Bring back "Assert that we have all use/users in the getters."

This reverts commit r257751, bringing back r256105.

The problem the assert found was fixed in r257915.

Original commit message:

Assert that we have all use/users in the getters.

An error that is pretty easy to make is to use the lazy bitcode reader
and then do something like

if (V.use_empty())

The problem is that uses in unmaterialized functions are not accounted
for.

This patch adds asserts that all uses are known.

llvm-svn: 257920

llvm/lib/IR/Verifier.cpp

@@ -470,7 +470,7 @@ static void forEachUser(const Value *User,
                         llvm::function_ref<bool(const Value *)> Callback) {
   if (!Visited.insert(User).second)
     return;
-  for (const Value *TheNextUser : User->users())
+  for (const Value *TheNextUser : User->materialized_users())
     if (Callback(TheNextUser))
       forEachUser(TheNextUser, Visited, Callback);
 }
@@ -1944,7 +1944,9 @@ void Verifier::visitFunction(const Function &F) {
 
   // If this function is actually an intrinsic, verify that it is only used in
   // direct call/invokes, never having its "address taken".
-  if (F.getIntrinsicID()) {
+  // Only do this if the module is materialized, otherwise we don't have all the
+  // uses.
+  if (F.getIntrinsicID() && F.getParent()->isMaterialized()) {
     const User *U;
     if (F.hasAddressTaken(&U))
       Assert(0, "Invalid user of intrinsic instruction!", U);