lib/Transforms/Scalar/LoopIndexSplit.cpp

   1 //===- LoopIndexSplit.cpp - Loop Index Splitting Pass ---------------------===//
   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 Loop Index Splitting Pass. This pass handles three
  11 // kinds of loops.
  12 //
  13 // [1] A loop may be eliminated if the body is executed exactly once.
  14 //     For example,
  15 //
  16 // for (i = 0; i < N; ++i) {
  17 //   if (i == X) {
  18 //     body;
  19 //   }
  20 // }
  21 //
  22 // is transformed to
  23 //
  24 // i = X;
  25 // body;
  26 //
  27 // [2] A loop's iteration space may be shrunk if the loop body is executed
  28 //     for a proper sub-range of the loop's iteration space. For example,
  29 //
  30 // for (i = 0; i < N; ++i) {
  31 //   if (i > A && i < B) {
  32 //     ...
  33 //   }
  34 // }
  35 //
  36 // is transformed to iterators from A to B, if A > 0 and B < N.
  37 //
  38 // [3] A loop may be split if the loop body is dominated by a branch.
  39 //     For example,
  40 //
  41 // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
  42 //
  43 // is transformed into
  44 //
  45 // AEV = BSV = SV
  46 // for (i = LB; i < min(UB, AEV); ++i)
  47 //    A;
  48 // for (i = max(LB, BSV); i < UB; ++i);
  49 //    B;
  50 //
  51 //===----------------------------------------------------------------------===//
  52
  53 #define DEBUG_TYPE "loop-index-split"
  54 #include "llvm/Transforms/Scalar.h"
  55 #include "llvm/IntrinsicInst.h"
  56 #include "llvm/LLVMContext.h"
  57 #include "llvm/Analysis/LoopPass.h"
  58 #include "llvm/Analysis/ScalarEvolution.h"
  59 #include "llvm/Analysis/Dominators.h"
  60 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  61 #include "llvm/Transforms/Utils/Cloning.h"
  62 #include "llvm/Transforms/Utils/Local.h"
  63 #include "llvm/ADT/DepthFirstIterator.h"
  64 #include "llvm/ADT/Statistic.h"
  65
  66 using namespace llvm;
  67
  68 STATISTIC(NumIndexSplit, "Number of loop index split");
  69 STATISTIC(NumIndexSplitRemoved, "Number of loops eliminated by loop index split");
  70 STATISTIC(NumRestrictBounds, "Number of loop iteration space restricted");
  71
  72 namespace {
  73
  74   class LoopIndexSplit : public LoopPass {
  75   public:
  76     static char ID; // Pass ID, replacement for typeid
  77     LoopIndexSplit() : LoopPass(&ID) {}
  78
  79     // Index split Loop L. Return true if loop is split.
  80     bool runOnLoop(Loop *L, LPPassManager &LPM);
  81
  82     void getAnalysisUsage(AnalysisUsage &AU) const {
  83       AU.addPreserved<ScalarEvolution>();
  84       AU.addRequiredID(LCSSAID);
  85       AU.addPreservedID(LCSSAID);
  86       AU.addRequired<LoopInfo>();
  87       AU.addPreserved<LoopInfo>();
  88       AU.addRequiredID(LoopSimplifyID);
  89       AU.addPreservedID(LoopSimplifyID);
  90       AU.addRequired<DominatorTree>();
  91       AU.addRequired<DominanceFrontier>();
  92       AU.addPreserved<DominatorTree>();
  93       AU.addPreserved<DominanceFrontier>();
  94     }
  95
  96   private:
  97     /// processOneIterationLoop -- Eliminate loop if loop body is executed
  98     /// only once. For example,
  99     /// for (i = 0; i < N; ++i) {
 100     ///   if ( i == X) {
 101     ///     ...
 102     ///   }
 103     /// }
 104     ///
 105     bool processOneIterationLoop();
 106
 107     // -- Routines used by updateLoopIterationSpace();
 108
 109     /// updateLoopIterationSpace -- Update loop's iteration space if loop
 110     /// body is executed for certain IV range only. For example,
 111     ///
 112     /// for (i = 0; i < N; ++i) {
 113     ///   if ( i > A && i < B) {
 114     ///     ...
 115     ///   }
 116     /// }
 117     /// is transformed to iterators from A to B, if A > 0 and B < N.
 118     ///
 119     bool updateLoopIterationSpace();
 120
 121     /// restrictLoopBound - Op dominates loop body. Op compares an IV based value
 122     /// with a loop invariant value. Update loop's lower and upper bound based on
 123     /// the loop invariant value.
 124     bool restrictLoopBound(ICmpInst &Op);
 125
 126     // --- Routines used by splitLoop(). --- /
 127
 128     bool splitLoop();
 129
 130     /// removeBlocks - Remove basic block DeadBB and all blocks dominated by
 131     /// DeadBB. This routine is used to remove split condition's dead branch,
 132     /// dominated by DeadBB. LiveBB dominates split conidition's other branch.
 133     void removeBlocks(BasicBlock *DeadBB, Loop *LP, BasicBlock *LiveBB);
 134
 135     /// moveExitCondition - Move exit condition EC into split condition block.
 136     void moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
 137                            BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
 138                            PHINode *IV, Instruction *IVAdd, Loop *LP,
 139                            unsigned);
 140
 141     /// updatePHINodes - CFG has been changed.
 142     /// Before
 143     ///   - ExitBB's single predecessor was Latch
 144     ///   - Latch's second successor was Header
 145     /// Now
 146     ///   - ExitBB's single predecessor was Header
 147     ///   - Latch's one and only successor was Header
 148     ///
 149     /// Update ExitBB PHINodes' to reflect this change.
 150     void updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
 151                         BasicBlock *Header,
 152                         PHINode *IV, Instruction *IVIncrement, Loop *LP);
 153
 154     // --- Utility routines --- /
 155
 156     /// cleanBlock - A block is considered clean if all non terminal
 157     /// instructions are either PHINodes or IV based values.
 158     bool cleanBlock(BasicBlock *BB);
 159
 160     /// IVisLT - If Op is comparing IV based value with an loop invariant and
 161     /// IV based value is less than  the loop invariant then return the loop
 162     /// invariant. Otherwise return NULL.
 163     Value * IVisLT(ICmpInst &Op);
 164
 165     /// IVisLE - If Op is comparing IV based value with an loop invariant and
 166     /// IV based value is less than or equal to the loop invariant then
 167     /// return the loop invariant. Otherwise return NULL.
 168     Value * IVisLE(ICmpInst &Op);
 169
 170     /// IVisGT - If Op is comparing IV based value with an loop invariant and
 171     /// IV based value is greater than  the loop invariant then return the loop
 172     /// invariant. Otherwise return NULL.
 173     Value * IVisGT(ICmpInst &Op);
 174
 175     /// IVisGE - If Op is comparing IV based value with an loop invariant and
 176     /// IV based value is greater than or equal to the loop invariant then
 177     /// return the loop invariant. Otherwise return NULL.
 178     Value * IVisGE(ICmpInst &Op);
 179
 180   private:
 181
 182     // Current Loop information.
 183     Loop *L;
 184     LPPassManager *LPM;
 185     LoopInfo *LI;
 186     DominatorTree *DT;
 187     DominanceFrontier *DF;
 188
 189     PHINode *IndVar;
 190     ICmpInst *ExitCondition;
 191     ICmpInst *SplitCondition;
 192     Value *IVStartValue;
 193     Value *IVExitValue;
 194     Instruction *IVIncrement;
 195     SmallPtrSet<Value *, 4> IVBasedValues;
 196   };
 197 }
 198
 199 char LoopIndexSplit::ID = 0;
 200 static RegisterPass<LoopIndexSplit>
 201 X("loop-index-split", "Index Split Loops");
 202
 203 Pass *llvm::createLoopIndexSplitPass() {
 204   return new LoopIndexSplit();
 205 }
 206
 207 // Index split Loop L. Return true if loop is split.
 208 bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
 209   L = IncomingLoop;
 210   LPM = &LPM_Ref;
 211
 212   // FIXME - Nested loops make dominator info updates tricky.
 213   if (!L->getSubLoops().empty())
 214     return false;
 215
 216   DT = &getAnalysis<DominatorTree>();
 217   LI = &getAnalysis<LoopInfo>();
 218   DF = &getAnalysis<DominanceFrontier>();
 219
 220   // Initialize loop data.
 221   IndVar = L->getCanonicalInductionVariable();
 222   if (!IndVar) return false;
 223
 224   bool P1InLoop = L->contains(IndVar->getIncomingBlock(1));
 225   IVStartValue = IndVar->getIncomingValue(!P1InLoop);
 226   IVIncrement = dyn_cast<Instruction>(IndVar->getIncomingValue(P1InLoop));
 227   if (!IVIncrement) return false;
 228
 229   IVBasedValues.clear();
 230   IVBasedValues.insert(IndVar);
 231   IVBasedValues.insert(IVIncrement);
 232   for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
 233        I != E; ++I)
 234     for(BasicBlock::iterator BI = (*I)->begin(), BE = (*I)->end();
 235         BI != BE; ++BI) {
 236       if (BinaryOperator *BO = dyn_cast<BinaryOperator>(BI))
 237         if (BO != IVIncrement
 238             && (BO->getOpcode() == Instruction::Add
 239                 || BO->getOpcode() == Instruction::Sub))
 240           if (IVBasedValues.count(BO->getOperand(0))
 241               && L->isLoopInvariant(BO->getOperand(1)))
 242             IVBasedValues.insert(BO);
 243     }
 244
 245   // Reject loop if loop exit condition is not suitable.
 246   BasicBlock *ExitingBlock = L->getExitingBlock();
 247   if (!ExitingBlock)
 248     return false;
 249   BranchInst *EBR = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
 250   if (!EBR) return false;
 251   ExitCondition = dyn_cast<ICmpInst>(EBR->getCondition());
 252   if (!ExitCondition) return false;
 253   if (ExitingBlock != L->getLoopLatch()) return false;
 254   IVExitValue = ExitCondition->getOperand(1);
 255   if (!L->isLoopInvariant(IVExitValue))
 256     IVExitValue = ExitCondition->getOperand(0);
 257   if (!L->isLoopInvariant(IVExitValue))
 258     return false;
 259   if (!IVBasedValues.count(
 260         ExitCondition->getOperand(IVExitValue == ExitCondition->getOperand(0))))
 261     return false;
 262
 263   // If start value is more then exit value where induction variable
 264   // increments by 1 then we are potentially dealing with an infinite loop.
 265   // Do not index split this loop.
 266   if (ConstantInt *SV = dyn_cast<ConstantInt>(IVStartValue))
 267     if (ConstantInt *EV = dyn_cast<ConstantInt>(IVExitValue))
 268       if (SV->getSExtValue() > EV->getSExtValue())
 269         return false;
 270
 271   if (processOneIterationLoop())
 272     return true;
 273
 274   if (updateLoopIterationSpace())
 275     return true;
 276
 277   if (splitLoop())
 278     return true;
 279
 280   return false;
 281 }
 282
 283 // --- Helper routines ---
 284 // isUsedOutsideLoop - Returns true iff V is used outside the loop L.
 285 static bool isUsedOutsideLoop(Value *V, Loop *L) {
 286   for(Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
 287     if (!L->contains(cast<Instruction>(*UI)->getParent()))
 288       return true;
 289   return false;
 290 }
 291
 292 // Return V+1
 293 static Value *getPlusOne(Value *V, bool Sign, Instruction *InsertPt,
 294                          LLVMContext &Context) {
 295   Constant *One = ConstantInt::get(V->getType(), 1, Sign);
 296   return BinaryOperator::CreateAdd(V, One, "lsp", InsertPt);
 297 }
 298
 299 // Return V-1
 300 static Value *getMinusOne(Value *V, bool Sign, Instruction *InsertPt,
 301                           LLVMContext &Context) {
 302   Constant *One = ConstantInt::get(V->getType(), 1, Sign);
 303   return BinaryOperator::CreateSub(V, One, "lsp", InsertPt);
 304 }
 305
 306 // Return min(V1, V1)
 307 static Value *getMin(Value *V1, Value *V2, bool Sign, Instruction *InsertPt) {
 308
 309   Value *C = new ICmpInst(InsertPt,
 310                           Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
 311                           V1, V2, "lsp");
 312   return SelectInst::Create(C, V1, V2, "lsp", InsertPt);
 313 }
 314
 315 // Return max(V1, V2)
 316 static Value *getMax(Value *V1, Value *V2, bool Sign, Instruction *InsertPt) {
 317
 318   Value *C = new ICmpInst(InsertPt,
 319                           Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
 320                           V1, V2, "lsp");
 321   return SelectInst::Create(C, V2, V1, "lsp", InsertPt);
 322 }
 323
 324 /// processOneIterationLoop -- Eliminate loop if loop body is executed
 325 /// only once. For example,
 326 /// for (i = 0; i < N; ++i) {
 327 ///   if ( i == X) {
 328 ///     ...
 329 ///   }
 330 /// }
 331 ///
 332 bool LoopIndexSplit::processOneIterationLoop() {
 333   SplitCondition = NULL;
 334   BasicBlock *Latch = L->getLoopLatch();
 335   BasicBlock *Header = L->getHeader();
 336   BranchInst *BR = dyn_cast<BranchInst>(Header->getTerminator());
 337   if (!BR) return false;
 338   if (!isa<BranchInst>(Latch->getTerminator())) return false;
 339   if (BR->isUnconditional()) return false;
 340   SplitCondition = dyn_cast<ICmpInst>(BR->getCondition());
 341   if (!SplitCondition) return false;
 342   if (SplitCondition == ExitCondition) return false;
 343   if (SplitCondition->getPredicate() != ICmpInst::ICMP_EQ) return false;
 344   if (BR->getOperand(1) != Latch) return false;
 345   if (!IVBasedValues.count(SplitCondition->getOperand(0))
 346       && !IVBasedValues.count(SplitCondition->getOperand(1)))
 347     return false;
 348
 349   // If IV is used outside the loop then this loop traversal is required.
 350   // FIXME: Calculate and use last IV value.
 351   if (isUsedOutsideLoop(IVIncrement, L))
 352     return false;
 353
 354   // If BR operands are not IV or not loop invariants then skip this loop.
 355   Value *OPV = SplitCondition->getOperand(0);
 356   Value *SplitValue = SplitCondition->getOperand(1);
 357   if (!L->isLoopInvariant(SplitValue))
 358     std::swap(OPV, SplitValue);
 359   if (!L->isLoopInvariant(SplitValue))
 360     return false;
 361   Instruction *OPI = dyn_cast<Instruction>(OPV);
 362   if (!OPI)
 363     return false;
 364   if (OPI->getParent() != Header || isUsedOutsideLoop(OPI, L))
 365     return false;
 366   Value *StartValue = IVStartValue;
 367   Value *ExitValue = IVExitValue;;
 368
 369   if (OPV != IndVar) {
 370     // If BR operand is IV based then use this operand to calculate
 371     // effective conditions for loop body.
 372     BinaryOperator *BOPV = dyn_cast<BinaryOperator>(OPV);
 373     if (!BOPV)
 374       return false;
 375     if (BOPV->getOpcode() != Instruction::Add)
 376       return false;
 377     StartValue = BinaryOperator::CreateAdd(OPV, StartValue, "" , BR);
 378     ExitValue = BinaryOperator::CreateAdd(OPV, ExitValue, "" , BR);
 379   }
 380
 381   if (!cleanBlock(Header))
 382     return false;
 383
 384   if (!cleanBlock(Latch))
 385     return false;
 386
 387   // If the merge point for BR is not loop latch then skip this loop.
 388   if (BR->getSuccessor(0) != Latch) {
 389     DominanceFrontier::iterator DF0 = DF->find(BR->getSuccessor(0));
 390     assert (DF0 != DF->end() && "Unable to find dominance frontier");
 391     if (!DF0->second.count(Latch))
 392       return false;
 393   }
 394
 395   if (BR->getSuccessor(1) != Latch) {
 396     DominanceFrontier::iterator DF1 = DF->find(BR->getSuccessor(1));
 397     assert (DF1 != DF->end() && "Unable to find dominance frontier");
 398     if (!DF1->second.count(Latch))
 399       return false;
 400   }
 401
 402   // Now, Current loop L contains compare instruction
 403   // that compares induction variable, IndVar, against loop invariant. And
 404   // entire (i.e. meaningful) loop body is dominated by this compare
 405   // instruction. In such case eliminate
 406   // loop structure surrounding this loop body. For example,
 407   //     for (int i = start; i < end; ++i) {
 408   //         if ( i == somevalue) {
 409   //           loop_body
 410   //         }
 411   //     }
 412   // can be transformed into
 413   //     if (somevalue >= start && somevalue < end) {
 414   //        i = somevalue;
 415   //        loop_body
 416   //     }
 417
 418   // Replace index variable with split value in loop body. Loop body is executed
 419   // only when index variable is equal to split value.
 420   IndVar->replaceAllUsesWith(SplitValue);
 421
 422   // Replace split condition in header.
 423   // Transform
 424   //      SplitCondition : icmp eq i32 IndVar, SplitValue
 425   // into
 426   //      c1 = icmp uge i32 SplitValue, StartValue
 427   //      c2 = icmp ult i32 SplitValue, ExitValue
 428   //      and i32 c1, c2
 429   Instruction *C1 = new ICmpInst(BR, ExitCondition->isSignedPredicate() ?
 430                                  ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE,
 431                                  SplitValue, StartValue, "lisplit");
 432
 433   CmpInst::Predicate C2P  = ExitCondition->getPredicate();
 434   BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator());
 435   if (LatchBR->getOperand(1) != Header)
 436     C2P = CmpInst::getInversePredicate(C2P);
 437   Instruction *C2 = new ICmpInst(BR, C2P, SplitValue, ExitValue, "lisplit");
 438   Instruction *NSplitCond = BinaryOperator::CreateAnd(C1, C2, "lisplit", BR);
 439
 440   SplitCondition->replaceAllUsesWith(NSplitCond);
 441   SplitCondition->eraseFromParent();
 442
 443   // Remove Latch to Header edge.
 444   BasicBlock *LatchSucc = NULL;
 445   Header->removePredecessor(Latch);
 446   for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
 447        SI != E; ++SI) {
 448     if (Header != *SI)
 449       LatchSucc = *SI;
 450   }
 451
 452   // Clean up latch block.
 453   Value *LatchBRCond = LatchBR->getCondition();
 454   LatchBR->setUnconditionalDest(LatchSucc);
 455   RecursivelyDeleteTriviallyDeadInstructions(LatchBRCond);
 456
 457   LPM->deleteLoopFromQueue(L);
 458
 459   // Update Dominator Info.
 460   // Only CFG change done is to remove Latch to Header edge. This
 461   // does not change dominator tree because Latch did not dominate
 462   // Header.
 463   if (DF) {
 464     DominanceFrontier::iterator HeaderDF = DF->find(Header);
 465     if (HeaderDF != DF->end())
 466       DF->removeFromFrontier(HeaderDF, Header);
 467
 468     DominanceFrontier::iterator LatchDF = DF->find(Latch);
 469     if (LatchDF != DF->end())
 470       DF->removeFromFrontier(LatchDF, Header);
 471   }
 472
 473   ++NumIndexSplitRemoved;
 474   return true;
 475 }
 476
 477 /// restrictLoopBound - Op dominates loop body. Op compares an IV based value
 478 /// with a loop invariant value. Update loop's lower and upper bound based on
 479 /// the loop invariant value.
 480 bool LoopIndexSplit::restrictLoopBound(ICmpInst &Op) {
 481   bool Sign = Op.isSignedPredicate();
 482   Instruction *PHTerm = L->getLoopPreheader()->getTerminator();
 483
 484   if (IVisGT(*ExitCondition) || IVisGE(*ExitCondition)) {
 485     BranchInst *EBR =
 486       cast<BranchInst>(ExitCondition->getParent()->getTerminator());
 487     ExitCondition->setPredicate(ExitCondition->getInversePredicate());
 488     BasicBlock *T = EBR->getSuccessor(0);
 489     EBR->setSuccessor(0, EBR->getSuccessor(1));
 490     EBR->setSuccessor(1, T);
 491   }
 492
 493   LLVMContext &Context = Op.getContext();
 494
 495   // New upper and lower bounds.
 496   Value *NLB = NULL;
 497   Value *NUB = NULL;
 498   if (Value *V = IVisLT(Op)) {
 499     // Restrict upper bound.
 500     if (IVisLE(*ExitCondition))
 501       V = getMinusOne(V, Sign, PHTerm, Context);
 502     NUB = getMin(V, IVExitValue, Sign, PHTerm);
 503   } else if (Value *V = IVisLE(Op)) {
 504     // Restrict upper bound.
 505     if (IVisLT(*ExitCondition))
 506       V = getPlusOne(V, Sign, PHTerm, Context);
 507     NUB = getMin(V, IVExitValue, Sign, PHTerm);
 508   } else if (Value *V = IVisGT(Op)) {
 509     // Restrict lower bound.
 510     V = getPlusOne(V, Sign, PHTerm, Context);
 511     NLB = getMax(V, IVStartValue, Sign, PHTerm);
 512   } else if (Value *V = IVisGE(Op))
 513     // Restrict lower bound.
 514     NLB = getMax(V, IVStartValue, Sign, PHTerm);
 515
 516   if (!NLB && !NUB)
 517     return false;
 518
 519   if (NLB) {
 520     unsigned i = IndVar->getBasicBlockIndex(L->getLoopPreheader());
 521     IndVar->setIncomingValue(i, NLB);
 522   }
 523
 524   if (NUB) {
 525     unsigned i = (ExitCondition->getOperand(0) != IVExitValue);
 526     ExitCondition->setOperand(i, NUB);
 527   }
 528   return true;
 529 }
 530
 531 /// updateLoopIterationSpace -- Update loop's iteration space if loop
 532 /// body is executed for certain IV range only. For example,
 533 ///
 534 /// for (i = 0; i < N; ++i) {
 535 ///   if ( i > A && i < B) {
 536 ///     ...
 537 ///   }
 538 /// }
 539 /// is transformed to iterators from A to B, if A > 0 and B < N.
 540 ///
 541 bool LoopIndexSplit::updateLoopIterationSpace() {
 542   SplitCondition = NULL;
 543   if (ExitCondition->getPredicate() == ICmpInst::ICMP_NE
 544       || ExitCondition->getPredicate() == ICmpInst::ICMP_EQ)
 545     return false;
 546   BasicBlock *Latch = L->getLoopLatch();
 547   BasicBlock *Header = L->getHeader();
 548   BranchInst *BR = dyn_cast<BranchInst>(Header->getTerminator());
 549   if (!BR) return false;
 550   if (!isa<BranchInst>(Latch->getTerminator())) return false;
 551   if (BR->isUnconditional()) return false;
 552   BinaryOperator *AND = dyn_cast<BinaryOperator>(BR->getCondition());
 553   if (!AND) return false;
 554   if (AND->getOpcode() != Instruction::And) return false;
 555   ICmpInst *Op0 = dyn_cast<ICmpInst>(AND->getOperand(0));
 556   ICmpInst *Op1 = dyn_cast<ICmpInst>(AND->getOperand(1));
 557   if (!Op0 || !Op1)
 558     return false;
 559   IVBasedValues.insert(AND);
 560   IVBasedValues.insert(Op0);
 561   IVBasedValues.insert(Op1);
 562   if (!cleanBlock(Header)) return false;
 563   BasicBlock *ExitingBlock = ExitCondition->getParent();
 564   if (!cleanBlock(ExitingBlock)) return false;
 565
 566   // If the merge point for BR is not loop latch then skip this loop.
 567   if (BR->getSuccessor(0) != Latch) {
 568     DominanceFrontier::iterator DF0 = DF->find(BR->getSuccessor(0));
 569     assert (DF0 != DF->end() && "Unable to find dominance frontier");
 570     if (!DF0->second.count(Latch))
 571       return false;
 572   }
 573
 574   if (BR->getSuccessor(1) != Latch) {
 575     DominanceFrontier::iterator DF1 = DF->find(BR->getSuccessor(1));
 576     assert (DF1 != DF->end() && "Unable to find dominance frontier");
 577     if (!DF1->second.count(Latch))
 578       return false;
 579   }
 580
 581   // Verify that loop exiting block has only two predecessor, where one pred
 582   // is split condition block. The other predecessor will become exiting block's
 583   // dominator after CFG is updated. TODO : Handle CFG's where exiting block has
 584   // more then two predecessors. This requires extra work in updating dominator
 585   // information.
 586   BasicBlock *ExitingBBPred = NULL;
 587   for (pred_iterator PI = pred_begin(ExitingBlock), PE = pred_end(ExitingBlock);
 588        PI != PE; ++PI) {
 589     BasicBlock *BB = *PI;
 590     if (Header == BB)
 591       continue;
 592     if (ExitingBBPred)
 593       return false;
 594     else
 595       ExitingBBPred = BB;
 596   }
 597
 598   if (!restrictLoopBound(*Op0))
 599     return false;
 600
 601   if (!restrictLoopBound(*Op1))
 602     return false;
 603
 604   // Update CFG.
 605   if (BR->getSuccessor(0) == ExitingBlock)
 606     BR->setUnconditionalDest(BR->getSuccessor(1));
 607   else
 608     BR->setUnconditionalDest(BR->getSuccessor(0));
 609
 610   AND->eraseFromParent();
 611   if (Op0->use_empty())
 612     Op0->eraseFromParent();
 613   if (Op1->use_empty())
 614     Op1->eraseFromParent();
 615
 616   // Update domiantor info. Now, ExitingBlock has only one predecessor,
 617   // ExitingBBPred, and it is ExitingBlock's immediate domiantor.
 618   DT->changeImmediateDominator(ExitingBlock, ExitingBBPred);
 619
 620   BasicBlock *ExitBlock = ExitingBlock->getTerminator()->getSuccessor(1);
 621   if (L->contains(ExitBlock))
 622     ExitBlock = ExitingBlock->getTerminator()->getSuccessor(0);
 623
 624   // If ExitingBlock is a member of the loop basic blocks' DF list then
 625   // replace ExitingBlock with header and exit block in the DF list
 626   DominanceFrontier::iterator ExitingBlockDF = DF->find(ExitingBlock);
 627   for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
 628        I != E; ++I) {
 629     BasicBlock *BB = *I;
 630     if (BB == Header || BB == ExitingBlock)
 631       continue;
 632     DominanceFrontier::iterator BBDF = DF->find(BB);
 633     DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
 634     DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
 635     while (DomSetI != DomSetE) {
 636       DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
 637       ++DomSetI;
 638       BasicBlock *DFBB = *CurrentItr;
 639       if (DFBB == ExitingBlock) {
 640         BBDF->second.erase(DFBB);
 641         for (DominanceFrontier::DomSetType::iterator
 642                EBI = ExitingBlockDF->second.begin(),
 643                EBE = ExitingBlockDF->second.end(); EBI != EBE; ++EBI)
 644           BBDF->second.insert(*EBI);
 645       }
 646     }
 647   }
 648   NumRestrictBounds++;
 649   return true;
 650 }
 651
 652 /// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
 653 /// This routine is used to remove split condition's dead branch, dominated by
 654 /// DeadBB. LiveBB dominates split conidition's other branch.
 655 void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
 656                                   BasicBlock *LiveBB) {
 657
 658   // First update DeadBB's dominance frontier.
 659   SmallVector<BasicBlock *, 8> FrontierBBs;
 660   DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
 661   if (DeadBBDF != DF->end()) {
 662     SmallVector<BasicBlock *, 8> PredBlocks;
 663
 664     DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
 665     for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
 666            DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI)
 667       {
 668       BasicBlock *FrontierBB = *DeadBBSetI;
 669       FrontierBBs.push_back(FrontierBB);
 670
 671       // Rremove any PHI incoming edge from blocks dominated by DeadBB.
 672       PredBlocks.clear();
 673       for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
 674           PI != PE; ++PI) {
 675         BasicBlock *P = *PI;
 676         if (P == DeadBB || DT->dominates(DeadBB, P))
 677           PredBlocks.push_back(P);
 678       }
 679
 680       for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
 681           FBI != FBE; ++FBI) {
 682         if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
 683           for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
 684                 PE = PredBlocks.end(); PI != PE; ++PI) {
 685             BasicBlock *P = *PI;
 686             PN->removeIncomingValue(P);
 687           }
 688         }
 689         else
 690           break;
 691       }
 692     }
 693   }
 694
 695   // Now remove DeadBB and all nodes dominated by DeadBB in df order.
 696   SmallVector<BasicBlock *, 32> WorkList;
 697   DomTreeNode *DN = DT->getNode(DeadBB);
 698   for (df_iterator<DomTreeNode*> DI = df_begin(DN),
 699          E = df_end(DN); DI != E; ++DI) {
 700     BasicBlock *BB = DI->getBlock();
 701     WorkList.push_back(BB);
 702     BB->replaceAllUsesWith(UndefValue::get(
 703                                        Type::getLabelTy(DeadBB->getContext())));
 704   }
 705
 706   while (!WorkList.empty()) {
 707     BasicBlock *BB = WorkList.back(); WorkList.pop_back();
 708     LPM->deleteSimpleAnalysisValue(BB, LP);
 709     for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
 710         BBI != BBE; ) {
 711       Instruction *I = BBI;
 712       ++BBI;
 713       I->replaceAllUsesWith(UndefValue::get(I->getType()));
 714       LPM->deleteSimpleAnalysisValue(I, LP);
 715       I->eraseFromParent();
 716     }
 717     DT->eraseNode(BB);
 718     DF->removeBlock(BB);
 719     LI->removeBlock(BB);
 720     BB->eraseFromParent();
 721   }
 722
 723   // Update Frontier BBs' dominator info.
 724   while (!FrontierBBs.empty()) {
 725     BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
 726     BasicBlock *NewDominator = FBB->getSinglePredecessor();
 727     if (!NewDominator) {
 728       pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
 729       NewDominator = *PI;
 730       ++PI;
 731       if (NewDominator != LiveBB) {
 732         for(; PI != PE; ++PI) {
 733           BasicBlock *P = *PI;
 734           if (P == LiveBB) {
 735             NewDominator = LiveBB;
 736             break;
 737           }
 738           NewDominator = DT->findNearestCommonDominator(NewDominator, P);
 739         }
 740       }
 741     }
 742     assert (NewDominator && "Unable to fix dominator info.");
 743     DT->changeImmediateDominator(FBB, NewDominator);
 744     DF->changeImmediateDominator(FBB, NewDominator, DT);
 745   }
 746
 747 }
 748
 749 // moveExitCondition - Move exit condition EC into split condition block CondBB.
 750 void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
 751                                        BasicBlock *ExitBB, ICmpInst *EC,
 752                                        ICmpInst *SC, PHINode *IV,
 753                                        Instruction *IVAdd, Loop *LP,
 754                                        unsigned ExitValueNum) {
 755
 756   BasicBlock *ExitingBB = EC->getParent();
 757   Instruction *CurrentBR = CondBB->getTerminator();
 758
 759   // Move exit condition into split condition block.
 760   EC->moveBefore(CurrentBR);
 761   EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
 762
 763   // Move exiting block's branch into split condition block. Update its branch
 764   // destination.
 765   BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
 766   ExitingBR->moveBefore(CurrentBR);
 767   BasicBlock *OrigDestBB = NULL;
 768   if (ExitingBR->getSuccessor(0) == ExitBB) {
 769     OrigDestBB = ExitingBR->getSuccessor(1);
 770     ExitingBR->setSuccessor(1, ActiveBB);
 771   }
 772   else {
 773     OrigDestBB = ExitingBR->getSuccessor(0);
 774     ExitingBR->setSuccessor(0, ActiveBB);
 775   }
 776
 777   // Remove split condition and current split condition branch.
 778   SC->eraseFromParent();
 779   CurrentBR->eraseFromParent();
 780
 781   // Connect exiting block to original destination.
 782   BranchInst::Create(OrigDestBB, ExitingBB);
 783
 784   // Update PHINodes
 785   updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd, LP);
 786
 787   // Fix dominator info.
 788   // ExitBB is now dominated by CondBB
 789   DT->changeImmediateDominator(ExitBB, CondBB);
 790   DF->changeImmediateDominator(ExitBB, CondBB, DT);
 791
 792   // Blocks outside the loop may have been in the dominance frontier of blocks
 793   // inside the condition; this is now impossible because the blocks inside the
 794   // condition no loger dominate the exit.  Remove the relevant blocks from
 795   // the dominance frontiers.
 796   for (Loop::block_iterator I = LP->block_begin(), E = LP->block_end();
 797        I != E; ++I) {
 798     if (*I == CondBB || !DT->dominates(CondBB, *I)) continue;
 799     DominanceFrontier::iterator BBDF = DF->find(*I);
 800     DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
 801     DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
 802     while (DomSetI != DomSetE) {
 803       DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
 804       ++DomSetI;
 805       BasicBlock *DFBB = *CurrentItr;
 806       if (!LP->contains(DFBB))
 807         BBDF->second.erase(DFBB);
 808     }
 809   }
 810 }
 811
 812 /// updatePHINodes - CFG has been changed.
 813 /// Before
 814 ///   - ExitBB's single predecessor was Latch
 815 ///   - Latch's second successor was Header
 816 /// Now
 817 ///   - ExitBB's single predecessor is Header
 818 ///   - Latch's one and only successor is Header
 819 ///
 820 /// Update ExitBB PHINodes' to reflect this change.
 821 void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
 822                                     BasicBlock *Header,
 823                                     PHINode *IV, Instruction *IVIncrement,
 824                                     Loop *LP) {
 825
 826   for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
 827        BI != BE; ) {
 828     PHINode *PN = dyn_cast<PHINode>(BI);
 829     ++BI;
 830     if (!PN)
 831       break;
 832
 833     Value *V = PN->getIncomingValueForBlock(Latch);
 834     if (PHINode *PHV = dyn_cast<PHINode>(V)) {
 835       // PHV is in Latch. PHV has one use is in ExitBB PHINode. And one use
 836       // in Header which is new incoming value for PN.
 837       Value *NewV = NULL;
 838       for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
 839            UI != E; ++UI)
 840         if (PHINode *U = dyn_cast<PHINode>(*UI))
 841           if (LP->contains(U->getParent())) {
 842             NewV = U;
 843             break;
 844           }
 845
 846       // Add incoming value from header only if PN has any use inside the loop.
 847       if (NewV)
 848         PN->addIncoming(NewV, Header);
 849
 850     } else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
 851       // If this instruction is IVIncrement then IV is new incoming value
 852       // from header otherwise this instruction must be incoming value from
 853       // header because loop is in LCSSA form.
 854       if (PHI == IVIncrement)
 855         PN->addIncoming(IV, Header);
 856       else
 857         PN->addIncoming(V, Header);
 858     } else
 859       // Otherwise this is an incoming value from header because loop is in
 860       // LCSSA form.
 861       PN->addIncoming(V, Header);
 862
 863     // Remove incoming value from Latch.
 864     PN->removeIncomingValue(Latch);
 865   }
 866 }
 867
 868 bool LoopIndexSplit::splitLoop() {
 869   SplitCondition = NULL;
 870   if (ExitCondition->getPredicate() == ICmpInst::ICMP_NE
 871       || ExitCondition->getPredicate() == ICmpInst::ICMP_EQ)
 872     return false;
 873   BasicBlock *Header = L->getHeader();
 874   BasicBlock *Latch = L->getLoopLatch();
 875   BranchInst *SBR = NULL; // Split Condition Branch
 876   BranchInst *EBR = cast<BranchInst>(ExitCondition->getParent()->getTerminator());
 877   // If Exiting block includes loop variant instructions then this
 878   // loop may not be split safely.
 879   BasicBlock *ExitingBlock = ExitCondition->getParent();
 880   if (!cleanBlock(ExitingBlock)) return false;
 881
 882   LLVMContext &Context = Header->getContext();
 883
 884   for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
 885        I != E; ++I) {
 886     BranchInst *BR = dyn_cast<BranchInst>((*I)->getTerminator());
 887     if (!BR || BR->isUnconditional()) continue;
 888     ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
 889     if (!CI || CI == ExitCondition
 890         || CI->getPredicate() == ICmpInst::ICMP_NE
 891         || CI->getPredicate() == ICmpInst::ICMP_EQ)
 892       continue;
 893
 894     // Unable to handle triangle loops at the moment.
 895     // In triangle loop, split condition is in header and one of the
 896     // the split destination is loop latch. If split condition is EQ
 897     // then such loops are already handle in processOneIterationLoop().
 898     if (Header == (*I)
 899         && (Latch == BR->getSuccessor(0) || Latch == BR->getSuccessor(1)))
 900       continue;
 901
 902     // If the block does not dominate the latch then this is not a diamond.
 903     // Such loop may not benefit from index split.
 904     if (!DT->dominates((*I), Latch))
 905       continue;
 906
 907     // If split condition branches heads do not have single predecessor,
 908     // SplitCondBlock, then is not possible to remove inactive branch.
 909     if (!BR->getSuccessor(0)->getSinglePredecessor()
 910         || !BR->getSuccessor(1)->getSinglePredecessor())
 911       return false;
 912
 913     // If the merge point for BR is not loop latch then skip this condition.
 914     if (BR->getSuccessor(0) != Latch) {
 915       DominanceFrontier::iterator DF0 = DF->find(BR->getSuccessor(0));
 916       assert (DF0 != DF->end() && "Unable to find dominance frontier");
 917       if (!DF0->second.count(Latch))
 918         continue;
 919     }
 920
 921     if (BR->getSuccessor(1) != Latch) {
 922       DominanceFrontier::iterator DF1 = DF->find(BR->getSuccessor(1));
 923       assert (DF1 != DF->end() && "Unable to find dominance frontier");
 924       if (!DF1->second.count(Latch))
 925         continue;
 926     }
 927     SplitCondition = CI;
 928     SBR = BR;
 929     break;
 930   }
 931
 932   if (!SplitCondition)
 933     return false;
 934
 935   // If the predicate sign does not match then skip.
 936   if (ExitCondition->isSignedPredicate() != SplitCondition->isSignedPredicate())
 937     return false;
 938
 939   unsigned EVOpNum = (ExitCondition->getOperand(1) == IVExitValue);
 940   unsigned SVOpNum = IVBasedValues.count(SplitCondition->getOperand(0));
 941   Value *SplitValue = SplitCondition->getOperand(SVOpNum);
 942   if (!L->isLoopInvariant(SplitValue))
 943     return false;
 944   if (!IVBasedValues.count(SplitCondition->getOperand(!SVOpNum)))
 945     return false;
 946
 947   // Normalize loop conditions so that it is easier to calculate new loop
 948   // bounds.
 949   if (IVisGT(*ExitCondition) || IVisGE(*ExitCondition)) {
 950     ExitCondition->setPredicate(ExitCondition->getInversePredicate());
 951     BasicBlock *T = EBR->getSuccessor(0);
 952     EBR->setSuccessor(0, EBR->getSuccessor(1));
 953     EBR->setSuccessor(1, T);
 954   }
 955
 956   if (IVisGT(*SplitCondition) || IVisGE(*SplitCondition)) {
 957     SplitCondition->setPredicate(SplitCondition->getInversePredicate());
 958     BasicBlock *T = SBR->getSuccessor(0);
 959     SBR->setSuccessor(0, SBR->getSuccessor(1));
 960     SBR->setSuccessor(1, T);
 961   }
 962
 963   //[*] Calculate new loop bounds.
 964   Value *AEV = SplitValue;
 965   Value *BSV = SplitValue;
 966   bool Sign = SplitCondition->isSignedPredicate();
 967   Instruction *PHTerm = L->getLoopPreheader()->getTerminator();
 968
 969   if (IVisLT(*ExitCondition)) {
 970     if (IVisLT(*SplitCondition)) {
 971       /* Do nothing */
 972     }
 973     else if (IVisLE(*SplitCondition)) {
 974       AEV = getPlusOne(SplitValue, Sign, PHTerm, Context);
 975       BSV = getPlusOne(SplitValue, Sign, PHTerm, Context);
 976     } else {
 977       assert (0 && "Unexpected split condition!");
 978     }
 979   }
 980   else if (IVisLE(*ExitCondition)) {
 981     if (IVisLT(*SplitCondition)) {
 982       AEV = getMinusOne(SplitValue, Sign, PHTerm, Context);
 983     }
 984     else if (IVisLE(*SplitCondition)) {
 985       BSV = getPlusOne(SplitValue, Sign, PHTerm, Context);
 986     } else {
 987       assert (0 && "Unexpected split condition!");
 988     }
 989   } else {
 990     assert (0 && "Unexpected exit condition!");
 991   }
 992   AEV = getMin(AEV, IVExitValue, Sign, PHTerm);
 993   BSV = getMax(BSV, IVStartValue, Sign, PHTerm);
 994
 995   // [*] Clone Loop
 996   DenseMap<const Value *, Value *> ValueMap;
 997   Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
 998   Loop *ALoop = L;
 999
1000   // [*] ALoop's exiting edge enters BLoop's header.
1001   //    ALoop's original exit block becomes BLoop's exit block.
1002   PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
1003   BasicBlock *A_ExitingBlock = ExitCondition->getParent();
1004   BranchInst *A_ExitInsn =
1005     dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
1006   assert (A_ExitInsn && "Unable to find suitable loop exit branch");
1007   BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
1008   BasicBlock *B_Header = BLoop->getHeader();
1009   if (ALoop->contains(B_ExitBlock)) {
1010     B_ExitBlock = A_ExitInsn->getSuccessor(0);
1011     A_ExitInsn->setSuccessor(0, B_Header);
1012   } else
1013     A_ExitInsn->setSuccessor(1, B_Header);
1014
1015   // [*] Update ALoop's exit value using new exit value.
1016   ExitCondition->setOperand(EVOpNum, AEV);
1017
1018   // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
1019   //     original loop's preheader. Add incoming PHINode values from
1020   //     ALoop's exiting block. Update BLoop header's domiantor info.
1021
1022   // Collect inverse map of Header PHINodes.
1023   DenseMap<Value *, Value *> InverseMap;
1024   for (BasicBlock::iterator BI = ALoop->getHeader()->begin(),
1025          BE = ALoop->getHeader()->end(); BI != BE; ++BI) {
1026     if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1027       PHINode *PNClone = cast<PHINode>(ValueMap[PN]);
1028       InverseMap[PNClone] = PN;
1029     } else
1030       break;
1031   }
1032
1033   BasicBlock *A_Preheader = ALoop->getLoopPreheader();
1034   for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1035        BI != BE; ++BI) {
1036     if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1037       // Remove incoming value from original preheader.
1038       PN->removeIncomingValue(A_Preheader);
1039
1040       // Add incoming value from A_ExitingBlock.
1041       if (PN == B_IndVar)
1042         PN->addIncoming(BSV, A_ExitingBlock);
1043       else {
1044         PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
1045         Value *V2 = NULL;
1046         // If loop header is also loop exiting block then
1047         // OrigPN is incoming value for B loop header.
1048         if (A_ExitingBlock == ALoop->getHeader())
1049           V2 = OrigPN;
1050         else
1051           V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
1052         PN->addIncoming(V2, A_ExitingBlock);
1053       }
1054     } else
1055       break;
1056   }
1057
1058   DT->changeImmediateDominator(B_Header, A_ExitingBlock);
1059   DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
1060
1061   // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
1062   //     block. Remove incoming PHINode values from ALoop's exiting block.
1063   //     Add new incoming values from BLoop's incoming exiting value.
1064   //     Update BLoop exit block's dominator info..
1065   BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
1066   for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
1067        BI != BE; ++BI) {
1068     if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1069       PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
1070                                                             B_ExitingBlock);
1071       PN->removeIncomingValue(A_ExitingBlock);
1072     } else
1073       break;
1074   }
1075
1076   DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
1077   DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
1078
1079   //[*] Split ALoop's exit edge. This creates a new block which
1080   //    serves two purposes. First one is to hold PHINode defnitions
1081   //    to ensure that ALoop's LCSSA form. Second use it to act
1082   //    as a preheader for BLoop.
1083   BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
1084
1085   //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
1086   //    in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
1087   for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
1088       BI != BE; ++BI) {
1089     if (PHINode *PN = dyn_cast<PHINode>(BI)) {
1090       Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
1091       PHINode *newPHI = PHINode::Create(PN->getType(), PN->getName());
1092       newPHI->addIncoming(V1, A_ExitingBlock);
1093       A_ExitBlock->getInstList().push_front(newPHI);
1094       PN->removeIncomingValue(A_ExitBlock);
1095       PN->addIncoming(newPHI, A_ExitBlock);
1096     } else
1097       break;
1098   }
1099
1100   //[*] Eliminate split condition's inactive branch from ALoop.
1101   BasicBlock *A_SplitCondBlock = SplitCondition->getParent();
1102   BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
1103   BasicBlock *A_InactiveBranch = NULL;
1104   BasicBlock *A_ActiveBranch = NULL;
1105   A_ActiveBranch = A_BR->getSuccessor(0);
1106   A_InactiveBranch = A_BR->getSuccessor(1);
1107   A_BR->setUnconditionalDest(A_ActiveBranch);
1108   removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
1109
1110   //[*] Eliminate split condition's inactive branch in from BLoop.
1111   BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
1112   BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
1113   BasicBlock *B_InactiveBranch = NULL;
1114   BasicBlock *B_ActiveBranch = NULL;
1115   B_ActiveBranch = B_BR->getSuccessor(1);
1116   B_InactiveBranch = B_BR->getSuccessor(0);
1117   B_BR->setUnconditionalDest(B_ActiveBranch);
1118   removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
1119
1120   BasicBlock *A_Header = ALoop->getHeader();
1121   if (A_ExitingBlock == A_Header)
1122     return true;
1123
1124   //[*] Move exit condition into split condition block to avoid
1125   //    executing dead loop iteration.
1126   ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
1127   Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IVIncrement]);
1128   ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SplitCondition]);
1129
1130   moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
1131                     cast<ICmpInst>(SplitCondition), IndVar, IVIncrement,
1132                     ALoop, EVOpNum);
1133
1134   moveExitCondition(B_SplitCondBlock, B_ActiveBranch,
1135                     B_ExitBlock, B_ExitCondition,
1136                     B_SplitCondition, B_IndVar, B_IndVarIncrement,
1137                     BLoop, EVOpNum);
1138
1139   NumIndexSplit++;
1140   return true;
1141 }
1142
1143 /// cleanBlock - A block is considered clean if all non terminal instructions
1144 /// are either, PHINodes, IV based.
1145 bool LoopIndexSplit::cleanBlock(BasicBlock *BB) {
1146   Instruction *Terminator = BB->getTerminator();
1147   for(BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1148       BI != BE; ++BI) {
1149     Instruction *I = BI;
1150
1151     if (isa<PHINode>(I) || I == Terminator || I == ExitCondition
1152         || I == SplitCondition || IVBasedValues.count(I)
1153         || isa<DbgInfoIntrinsic>(I))
1154       continue;
1155
1156     if (I->mayHaveSideEffects())
1157       return false;
1158
1159     // I is used only inside this block then it is OK.
1160     bool usedOutsideBB = false;
1161     for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
1162          UI != UE; ++UI) {
1163       Instruction *U = cast<Instruction>(UI);
1164       if (U->getParent() != BB)
1165         usedOutsideBB = true;
1166     }
1167     if (!usedOutsideBB)
1168       continue;
1169
1170     // Otherwise we have a instruction that may not allow loop spliting.
1171     return false;
1172   }
1173   return true;
1174 }
1175
1176 /// IVisLT - If Op is comparing IV based value with an loop invariant and
1177 /// IV based value is less than  the loop invariant then return the loop
1178 /// invariant. Otherwise return NULL.
1179 Value * LoopIndexSplit::IVisLT(ICmpInst &Op) {
1180   ICmpInst::Predicate P = Op.getPredicate();
1181   if ((P == ICmpInst::ICMP_SLT || P == ICmpInst::ICMP_ULT)
1182       && IVBasedValues.count(Op.getOperand(0))
1183       && L->isLoopInvariant(Op.getOperand(1)))
1184     return Op.getOperand(1);
1185
1186   if ((P == ICmpInst::ICMP_SGT || P == ICmpInst::ICMP_UGT)
1187       && IVBasedValues.count(Op.getOperand(1))
1188       && L->isLoopInvariant(Op.getOperand(0)))
1189     return Op.getOperand(0);
1190
1191   return NULL;
1192 }
1193
1194 /// IVisLE - If Op is comparing IV based value with an loop invariant and
1195 /// IV based value is less than or equal to the loop invariant then
1196 /// return the loop invariant. Otherwise return NULL.
1197 Value * LoopIndexSplit::IVisLE(ICmpInst &Op) {
1198   ICmpInst::Predicate P = Op.getPredicate();
1199   if ((P == ICmpInst::ICMP_SLE || P == ICmpInst::ICMP_ULE)
1200       && IVBasedValues.count(Op.getOperand(0))
1201       && L->isLoopInvariant(Op.getOperand(1)))
1202     return Op.getOperand(1);
1203
1204   if ((P == ICmpInst::ICMP_SGE || P == ICmpInst::ICMP_UGE)
1205       && IVBasedValues.count(Op.getOperand(1))
1206       && L->isLoopInvariant(Op.getOperand(0)))
1207     return Op.getOperand(0);
1208
1209   return NULL;
1210 }
1211
1212 /// IVisGT - If Op is comparing IV based value with an loop invariant and
1213 /// IV based value is greater than  the loop invariant then return the loop
1214 /// invariant. Otherwise return NULL.
1215 Value * LoopIndexSplit::IVisGT(ICmpInst &Op) {
1216   ICmpInst::Predicate P = Op.getPredicate();
1217   if ((P == ICmpInst::ICMP_SGT || P == ICmpInst::ICMP_UGT)
1218       && IVBasedValues.count(Op.getOperand(0))
1219       && L->isLoopInvariant(Op.getOperand(1)))
1220     return Op.getOperand(1);
1221
1222   if ((P == ICmpInst::ICMP_SLT || P == ICmpInst::ICMP_ULT)
1223       && IVBasedValues.count(Op.getOperand(1))
1224       && L->isLoopInvariant(Op.getOperand(0)))
1225     return Op.getOperand(0);
1226
1227   return NULL;
1228 }
1229
1230 /// IVisGE - If Op is comparing IV based value with an loop invariant and
1231 /// IV based value is greater than or equal to the loop invariant then
1232 /// return the loop invariant. Otherwise return NULL.
1233 Value * LoopIndexSplit::IVisGE(ICmpInst &Op) {
1234   ICmpInst::Predicate P = Op.getPredicate();
1235   if ((P == ICmpInst::ICMP_SGE || P == ICmpInst::ICMP_UGE)
1236       && IVBasedValues.count(Op.getOperand(0))
1237       && L->isLoopInvariant(Op.getOperand(1)))
1238     return Op.getOperand(1);
1239
1240   if ((P == ICmpInst::ICMP_SLE || P == ICmpInst::ICMP_ULE)
1241       && IVBasedValues.count(Op.getOperand(1))
1242       && L->isLoopInvariant(Op.getOperand(0)))
1243     return Op.getOperand(0);
1244
1245   return NULL;
1246 }
1247