1 //===-- LoopUnroll.cpp - Loop unroller 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 pass implements a simple loop unroller. It works best when loops have 11 // been canonicalized by the -indvars pass, allowing it to determine the trip 12 // counts of loops easily. 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Transforms/Scalar.h" 16 #include "llvm/ADT/SetVector.h" 17 #include "llvm/Analysis/GlobalsModRef.h" 18 #include "llvm/Analysis/AssumptionCache.h" 19 #include "llvm/Analysis/CodeMetrics.h" 20 #include "llvm/Analysis/InstructionSimplify.h" 21 #include "llvm/Analysis/LoopPass.h" 22 #include "llvm/Analysis/ScalarEvolution.h" 23 #include "llvm/Analysis/ScalarEvolutionExpressions.h" 24 #include "llvm/Analysis/TargetTransformInfo.h" 25 #include "llvm/IR/DataLayout.h" 26 #include "llvm/IR/DiagnosticInfo.h" 27 #include "llvm/IR/Dominators.h" 28 #include "llvm/IR/InstVisitor.h" 29 #include "llvm/IR/IntrinsicInst.h" 30 #include "llvm/IR/Metadata.h" 31 #include "llvm/Support/CommandLine.h" 32 #include "llvm/Support/Debug.h" 33 #include "llvm/Support/raw_ostream.h" 34 #include "llvm/Transforms/Utils/UnrollLoop.h" 35 #include <climits> 36 37 using namespace llvm; 38 39 #define DEBUG_TYPE "loop-unroll" 40 41 static cl::opt<unsigned> 42 UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden, 43 cl::desc("The baseline cost threshold for loop unrolling")); 44 45 static cl::opt<unsigned> UnrollPercentDynamicCostSavedThreshold( 46 "unroll-percent-dynamic-cost-saved-threshold", cl::init(20), cl::Hidden, 47 cl::desc("The percentage of estimated dynamic cost which must be saved by " 48 "unrolling to allow unrolling up to the max threshold.")); 49 50 static cl::opt<unsigned> UnrollDynamicCostSavingsDiscount( 51 "unroll-dynamic-cost-savings-discount", cl::init(2000), cl::Hidden, 52 cl::desc("This is the amount discounted from the total unroll cost when " 53 "the unrolled form has a high dynamic cost savings (triggered by " 54 "the '-unroll-perecent-dynamic-cost-saved-threshold' flag).")); 55 56 static cl::opt<unsigned> UnrollMaxIterationsCountToAnalyze( 57 "unroll-max-iteration-count-to-analyze", cl::init(0), cl::Hidden, 58 cl::desc("Don't allow loop unrolling to simulate more than this number of" 59 "iterations when checking full unroll profitability")); 60 61 static cl::opt<unsigned> 62 UnrollCount("unroll-count", cl::init(0), cl::Hidden, 63 cl::desc("Use this unroll count for all loops including those with " 64 "unroll_count pragma values, for testing purposes")); 65 66 static cl::opt<bool> 67 UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden, 68 cl::desc("Allows loops to be partially unrolled until " 69 "-unroll-threshold loop size is reached.")); 70 71 static cl::opt<bool> 72 UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden, 73 cl::desc("Unroll loops with run-time trip counts")); 74 75 static cl::opt<unsigned> 76 PragmaUnrollThreshold("pragma-unroll-threshold", cl::init(16 * 1024), cl::Hidden, 77 cl::desc("Unrolled size limit for loops with an unroll(full) or " 78 "unroll_count pragma.")); 79 80 namespace { 81 class LoopUnroll : public LoopPass { 82 public: 83 static char ID; // Pass ID, replacement for typeid 84 LoopUnroll(int T = -1, int C = -1, int P = -1, int R = -1) : LoopPass(ID) { 85 CurrentThreshold = (T == -1) ? UnrollThreshold : unsigned(T); 86 CurrentPercentDynamicCostSavedThreshold = 87 UnrollPercentDynamicCostSavedThreshold; 88 CurrentDynamicCostSavingsDiscount = UnrollDynamicCostSavingsDiscount; 89 CurrentCount = (C == -1) ? UnrollCount : unsigned(C); 90 CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P; 91 CurrentRuntime = (R == -1) ? UnrollRuntime : (bool)R; 92 93 UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0); 94 UserPercentDynamicCostSavedThreshold = 95 (UnrollPercentDynamicCostSavedThreshold.getNumOccurrences() > 0); 96 UserDynamicCostSavingsDiscount = 97 (UnrollDynamicCostSavingsDiscount.getNumOccurrences() > 0); 98 UserAllowPartial = (P != -1) || 99 (UnrollAllowPartial.getNumOccurrences() > 0); 100 UserRuntime = (R != -1) || (UnrollRuntime.getNumOccurrences() > 0); 101 UserCount = (C != -1) || (UnrollCount.getNumOccurrences() > 0); 102 103 initializeLoopUnrollPass(*PassRegistry::getPassRegistry()); 104 } 105 106 /// A magic value for use with the Threshold parameter to indicate 107 /// that the loop unroll should be performed regardless of how much 108 /// code expansion would result. 109 static const unsigned NoThreshold = UINT_MAX; 110 111 // Threshold to use when optsize is specified (and there is no 112 // explicit -unroll-threshold). 113 static const unsigned OptSizeUnrollThreshold = 50; 114 115 // Default unroll count for loops with run-time trip count if 116 // -unroll-count is not set 117 static const unsigned UnrollRuntimeCount = 8; 118 119 unsigned CurrentCount; 120 unsigned CurrentThreshold; 121 unsigned CurrentPercentDynamicCostSavedThreshold; 122 unsigned CurrentDynamicCostSavingsDiscount; 123 bool CurrentAllowPartial; 124 bool CurrentRuntime; 125 126 // Flags for whether the 'current' settings are user-specified. 127 bool UserCount; 128 bool UserThreshold; 129 bool UserPercentDynamicCostSavedThreshold; 130 bool UserDynamicCostSavingsDiscount; 131 bool UserAllowPartial; 132 bool UserRuntime; 133 134 bool runOnLoop(Loop *L, LPPassManager &) override; 135 136 /// This transformation requires natural loop information & requires that 137 /// loop preheaders be inserted into the CFG... 138 /// 139 void getAnalysisUsage(AnalysisUsage &AU) const override { 140 AU.addRequired<AssumptionCacheTracker>(); 141 AU.addRequired<DominatorTreeWrapperPass>(); 142 AU.addRequired<LoopInfoWrapperPass>(); 143 AU.addPreserved<LoopInfoWrapperPass>(); 144 AU.addRequiredID(LoopSimplifyID); 145 AU.addPreservedID(LoopSimplifyID); 146 AU.addRequiredID(LCSSAID); 147 AU.addPreservedID(LCSSAID); 148 AU.addRequired<ScalarEvolutionWrapperPass>(); 149 AU.addPreserved<ScalarEvolutionWrapperPass>(); 150 AU.addRequired<TargetTransformInfoWrapperPass>(); 151 // FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info. 152 // If loop unroll does not preserve dom info then LCSSA pass on next 153 // loop will receive invalid dom info. 154 // For now, recreate dom info, if loop is unrolled. 155 AU.addPreserved<DominatorTreeWrapperPass>(); 156 AU.addPreserved<GlobalsAAWrapperPass>(); 157 } 158 159 // Fill in the UnrollingPreferences parameter with values from the 160 // TargetTransformationInfo. 161 void getUnrollingPreferences(Loop *L, const TargetTransformInfo &TTI, 162 TargetTransformInfo::UnrollingPreferences &UP) { 163 UP.Threshold = CurrentThreshold; 164 UP.PercentDynamicCostSavedThreshold = 165 CurrentPercentDynamicCostSavedThreshold; 166 UP.DynamicCostSavingsDiscount = CurrentDynamicCostSavingsDiscount; 167 UP.OptSizeThreshold = OptSizeUnrollThreshold; 168 UP.PartialThreshold = CurrentThreshold; 169 UP.PartialOptSizeThreshold = OptSizeUnrollThreshold; 170 UP.Count = CurrentCount; 171 UP.MaxCount = UINT_MAX; 172 UP.Partial = CurrentAllowPartial; 173 UP.Runtime = CurrentRuntime; 174 UP.AllowExpensiveTripCount = false; 175 TTI.getUnrollingPreferences(L, UP); 176 } 177 178 // Select and return an unroll count based on parameters from 179 // user, unroll preferences, unroll pragmas, or a heuristic. 180 // SetExplicitly is set to true if the unroll count is is set by 181 // the user or a pragma rather than selected heuristically. 182 unsigned 183 selectUnrollCount(const Loop *L, unsigned TripCount, bool PragmaFullUnroll, 184 unsigned PragmaCount, 185 const TargetTransformInfo::UnrollingPreferences &UP, 186 bool &SetExplicitly); 187 188 // Select threshold values used to limit unrolling based on a 189 // total unrolled size. Parameters Threshold and PartialThreshold 190 // are set to the maximum unrolled size for fully and partially 191 // unrolled loops respectively. 192 void selectThresholds(const Loop *L, bool UsePragmaThreshold, 193 const TargetTransformInfo::UnrollingPreferences &UP, 194 unsigned &Threshold, unsigned &PartialThreshold, 195 unsigned &PercentDynamicCostSavedThreshold, 196 unsigned &DynamicCostSavingsDiscount) { 197 // Determine the current unrolling threshold. While this is 198 // normally set from UnrollThreshold, it is overridden to a 199 // smaller value if the current function is marked as 200 // optimize-for-size, and the unroll threshold was not user 201 // specified. 202 Threshold = UserThreshold ? CurrentThreshold : UP.Threshold; 203 PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold; 204 PercentDynamicCostSavedThreshold = 205 UserPercentDynamicCostSavedThreshold 206 ? CurrentPercentDynamicCostSavedThreshold 207 : UP.PercentDynamicCostSavedThreshold; 208 DynamicCostSavingsDiscount = UserDynamicCostSavingsDiscount 209 ? CurrentDynamicCostSavingsDiscount 210 : UP.DynamicCostSavingsDiscount; 211 212 if (!UserThreshold && 213 // FIXME: Use Function::optForSize(). 214 L->getHeader()->getParent()->hasFnAttribute( 215 Attribute::OptimizeForSize)) { 216 Threshold = UP.OptSizeThreshold; 217 PartialThreshold = UP.PartialOptSizeThreshold; 218 } 219 if (UsePragmaThreshold) { 220 // If the loop has an unrolling pragma, we want to be more 221 // aggressive with unrolling limits. Set thresholds to at 222 // least the PragmaTheshold value which is larger than the 223 // default limits. 224 if (Threshold != NoThreshold) 225 Threshold = std::max<unsigned>(Threshold, PragmaUnrollThreshold); 226 if (PartialThreshold != NoThreshold) 227 PartialThreshold = 228 std::max<unsigned>(PartialThreshold, PragmaUnrollThreshold); 229 } 230 } 231 bool canUnrollCompletely(Loop *L, unsigned Threshold, 232 unsigned PercentDynamicCostSavedThreshold, 233 unsigned DynamicCostSavingsDiscount, 234 uint64_t UnrolledCost, uint64_t RolledDynamicCost); 235 }; 236 } 237 238 char LoopUnroll::ID = 0; 239 INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false) 240 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) 241 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 242 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 243 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) 244 INITIALIZE_PASS_DEPENDENCY(LoopSimplify) 245 INITIALIZE_PASS_DEPENDENCY(LCSSA) 246 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass) 247 INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false) 248 249 Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial, 250 int Runtime) { 251 return new LoopUnroll(Threshold, Count, AllowPartial, Runtime); 252 } 253 254 Pass *llvm::createSimpleLoopUnrollPass() { 255 return llvm::createLoopUnrollPass(-1, -1, 0, 0); 256 } 257 258 namespace { 259 // This class is used to get an estimate of the optimization effects that we 260 // could get from complete loop unrolling. It comes from the fact that some 261 // loads might be replaced with concrete constant values and that could trigger 262 // a chain of instruction simplifications. 263 // 264 // E.g. we might have: 265 // int a[] = {0, 1, 0}; 266 // v = 0; 267 // for (i = 0; i < 3; i ++) 268 // v += b[i]*a[i]; 269 // If we completely unroll the loop, we would get: 270 // v = b[0]*a[0] + b[1]*a[1] + b[2]*a[2] 271 // Which then will be simplified to: 272 // v = b[0]* 0 + b[1]* 1 + b[2]* 0 273 // And finally: 274 // v = b[1] 275 class UnrolledInstAnalyzer : private InstVisitor<UnrolledInstAnalyzer, bool> { 276 typedef InstVisitor<UnrolledInstAnalyzer, bool> Base; 277 friend class InstVisitor<UnrolledInstAnalyzer, bool>; 278 struct SimplifiedAddress { 279 Value *Base = nullptr; 280 ConstantInt *Offset = nullptr; 281 }; 282 283 public: 284 UnrolledInstAnalyzer(unsigned Iteration, 285 DenseMap<Value *, Constant *> &SimplifiedValues, 286 ScalarEvolution &SE) 287 : SimplifiedValues(SimplifiedValues), SE(SE) { 288 IterationNumber = SE.getConstant(APInt(64, Iteration)); 289 } 290 291 // Allow access to the initial visit method. 292 using Base::visit; 293 294 private: 295 /// \brief A cache of pointer bases and constant-folded offsets corresponding 296 /// to GEP (or derived from GEP) instructions. 297 /// 298 /// In order to find the base pointer one needs to perform non-trivial 299 /// traversal of the corresponding SCEV expression, so it's good to have the 300 /// results saved. 301 DenseMap<Value *, SimplifiedAddress> SimplifiedAddresses; 302 303 /// \brief SCEV expression corresponding to number of currently simulated 304 /// iteration. 305 const SCEV *IterationNumber; 306 307 /// \brief A Value->Constant map for keeping values that we managed to 308 /// constant-fold on the given iteration. 309 /// 310 /// While we walk the loop instructions, we build up and maintain a mapping 311 /// of simplified values specific to this iteration. The idea is to propagate 312 /// any special information we have about loads that can be replaced with 313 /// constants after complete unrolling, and account for likely simplifications 314 /// post-unrolling. 315 DenseMap<Value *, Constant *> &SimplifiedValues; 316 317 ScalarEvolution &SE; 318 319 /// \brief Try to simplify instruction \param I using its SCEV expression. 320 /// 321 /// The idea is that some AddRec expressions become constants, which then 322 /// could trigger folding of other instructions. However, that only happens 323 /// for expressions whose start value is also constant, which isn't always the 324 /// case. In another common and important case the start value is just some 325 /// address (i.e. SCEVUnknown) - in this case we compute the offset and save 326 /// it along with the base address instead. 327 bool simplifyInstWithSCEV(Instruction *I) { 328 if (!SE.isSCEVable(I->getType())) 329 return false; 330 331 const SCEV *S = SE.getSCEV(I); 332 if (auto *SC = dyn_cast<SCEVConstant>(S)) { 333 SimplifiedValues[I] = SC->getValue(); 334 return true; 335 } 336 337 auto *AR = dyn_cast<SCEVAddRecExpr>(S); 338 if (!AR) 339 return false; 340 341 const SCEV *ValueAtIteration = AR->evaluateAtIteration(IterationNumber, SE); 342 // Check if the AddRec expression becomes a constant. 343 if (auto *SC = dyn_cast<SCEVConstant>(ValueAtIteration)) { 344 SimplifiedValues[I] = SC->getValue(); 345 return true; 346 } 347 348 // Check if the offset from the base address becomes a constant. 349 auto *Base = dyn_cast<SCEVUnknown>(SE.getPointerBase(S)); 350 if (!Base) 351 return false; 352 auto *Offset = 353 dyn_cast<SCEVConstant>(SE.getMinusSCEV(ValueAtIteration, Base)); 354 if (!Offset) 355 return false; 356 SimplifiedAddress Address; 357 Address.Base = Base->getValue(); 358 Address.Offset = Offset->getValue(); 359 SimplifiedAddresses[I] = Address; 360 return true; 361 } 362 363 /// Base case for the instruction visitor. 364 bool visitInstruction(Instruction &I) { 365 return simplifyInstWithSCEV(&I); 366 } 367 368 /// Try to simplify binary operator I. 369 /// 370 /// TODO: Probably it's worth to hoist the code for estimating the 371 /// simplifications effects to a separate class, since we have a very similar 372 /// code in InlineCost already. 373 bool visitBinaryOperator(BinaryOperator &I) { 374 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1); 375 if (!isa<Constant>(LHS)) 376 if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS)) 377 LHS = SimpleLHS; 378 if (!isa<Constant>(RHS)) 379 if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS)) 380 RHS = SimpleRHS; 381 382 Value *SimpleV = nullptr; 383 const DataLayout &DL = I.getModule()->getDataLayout(); 384 if (auto FI = dyn_cast<FPMathOperator>(&I)) 385 SimpleV = 386 SimplifyFPBinOp(I.getOpcode(), LHS, RHS, FI->getFastMathFlags(), DL); 387 else 388 SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS, DL); 389 390 if (Constant *C = dyn_cast_or_null<Constant>(SimpleV)) 391 SimplifiedValues[&I] = C; 392 393 if (SimpleV) 394 return true; 395 return Base::visitBinaryOperator(I); 396 } 397 398 /// Try to fold load I. 399 bool visitLoad(LoadInst &I) { 400 Value *AddrOp = I.getPointerOperand(); 401 402 auto AddressIt = SimplifiedAddresses.find(AddrOp); 403 if (AddressIt == SimplifiedAddresses.end()) 404 return false; 405 ConstantInt *SimplifiedAddrOp = AddressIt->second.Offset; 406 407 auto *GV = dyn_cast<GlobalVariable>(AddressIt->second.Base); 408 // We're only interested in loads that can be completely folded to a 409 // constant. 410 if (!GV || !GV->hasDefinitiveInitializer() || !GV->isConstant()) 411 return false; 412 413 ConstantDataSequential *CDS = 414 dyn_cast<ConstantDataSequential>(GV->getInitializer()); 415 if (!CDS) 416 return false; 417 418 // We might have a vector load from an array. FIXME: for now we just bail 419 // out in this case, but we should be able to resolve and simplify such 420 // loads. 421 if(!CDS->isElementTypeCompatible(I.getType())) 422 return false; 423 424 int ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U; 425 assert(SimplifiedAddrOp->getValue().getActiveBits() < 64 && 426 "Unexpectedly large index value."); 427 int64_t Index = SimplifiedAddrOp->getSExtValue() / ElemSize; 428 if (Index >= CDS->getNumElements()) { 429 // FIXME: For now we conservatively ignore out of bound accesses, but 430 // we're allowed to perform the optimization in this case. 431 return false; 432 } 433 434 Constant *CV = CDS->getElementAsConstant(Index); 435 assert(CV && "Constant expected."); 436 SimplifiedValues[&I] = CV; 437 438 return true; 439 } 440 441 bool visitCastInst(CastInst &I) { 442 // Propagate constants through casts. 443 Constant *COp = dyn_cast<Constant>(I.getOperand(0)); 444 if (!COp) 445 COp = SimplifiedValues.lookup(I.getOperand(0)); 446 if (COp) 447 if (Constant *C = 448 ConstantExpr::getCast(I.getOpcode(), COp, I.getType())) { 449 SimplifiedValues[&I] = C; 450 return true; 451 } 452 453 return Base::visitCastInst(I); 454 } 455 456 bool visitCmpInst(CmpInst &I) { 457 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1); 458 459 // First try to handle simplified comparisons. 460 if (!isa<Constant>(LHS)) 461 if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS)) 462 LHS = SimpleLHS; 463 if (!isa<Constant>(RHS)) 464 if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS)) 465 RHS = SimpleRHS; 466 467 if (!isa<Constant>(LHS) && !isa<Constant>(RHS)) { 468 auto SimplifiedLHS = SimplifiedAddresses.find(LHS); 469 if (SimplifiedLHS != SimplifiedAddresses.end()) { 470 auto SimplifiedRHS = SimplifiedAddresses.find(RHS); 471 if (SimplifiedRHS != SimplifiedAddresses.end()) { 472 SimplifiedAddress &LHSAddr = SimplifiedLHS->second; 473 SimplifiedAddress &RHSAddr = SimplifiedRHS->second; 474 if (LHSAddr.Base == RHSAddr.Base) { 475 LHS = LHSAddr.Offset; 476 RHS = RHSAddr.Offset; 477 } 478 } 479 } 480 } 481 482 if (Constant *CLHS = dyn_cast<Constant>(LHS)) { 483 if (Constant *CRHS = dyn_cast<Constant>(RHS)) { 484 if (Constant *C = ConstantExpr::getCompare(I.getPredicate(), CLHS, CRHS)) { 485 SimplifiedValues[&I] = C; 486 return true; 487 } 488 } 489 } 490 491 return Base::visitCmpInst(I); 492 } 493 }; 494 } // namespace 495 496 497 namespace { 498 struct EstimatedUnrollCost { 499 /// \brief The estimated cost after unrolling. 500 int UnrolledCost; 501 502 /// \brief The estimated dynamic cost of executing the instructions in the 503 /// rolled form. 504 int RolledDynamicCost; 505 }; 506 } 507 508 /// \brief Figure out if the loop is worth full unrolling. 509 /// 510 /// Complete loop unrolling can make some loads constant, and we need to know 511 /// if that would expose any further optimization opportunities. This routine 512 /// estimates this optimization. It computes cost of unrolled loop 513 /// (UnrolledCost) and dynamic cost of the original loop (RolledDynamicCost). By 514 /// dynamic cost we mean that we won't count costs of blocks that are known not 515 /// to be executed (i.e. if we have a branch in the loop and we know that at the 516 /// given iteration its condition would be resolved to true, we won't add up the 517 /// cost of the 'false'-block). 518 /// \returns Optional value, holding the RolledDynamicCost and UnrolledCost. If 519 /// the analysis failed (no benefits expected from the unrolling, or the loop is 520 /// too big to analyze), the returned value is None. 521 static Optional<EstimatedUnrollCost> 522 analyzeLoopUnrollCost(const Loop *L, unsigned TripCount, DominatorTree &DT, 523 ScalarEvolution &SE, const TargetTransformInfo &TTI, 524 int MaxUnrolledLoopSize) { 525 // We want to be able to scale offsets by the trip count and add more offsets 526 // to them without checking for overflows, and we already don't want to 527 // analyze *massive* trip counts, so we force the max to be reasonably small. 528 assert(UnrollMaxIterationsCountToAnalyze < (INT_MAX / 2) && 529 "The unroll iterations max is too large!"); 530 531 // Don't simulate loops with a big or unknown tripcount 532 if (!UnrollMaxIterationsCountToAnalyze || !TripCount || 533 TripCount > UnrollMaxIterationsCountToAnalyze) 534 return None; 535 536 SmallSetVector<BasicBlock *, 16> BBWorklist; 537 DenseMap<Value *, Constant *> SimplifiedValues; 538 SmallVector<std::pair<Value *, Constant *>, 4> SimplifiedInputValues; 539 540 // The estimated cost of the unrolled form of the loop. We try to estimate 541 // this by simplifying as much as we can while computing the estimate. 542 int UnrolledCost = 0; 543 // We also track the estimated dynamic (that is, actually executed) cost in 544 // the rolled form. This helps identify cases when the savings from unrolling 545 // aren't just exposing dead control flows, but actual reduced dynamic 546 // instructions due to the simplifications which we expect to occur after 547 // unrolling. 548 int RolledDynamicCost = 0; 549 550 // Ensure that we don't violate the loop structure invariants relied on by 551 // this analysis. 552 assert(L->isLoopSimplifyForm() && "Must put loop into normal form first."); 553 assert(L->isLCSSAForm(DT) && 554 "Must have loops in LCSSA form to track live-out values."); 555 556 DEBUG(dbgs() << "Starting LoopUnroll profitability analysis...\n"); 557 558 // Simulate execution of each iteration of the loop counting instructions, 559 // which would be simplified. 560 // Since the same load will take different values on different iterations, 561 // we literally have to go through all loop's iterations. 562 for (unsigned Iteration = 0; Iteration < TripCount; ++Iteration) { 563 DEBUG(dbgs() << " Analyzing iteration " << Iteration << "\n"); 564 565 // Prepare for the iteration by collecting any simplified entry or backedge 566 // inputs. 567 for (Instruction &I : *L->getHeader()) { 568 auto *PHI = dyn_cast<PHINode>(&I); 569 if (!PHI) 570 break; 571 572 // The loop header PHI nodes must have exactly two input: one from the 573 // loop preheader and one from the loop latch. 574 assert( 575 PHI->getNumIncomingValues() == 2 && 576 "Must have an incoming value only for the preheader and the latch."); 577 578 Value *V = PHI->getIncomingValueForBlock( 579 Iteration == 0 ? L->getLoopPreheader() : L->getLoopLatch()); 580 Constant *C = dyn_cast<Constant>(V); 581 if (Iteration != 0 && !C) 582 C = SimplifiedValues.lookup(V); 583 if (C) 584 SimplifiedInputValues.push_back({PHI, C}); 585 } 586 587 // Now clear and re-populate the map for the next iteration. 588 SimplifiedValues.clear(); 589 while (!SimplifiedInputValues.empty()) 590 SimplifiedValues.insert(SimplifiedInputValues.pop_back_val()); 591 592 UnrolledInstAnalyzer Analyzer(Iteration, SimplifiedValues, SE); 593 594 BBWorklist.clear(); 595 BBWorklist.insert(L->getHeader()); 596 // Note that we *must not* cache the size, this loop grows the worklist. 597 for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) { 598 BasicBlock *BB = BBWorklist[Idx]; 599 600 // Visit all instructions in the given basic block and try to simplify 601 // it. We don't change the actual IR, just count optimization 602 // opportunities. 603 for (Instruction &I : *BB) { 604 int InstCost = TTI.getUserCost(&I); 605 606 // Visit the instruction to analyze its loop cost after unrolling, 607 // and if the visitor returns false, include this instruction in the 608 // unrolled cost. 609 if (!Analyzer.visit(I)) 610 UnrolledCost += InstCost; 611 else { 612 DEBUG(dbgs() << " " << I 613 << " would be simplified if loop is unrolled.\n"); 614 (void)0; 615 } 616 617 // Also track this instructions expected cost when executing the rolled 618 // loop form. 619 RolledDynamicCost += InstCost; 620 621 // If unrolled body turns out to be too big, bail out. 622 if (UnrolledCost > MaxUnrolledLoopSize) { 623 DEBUG(dbgs() << " Exceeded threshold.. exiting.\n" 624 << " UnrolledCost: " << UnrolledCost 625 << ", MaxUnrolledLoopSize: " << MaxUnrolledLoopSize 626 << "\n"); 627 return None; 628 } 629 } 630 631 TerminatorInst *TI = BB->getTerminator(); 632 633 // Add in the live successors by first checking whether we have terminator 634 // that may be simplified based on the values simplified by this call. 635 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 636 if (BI->isConditional()) { 637 if (Constant *SimpleCond = 638 SimplifiedValues.lookup(BI->getCondition())) { 639 BasicBlock *Succ = nullptr; 640 // Just take the first successor if condition is undef 641 if (isa<UndefValue>(SimpleCond)) 642 Succ = BI->getSuccessor(0); 643 else 644 Succ = BI->getSuccessor( 645 cast<ConstantInt>(SimpleCond)->isZero() ? 1 : 0); 646 if (L->contains(Succ)) 647 BBWorklist.insert(Succ); 648 continue; 649 } 650 } 651 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 652 if (Constant *SimpleCond = 653 SimplifiedValues.lookup(SI->getCondition())) { 654 BasicBlock *Succ = nullptr; 655 // Just take the first successor if condition is undef 656 if (isa<UndefValue>(SimpleCond)) 657 Succ = SI->getSuccessor(0); 658 else 659 Succ = SI->findCaseValue(cast<ConstantInt>(SimpleCond)) 660 .getCaseSuccessor(); 661 if (L->contains(Succ)) 662 BBWorklist.insert(Succ); 663 continue; 664 } 665 } 666 667 // Add BB's successors to the worklist. 668 for (BasicBlock *Succ : successors(BB)) 669 if (L->contains(Succ)) 670 BBWorklist.insert(Succ); 671 } 672 673 // If we found no optimization opportunities on the first iteration, we 674 // won't find them on later ones too. 675 if (UnrolledCost == RolledDynamicCost) { 676 DEBUG(dbgs() << " No opportunities found.. exiting.\n" 677 << " UnrolledCost: " << UnrolledCost << "\n"); 678 return None; 679 } 680 } 681 DEBUG(dbgs() << "Analysis finished:\n" 682 << "UnrolledCost: " << UnrolledCost << ", " 683 << "RolledDynamicCost: " << RolledDynamicCost << "\n"); 684 return {{UnrolledCost, RolledDynamicCost}}; 685 } 686 687 /// ApproximateLoopSize - Approximate the size of the loop. 688 static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, 689 bool &NotDuplicatable, 690 const TargetTransformInfo &TTI, 691 AssumptionCache *AC) { 692 SmallPtrSet<const Value *, 32> EphValues; 693 CodeMetrics::collectEphemeralValues(L, AC, EphValues); 694 695 CodeMetrics Metrics; 696 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 697 I != E; ++I) 698 Metrics.analyzeBasicBlock(*I, TTI, EphValues); 699 NumCalls = Metrics.NumInlineCandidates; 700 NotDuplicatable = Metrics.notDuplicatable; 701 702 unsigned LoopSize = Metrics.NumInsts; 703 704 // Don't allow an estimate of size zero. This would allows unrolling of loops 705 // with huge iteration counts, which is a compile time problem even if it's 706 // not a problem for code quality. Also, the code using this size may assume 707 // that each loop has at least three instructions (likely a conditional 708 // branch, a comparison feeding that branch, and some kind of loop increment 709 // feeding that comparison instruction). 710 LoopSize = std::max(LoopSize, 3u); 711 712 return LoopSize; 713 } 714 715 // Returns the loop hint metadata node with the given name (for example, 716 // "llvm.loop.unroll.count"). If no such metadata node exists, then nullptr is 717 // returned. 718 static MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) { 719 if (MDNode *LoopID = L->getLoopID()) 720 return GetUnrollMetadata(LoopID, Name); 721 return nullptr; 722 } 723 724 // Returns true if the loop has an unroll(full) pragma. 725 static bool HasUnrollFullPragma(const Loop *L) { 726 return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.full"); 727 } 728 729 // Returns true if the loop has an unroll(enable) pragma. This metadata is used 730 // for both "#pragma unroll" and "#pragma clang loop unroll(enable)" directives. 731 static bool HasUnrollEnablePragma(const Loop *L) { 732 return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.enable"); 733 } 734 735 // Returns true if the loop has an unroll(disable) pragma. 736 static bool HasUnrollDisablePragma(const Loop *L) { 737 return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.disable"); 738 } 739 740 // Returns true if the loop has an runtime unroll(disable) pragma. 741 static bool HasRuntimeUnrollDisablePragma(const Loop *L) { 742 return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.runtime.disable"); 743 } 744 745 // If loop has an unroll_count pragma return the (necessarily 746 // positive) value from the pragma. Otherwise return 0. 747 static unsigned UnrollCountPragmaValue(const Loop *L) { 748 MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count"); 749 if (MD) { 750 assert(MD->getNumOperands() == 2 && 751 "Unroll count hint metadata should have two operands."); 752 unsigned Count = 753 mdconst::extract<ConstantInt>(MD->getOperand(1))->getZExtValue(); 754 assert(Count >= 1 && "Unroll count must be positive."); 755 return Count; 756 } 757 return 0; 758 } 759 760 // Remove existing unroll metadata and add unroll disable metadata to 761 // indicate the loop has already been unrolled. This prevents a loop 762 // from being unrolled more than is directed by a pragma if the loop 763 // unrolling pass is run more than once (which it generally is). 764 static void SetLoopAlreadyUnrolled(Loop *L) { 765 MDNode *LoopID = L->getLoopID(); 766 if (!LoopID) return; 767 768 // First remove any existing loop unrolling metadata. 769 SmallVector<Metadata *, 4> MDs; 770 // Reserve first location for self reference to the LoopID metadata node. 771 MDs.push_back(nullptr); 772 for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) { 773 bool IsUnrollMetadata = false; 774 MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i)); 775 if (MD) { 776 const MDString *S = dyn_cast<MDString>(MD->getOperand(0)); 777 IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll."); 778 } 779 if (!IsUnrollMetadata) 780 MDs.push_back(LoopID->getOperand(i)); 781 } 782 783 // Add unroll(disable) metadata to disable future unrolling. 784 LLVMContext &Context = L->getHeader()->getContext(); 785 SmallVector<Metadata *, 1> DisableOperands; 786 DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable")); 787 MDNode *DisableNode = MDNode::get(Context, DisableOperands); 788 MDs.push_back(DisableNode); 789 790 MDNode *NewLoopID = MDNode::get(Context, MDs); 791 // Set operand 0 to refer to the loop id itself. 792 NewLoopID->replaceOperandWith(0, NewLoopID); 793 L->setLoopID(NewLoopID); 794 } 795 796 bool LoopUnroll::canUnrollCompletely(Loop *L, unsigned Threshold, 797 unsigned PercentDynamicCostSavedThreshold, 798 unsigned DynamicCostSavingsDiscount, 799 uint64_t UnrolledCost, 800 uint64_t RolledDynamicCost) { 801 802 if (Threshold == NoThreshold) { 803 DEBUG(dbgs() << " Can fully unroll, because no threshold is set.\n"); 804 return true; 805 } 806 807 if (UnrolledCost <= Threshold) { 808 DEBUG(dbgs() << " Can fully unroll, because unrolled cost: " 809 << UnrolledCost << "<" << Threshold << "\n"); 810 return true; 811 } 812 813 assert(UnrolledCost && "UnrolledCost can't be 0 at this point."); 814 assert(RolledDynamicCost >= UnrolledCost && 815 "Cannot have a higher unrolled cost than a rolled cost!"); 816 817 // Compute the percentage of the dynamic cost in the rolled form that is 818 // saved when unrolled. If unrolling dramatically reduces the estimated 819 // dynamic cost of the loop, we use a higher threshold to allow more 820 // unrolling. 821 unsigned PercentDynamicCostSaved = 822 (uint64_t)(RolledDynamicCost - UnrolledCost) * 100ull / RolledDynamicCost; 823 824 if (PercentDynamicCostSaved >= PercentDynamicCostSavedThreshold && 825 (int64_t)UnrolledCost - (int64_t)DynamicCostSavingsDiscount <= 826 (int64_t)Threshold) { 827 DEBUG(dbgs() << " Can fully unroll, because unrolling will reduce the " 828 "expected dynamic cost by " << PercentDynamicCostSaved 829 << "% (threshold: " << PercentDynamicCostSavedThreshold 830 << "%)\n" 831 << " and the unrolled cost (" << UnrolledCost 832 << ") is less than the max threshold (" 833 << DynamicCostSavingsDiscount << ").\n"); 834 return true; 835 } 836 837 DEBUG(dbgs() << " Too large to fully unroll:\n"); 838 DEBUG(dbgs() << " Threshold: " << Threshold << "\n"); 839 DEBUG(dbgs() << " Max threshold: " << DynamicCostSavingsDiscount << "\n"); 840 DEBUG(dbgs() << " Percent cost saved threshold: " 841 << PercentDynamicCostSavedThreshold << "%\n"); 842 DEBUG(dbgs() << " Unrolled cost: " << UnrolledCost << "\n"); 843 DEBUG(dbgs() << " Rolled dynamic cost: " << RolledDynamicCost << "\n"); 844 DEBUG(dbgs() << " Percent cost saved: " << PercentDynamicCostSaved 845 << "\n"); 846 return false; 847 } 848 849 unsigned LoopUnroll::selectUnrollCount( 850 const Loop *L, unsigned TripCount, bool PragmaFullUnroll, 851 unsigned PragmaCount, const TargetTransformInfo::UnrollingPreferences &UP, 852 bool &SetExplicitly) { 853 SetExplicitly = true; 854 855 // User-specified count (either as a command-line option or 856 // constructor parameter) has highest precedence. 857 unsigned Count = UserCount ? CurrentCount : 0; 858 859 // If there is no user-specified count, unroll pragmas have the next 860 // highest precedence. 861 if (Count == 0) { 862 if (PragmaCount) { 863 Count = PragmaCount; 864 } else if (PragmaFullUnroll) { 865 Count = TripCount; 866 } 867 } 868 869 if (Count == 0) 870 Count = UP.Count; 871 872 if (Count == 0) { 873 SetExplicitly = false; 874 if (TripCount == 0) 875 // Runtime trip count. 876 Count = UnrollRuntimeCount; 877 else 878 // Conservative heuristic: if we know the trip count, see if we can 879 // completely unroll (subject to the threshold, checked below); otherwise 880 // try to find greatest modulo of the trip count which is still under 881 // threshold value. 882 Count = TripCount; 883 } 884 if (TripCount && Count > TripCount) 885 return TripCount; 886 return Count; 887 } 888 889 bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &) { 890 if (skipOptnoneFunction(L)) 891 return false; 892 893 Function &F = *L->getHeader()->getParent(); 894 895 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 896 LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); 897 ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); 898 const TargetTransformInfo &TTI = 899 getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); 900 auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); 901 bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID); 902 903 BasicBlock *Header = L->getHeader(); 904 DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName() 905 << "] Loop %" << Header->getName() << "\n"); 906 907 if (HasUnrollDisablePragma(L)) { 908 return false; 909 } 910 bool PragmaFullUnroll = HasUnrollFullPragma(L); 911 bool PragmaEnableUnroll = HasUnrollEnablePragma(L); 912 unsigned PragmaCount = UnrollCountPragmaValue(L); 913 bool HasPragma = PragmaFullUnroll || PragmaEnableUnroll || PragmaCount > 0; 914 915 TargetTransformInfo::UnrollingPreferences UP; 916 getUnrollingPreferences(L, TTI, UP); 917 918 // Find trip count and trip multiple if count is not available 919 unsigned TripCount = 0; 920 unsigned TripMultiple = 1; 921 // If there are multiple exiting blocks but one of them is the latch, use the 922 // latch for the trip count estimation. Otherwise insist on a single exiting 923 // block for the trip count estimation. 924 BasicBlock *ExitingBlock = L->getLoopLatch(); 925 if (!ExitingBlock || !L->isLoopExiting(ExitingBlock)) 926 ExitingBlock = L->getExitingBlock(); 927 if (ExitingBlock) { 928 TripCount = SE->getSmallConstantTripCount(L, ExitingBlock); 929 TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock); 930 } 931 932 // Select an initial unroll count. This may be reduced later based 933 // on size thresholds. 934 bool CountSetExplicitly; 935 unsigned Count = selectUnrollCount(L, TripCount, PragmaFullUnroll, 936 PragmaCount, UP, CountSetExplicitly); 937 938 unsigned NumInlineCandidates; 939 bool notDuplicatable; 940 unsigned LoopSize = 941 ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI, &AC); 942 DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); 943 944 // When computing the unrolled size, note that the conditional branch on the 945 // backedge and the comparison feeding it are not replicated like the rest of 946 // the loop body (which is why 2 is subtracted). 947 uint64_t UnrolledSize = (uint64_t)(LoopSize-2) * Count + 2; 948 if (notDuplicatable) { 949 DEBUG(dbgs() << " Not unrolling loop which contains non-duplicatable" 950 << " instructions.\n"); 951 return false; 952 } 953 if (NumInlineCandidates != 0) { 954 DEBUG(dbgs() << " Not unrolling loop with inlinable calls.\n"); 955 return false; 956 } 957 958 unsigned Threshold, PartialThreshold; 959 unsigned PercentDynamicCostSavedThreshold; 960 unsigned DynamicCostSavingsDiscount; 961 // Only use the high pragma threshold when we have a target unroll factor such 962 // as with "#pragma unroll N" or a pragma indicating full unrolling and the 963 // trip count is known. Otherwise we rely on the standard threshold to 964 // heuristically select a reasonable unroll count. 965 bool UsePragmaThreshold = 966 PragmaCount > 0 || 967 ((PragmaFullUnroll || PragmaEnableUnroll) && TripCount != 0); 968 969 selectThresholds(L, UsePragmaThreshold, UP, Threshold, PartialThreshold, 970 PercentDynamicCostSavedThreshold, 971 DynamicCostSavingsDiscount); 972 973 // Given Count, TripCount and thresholds determine the type of 974 // unrolling which is to be performed. 975 enum { Full = 0, Partial = 1, Runtime = 2 }; 976 int Unrolling; 977 if (TripCount && Count == TripCount) { 978 Unrolling = Partial; 979 // If the loop is really small, we don't need to run an expensive analysis. 980 if (canUnrollCompletely(L, Threshold, 100, DynamicCostSavingsDiscount, 981 UnrolledSize, UnrolledSize)) { 982 Unrolling = Full; 983 } else { 984 // The loop isn't that small, but we still can fully unroll it if that 985 // helps to remove a significant number of instructions. 986 // To check that, run additional analysis on the loop. 987 if (Optional<EstimatedUnrollCost> Cost = 988 analyzeLoopUnrollCost(L, TripCount, DT, *SE, TTI, 989 Threshold + DynamicCostSavingsDiscount)) 990 if (canUnrollCompletely(L, Threshold, PercentDynamicCostSavedThreshold, 991 DynamicCostSavingsDiscount, Cost->UnrolledCost, 992 Cost->RolledDynamicCost)) { 993 Unrolling = Full; 994 } 995 } 996 } else if (TripCount && Count < TripCount) { 997 Unrolling = Partial; 998 } else { 999 Unrolling = Runtime; 1000 } 1001 1002 // Reduce count based on the type of unrolling and the threshold values. 1003 unsigned OriginalCount = Count; 1004 bool AllowRuntime = PragmaEnableUnroll || (PragmaCount > 0) || 1005 (UserRuntime ? CurrentRuntime : UP.Runtime); 1006 // Don't unroll a runtime trip count loop with unroll full pragma. 1007 if (HasRuntimeUnrollDisablePragma(L) || PragmaFullUnroll) { 1008 AllowRuntime = false; 1009 } 1010 if (Unrolling == Partial) { 1011 bool AllowPartial = PragmaEnableUnroll || 1012 (UserAllowPartial ? CurrentAllowPartial : UP.Partial); 1013 if (!AllowPartial && !CountSetExplicitly) { 1014 DEBUG(dbgs() << " will not try to unroll partially because " 1015 << "-unroll-allow-partial not given\n"); 1016 return false; 1017 } 1018 if (PartialThreshold != NoThreshold && UnrolledSize > PartialThreshold) { 1019 // Reduce unroll count to be modulo of TripCount for partial unrolling. 1020 Count = (std::max(PartialThreshold, 3u)-2) / (LoopSize-2); 1021 while (Count != 0 && TripCount % Count != 0) 1022 Count--; 1023 } 1024 } else if (Unrolling == Runtime) { 1025 if (!AllowRuntime && !CountSetExplicitly) { 1026 DEBUG(dbgs() << " will not try to unroll loop with runtime trip count " 1027 << "-unroll-runtime not given\n"); 1028 return false; 1029 } 1030 // Reduce unroll count to be the largest power-of-two factor of 1031 // the original count which satisfies the threshold limit. 1032 while (Count != 0 && UnrolledSize > PartialThreshold) { 1033 Count >>= 1; 1034 UnrolledSize = (LoopSize-2) * Count + 2; 1035 } 1036 if (Count > UP.MaxCount) 1037 Count = UP.MaxCount; 1038 DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n"); 1039 } 1040 1041 if (HasPragma) { 1042 if (PragmaCount != 0) 1043 // If loop has an unroll count pragma mark loop as unrolled to prevent 1044 // unrolling beyond that requested by the pragma. 1045 SetLoopAlreadyUnrolled(L); 1046 1047 // Emit optimization remarks if we are unable to unroll the loop 1048 // as directed by a pragma. 1049 DebugLoc LoopLoc = L->getStartLoc(); 1050 Function *F = Header->getParent(); 1051 LLVMContext &Ctx = F->getContext(); 1052 if ((PragmaCount > 0) && Count != OriginalCount) { 1053 emitOptimizationRemarkMissed( 1054 Ctx, DEBUG_TYPE, *F, LoopLoc, 1055 "Unable to unroll loop the number of times directed by " 1056 "unroll_count pragma because unrolled size is too large."); 1057 } else if (PragmaFullUnroll && !TripCount) { 1058 emitOptimizationRemarkMissed( 1059 Ctx, DEBUG_TYPE, *F, LoopLoc, 1060 "Unable to fully unroll loop as directed by unroll(full) pragma " 1061 "because loop has a runtime trip count."); 1062 } else if (PragmaEnableUnroll && Count != TripCount && Count < 2) { 1063 emitOptimizationRemarkMissed( 1064 Ctx, DEBUG_TYPE, *F, LoopLoc, 1065 "Unable to unroll loop as directed by unroll(enable) pragma because " 1066 "unrolled size is too large."); 1067 } else if ((PragmaFullUnroll || PragmaEnableUnroll) && TripCount && 1068 Count != TripCount) { 1069 emitOptimizationRemarkMissed( 1070 Ctx, DEBUG_TYPE, *F, LoopLoc, 1071 "Unable to fully unroll loop as directed by unroll pragma because " 1072 "unrolled size is too large."); 1073 } 1074 } 1075 1076 if (Unrolling != Full && Count < 2) { 1077 // Partial unrolling by 1 is a nop. For full unrolling, a factor 1078 // of 1 makes sense because loop control can be eliminated. 1079 return false; 1080 } 1081 1082 // Unroll the loop. 1083 if (!UnrollLoop(L, Count, TripCount, AllowRuntime, UP.AllowExpensiveTripCount, 1084 TripMultiple, LI, SE, &DT, &AC, PreserveLCSSA)) 1085 return false; 1086 1087 return true; 1088 } 1089