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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130756 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/DIBuilder.cpp

@@ -51,6 +51,10 @@ void DIBuilder::createCompileUnit(unsigned Lang, StringRef Filename,
     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