diff --git a/llvm/include/llvm/CodeGen/TargetInstrInfo.h b/llvm/include/llvm/CodeGen/TargetInstrInfo.h
--- a/llvm/include/llvm/CodeGen/TargetInstrInfo.h
+++ b/llvm/include/llvm/CodeGen/TargetInstrInfo.h
@@ -1148,8 +1148,8 @@
   /// Return true if target supports reassociation of instructions in machine
   /// combiner pass to reduce register pressure for a given BB.
   virtual bool
-  shouldReduceRegisterPressure(MachineBasicBlock *MBB,
-                               RegisterClassInfo *RegClassInfo) const {
+  shouldReduceRegisterPressure(const MachineBasicBlock *MBB,
+                               const RegisterClassInfo *RegClassInfo) const {
     return false;
   }
 
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.h b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.h
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
@@ -471,9 +471,9 @@
   /// when the register pressure is high for one BB.
   /// Return true if register pressure for \p MBB is high and ABI is supported
   /// to reduce register pressure. Otherwise return false.
-  bool
-  shouldReduceRegisterPressure(MachineBasicBlock *MBB,
-                               RegisterClassInfo *RegClassInfo) const override;
+  bool shouldReduceRegisterPressure(
+      const MachineBasicBlock *MBB,
+      const RegisterClassInfo *RegClassInfo) const override;
 
   /// Fixup the placeholders we put in genAlternativeCodeSequence() for
   /// MachineCombiner.
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -613,7 +613,7 @@
 }
 
 bool PPCInstrInfo::shouldReduceRegisterPressure(
-    MachineBasicBlock *MBB, RegisterClassInfo *RegClassInfo) const {
+    const MachineBasicBlock *MBB, const RegisterClassInfo *RegClassInfo) const {
 
   if (!EnableFMARegPressureReduction)
     return false;
@@ -635,10 +635,11 @@
     return false;
 
   const TargetRegisterInfo *TRI = &getRegisterInfo();
-  MachineFunction *MF = MBB->getParent();
-  MachineRegisterInfo *MRI = &MF->getRegInfo();
+  const MachineFunction *MF = MBB->getParent();
+  const MachineRegisterInfo *MRI = &MF->getRegInfo();
 
-  auto GetMBBPressure = [&](MachineBasicBlock *MBB) -> std::vector<unsigned> {
+  auto GetMBBPressure =
+      [&](const MachineBasicBlock *MBB) -> std::vector<unsigned> {
     RegionPressure Pressure;
     RegPressureTracker RPTracker(Pressure);
 
@@ -646,10 +647,7 @@
     RPTracker.init(MBB->getParent(), RegClassInfo, nullptr, MBB, MBB->end(),
                    /*TrackLaneMasks*/ false, /*TrackUntiedDefs=*/true);
 
-    for (MachineBasicBlock::iterator MII = MBB->instr_end(),
-                                     MIE = MBB->instr_begin();
-         MII != MIE; --MII) {
-      MachineInstr &MI = *std::prev(MII);
+    for (const auto &MI : reverse(*MBB)) {
       if (MI.isDebugValue() || MI.isDebugLabel())
         continue;
       RegisterOperands RegOpers;