diff --git a/llvm/lib/Transforms/IPO/ConstantMerge.cpp b/llvm/lib/Transforms/IPO/ConstantMerge.cpp
--- a/llvm/lib/Transforms/IPO/ConstantMerge.cpp
+++ b/llvm/lib/Transforms/IPO/ConstantMerge.cpp
@@ -101,7 +101,7 @@
 
 enum class CanMerge { No, Yes };
 static CanMerge makeMergeable(GlobalVariable *Old, GlobalVariable *New) {
-  if (!Old->hasGlobalUnnamedAddr() && !New->hasGlobalUnnamedAddr())
+  if (!Old->hasGlobalUnnamedAddr() || !New->hasGlobalUnnamedAddr())
     return CanMerge::No;
   if (hasMetadataOtherThanDebugLoc(Old))
     return CanMerge::No;
diff --git a/llvm/test/Transforms/ConstantMerge/2011-01-15-EitherOrder.ll b/llvm/test/Transforms/ConstantMerge/2011-01-15-EitherOrder.ll
--- a/llvm/test/Transforms/ConstantMerge/2011-01-15-EitherOrder.ll
+++ b/llvm/test/Transforms/ConstantMerge/2011-01-15-EitherOrder.ll
@@ -6,7 +6,7 @@
 %struct.foobar = type { i32 }
 ; CHECK: bar.d
 @bar.d =  unnamed_addr constant %struct.foobar zeroinitializer, align 4
-; CHECK-NOT: foo.d
+; CHECK: foo.d
 @foo.d = internal constant %struct.foobar zeroinitializer, align 4
 define i32 @main() nounwind ssp {
 entry:
diff --git a/llvm/test/Transforms/ConstantMerge/merge-both.ll b/llvm/test/Transforms/ConstantMerge/merge-both.ll
--- a/llvm/test/Transforms/ConstantMerge/merge-both.ll
+++ b/llvm/test/Transforms/ConstantMerge/merge-both.ll
@@ -1,20 +1,21 @@
 ; RUN: opt -S < %s -passes=constmerge | FileCheck %s
-; Test that in one run var3 is merged into var2 and var1 into var4.
-; Test that we merge @var5 and @var6 into one with the higher alignment
+; Test that in one run var2 is merged into var4 and var6 is merged into var8.
+; Test that we merge @var6 and @var8 into one with the higher alignment
 
 declare void @zed(ptr, ptr)
 
 %struct.foobar = type { i32 }
 
 @var1 = internal constant %struct.foobar { i32 2 }
-@var2 = unnamed_addr constant %struct.foobar { i32 2 }
+@var2 = private unnamed_addr constant %struct.foobar { i32 2 }
 @var3 = internal constant %struct.foobar { i32 2 }
-@var4 = unnamed_addr constant %struct.foobar { i32 2 }
+@var4 = private unnamed_addr constant %struct.foobar { i32 2 }
 
 ; CHECK:      %struct.foobar = type { i32 }
 ; CHECK-NOT: @
-; CHECK: @var2 = constant %struct.foobar { i32 2 }
-; CHECK-NEXT: @var4 = constant %struct.foobar { i32 2 }
+; CHECK: @var1 = internal constant %struct.foobar { i32 2 }
+; CHECK-NEXT: @var3 = internal constant %struct.foobar { i32 2 }
+; CHECK-NEXT: @var4 = private unnamed_addr constant %struct.foobar { i32 2 }
 
 declare void @helper(ptr)
 @var5 = internal constant [16 x i8] c"foo1bar2foo3bar\00", align 16
@@ -22,8 +23,9 @@
 @var7 = internal constant [16 x i8] c"foo1bar2foo3bar\00"
 @var8 = private unnamed_addr constant [16 x i8] c"foo1bar2foo3bar\00"
 
+; CHECK: @var5 = internal constant [16 x i8] c"foo1bar2foo3bar\00", align 16
 ; CHECK-NEXT: @var7 = internal constant [16 x i8] c"foo1bar2foo3bar\00"
-; CHECK-NEXT: @var8 = private constant [16 x i8] c"foo1bar2foo3bar\00", align 16
+; CHECK-NEXT: @var8 = private unnamed_addr constant [16 x i8] c"foo1bar2foo3bar\00", align 1
 
 @var4a = alias %struct.foobar, ptr @var4
 @llvm.used = appending global [1 x ptr] [ptr @var4a], section "llvm.metadata"
@@ -38,4 +40,3 @@
   call void @helper(ptr @var8)
   ret i32 0
 }
-
diff --git a/llvm/test/Transforms/ConstantMerge/merge-dbg.ll b/llvm/test/Transforms/ConstantMerge/merge-dbg.ll
--- a/llvm/test/Transforms/ConstantMerge/merge-dbg.ll
+++ b/llvm/test/Transforms/ConstantMerge/merge-dbg.ll
@@ -1,8 +1,8 @@
 ; RUN: opt < %s -passes=constmerge -S | FileCheck %s
 
-; CHECK: = constant i32 1, !dbg [[A:![0-9]+]], !dbg [[B:![0-9]+]]
-@a = internal constant i32 1, !dbg !0
-@b = unnamed_addr constant i32 1, !dbg !9
+; CHECK: = private unnamed_addr constant i32 1, !dbg [[A:![0-9]+]], !dbg [[B:![0-9]+]]
+@a = private unnamed_addr constant i32 1, !dbg !0
+@b = private unnamed_addr constant i32 1, !dbg !9
 
 define void @test1(ptr %P1, ptr %P2) {
   store ptr @a, ptr %P1
diff --git a/llvm/test/Transforms/ConstantMerge/unnamed-addr.ll b/llvm/test/Transforms/ConstantMerge/unnamed-addr.ll
--- a/llvm/test/Transforms/ConstantMerge/unnamed-addr.ll
+++ b/llvm/test/Transforms/ConstantMerge/unnamed-addr.ll
@@ -1,6 +1,6 @@
 ; RUN: opt -passes=constmerge -S < %s | FileCheck %s
-; Test which corresponding x and y are merged and that unnamed_addr
-; is correctly set.
+; Test which corresponding x and y are merged when they both are marked with
+; unnamed_addr attribute.
 
 declare void @zed(ptr, ptr)
 
@@ -23,7 +23,9 @@
 ; CHECK-NOT: @
 ; CHECK: @test1.x = internal constant %struct.foobar { i32 1 }
 ; CHECK-NEXT: @test1.y = constant %struct.foobar { i32 1 }
-; CHECK-NEXT: @test2.y = constant %struct.foobar { i32 2 }
+; CHECK-NEXT: @test2.x = internal constant %struct.foobar { i32 2 }
+; CHECK-NEXT: @test2.y = unnamed_addr constant %struct.foobar { i32 2 }
+; CHECK-NEXT: @test3.x = internal unnamed_addr constant %struct.foobar { i32 3 }
 ; CHECK-NEXT: @test3.y = constant %struct.foobar { i32 3 }
 ; CHECK-NEXT: @test4.y = unnamed_addr constant %struct.foobar { i32 4 }
 ; CHECK-NOT: @