Run clang-tidy's performance-unnecessary-copy-initialization over LLVM.

No functionality change intended.

llvm-svn: 272516
diff --git a/llvm/utils/TableGen/DFAPacketizerEmitter.cpp b/llvm/utils/TableGen/DFAPacketizerEmitter.cpp
index 0e74a2f..e31caaf 100644
--- a/llvm/utils/TableGen/DFAPacketizerEmitter.cpp
+++ b/llvm/utils/TableGen/DFAPacketizerEmitter.cpp
@@ -709,7 +709,7 @@
       Record *ComboFunc = FuncData->getValueAsDef("TheComboFunc");
       const std::vector<Record*> &FuncList =
                                    FuncData->getValueAsListOfDefs("FuncList");
-      std::string ComboFuncName = ComboFunc->getName();
+      const std::string &ComboFuncName = ComboFunc->getName();
       unsigned ComboBit = FUNameToBitsMap[ComboFuncName];
       unsigned ComboResources = ComboBit;
       DEBUG(dbgs() << "      combo: " << ComboFuncName