Extend Hexagon hardware loop generation to handle various additional cases:

- variety of compare instructions,
- loops with no preheader,
- arbitrary lower and upper bounds.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174904 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 1283 insertions, 382 deletions

diff --git a/lib/Target/Hexagon/HexagonHardwareLoops.cpp b/lib/Target/Hexagon/HexagonHardwareLoops.cpp
index 2a00a9f7bd..62aed1353c 100644
--- a/lib/Target/Hexagon/HexagonHardwareLoops.cpp
+++ b/lib/Target/Hexagon/HexagonHardwareLoops.cpp
@@ -27,9 +27,7 @@
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "hwloops"
-#include "Hexagon.h"
-#include "HexagonTargetMachine.h"
-#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -37,79 +35,194 @@
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineLoopInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/CodeGen/Passes.h"
-#include "llvm/CodeGen/RegisterScavenging.h"
-#include "llvm/IR/Constants.h"
 #include "llvm/PassSupport.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetInstrInfo.h"
+#include "Hexagon.h"
+#include "HexagonTargetMachine.h"
+
 #include <algorithm>
+#include <vector>
 
 using namespace llvm;
 
+#ifndef NDEBUG
+static cl::opt<int> HWLoopLimit("max-hwloop", cl::Hidden, cl::init(-1));
+#endif
+
 STATISTIC(NumHWLoops, "Number of loops converted to hardware loops");
 
+namespace llvm {
+  void initializeHexagonHardwareLoopsPass(PassRegistry&);
+}
+
 namespace {
   class CountValue;
   struct HexagonHardwareLoops : public MachineFunctionPass {
-    MachineLoopInfo       *MLI;
-    MachineRegisterInfo   *MRI;
-    const TargetInstrInfo *TII;
+    MachineLoopInfo            *MLI;
+    MachineRegisterInfo        *MRI;
+    MachineDominatorTree       *MDT;
+    const HexagonTargetMachine *TM;
+    const HexagonInstrInfo     *TII;
+    const HexagonRegisterInfo  *TRI;
+#ifndef NDEBUG
+    static int Counter;
+#endif
 
   public:
-    static char ID;   // Pass identification, replacement for typeid
+    static char ID;
 
-    HexagonHardwareLoops() : MachineFunctionPass(ID) {}
+    HexagonHardwareLoops() : MachineFunctionPass(ID) {
+      initializeHexagonHardwareLoopsPass(*PassRegistry::getPassRegistry());
+    }
 
     virtual bool runOnMachineFunction(MachineFunction &MF);
 
     const char *getPassName() const { return "Hexagon Hardware 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.
-    const MachineInstr *getCanonicalInductionVariable(MachineLoop *L) 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) 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;
+    /// Kinds of comparisons in the compare instructions.
+    struct Comparison {
+      enum Kind {
+        EQ  = 0x01,
+        NE  = 0x02,
+        L   = 0x04, // Less-than property.
+        G   = 0x08, // Greater-than property.
+        U   = 0x40, // Unsigned property.
+        LTs = L,
+        LEs = L | EQ,
+        GTs = G,
+        GEs = G | EQ,
+        LTu = L      | U,
+        LEu = L | EQ | U,
+        GTu = G      | U,
+        GEu = G | EQ | U
+      };
+
+      static Kind getSwappedComparison(Kind Cmp) {
+        assert ((!((Cmp & L) && (Cmp & G))) && "Malformed comparison operator");
+        if ((Cmp & L) || (Cmp & G))
+          return (Kind)(Cmp ^ (L|G));
+        return Cmp;
+      }
+    };
 
-    /// isInvalidOperation - Return true if the instruction is not valid within
-    /// a hardware loop.
+    /// \brief Find the register that contains the loop controlling
+    /// induction variable.
+    /// If successful, it will return true and set the \p Reg, \p IVBump
+    /// and \p IVOp arguments.  Otherwise it will return false.
+    /// The returned induction register is the register R that follows the
+    /// following induction pattern:
+    /// loop:
+    ///   R = phi ..., [ R.next, LatchBlock ]
+    ///   R.next = R + #bump
+    ///   if (R.next < #N) goto loop
+    /// IVBump is the immediate value added to R, and IVOp is the instruction
+    /// "R.next = R + #bump".
+    bool findInductionRegister(MachineLoop *L, unsigned &Reg,
+                               int64_t &IVBump, MachineInstr *&IVOp) const;
+
+    /// \brief Analyze the statements in a loop to determine if the loop
+    /// has a computable trip count and, if so, return a value that represents
+    /// the trip count expression.
+    CountValue *getLoopTripCount(MachineLoop *L,
+                                 SmallVector<MachineInstr*, 2> &OldInsts);
+
+    /// \brief Return the expression that represents the number of times
+    /// a loop iterates.  The function takes the operands that represent the
+    /// loop start value, loop end value, and induction value.  Based upon
+    /// these operands, the function attempts to compute the trip count.
+    /// If the trip count is not directly available (as an immediate value,
+    /// or a register), the function will attempt to insert computation of it
+    /// to the loop's preheader.
+    CountValue *computeCount(MachineLoop *Loop,
+                             const MachineOperand *Start,
+                             const MachineOperand *End,
+                             unsigned IVReg,
+                             int64_t IVBump,
+                             Comparison::Kind Cmp) const;
+
+    /// \brief Return true if the instruction is not valid within a hardware
+    /// loop.
     bool isInvalidLoopOperation(const MachineInstr *MI) const;
 
-    /// containsInavlidInstruction - Return true if the loop contains an
-    /// instruction that inhibits using the hardware loop.
+    /// \brief Return true if the loop contains an instruction that inhibits
+    /// using the hardware loop.
     bool containsInvalidInstruction(MachineLoop *L) const;
 
-    /// converToHardwareLoop - Given a loop, check if we can convert it to a
-    /// hardware loop.  If so, then perform the conversion and return true.
+    /// \brief Given a loop, check if we can convert it to a hardware loop.
+    /// If so, then perform the conversion and return true.
     bool convertToHardwareLoop(MachineLoop *L);
 
+    /// \brief Return true if the instruction is now dead.
+    bool isDead(const MachineInstr *MI,
+                SmallVector<MachineInstr*, 1> &DeadPhis) const;
+
+    /// \brief Remove the instruction if it is now dead.
+    void removeIfDead(MachineInstr *MI);
+
+    /// \brief Make sure that the "bump" instruction executes before the
+    /// compare.  We need that for the IV fixup, so that the compare
+    /// instruction would not use a bumped value that has not yet been
+    /// defined.  If the instructions are out of order, try to reorder them.
+    bool orderBumpCompare(MachineInstr *BumpI, MachineInstr *CmpI);
+
+    /// \brief Get the instruction that loads an immediate value into \p R,
+    /// or 0 if such an instruction does not exist.
+    MachineInstr *defWithImmediate(unsigned R);
+
+    /// \brief Get the immediate value referenced to by \p MO, either for
+    /// immediate operands, or for register operands, where the register
+    /// was defined with an immediate value.
+    int64_t getImmediate(MachineOperand &MO);
+
+    /// \brief Reset the given machine operand to now refer to a new immediate
+    /// value.  Assumes that the operand was already referencing an immediate
+    /// value, either directly, or via a register.
+    void setImmediate(MachineOperand &MO, int64_t Val);
+
+    /// \brief Fix the data flow of the induction varible.
+    /// The desired flow is: phi ---> bump -+-> comparison-in-latch.
+    ///                                     |
+    ///                                     +-> back to phi
+    /// where "bump" is the increment of the induction variable:
+    ///   iv = iv + #const.
+    /// Due to some prior code transformations, the actual flow may look
+    /// like this:
+    ///   phi -+-> bump ---> back to phi
+    ///        |
+    ///        +-> comparison-in-latch (against upper_bound-bump),
+    /// i.e. the comparison that controls the loop execution may be using
+    /// the value of the induction variable from before the increment.
+    ///
+    /// Return true if the loop's flow is the desired one (i.e. it's
+    /// either been fixed, or no fixing was necessary).
+    /// Otherwise, return false.  This can happen if the induction variable
+    /// couldn't be identified, or if the value in the latch's comparison
+    /// cannot be adjusted to reflect the post-bump value.
+    bool fixupInductionVariable(MachineLoop *L);
+
+    /// \brief Given a loop, if it does not have a preheader, create one.
+    /// Return the block that is the preheader.
+    MachineBasicBlock *createPreheaderForLoop(MachineLoop *L);
   };
 
   char HexagonHardwareLoops::ID = 0;
+#ifndef NDEBUG
+  int HexagonHardwareLoops::Counter = 0;
+#endif
 
-
-  // 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.
+  /// \brief 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 {
@@ -119,101 +232,62 @@ namespace {
   private:
     CountValueType Kind;
     union Values {
-      unsigned RegNum;
-      int64_t ImmVal;
-      Values(unsigned r) : RegNum(r) {}
-      Values(int64_t i) : ImmVal(i) {}
+      struct {
+        unsigned Reg;
+        unsigned Sub;
+      } R;
+      unsigned ImmVal;
     } 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; }
+    explicit CountValue(CountValueType t, unsigned v, unsigned u = 0) {
+      Kind = t;
+      if (Kind == CV_Register) {
+        Contents.R.Reg = v;
+        Contents.R.Sub = u;
+      } else {
+        Contents.ImmVal = v;
+      }
+    }
     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;
+      return Contents.R.Reg;
     }
-    void setReg(unsigned Val) {
-      Contents.RegNum = Val;
+    unsigned getSubReg() const {
+      assert(isReg() && "Wrong CountValue accessor");
+      return Contents.R.Sub;
     }
-    int64_t getImm() const {
+    unsigned 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(); }
-    }
-  };
-
-  struct HexagonFixupHwLoops : public MachineFunctionPass {
-  public:
-    static char ID;     // Pass identification, replacement for typeid.
-
-    HexagonFixupHwLoops() : MachineFunctionPass(ID) {}
-
-    virtual bool runOnMachineFunction(MachineFunction &MF);
-
-    const char *getPassName() const { return "Hexagon Hardware Loop Fixup"; }
-
-    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
-      AU.setPreservesCFG();
-      MachineFunctionPass::getAnalysisUsage(AU);
+      const TargetRegisterInfo *TRI = TM ? TM->getRegisterInfo() : 0;
+      if (isReg()) { OS << PrintReg(Contents.R.Reg, TRI, Contents.R.Sub); }
+      if (isImm()) { OS << Contents.ImmVal; }
     }
-
-  private:
-    /// Maximum distance between the loop instr and the basic block.
-    /// Just an estimate.
-    static const unsigned MAX_LOOP_DISTANCE = 200;
-
-    /// fixupLoopInstrs - Check the offset between each loop instruction and
-    /// the loop basic block to determine if we can use the LOOP instruction
-    /// or if we need to set the LC/SA registers explicitly.
-    bool fixupLoopInstrs(MachineFunction &MF);
-
-    /// convertLoopInstr - Add the instruction to set the LC and SA registers
-    /// explicitly.
-    void convertLoopInstr(MachineFunction &MF,
-                          MachineBasicBlock::iterator &MII,
-                          RegScavenger &RS);
-
   };
+} // end anonymous namespace
 
-  char HexagonFixupHwLoops::ID = 0;
 
-} // end anonymous namespace
+INITIALIZE_PASS_BEGIN(HexagonHardwareLoops, "hwloops",
+                      "Hexagon Hardware Loops", false, false)
+INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
+INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
+INITIALIZE_PASS_END(HexagonHardwareLoops, "hwloops",
+                    "Hexagon Hardware Loops", false, false)
 
 
-/// isHardwareLoop - Returns true if the instruction is a hardware loop
-/// instruction.
+/// \brief Returns true if the instruction is a hardware loop instruction.
 static bool isHardwareLoop(const MachineInstr *MI) {
   return MI->getOpcode() == Hexagon::LOOP0_r ||
     MI->getOpcode() == Hexagon::LOOP0_i;
 }
 
-/// isCompareEquals - Returns true if the instruction is a compare equals
-/// instruction with an immediate operand.
-static bool isCompareEqualsImm(const MachineInstr *MI) {
-  return MI->getOpcode() == Hexagon::CMPEQri;
-}
-
-
-/// createHexagonHardwareLoops - Factory for creating
-/// the hardware loop phase.
 FunctionPass *llvm::createHexagonHardwareLoops() {
   return new HexagonHardwareLoops();
 }
@@ -224,45 +298,149 @@ bool HexagonHardwareLoops::runOnMachineFunction(MachineFunction &MF) {
 
   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();
+  MDT = &getAnalysis<MachineDominatorTree>();
+  TM  = static_cast<const HexagonTargetMachine*>(&MF.getTarget());
+  TII = static_cast<const HexagonInstrInfo*>(TM->getInstrInfo());
+  TRI = static_cast<const HexagonRegisterInfo*>(TM->getRegisterInfo());
 
   for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end();
        I != E; ++I) {
     MachineLoop *L = *I;
-    if (!L->getParentLoop()) {
+    if (!L->getParentLoop())
       Changed |= convertToHardwareLoop(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'.
+
+bool HexagonHardwareLoops::findInductionRegister(MachineLoop *L,
+                                                 unsigned &Reg,
+                                                 int64_t &IVBump,
+                                                 MachineInstr *&IVOp
+                                                 ) const {
+  MachineBasicBlock *Header = L->getHeader();
+  MachineBasicBlock *Preheader = L->getLoopPreheader();
+  MachineBasicBlock *Latch = L->getLoopLatch();
+  if (!Header || !Preheader || !Latch)
+    return false;
+
+  // This pair represents an induction register together with an immediate
+  // value that will be added to it in each loop iteration.
+  typedef std::pair<unsigned,int64_t> RegisterBump;
+
+  // Mapping:  R.next -> (R, bump), where R, R.next and bump are derived
+  // from an induction operation
+  //   R.next = R + bump
+  // where bump is an immediate value.
+  typedef std::map<unsigned,RegisterBump> InductionMap;
+
+  InductionMap IndMap;
+
+  typedef MachineBasicBlock::instr_iterator instr_iterator;
+  for (instr_iterator I = Header->instr_begin(), E = Header->instr_end();
+       I != E && I->isPHI(); ++I) {
+    MachineInstr *Phi = &*I;
+
+    // Have a PHI instruction.  Get the operand that corresponds to the
+    // latch block, and see if is a result of an addition of form "reg+imm",
+    // where the "reg" is defined by the PHI node we are looking at.
+    for (unsigned i = 1, n = Phi->getNumOperands(); i < n; i += 2) {
+      if (Phi->getOperand(i+1).getMBB() != Latch)
+        continue;
+
+      unsigned PhiOpReg = Phi->getOperand(i).getReg();
+      MachineInstr *DI = MRI->getVRegDef(PhiOpReg);
+      unsigned UpdOpc = DI->getOpcode();
+      bool isAdd = (UpdOpc == Hexagon::ADD_ri);
+
+      if (isAdd) {
+        // If the register operand to the add is the PHI we're
+        // looking at, this meets the induction pattern.
+        unsigned IndReg = DI->getOperand(1).getReg();
+        if (MRI->getVRegDef(IndReg) == Phi) {
+          unsigned UpdReg = DI->getOperand(0).getReg();
+          int64_t V = DI->getOperand(2).getImm();
+          IndMap.insert(std::make_pair(UpdReg, std::make_pair(IndReg, V)));
+        }
+      }
+    }  // for (i)
+  }  // for (instr)
+
+  SmallVector<MachineOperand,2> Cond;
+  MachineBasicBlock *TB = 0, *FB = 0;
+  bool NotAnalyzed = TII->AnalyzeBranch(*Latch, TB, FB, Cond, false);
+  if (NotAnalyzed)
+    return false;
+
+  unsigned CSz = Cond.size();
+  assert (CSz == 1 || CSz == 2);
+  unsigned PredR = Cond[CSz-1].getReg();
+
+  MachineInstr *PredI = MRI->getVRegDef(PredR);
+  if (!PredI->isCompare())
+    return false;
+
+  unsigned CmpReg1 = 0, CmpReg2 = 0;
+  int CmpImm = 0, CmpMask = 0;
+  bool CmpAnalyzed = TII->analyzeCompare(PredI, CmpReg1, CmpReg2,
+                                         CmpMask, CmpImm);
+  // Fail if the compare was not analyzed, or it's not comparing a register
+  // with an immediate value.  Not checking the mask here, since we handle
+  // the individual compare opcodes (including CMPb) later on.
+  if (!CmpAnalyzed)
+    return false;
+
+  // Exactly one of the input registers to the comparison should be among
+  // the induction registers.
+  InductionMap::iterator IndMapEnd = IndMap.end();
+  InductionMap::iterator F = IndMapEnd;
+  if (CmpReg1 != 0) {
+    InductionMap::iterator F1 = IndMap.find(CmpReg1);
+    if (F1 != IndMapEnd)
+      F = F1;
+  }
+  if (CmpReg2 != 0) {
+    InductionMap::iterator F2 = IndMap.find(CmpReg2);
+    if (F2 != IndMapEnd) {
+      if (F != IndMapEnd)
+        return false;
+      F = F2;
+    }
+  }
+  if (F == IndMapEnd)
+    return false;
+
+  Reg = F->second.first;
+  IVBump = F->second.second;
+  IVOp = MRI->getVRegDef(F->first);
+  return true;
+}
+
+
+/// \brief Analyze the statements in a loop to determine if the loop has
+/// a computable trip count and, if so, return a value that represents
+/// the trip count expression.
 ///
-const MachineInstr
-*HexagonHardwareLoops::getCanonicalInductionVariable(MachineLoop *L) const {
+/// This function iterates over the phi nodes in the loop to check for
+/// induction variable patterns that are used in the calculation for
+/// the number of time the loop is executed.
+CountValue *HexagonHardwareLoops::getLoopTripCount(MachineLoop *L,
+                                SmallVector<MachineInstr*, 2> &OldInsts) {
   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
+  if (PI == TopMBB->pred_end())  // dead loop?
+    return 0;
   MachineBasicBlock *Incoming = *PI++;
-  if (PI != TopMBB->pred_end()) return 0;  // multiple backedges?
+  if (PI != TopMBB->pred_end())  // multiple backedges?
+    return 0;
 
-  // make sure there is one incoming and one backedge and determine which
+  // Make sure there is one incoming and one backedge and determine which
   // is which.
   if (L->contains(Incoming)) {
     if (L->contains(Backedge))
@@ -271,139 +449,433 @@ const MachineInstr
   } 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) {
-    const 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.
-        const MachineInstr *DI = MRI->getVRegDef(MPhi->getOperand(i).getReg());
-        if (isInductionOperation(DI, DefReg)) {
-          return MPhi;
-        }
-      }
+  // 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).
+  MachineBasicBlock *Latch = L->getLoopLatch();
+  if (!Latch)
+    return 0;
+
+  unsigned IVReg = 0;
+  int64_t IVBump = 0;
+  MachineInstr *IVOp;
+  bool FoundIV = findInductionRegister(L, IVReg, IVBump, IVOp);
+  if (!FoundIV)
+    return 0;
+
+  MachineBasicBlock *Preheader = L->getLoopPreheader();
+
+  MachineOperand *InitialValue = 0;
+  MachineInstr *IV_Phi = MRI->getVRegDef(IVReg);
+  for (unsigned i = 1, n = IV_Phi->getNumOperands(); i < n; i += 2) {
+    MachineBasicBlock *MBB = IV_Phi->getOperand(i+1).getMBB();
+    if (MBB == Preheader)
+      InitialValue = &IV_Phi->getOperand(i);
+    else if (MBB == Latch)
+      IVReg = IV_Phi->getOperand(i).getReg();  // Want IV reg after bump.
+  }
+  if (!InitialValue)
+    return 0;
+
+  SmallVector<MachineOperand,2> Cond;
+  MachineBasicBlock *TB = 0, *FB = 0;
+  bool NotAnalyzed = TII->AnalyzeBranch(*Latch, TB, FB, Cond, false);
+  if (NotAnalyzed)
+    return 0;
+
+  MachineBasicBlock *Header = L->getHeader();
+  // TB must be non-null.  If FB is also non-null, one of them must be
+  // the header.  Otherwise, branch to TB could be exiting the loop, and
+  // the fall through can go to the header.
+  assert (TB && "Latch block without a branch?");
+  assert ((!FB || TB == Header || FB == Header) && "Branches not to header?");
+  if (!TB || (FB && TB != Header && FB != Header))
+    return 0;
+
+  // Branches of form "if (!P) ..." cause HexagonInstrInfo::AnalyzeBranch
+  // to put imm(0), followed by P in the vector Cond.
+  // If TB is not the header, it means that the "not-taken" path must lead
+  // to the header.
+  bool Negated = (Cond.size() > 1) ^ (TB != Header);
+  unsigned PredReg = Cond[Cond.size()-1].getReg();
+  MachineInstr *CondI = MRI->getVRegDef(PredReg);
+  unsigned CondOpc = CondI->getOpcode();
+
+  unsigned CmpReg1 = 0, CmpReg2 = 0;
+  int Mask = 0, ImmValue = 0;
+  bool AnalyzedCmp = TII->analyzeCompare(CondI, CmpReg1, CmpReg2,
+                                         Mask, ImmValue);
+  if (!AnalyzedCmp)
+    return 0;
+
+  // The comparison operator type determines how we compute the loop
+  // trip count.
+  OldInsts.push_back(CondI);
+  OldInsts.push_back(IVOp);
+
+  // Sadly, the following code gets information based on the position
+  // of the operands in the compare instruction.  This has to be done
+  // this way, because the comparisons check for a specific relationship
+  // between the operands (e.g. is-less-than), rather than to find out
+  // what relationship the operands are in (as on PPC).
+  Comparison::Kind Cmp;
+  bool isSwapped = false;
+  const MachineOperand &Op1 = CondI->getOperand(1);
+  const MachineOperand &Op2 = CondI->getOperand(2);
+  const MachineOperand *EndValue = 0;
+
+  if (Op1.isReg()) {
+    if (Op2.isImm() || Op1.getReg() == IVReg)
+      EndValue = &Op2;
+    else {
+      EndValue = &Op1;
+      isSwapped = true;
     }
   }
-  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 *HexagonHardwareLoops::getTripCount(MachineLoop *L) const {
-  // Check that the loop has a induction variable.
-  const MachineInstr *IV_Inst = getCanonicalInductionVariable(L);
-  if (IV_Inst == 0) return 0;
-
-  // Canonical loops will end with a 'cmpeq_ri 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
-  const 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).
-  for (MachineRegisterInfo::reg_iterator
-       RI = MRI->reg_begin(IV_Opnd->getReg()), RE = MRI->reg_end();
-       RI != RE; ++RI) {
-    IV_Opnd = &RI.getOperand();
-    const MachineInstr *MI = IV_Opnd->getParent();
-    if (L->contains(MI) && isCompareEqualsImm(MI)) {
-      const MachineOperand &MO = MI->getOperand(2);
-      assert(MO.isImm() && "IV Cmp Operand should be 0");
-      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) {
+  if (!EndValue)
+    return 0;
+
+  switch (CondOpc) {
+    case Hexagon::CMPEQri:
+    case Hexagon::CMPEQrr:
+      Cmp = !Negated ? Comparison::EQ : Comparison::NE;
+      break;
+    case Hexagon::CMPLTrr:
+      Cmp = !Negated ? Comparison::LTs : Comparison::GEs;
+      break;
+    case Hexagon::CMPLTUrr:
+      Cmp = !Negated ? Comparison::LTu : Comparison::GEu;
+      break;
+    case Hexagon::CMPGTUri:
+    case Hexagon::CMPGTUrr:
+      Cmp = !Negated ? Comparison::GTu : Comparison::LEu;
+      break;
+    case Hexagon::CMPGTri:
+    case Hexagon::CMPGTrr:
+      Cmp = !Negated ? Comparison::GTs : Comparison::LEs;
+      break;
+    // Very limited support for byte/halfword compares.
+    case Hexagon::CMPbEQri_V4:
+    case Hexagon::CMPhEQri_V4: {
+      if (IVBump != 1)
+        return 0;
+
+      int64_t InitV, EndV;
+      // Since the comparisons are "ri", the EndValue should be an
+      // immediate.  Check it just in case.
+      assert(EndValue->isImm() && "Unrecognized latch comparison");
+      EndV = EndValue->getImm();
+      // Allow InitialValue to be a register defined with an immediate.
+      if (InitialValue->isReg()) {
+        if (!defWithImmediate(InitialValue->getReg()))
           return 0;
-        }
-        return new CountValue(InitialValue->getReg(), iv_value > 0);
+        InitV = getImmediate(*InitialValue);
       } else {
-        assert(InitialValue->isReg() && "Expecting register for init value");
-        const MachineInstr *DefInstr = MRI->getVRegDef(InitialValue->getReg());
-        if (DefInstr && DefInstr->getOpcode() == Hexagon::TFRI) {
-          int64_t count = ImmVal - DefInstr->getOperand(1).getImm();
-          if ((count % iv_value) != 0) {
-            return 0;
-          }
-          return new CountValue(count/iv_value);
-        }
+        assert(InitialValue->isImm());
+        InitV = InitialValue->getImm();
+      }
+      if (InitV >= EndV)
+        return 0;
+      if (CondOpc == Hexagon::CMPbEQri_V4) {
+        if (!isInt<8>(InitV) || !isInt<8>(EndV))
+          return 0;
+      } else {  // Hexagon::CMPhEQri_V4
+        if (!isInt<16>(InitV) || !isInt<16>(EndV))
+          return 0;
       }
+      Cmp = !Negated ? Comparison::EQ : Comparison::NE;
+      break;
     }
+    default:
+      return 0;
   }
-  return 0;
+
+  if (isSwapped)
+   Cmp = Comparison::getSwappedComparison(Cmp);
+
+  if (InitialValue->isReg()) {
+    unsigned R = InitialValue->getReg();
+    MachineBasicBlock *DefBB = MRI->getVRegDef(R)->getParent();
+    if (!MDT->properlyDominates(DefBB, Header))
+      return 0;
+    OldInsts.push_back(MRI->getVRegDef(R));
+  }
+  if (EndValue->isReg()) {
+    unsigned R = EndValue->getReg();
+    MachineBasicBlock *DefBB = MRI->getVRegDef(R)->getParent();
+    if (!MDT->properlyDominates(DefBB, Header))
+      return 0;
+  }
+
+  return computeCount(L, InitialValue, EndValue, IVReg, IVBump, Cmp);
 }
 
-/// isInductionOperation - return true if the operation is matches the
-/// pattern that defines an induction variable:
-///    add iv, c
-///
-bool
-HexagonHardwareLoops::isInductionOperation(const MachineInstr *MI,
-                                           unsigned IVReg) const {
-  return (MI->getOpcode() ==
-          Hexagon::ADD_ri && MI->getOperand(1).getReg() == IVReg);
+/// \brief Helper function that returns the expression that represents the
+/// number of times a loop iterates.  The function takes the operands that
+/// represent the loop start value, loop end value, and induction value.
+/// Based upon these operands, the function attempts to compute the trip count.
+CountValue *HexagonHardwareLoops::computeCount(MachineLoop *Loop,
+                                               const MachineOperand *Start,
+                                               const MachineOperand *End,
+                                               unsigned IVReg,
+                                               int64_t IVBump,
+                                               Comparison::Kind Cmp) const {
+  // Cannot handle comparison EQ, i.e. while (A == B).
+  if (Cmp == Comparison::EQ)
+    return 0;
+
+  // Check if either the start or end values are an assignment of an immediate.
+  // If so, use the immediate value rather than the register.
+  if (Start->isReg()) {
+    const MachineInstr *StartValInstr = MRI->getVRegDef(Start->getReg());
+    if (StartValInstr && StartValInstr->getOpcode() == Hexagon::TFRI)
+      Start = &StartValInstr->getOperand(1);
+  }
+  if (End->isReg()) {
+    const MachineInstr *EndValInstr = MRI->getVRegDef(End->getReg());
+    if (EndValInstr && EndValInstr->getOpcode() == Hexagon::TFRI)
+      End = &EndValInstr->getOperand(1);
+  }
+
+  assert (Start->isReg() || Start->isImm());
+  assert (End->isReg() || End->isImm());
+
+  bool CmpLess =     Cmp & Comparison::L;
+  bool CmpGreater =  Cmp & Comparison::G;
+  bool CmpHasEqual = Cmp & Comparison::EQ;
+
+  // Avoid certain wrap-arounds.  This doesn't detect all wrap-arounds.
+  // If loop executes while iv is "less" with the iv value going down, then
+  // the iv must wrap.
+  if (CmpLess && IVBump < 0)
+    return 0;
+  // If loop executes while iv is "greater" with the iv value going up, then
+  // the iv must wrap.
+  if (CmpGreater && IVBump > 0)
+    return 0;
+
+  if (Start->isImm() && End->isImm()) {
+    // Both, start and end are immediates.
+    int64_t StartV = Start->getImm();
+    int64_t EndV = End->getImm();
+    int64_t Dist = EndV - StartV;
+    if (Dist == 0)
+      return 0;
+
+    bool Exact = (Dist % IVBump) == 0;
+
+    if (Cmp == Comparison::NE) {
+      if (!Exact)
+        return 0;
+      if ((Dist < 0) ^ (IVBump < 0))
+        return 0;
+    }
+
+    // For comparisons that include the final value (i.e. include equality
+    // with the final value), we need to increase the distance by 1.
+    if (CmpHasEqual)
+      Dist = Dist > 0 ? Dist+1 : Dist-1;
+
+    // assert (CmpLess => Dist > 0);
+    assert ((!CmpLess || Dist > 0) && "Loop should never iterate!");
+    // assert (CmpGreater => Dist < 0);
+    assert ((!CmpGreater || Dist < 0) && "Loop should never iterate!");
+
+    // "Normalized" distance, i.e. with the bump set to +-1.
+    int64_t Dist1 = (IVBump > 0) ? (Dist +  (IVBump-1)) /   IVBump
+                               :  (-Dist + (-IVBump-1)) / (-IVBump);
+    assert (Dist1 > 0 && "Fishy thing.  Both operands have the same sign.");
+
+    uint64_t Count = Dist1;
+
+    if (Count > 0xFFFFFFFFULL)
+      return 0;
+
+    return new CountValue(CountValue::CV_Immediate, Count);
+  }
+
+  // A general case: Start and End are some values, but the actual
+  // iteration count may not be available.  If it is not, insert
+  // a computation of it into the preheader.
+
+  // If the induction variable bump is not a power of 2, quit.
+  // Othwerise we'd need a general integer division.
+  if (!isPowerOf2_64(abs(IVBump)))
+    return 0;
+
+  MachineBasicBlock *PH = Loop->getLoopPreheader();
+  assert (PH && "Should have a preheader by now");
+  MachineBasicBlock::iterator InsertPos = PH->getFirstTerminator();
+  DebugLoc DL = (InsertPos != PH->end()) ? InsertPos->getDebugLoc()
+                                         : DebugLoc();
+
+  // If Start is an immediate and End is a register, the trip count
+  // will be "reg - imm".  Hexagon's "subtract immediate" instruction
+  // is actually "reg + -imm".
+
+  // If the loop IV is going downwards, i.e. if the bump is negative,
+  // then the iteration count (computed as End-Start) will need to be
+  // negated.  To avoid the negation, just swap Start and End.
+  if (IVBump < 0) {
+    std::swap(Start, End);
+    IVBump = -IVBump;
+  }
+  // Cmp may now have a wrong direction, e.g.  LEs may now be GEs.<