lib/Target/PowerPC/PPCInstrInfo.h

   1 //===-- PPCInstrInfo.h - PowerPC Instruction Information --------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file contains the PowerPC implementation of the TargetInstrInfo class.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_LIB_TARGET_POWERPC_PPCINSTRINFO_H
  14 #define LLVM_LIB_TARGET_POWERPC_PPCINSTRINFO_H
  15
  16 #include "PPCRegisterInfo.h"
  17 #include "llvm/CodeGen/TargetInstrInfo.h"
  18
  19 #define GET_INSTRINFO_HEADER
  20 #include "PPCGenInstrInfo.inc"
  21
  22 namespace llvm {
  23
  24 /// PPCII - This namespace holds all of the PowerPC target-specific
  25 /// per-instruction flags.  These must match the corresponding definitions in
  26 /// PPC.td and PPCInstrFormats.td.
  27 namespace PPCII {
  28 enum {
  29   // PPC970 Instruction Flags.  These flags describe the characteristics of the
  30   // PowerPC 970 (aka G5) dispatch groups and how they are formed out of
  31   // raw machine instructions.
  32
  33   /// PPC970_First - This instruction starts a new dispatch group, so it will
  34   /// always be the first one in the group.
  35   PPC970_First = 0x1,
  36
  37   /// PPC970_Single - This instruction starts a new dispatch group and
  38   /// terminates it, so it will be the sole instruction in the group.
  39   PPC970_Single = 0x2,
  40
  41   /// PPC970_Cracked - This instruction is cracked into two pieces, requiring
  42   /// two dispatch pipes to be available to issue.
  43   PPC970_Cracked = 0x4,
  44
  45   /// PPC970_Mask/Shift - This is a bitmask that selects the pipeline type that
  46   /// an instruction is issued to.
  47   PPC970_Shift = 3,
  48   PPC970_Mask = 0x07 << PPC970_Shift
  49 };
  50 enum PPC970_Unit {
  51   /// These are the various PPC970 execution unit pipelines.  Each instruction
  52   /// is one of these.
  53   PPC970_Pseudo = 0 << PPC970_Shift,   // Pseudo instruction
  54   PPC970_FXU    = 1 << PPC970_Shift,   // Fixed Point (aka Integer/ALU) Unit
  55   PPC970_LSU    = 2 << PPC970_Shift,   // Load Store Unit
  56   PPC970_FPU    = 3 << PPC970_Shift,   // Floating Point Unit
  57   PPC970_CRU    = 4 << PPC970_Shift,   // Control Register Unit
  58   PPC970_VALU   = 5 << PPC970_Shift,   // Vector ALU
  59   PPC970_VPERM  = 6 << PPC970_Shift,   // Vector Permute Unit
  60   PPC970_BRU    = 7 << PPC970_Shift    // Branch Unit
  61 };
  62
  63 enum {
  64   /// Shift count to bypass PPC970 flags
  65   NewDef_Shift = 6,
  66
  67   /// This instruction is an X-Form memory operation.
  68   XFormMemOp = 0x1 << (NewDef_Shift+1)
  69 };
  70 } // end namespace PPCII
  71
  72 // Instructions that have an immediate form might be convertible to that
  73 // form if the correct input is a result of a load immediate. In order to
  74 // know whether the transformation is special, we might need to know some
  75 // of the details of the two forms.
  76 struct ImmInstrInfo {
  77   // Is the immediate field in the immediate form signed or unsigned?
  78   uint64_t SignedImm : 1;
  79   // Does the immediate need to be a multiple of some value?
  80   uint64_t ImmMustBeMultipleOf : 5;
  81   // Is R0/X0 treated specially by the original r+r instruction?
  82   // If so, in which operand?
  83   uint64_t ZeroIsSpecialOrig : 3;
  84   // Is R0/X0 treated specially by the new r+i instruction?
  85   // If so, in which operand?
  86   uint64_t ZeroIsSpecialNew : 3;
  87   // Is the operation commutative?
  88   uint64_t IsCommutative : 1;
  89   // The operand number to check for add-immediate def.
  90   uint64_t OpNoForForwarding : 3;
  91   // The operand number for the immediate.
  92   uint64_t ImmOpNo : 3;
  93   // The opcode of the new instruction.
  94   uint64_t ImmOpcode : 16;
  95   // The size of the immediate.
  96   uint64_t ImmWidth : 5;
  97   // The immediate should be truncated to N bits.
  98   uint64_t TruncateImmTo : 5;
  99   // Is the instruction summing the operand
 100   uint64_t IsSummingOperands : 1;
 101 };
 102
 103 // Information required to convert an instruction to just a materialized
 104 // immediate.
 105 struct LoadImmediateInfo {
 106   unsigned Imm : 16;
 107   unsigned Is64Bit : 1;
 108   unsigned SetCR : 1;
 109 };
 110
 111 class PPCSubtarget;
 112 class PPCInstrInfo : public PPCGenInstrInfo {
 113   PPCSubtarget &Subtarget;
 114   const PPCRegisterInfo RI;
 115
 116   void StoreRegToStackSlot(MachineFunction &MF, unsigned SrcReg, bool isKill,
 117                            int FrameIdx, const TargetRegisterClass *RC,
 118                            SmallVectorImpl<MachineInstr *> &NewMIs) const;
 119   void LoadRegFromStackSlot(MachineFunction &MF, const DebugLoc &DL,
 120                             unsigned DestReg, int FrameIdx,
 121                             const TargetRegisterClass *RC,
 122                             SmallVectorImpl<MachineInstr *> &NewMIs) const;
 123
 124   // If the inst has imm-form and one of its operand is produced by a LI,
 125   // put the imm into the inst directly and remove the LI if possible.
 126   bool transformToImmFormFedByLI(MachineInstr &MI, const ImmInstrInfo &III,
 127                                  unsigned ConstantOpNo, MachineInstr &DefMI,
 128                                  int64_t Imm) const;
 129   // If the inst has imm-form and one of its operand is produced by an
 130   // add-immediate, try to transform it when possible.
 131   bool transformToImmFormFedByAdd(MachineInstr &MI, const ImmInstrInfo &III,
 132                                   unsigned ConstantOpNo, MachineInstr &DefMI,
 133                                   bool KillDefMI) const;
 134   // Try to find that, if the instruction 'MI' contains any operand that
 135   // could be forwarded from some inst that feeds it. If yes, return the
 136   // Def of that operand. And OpNoForForwarding is the operand index in
 137   // the 'MI' for that 'Def'. If we see another use of this Def between
 138   // the Def and the MI, SeenIntermediateUse becomes 'true'.
 139   MachineInstr *getForwardingDefMI(MachineInstr &MI,
 140                                    unsigned &OpNoForForwarding,
 141                                    bool &SeenIntermediateUse) const;
 142
 143   // Can the user MI have it's source at index \p OpNoForForwarding
 144   // forwarded from an add-immediate that feeds it?
 145   bool isUseMIElgibleForForwarding(MachineInstr &MI, const ImmInstrInfo &III,
 146                                    unsigned OpNoForForwarding) const;
 147   bool isDefMIElgibleForForwarding(MachineInstr &DefMI,
 148                                    const ImmInstrInfo &III,
 149                                    MachineOperand *&ImmMO,
 150                                    MachineOperand *&RegMO) const;
 151   bool isImmElgibleForForwarding(const MachineOperand &ImmMO,
 152                                  const MachineInstr &DefMI,
 153                                  const ImmInstrInfo &III,
 154                                  int64_t &Imm) const;
 155   bool isRegElgibleForForwarding(const MachineOperand &RegMO,
 156                                  const MachineInstr &DefMI,
 157                                  const MachineInstr &MI, bool KillDefMI,
 158                                  bool &IsFwdFeederRegKilled) const;
 159   const unsigned *getStoreOpcodesForSpillArray() const;
 160   const unsigned *getLoadOpcodesForSpillArray() const;
 161   virtual void anchor();
 162
 163 protected:
 164   /// Commutes the operands in the given instruction.
 165   /// The commutable operands are specified by their indices OpIdx1 and OpIdx2.
 166   ///
 167   /// Do not call this method for a non-commutable instruction or for
 168   /// non-commutable pair of operand indices OpIdx1 and OpIdx2.
 169   /// Even though the instruction is commutable, the method may still
 170   /// fail to commute the operands, null pointer is returned in such cases.
 171   ///
 172   /// For example, we can commute rlwimi instructions, but only if the
 173   /// rotate amt is zero.  We also have to munge the immediates a bit.
 174   MachineInstr *commuteInstructionImpl(MachineInstr &MI, bool NewMI,
 175                                        unsigned OpIdx1,
 176                                        unsigned OpIdx2) const override;
 177
 178 public:
 179   explicit PPCInstrInfo(PPCSubtarget &STI);
 180
 181   /// getRegisterInfo - TargetInstrInfo is a superset of MRegister info.  As
 182   /// such, whenever a client has an instance of instruction info, it should
 183   /// always be able to get register info as well (through this method).
 184   ///
 185   const PPCRegisterInfo &getRegisterInfo() const { return RI; }
 186
 187   bool isXFormMemOp(unsigned Opcode) const {
 188     return get(Opcode).TSFlags & PPCII::XFormMemOp;
 189   }
 190   static bool isSameClassPhysRegCopy(unsigned Opcode) {
 191     unsigned CopyOpcodes[] =
 192       { PPC::OR, PPC::OR8, PPC::FMR, PPC::VOR, PPC::XXLOR, PPC::XXLORf,
 193         PPC::XSCPSGNDP, PPC::MCRF, PPC::QVFMR, PPC::QVFMRs, PPC::QVFMRb,
 194         PPC::CROR, PPC::EVOR, -1U };
 195     for (int i = 0; CopyOpcodes[i] != -1U; i++)
 196       if (Opcode == CopyOpcodes[i])
 197         return true;
 198     return false;
 199   }
 200
 201   ScheduleHazardRecognizer *
 202   CreateTargetHazardRecognizer(const TargetSubtargetInfo *STI,
 203                                const ScheduleDAG *DAG) const override;
 204   ScheduleHazardRecognizer *
 205   CreateTargetPostRAHazardRecognizer(const InstrItineraryData *II,
 206                                      const ScheduleDAG *DAG) const override;
 207
 208   unsigned getInstrLatency(const InstrItineraryData *ItinData,
 209                            const MachineInstr &MI,
 210                            unsigned *PredCost = nullptr) const override;
 211
 212   int getOperandLatency(const InstrItineraryData *ItinData,
 213                         const MachineInstr &DefMI, unsigned DefIdx,
 214                         const MachineInstr &UseMI,
 215                         unsigned UseIdx) const override;
 216   int getOperandLatency(const InstrItineraryData *ItinData,
 217                         SDNode *DefNode, unsigned DefIdx,
 218                         SDNode *UseNode, unsigned UseIdx) const override {
 219     return PPCGenInstrInfo::getOperandLatency(ItinData, DefNode, DefIdx,
 220                                               UseNode, UseIdx);
 221   }
 222
 223   bool hasLowDefLatency(const TargetSchedModel &SchedModel,
 224                         const MachineInstr &DefMI,
 225                         unsigned DefIdx) const override {
 226     // Machine LICM should hoist all instructions in low-register-pressure
 227     // situations; none are sufficiently free to justify leaving in a loop
 228     // body.
 229     return false;
 230   }
 231
 232   bool useMachineCombiner() const override {
 233     return true;
 234   }
 235
 236   /// Return true when there is potentially a faster code sequence
 237   /// for an instruction chain ending in <Root>. All potential patterns are
 238   /// output in the <Pattern> array.
 239   bool getMachineCombinerPatterns(
 240       MachineInstr &Root,
 241       SmallVectorImpl<MachineCombinerPattern> &P) const override;
 242
 243   bool isAssociativeAndCommutative(const MachineInstr &Inst) const override;
 244
 245   bool isCoalescableExtInstr(const MachineInstr &MI,
 246                              unsigned &SrcReg, unsigned &DstReg,
 247                              unsigned &SubIdx) const override;
 248   unsigned isLoadFromStackSlot(const MachineInstr &MI,
 249                                int &FrameIndex) const override;
 250   bool isReallyTriviallyReMaterializable(const MachineInstr &MI,
 251                                          AliasAnalysis *AA) const override;
 252   unsigned isStoreToStackSlot(const MachineInstr &MI,
 253                               int &FrameIndex) const override;
 254
 255   bool findCommutedOpIndices(MachineInstr &MI, unsigned &SrcOpIdx1,
 256                              unsigned &SrcOpIdx2) const override;
 257
 258   void insertNoop(MachineBasicBlock &MBB,
 259                   MachineBasicBlock::iterator MI) const override;
 260
 261
 262   // Branch analysis.
 263   bool analyzeBranch(MachineBasicBlock &MBB, MachineBasicBlock *&TBB,
 264                      MachineBasicBlock *&FBB,
 265                      SmallVectorImpl<MachineOperand> &Cond,
 266                      bool AllowModify) const override;
 267   unsigned removeBranch(MachineBasicBlock &MBB,
 268                         int *BytesRemoved = nullptr) const override;
 269   unsigned insertBranch(MachineBasicBlock &MBB, MachineBasicBlock *TBB,
 270                         MachineBasicBlock *FBB, ArrayRef<MachineOperand> Cond,
 271                         const DebugLoc &DL,
 272                         int *BytesAdded = nullptr) const override;
 273
 274   // Select analysis.
 275   bool canInsertSelect(const MachineBasicBlock &, ArrayRef<MachineOperand> Cond,
 276                        unsigned, unsigned, int &, int &, int &) const override;
 277   void insertSelect(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI,
 278                     const DebugLoc &DL, unsigned DstReg,
 279                     ArrayRef<MachineOperand> Cond, unsigned TrueReg,
 280                     unsigned FalseReg) const override;
 281
 282   void copyPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
 283                    const DebugLoc &DL, unsigned DestReg, unsigned SrcReg,
 284                    bool KillSrc) const override;
 285
 286   void storeRegToStackSlot(MachineBasicBlock &MBB,
 287                            MachineBasicBlock::iterator MBBI,
 288                            unsigned SrcReg, bool isKill, int FrameIndex,
 289                            const TargetRegisterClass *RC,
 290                            const TargetRegisterInfo *TRI) const override;
 291
 292   void loadRegFromStackSlot(MachineBasicBlock &MBB,
 293                             MachineBasicBlock::iterator MBBI,
 294                             unsigned DestReg, int FrameIndex,
 295                             const TargetRegisterClass *RC,
 296                             const TargetRegisterInfo *TRI) const override;
 297
 298   unsigned getStoreOpcodeForSpill(unsigned Reg,
 299                                   const TargetRegisterClass *RC = nullptr) const;
 300
 301   unsigned getLoadOpcodeForSpill(unsigned Reg,
 302                                  const TargetRegisterClass *RC = nullptr) const;
 303
 304   bool
 305   reverseBranchCondition(SmallVectorImpl<MachineOperand> &Cond) const override;
 306
 307   bool FoldImmediate(MachineInstr &UseMI, MachineInstr &DefMI, unsigned Reg,
 308                      MachineRegisterInfo *MRI) const override;
 309
 310   // If conversion by predication (only supported by some branch instructions).
 311   // All of the profitability checks always return true; it is always
 312   // profitable to use the predicated branches.
 313   bool isProfitableToIfCvt(MachineBasicBlock &MBB,
 314                           unsigned NumCycles, unsigned ExtraPredCycles,
 315                           BranchProbability Probability) const override {
 316     return true;
 317   }
 318
 319   bool isProfitableToIfCvt(MachineBasicBlock &TMBB,
 320                            unsigned NumT, unsigned ExtraT,
 321                            MachineBasicBlock &FMBB,
 322                            unsigned NumF, unsigned ExtraF,
 323                            BranchProbability Probability) const override;
 324
 325   bool isProfitableToDupForIfCvt(MachineBasicBlock &MBB, unsigned NumCycles,
 326                                  BranchProbability Probability) const override {
 327     return true;
 328   }
 329
 330   bool isProfitableToUnpredicate(MachineBasicBlock &TMBB,
 331                                  MachineBasicBlock &FMBB) const override {
 332     return false;
 333   }
 334
 335   // Predication support.
 336   bool isPredicated(const MachineInstr &MI) const override;
 337
 338   bool isUnpredicatedTerminator(const MachineInstr &MI) const override;
 339
 340   bool PredicateInstruction(MachineInstr &MI,
 341                             ArrayRef<MachineOperand> Pred) const override;
 342
 343   bool SubsumesPredicate(ArrayRef<MachineOperand> Pred1,
 344                          ArrayRef<MachineOperand> Pred2) const override;
 345
 346   bool DefinesPredicate(MachineInstr &MI,
 347                         std::vector<MachineOperand> &Pred) const override;
 348
 349   bool isPredicable(const MachineInstr &MI) const override;
 350
 351   // Comparison optimization.
 352
 353   bool analyzeCompare(const MachineInstr &MI, unsigned &SrcReg,
 354                       unsigned &SrcReg2, int &Mask, int &Value) const override;
 355
 356   bool optimizeCompareInstr(MachineInstr &CmpInstr, unsigned SrcReg,
 357                             unsigned SrcReg2, int Mask, int Value,
 358                             const MachineRegisterInfo *MRI) const override;
 359
 360
 361   /// Return true if get the base operand, byte offset of an instruction and
 362   /// the memory width. Width is the size of memory that is being
 363   /// loaded/stored (e.g. 1, 2, 4, 8).
 364   bool getMemOperandWithOffsetWidth(const MachineInstr &LdSt,
 365                                     const MachineOperand *&BaseOp,
 366                                     int64_t &Offset, unsigned &Width,
 367                                     const TargetRegisterInfo *TRI) const;
 368
 369   /// Return true if two MIs access different memory addresses and false
 370   /// otherwise
 371   bool
 372   areMemAccessesTriviallyDisjoint(const MachineInstr &MIa,
 373                                   const MachineInstr &MIb,
 374                                   AliasAnalysis *AA = nullptr) const override;
 375
 376   /// GetInstSize - Return the number of bytes of code the specified
 377   /// instruction may be.  This returns the maximum number of bytes.
 378   ///
 379   unsigned getInstSizeInBytes(const MachineInstr &MI) const override;
 380
 381   void getNoop(MCInst &NopInst) const override;
 382
 383   std::pair<unsigned, unsigned>
 384   decomposeMachineOperandsTargetFlags(unsigned TF) const override;
 385
 386   ArrayRef<std::pair<unsigned, const char *>>
 387   getSerializableDirectMachineOperandTargetFlags() const override;
 388
 389   ArrayRef<std::pair<unsigned, const char *>>
 390   getSerializableBitmaskMachineOperandTargetFlags() const override;
 391
 392   // Expand VSX Memory Pseudo instruction to either a VSX or a FP instruction.
 393   bool expandVSXMemPseudo(MachineInstr &MI) const;
 394
 395   // Lower pseudo instructions after register allocation.
 396   bool expandPostRAPseudo(MachineInstr &MI) const override;
 397
 398   static bool isVFRegister(unsigned Reg) {
 399     return Reg >= PPC::VF0 && Reg <= PPC::VF31;
 400   }
 401   static bool isVRRegister(unsigned Reg) {
 402     return Reg >= PPC::V0 && Reg <= PPC::V31;
 403   }
 404   const TargetRegisterClass *updatedRC(const TargetRegisterClass *RC) const;
 405   static int getRecordFormOpcode(unsigned Opcode);
 406
 407   bool isTOCSaveMI(const MachineInstr &MI) const;
 408
 409   bool isSignOrZeroExtended(const MachineInstr &MI, bool SignExt,
 410                             const unsigned PhiDepth) const;
 411
 412   /// Return true if the output of the instruction is always a sign-extended,
 413   /// i.e. 0 to 31-th bits are same as 32-th bit.
 414   bool isSignExtended(const MachineInstr &MI, const unsigned depth = 0) const {
 415     return isSignOrZeroExtended(MI, true, depth);
 416   }
 417
 418   /// Return true if the output of the instruction is always zero-extended,
 419   /// i.e. 0 to 31-th bits are all zeros
 420   bool isZeroExtended(const MachineInstr &MI, const unsigned depth = 0) const {
 421    return isSignOrZeroExtended(MI, false, depth);
 422   }
 423
 424   bool convertToImmediateForm(MachineInstr &MI,
 425                               MachineInstr **KilledDef = nullptr) const;
 426
 427   /// Fixup killed/dead flag for register \p RegNo between instructions [\p
 428   /// StartMI, \p EndMI]. Some PostRA transformations may violate register
 429   /// killed/dead flags semantics, this function can be called to fix up. Before
 430   /// calling this function,
 431   /// 1. Ensure that \p RegNo liveness is killed after instruction \p EndMI.
 432   /// 2. Ensure that there is no new definition between (\p StartMI, \p EndMI)
 433   ///    and possible definition for \p RegNo is \p StartMI or \p EndMI.
 434   /// 3. Ensure that all instructions between [\p StartMI, \p EndMI] are in same
 435   ///    basic block.
 436   void fixupIsDeadOrKill(MachineInstr &StartMI, MachineInstr &EndMI,
 437                          unsigned RegNo) const;
 438   void replaceInstrWithLI(MachineInstr &MI, const LoadImmediateInfo &LII) const;
 439   void replaceInstrOperandWithImm(MachineInstr &MI, unsigned OpNo,
 440                                   int64_t Imm) const;
 441
 442   bool instrHasImmForm(const MachineInstr &MI, ImmInstrInfo &III,
 443                        bool PostRA) const;
 444
 445   /// getRegNumForOperand - some operands use different numbering schemes
 446   /// for the same registers. For example, a VSX instruction may have any of
 447   /// vs0-vs63 allocated whereas an Altivec instruction could only have
 448   /// vs32-vs63 allocated (numbered as v0-v31). This function returns the actual
 449   /// register number needed for the opcode/operand number combination.
 450   /// The operand number argument will be useful when we need to extend this
 451   /// to instructions that use both Altivec and VSX numbering (for different
 452   /// operands).
 453   static unsigned getRegNumForOperand(const MCInstrDesc &Desc, unsigned Reg,
 454                                       unsigned OpNo) {
 455     int16_t regClass = Desc.OpInfo[OpNo].RegClass;
 456     switch (regClass) {
 457       // We store F0-F31, VF0-VF31 in MCOperand and it should be F0-F31,
 458       // VSX32-VSX63 during encoding/disassembling
 459       case PPC::VSSRCRegClassID:
 460       case PPC::VSFRCRegClassID:
 461         if (isVFRegister(Reg))
 462           return PPC::VSX32 + (Reg - PPC::VF0);
 463         break;
 464       // We store VSL0-VSL31, V0-V31 in MCOperand and it should be VSL0-VSL31,
 465       // VSX32-VSX63 during encoding/disassembling
 466       case PPC::VSRCRegClassID:
 467         if (isVRRegister(Reg))
 468           return PPC::VSX32 + (Reg - PPC::V0);
 469         break;
 470       // Other RegClass doesn't need mapping
 471       default:
 472         break;
 473     }
 474     return Reg;
 475   }
 476
 477   /// Check \p Opcode is BDNZ (Decrement CTR and branch if it is still nonzero).
 478   bool isBDNZ(unsigned Opcode) const;
 479
 480   /// Find the hardware loop instruction used to set-up the specified loop.
 481   /// On PPC, we have two instructions used to set-up the hardware loop
 482   /// (MTCTRloop, MTCTR8loop) with corresponding endloop (BDNZ, BDNZ8)
 483   /// instructions to indicate the end of a loop.
 484   MachineInstr *findLoopInstr(MachineBasicBlock &PreHeader) const;
 485
 486   /// Analyze the loop code to find the loop induction variable and compare used
 487   /// to compute the number of iterations. Currently, we analyze loop that are
 488   /// controlled using hardware loops.  In this case, the induction variable
 489   /// instruction is null.  For all other cases, this function returns true,
 490   /// which means we're unable to analyze it. \p IndVarInst and \p CmpInst will
 491   /// return new values when we can analyze the readonly loop \p L, otherwise,
 492   /// nothing got changed
 493   bool analyzeLoop(MachineLoop &L, MachineInstr *&IndVarInst,
 494                    MachineInstr *&CmpInst) const override;
 495   /// Generate code to reduce the loop iteration by one and check if the loop
 496   /// is finished.  Return the value/register of the new loop count.  We need
 497   /// this function when peeling off one or more iterations of a loop. This
 498   /// function assumes the last iteration is peeled first.
 499   unsigned reduceLoopCount(MachineBasicBlock &MBB, MachineBasicBlock &PreHeader,
 500                            MachineInstr *IndVar, MachineInstr &Cmp,
 501                            SmallVectorImpl<MachineOperand> &Cond,
 502                            SmallVectorImpl<MachineInstr *> &PrevInsts,
 503                            unsigned Iter, unsigned MaxIter) const override;
 504 };
 505
 506 }
 507
 508 #endif