Add the PPCCTRLoops pass: a PPC machine-code-level optimization pass to form CTR-based loop branching code.

This pass is derived from the Hexagon HardwareLoops pass. The only significant enhancement over the Hexagon
pass is that PPCCTRLoops will also attempt to delete the replaced add and compare operations if they are
no longer otherwise used. Also, invalid preheader DebugLoc is not used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158204 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 679 insertions, 0 deletions

diff --git a/lib/Target/PowerPC/PPCCTRLoops.cpp b/lib/Target/PowerPC/PPCCTRLoops.cpp
new file mode 100644
index 0000000000..4671893c3e
--- /dev/null
+++ b/lib/Target/PowerPC/PPCCTRLoops.cpp
@@ -0,0 +1,679 @@
+//===-- PPCCTRLoops.cpp - Identify and generate CTR loops -----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass identifies loops where we can generate the PPC branch instructions
+// that decrement and test the count register (CTR) (bdnz and friends).
+// This pass is based on the HexagonHardwareLoops pass.
+//
+// The pattern that defines the induction variable can changed depending on
+// prior optimizations.  For example, the IndVarSimplify phase run by 'opt'
+// normalizes induction variables, and the Loop Strength Reduction pass
+// run by 'llc' may also make changes to the induction variable.
+// The pattern detected by this phase is due to running Strength Reduction.
+//
+// Criteria for CTR loops:
+//  - Countable loops (w/ ind. var for a trip count)
+//  - Assumes loops are normalized by IndVarSimplify
+//  - Try inner-most loops first
+//  - No nested CTR loops.
+//  - No function calls in loops.
+//
+//  Note: As with unconverted loops, PPCBranchSelector must be run after this
+//  pass in order to convert long-displacement jumps into jump pairs.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "ctrloops"
+#include "PPC.h"
+#include "PPCTargetMachine.h"
+#include "llvm/Constants.h"
+#include "llvm/PassSupport.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include <algorithm>
+
+using namespace llvm;
+
+STATISTIC(NumCTRLoops, "Number of loops converted to CTR loops");
+
+namespace {
+  class CountValue;
+  struct PPCCTRLoops : public MachineFunctionPass {
+    MachineLoopInfo       *MLI;
+    MachineRegisterInfo   *MRI;
+    const TargetInstrInfo *TII;
+
+  public:
+    static char ID;   // Pass identification, replacement for typeid
+
+    PPCCTRLoops() : MachineFunctionPass(ID) {}
+
+    virtual bool runOnMachineFunction(MachineFunction &MF);
+
+    const char *getPassName() const { return "PPC CTR Loops"; }
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+      AU.addRequired<MachineDominatorTree>();
+      AU.addPreserved<MachineDominatorTree>();
+      AU.addRequired<MachineLoopInfo>();
+      AU.addPreserved<MachineLoopInfo>();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+
+  private:
+    /// getCanonicalInductionVariable - Check to see if the loop has a canonical
+    /// induction variable.
+    /// Should be defined in MachineLoop. Based upon version in class Loop.
+    MachineInstr *getCanonicalInductionVariable(MachineLoop *L,
+                                                MachineInstr *&IOp) const;
+
+    /// getTripCount - Return a loop-invariant LLVM register indicating the
+    /// number of times the loop will be executed.  If the trip-count cannot
+    /// be determined, this return null.
+    CountValue *getTripCount(MachineLoop *L, bool &WordCmp,
+                             SmallVector<MachineInstr *, 2> &OldInsts) const;
+
+    /// isInductionOperation - Return true if the instruction matches the
+    /// pattern for an opertion that defines an induction variable.
+    bool isInductionOperation(const MachineInstr *MI, unsigned IVReg) const;
+
+    /// isInvalidOperation - Return true if the instruction is not valid within
+    /// a CTR loop.
+    bool isInvalidLoopOperation(const MachineInstr *MI) const;
+
+    /// containsInavlidInstruction - Return true if the loop contains an
+    /// instruction that inhibits using the CTR loop.
+    bool containsInvalidInstruction(MachineLoop *L) const;
+
+    /// converToCTRLoop - Given a loop, check if we can convert it to a
+    /// CTR loop.  If so, then perform the conversion and return true.
+    bool convertToCTRLoop(MachineLoop *L);
+
+    /// isDead - Return true if the instruction is now dead.
+    bool isDead(const MachineInstr *MI,
+                SmallVector<MachineInstr *, 1> &DeadPhis) const;
+
+    /// removeIfDead - Remove the instruction if it is now dead.
+    void removeIfDead(MachineInstr *MI);
+  };
+
+  char PPCCTRLoops::ID = 0;
+
+
+  // CountValue class - Abstraction for a trip count of a loop. A
+  // smaller vesrsion of the MachineOperand class without the concerns
+  // of changing the operand representation.
+  class CountValue {
+  public:
+    enum CountValueType {
+      CV_Register,
+      CV_Immediate
+    };
+  private:
+    CountValueType Kind;
+    union Values {
+      unsigned RegNum;
+      int64_t ImmVal;
+      Values(unsigned r) : RegNum(r) {}
+      Values(int64_t i) : ImmVal(i) {}
+    } Contents;
+    bool isNegative;
+
+  public:
+    CountValue(unsigned r, bool neg) : Kind(CV_Register), Contents(r),
+                                       isNegative(neg) {}
+    explicit CountValue(int64_t i) : Kind(CV_Immediate), Contents(i),
+                                     isNegative(i < 0) {}
+    CountValueType getType() const { return Kind; }
+    bool isReg() const { return Kind == CV_Register; }
+    bool isImm() const { return Kind == CV_Immediate; }
+    bool isNeg() const { return isNegative; }
+
+    unsigned getReg() const {
+      assert(isReg() && "Wrong CountValue accessor");
+      return Contents.RegNum;
+    }
+    void setReg(unsigned Val) {
+      Contents.RegNum = Val;
+    }
+    int64_t getImm() const {
+      assert(isImm() && "Wrong CountValue accessor");
+      if (isNegative) {
+        return -Contents.ImmVal;
+      }
+      return Contents.ImmVal;
+    }
+    void setImm(int64_t Val) {
+      Contents.ImmVal = Val;
+    }
+
+    void print(raw_ostream &OS, const TargetMachine *TM = 0) const {
+      if (isReg()) { OS << PrintReg(getReg()); }
+      if (isImm()) { OS << getImm(); }
+    }
+  };
+} // end anonymous namespace
+
+
+/// isCompareEquals - Returns true if the instruction is a compare equals
+/// instruction with an immediate operand.
+static bool isCompareEqualsImm(const MachineInstr *MI, bool &WordCmp) {
+  if (MI->getOpcode() == PPC::CMPWI || MI->getOpcode() == PPC::CMPLWI) {
+    WordCmp = true;
+    return true;
+  } else if (MI->getOpcode() == PPC::CMPDI || MI->getOpcode() == PPC::CMPLDI) {
+    WordCmp = false;
+    return true;
+  }
+
+  return false;
+}
+
+
+/// createPPCCTRLoops - Factory for creating
+/// the CTR loop phase.
+FunctionPass *llvm::createPPCCTRLoops() {
+  return new PPCCTRLoops();
+}
+
+
+bool PPCCTRLoops::runOnMachineFunction(MachineFunction &MF) {
+  DEBUG(dbgs() << "********* PPC CTR Loops *********\n");
+
+  bool Changed = false;
+
+  // get the loop information
+  MLI = &getAnalysis<MachineLoopInfo>();
+  // get the register information
+  MRI = &MF.getRegInfo();
+  // the target specific instructio info.
+  TII = MF.getTarget().getInstrInfo();
+
+  for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end();
+       I != E; ++I) {
+    MachineLoop *L = *I;
+    if (!L->getParentLoop()) {
+      Changed |= convertToCTRLoop(L);
+    }
+  }
+
+  return Changed;
+}
+
+/// getCanonicalInductionVariable - Check to see if the loop has a canonical
+/// induction variable. We check for a simple recurrence pattern - an
+/// integer recurrence that decrements by one each time through the loop and
+/// ends at zero.  If so, return the phi node that corresponds to it.
+///
+/// Based upon the similar code in LoopInfo except this code is specific to
+/// the machine.
+/// This method assumes that the IndVarSimplify pass has been run by 'opt'.
+///
+MachineInstr
+*PPCCTRLoops::getCanonicalInductionVariable(MachineLoop *L,
+                                            MachineInstr *&IOp) const {
+  MachineBasicBlock *TopMBB = L->getTopBlock();
+  MachineBasicBlock::pred_iterator PI = TopMBB->pred_begin();
+  assert(PI != TopMBB->pred_end() &&
+         "Loop must have more than one incoming edge!");
+  MachineBasicBlock *Backedge = *PI++;
+  if (PI == TopMBB->pred_end()) return 0;  // dead loop
+  MachineBasicBlock *Incoming = *PI++;
+  if (PI != TopMBB->pred_end()) return 0;  // multiple backedges?
+
+  // make sure there is one incoming and one backedge and determine which
+  // is which.
+  if (L->contains(Incoming)) {
+    if (L->contains(Backedge))
+      return 0;
+    std::swap(Incoming, Backedge);
+  } else if (!L->contains(Backedge))
+    return 0;
+
+  // Loop over all of the PHI nodes, looking for a canonical induction variable:
+  //   - The PHI node is "reg1 = PHI reg2, BB1, reg3, BB2".
+  //   - The recurrence comes from the backedge.
+  //   - the definition is an induction operatio.n
+  for (MachineBasicBlock::iterator I = TopMBB->begin(), E = TopMBB->end();
+       I != E && I->isPHI(); ++I) {
+    MachineInstr *MPhi = &*I;
+    unsigned DefReg = MPhi->getOperand(0).getReg();
+    for (unsigned i = 1; i != MPhi->getNumOperands(); i += 2) {
+      // Check each operand for the value from the backedge.
+      MachineBasicBlock *MBB = MPhi->getOperand(i+1).getMBB();
+      if (L->contains(MBB)) { // operands comes from the backedge
+        // Check if the definition is an induction operation.
+        MachineInstr *DI = MRI->getVRegDef(MPhi->getOperand(i).getReg());
+        if (isInductionOperation(DI, DefReg)) {
+          IOp = DI;
+          return MPhi;
+        }
+      }
+    }
+  }
+  return 0;
+}
+
+/// getTripCount - Return a loop-invariant LLVM value indicating the
+/// number of times the loop will be executed.  The trip count can
+/// be either a register or a constant value.  If the trip-count
+/// cannot be determined, this returns null.
+///
+/// We find the trip count from the phi instruction that defines the
+/// induction variable.  We follow the links to the CMP instruction
+/// to get the trip count.
+///
+/// Based upon getTripCount in LoopInfo.
+///
+CountValue *PPCCTRLoops::getTripCount(MachineLoop *L, bool &WordCmp,
+                           SmallVector<MachineInstr *, 2> &OldInsts) const {
+  // Check that the loop has a induction variable.
+  MachineInstr *IOp;
+  MachineInstr *IV_Inst = getCanonicalInductionVariable(L, IOp);
+  if (IV_Inst == 0) return 0;
+
+  // Canonical loops will end with a 'cmpwi/cmpdi cr, IV, Imm',
+  //  if Imm is 0, get the count from the PHI opnd
+  //  if Imm is -M, than M is the count
+  //  Otherwise, Imm is the count
+  MachineOperand *IV_Opnd;
+  const MachineOperand *InitialValue;
+  if (!L->contains(IV_Inst->getOperand(2).getMBB())) {
+    InitialValue = &IV_Inst->getOperand(1);
+    IV_Opnd = &IV_Inst->getOperand(3);
+  } else {
+    InitialValue = &IV_Inst->getOperand(3);
+    IV_Opnd = &IV_Inst->getOperand(1);
+  }
+
+  // Look for the cmp instruction to determine if we
+  // can get a useful trip count.  The trip count can
+  // be either a register or an immediate.  The location
+  // of the value depends upon the type (reg or imm).
+  while ((IV_Opnd = IV_Opnd->getNextOperandForReg())) {
+    MachineInstr *MI = IV_Opnd->getParent();
+    if (L->contains(MI) && isCompareEqualsImm(MI, WordCmp)) {
+      OldInsts.push_back(MI);
+      OldInsts.push_back(IOp);
+
+      const MachineOperand &MO = MI->getOperand(2);
+      assert(MO.isImm() && "IV Cmp Operand should be an immediate");
+      int64_t ImmVal = MO.getImm();
+
+      const MachineInstr *IV_DefInstr = MRI->getVRegDef(IV_Opnd->getReg());
+      assert(L->contains(IV_DefInstr->getParent()) &&
+             "IV definition should occurs in loop");
+      int64_t iv_value = IV_DefInstr->getOperand(2).getImm();
+
+      if (ImmVal == 0) {
+        // Make sure the induction variable changes by one on each iteration.
+        if (iv_value != 1 && iv_value != -1) {
+          return 0;
+        }
+        return new CountValue(InitialValue->getReg(), iv_value > 0);
+      } else {
+        assert(InitialValue->isReg() && "Expecting register for init value");
+        const MachineInstr *DefInstr = MRI->getVRegDef(InitialValue->getReg());
+
+        // Here we need to look for an immediate load (an li or lis/ori pair).
+        if (DefInstr && (DefInstr->getOpcode() == PPC::ORI8 ||
+                         DefInstr->getOpcode() == PPC::ORI)) {
+          int64_t start = DefInstr->getOperand(2).getImm();
+          const MachineInstr *DefInstr2 =
+            MRI->getVRegDef(DefInstr->getOperand(0).getReg());
+          if (DefInstr2 && (DefInstr2->getOpcode() == PPC::LIS8 ||
+                            DefInstr2->getOpcode() == PPC::LIS)) {
+            start |= DefInstr2->getOperand(1).getImm() << 16;
+
+            int64_t count = ImmVal - start;
+            if ((count % iv_value) != 0) {
+              return 0;
+            }
+            return new CountValue(count/iv_value);
+          }
+        } else if (DefInstr && (DefInstr->getOpcode() == PPC::LI8 ||
+                                DefInstr->getOpcode() == PPC::LI)) {
+          int64_t count = ImmVal - DefInstr->getOperand(1).getImm();
+          if ((count % iv_value) != 0) {
+            return 0;
+          }
+          return new CountValue(count/iv_value);
+        }
+      }
+    }
+  }
+  return 0;
+}
+
+/// isInductionOperation - return true if the operation is matches the
+/// pattern that defines an induction variable:
+///    addi iv, c
+///
+bool
+PPCCTRLoops::isInductionOperation(const MachineInstr *MI,
+                                           unsigned IVReg) const {
+  return ((MI->getOpcode() == PPC::ADDI || MI->getOpcode() == PPC::ADDI8) &&
+          MI->getOperand(1).getReg() == IVReg);
+}
+
+/// isInvalidOperation - Return true if the operation is invalid within
+/// CTR loop.
+bool
+PPCCTRLoops::isInvalidLoopOperation(const MachineInstr *MI) const {
+
+  // call is not allowed because the callee may use a CTR loop
+  if (MI->getDesc().isCall()) {
+    return true;
+  }
+  // check if the instruction defines a CTR loop register
+  // (this will also catch nested CTR loops)
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (MO.isReg() && MO.isDef() &&
+        (MO.getReg() == PPC::CTR || MO.getReg() == PPC::CTR8)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+/// containsInvalidInstruction - Return true if the loop contains
+/// an instruction that inhibits the use of the CTR loop function.
+///
+bool PPCCTRLoops::containsInvalidInstruction(MachineLoop *L) const {
+  const std::vector<MachineBasicBlock*> Blocks = L->getBlocks();
+  for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
+    MachineBasicBlock *MBB = Blocks[i];
+    for (MachineBasicBlock::iterator
+           MII = MBB->begin(), E = MBB->end(); MII != E; ++MII) {
+      const MachineInstr *MI = &*MII;
+      if (isInvalidLoopOperation(MI)) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+/// isDead returns true if the instruction is dead
+/// (this was essentially copied from DeadMachineInstructionElim::isDead, but
+/// with special cases for inline asm, physical registers and instructions with
+/// side effects removed)
+bool PPCCTRLoops::isDead(const MachineInstr *MI,
+                         SmallVector<MachineInstr *, 1> &DeadPhis) const {
+  // Examine each operand.
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (MO.isReg() && MO.isDef()) {
+      unsigned Reg = MO.getReg();
+      if (!MRI->use_nodbg_empty(Reg)) {
+        // This instruction has users, but if the only user is the phi node for the
+        // parent block, and the only use of that phi node is this instruction, then
+        // this instruction is dead: both it (and the phi node) can be removed.
+        MachineRegisterInfo::use_iterator I = MRI->use_begin(Reg);
+        if (llvm::next(I) == MRI->use_end() &&
+            I.getOperand().getParent()->isPHI()) {
+          MachineInstr *OnePhi = I.getOperand().getParent();
+
+          for (unsigned j = 0, f = OnePhi->getNumOperands(); j != f; ++j) {
+            const MachineOperand &OPO = OnePhi->getOperand(j);
+            if (OPO.isReg() && OPO.isDef()) {
+              unsigned OPReg = OPO.getReg();
+
+              MachineRegisterInfo::use_iterator nextJ;
+              for (MachineRegisterInfo::use_iterator J = MRI->use_begin(OPReg),
+                   E = MRI->use_end(); J!=E; J=nextJ) {
+                nextJ = llvm::next(J);
+                MachineOperand& Use = J.getOperand();
+                MachineInstr *UseMI = Use.getParent();
+
+                if (MI != UseMI) {
+                  // The phi node has a user that is not MI, bail...
+                  return false;
+                }
+              }
+            }
+          }
+
+          DeadPhis.push_back(OnePhi);
+        } else {
+          // This def has a non-debug use. Don't delete the instruction!
+          return false;
+        }
+      }
+    }
+  }
+
+  // If there are no defs with uses, the instruction is dead.
+  return true;
+}
+
+void PPCCTRLoops::removeIfDead(MachineInstr *MI) {
+  // This procedure was essentially copied from DeadMachineInstructionElim
+
+  SmallVector<MachineInstr *, 1> DeadPhis;
+  if (isDead(MI, DeadPhis)) {
+    DEBUG(dbgs() << "CTR looping will remove: " << *MI);
+
+    // It is possible that some DBG_VALUE instructions refer to this
+    // instruction.  Examine each def operand for such references;
+    // if found, mark the DBG_VALUE as undef (but don't delete it).
+    for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+      const MachineOperand &MO = MI->getOperand(i);
+      if (!MO.isReg() || !MO.isDef())
+        continue;
+      unsigned Reg = MO.getReg();
+      MachineRegisterInfo::use_iterator nextI;
+      for (MachineRegisterInfo::use_iterator I = MRI->use_begin(Reg),
+           E = MRI->use_end(); I!=E; I=nextI) {
+        nextI = llvm::next(I);  // I is invalidated by the setReg
+        MachineOperand& Use = I.getOperand();
+        MachineInstr *UseMI = Use.getParent();
+        if (UseMI==MI)
+          continue;
+        if (Use.isDebug()) // this might also be a instr -> phi -> instr case
+                           // which can also be removed.
+          UseMI->getOperand(0).setReg(0U);
+      }
+    }
+
+    MI->eraseFromParent();
+    for (unsigned i = 0; i < DeadPhis.size(); ++i) {
+      DeadPhis[i]->eraseFromParent();
+    }
+  }
+}
+
+/// converToCTRLoop - check if the loop is a candidate for
+/// converting to a CTR loop.  If so, then perform the
+/// transformation.
+///
+/// This function works on innermost loops first.  A loop can
+/// be converted if it is a counting loop; either a register
+/// value or an immediate.
+///
+/// The code makes several assumptions about the representation
+/// of the loop in llvm.
+bool PPCCTRLoops::convertToCTRLoop(MachineLoop *L) {
+  bool Changed = false;
+  // Process nested loops first.
+  for (MachineLoop::iterator I = L->begin(), E = L->end(); I != E; ++I) {
+    Changed |= convertToCTRLoop(*I);
+  }
+  // If a nested loop has been converted, then we can't convert this loop.
+  if (Changed) {
+    return Changed;
+  }
+
+  bool WordCmp;
+  SmallVector<MachineInstr *, 2> OldInsts;
+  // Are we able to determine the trip count for the loop?
+  CountValue *TripCount = getTripCount(L, WordCmp, OldInsts);
+  if (TripCount == 0) {
+    DEBUG(dbgs() << "failed to get trip count!\n");
+    return false;
+  }
+  // Does the loop contain any invalid instructions?
+  if (containsInvalidInstruction(L)) {
+    return false;
+  }
+  MachineBasicBlock *Preheader = L->getLoopPreheader();
+  // No preheader means there's not place for the loop instr.
+  if (Preheader == 0) {
+    return false;
+  }
+  MachineBasicBlock::iterator InsertPos = Preheader->getFirstTerminator();
+
+  DebugLoc dl;
+  if (InsertPos != Preheader->end())
+    dl = InsertPos->getDebugLoc();
+
+  MachineBasicBlock *LastMBB = L->getExitingBlock();
+  // Don't generate CTR loop if the loop has more than one exit.
+  if (LastMBB == 0) {
+    return false;
+  }
+  MachineBasicBlock::iterator LastI = LastMBB->getFirstTerminator();
+
+  // Determine the loop start.
+  MachineBasicBlock *LoopStart = L->getTopBlock();
+  if (L->getLoopLatch() != LastMBB) {
+    // When the exit and latch are not the same, use the latch block as the
+    // start.
+    // The loop start address is used only after the 1st iteration, and the loop
+    // latch may contains instrs. that need to be executed after the 1st iter.
+    LoopStart = L->getLoopLatch();
+    // Make sure the latch is a successor of the exit, otherwise it won't work.
+    if (!LastMBB->isSuccessor(LoopStart)) {
+      return false;
+    }
+  }
+
+  // Convert the loop to a CTR loop
+  DEBUG(dbgs() << "Change to CTR loop at "; L->dump());
+
+  MachineFunction *MF = LastMBB->getParent();
+  const PPCSubtarget &Subtarget = MF->getTarget().getSubtarget<PPCSubtarget>();
+  bool isPPC64 = Subtarget.isPPC64();
+
+  unsigned CountReg;
+  if (TripCount->isReg()) {
+    // Create a copy of the loop count register.
+    const TargetRegisterClass *RC =
+      MF->getRegInfo().getRegClass(TripCount->getReg());
+    CountReg = MF->getRegInfo().createVirtualRegister(RC);
+    BuildMI(*Preheader, InsertPos, dl,
+            TII->get(TargetOpcode::COPY), CountReg).addReg(TripCount->getReg());
+    if (TripCount->isNeg()) {
+      unsigned CountReg1 = CountReg;
+      CountReg = MF->getRegInfo().createVirtualRegister(RC);
+      BuildMI(*Preheader, InsertPos, dl,
+              TII->get(isPPC64 ? PPC::NEG8 : PPC::NEG),
+                       CountReg).addReg(CountReg1);
+    }
+
+    // On a 64-bit system, if the original comparison was only 32-bit, then
+    // mask out the higher-order part of the count.
+    if (isPPC64 && WordCmp) {
+       unsigned CountReg1 = CountReg;
+       CountReg = MF->getRegInfo().createVirtualRegister(RC);
+       BuildMI(*Preheader, InsertPos, dl,
+               TII->get(PPC::RLDICL), CountReg).addReg(CountReg1
+              ).addImm(0).addImm(32);
+    }
+  } else {
+    assert(TripCount->isImm() && "Expecting immedate vaule for trip count");
+    // Put the trip count in a register for transfer into the count register.
+    const TargetRegisterClass *GPRC = &PPC::GPRCRegClass;
+    const TargetRegisterClass *G8RC = &PPC::G8RCRegClass;
+    const TargetRegisterClass *RC = isPPC64 ? G8RC : GPRC;
+
+    int64_t CountImm = TripCount->getImm();
+    if (TripCount->isNeg())
+      CountImm = -CountImm;
+
+    CountReg = MF->getRegInfo().createVirtualRegister(RC);
+    if (CountImm > 0xFFFF) {
+      BuildMI(*Preheader, InsertPos, dl,
+              TII->get(isPPC64 ? PPC::LIS8 : PPC::LIS),
+              CountReg).addImm(CountImm >> 16);
+      unsigned CountReg1 = CountReg;
+      CountReg = MF->getRegInfo().createVirtualRegister(RC);
+      BuildMI(*Preheader, InsertPos, dl,
+              TII->get(isPPC64 ? PPC::ORI8 : PPC::ORI),
+              CountReg).addReg(CountReg1).addImm(CountImm & 0xFFFF);
+    } else {
+      BuildMI(*Preheader, InsertPos, dl,
+              TII->get(isPPC64 ? PPC::LI8 : PPC::LI),
+              CountReg).addImm(CountImm);
+    }
+  }
+
+  // Add the mtctr instruction to the beginning of the loop.
+  BuildMI(*Preheader, InsertPos, dl,
+          TII->get(isPPC64 ? PPC::MTCTR8 : PPC::MTCTR)).addReg(CountReg,
+            TripCount->isImm() ? RegState::Kill : 0);
+
+  // Make sure the loop start always has a reference in the CFG.  We need to
+  // create a BlockAddress operand to get this mechanism to work both the
+  // MachineBasicBlock and BasicBlock objects need the flag set.
+  LoopStart->setHasAddressTaken();
+  // This line is needed to set the hasAddressTaken flag on the BasicBlock
+  // object
+  BlockAddress::get(const_cast<BasicBlock *>(LoopStart->getBasicBlock()));
+
+  // Replace the loop branch with a bdnz instruction.
+  dl = LastI->getDebugLoc();
+  const std::vector<MachineBasicBlock*> Blocks = L->getBlocks();
+  for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
+    MachineBasicBlock *MBB = Blocks[i];
+    if (MBB != Preheader)
+      MBB->addLiveIn(isPPC64 ? PPC::CTR8 : PPC::CTR);
+  }
+
+  // The loop ends with either:
+  //  - a conditional branch followed by an unconditional branch, or
+  //  - a conditional branch to the loop start.
+  assert(LastI->getOpcode() == PPC::BCC &&
+         "loop end must start with a BCC instruction");
+  // Either the BCC branches to the beginning of the loop, or it
+  // branches out of the loop and there is an unconditional branch
+  // to the start of the loop.
+  MachineBasicBlock *BranchTarget = LastI->getOperand(2).getMBB();
+  BuildMI(*LastMBB, LastI, dl,
+        TII->get((BranchTarget == LoopStart) ?
+                 (isPPC64 ? PPC::BDNZ8 : PPC::BDNZ) :
+                 (isPPC64 ? PPC::BDZ8 : PPC::BDZ))).addMBB(BranchTarget);
+
+  // Conditional branch; just delete it.
+  LastMBB->erase(LastI);
+
+  delete TripCount;
+
+  // The induction operation (add) and the comparison (cmpwi) may now be
+  // unneeded. If these are unneeded, then remove them.
+  for (unsigned i = 0; i < OldInsts.size(); ++i)
+    removeIfDead(OldInsts[i]);
+
+  ++NumCTRLoops;
+  return true;
+}
+