PPCCTRLoops.cpp revision 263508 
1//===-- PPCCTRLoops.cpp - Identify and generate CTR loops -----------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This pass identifies loops where we can generate the PPC branch instructions
11// that decrement and test the count register (CTR) (bdnz and friends).
12//
13// The pattern that defines the induction variable can changed depending on
14// prior optimizations.  For example, the IndVarSimplify phase run by 'opt'
15// normalizes induction variables, and the Loop Strength Reduction pass
16// run by 'llc' may also make changes to the induction variable.
17//
18// Criteria for CTR loops:
19//  - Countable loops (w/ ind. var for a trip count)
20//  - Try inner-most loops first
21//  - No nested CTR loops.
22//  - No function calls in loops.
23//
24//===----------------------------------------------------------------------===//
25
26#define DEBUG_TYPE "ctrloops"
27
28#include "llvm/Transforms/Scalar.h"
29#include "llvm/ADT/Statistic.h"
30#include "llvm/ADT/STLExtras.h"
31#include "llvm/Analysis/Dominators.h"
32#include "llvm/Analysis/LoopInfo.h"
33#include "llvm/Analysis/ScalarEvolutionExpander.h"
34#include "llvm/IR/Constants.h"
35#include "llvm/IR/DerivedTypes.h"
36#include "llvm/IR/InlineAsm.h"
37#include "llvm/IR/Instructions.h"
38#include "llvm/IR/IntrinsicInst.h"
39#include "llvm/IR/Module.h"
40#include "llvm/PassSupport.h"
41#include "llvm/Support/CommandLine.h"
42#include "llvm/Support/Debug.h"
43#include "llvm/Support/ValueHandle.h"
44#include "llvm/Support/raw_ostream.h"
45#include "llvm/Transforms/Utils/BasicBlockUtils.h"
46#include "llvm/Transforms/Utils/Local.h"
47#include "llvm/Transforms/Utils/LoopUtils.h"
48#include "llvm/Target/TargetLibraryInfo.h"
49#include "PPCTargetMachine.h"
50#include "PPC.h"
51
52#ifndef NDEBUG
53#include "llvm/CodeGen/MachineDominators.h"
54#include "llvm/CodeGen/MachineFunction.h"
55#include "llvm/CodeGen/MachineFunctionPass.h"
56#include "llvm/CodeGen/MachineRegisterInfo.h"
57#endif
58
59#include <algorithm>
60#include <vector>
61
62using namespace llvm;
63
64#ifndef NDEBUG
65static cl::opt<int> CTRLoopLimit("ppc-max-ctrloop", cl::Hidden, cl::init(-1));
66#endif
67
68STATISTIC(NumCTRLoops, "Number of loops converted to CTR loops");
69
70namespace llvm {
71  void initializePPCCTRLoopsPass(PassRegistry&);
72#ifndef NDEBUG
73  void initializePPCCTRLoopsVerifyPass(PassRegistry&);
74#endif
75}
76
77namespace {
78  struct PPCCTRLoops : public FunctionPass {
79
80#ifndef NDEBUG
81    static int Counter;
82#endif
83
84  public:
85    static char ID;
86
87    PPCCTRLoops() : FunctionPass(ID), TM(0) {
88      initializePPCCTRLoopsPass(*PassRegistry::getPassRegistry());
89    }
90    PPCCTRLoops(PPCTargetMachine &TM) : FunctionPass(ID), TM(&TM) {
91      initializePPCCTRLoopsPass(*PassRegistry::getPassRegistry());
92    }
93
94    virtual bool runOnFunction(Function &F);
95
96    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
97      AU.addRequired<LoopInfo>();
98      AU.addPreserved<LoopInfo>();
99      AU.addRequired<DominatorTree>();
100      AU.addPreserved<DominatorTree>();
101      AU.addRequired<ScalarEvolution>();
102    }
103
104  private:
105    bool mightUseCTR(const Triple &TT, BasicBlock *BB);
106    bool convertToCTRLoop(Loop *L);
107
108  private:
109    PPCTargetMachine *TM;
110    LoopInfo *LI;
111    ScalarEvolution *SE;
112    DataLayout *TD;
113    DominatorTree *DT;
114    const TargetLibraryInfo *LibInfo;
115  };
116
117  char PPCCTRLoops::ID = 0;
118#ifndef NDEBUG
119  int PPCCTRLoops::Counter = 0;
120#endif
121
122#ifndef NDEBUG
123  struct PPCCTRLoopsVerify : public MachineFunctionPass {
124  public:
125    static char ID;
126
127    PPCCTRLoopsVerify() : MachineFunctionPass(ID) {
128      initializePPCCTRLoopsVerifyPass(*PassRegistry::getPassRegistry());
129    }
130
131    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
132      AU.addRequired<MachineDominatorTree>();
133      MachineFunctionPass::getAnalysisUsage(AU);
134    }
135
136    virtual bool runOnMachineFunction(MachineFunction &MF);
137
138  private:
139    MachineDominatorTree *MDT;
140  };
141
142  char PPCCTRLoopsVerify::ID = 0;
143#endif // NDEBUG
144} // end anonymous namespace
145
146INITIALIZE_PASS_BEGIN(PPCCTRLoops, "ppc-ctr-loops", "PowerPC CTR Loops",
147                      false, false)
148INITIALIZE_PASS_DEPENDENCY(DominatorTree)
149INITIALIZE_PASS_DEPENDENCY(LoopInfo)
150INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
151INITIALIZE_PASS_END(PPCCTRLoops, "ppc-ctr-loops", "PowerPC CTR Loops",
152                    false, false)
153
154FunctionPass *llvm::createPPCCTRLoops(PPCTargetMachine &TM) {
155  return new PPCCTRLoops(TM);
156}
157
158#ifndef NDEBUG
159INITIALIZE_PASS_BEGIN(PPCCTRLoopsVerify, "ppc-ctr-loops-verify",
160                      "PowerPC CTR Loops Verify", false, false)
161INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
162INITIALIZE_PASS_END(PPCCTRLoopsVerify, "ppc-ctr-loops-verify",
163                    "PowerPC CTR Loops Verify", false, false)
164
165FunctionPass *llvm::createPPCCTRLoopsVerify() {
166  return new PPCCTRLoopsVerify();
167}
168#endif // NDEBUG
169
170bool PPCCTRLoops::runOnFunction(Function &F) {
171  LI = &getAnalysis<LoopInfo>();
172  SE = &getAnalysis<ScalarEvolution>();
173  DT = &getAnalysis<DominatorTree>();
174  TD = getAnalysisIfAvailable<DataLayout>();
175  LibInfo = getAnalysisIfAvailable<TargetLibraryInfo>();
176
177  bool MadeChange = false;
178
179  for (LoopInfo::iterator I = LI->begin(), E = LI->end();
180       I != E; ++I) {
181    Loop *L = *I;
182    if (!L->getParentLoop())
183      MadeChange |= convertToCTRLoop(L);
184  }
185
186  return MadeChange;
187}
188
189bool PPCCTRLoops::mightUseCTR(const Triple &TT, BasicBlock *BB) {
190  for (BasicBlock::iterator J = BB->begin(), JE = BB->end();
191       J != JE; ++J) {
192    if (CallInst *CI = dyn_cast<CallInst>(J)) {
193      if (InlineAsm *IA = dyn_cast<InlineAsm>(CI->getCalledValue())) {
194        // Inline ASM is okay, unless it clobbers the ctr register.
195        InlineAsm::ConstraintInfoVector CIV = IA->ParseConstraints();
196        for (unsigned i = 0, ie = CIV.size(); i < ie; ++i) {
197          InlineAsm::ConstraintInfo &C = CIV[i];
198          if (C.Type != InlineAsm::isInput)
199            for (unsigned j = 0, je = C.Codes.size(); j < je; ++j)
200              if (StringRef(C.Codes[j]).equals_lower("{ctr}"))
201                return true;
202        }
203
204        continue;
205      }
206
207      if (!TM)
208        return true;
209      const TargetLowering *TLI = TM->getTargetLowering();
210
211      if (Function *F = CI->getCalledFunction()) {
212        // Most intrinsics don't become function calls, but some might.
213        // sin, cos, exp and log are always calls.
214        unsigned Opcode;
215        if (F->getIntrinsicID() != Intrinsic::not_intrinsic) {
216          switch (F->getIntrinsicID()) {
217          default: continue;
218
219// VisualStudio defines setjmp as _setjmp
220#if defined(_MSC_VER) && defined(setjmp) && \
221                       !defined(setjmp_undefined_for_msvc)
222#  pragma push_macro("setjmp")
223#  undef setjmp
224#  define setjmp_undefined_for_msvc
225#endif
226
227          case Intrinsic::setjmp:
228
229#if defined(_MSC_VER) && defined(setjmp_undefined_for_msvc)
230 // let's return it to _setjmp state
231#  pragma pop_macro("setjmp")
232#  undef setjmp_undefined_for_msvc
233#endif
234
235          case Intrinsic::longjmp:
236
237          // Exclude eh_sjlj_setjmp; we don't need to exclude eh_sjlj_longjmp
238          // because, although it does clobber the counter register, the
239          // control can't then return to inside the loop unless there is also
240          // an eh_sjlj_setjmp.
241          case Intrinsic::eh_sjlj_setjmp:
242
243          case Intrinsic::memcpy:
244          case Intrinsic::memmove:
245          case Intrinsic::memset:
246          case Intrinsic::powi:
247          case Intrinsic::log:
248          case Intrinsic::log2:
249          case Intrinsic::log10:
250          case Intrinsic::exp:
251          case Intrinsic::exp2:
252          case Intrinsic::pow:
253          case Intrinsic::sin:
254          case Intrinsic::cos:
255            return true;
256          case Intrinsic::copysign:
257            if (CI->getArgOperand(0)->getType()->getScalarType()->
258                isPPC_FP128Ty())
259              return true;
260            else
261              continue; // ISD::FCOPYSIGN is never a library call.
262          case Intrinsic::sqrt:      Opcode = ISD::FSQRT;      break;
263          case Intrinsic::floor:     Opcode = ISD::FFLOOR;     break;
264          case Intrinsic::ceil:      Opcode = ISD::FCEIL;      break;
265          case Intrinsic::trunc:     Opcode = ISD::FTRUNC;     break;
266          case Intrinsic::rint:      Opcode = ISD::FRINT;      break;
267          case Intrinsic::nearbyint: Opcode = ISD::FNEARBYINT; break;
268          case Intrinsic::round:     Opcode = ISD::FROUND;     break;
269          }
270        }
271
272        // PowerPC does not use [US]DIVREM or other library calls for
273        // operations on regular types which are not otherwise library calls
274        // (i.e. soft float or atomics). If adapting for targets that do,
275        // additional care is required here.
276
277        LibFunc::Func Func;
278        if (!F->hasLocalLinkage() && F->hasName() && LibInfo &&
279            LibInfo->getLibFunc(F->getName(), Func) &&
280            LibInfo->hasOptimizedCodeGen(Func)) {
281          // Non-read-only functions are never treated as intrinsics.
282          if (!CI->onlyReadsMemory())
283            return true;
284
285          // Conversion happens only for FP calls.
286          if (!CI->getArgOperand(0)->getType()->isFloatingPointTy())
287            return true;
288
289          switch (Func) {
290          default: return true;
291          case LibFunc::copysign:
292          case LibFunc::copysignf:
293            continue; // ISD::FCOPYSIGN is never a library call.
294          case LibFunc::copysignl:
295            return true;
296          case LibFunc::fabs:
297          case LibFunc::fabsf:
298          case LibFunc::fabsl:
299            continue; // ISD::FABS is never a library call.
300          case LibFunc::sqrt:
301          case LibFunc::sqrtf:
302          case LibFunc::sqrtl:
303            Opcode = ISD::FSQRT; break;
304          case LibFunc::floor:
305          case LibFunc::floorf:
306          case LibFunc::floorl:
307            Opcode = ISD::FFLOOR; break;
308          case LibFunc::nearbyint:
309          case LibFunc::nearbyintf:
310          case LibFunc::nearbyintl:
311            Opcode = ISD::FNEARBYINT; break;
312          case LibFunc::ceil:
313          case LibFunc::ceilf:
314          case LibFunc::ceill:
315            Opcode = ISD::FCEIL; break;
316          case LibFunc::rint:
317          case LibFunc::rintf:
318          case LibFunc::rintl:
319            Opcode = ISD::FRINT; break;
320          case LibFunc::round:
321          case LibFunc::roundf:
322          case LibFunc::roundl:
323            Opcode = ISD::FROUND; break;
324          case LibFunc::trunc:
325          case LibFunc::truncf:
326          case LibFunc::truncl:
327            Opcode = ISD::FTRUNC; break;
328          }
329
330          MVT VTy =
331            TLI->getSimpleValueType(CI->getArgOperand(0)->getType(), true);
332          if (VTy == MVT::Other)
333            return true;
334
335          if (TLI->isOperationLegalOrCustom(Opcode, VTy))
336            continue;
337          else if (VTy.isVector() &&
338                   TLI->isOperationLegalOrCustom(Opcode, VTy.getScalarType()))
339            continue;
340
341          return true;
342        }
343      }
344
345      return true;
346    } else if (isa<BinaryOperator>(J) &&
347               J->getType()->getScalarType()->isPPC_FP128Ty()) {
348      // Most operations on ppc_f128 values become calls.
349      return true;
350    } else if (isa<UIToFPInst>(J) || isa<SIToFPInst>(J) ||
351               isa<FPToUIInst>(J) || isa<FPToSIInst>(J)) {
352      CastInst *CI = cast<CastInst>(J);
353      if (CI->getSrcTy()->getScalarType()->isPPC_FP128Ty() ||
354          CI->getDestTy()->getScalarType()->isPPC_FP128Ty() ||
355          (TT.isArch32Bit() &&
356           (CI->getSrcTy()->getScalarType()->isIntegerTy(64) ||
357            CI->getDestTy()->getScalarType()->isIntegerTy(64))
358          ))
359        return true;
360    } else if (TT.isArch32Bit() &&
361               J->getType()->getScalarType()->isIntegerTy(64) &&
362               (J->getOpcode() == Instruction::UDiv ||
363                J->getOpcode() == Instruction::SDiv ||
364                J->getOpcode() == Instruction::URem ||
365                J->getOpcode() == Instruction::SRem)) {
366      return true;
367    } else if (isa<IndirectBrInst>(J) || isa<InvokeInst>(J)) {
368      // On PowerPC, indirect jumps use the counter register.
369      return true;
370    } else if (SwitchInst *SI = dyn_cast<SwitchInst>(J)) {
371      if (!TM)
372        return true;
373      const TargetLowering *TLI = TM->getTargetLowering();
374
375      if (TLI->supportJumpTables() &&
376          SI->getNumCases()+1 >= (unsigned) TLI->getMinimumJumpTableEntries())
377        return true;
378    }
379  }
380
381  return false;
382}
383
384bool PPCCTRLoops::convertToCTRLoop(Loop *L) {
385  bool MadeChange = false;
386
387  Triple TT = Triple(L->getHeader()->getParent()->getParent()->
388                     getTargetTriple());
389  if (!TT.isArch32Bit() && !TT.isArch64Bit())
390    return MadeChange; // Unknown arch. type.
391
392  // Process nested loops first.
393  for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) {
394    MadeChange |= convertToCTRLoop(*I);
395  }
396
397  // If a nested loop has been converted, then we can't convert this loop.
398  if (MadeChange)
399    return MadeChange;
400
401#ifndef NDEBUG
402  // Stop trying after reaching the limit (if any).
403  int Limit = CTRLoopLimit;
404  if (Limit >= 0) {
405    if (Counter >= CTRLoopLimit)
406      return false;
407    Counter++;
408  }
409#endif
410
411  // We don't want to spill/restore the counter register, and so we don't
412  // want to use the counter register if the loop contains calls.
413  for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
414       I != IE; ++I)
415    if (mightUseCTR(TT, *I))
416      return MadeChange;
417
418  SmallVector<BasicBlock*, 4> ExitingBlocks;
419  L->getExitingBlocks(ExitingBlocks);
420
421  BasicBlock *CountedExitBlock = 0;
422  const SCEV *ExitCount = 0;
423  BranchInst *CountedExitBranch = 0;
424  for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(),
425       IE = ExitingBlocks.end(); I != IE; ++I) {
426    const SCEV *EC = SE->getExitCount(L, *I);
427    DEBUG(dbgs() << "Exit Count for " << *L << " from block " <<
428                    (*I)->getName() << ": " << *EC << "\n");
429    if (isa<SCEVCouldNotCompute>(EC))
430      continue;
431    if (const SCEVConstant *ConstEC = dyn_cast<SCEVConstant>(EC)) {
432      if (ConstEC->getValue()->isZero())
433        continue;
434    } else if (!SE->isLoopInvariant(EC, L))
435      continue;
436
437    if (SE->getTypeSizeInBits(EC->getType()) > (TT.isArch64Bit() ? 64 : 32))
438      continue;
439
440    // We now have a loop-invariant count of loop iterations (which is not the
441    // constant zero) for which we know that this loop will not exit via this
442    // exisiting block.
443
444    // We need to make sure that this block will run on every loop iteration.
445    // For this to be true, we must dominate all blocks with backedges. Such
446    // blocks are in-loop predecessors to the header block.
447    bool NotAlways = false;
448    for (pred_iterator PI = pred_begin(L->getHeader()),
449         PIE = pred_end(L->getHeader()); PI != PIE; ++PI) {
450      if (!L->contains(*PI))
451        continue;
452
453      if (!DT->dominates(*I, *PI)) {
454        NotAlways = true;
455        break;
456      }
457    }
458
459    if (NotAlways)
460      continue;
461
462    // Make sure this blocks ends with a conditional branch.
463    Instruction *TI = (*I)->getTerminator();
464    if (!TI)
465      continue;
466
467    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
468      if (!BI->isConditional())
469        continue;
470
471      CountedExitBranch = BI;
472    } else
473      continue;
474
475    // Note that this block may not be the loop latch block, even if the loop
476    // has a latch block.
477    CountedExitBlock = *I;
478    ExitCount = EC;
479    break;
480  }
481
482  if (!CountedExitBlock)
483    return MadeChange;
484
485  BasicBlock *Preheader = L->getLoopPreheader();
486
487  // If we don't have a preheader, then insert one. If we already have a
488  // preheader, then we can use it (except if the preheader contains a use of
489  // the CTR register because some such uses might be reordered by the
490  // selection DAG after the mtctr instruction).
491  if (!Preheader || mightUseCTR(TT, Preheader))
492    Preheader = InsertPreheaderForLoop(L, this);
493  if (!Preheader)
494    return MadeChange;
495
496  DEBUG(dbgs() << "Preheader for exit count: " << Preheader->getName() << "\n");
497
498  // Insert the count into the preheader and replace the condition used by the
499  // selected branch.
500  MadeChange = true;
501
502  SCEVExpander SCEVE(*SE, "loopcnt");
503  LLVMContext &C = SE->getContext();
504  Type *CountType = TT.isArch64Bit() ? Type::getInt64Ty(C) :
505                                       Type::getInt32Ty(C);
506  if (!ExitCount->getType()->isPointerTy() &&
507      ExitCount->getType() != CountType)
508    ExitCount = SE->getZeroExtendExpr(ExitCount, CountType);
509  ExitCount = SE->getAddExpr(ExitCount,
510                             SE->getConstant(CountType, 1));
511  Value *ECValue = SCEVE.expandCodeFor(ExitCount, CountType,
512                                       Preheader->getTerminator());
513
514  IRBuilder<> CountBuilder(Preheader->getTerminator());
515  Module *M = Preheader->getParent()->getParent();
516  Value *MTCTRFunc = Intrinsic::getDeclaration(M, Intrinsic::ppc_mtctr,
517                                               CountType);
518  CountBuilder.CreateCall(MTCTRFunc, ECValue);
519
520  IRBuilder<> CondBuilder(CountedExitBranch);
521  Value *DecFunc =
522    Intrinsic::getDeclaration(M, Intrinsic::ppc_is_decremented_ctr_nonzero);
523  Value *NewCond = CondBuilder.CreateCall(DecFunc);
524  Value *OldCond = CountedExitBranch->getCondition();
525  CountedExitBranch->setCondition(NewCond);
526
527  // The false branch must exit the loop.
528  if (!L->contains(CountedExitBranch->getSuccessor(0)))
529    CountedExitBranch->swapSuccessors();
530
531  // The old condition may be dead now, and may have even created a dead PHI
532  // (the original induction variable).
533  RecursivelyDeleteTriviallyDeadInstructions(OldCond);
534  DeleteDeadPHIs(CountedExitBlock);
535
536  ++NumCTRLoops;
537  return MadeChange;
538}
539
540#ifndef NDEBUG
541static bool clobbersCTR(const MachineInstr *MI) {
542  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
543    const MachineOperand &MO = MI->getOperand(i);
544    if (MO.isReg()) {
545      if (MO.isDef() && (MO.getReg() == PPC::CTR || MO.getReg() == PPC::CTR8))
546        return true;
547    } else if (MO.isRegMask()) {
548      if (MO.clobbersPhysReg(PPC::CTR) || MO.clobbersPhysReg(PPC::CTR8))
549        return true;
550    }
551  }
552
553  return false;
554}
555
556static bool verifyCTRBranch(MachineBasicBlock *MBB,
557                            MachineBasicBlock::iterator I) {
558  MachineBasicBlock::iterator BI = I;
559  SmallSet<MachineBasicBlock *, 16>   Visited;
560  SmallVector<MachineBasicBlock *, 8> Preds;
561  bool CheckPreds;
562
563  if (I == MBB->begin()) {
564    Visited.insert(MBB);
565    goto queue_preds;
566  } else
567    --I;
568
569check_block:
570  Visited.insert(MBB);
571  if (I == MBB->end())
572    goto queue_preds;
573
574  CheckPreds = true;
575  for (MachineBasicBlock::iterator IE = MBB->begin();; --I) {
576    unsigned Opc = I->getOpcode();
577    if (Opc == PPC::MTCTRloop || Opc == PPC::MTCTR8loop) {
578      CheckPreds = false;
579      break;
580    }
581
582    if (I != BI && clobbersCTR(I)) {
583      DEBUG(dbgs() << "BB#" << MBB->getNumber() << " (" <<
584                      MBB->getFullName() << ") instruction " << *I <<
585                      " clobbers CTR, invalidating " << "BB#" <<
586                      BI->getParent()->getNumber() << " (" <<
587                      BI->getParent()->getFullName() << ") instruction " <<
588                      *BI << "\n");
589      return false;
590    }
591
592    if (I == IE)
593      break;
594  }
595
596  if (!CheckPreds && Preds.empty())
597    return true;
598
599  if (CheckPreds) {
600queue_preds:
601    if (MachineFunction::iterator(MBB) == MBB->getParent()->begin()) {
602      DEBUG(dbgs() << "Unable to find a MTCTR instruction for BB#" <<
603                      BI->getParent()->getNumber() << " (" <<
604                      BI->getParent()->getFullName() << ") instruction " <<
605                      *BI << "\n");
606      return false;
607    }
608
609    for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
610         PIE = MBB->pred_end(); PI != PIE; ++PI)
611      Preds.push_back(*PI);
612  }
613
614  do {
615    MBB = Preds.pop_back_val();
616    if (!Visited.count(MBB)) {
617      I = MBB->getLastNonDebugInstr();
618      goto check_block;
619    }
620  } while (!Preds.empty());
621
622  return true;
623}
624
625bool PPCCTRLoopsVerify::runOnMachineFunction(MachineFunction &MF) {
626  MDT = &getAnalysis<MachineDominatorTree>();
627
628  // Verify that all bdnz/bdz instructions are dominated by a loop mtctr before
629  // any other instructions that might clobber the ctr register.
630  for (MachineFunction::iterator I = MF.begin(), IE = MF.end();
631       I != IE; ++I) {
632    MachineBasicBlock *MBB = I;
633    if (!MDT->isReachableFromEntry(MBB))
634      continue;
635
636    for (MachineBasicBlock::iterator MII = MBB->getFirstTerminator(),
637      MIIE = MBB->end(); MII != MIIE; ++MII) {
638      unsigned Opc = MII->getOpcode();
639      if (Opc == PPC::BDNZ8 || Opc == PPC::BDNZ ||
640          Opc == PPC::BDZ8  || Opc == PPC::BDZ)
641        if (!verifyCTRBranch(MBB, MII))
642          llvm_unreachable("Invalid PPC CTR loop!");
643    }
644  }
645
646  return false;
647}
648#endif // NDEBUG
649
650