Index: llvm/lib/LTO/LTO.cpp
===================================================================
--- llvm/lib/LTO/LTO.cpp
+++ llvm/lib/LTO/LTO.cpp
@@ -567,6 +567,18 @@
       GlobalRes.IRName = std::string(Sym.getIRName());
     }
 
+    // In rare occasion, the symbol used to initialize GlobalRes has a different
+    // IRName from the inspected Symbol. This can happen on OSX when a symbol
+    // is referenced through its mangled name, say @"\01_symbol" while the
+    // IRName is @symbol (the prefix underscore corms from MachO mangling). In
+    // that case, we have the same actual Symbol that can get two different
+    // GUID, leading to some invalid internalization. Workaround this by marking
+    // the GlobalRes external.
+    if (GlobalRes.IRName != Sym.getIRName()) {
+      GlobalRes.Partition = GlobalResolution::External;
+      GlobalRes.VisibleOutsideSummary = true;
+    }
+
     // Set the partition to external if we know it is re-defined by the linker
     // with -defsym or -wrap options, used elsewhere, e.g. it is visible to a
     // regular object, is referenced from llvm.compiler.used/llvm.used, or was
Index: llvm/test/LTO/X86/hidden-escaped-symbols-alt.ll
===================================================================
--- /dev/null
+++ llvm/test/LTO/X86/hidden-escaped-symbols-alt.ll
@@ -0,0 +1,39 @@
+; RUN: split-file %s %t
+; RUN: opt %t/hide-me.ll -o %t/hide-me.bc
+; RUN: opt %t/ref.ll -o %t/ref.bc
+; RUN: llvm-lto2 run \
+; RUN:               -r %t/hide-me.bc,_hide_me,p \
+; RUN:               -r %t/ref.bc,_main,plx  \
+; RUN:               -r %t/ref.bc,_hide_me,l \
+; RUN:               --select-save-temps=precodegen \
+; RUN:               -o %t/out \
+; RUN:               %t/hide-me.bc  %t/ref.bc
+; RUN: llvm-dis %t/out.0.5.precodegen.bc -o - | FileCheck %s
+
+
+;--- hide-me.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7.0"
+
+@"\01_hide_me" = hidden local_unnamed_addr global i8 8, align 1
+
+;--- ref.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7.0"
+
+@hide_me = external local_unnamed_addr global i8
+
+define i8 @main() {
+  %1 = load i8, ptr @hide_me, align 1
+  ret i8 %1
+}
+
+
+; CHECK: @"\01_hide_me" = hidden local_unnamed_addr global i8 8, align 1
+; CHECK: @hide_me = external dso_local local_unnamed_addr global i8
+
+; CHECK: define dso_local i8 @main() local_unnamed_addr #0 {
+; CHECK:   %1 = load i8, ptr @hide_me, align 1
+; CHECK:   ret i8 %1
+; CHECK: }
+
Index: llvm/test/LTO/X86/hidden-escaped-symbols.ll
===================================================================
--- /dev/null
+++ llvm/test/LTO/X86/hidden-escaped-symbols.ll
@@ -0,0 +1,39 @@
+; RUN: split-file %s %t
+; RUN: opt %t/hide-me.ll -o %t/hide-me.bc
+; RUN: opt %t/ref.ll -o %t/ref.bc
+; RUN: llvm-lto2 run \
+; RUN:               -r %t/hide-me.bc,_hide_me,p \
+; RUN:               -r %t/ref.bc,_main,plx  \
+; RUN:               -r %t/ref.bc,_hide_me,l \
+; RUN:               --select-save-temps=precodegen \
+; RUN:               -o %t/out \
+; RUN:               %t/hide-me.bc  %t/ref.bc
+; RUN: llvm-dis %t/out.0.5.precodegen.bc -o - | FileCheck %s
+
+
+;--- hide-me.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7.0"
+
+@hide_me = hidden local_unnamed_addr global i8 8, align 1
+
+;--- ref.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7.0"
+
+@"\01_hide_me" = external local_unnamed_addr global i8
+
+define i8 @main() {
+  %1 = load i8, ptr @"\01_hide_me", align 1
+  ret i8 %1
+}
+
+
+; CHECK: @hide_me = hidden local_unnamed_addr global i8 8, align 1
+; CHECK: @"\01_hide_me" = external dso_local local_unnamed_addr global i8
+
+; CHECK: define dso_local i8 @main() local_unnamed_addr #0 {
+; CHECK:   %1 = load i8, ptr @"\01_hide_me", align 1
+; CHECK:   ret i8 %1
+; CHECK: }
+
Index: llvm/test/ThinLTO/X86/hidden-escaped-symbols-alt.ll
===================================================================
--- /dev/null
+++ llvm/test/ThinLTO/X86/hidden-escaped-symbols-alt.ll
@@ -0,0 +1,40 @@
+; RUN: split-file %s %t
+; RUN: opt -module-summary %t/hide-me.ll -o %t/hide-me.bc
+; RUN: opt -module-summary %t/ref.ll -o %t/ref.bc
+; RUN: llvm-lto2 run \
+; RUN:               -r %t/hide-me.bc,_hide_me,p \
+; RUN:               -r %t/ref.bc,_main,plx  \
+; RUN:               -r %t/ref.bc,_hide_me,l \
+; RUN:               --select-save-temps=precodegen \
+; RUN:               -o %t/out \
+; RUN:               %t/hide-me.bc  %t/ref.bc
+; RUN: llvm-dis %t/out.1.5.precodegen.bc -o - | FileCheck --check-prefix=CHECK-HIDE %s
+; RUN: llvm-dis %t/out.2.5.precodegen.bc -o - | FileCheck --check-prefix=CHECK-REF %s
+
+
+;--- hide-me.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7.0"
+
+@"\01_hide_me" = hidden local_unnamed_addr global i8 8, align 1
+
+;--- ref.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7.0"
+
+@hide_me = external local_unnamed_addr global i8
+
+define i8 @main() {
+  %1 = load i8, ptr @hide_me, align 1
+  ret i8 %1
+}
+
+
+; CHECK-HIDE: @"\01_hide_me" = hidden local_unnamed_addr global i8 8, align 1
+
+; CHECK-REF: @hide_me = external local_unnamed_addr global i8
+; CHECK-REF: define dso_local i8 @main() local_unnamed_addr #0 {
+; CHECK-REF:   %1 = load i8, ptr @hide_me, align 1
+; CHECK-REF:   ret i8 %1
+; CHECK-REF: }
+
Index: llvm/test/ThinLTO/X86/hidden-escaped-symbols.ll
===================================================================
--- /dev/null
+++ llvm/test/ThinLTO/X86/hidden-escaped-symbols.ll
@@ -0,0 +1,40 @@
+; RUN: split-file %s %t
+; RUN: opt -module-summary %t/hide-me.ll -o %t/hide-me.bc
+; RUN: opt -module-summary %t/ref.ll -o %t/ref.bc
+; RUN: llvm-lto2 run \
+; RUN:               -r %t/hide-me.bc,_hide_me,p \
+; RUN:               -r %t/ref.bc,_main,plx  \
+; RUN:               -r %t/ref.bc,_hide_me,l \
+; RUN:               --select-save-temps=precodegen \
+; RUN:               -o %t/out \
+; RUN:               %t/hide-me.bc  %t/ref.bc
+; RUN: llvm-dis %t/out.1.5.precodegen.bc -o - | FileCheck --check-prefix=CHECK-HIDE %s
+; RUN: llvm-dis %t/out.2.5.precodegen.bc -o - | FileCheck --check-prefix=CHECK-REF %s
+
+
+;--- hide-me.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7.0"
+
+@hide_me = hidden local_unnamed_addr global i8 8, align 1
+
+;--- ref.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7.0"
+
+@"\01_hide_me" = external local_unnamed_addr global i8
+
+define i8 @main() {
+  %1 = load i8, ptr @"\01_hide_me", align 1
+  ret i8 %1
+}
+
+
+; CHECK-HIDE: @hide_me = hidden local_unnamed_addr global i8 8, align 1
+
+; CHECK-REF: @"\01_hide_me" = external local_unnamed_addr global i8
+; CHECK-REF: define dso_local i8 @main() local_unnamed_addr #0 {
+; CHECK-REF:   %1 = load i8, ptr @"\01_hide_me", align 1
+; CHECK-REF:   ret i8 %1
+; CHECK-REF: }
+