization=false \
+; RUN:     -r=%t1.bc,_foo,pxl \
+; RUN:     -r=%t1.bc,_bar,pl
+; RUN: llvm-dis < %t.o.0.2.internalize.bc | FileCheck  %s --check-prefix=INTERNALIZE2-OPTION-DISABLE
+
+; INTERNALIZE: define void @foo
+; INTERNALIZE: define internal void @bar
+; INTERNALIZE-OPTION-DISABLE: define void @foo
+; INTERNALIZE-OPTION-DISABLE: define void @bar
+; INTERNALIZE2: define dso_local void @foo
+; INTERNALIZE2: define internal void @bar
+; INTERNALIZE2-OPTION-DISABLE: define dso_local void @foo
+; INTERNALIZE2-OPTION-DISABLE: define dso_local void @bar
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+define void @foo() {
+    call void @bar()
+    ret void
+}
+define void @bar() {
+    ret void
+}
Index: test/ThinLTO/X86/internalize.ll
===================================================================
--- test/ThinLTO/X86/internalize.ll
+++ test/ThinLTO/X86/internalize.ll
@@ -3,12 +3,27 @@
 ; RUN: llvm-lto -thinlto-action=internalize -thinlto-index %t.index.bc %t1.bc -o - | llvm-dis -o - | FileCheck %s --check-prefix=REGULAR
 ; RUN: llvm-lto -thinlto-action=internalize -thinlto-index %t.index.bc %t1.bc -o -  --exported-symbol=foo | llvm-dis -o - | FileCheck %s --check-prefix=INTERNALIZE
 
+; Test the enable-lto-internalization option by setting it to false.
+; enable-lto-internalization makes sure indices are not marked as
+; internallinkage and therefore internalization does not happen.
+; RUN: llvm-lto -thinlto-action=internalize -thinlto-index %t.index.bc %t1.bc \
+; RUN:          -enable-lto-internalization=false --exported-symbol=foo
+; RUN: llvm-dis < %t1.bc.thinlto.internalized.bc | FileCheck %s --check-prefix=INTERNALIZE-OPTION-DISABLE
+
 ; RUN: llvm-lto2 run %t1.bc -o %t.o -save-temps \
 ; RUN:     -r=%t1.bc,_foo,pxl \
 ; RUN:     -r=%t1.bc,_bar,pl \
 ; RUN:     -r=%t1.bc,_linkonce_func,pl
 ; RUN: llvm-dis < %t.o.1.2.internalize.bc | FileCheck  %s --check-prefix=INTERNALIZE2
 
+; Test the enable-lto-internalization option by setting it to false.
+; enable-lto-internalization makes sure indices are not marked as
+; internallinkage and therefore internalization does not happen.
+; RUN: llvm-lto2 run %t1.bc -o %t.o -save-temps -enable-lto-internalization=false \
+; RUN:     -r=%t1.bc,_foo,pxl \
+; RUN:     -r=%t1.bc,_bar,pl \
+; RUN:     -r=%t1.bc,_linkonce_func,pl
+; RUN: llvm-dis < %t.o.1.2.internalize.bc | FileCheck  %s --check-prefix=INTERNALIZE2-OPTION-DISABLE
 
 ; REGULAR: define void @foo
 ; REGULAR: define void @bar
@@ -16,9 +31,15 @@
 ; INTERNALIZE: define void @foo
 ; INTERNALIZE: define internal void @bar
 ; INTERNALIZE: define internal void @linkonce_func()
+; INTERNALIZE-OPTION-DISABLE: define void @foo
+; INTERNALIZE-OPTION-DISABLE: define void @bar
+; INTERNALIZE-OPTION-DISABLE: define linkonce void @linkonce_func()
 ; INTERNALIZE2: define dso_local void @foo
 ; INTERNALIZE2: define internal void @bar
 ; INTERNALIZE2: define internal void @linkonce_func()
+; INTERNALIZE2-OPTION-DISABLE: define dso_local void @foo
+; INTERNALIZE2-OPTION-DISABLE: define dso_local void @bar
+; INTERNALIZE2-OPTION-DISABLE: define weak dso_local void @linkonce_func()
 
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx10.11.0"