diff --git a/mlir/examples/toy/Ch2/mlir/MLIRGen.cpp b/mlir/examples/toy/Ch2/mlir/MLIRGen.cpp
--- a/mlir/examples/toy/Ch2/mlir/MLIRGen.cpp
+++ b/mlir/examples/toy/Ch2/mlir/MLIRGen.cpp
@@ -136,7 +136,7 @@
     auto protoArgs = funcAST.getProto()->getArgs();
 
     // Declare all the function arguments in the symbol table.
-    for (const auto &name_value :
+    for (const auto name_value :
          llvm::zip(protoArgs, entryBlock.getArguments())) {
       if (failed(declare(std::get<0>(name_value)->getName(),
                          std::get<1>(name_value))))
diff --git a/mlir/examples/toy/Ch3/mlir/MLIRGen.cpp b/mlir/examples/toy/Ch3/mlir/MLIRGen.cpp
--- a/mlir/examples/toy/Ch3/mlir/MLIRGen.cpp
+++ b/mlir/examples/toy/Ch3/mlir/MLIRGen.cpp
@@ -136,7 +136,7 @@
     auto protoArgs = funcAST.getProto()->getArgs();
 
     // Declare all the function arguments in the symbol table.
-    for (const auto &name_value :
+    for (const auto name_value :
          llvm::zip(protoArgs, entryBlock.getArguments())) {
       if (failed(declare(std::get<0>(name_value)->getName(),
                          std::get<1>(name_value))))
diff --git a/mlir/examples/toy/Ch4/mlir/MLIRGen.cpp b/mlir/examples/toy/Ch4/mlir/MLIRGen.cpp
--- a/mlir/examples/toy/Ch4/mlir/MLIRGen.cpp
+++ b/mlir/examples/toy/Ch4/mlir/MLIRGen.cpp
@@ -136,7 +136,7 @@
     auto protoArgs = funcAST.getProto()->getArgs();
 
     // Declare all the function arguments in the symbol table.
-    for (const auto &name_value :
+    for (const auto name_value :
          llvm::zip(protoArgs, entryBlock.getArguments())) {
       if (failed(declare(std::get<0>(name_value)->getName(),
                          std::get<1>(name_value))))
diff --git a/mlir/examples/toy/Ch5/mlir/MLIRGen.cpp b/mlir/examples/toy/Ch5/mlir/MLIRGen.cpp
--- a/mlir/examples/toy/Ch5/mlir/MLIRGen.cpp
+++ b/mlir/examples/toy/Ch5/mlir/MLIRGen.cpp
@@ -136,7 +136,7 @@
     auto protoArgs = funcAST.getProto()->getArgs();
 
     // Declare all the function arguments in the symbol table.
-    for (const auto &name_value :
+    for (const auto name_value :
          llvm::zip(protoArgs, entryBlock.getArguments())) {
       if (failed(declare(std::get<0>(name_value)->getName(),
                          std::get<1>(name_value))))
diff --git a/mlir/examples/toy/Ch6/mlir/MLIRGen.cpp b/mlir/examples/toy/Ch6/mlir/MLIRGen.cpp
--- a/mlir/examples/toy/Ch6/mlir/MLIRGen.cpp
+++ b/mlir/examples/toy/Ch6/mlir/MLIRGen.cpp
@@ -136,7 +136,7 @@
     auto protoArgs = funcAST.getProto()->getArgs();
 
     // Declare all the function arguments in the symbol table.
-    for (const auto &name_value :
+    for (const auto name_value :
          llvm::zip(protoArgs, entryBlock.getArguments())) {
       if (failed(declare(std::get<0>(name_value)->getName(),
                          std::get<1>(name_value))))
diff --git a/mlir/examples/toy/Ch7/mlir/Dialect.cpp b/mlir/examples/toy/Ch7/mlir/Dialect.cpp
--- a/mlir/examples/toy/Ch7/mlir/Dialect.cpp
+++ b/mlir/examples/toy/Ch7/mlir/Dialect.cpp
@@ -244,7 +244,7 @@
 
   // Check that each of the elements are valid.
   llvm::ArrayRef<mlir::Attribute> attrElementValues = attrValue.getValue();
-  for (const auto &it : llvm::zip(resultElementTypes, attrElementValues))
+  for (const auto it : llvm::zip(resultElementTypes, attrElementValues))
     if (failed(verifyConstantForType(std::get<0>(it), std::get<1>(it), op)))
       return mlir::failure();
   return mlir::success();
diff --git a/mlir/examples/toy/Ch7/mlir/MLIRGen.cpp b/mlir/examples/toy/Ch7/mlir/MLIRGen.cpp
--- a/mlir/examples/toy/Ch7/mlir/MLIRGen.cpp
+++ b/mlir/examples/toy/Ch7/mlir/MLIRGen.cpp
@@ -190,7 +190,7 @@
     auto protoArgs = funcAST.getProto()->getArgs();
 
     // Declare all the function arguments in the symbol table.
-    for (const auto &name_value :
+    for (const auto name_value :
          llvm::zip(protoArgs, entryBlock.getArguments())) {
       if (failed(declare(*std::get<0>(name_value), std::get<1>(name_value))))
         return nullptr;
diff --git a/mlir/tools/mlir-tblgen/TypeDefGen.cpp b/mlir/tools/mlir-tblgen/TypeDefGen.cpp
--- a/mlir/tools/mlir-tblgen/TypeDefGen.cpp
+++ b/mlir/tools/mlir-tblgen/TypeDefGen.cpp
@@ -47,7 +47,7 @@
       return;
 
     llvm::SmallSet<Dialect, 4> dialects;
-    for (const TypeDef &typeDef : defs)
+    for (const TypeDef typeDef : defs)
       dialects.insert(typeDef.getDialect());
     if (dialects.size() != 1)
       llvm::PrintFatalError("TypeDefs belonging to more than one dialect. Must "
@@ -61,7 +61,7 @@
                           "generate types via '--typedefs-dialect'.");
   }
 
-  for (const TypeDef &typeDef : defs)
+  for (const TypeDef typeDef : defs)
     if (typeDef.getDialect().getName().equals(dialectName))
       typeDefs.push_back(typeDef);
 }