[Target] Prevent copying in loop variables (NFC)

/llvm-project/llvm/lib/Target/ARM/ARMISelLowering.cpp:2769:19: error: loop variable '[Reg, N]' creates a copy from type 'std::pair<unsigned int, llvm::SDValue> const' [-Werror,-Wrange-loop-construct]
  for (const auto [Reg, N] : RegsToPass) {
                  ^
/llvm-project/llvm/lib/Target/ARM/ARMISelLowering.cpp:2769:8: note: use reference type 'std::pair<unsigned int, llvm::SDValue> const &' to prevent copying
  for (const auto [Reg, N] : RegsToPass) {
       ^~~~~~~~~~~~~~~~~~~~~
                  &
/llvm-project/llvm/lib/Target/ARM/ARMISelLowering.cpp:2954:19: error: loop variable '[Reg, N]' creates a copy from type 'std::pair<unsigned int, llvm::SDValue> const' [-Werror,-Wrange-loop-construct]
  for (const auto [Reg, N] : RegsToPass)
                  ^
/llvm-project/llvm/lib/Target/ARM/ARMISelLowering.cpp:2954:8: note: use reference type 'std::pair<unsigned int, llvm::SDValue> const &' to prevent copying
  for (const auto [Reg, N] : RegsToPass)
       ^~~~~~~~~~~~~~~~~~~~~
                  &
2 errors generated.

Author: DamonFool

llvm/lib/Target/ARM/ARMFrameLowering.cpp

@@ -1701,7 +1701,7 @@ void ARMFrameLowering::emitPushInst(MachineBasicBlock &MBB,
                                     .addReg(ARM::SP)
                                     .setMIFlags(MachineInstr::FrameSetup)
                                     .add(predOps(ARMCC::AL));
-      for (const auto [Reg, Kill] : Regs)
+      for (const auto &[Reg, Kill] : Regs)
         MIB.addReg(Reg, getKillRegState(Kill));
     } else if (Regs.size() == 1) {
       BuildMI(MBB, MI, DL, TII.get(StrOpc), ARM::SP)

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -2766,7 +2766,7 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   // Build a sequence of copy-to-reg nodes chained together with token chain
   // and flag operands which copy the outgoing args into the appropriate regs.
   SDValue InGlue;
-  for (const auto [Reg, N] : RegsToPass) {
+  for (const auto &[Reg, N] : RegsToPass) {
     Chain = DAG.getCopyToReg(Chain, dl, Reg, N, InGlue);
     InGlue = Chain.getValue(1);
   }
@@ -2951,7 +2951,7 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
 
   // Add argument registers to the end of the list so that they are known live
   // into the call.
-  for (const auto [Reg, N] : RegsToPass)
+  for (const auto &[Reg, N] : RegsToPass)
     Ops.push_back(DAG.getRegister(Reg, N.getValueType()));
 
   // Add a register mask operand representing the call-preserved registers.

llvm/lib/Target/X86/X86ISelLoweringCall.cpp

@@ -2421,7 +2421,7 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   // Build a sequence of copy-to-reg nodes chained together with token chain
   // and glue operands which copy the outgoing args into registers.
   SDValue InGlue;
-  for (const auto [Reg, N] : RegsToPass) {
+  for (const auto &[Reg, N] : RegsToPass) {
     Chain = DAG.getCopyToReg(Chain, dl, Reg, N, InGlue);
     InGlue = Chain.getValue(1);
   }
@@ -2461,7 +2461,7 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
 
   // Add argument registers to the end of the list so that they are known live
   // into the call.
-  for (const auto [Reg, N] : RegsToPass)
+  for (const auto &[Reg, N] : RegsToPass)
     Ops.push_back(DAG.getRegister(Reg, N.getValueType()));
 
   // Add a register mask operand representing the call-preserved registers.