Index: llvm/lib/Transforms/Utils/CloneFunction.cpp
===================================================================
--- llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -260,6 +260,9 @@
   // visiting the metadata attached to global values, which would allow this
   // code to be deleted. Alternatively, perhaps give responsibility for this
   // update to CloneFunctionInto's callers.
+  if (!OldFunc->getParent()->getNamedMetadata("llvm.dbg.cu"))
+    return;
+
   auto *NewModule = NewFunc->getParent();
   auto *NMD = NewModule->getOrInsertNamedMetadata("llvm.dbg.cu");
   // Avoid multiple insertions of the same DICompileUnit to NMD.
Index: llvm/unittests/Transforms/Utils/CloningTest.cpp
===================================================================
--- llvm/unittests/Transforms/Utils/CloningTest.cpp
+++ llvm/unittests/Transforms/Utils/CloningTest.cpp
@@ -849,6 +849,49 @@
   EXPECT_FALSE(haveCompileUnitsInCommon(*ImplModule, *DeclModule));
 }
 
+TEST(CloneFunction, CloneFunctionToDifferentModuleNoCU) {
+  StringRef ImplAssembly = R"(
+    define void @foo() {
+      ret void
+    }
+  )";
+  StringRef DeclAssembly = R"(
+    declare void @foo()
+  )";
+
+  LLVMContext Context;
+  SMDiagnostic Error;
+
+  auto ImplModule = parseAssemblyString(ImplAssembly, Error, Context);
+  EXPECT_TRUE(ImplModule != nullptr);
+  EXPECT_TRUE(ImplModule->getNamedMetadata("llvm.dbg.cu") == nullptr);
+  auto *ImplFunction = ImplModule->getFunction("foo");
+  EXPECT_TRUE(ImplFunction != nullptr);
+
+  auto DeclModule = parseAssemblyString(DeclAssembly, Error, Context);
+  EXPECT_TRUE(DeclModule != nullptr);
+  // No DICompileUnits defined here.
+  EXPECT_TRUE(GetDICompileUnitCount(*DeclModule) == 0);
+  auto *DeclFunction = DeclModule->getFunction("foo");
+  EXPECT_TRUE(DeclFunction != nullptr);
+
+  EXPECT_FALSE(verifyModule(*ImplModule, &errs()));
+  EXPECT_FALSE(verifyModule(*DeclModule, &errs()));
+
+  ValueToValueMapTy VMap;
+  VMap[ImplFunction] = DeclFunction;
+  // No args to map
+  SmallVector<ReturnInst *, 8> Returns;
+  CloneFunctionInto(DeclFunction, ImplFunction, VMap,
+                    CloneFunctionChangeType::DifferentModule, Returns);
+
+  EXPECT_FALSE(verifyModule(*ImplModule, &errs()));
+  EXPECT_FALSE(verifyModule(*DeclModule, &errs()));
+  // DeclModule should not have a compile unit because it didn't start with one
+  // and nor did ImplModule
+  EXPECT_TRUE(DeclModule->getNamedMetadata("llvm.dbg.cu") == nullptr);
+}
+
 class CloneModule : public ::testing::Test {
 protected:
   void SetUp() override {