use ref to avoid copy in range for-loop

Use big obj copy in range for-loop will call copy constructor every time,
which can be avoided by use ref instead.

Reviewed By: skan

Differential Revision: https://reviews.llvm.org/D150024

Author: XinWang10

llvm/include/llvm/MC/MCParser/MCAsmParser.h

@@ -236,7 +236,7 @@ class MCAsmParser {
 
   bool printPendingErrors() {
     bool rv = !PendingErrors.empty();
-    for (auto Err : PendingErrors) {
+    for (auto &Err : PendingErrors) {
       printError(Err.Loc, Twine(Err.Msg), Err.Range);
     }
     PendingErrors.clear();

llvm/lib/CodeGen/LiveDebugValues/VarLocBasedImpl.cpp

@@ -1312,7 +1312,7 @@ void VarLocBasedLDV::cleanupEntryValueTransfers(
     return;
 
   auto TransRange = EntryValTransfers.equal_range(TRInst);
-  for (auto TDPair : llvm::make_range(TransRange.first, TransRange.second)) {
+  for (auto &TDPair : llvm::make_range(TransRange.first, TransRange.second)) {
     const VarLoc &EmittedEV = VarLocIDs[TDPair.second];
     if (std::tie(EntryVL.Var, EntryVL.Locs[0].Value.RegNo, EntryVL.Expr) ==
         std::tie(EmittedEV.Var, EmittedEV.Locs[0].Value.RegNo,

llvm/lib/CodeGen/MIRParser/MIRParser.cpp

@@ -402,7 +402,7 @@ bool MIRParserImpl::initializeCallSiteInfo(
   MachineFunction &MF = PFS.MF;
   SMDiagnostic Error;
   const LLVMTargetMachine &TM = MF.getTarget();
-  for (auto YamlCSInfo : YamlMF.CallSitesInfo) {
+  for (auto &YamlCSInfo : YamlMF.CallSitesInfo) {
     yaml::CallSiteInfo::MachineInstrLoc MILoc = YamlCSInfo.CallLocation;
     if (MILoc.BlockNum >= MF.size())
       return error(Twine(MF.getName()) +

llvm/lib/ObjectYAML/MachOEmitter.cpp

@@ -426,7 +426,7 @@ void MachOWriter::writeRelocations(raw_ostream &OS) {
 void MachOWriter::writeBindOpcodes(
     raw_ostream &OS, std::vector<MachOYAML::BindOpcode> &BindOpcodes) {
 
-  for (auto Opcode : BindOpcodes) {
+  for (auto &Opcode : BindOpcodes) {
     uint8_t OpByte = Opcode.Opcode | Opcode.Imm;
     OS.write(reinterpret_cast<char *>(&OpByte), 1);
     for (auto Data : Opcode.ULEBExtraData) {

llvm/utils/TableGen/GlobalISel/GIMatchTree.cpp

@@ -733,7 +733,7 @@ void GIMatchTreeVRegDefPartitioner::applyForPartition(
   NewInstrID = SubBuilder.allocInstrID();
 
   GIMatchTreeBuilder::LeafVec &NewLeaves = SubBuilder.getPossibleLeaves();
-  for (const auto I : zip(NewLeaves, TraversedEdgesByNewLeaves)) {
+  for (const auto &I : zip(NewLeaves, TraversedEdgesByNewLeaves)) {
     auto &Leaf = std::get<0>(I);
     auto &TraversedEdgesForLeaf = std::get<1>(I);
     GIMatchTreeInstrInfo *InstrInfo = Leaf.getInstrInfo(InstrID);