Clarify that llvm.used can contain aliases.

Also add a check for llvm.used in the verifier and simplify clients now that
they can assume they have a ConstantArray.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180019 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineModuleInfo.cpp b/lib/CodeGen/MachineModuleInfo.cpp
index 0ea9ae0..8af9d05 100644
--- a/lib/CodeGen/MachineModuleInfo.cpp
+++ b/lib/CodeGen/MachineModuleInfo.cpp
@@ -326,8 +326,7 @@
   if (!GV || !GV->hasInitializer()) return;
 
   // Should be an array of 'i8*'.
-  const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer());
-  if (InitList == 0) return;
+  const ConstantArray *InitList = cast<ConstantArray>(GV->getInitializer());
 
   for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
     if (const Function *F =