Replace copy with a reference. (#87975)

Author: MalaySanghi

llvm/lib/CodeGen/MachinePipeliner.cpp

@@ -1247,7 +1247,7 @@ class HighRegisterPressureDetector {
     for (auto &MI : *OrigMBB) {
       if (MI.isDebugInstr())
         continue;
-      for (auto Use : ROMap[&MI].Uses) {
+      for (auto &Use : ROMap[&MI].Uses) {
         auto Reg = Use.RegUnit;
         // Ignore the variable that appears only on one side of phi instruction
         // because it's used only at the first iteration.
@@ -1345,7 +1345,7 @@ class HighRegisterPressureDetector {
 
     DenseMap<Register, MachineInstr *> LastUseMI;
     for (MachineInstr *MI : llvm::reverse(OrderedInsts)) {
-      for (auto Use : ROMap.find(MI)->getSecond().Uses) {
+      for (auto &Use : ROMap.find(MI)->getSecond().Uses) {
         auto Reg = Use.RegUnit;
         if (!TargetRegs.contains(Reg))
           continue;