src/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp

   1 //===-- SimplifyIndVar.cpp - Induction variable simplification ------------===//
   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 file implements induction variable simplification. It does
  11 // not define any actual pass or policy, but provides a single function to
  12 // simplify a loop's induction variables based on ScalarEvolution.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "llvm/Transforms/Utils/SimplifyIndVar.h"
  17 #include "llvm/ADT/STLExtras.h"
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/ADT/Statistic.h"
  20 #include "llvm/Analysis/IVUsers.h"
  21 #include "llvm/Analysis/LoopInfo.h"
  22 #include "llvm/Analysis/LoopPass.h"
  23 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
  24 #include "llvm/IR/DataLayout.h"
  25 #include "llvm/IR/Dominators.h"
  26 #include "llvm/IR/IRBuilder.h"
  27 #include "llvm/IR/Instructions.h"
  28 #include "llvm/IR/IntrinsicInst.h"
  29 #include "llvm/Support/CommandLine.h"
  30 #include "llvm/Support/Debug.h"
  31 #include "llvm/Support/raw_ostream.h"
  32
  33 using namespace llvm;
  34
  35 #define DEBUG_TYPE "indvars"
  36
  37 STATISTIC(NumElimIdentity, "Number of IV identities eliminated");
  38 STATISTIC(NumElimOperand,  "Number of IV operands folded into a use");
  39 STATISTIC(NumElimRem     , "Number of IV remainder operations eliminated");
  40 STATISTIC(NumElimCmp     , "Number of IV comparisons eliminated");
  41
  42 namespace {
  43   /// This is a utility for simplifying induction variables
  44   /// based on ScalarEvolution. It is the primary instrument of the
  45   /// IndvarSimplify pass, but it may also be directly invoked to cleanup after
  46   /// other loop passes that preserve SCEV.
  47   class SimplifyIndvar {
  48     Loop             *L;
  49     LoopInfo         *LI;
  50     ScalarEvolution  *SE;
  51     const DataLayout *DL; // May be NULL
  52
  53     SmallVectorImpl<WeakVH> &DeadInsts;
  54
  55     bool Changed;
  56
  57   public:
  58     SimplifyIndvar(Loop *Loop, ScalarEvolution *SE, LPPassManager *LPM,
  59                    SmallVectorImpl<WeakVH> &Dead, IVUsers *IVU = nullptr) :
  60       L(Loop),
  61       LI(LPM->getAnalysisIfAvailable<LoopInfo>()),
  62       SE(SE),
  63       DeadInsts(Dead),
  64       Changed(false) {
  65       DataLayoutPass *DLP = LPM->getAnalysisIfAvailable<DataLayoutPass>();
  66       DL = DLP ? &DLP->getDataLayout() : nullptr;
  67       assert(LI && "IV simplification requires LoopInfo");
  68     }
  69
  70     bool hasChanged() const { return Changed; }
  71
  72     /// Iteratively perform simplification on a worklist of users of the
  73     /// specified induction variable. This is the top-level driver that applies
  74     /// all simplicitions to users of an IV.
  75     void simplifyUsers(PHINode *CurrIV, IVVisitor *V = nullptr);
  76
  77     Value *foldIVUser(Instruction *UseInst, Instruction *IVOperand);
  78
  79     bool eliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
  80     void eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
  81     void eliminateIVRemainder(BinaryOperator *Rem, Value *IVOperand,
  82                               bool IsSigned);
  83     bool strengthenOverflowingOperation(BinaryOperator *OBO, Value *IVOperand);
  84
  85     Instruction *splitOverflowIntrinsic(Instruction *IVUser,
  86                                         const DominatorTree *DT);
  87   };
  88 }
  89
  90 /// Fold an IV operand into its use.  This removes increments of an
  91 /// aligned IV when used by a instruction that ignores the low bits.
  92 ///
  93 /// IVOperand is guaranteed SCEVable, but UseInst may not be.
  94 ///
  95 /// Return the operand of IVOperand for this induction variable if IVOperand can
  96 /// be folded (in case more folding opportunities have been exposed).
  97 /// Otherwise return null.
  98 Value *SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
  99   Value *IVSrc = nullptr;
 100   unsigned OperIdx = 0;
 101   const SCEV *FoldedExpr = nullptr;
 102   switch (UseInst->getOpcode()) {
 103   default:
 104     return nullptr;
 105   case Instruction::UDiv:
 106   case Instruction::LShr:
 107     // We're only interested in the case where we know something about
 108     // the numerator and have a constant denominator.
 109     if (IVOperand != UseInst->getOperand(OperIdx) ||
 110         !isa<ConstantInt>(UseInst->getOperand(1)))
 111       return nullptr;
 112
 113     // Attempt to fold a binary operator with constant operand.
 114     // e.g. ((I + 1) >> 2) => I >> 2
 115     if (!isa<BinaryOperator>(IVOperand)
 116         || !isa<ConstantInt>(IVOperand->getOperand(1)))
 117       return nullptr;
 118
 119     IVSrc = IVOperand->getOperand(0);
 120     // IVSrc must be the (SCEVable) IV, since the other operand is const.
 121     assert(SE->isSCEVable(IVSrc->getType()) && "Expect SCEVable IV operand");
 122
 123     ConstantInt *D = cast<ConstantInt>(UseInst->getOperand(1));
 124     if (UseInst->getOpcode() == Instruction::LShr) {
 125       // Get a constant for the divisor. See createSCEV.
 126       uint32_t BitWidth = cast<IntegerType>(UseInst->getType())->getBitWidth();
 127       if (D->getValue().uge(BitWidth))
 128         return nullptr;
 129
 130       D = ConstantInt::get(UseInst->getContext(),
 131                            APInt::getOneBitSet(BitWidth, D->getZExtValue()));
 132     }
 133     FoldedExpr = SE->getUDivExpr(SE->getSCEV(IVSrc), SE->getSCEV(D));
 134   }
 135   // We have something that might fold it's operand. Compare SCEVs.
 136   if (!SE->isSCEVable(UseInst->getType()))
 137     return nullptr;
 138
 139   // Bypass the operand if SCEV can prove it has no effect.
 140   if (SE->getSCEV(UseInst) != FoldedExpr)
 141     return nullptr;
 142
 143   DEBUG(dbgs() << "INDVARS: Eliminated IV operand: " << *IVOperand
 144         << " -> " << *UseInst << '\n');
 145
 146   UseInst->setOperand(OperIdx, IVSrc);
 147   assert(SE->getSCEV(UseInst) == FoldedExpr && "bad SCEV with folded oper");
 148
 149   ++NumElimOperand;
 150   Changed = true;
 151   if (IVOperand->use_empty())
 152     DeadInsts.push_back(IVOperand);
 153   return IVSrc;
 154 }
 155
 156 /// SimplifyIVUsers helper for eliminating useless
 157 /// comparisons against an induction variable.
 158 void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
 159   unsigned IVOperIdx = 0;
 160   ICmpInst::Predicate Pred = ICmp->getPredicate();
 161   if (IVOperand != ICmp->getOperand(0)) {
 162     // Swapped
 163     assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand");
 164     IVOperIdx = 1;
 165     Pred = ICmpInst::getSwappedPredicate(Pred);
 166   }
 167
 168   // Get the SCEVs for the ICmp operands.
 169   const SCEV *S = SE->getSCEV(ICmp->getOperand(IVOperIdx));
 170   const SCEV *X = SE->getSCEV(ICmp->getOperand(1 - IVOperIdx));
 171
 172   // Simplify unnecessary loops away.
 173   const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
 174   S = SE->getSCEVAtScope(S, ICmpLoop);
 175   X = SE->getSCEVAtScope(X, ICmpLoop);
 176
 177   // If the condition is always true or always false, replace it with
 178   // a constant value.
 179   if (SE->isKnownPredicate(Pred, S, X))
 180     ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
 181   else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
 182     ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
 183   else
 184     return;
 185
 186   DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
 187   ++NumElimCmp;
 188   Changed = true;
 189   DeadInsts.push_back(ICmp);
 190 }
 191
 192 /// SimplifyIVUsers helper for eliminating useless
 193 /// remainder operations operating on an induction variable.
 194 void SimplifyIndvar::eliminateIVRemainder(BinaryOperator *Rem,
 195                                       Value *IVOperand,
 196                                       bool IsSigned) {
 197   // We're only interested in the case where we know something about
 198   // the numerator.
 199   if (IVOperand != Rem->getOperand(0))
 200     return;
 201
 202   // Get the SCEVs for the ICmp operands.
 203   const SCEV *S = SE->getSCEV(Rem->getOperand(0));
 204   const SCEV *X = SE->getSCEV(Rem->getOperand(1));
 205
 206   // Simplify unnecessary loops away.
 207   const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
 208   S = SE->getSCEVAtScope(S, ICmpLoop);
 209   X = SE->getSCEVAtScope(X, ICmpLoop);
 210
 211   // i % n  -->  i  if i is in [0,n).
 212   if ((!IsSigned || SE->isKnownNonNegative(S)) &&
 213       SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
 214                            S, X))
 215     Rem->replaceAllUsesWith(Rem->getOperand(0));
 216   else {
 217     // (i+1) % n  -->  (i+1)==n?0:(i+1)  if i is in [0,n).
 218     const SCEV *LessOne =
 219       SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1));
 220     if (IsSigned && !SE->isKnownNonNegative(LessOne))
 221       return;
 222
 223     if (!SE->isKnownPredicate(IsSigned ?
 224                               ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
 225                               LessOne, X))
 226       return;
 227
 228     ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ,
 229                                   Rem->getOperand(0), Rem->getOperand(1));
 230     SelectInst *Sel =
 231       SelectInst::Create(ICmp,
 232                          ConstantInt::get(Rem->getType(), 0),
 233                          Rem->getOperand(0), "tmp", Rem);
 234     Rem->replaceAllUsesWith(Sel);
 235   }
 236
 237   DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
 238   ++NumElimRem;
 239   Changed = true;
 240   DeadInsts.push_back(Rem);
 241 }
 242
 243 /// Eliminate an operation that consumes a simple IV and has
 244 /// no observable side-effect given the range of IV values.
 245 /// IVOperand is guaranteed SCEVable, but UseInst may not be.
 246 bool SimplifyIndvar::eliminateIVUser(Instruction *UseInst,
 247                                      Instruction *IVOperand) {
 248   if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
 249     eliminateIVComparison(ICmp, IVOperand);
 250     return true;
 251   }
 252   if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) {
 253     bool IsSigned = Rem->getOpcode() == Instruction::SRem;
 254     if (IsSigned || Rem->getOpcode() == Instruction::URem) {
 255       eliminateIVRemainder(Rem, IVOperand, IsSigned);
 256       return true;
 257     }
 258   }
 259
 260   // Eliminate any operation that SCEV can prove is an identity function.
 261   if (!SE->isSCEVable(UseInst->getType()) ||
 262       (UseInst->getType() != IVOperand->getType()) ||
 263       (SE->getSCEV(UseInst) != SE->getSCEV(IVOperand)))
 264     return false;
 265
 266   DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n');
 267
 268   UseInst->replaceAllUsesWith(IVOperand);
 269   ++NumElimIdentity;
 270   Changed = true;
 271   DeadInsts.push_back(UseInst);
 272   return true;
 273 }
 274
 275 /// Annotate BO with nsw / nuw if it provably does not signed-overflow /
 276 /// unsigned-overflow.  Returns true if anything changed, false otherwise.
 277 bool SimplifyIndvar::strengthenOverflowingOperation(BinaryOperator *BO,
 278                                                     Value *IVOperand) {
 279
 280   // Currently we only handle instructions of the form "add <indvar> <value>"
 281   unsigned Op = BO->getOpcode();
 282   if (Op != Instruction::Add)
 283     return false;
 284
 285   // If BO is already both nuw and nsw then there is nothing left to do
 286   if (BO->hasNoUnsignedWrap() && BO->hasNoSignedWrap())
 287     return false;
 288
 289   IntegerType *IT = cast<IntegerType>(IVOperand->getType());
 290   Value *OtherOperand = nullptr;
 291   int OtherOperandIdx = -1;
 292   if (BO->getOperand(0) == IVOperand) {
 293     OtherOperand = BO->getOperand(1);
 294     OtherOperandIdx = 1;
 295   } else {
 296     assert(BO->getOperand(1) == IVOperand && "only other use!");
 297     OtherOperand = BO->getOperand(0);
 298     OtherOperandIdx = 0;
 299   }
 300
 301   bool Changed = false;
 302   const SCEV *OtherOpSCEV = SE->getSCEV(OtherOperand);
 303   if (OtherOpSCEV == SE->getCouldNotCompute())
 304     return false;
 305
 306   const SCEV *IVOpSCEV = SE->getSCEV(IVOperand);
 307   const SCEV *ZeroSCEV = SE->getConstant(IVOpSCEV->getType(), 0);
 308
 309   if (!BO->hasNoSignedWrap()) {
 310     // Upgrade the add to an "add nsw" if we can prove that it will never
 311     // sign-overflow or sign-underflow.
 312
 313     const SCEV *SignedMax =
 314       SE->getConstant(APInt::getSignedMaxValue(IT->getBitWidth()));
 315     const SCEV *SignedMin =
 316       SE->getConstant(APInt::getSignedMinValue(IT->getBitWidth()));
 317
 318     // The addition "IVOperand + OtherOp" does not sign-overflow if the result
 319     // is sign-representable in 2's complement in the given bit-width.
 320     //
 321     // If OtherOp is SLT 0, then for an IVOperand in [SignedMin - OtherOp,
 322     // SignedMax], "IVOperand + OtherOp" is in [SignedMin, SignedMax + OtherOp].
 323     // Everything in [SignedMin, SignedMax + OtherOp] is representable since
 324     // SignedMax + OtherOp is at least -1.
 325     //
 326     // If OtherOp is SGE 0, then for an IVOperand in [SignedMin, SignedMax -
 327     // OtherOp], "IVOperand + OtherOp" is in [SignedMin + OtherOp, SignedMax].
 328     // Everything in [SignedMin + OtherOp, SignedMax] is representable since
 329     // SignedMin + OtherOp is at most -1.
 330     //
 331     // It follows that for all values of IVOperand in [SignedMin - smin(0,
 332     // OtherOp), SignedMax - smax(0, OtherOp)] the result of the add is
 333     // representable (i.e. there is no sign-overflow).
 334
 335     const SCEV *UpperDelta = SE->getSMaxExpr(ZeroSCEV, OtherOpSCEV);
 336     const SCEV *UpperLimit = SE->getMinusSCEV(SignedMax, UpperDelta);
 337
 338     bool NeverSignedOverflows =
 339       SE->isKnownPredicate(ICmpInst::ICMP_SLE, IVOpSCEV, UpperLimit);
 340
 341     if (NeverSignedOverflows) {
 342       const SCEV *LowerDelta = SE->getSMinExpr(ZeroSCEV, OtherOpSCEV);
 343       const SCEV *LowerLimit = SE->getMinusSCEV(SignedMin, LowerDelta);
 344
 345       bool NeverSignedUnderflows =
 346         SE->isKnownPredicate(ICmpInst::ICMP_SGE, IVOpSCEV, LowerLimit);
 347       if (NeverSignedUnderflows) {
 348         BO->setHasNoSignedWrap(true);
 349         Changed = true;
 350       }
 351     }
 352   }
 353
 354   if (!BO->hasNoUnsignedWrap()) {
 355     // Upgrade the add computing "IVOperand + OtherOp" to an "add nuw" if we can
 356     // prove that it will never unsigned-overflow (i.e. the result will always
 357     // be representable in the given bit-width).
 358     //
 359     // "IVOperand + OtherOp" is unsigned-representable in 2's complement iff it
 360     // does not produce a carry.  "IVOperand + OtherOp" produces no carry iff
 361     // IVOperand ULE (UnsignedMax - OtherOp).
 362
 363     const SCEV *UnsignedMax =
 364       SE->getConstant(APInt::getMaxValue(IT->getBitWidth()));
 365     const SCEV *UpperLimit = SE->getMinusSCEV(UnsignedMax, OtherOpSCEV);
 366
 367     bool NeverUnsignedOverflows =
 368         SE->isKnownPredicate(ICmpInst::ICMP_ULE, IVOpSCEV, UpperLimit);
 369
 370     if (NeverUnsignedOverflows) {
 371       BO->setHasNoUnsignedWrap(true);
 372       Changed = true;
 373     }
 374   }
 375
 376   return Changed;
 377 }
 378
 379 /// \brief Split sadd.with.overflow into add + sadd.with.overflow to allow
 380 /// analysis and optimization.
 381 ///
 382 /// \return A new value representing the non-overflowing add if possible,
 383 /// otherwise return the original value.
 384 Instruction *SimplifyIndvar::splitOverflowIntrinsic(Instruction *IVUser,
 385                                                     const DominatorTree *DT) {
 386   IntrinsicInst *II = dyn_cast<IntrinsicInst>(IVUser);
 387   if (!II || II->getIntrinsicID() != Intrinsic::sadd_with_overflow)
 388     return IVUser;
 389
 390   // Find a branch guarded by the overflow check.
 391   BranchInst *Branch = nullptr;
 392   Instruction *AddVal = nullptr;
 393   for (User *U : II->users()) {
 394     if (ExtractValueInst *ExtractInst = dyn_cast<ExtractValueInst>(U)) {
 395       if (ExtractInst->getNumIndices() != 1)
 396         continue;
 397       if (ExtractInst->getIndices()[0] == 0)
 398         AddVal = ExtractInst;
 399       else if (ExtractInst->getIndices()[0] == 1 && ExtractInst->hasOneUse())
 400         Branch = dyn_cast<BranchInst>(ExtractInst->user_back());
 401     }
 402   }
 403   if (!AddVal || !Branch)
 404     return IVUser;
 405
 406   BasicBlock *ContinueBB = Branch->getSuccessor(1);
 407   if (std::next(pred_begin(ContinueBB)) != pred_end(ContinueBB))
 408     return IVUser;
 409
 410   // Check if all users of the add are provably NSW.
 411   bool AllNSW = true;
 412   for (Use &U : AddVal->uses()) {
 413     if (Instruction *UseInst = dyn_cast<Instruction>(U.getUser())) {
 414       BasicBlock *UseBB = UseInst->getParent();
 415       if (PHINode *PHI = dyn_cast<PHINode>(UseInst))
 416         UseBB = PHI->getIncomingBlock(U);
 417       if (!DT->dominates(ContinueBB, UseBB)) {
 418         AllNSW = false;
 419         break;
 420       }
 421     }
 422   }
 423   if (!AllNSW)
 424     return IVUser;
 425
 426   // Go for it...
 427   IRBuilder<> Builder(IVUser);
 428   Instruction *AddInst = dyn_cast<Instruction>(
 429     Builder.CreateNSWAdd(II->getOperand(0), II->getOperand(1)));
 430
 431   // The caller expects the new add to have the same form as the intrinsic. The
 432   // IV operand position must be the same.
 433   assert((AddInst->getOpcode() == Instruction::Add &&
 434           AddInst->getOperand(0) == II->getOperand(0)) &&
 435          "Bad add instruction created from overflow intrinsic.");
 436
 437   AddVal->replaceAllUsesWith(AddInst);
 438   DeadInsts.push_back(AddVal);
 439   return AddInst;
 440 }
 441
 442 /// Add all uses of Def to the current IV's worklist.
 443 static void pushIVUsers(
 444   Instruction *Def,
 445   SmallPtrSet<Instruction*,16> &Simplified,
 446   SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) {
 447
 448   for (User *U : Def->users()) {
 449     Instruction *UI = cast<Instruction>(U);
 450
 451     // Avoid infinite or exponential worklist processing.
 452     // Also ensure unique worklist users.
 453     // If Def is a LoopPhi, it may not be in the Simplified set, so check for
 454     // self edges first.
 455     if (UI != Def && Simplified.insert(UI).second)
 456       SimpleIVUsers.push_back(std::make_pair(UI, Def));
 457   }
 458 }
 459
 460 /// Return true if this instruction generates a simple SCEV
 461 /// expression in terms of that IV.
 462 ///
 463 /// This is similar to IVUsers' isInteresting() but processes each instruction
 464 /// non-recursively when the operand is already known to be a simpleIVUser.
 465 ///
 466 static bool isSimpleIVUser(Instruction *I, const Loop *L, ScalarEvolution *SE) {
 467   if (!SE->isSCEVable(I->getType()))
 468     return false;
 469
 470   // Get the symbolic expression for this instruction.
 471   const SCEV *S = SE->getSCEV(I);
 472
 473   // Only consider affine recurrences.
 474   const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S);
 475   if (AR && AR->getLoop() == L)
 476     return true;
 477
 478   return false;
 479 }
 480
 481 /// Iteratively perform simplification on a worklist of users
 482 /// of the specified induction variable. Each successive simplification may push
 483 /// more users which may themselves be candidates for simplification.
 484 ///
 485 /// This algorithm does not require IVUsers analysis. Instead, it simplifies
 486 /// instructions in-place during analysis. Rather than rewriting induction
 487 /// variables bottom-up from their users, it transforms a chain of IVUsers
 488 /// top-down, updating the IR only when it encouters a clear optimization
 489 /// opportunitiy.
 490 ///
 491 /// Once DisableIVRewrite is default, LSR will be the only client of IVUsers.
 492 ///
 493 void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
 494   if (!SE->isSCEVable(CurrIV->getType()))
 495     return;
 496
 497   // Instructions processed by SimplifyIndvar for CurrIV.
 498   SmallPtrSet<Instruction*,16> Simplified;
 499
 500   // Use-def pairs if IV users waiting to be processed for CurrIV.
 501   SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers;
 502
 503   // Push users of the current LoopPhi. In rare cases, pushIVUsers may be
 504   // called multiple times for the same LoopPhi. This is the proper thing to
 505   // do for loop header phis that use each other.
 506   pushIVUsers(CurrIV, Simplified, SimpleIVUsers);
 507
 508   while (!SimpleIVUsers.empty()) {
 509     std::pair<Instruction*, Instruction*> UseOper =
 510       SimpleIVUsers.pop_back_val();
 511     Instruction *UseInst = UseOper.first;
 512
 513     // Bypass back edges to avoid extra work.
 514     if (UseInst == CurrIV) continue;
 515
 516     if (V && V->shouldSplitOverflowInstrinsics()) {
 517       UseInst = splitOverflowIntrinsic(UseInst, V->getDomTree());
 518       if (!UseInst)
 519         continue;
 520     }
 521
 522     Instruction *IVOperand = UseOper.second;
 523     for (unsigned N = 0; IVOperand; ++N) {
 524       assert(N <= Simplified.size() && "runaway iteration");
 525
 526       Value *NewOper = foldIVUser(UseOper.first, IVOperand);
 527       if (!NewOper)
 528         break; // done folding
 529       IVOperand = dyn_cast<Instruction>(NewOper);
 530     }
 531     if (!IVOperand)
 532       continue;
 533
 534     if (eliminateIVUser(UseOper.first, IVOperand)) {
 535       pushIVUsers(IVOperand, Simplified, SimpleIVUsers);
 536       continue;
 537     }
 538
 539     if (BinaryOperator *BO = dyn_cast<BinaryOperator>(UseOper.first)) {
 540       if (isa<OverflowingBinaryOperator>(BO) &&
 541           strengthenOverflowingOperation(BO, IVOperand)) {
 542         // re-queue uses of the now modified binary operator and fall
 543         // through to the checks that remain.
 544         pushIVUsers(IVOperand, Simplified, SimpleIVUsers);
 545       }
 546     }
 547
 548     CastInst *Cast = dyn_cast<CastInst>(UseOper.first);
 549     if (V && Cast) {
 550       V->visitCast(Cast);
 551       continue;
 552     }
 553     if (isSimpleIVUser(UseOper.first, L, SE)) {
 554       pushIVUsers(UseOper.first, Simplified, SimpleIVUsers);
 555     }
 556   }
 557 }
 558
 559 namespace llvm {
 560
 561 void IVVisitor::anchor() { }
 562
 563 /// Simplify instructions that use this induction variable
 564 /// by using ScalarEvolution to analyze the IV's recurrence.
 565 bool simplifyUsersOfIV(PHINode *CurrIV, ScalarEvolution *SE, LPPassManager *LPM,
 566                        SmallVectorImpl<WeakVH> &Dead, IVVisitor *V)
 567 {
 568   LoopInfo *LI = &LPM->getAnalysis<LoopInfo>();
 569   SimplifyIndvar SIV(LI->getLoopFor(CurrIV->getParent()), SE, LPM, Dead);
 570   SIV.simplifyUsers(CurrIV, V);
 571   return SIV.hasChanged();
 572 }
 573
 574 /// Simplify users of induction variables within this
 575 /// loop. This does not actually change or add IVs.
 576 bool simplifyLoopIVs(Loop *L, ScalarEvolution *SE, LPPassManager *LPM,
 577                      SmallVectorImpl<WeakVH> &Dead) {
 578   bool Changed = false;
 579   for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
 580     Changed |= simplifyUsersOfIV(cast<PHINode>(I), SE, LPM, Dead);
 581   }
 582   return Changed;
 583 }
 584
 585 } // namespace llvm