Use llvm.dbg.cu  named metadata to collect compile units.

llvm-svn: 130756
diff --git a/llvm/lib/Analysis/DIBuilder.cpp b/llvm/lib/Analysis/DIBuilder.cpp
index dc98c9e..1375e49 100644
--- a/llvm/lib/Analysis/DIBuilder.cpp
+++ b/llvm/lib/Analysis/DIBuilder.cpp
@@ -51,6 +51,10 @@
     ConstantInt::get(Type::getInt32Ty(VMContext), RunTimeVer)
   };
   TheCU = DICompileUnit(MDNode::get(VMContext, Elts));
+
+  // Create a named metadata so that it is easier to find cu in a module.
+  NamedMDNode *NMD = M.getOrInsertNamedMetadata("llvm.dbg.cu");
+  NMD->addOperand(TheCU);
 }
 
 /// createFile - Create a file descriptor to hold debugging information