diff --git a/llvm/lib/CodeGen/MachineLoopUtils.cpp b/llvm/lib/CodeGen/MachineLoopUtils.cpp
new file mode 100644
index 0000000..e074b76
--- /dev/null
+++ b/llvm/lib/CodeGen/MachineLoopUtils.cpp
@@ -0,0 +1,132 @@
+//=- MachineLoopUtils.cpp - Functions for manipulating loops ----------------=//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/MachineLoopUtils.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+using namespace llvm;
+
+namespace {
+// MI's parent and BB are clones of each other. Find the equivalent copy of MI
+// in BB.
+MachineInstr &findEquivalentInstruction(MachineInstr &MI,
+                                        MachineBasicBlock *BB) {
+  MachineBasicBlock *PB = MI.getParent();
+  unsigned Offset = std::distance(PB->instr_begin(), MachineBasicBlock::instr_iterator(MI));
+  return *std::next(BB->instr_begin(), Offset);
+}
+} // namespace
+
+MachineBasicBlock *llvm::PeelSingleBlockLoop(LoopPeelDirection Direction,
+                                             MachineBasicBlock *Loop,
+                                             MachineRegisterInfo &MRI,
+                                             const TargetInstrInfo *TII) {
+  MachineFunction &MF = *Loop->getParent();
+  MachineBasicBlock *Preheader = *Loop->pred_begin();
+  if (Preheader == Loop)
+    Preheader = *std::next(Loop->pred_begin());
+  MachineBasicBlock *Exit = *Loop->succ_begin();
+  if (Exit == Loop)
+    Exit = *std::next(Loop->succ_begin());
+
+  MachineBasicBlock *NewBB = MF.CreateMachineBasicBlock(Loop->getBasicBlock());
+  if (Direction == LPD_Front)
+    MF.insert(Loop->getIterator(), NewBB);
+  else
+    MF.insert(std::next(Loop->getIterator()), NewBB);
+
+  // FIXME: Add DenseMapInfo trait for Register so we can use it as a key.
+  DenseMap<unsigned, Register> Remaps;
+  auto InsertPt = NewBB->end();
+  for (MachineInstr &MI : *Loop) {
+    MachineInstr *NewMI = MF.CloneMachineInstr(&MI);
+    NewBB->insert(InsertPt, NewMI);
+    for (MachineOperand &MO : NewMI->defs()) {
+      Register OrigR = MO.getReg();
+      if (OrigR.isPhysical())
+        continue;
+      Register &R = Remaps[OrigR];
+      R = MRI.createVirtualRegister(MRI.getRegClass(OrigR));
+      MO.setReg(R);
+
+      if (Direction == LPD_Back) {
+        // Replace all uses outside the original loop with the new register.
+        // FIXME: is the use_iterator stable enough to mutate register uses
+        // while iterating?
+        SmallVector<MachineOperand *, 4> Uses;
+        for (auto &Use : MRI.use_operands(OrigR))
+          if (Use.getParent()->getParent() != Loop)
+            Uses.push_back(&Use);
+        for (auto *Use : Uses) {
+          MRI.constrainRegClass(R, MRI.getRegClass(Use->getReg()));
+          Use->setReg(R);
+        }
+      }
+    }
+  }
+
+  for (auto I = NewBB->getFirstNonPHI(); I != NewBB->end(); ++I)
+    for (MachineOperand &MO : I->uses())
+      if (MO.isReg() && Remaps.count(MO.getReg()))
+        MO.setReg(Remaps[MO.getReg()]);
+
+  for (auto I = NewBB->begin(); I->isPHI(); ++I) {
+    MachineInstr &MI = *I;
+    unsigned LoopRegIdx = 3, InitRegIdx = 1;
+    if (MI.getOperand(2).getMBB() != Preheader)
+      std::swap(LoopRegIdx, InitRegIdx);
+    MachineInstr &OrigPhi = findEquivalentInstruction(MI, Loop);
+    assert(OrigPhi.isPHI());
+    if (Direction == LPD_Front) {
+      // When peeling front, we are only left with the initial value from the
+      // preheader.
+      Register R = MI.getOperand(LoopRegIdx).getReg();
+      if (Remaps.count(R))
+        R = Remaps[R];
+      OrigPhi.getOperand(InitRegIdx).setReg(R);
+      MI.RemoveOperand(LoopRegIdx + 1);
+      MI.RemoveOperand(LoopRegIdx + 0);
+    } else {
+      // When peeling back, the initial value is the loop-carried value from
+      // the original loop.
+      Register LoopReg = OrigPhi.getOperand(LoopRegIdx).getReg();
+      MI.getOperand(LoopRegIdx).setReg(LoopReg);
+      MI.RemoveOperand(InitRegIdx + 1);
+      MI.RemoveOperand(InitRegIdx + 0);
+    }
+  }
+
+  DebugLoc DL;
+  if (Direction == LPD_Front) {
+    Preheader->replaceSuccessor(Loop, NewBB);
+    NewBB->addSuccessor(Loop);
+    Loop->replacePhiUsesWith(Preheader, NewBB);
+    if (TII->removeBranch(*Preheader) > 0)
+      TII->insertBranch(*Preheader, NewBB, nullptr, {}, DL);
+    TII->removeBranch(*NewBB);
+    TII->insertBranch(*NewBB, Loop, nullptr, {}, DL);
+  } else {
+    Loop->replaceSuccessor(Exit, NewBB);
+    Exit->replacePhiUsesWith(Loop, NewBB);
+    NewBB->addSuccessor(Exit);
+
+    MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
+    SmallVector<MachineOperand, 4> Cond;
+    bool CanAnalyzeBr = !TII->analyzeBranch(*Loop, TBB, FBB, Cond);
+    (void)CanAnalyzeBr;
+    assert(CanAnalyzeBr && "Must be able to analyze the loop branch!");
+    TII->removeBranch(*Loop);
+    TII->insertBranch(*Loop, TBB == Exit ? NewBB : TBB,
+                      FBB == Exit ? NewBB : FBB, Cond, DL);
+    if (TII->removeBranch(*NewBB) > 0)
+      TII->insertBranch(*NewBB, Exit, nullptr, {}, DL);
+  }
+
+  return NewBB;
+}