Index: lib/Transforms/Utils/CloneModule.cpp
===================================================================
--- lib/Transforms/Utils/CloneModule.cpp
+++ lib/Transforms/Utils/CloneModule.cpp
@@ -109,6 +109,9 @@
   //
   for (Module::const_global_iterator I = M->global_begin(), E = M->global_end();
        I != E; ++I) {
+    if (I->isDeclaration())
+      continue;
+
     GlobalVariable *GV = cast<GlobalVariable>(VMap[&*I]);
     if (!ShouldCloneDefinition(&*I)) {
       // Skip after setting the correct linkage for an external reference.
@@ -122,6 +125,9 @@
   // Similarly, copy over function bodies now...
   //
   for (Module::const_iterator I = M->begin(), E = M->end(); I != E; ++I) {
+    if (I->isDeclaration())
+      continue;
+
     Function *F = cast<Function>(VMap[&*I]);
     if (!ShouldCloneDefinition(&*I)) {
       // Skip after setting the correct linkage for an external reference.
@@ -130,18 +136,17 @@
       F->setPersonalityFn(nullptr);
       continue;
     }
-    if (!I->isDeclaration()) {
-      Function::arg_iterator DestI = F->arg_begin();
-      for (Function::const_arg_iterator J = I->arg_begin(); J != I->arg_end();
-           ++J) {
-        DestI->setName(J->getName());
-        VMap[&*J] = &*DestI++;
-      }
-
-      SmallVector<ReturnInst*, 8> Returns;  // Ignore returns cloned.
-      CloneFunctionInto(F, &*I, VMap, /*ModuleLevelChanges=*/true, Returns);
+
+    Function::arg_iterator DestI = F->arg_begin();
+    for (Function::const_arg_iterator J = I->arg_begin(); J != I->arg_end();
+         ++J) {
+      DestI->setName(J->getName());
+      VMap[&*J] = &*DestI++;
     }
 
+    SmallVector<ReturnInst *, 8> Returns; // Ignore returns cloned.
+    CloneFunctionInto(F, &*I, VMap, /*ModuleLevelChanges=*/true, Returns);
+
     if (I->hasPersonalityFn())
       F->setPersonalityFn(MapValue(I->getPersonalityFn(), VMap));
   }
Index: test/tools/llvm-split/extern_linkage.ll
===================================================================
--- /dev/null
+++ test/tools/llvm-split/extern_linkage.ll
@@ -0,0 +1,20 @@
+; Test that extern_weak linkage is preserved.
+; RUN: llvm-split -o %t %s
+; RUN: llvm-dis -o - %t0 | FileCheck %s
+; RUN: llvm-dis -o - %t1 | FileCheck %s
+
+define void @g() {
+entry:
+  br i1 icmp ne (void (...)* @f, void (...)* null), label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  tail call void (...) @f()
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  ret void
+}
+
+; @f is an extern_weak declaration in both partitions
+; CHECK: declare extern_weak void @f(...)
+declare extern_weak void @f(...)