[Target] Prevent copying in loop variables (NFC)

/data/llvm-project/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp:2390:19: 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) {
                  ^
/data/llvm-project/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp:2390:8: note: use reference type 'std::pair<unsigned int, llvm::SDValue> const &' to prevent copying
  for (const auto [Reg, N] : RegsToPass) {
       ^~~~~~~~~~~~~~~~~~~~~
                  &
/data/llvm-project/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp:2402:19: 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)
                  ^
/data/llvm-project/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp:2402:8: 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/Sparc/SparcISelLowering.cpp

@@ -1044,7 +1044,7 @@ SparcTargetLowering::LowerCall_32(TargetLowering::CallLoweringInfo &CLI,
   // The InGlue in necessary since all emitted instructions must be
   // stuck together.
   SDValue InGlue;
-  for (const auto [OrigReg, N] : RegsToPass) {
+  for (const auto &[OrigReg, N] : RegsToPass) {
     Register Reg = isTailCall ? OrigReg : toCallerWindow(OrigReg);
     Chain = DAG.getCopyToReg(Chain, dl, Reg, N, InGlue);
     InGlue = Chain.getValue(1);
@@ -1067,7 +1067,7 @@ SparcTargetLowering::LowerCall_32(TargetLowering::CallLoweringInfo &CLI,
   Ops.push_back(Callee);
   if (hasStructRetAttr)
     Ops.push_back(DAG.getTargetConstant(SRetArgSize, dl, MVT::i32));
-  for (const auto [OrigReg, N] : RegsToPass) {
+  for (const auto &[OrigReg, N] : RegsToPass) {
     Register Reg = isTailCall ? OrigReg : toCallerWindow(OrigReg);
     Ops.push_back(DAG.getRegister(Reg, N.getValueType()));
   }
@@ -1371,7 +1371,7 @@ SparcTargetLowering::LowerCall_64(TargetLowering::CallLoweringInfo &CLI,
   // necessary since all emitted instructions must be stuck together in order
   // to pass the live physical 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);
   }
@@ -1390,7 +1390,7 @@ SparcTargetLowering::LowerCall_64(TargetLowering::CallLoweringInfo &CLI,
   SmallVector<SDValue, 8> Ops;
   Ops.push_back(Chain);
   Ops.push_back(Callee);
-  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/SystemZ/SystemZISelLowering.cpp

@@ -2387,7 +2387,7 @@ SystemZTargetLowering::LowerCall(CallLoweringInfo &CLI,
   }
 
   // Build a sequence of copy-to-reg nodes, chained and glued together.
-  for (const auto [Reg, N] : RegsToPass) {
+  for (const auto &[Reg, N] : RegsToPass) {
     Chain = DAG.getCopyToReg(Chain, DL, Reg, N, Glue);
     Glue = Chain.getValue(1);
   }
@@ -2399,7 +2399,7 @@ SystemZTargetLowering::LowerCall(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.