Index: include/llvm/IR/Value.h
===================================================================
--- include/llvm/IR/Value.h
+++ include/llvm/IR/Value.h
@@ -351,13 +351,19 @@
     assertModuleIsMaterialized();
     return *materialized_user_begin();
   }
+  iterator_range<user_iterator> materialized_users() {
+    return make_range(materialized_user_begin(), user_end());
+  }
+  iterator_range<const_user_iterator> materialized_users() const {
+    return make_range(materialized_user_begin(), user_end());
+  }
   iterator_range<user_iterator> users() {
     assertModuleIsMaterialized();
-    return make_range(materialized_user_begin(), user_end());
+    return materialized_users();
   }
   iterator_range<const_user_iterator> users() const {
     assertModuleIsMaterialized();
-    return make_range(materialized_user_begin(), user_end());
+    return materialized_users();
   }
 
   /// \brief Return true if there is exactly one user of this value.
Index: lib/IR/Verifier.cpp
===================================================================
--- lib/IR/Verifier.cpp
+++ lib/IR/Verifier.cpp
@@ -448,6 +448,24 @@
   InstVisitor<Verifier>::visit(I);
 }
 
+// Helper to recursively iterate over indirect users that are
+// associated to a given module (i.e. we pass through constants, etc.
+// but stop at Instructions and Functions)
+static void forEachInstructionAndFunctionUser(
+    const Value *User, SmallPtrSet<const Value *, 32> &Visited,
+    llvm::function_ref<void(const Instruction *)> InstCallback,
+    llvm::function_ref<void(const Function *)> FuncCallback) {
+  if (!Visited.insert(User).second)
+    return;
+  if (const Instruction *I = dyn_cast<Instruction>(User))
+    InstCallback(I);
+  else if (const Function *F = dyn_cast<Function>(User))
+    FuncCallback(F);
+  else
+    for (const Value *TheNextUser : User->materialized_users())
+      forEachInstructionAndFunctionUser(TheNextUser, Visited, InstCallback,
+                                        FuncCallback);
+}
 
 void Verifier::visitGlobalValue(const GlobalValue &GV) {
   Assert(!GV.isDeclaration() || GV.hasExternalLinkage() ||
@@ -467,6 +485,29 @@
 
   if (GV.isDeclarationForLinker())
     Assert(!GV.hasComdat(), "Declaration may not be in a Comdat!", &GV);
+
+  // Verify that this GlobalValue is only used in this module.
+  // This map is used to avoid visiting uses twice. We can arrive at a user
+  // twice, if they have multiple operands. In particular for very large
+  // constant expressions, we can arrive at a particular user many times.
+  SmallPtrSet<const Value *, 32> Visited;
+  for (const Value *TheUser : GV.materialized_users())
+    forEachInstructionAndFunctionUser(
+        TheUser, Visited,
+        [&](const Instruction *I) {
+          Assert(I->getParent() && I->getParent()->getParent(),
+                 "Global is referenced by parentless instruction!", &GV,
+                 GV.getParent(), I);
+          Assert(I->getParent()->getParent()->getParent() == GV.getParent(),
+                 "Global is referenced in a different module!", &GV,
+                 GV.getParent(), I, I->getParent()->getParent(),
+                 I->getParent()->getParent()->getParent());
+        },
+        [&](const Function *F) {
+          Assert(F->getParent() == GV.getParent(),
+                 "Global is used by function in a different module", &GV,
+                 GV.getParent(), F, F->getParent());
+        });
 }
 
 void Verifier::visitGlobalVariable(const GlobalVariable &GV) {
Index: unittests/IR/VerifierTest.cpp
===================================================================
--- unittests/IR/VerifierTest.cpp
+++ unittests/IR/VerifierTest.cpp
@@ -64,7 +64,7 @@
   LLVMContext &C = getGlobalContext();
   Module M1("M1", C);
   Module M2("M2", C);
-  Module M3("M2", C);
+  Module M3("M3", C);
   FunctionType *FTy = FunctionType::get(Type::getInt32Ty(C), /*isVarArg=*/false);
   Function *F1 = cast<Function>(M1.getOrInsertFunction("foo1", FTy));
   Function *F2 = cast<Function>(M2.getOrInsertFunction("foo2", FTy));
@@ -86,7 +86,21 @@
 
   std::string Error;
   raw_string_ostream ErrorOS(Error);
-  EXPECT_FALSE(verifyModule(M2, &ErrorOS));
+  EXPECT_TRUE(verifyModule(M2, &ErrorOS));
+  EXPECT_TRUE(StringRef(ErrorOS.str())
+                  .equals("Global is used by function in a different module\n"
+                          "i32 ()* @foo2\n"
+                          "; ModuleID = 'M2'\n"
+                          "i32 ()* @foo3\n"
+                          "; ModuleID = 'M3'\n"
+                          "Global is referenced in a different module!\n"
+                          "i32 ()* @foo2\n"
+                          "; ModuleID = 'M2'\n"
+                          "  %call = call i32 @foo2()\n"
+                          "i32 ()* @foo1\n"
+                          "; ModuleID = 'M1'\n"));
+
+  Error.clear();
   EXPECT_TRUE(verifyModule(M1, &ErrorOS));
   EXPECT_TRUE(StringRef(ErrorOS.str()).equals(
       "Referencing function in another module!\n"