diff --git a/clang/lib/AST/ODRHash.cpp b/clang/lib/AST/ODRHash.cpp
--- a/clang/lib/AST/ODRHash.cpp
+++ b/clang/lib/AST/ODRHash.cpp
@@ -594,7 +594,7 @@
 
   ID.AddInteger(Record->getNumBases());
   auto Bases = Record->bases();
-  for (auto Base : Bases) {
+  for (const auto &Base : Bases) {
     AddQualType(Base.getType());
     ID.AddInteger(Base.isVirtual());
     ID.AddInteger(Base.getAccessSpecifierAsWritten());
diff --git a/clang/lib/Basic/TargetID.cpp b/clang/lib/Basic/TargetID.cpp
--- a/clang/lib/Basic/TargetID.cpp
+++ b/clang/lib/Basic/TargetID.cpp
@@ -133,7 +133,7 @@
   std::map<const llvm::StringRef, bool> OrderedMap;
   for (const auto &F : Features)
     OrderedMap[F.first()] = F.second;
-  for (auto F : OrderedMap)
+  for (const auto &F : OrderedMap)
     TargetID = TargetID + ':' + F.first.str() + (F.second ? "+" : "-");
   return TargetID;
 }
diff --git a/clang/lib/Tooling/Syntax/Tokens.cpp b/clang/lib/Tooling/Syntax/Tokens.cpp
--- a/clang/lib/Tooling/Syntax/Tokens.cpp
+++ b/clang/lib/Tooling/Syntax/Tokens.cpp
@@ -986,7 +986,7 @@
   OS << "\n";
 
   std::vector<FileID> Keys;
-  for (auto F : Files)
+  for (const auto &F : Files)
     Keys.push_back(F.first);
   llvm::sort(Keys);