Index: lib/Linker/LinkModules.cpp
===================================================================
--- lib/Linker/LinkModules.cpp
+++ lib/Linker/LinkModules.cpp
@@ -329,8 +329,18 @@
 bool ModuleLinker::linkIfNeeded(GlobalValue &GV) {
   GlobalValue *DGV = getLinkedToGlobal(&GV);
 
-  if (shouldLinkOnlyNeeded() && !(DGV && DGV->isDeclaration()))
-    return false;
+  if (shouldLinkOnlyNeeded()) {
+    // Always import variables with appending linkage.
+    if (!GV.hasAppendingLinkage()) {
+      // Don't import globals unless they are referenced by the destination
+      // module.
+      if (!DGV)
+        return false;
+      // Don't import globals that are already defined in the destination module
+      if (!DGV->isDeclaration())
+        return false;
+    }
+  }
 
   if (DGV && !GV.hasLocalLinkage() && !GV.hasAppendingLinkage()) {
     auto *DGVar = dyn_cast<GlobalVariable>(DGV);
Index: test/Linker/Inputs/only-needed-compiler-used.src.ll
===================================================================
--- /dev/null
+++ test/Linker/Inputs/only-needed-compiler-used.src.ll
@@ -0,0 +1,7 @@
+@used1 = global i8 4
+@used2 = global i32 123
+
+@llvm.compiler.used = appending global [2 x i8*] [
+   i8* @used1,
+   i8* bitcast (i32* @used2 to i8*)
+], section "llvm.metadata"
Index: test/Linker/Inputs/only-needed-ctors.src.a.ll
===================================================================
--- /dev/null
+++ test/Linker/Inputs/only-needed-ctors.src.a.ll
@@ -0,0 +1,16 @@
+define internal void @ctor1() {
+  call void @func1()
+  ret void
+}
+
+define internal void @ctor2() {
+  ret void
+}
+
+define void @func1() {
+  ret void
+}
+
+@llvm.global_ctors = appending global[2 x{i32, void() *, i8 * }] [
+    {i32, void() *, i8 * } { i32 2, void() *@ctor1, i8 *null},
+    {i32, void() *, i8 * } { i32 7, void() *@ctor2, i8 *null}]
Index: test/Linker/Inputs/only-needed-ctors.src.b.ll
===================================================================
--- /dev/null
+++ test/Linker/Inputs/only-needed-ctors.src.b.ll
@@ -0,0 +1,16 @@
+define internal void @ctor3() {
+  call void @func1()
+  ret void
+}
+
+define internal void @ctor4() {
+  ret void
+}
+
+define void @func1() {
+  ret void
+}
+
+@llvm.global_ctors = appending global[2 x{i32, void() *, i8 * }] [
+    {i32, void() *, i8 * } { i32 1, void() *@ctor3, i8 *null},
+    {i32, void() *, i8 * } { i32 9, void() *@ctor4, i8 *null}]
Index: test/Linker/Inputs/only-needed-dtors.src.a.ll
===================================================================
--- /dev/null
+++ test/Linker/Inputs/only-needed-dtors.src.a.ll
@@ -0,0 +1,16 @@
+define internal void @ctor1() {
+  call void @func1()
+  ret void
+}
+
+define internal void @ctor2() {
+  ret void
+}
+
+define void @func1() {
+  ret void
+}
+
+@llvm.global_dtors = appending global[2 x{i32, void() *, i8 * }] [
+    {i32, void() *, i8 * } { i32 2, void() *@ctor1, i8 *null},
+    {i32, void() *, i8 * } { i32 7, void() *@ctor2, i8 *null}]
Index: test/Linker/Inputs/only-needed-dtors.src.b.ll
===================================================================
--- /dev/null
+++ test/Linker/Inputs/only-needed-dtors.src.b.ll
@@ -0,0 +1,16 @@
+define internal void @ctor3() {
+  call void @func1()
+  ret void
+}
+
+define internal void @ctor4() {
+  ret void
+}
+
+define void @func1() {
+  ret void
+}
+
+@llvm.global_dtors = appending global[2 x{i32, void() *, i8 * }] [
+    {i32, void() *, i8 * } { i32 1, void() *@ctor3, i8 *null},
+    {i32, void() *, i8 * } { i32 9, void() *@ctor4, i8 *null}]
Index: test/Linker/Inputs/only-needed-used.src.ll
===================================================================
--- /dev/null
+++ test/Linker/Inputs/only-needed-used.src.ll
@@ -0,0 +1,7 @@
+@used1 = global i8 4
+@used2 = global i32 123
+
+@llvm.used = appending global [2 x i8*] [
+   i8* @used1,
+   i8* bitcast (i32* @used2 to i8*)
+], section "llvm.metadata"
Index: test/Linker/only-needed-compiler-used.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-compiler-used.ll
@@ -0,0 +1,13 @@
+; RUN: llvm-link -S                           %s %p/Inputs/only-needed-compiler-used.src.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-compiler-used.src.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-compiler-used.src.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-compiler-used.src.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Empty destination module!
+
+
+; CHECK-DAG:          @llvm.compiler.used = appending global [2 x i8*] [i8* @used1, i8* bitcast (i32* @used2 to i8*)], section "llvm.metadata"
+; NO-INTERNALIZE-DAG: @used1 = global i8 4
+; INTERNALIZE-DAG:    @used1 = internal global i8 4
+; NO-INTERNALIZE-DAG: @used2 = global i32 123
+; INTERNALIZE-DAG:    @used2 = internal global i32 123
Index: test/Linker/only-needed-ctors1.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-ctors1.ll
@@ -0,0 +1,13 @@
+; RUN: llvm-link -S                           %s %p/Inputs/only-needed-ctors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-ctors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-ctors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-ctors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Empty destination module!
+
+
+; CHECK:          @llvm.global_ctors = appending global [2 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 2, void ()* @ctor1, i8* null }, { i32, void ()*, i8* } { i32 7, void ()* @ctor2, i8* null }]
+; CHECK:          define internal void @ctor1()
+; CHECK:          define internal void @ctor2()
+; NO-INTERNALIZE: define void @func1()
+; INTERNALIZE:    define internal void @func1()
Index: test/Linker/only-needed-ctors2.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-ctors2.ll
@@ -0,0 +1,15 @@
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-ctors.src.a.ll %p/Inputs/only-needed-ctors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-ctors.src.a.ll %p/Inputs/only-needed-ctors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-ctors.src.a.ll %p/Inputs/only-needed-ctors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Empty destination module!
+
+
+; CHECK:          @llvm.global_ctors = appending global [4 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 2, void ()* @ctor1, i8* null }, { i32, void ()*, i8* } { i32 7, void ()* @ctor2, i8* null }, { i32, void ()*, i8* } { i32 1, void ()* @ctor3, i8* null }, { i32, void ()*, i8* } { i32 9, void ()* @ctor4, i8* null }]
+; CHECK:          define internal void @ctor1()
+; CHECK:          define internal void @ctor2()
+; NO-INTERNALIZE: define void @func1()
+; INTERNALIZE:    define internal void @func1.{{[0-9]+}}()
+; CHECK:          define internal void @ctor3()
+; CHECK:          define internal void @ctor4()
+; INTERNALIZE:    define internal void @func1()
Index: test/Linker/only-needed-ctors3.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-ctors3.ll
@@ -0,0 +1,26 @@
+; RUN: llvm-link -S                           %s %p/Inputs/only-needed-ctors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-ctors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-ctors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-ctors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Destination module:
+
+define void @foo() {
+  ret void
+}
+
+define internal void @ctor1() {
+  ret void
+}
+
+@llvm.global_ctors = appending global[1 x{i32, void() *, i8 * }] [
+    {i32, void() *, i8 * } { i32 4, void() *@ctor1, i8 *null}]
+
+
+; CHECK:          @llvm.global_ctors = appending global [3 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 4, void ()* @ctor1, i8* null }, { i32, void ()*, i8* } { i32 2, void ()* @ctor1.2, i8* null }, { i32, void ()*, i8* } { i32 7, void ()* @ctor2, i8* null }]
+; CHECK:          define internal void @ctor1()
+; CHECK:          define void @foo()
+; CHECK:          define internal void @ctor1.{{[0-9]+}}()
+; CHECK:          define internal void @ctor2()
+; NO-INTERNALIZE: define void @func1()
+; INTERNALIZE:    define internal void @func1()
Index: test/Linker/only-needed-ctors4.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-ctors4.ll
@@ -0,0 +1,28 @@
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-ctors.src.a.ll %p/Inputs/only-needed-ctors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-ctors.src.a.ll %p/Inputs/only-needed-ctors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-ctors.src.a.ll %p/Inputs/only-needed-ctors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Destination module:
+
+define void @foo() {
+  ret void
+}
+
+define internal void @ctor1() {
+  ret void
+}
+
+@llvm.global_ctors = appending global[1 x{i32, void() *, i8 * }] [
+    {i32, void() *, i8 * } { i32 4, void() *@ctor1, i8 *null}]
+
+
+; CHECK:          @llvm.global_ctors = appending global [5 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 4, void ()* @ctor1, i8* null }, { i32, void ()*, i8* } { i32 2, void ()* @ctor1.2, i8* null }, { i32, void ()*, i8* } { i32 7, void ()* @ctor2, i8* null }, { i32, void ()*, i8* } { i32 1, void ()* @ctor3, i8* null }, { i32, void ()*, i8* } { i32 9, void ()* @ctor4, i8* null }]
+; CHECK:          define internal void @ctor1()
+; CHECK:          define void @foo()
+; CHECK:          define internal void @ctor1.{{[0-9]+}}()
+; CHECK:          define internal void @ctor2()
+; NO-INTERNALIZE: define void @func1()
+; INTERNALIZE:    define internal void @func1.{{[0-9]+}}()
+; CHECK:          define internal void @ctor3()
+; CHECK:          define internal void @ctor4()
+; INTERNALIZE:    define internal void @func1()
Index: test/Linker/only-needed-dtors1.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-dtors1.ll
@@ -0,0 +1,13 @@
+; RUN: llvm-link -S                           %s %p/Inputs/only-needed-dtors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-dtors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-dtors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-dtors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Empty destination module!
+
+
+; CHECK:          @llvm.global_dtors = appending global [2 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 2, void ()* @ctor1, i8* null }, { i32, void ()*, i8* } { i32 7, void ()* @ctor2, i8* null }]
+; CHECK:          define internal void @ctor1()
+; CHECK:          define internal void @ctor2()
+; NO-INTERNALIZE: define void @func1()
+; INTERNALIZE:    define internal void @func1()
Index: test/Linker/only-needed-dtors2.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-dtors2.ll
@@ -0,0 +1,15 @@
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-dtors.src.a.ll %p/Inputs/only-needed-dtors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-dtors.src.a.ll %p/Inputs/only-needed-dtors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-dtors.src.a.ll %p/Inputs/only-needed-dtors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Empty destination module!
+
+
+; CHECK:          @llvm.global_dtors = appending global [4 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 2, void ()* @ctor1, i8* null }, { i32, void ()*, i8* } { i32 7, void ()* @ctor2, i8* null }, { i32, void ()*, i8* } { i32 1, void ()* @ctor3, i8* null }, { i32, void ()*, i8* } { i32 9, void ()* @ctor4, i8* null }]
+; CHECK:          define internal void @ctor1()
+; CHECK:          define internal void @ctor2()
+; NO-INTERNALIZE: define void @func1()
+; INTERNALIZE:    define internal void @func1.{{[0-9]+}}()
+; CHECK:          define internal void @ctor3()
+; CHECK:          define internal void @ctor4()
+; INTERNALIZE:    define internal void @func1()
Index: test/Linker/only-needed-dtors3.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-dtors3.ll
@@ -0,0 +1,25 @@
+; RUN: llvm-link -S                           %s %p/Inputs/only-needed-dtors.src.a.ll | FileCheck %s --check-prefix=CHECK
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-dtors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-dtors.src.a.ll | FileCheck %s --check-prefix=CHECK
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-dtors.src.a.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Destination module:
+
+define void @foo() {
+  ret void
+}
+
+define internal void @ctor1() {
+  ret void
+}
+
+@llvm.global_dtors = appending global[1 x{i32, void() *, i8 * }] [
+    {i32, void() *, i8 * } { i32 4, void() *@ctor1, i8 *null}]
+
+
+; CHECK:       @llvm.global_dtors = appending global [3 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 4, void ()* @ctor1, i8* null }, { i32, void ()*, i8* } { i32 2, void ()* @ctor1.2, i8* null }, { i32, void ()*, i8* } { i32 7, void ()* @ctor2, i8* null }]
+; CHECK:       define internal void @ctor1()
+; CHECK:       define void @foo()
+; CHECK:       define internal void @ctor1.{{[0-9]+}}()
+; CHECK:       define internal void @ctor2()
+; INTERNALIZE: define internal void @func1()
Index: test/Linker/only-needed-dtors4.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-dtors4.ll
@@ -0,0 +1,28 @@
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-dtors.src.a.ll %p/Inputs/only-needed-dtors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-dtors.src.a.ll %p/Inputs/only-needed-dtors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=NO-INTERNALIZE
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-dtors.src.a.ll %p/Inputs/only-needed-dtors.src.b.ll | FileCheck %s --check-prefix=CHECK --check-prefix=INTERNALIZE
+
+; Destination module:
+
+define void @foo() {
+  ret void
+}
+
+define internal void @ctor1() {
+  ret void
+}
+
+@llvm.global_dtors = appending global[1 x{i32, void() *, i8 * }] [
+    {i32, void() *, i8 * } { i32 4, void() *@ctor1, i8 *null}]
+
+
+; CHECK:          @llvm.global_dtors = appending global [5 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 4, void ()* @ctor1, i8* null }, { i32, void ()*, i8* } { i32 2, void ()* @ctor1.2, i8* null }, { i32, void ()*, i8* } { i32 7, void ()* @ctor2, i8* null }, { i32, void ()*, i8* } { i32 1, void ()* @ctor3, i8* null }, { i32, void ()*, i8* } { i32 9, void ()* @ctor4, i8* null }]
+; CHECK:          define internal void @ctor1()
+; CHECK:          define void @foo()
+; CHECK:          define internal void @ctor1.{{[0-9]+}}()
+; CHECK:          define internal void @ctor2()
+; NO-INTERNALIZE: define void @func1()
+; INTERNALIZE:    define internal void @func1.{{[0-9]+}}()
+; CHECK:          define internal void @ctor3()
+; CHECK:          define internal void @ctor4()
+; INTERNALIZE:    define internal void @func1()
Index: test/Linker/only-needed-used.ll
===================================================================
--- /dev/null
+++ test/Linker/only-needed-used.ll
@@ -0,0 +1,11 @@
+; RUN: llvm-link -S                           %s %p/Inputs/only-needed-used.src.ll | FileCheck %s
+; RUN: llvm-link -S              -internalize %s %p/Inputs/only-needed-used.src.ll | FileCheck %s
+; RUN: llvm-link -S -only-needed              %s %p/Inputs/only-needed-used.src.ll | FileCheck %s
+; RUN: llvm-link -S -only-needed -internalize %s %p/Inputs/only-needed-used.src.ll | FileCheck %s
+
+; Empty destination module!
+
+
+; CHECK-DAG:          @llvm.used = appending global [2 x i8*] [i8* @used1, i8* bitcast (i32* @used2 to i8*)], section "llvm.metadata"
+; CHECK-DAG: @used1 = global i8 4
+; CHECK-DAG: @used2 = global i32 123