[mlir] Apply ClangTidy performance finding

loop variable is copied but only used as const reference

Author: akuegel

mlir/tools/mlir-rewrite/mlir-rewrite.cpp

@@ -38,7 +38,7 @@ SMRange getOpRange(const OperationDefinition &op) {
   const char *startOp = op.scopeLoc.Start.getPointer();
   const char *endOp = op.scopeLoc.End.getPointer();
 
-  for (auto res : op.resultGroups) {
+  for (const auto &res : op.resultGroups) {
     SMRange range = res.definition.loc;
     startOp = std::min(startOp, range.Start.getPointer());
   }
@@ -317,7 +317,7 @@ static mlir::RewriterRegistration rewriteSimpleRename("simple-rename",
 
 // Rewriter that insert range markers.
 LogicalResult markRanges(RewritePad &rewriteState, raw_ostream &os) {
-  for (auto it : rewriteState.getOpDefs()) {
+  for (const auto &it : rewriteState.getOpDefs()) {
     auto [startOp, endOp] = getOpRange(it);
 
     rewriteState.insertText(startOp, "<");