Index: llvm/trunk/lib/IR/Verifier.cpp
===================================================================
--- llvm/trunk/lib/IR/Verifier.cpp
+++ llvm/trunk/lib/IR/Verifier.cpp
@@ -462,6 +462,18 @@
   InstVisitor<Verifier>::visit(I);
 }
 
+// Helper to recursively iterate over indirect users. By
+// returning false, the callback can ask to stop recursing
+// further.
+static void forEachUser(const Value *User,
+                        SmallPtrSet<const Value *, 32> &Visited,
+                        llvm::function_ref<bool(const Value *)> Callback) {
+  if (!Visited.insert(User).second)
+    return;
+  for (const Value *TheNextUser : User->users())
+    if (Callback(TheNextUser))
+      forEachUser(TheNextUser, Visited, Callback);
+}
 
 void Verifier::visitGlobalValue(const GlobalValue &GV) {
   Assert(!GV.isDeclaration() || GV.hasExternalLinkage() ||
@@ -481,6 +493,30 @@
 
   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;
+  forEachUser(&GV, Visited, [&](const Value *V) -> bool {
+    if (const Instruction *I = dyn_cast<Instruction>(V)) {
+      if (!I->getParent() || !I->getParent()->getParent())
+        CheckFailed("Global is referenced by parentless instruction!", &GV,
+                    M, I);
+      else if (I->getParent()->getParent()->getParent() != M)
+        CheckFailed("Global is referenced in a different module!", &GV,
+                    M, I, I->getParent()->getParent(),
+                    I->getParent()->getParent()->getParent());
+      return false;
+    } else if (const Function *F = dyn_cast<Function>(V)) {
+      if (F->getParent() != M)
+        CheckFailed("Global is used by function in a different module", &GV,
+                    M, F, F->getParent());
+      return false;
+    }
+    return true;
+  });
 }
 
 void Verifier::visitGlobalVariable(const GlobalVariable &GV) {
Index: llvm/trunk/unittests/IR/VerifierTest.cpp
===================================================================
--- llvm/trunk/unittests/IR/VerifierTest.cpp
+++ llvm/trunk/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"