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 #include "llvm/Transforms/Scalar.h"
27 #include "PPC.h"
28 #include "PPCTargetMachine.h"
29 #include "llvm/ADT/STLExtras.h"
30 #include "llvm/ADT/Statistic.h"
31 #include "llvm/Analysis/LoopInfo.h"
32 #include "llvm/Analysis/ScalarEvolutionExpander.h"
33 #include "llvm/IR/Constants.h"
34 #include "llvm/IR/DerivedTypes.h"
35 #include "llvm/IR/Dominators.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/IR/ValueHandle.h"
41 #include "llvm/PassSupport.h"
42 #include "llvm/Support/CommandLine.h"
43 #include "llvm/Support/Debug.h"
44 #include "llvm/Support/raw_ostream.h"
45 #include "llvm/Target/TargetLibraryInfo.h"
46 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
47 #include "llvm/Transforms/Utils/Local.h"
48 #include "llvm/Transforms/Utils/LoopUtils.h"
49 
50 #ifndef NDEBUG
51 #include "llvm/CodeGen/MachineDominators.h"
52 #include "llvm/CodeGen/MachineFunction.h"
53 #include "llvm/CodeGen/MachineFunctionPass.h"
54 #include "llvm/CodeGen/MachineRegisterInfo.h"
55 #endif
56 
57 #include <algorithm>
58 #include <vector>
59 
60 using namespace llvm;
61 
62 #define DEBUG_TYPE "ctrloops"
63 
64 #ifndef NDEBUG
65 static cl::opt<int> CTRLoopLimit("ppc-max-ctrloop", cl::Hidden, cl::init(-1));
66 #endif
67 
68 STATISTIC(NumCTRLoops, "Number of loops converted to CTR loops");
69 
70 namespace llvm {
71   void initializePPCCTRLoopsPass(PassRegistry&);
72 #ifndef NDEBUG
73   void initializePPCCTRLoopsVerifyPass(PassRegistry&);
74 #endif
75 }
76 
77 namespace {
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(nullptr) {
88       initializePPCCTRLoopsPass(*PassRegistry::getPassRegistry());
89     }
90     PPCCTRLoops(PPCTargetMachine &TM) : FunctionPass(ID), TM(&TM) {
91       initializePPCCTRLoopsPass(*PassRegistry::getPassRegistry());
92     }
93 
94     bool runOnFunction(Function &F) override;
95 
96     void getAnalysisUsage(AnalysisUsage &AU) const override {
97       AU.addRequired<LoopInfo>();
98       AU.addPreserved<LoopInfo>();
99       AU.addRequired<DominatorTreeWrapperPass>();
100       AU.addPreserved<DominatorTreeWrapperPass>();
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     const DataLayout *DL;
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     void getAnalysisUsage(AnalysisUsage &AU) const override {
132       AU.addRequired<MachineDominatorTree>();
133       MachineFunctionPass::getAnalysisUsage(AU);
134     }
135 
136     bool runOnMachineFunction(MachineFunction &MF) override;
137 
138   private:
139     MachineDominatorTree *MDT;
140   };
141 
142   char PPCCTRLoopsVerify::ID = 0;
143 #endif // NDEBUG
144 } // end anonymous namespace
145 
146 INITIALIZE_PASS_BEGIN(PPCCTRLoops, "ppc-ctr-loops", "PowerPC CTR Loops",
147                       false, false)
148 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
149 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
150 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
151 INITIALIZE_PASS_END(PPCCTRLoops, "ppc-ctr-loops", "PowerPC CTR Loops",
152                     false, false)
153 
154 FunctionPass *llvm::createPPCCTRLoops(PPCTargetMachine &TM) {
155   return new PPCCTRLoops(TM);
156 }
157 
158 #ifndef NDEBUG
159 INITIALIZE_PASS_BEGIN(PPCCTRLoopsVerify, "ppc-ctr-loops-verify",
160                       "PowerPC CTR Loops Verify", false, false)
161 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
162 INITIALIZE_PASS_END(PPCCTRLoopsVerify, "ppc-ctr-loops-verify",
163                     "PowerPC CTR Loops Verify", false, false)
164 
165 FunctionPass *llvm::createPPCCTRLoopsVerify() {
166   return new PPCCTRLoopsVerify();
167 }
168 #endif // NDEBUG
169 
170 bool PPCCTRLoops::runOnFunction(Function &F) {
171   LI = &getAnalysis<LoopInfo>();
172   SE = &getAnalysis<ScalarEvolution>();
173   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
174   DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
175   DL = DLP ? &DLP->getDataLayout() : nullptr;
176   LibInfo = getAnalysisIfAvailable<TargetLibraryInfo>();
177 
178   bool MadeChange = false;
179 
180   for (LoopInfo::iterator I = LI->begin(), E = LI->end();
181        I != E; ++I) {
182     Loop *L = *I;
183     if (!L->getParentLoop())
184       MadeChange |= convertToCTRLoop(L);
185   }
186 
187   return MadeChange;
188 }
189 
190 static bool isLargeIntegerTy(bool Is32Bit, Type *Ty) {
191   if (IntegerType *ITy = dyn_cast<IntegerType>(Ty))
192     return ITy->getBitWidth() > (Is32Bit ? 32U : 64U);
193 
194   return false;
195 }
196 
197 bool PPCCTRLoops::mightUseCTR(const Triple &TT, BasicBlock *BB) {
198   for (BasicBlock::iterator J = BB->begin(), JE = BB->end();
199        J != JE; ++J) {
200     if (CallInst *CI = dyn_cast<CallInst>(J)) {
201       if (InlineAsm *IA = dyn_cast<InlineAsm>(CI->getCalledValue())) {
202         // Inline ASM is okay, unless it clobbers the ctr register.
203         InlineAsm::ConstraintInfoVector CIV = IA->ParseConstraints();
204         for (unsigned i = 0, ie = CIV.size(); i < ie; ++i) {
205           InlineAsm::ConstraintInfo &C = CIV[i];
206           if (C.Type != InlineAsm::isInput)
207             for (unsigned j = 0, je = C.Codes.size(); j < je; ++j)
208               if (StringRef(C.Codes[j]).equals_lower("{ctr}"))
209                 return true;
210         }
211 
212         continue;
213       }
214 
215       if (!TM)
216         return true;
217       const TargetLowering *TLI = TM->getSubtargetImpl()->getTargetLowering();
218 
219       if (Function *F = CI->getCalledFunction()) {
220         // Most intrinsics don't become function calls, but some might.
221         // sin, cos, exp and log are always calls.
222         unsigned Opcode;
223         if (F->getIntrinsicID() != Intrinsic::not_intrinsic) {
224           switch (F->getIntrinsicID()) {
225           default: continue;
226 
227 // VisualStudio defines setjmp as _setjmp
228 #if defined(_MSC_VER) && defined(setjmp) && \
229                        !defined(setjmp_undefined_for_msvc)
230 #  pragma push_macro("setjmp")
231 #  undef setjmp
232 #  define setjmp_undefined_for_msvc
233 #endif
234 
235           case Intrinsic::setjmp:
236 
237 #if defined(_MSC_VER) && defined(setjmp_undefined_for_msvc)
238  // let's return it to _setjmp state
239 #  pragma pop_macro("setjmp")
240 #  undef setjmp_undefined_for_msvc
241 #endif
242 
243           case Intrinsic::longjmp:
244 
245           // Exclude eh_sjlj_setjmp; we don't need to exclude eh_sjlj_longjmp
246           // because, although it does clobber the counter register, the
247           // control can't then return to inside the loop unless there is also
248           // an eh_sjlj_setjmp.
249           case Intrinsic::eh_sjlj_setjmp:
250 
251           case Intrinsic::memcpy:
252           case Intrinsic::memmove:
253           case Intrinsic::memset:
254           case Intrinsic::powi:
255           case Intrinsic::log:
256           case Intrinsic::log2:
257           case Intrinsic::log10:
258           case Intrinsic::exp:
259           case Intrinsic::exp2:
260           case Intrinsic::pow:
261           case Intrinsic::sin:
262           case Intrinsic::cos:
263             return true;
264           case Intrinsic::copysign:
265             if (CI->getArgOperand(0)->getType()->getScalarType()->
266                 isPPC_FP128Ty())
267               return true;
268             else
269               continue; // ISD::FCOPYSIGN is never a library call.
270           case Intrinsic::sqrt:      Opcode = ISD::FSQRT;      break;
271           case Intrinsic::floor:     Opcode = ISD::FFLOOR;     break;
272           case Intrinsic::ceil:      Opcode = ISD::FCEIL;      break;
273           case Intrinsic::trunc:     Opcode = ISD::FTRUNC;     break;
274           case Intrinsic::rint:      Opcode = ISD::FRINT;      break;
275           case Intrinsic::nearbyint: Opcode = ISD::FNEARBYINT; break;
276           case Intrinsic::round:     Opcode = ISD::FROUND;     break;
277           }
278         }
279 
280         // PowerPC does not use [US]DIVREM or other library calls for
281         // operations on regular types which are not otherwise library calls
282         // (i.e. soft float or atomics). If adapting for targets that do,
283         // additional care is required here.
284 
285         LibFunc::Func Func;
286         if (!F->hasLocalLinkage() && F->hasName() && LibInfo &&
287             LibInfo->getLibFunc(F->getName(), Func) &&
288             LibInfo->hasOptimizedCodeGen(Func)) {
289           // Non-read-only functions are never treated as intrinsics.
290           if (!CI->onlyReadsMemory())
291             return true;
292 
293           // Conversion happens only for FP calls.
294           if (!CI->getArgOperand(0)->getType()->isFloatingPointTy())
295             return true;
296 
297           switch (Func) {
298           default: return true;
299           case LibFunc::copysign:
300           case LibFunc::copysignf:
301             continue; // ISD::FCOPYSIGN is never a library call.
302           case LibFunc::copysignl:
303             return true;
304           case LibFunc::fabs:
305           case LibFunc::fabsf:
306           case LibFunc::fabsl:
307             continue; // ISD::FABS is never a library call.
308           case LibFunc::sqrt:
309           case LibFunc::sqrtf:
310           case LibFunc::sqrtl:
311             Opcode = ISD::FSQRT; break;
312           case LibFunc::floor:
313           case LibFunc::floorf:
314           case LibFunc::floorl:
315             Opcode = ISD::FFLOOR; break;
316           case LibFunc::nearbyint:
317           case LibFunc::nearbyintf:
318           case LibFunc::nearbyintl:
319             Opcode = ISD::FNEARBYINT; break;
320           case LibFunc::ceil:
321           case LibFunc::ceilf:
322           case LibFunc::ceill:
323             Opcode = ISD::FCEIL; break;
324           case LibFunc::rint:
325           case LibFunc::rintf:
326           case LibFunc::rintl:
327             Opcode = ISD::FRINT; break;
328           case LibFunc::round:
329           case LibFunc::roundf:
330           case LibFunc::roundl:
331             Opcode = ISD::FROUND; break;
332           case LibFunc::trunc:
333           case LibFunc::truncf:
334           case LibFunc::truncl:
335             Opcode = ISD::FTRUNC; break;
336           }
337 
338           MVT VTy =
339             TLI->getSimpleValueType(CI->getArgOperand(0)->getType(), true);
340           if (VTy == MVT::Other)
341             return true;
342 
343           if (TLI->isOperationLegalOrCustom(Opcode, VTy))
344             continue;
345           else if (VTy.isVector() &&
346                    TLI->isOperationLegalOrCustom(Opcode, VTy.getScalarType()))
347             continue;
348 
349           return true;
350         }
351       }
352 
353       return true;
354     } else if (isa<BinaryOperator>(J) &&
355                J->getType()->getScalarType()->isPPC_FP128Ty()) {
356       // Most operations on ppc_f128 values become calls.
357       return true;
358     } else if (isa<UIToFPInst>(J) || isa<SIToFPInst>(J) ||
359                isa<FPToUIInst>(J) || isa<FPToSIInst>(J)) {
360       CastInst *CI = cast<CastInst>(J);
361       if (CI->getSrcTy()->getScalarType()->isPPC_FP128Ty() ||
362           CI->getDestTy()->getScalarType()->isPPC_FP128Ty() ||
363           isLargeIntegerTy(TT.isArch32Bit(), CI->getSrcTy()->getScalarType()) ||
364           isLargeIntegerTy(TT.isArch32Bit(), CI->getDestTy()->getScalarType()))
365         return true;
366     } else if (isLargeIntegerTy(TT.isArch32Bit(),
367                                 J->getType()->getScalarType()) &&
368                (J->getOpcode() == Instruction::UDiv ||
369                 J->getOpcode() == Instruction::SDiv ||
370                 J->getOpcode() == Instruction::URem ||
371                 J->getOpcode() == Instruction::SRem)) {
372       return true;
373     } else if (TT.isArch32Bit() &&
374                isLargeIntegerTy(false, J->getType()->getScalarType()) &&
375                (J->getOpcode() == Instruction::Shl ||
376                 J->getOpcode() == Instruction::AShr ||
377                 J->getOpcode() == Instruction::LShr)) {
378       // Only on PPC32, for 128-bit integers (specifically not 64-bit
379       // integers), these might be runtime calls.
380       return true;
381     } else if (isa<IndirectBrInst>(J) || isa<InvokeInst>(J)) {
382       // On PowerPC, indirect jumps use the counter register.
383       return true;
384     } else if (SwitchInst *SI = dyn_cast<SwitchInst>(J)) {
385       if (!TM)
386         return true;
387       const TargetLowering *TLI = TM->getSubtargetImpl()->getTargetLowering();
388 
389       if (SI->getNumCases() + 1 >= (unsigned)TLI->getMinimumJumpTableEntries())
390         return true;
391     }
392   }
393 
394   return false;
395 }
396 
397 bool PPCCTRLoops::convertToCTRLoop(Loop *L) {
398   bool MadeChange = false;
399 
400   Triple TT = Triple(L->getHeader()->getParent()->getParent()->
401                      getTargetTriple());
402   if (!TT.isArch32Bit() && !TT.isArch64Bit())
403     return MadeChange; // Unknown arch. type.
404 
405   // Process nested loops first.
406   for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) {
407     MadeChange |= convertToCTRLoop(*I);
408   }
409 
410   // If a nested loop has been converted, then we can't convert this loop.
411   if (MadeChange)
412     return MadeChange;
413 
414 #ifndef NDEBUG
415   // Stop trying after reaching the limit (if any).
416   int Limit = CTRLoopLimit;
417   if (Limit >= 0) {
418     if (Counter >= CTRLoopLimit)
419       return false;
420     Counter++;
421   }
422 #endif
423 
424   // We don't want to spill/restore the counter register, and so we don't
425   // want to use the counter register if the loop contains calls.
426   for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
427        I != IE; ++I)
428     if (mightUseCTR(TT, *I))
429       return MadeChange;
430 
431   SmallVector<BasicBlock*, 4> ExitingBlocks;
432   L->getExitingBlocks(ExitingBlocks);
433 
434   BasicBlock *CountedExitBlock = nullptr;
435   const SCEV *ExitCount = nullptr;
436   BranchInst *CountedExitBranch = nullptr;
437   for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(),
438        IE = ExitingBlocks.end(); I != IE; ++I) {
439     const SCEV *EC = SE->getExitCount(L, *I);
440     DEBUG(dbgs() << "Exit Count for " << *L << " from block " <<
441                     (*I)->getName() << ": " << *EC << "\n");
442     if (isa<SCEVCouldNotCompute>(EC))
443       continue;
444     if (const SCEVConstant *ConstEC = dyn_cast<SCEVConstant>(EC)) {
445       if (ConstEC->getValue()->isZero())
446         continue;
447     } else if (!SE->isLoopInvariant(EC, L))
448       continue;
449 
450     if (SE->getTypeSizeInBits(EC->getType()) > (TT.isArch64Bit() ? 64 : 32))
451       continue;
452 
453     // We now have a loop-invariant count of loop iterations (which is not the
454     // constant zero) for which we know that this loop will not exit via this
455     // exisiting block.
456 
457     // We need to make sure that this block will run on every loop iteration.
458     // For this to be true, we must dominate all blocks with backedges. Such
459     // blocks are in-loop predecessors to the header block.
460     bool NotAlways = false;
461     for (pred_iterator PI = pred_begin(L->getHeader()),
462          PIE = pred_end(L->getHeader()); PI != PIE; ++PI) {
463       if (!L->contains(*PI))
464         continue;
465 
466       if (!DT->dominates(*I, *PI)) {
467         NotAlways = true;
468         break;
469       }
470     }
471 
472     if (NotAlways)
473       continue;
474 
475     // Make sure this blocks ends with a conditional branch.
476     Instruction *TI = (*I)->getTerminator();
477     if (!TI)
478       continue;
479 
480     if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
481       if (!BI->isConditional())
482         continue;
483 
484       CountedExitBranch = BI;
485     } else
486       continue;
487 
488     // Note that this block may not be the loop latch block, even if the loop
489     // has a latch block.
490     CountedExitBlock = *I;
491     ExitCount = EC;
492     break;
493   }
494 
495   if (!CountedExitBlock)
496     return MadeChange;
497 
498   BasicBlock *Preheader = L->getLoopPreheader();
499 
500   // If we don't have a preheader, then insert one. If we already have a
501   // preheader, then we can use it (except if the preheader contains a use of
502   // the CTR register because some such uses might be reordered by the
503   // selection DAG after the mtctr instruction).
504   if (!Preheader || mightUseCTR(TT, Preheader))
505     Preheader = InsertPreheaderForLoop(L, this);
506   if (!Preheader)
507     return MadeChange;
508 
509   DEBUG(dbgs() << "Preheader for exit count: " << Preheader->getName() << "\n");
510 
511   // Insert the count into the preheader and replace the condition used by the
512   // selected branch.
513   MadeChange = true;
514 
515   SCEVExpander SCEVE(*SE, "loopcnt");
516   LLVMContext &C = SE->getContext();
517   Type *CountType = TT.isArch64Bit() ? Type::getInt64Ty(C) :
518                                        Type::getInt32Ty(C);
519   if (!ExitCount->getType()->isPointerTy() &&
520       ExitCount->getType() != CountType)
521     ExitCount = SE->getZeroExtendExpr(ExitCount, CountType);
522   ExitCount = SE->getAddExpr(ExitCount,
523                              SE->getConstant(CountType, 1));
524   Value *ECValue = SCEVE.expandCodeFor(ExitCount, CountType,
525                                        Preheader->getTerminator());
526 
527   IRBuilder<> CountBuilder(Preheader->getTerminator());
528   Module *M = Preheader->getParent()->getParent();
529   Value *MTCTRFunc = Intrinsic::getDeclaration(M, Intrinsic::ppc_mtctr,
530                                                CountType);
531   CountBuilder.CreateCall(MTCTRFunc, ECValue);
532 
533   IRBuilder<> CondBuilder(CountedExitBranch);
534   Value *DecFunc =
535     Intrinsic::getDeclaration(M, Intrinsic::ppc_is_decremented_ctr_nonzero);
536   Value *NewCond = CondBuilder.CreateCall(DecFunc);
537   Value *OldCond = CountedExitBranch->getCondition();
538   CountedExitBranch->setCondition(NewCond);
539 
540   // The false branch must exit the loop.
541   if (!L->contains(CountedExitBranch->getSuccessor(0)))
542     CountedExitBranch->swapSuccessors();
543 
544   // The old condition may be dead now, and may have even created a dead PHI
545   // (the original induction variable).
546   RecursivelyDeleteTriviallyDeadInstructions(OldCond);
547   DeleteDeadPHIs(CountedExitBlock);
548 
549   ++NumCTRLoops;
550   return MadeChange;
551 }
552 
553 #ifndef NDEBUG
554 static bool clobbersCTR(const MachineInstr *MI) {
555   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
556     const MachineOperand &MO = MI->getOperand(i);
557     if (MO.isReg()) {
558       if (MO.isDef() && (MO.getReg() == PPC::CTR || MO.getReg() == PPC::CTR8))
559         return true;
560     } else if (MO.isRegMask()) {
561       if (MO.clobbersPhysReg(PPC::CTR) || MO.clobbersPhysReg(PPC::CTR8))
562         return true;
563     }
564   }
565 
566   return false;
567 }
568 
569 static bool verifyCTRBranch(MachineBasicBlock *MBB,
570                             MachineBasicBlock::iterator I) {
571   MachineBasicBlock::iterator BI = I;
572   SmallSet<MachineBasicBlock *, 16>   Visited;
573   SmallVector<MachineBasicBlock *, 8> Preds;
574   bool CheckPreds;
575 
576   if (I == MBB->begin()) {
577     Visited.insert(MBB);
578     goto queue_preds;
579   } else
580     --I;
581 
582 check_block:
583   Visited.insert(MBB);
584   if (I == MBB->end())
585     goto queue_preds;
586 
587   CheckPreds = true;
588   for (MachineBasicBlock::iterator IE = MBB->begin();; --I) {
589     unsigned Opc = I->getOpcode();
590     if (Opc == PPC::MTCTRloop || Opc == PPC::MTCTR8loop) {
591       CheckPreds = false;
592       break;
593     }
594 
595     if (I != BI && clobbersCTR(I)) {
596       DEBUG(dbgs() << "BB#" << MBB->getNumber() << " (" <<
597                       MBB->getFullName() << ") instruction " << *I <<
598                       " clobbers CTR, invalidating " << "BB#" <<
599                       BI->getParent()->getNumber() << " (" <<
600                       BI->getParent()->getFullName() << ") instruction " <<
601                       *BI << "\n");
602       return false;
603     }
604 
605     if (I == IE)
606       break;
607   }
608 
609   if (!CheckPreds && Preds.empty())
610     return true;
611 
612   if (CheckPreds) {
613 queue_preds:
614     if (MachineFunction::iterator(MBB) == MBB->getParent()->begin()) {
615       DEBUG(dbgs() << "Unable to find a MTCTR instruction for BB#" <<
616                       BI->getParent()->getNumber() << " (" <<
617                       BI->getParent()->getFullName() << ") instruction " <<
618                       *BI << "\n");
619       return false;
620     }
621 
622     for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
623          PIE = MBB->pred_end(); PI != PIE; ++PI)
624       Preds.push_back(*PI);
625   }
626 
627   do {
628     MBB = Preds.pop_back_val();
629     if (!Visited.count(MBB)) {
630       I = MBB->getLastNonDebugInstr();
631       goto check_block;
632     }
633   } while (!Preds.empty());
634 
635   return true;
636 }
637 
638 bool PPCCTRLoopsVerify::runOnMachineFunction(MachineFunction &MF) {
639   MDT = &getAnalysis<MachineDominatorTree>();
640 
641   // Verify that all bdnz/bdz instructions are dominated by a loop mtctr before
642   // any other instructions that might clobber the ctr register.
643   for (MachineFunction::iterator I = MF.begin(), IE = MF.end();
644        I != IE; ++I) {
645     MachineBasicBlock *MBB = I;
646     if (!MDT->isReachableFromEntry(MBB))
647       continue;
648 
649     for (MachineBasicBlock::iterator MII = MBB->getFirstTerminator(),
650       MIIE = MBB->end(); MII != MIIE; ++MII) {
651       unsigned Opc = MII->getOpcode();
652       if (Opc == PPC::BDNZ8 || Opc == PPC::BDNZ ||
653           Opc == PPC::BDZ8  || Opc == PPC::BDZ)
654         if (!verifyCTRBranch(MBB, MII))
655           llvm_unreachable("Invalid PPC CTR loop!");
656     }
657   }
658 
659   return false;
660 }
661 #endif // NDEBUG
662 
663