1 //===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===// 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 transforms loops that contain branches on loop-invariant conditions 11 // to have multiple loops. For example, it turns the left into the right code: 12 // 13 // for (...) if (lic) 14 // A for (...) 15 // if (lic) A; B; C 16 // B else 17 // C for (...) 18 // A; C 19 // 20 // This can increase the size of the code exponentially (doubling it every time 21 // a loop is unswitched) so we only unswitch if the resultant code will be 22 // smaller than a threshold. 23 // 24 // This pass expects LICM to be run before it to hoist invariant conditions out 25 // of the loop, to make the unswitching opportunity obvious. 26 // 27 //===----------------------------------------------------------------------===// 28 29 #define DEBUG_TYPE "loop-unswitch" 30 #include "llvm/Transforms/Scalar.h" 31 #include "llvm/ADT/STLExtras.h" 32 #include "llvm/ADT/SmallPtrSet.h" 33 #include "llvm/ADT/Statistic.h" 34 #include "llvm/Analysis/CodeMetrics.h" 35 #include "llvm/Analysis/Dominators.h" 36 #include "llvm/Analysis/InstructionSimplify.h" 37 #include "llvm/Analysis/LoopInfo.h" 38 #include "llvm/Analysis/LoopPass.h" 39 #include "llvm/Analysis/ScalarEvolution.h" 40 #include "llvm/Analysis/TargetTransformInfo.h" 41 #include "llvm/IR/Constants.h" 42 #include "llvm/IR/DerivedTypes.h" 43 #include "llvm/IR/Function.h" 44 #include "llvm/IR/Instructions.h" 45 #include "llvm/Support/CommandLine.h" 46 #include "llvm/Support/Debug.h" 47 #include "llvm/Support/raw_ostream.h" 48 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 49 #include "llvm/Transforms/Utils/Cloning.h" 50 #include "llvm/Transforms/Utils/Local.h" 51 #include <algorithm> 52 #include <map> 53 #include <set> 54 using namespace llvm; 55 56 STATISTIC(NumBranches, "Number of branches unswitched"); 57 STATISTIC(NumSwitches, "Number of switches unswitched"); 58 STATISTIC(NumSelects , "Number of selects unswitched"); 59 STATISTIC(NumTrivial , "Number of unswitches that are trivial"); 60 STATISTIC(NumSimplify, "Number of simplifications of unswitched code"); 61 STATISTIC(TotalInsts, "Total number of instructions analyzed"); 62 63 // The specific value of 100 here was chosen based only on intuition and a 64 // few specific examples. 65 static cl::opt<unsigned> 66 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), 67 cl::init(100), cl::Hidden); 68 69 namespace { 70 71 class LUAnalysisCache { 72 73 typedef DenseMap<const SwitchInst*, SmallPtrSet<const Value *, 8> > 74 UnswitchedValsMap; 75 76 typedef UnswitchedValsMap::iterator UnswitchedValsIt; 77 78 struct LoopProperties { 79 unsigned CanBeUnswitchedCount; 80 unsigned SizeEstimation; 81 UnswitchedValsMap UnswitchedVals; 82 }; 83 84 // Here we use std::map instead of DenseMap, since we need to keep valid 85 // LoopProperties pointer for current loop for better performance. 86 typedef std::map<const Loop*, LoopProperties> LoopPropsMap; 87 typedef LoopPropsMap::iterator LoopPropsMapIt; 88 89 LoopPropsMap LoopsProperties; 90 UnswitchedValsMap *CurLoopInstructions; 91 LoopProperties *CurrentLoopProperties; 92 93 // Max size of code we can produce on remained iterations. 94 unsigned MaxSize; 95 96 public: 97 98 LUAnalysisCache() : 99 CurLoopInstructions(0), CurrentLoopProperties(0), 100 MaxSize(Threshold) 101 {} 102 103 // Analyze loop. Check its size, calculate is it possible to unswitch 104 // it. Returns true if we can unswitch this loop. 105 bool countLoop(const Loop *L, const TargetTransformInfo &TTI); 106 107 // Clean all data related to given loop. 108 void forgetLoop(const Loop *L); 109 110 // Mark case value as unswitched. 111 // Since SI instruction can be partly unswitched, in order to avoid 112 // extra unswitching in cloned loops keep track all unswitched values. 113 void setUnswitched(const SwitchInst *SI, const Value *V); 114 115 // Check was this case value unswitched before or not. 116 bool isUnswitched(const SwitchInst *SI, const Value *V); 117 118 // Clone all loop-unswitch related loop properties. 119 // Redistribute unswitching quotas. 120 // Note, that new loop data is stored inside the VMap. 121 void cloneData(const Loop *NewLoop, const Loop *OldLoop, 122 const ValueToValueMapTy &VMap); 123 }; 124 125 class LoopUnswitch : public LoopPass { 126 LoopInfo *LI; // Loop information 127 LPPassManager *LPM; 128 129 // LoopProcessWorklist - Used to check if second loop needs processing 130 // after RewriteLoopBodyWithConditionConstant rewrites first loop. 131 std::vector<Loop*> LoopProcessWorklist; 132 133 LUAnalysisCache BranchesInfo; 134 135 bool OptimizeForSize; 136 bool redoLoop; 137 138 Loop *currentLoop; 139 DominatorTree *DT; 140 BasicBlock *loopHeader; 141 BasicBlock *loopPreheader; 142 143 // LoopBlocks contains all of the basic blocks of the loop, including the 144 // preheader of the loop, the body of the loop, and the exit blocks of the 145 // loop, in that order. 146 std::vector<BasicBlock*> LoopBlocks; 147 // NewBlocks contained cloned copy of basic blocks from LoopBlocks. 148 std::vector<BasicBlock*> NewBlocks; 149 150 public: 151 static char ID; // Pass ID, replacement for typeid 152 explicit LoopUnswitch(bool Os = false) : 153 LoopPass(ID), OptimizeForSize(Os), redoLoop(false), 154 currentLoop(0), DT(0), loopHeader(0), 155 loopPreheader(0) { 156 initializeLoopUnswitchPass(*PassRegistry::getPassRegistry()); 157 } 158 159 bool runOnLoop(Loop *L, LPPassManager &LPM); 160 bool processCurrentLoop(); 161 162 /// This transformation requires natural loop information & requires that 163 /// loop preheaders be inserted into the CFG. 164 /// 165 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 166 AU.addRequiredID(LoopSimplifyID); 167 AU.addPreservedID(LoopSimplifyID); 168 AU.addRequired<LoopInfo>(); 169 AU.addPreserved<LoopInfo>(); 170 AU.addRequiredID(LCSSAID); 171 AU.addPreservedID(LCSSAID); 172 AU.addPreserved<DominatorTree>(); 173 AU.addPreserved<ScalarEvolution>(); 174 AU.addRequired<TargetTransformInfo>(); 175 } 176 177 private: 178 179 virtual void releaseMemory() { 180 BranchesInfo.forgetLoop(currentLoop); 181 } 182 183 /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist, 184 /// remove it. 185 void RemoveLoopFromWorklist(Loop *L) { 186 std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(), 187 LoopProcessWorklist.end(), L); 188 if (I != LoopProcessWorklist.end()) 189 LoopProcessWorklist.erase(I); 190 } 191 192 void initLoopData() { 193 loopHeader = currentLoop->getHeader(); 194 loopPreheader = currentLoop->getLoopPreheader(); 195 } 196 197 /// Split all of the edges from inside the loop to their exit blocks. 198 /// Update the appropriate Phi nodes as we do so. 199 void SplitExitEdges(Loop *L, const SmallVectorImpl<BasicBlock *> &ExitBlocks); 200 201 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val); 202 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, 203 BasicBlock *ExitBlock); 204 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L); 205 206 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, 207 Constant *Val, bool isEqual); 208 209 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, 210 BasicBlock *TrueDest, 211 BasicBlock *FalseDest, 212 Instruction *InsertPt); 213 214 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L); 215 void RemoveLoopFromHierarchy(Loop *L); 216 bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = 0, 217 BasicBlock **LoopExit = 0); 218 219 }; 220 } 221 222 // Analyze loop. Check its size, calculate is it possible to unswitch 223 // it. Returns true if we can unswitch this loop. 224 bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI) { 225 226 LoopPropsMapIt PropsIt; 227 bool Inserted; 228 llvm::tie(PropsIt, Inserted) = 229 LoopsProperties.insert(std::make_pair(L, LoopProperties())); 230 231 LoopProperties &Props = PropsIt->second; 232 233 if (Inserted) { 234 // New loop. 235 236 // Limit the number of instructions to avoid causing significant code 237 // expansion, and the number of basic blocks, to avoid loops with 238 // large numbers of branches which cause loop unswitching to go crazy. 239 // This is a very ad-hoc heuristic. 240 241 // FIXME: This is overly conservative because it does not take into 242 // consideration code simplification opportunities and code that can 243 // be shared by the resultant unswitched loops. 244 CodeMetrics Metrics; 245 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 246 I != E; ++I) 247 Metrics.analyzeBasicBlock(*I, TTI); 248 249 Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5); 250 Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation); 251 MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount; 252 253 if (Metrics.notDuplicatable) { 254 DEBUG(dbgs() << "NOT unswitching loop %" 255 << L->getHeader()->getName() << ", contents cannot be " 256 << "duplicated!\n"); 257 return false; 258 } 259 } 260 261 if (!Props.CanBeUnswitchedCount) { 262 DEBUG(dbgs() << "NOT unswitching loop %" 263 << L->getHeader()->getName() << ", cost too high: " 264 << L->getBlocks().size() << "\n"); 265 return false; 266 } 267 268 // Be careful. This links are good only before new loop addition. 269 CurrentLoopProperties = &Props; 270 CurLoopInstructions = &Props.UnswitchedVals; 271 272 return true; 273 } 274 275 // Clean all data related to given loop. 276 void LUAnalysisCache::forgetLoop(const Loop *L) { 277 278 LoopPropsMapIt LIt = LoopsProperties.find(L); 279 280 if (LIt != LoopsProperties.end()) { 281 LoopProperties &Props = LIt->second; 282 MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation; 283 LoopsProperties.erase(LIt); 284 } 285 286 CurrentLoopProperties = 0; 287 CurLoopInstructions = 0; 288 } 289 290 // Mark case value as unswitched. 291 // Since SI instruction can be partly unswitched, in order to avoid 292 // extra unswitching in cloned loops keep track all unswitched values. 293 void LUAnalysisCache::setUnswitched(const SwitchInst *SI, const Value *V) { 294 (*CurLoopInstructions)[SI].insert(V); 295 } 296 297 // Check was this case value unswitched before or not. 298 bool LUAnalysisCache::isUnswitched(const SwitchInst *SI, const Value *V) { 299 return (*CurLoopInstructions)[SI].count(V); 300 } 301 302 // Clone all loop-unswitch related loop properties. 303 // Redistribute unswitching quotas. 304 // Note, that new loop data is stored inside the VMap. 305 void LUAnalysisCache::cloneData(const Loop *NewLoop, const Loop *OldLoop, 306 const ValueToValueMapTy &VMap) { 307 308 LoopProperties &NewLoopProps = LoopsProperties[NewLoop]; 309 LoopProperties &OldLoopProps = *CurrentLoopProperties; 310 UnswitchedValsMap &Insts = OldLoopProps.UnswitchedVals; 311 312 // Reallocate "can-be-unswitched quota" 313 314 --OldLoopProps.CanBeUnswitchedCount; 315 unsigned Quota = OldLoopProps.CanBeUnswitchedCount; 316 NewLoopProps.CanBeUnswitchedCount = Quota / 2; 317 OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2; 318 319 NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation; 320 321 // Clone unswitched values info: 322 // for new loop switches we clone info about values that was 323 // already unswitched and has redundant successors. 324 for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) { 325 const SwitchInst *OldInst = I->first; 326 Value *NewI = VMap.lookup(OldInst); 327 const SwitchInst *NewInst = cast_or_null<SwitchInst>(NewI); 328 assert(NewInst && "All instructions that are in SrcBB must be in VMap."); 329 330 NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst]; 331 } 332 } 333 334 char LoopUnswitch::ID = 0; 335 INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops", 336 false, false) 337 INITIALIZE_AG_DEPENDENCY(TargetTransformInfo) 338 INITIALIZE_PASS_DEPENDENCY(LoopSimplify) 339 INITIALIZE_PASS_DEPENDENCY(LoopInfo) 340 INITIALIZE_PASS_DEPENDENCY(LCSSA) 341 INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops", 342 false, false) 343 344 Pass *llvm::createLoopUnswitchPass(bool Os) { 345 return new LoopUnswitch(Os); 346 } 347 348 /// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is 349 /// invariant in the loop, or has an invariant piece, return the invariant. 350 /// Otherwise, return null. 351 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) { 352 353 // We started analyze new instruction, increment scanned instructions counter. 354 ++TotalInsts; 355 356 // We can never unswitch on vector conditions. 357 if (Cond->getType()->isVectorTy()) 358 return 0; 359 360 // Constants should be folded, not unswitched on! 361 if (isa<Constant>(Cond)) return 0; 362 363 // TODO: Handle: br (VARIANT|INVARIANT). 364 365 // Hoist simple values out. 366 if (L->makeLoopInvariant(Cond, Changed)) 367 return Cond; 368 369 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond)) 370 if (BO->getOpcode() == Instruction::And || 371 BO->getOpcode() == Instruction::Or) { 372 // If either the left or right side is invariant, we can unswitch on this, 373 // which will cause the branch to go away in one loop and the condition to 374 // simplify in the other one. 375 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed)) 376 return LHS; 377 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed)) 378 return RHS; 379 } 380 381 return 0; 382 } 383 384 bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { 385 LI = &getAnalysis<LoopInfo>(); 386 LPM = &LPM_Ref; 387 DT = getAnalysisIfAvailable<DominatorTree>(); 388 currentLoop = L; 389 Function *F = currentLoop->getHeader()->getParent(); 390 bool Changed = false; 391 do { 392 assert(currentLoop->isLCSSAForm(*DT)); 393 redoLoop = false; 394 Changed |= processCurrentLoop(); 395 } while(redoLoop); 396 397 if (Changed) { 398 // FIXME: Reconstruct dom info, because it is not preserved properly. 399 if (DT) 400 DT->runOnFunction(*F); 401 } 402 return Changed; 403 } 404 405 /// processCurrentLoop - Do actual work and unswitch loop if possible 406 /// and profitable. 407 bool LoopUnswitch::processCurrentLoop() { 408 bool Changed = false; 409 410 initLoopData(); 411 412 // If LoopSimplify was unable to form a preheader, don't do any unswitching. 413 if (!loopPreheader) 414 return false; 415 416 // Loops with indirectbr cannot be cloned. 417 if (!currentLoop->isSafeToClone()) 418 return false; 419 420 // Without dedicated exits, splitting the exit edge may fail. 421 if (!currentLoop->hasDedicatedExits()) 422 return false; 423 424 LLVMContext &Context = loopHeader->getContext(); 425 426 // Probably we reach the quota of branches for this loop. If so 427 // stop unswitching. 428 if (!BranchesInfo.countLoop(currentLoop, getAnalysis<TargetTransformInfo>())) 429 return false; 430 431 // Loop over all of the basic blocks in the loop. If we find an interior 432 // block that is branching on a loop-invariant condition, we can unswitch this 433 // loop. 434 for (Loop::block_iterator I = currentLoop->block_begin(), 435 E = currentLoop->block_end(); I != E; ++I) { 436 TerminatorInst *TI = (*I)->getTerminator(); 437 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 438 // If this isn't branching on an invariant condition, we can't unswitch 439 // it. 440 if (BI->isConditional()) { 441 // See if this, or some part of it, is loop invariant. If so, we can 442 // unswitch on it if we desire. 443 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), 444 currentLoop, Changed); 445 if (LoopCond && UnswitchIfProfitable(LoopCond, 446 ConstantInt::getTrue(Context))) { 447 ++NumBranches; 448 return true; 449 } 450 } 451 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 452 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), 453 currentLoop, Changed); 454 unsigned NumCases = SI->getNumCases(); 455 if (LoopCond && NumCases) { 456 // Find a value to unswitch on: 457 // FIXME: this should chose the most expensive case! 458 // FIXME: scan for a case with a non-critical edge? 459 Constant *UnswitchVal = 0; 460 461 // Do not process same value again and again. 462 // At this point we have some cases already unswitched and 463 // some not yet unswitched. Let's find the first not yet unswitched one. 464 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 465 i != e; ++i) { 466 Constant *UnswitchValCandidate = i.getCaseValue(); 467 if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) { 468 UnswitchVal = UnswitchValCandidate; 469 break; 470 } 471 } 472 473 if (!UnswitchVal) 474 continue; 475 476 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) { 477 ++NumSwitches; 478 return true; 479 } 480 } 481 } 482 483 // Scan the instructions to check for unswitchable values. 484 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end(); 485 BBI != E; ++BBI) 486 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) { 487 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), 488 currentLoop, Changed); 489 if (LoopCond && UnswitchIfProfitable(LoopCond, 490 ConstantInt::getTrue(Context))) { 491 ++NumSelects; 492 return true; 493 } 494 } 495 } 496 return Changed; 497 } 498 499 /// isTrivialLoopExitBlock - Check to see if all paths from BB exit the 500 /// loop with no side effects (including infinite loops). 501 /// 502 /// If true, we return true and set ExitBB to the block we 503 /// exit through. 504 /// 505 static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB, 506 BasicBlock *&ExitBB, 507 std::set<BasicBlock*> &Visited) { 508 if (!Visited.insert(BB).second) { 509 // Already visited. Without more analysis, this could indicate an infinite 510 // loop. 511 return false; 512 } 513 if (!L->contains(BB)) { 514 // Otherwise, this is a loop exit, this is fine so long as this is the 515 // first exit. 516 if (ExitBB != 0) return false; 517 ExitBB = BB; 518 return true; 519 } 520 521 // Otherwise, this is an unvisited intra-loop node. Check all successors. 522 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) { 523 // Check to see if the successor is a trivial loop exit. 524 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited)) 525 return false; 526 } 527 528 // Okay, everything after this looks good, check to make sure that this block 529 // doesn't include any side effects. 530 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 531 if (I->mayHaveSideEffects()) 532 return false; 533 534 return true; 535 } 536 537 /// isTrivialLoopExitBlock - Return true if the specified block unconditionally 538 /// leads to an exit from the specified loop, and has no side-effects in the 539 /// process. If so, return the block that is exited to, otherwise return null. 540 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { 541 std::set<BasicBlock*> Visited; 542 Visited.insert(L->getHeader()); // Branches to header make infinite loops. 543 BasicBlock *ExitBB = 0; 544 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited)) 545 return ExitBB; 546 return 0; 547 } 548 549 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is 550 /// trivial: that is, that the condition controls whether or not the loop does 551 /// anything at all. If this is a trivial condition, unswitching produces no 552 /// code duplications (equivalently, it produces a simpler loop and a new empty 553 /// loop, which gets deleted). 554 /// 555 /// If this is a trivial condition, return true, otherwise return false. When 556 /// returning true, this sets Cond and Val to the condition that controls the 557 /// trivial condition: when Cond dynamically equals Val, the loop is known to 558 /// exit. Finally, this sets LoopExit to the BB that the loop exits to when 559 /// Cond == Val. 560 /// 561 bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val, 562 BasicBlock **LoopExit) { 563 BasicBlock *Header = currentLoop->getHeader(); 564 TerminatorInst *HeaderTerm = Header->getTerminator(); 565 LLVMContext &Context = Header->getContext(); 566 567 BasicBlock *LoopExitBB = 0; 568 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) { 569 // If the header block doesn't end with a conditional branch on Cond, we 570 // can't handle it. 571 if (!BI->isConditional() || BI->getCondition() != Cond) 572 return false; 573 574 // Check to see if a successor of the branch is guaranteed to 575 // exit through a unique exit block without having any 576 // side-effects. If so, determine the value of Cond that causes it to do 577 // this. 578 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, 579 BI->getSuccessor(0)))) { 580 if (Val) *Val = ConstantInt::getTrue(Context); 581 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, 582 BI->getSuccessor(1)))) { 583 if (Val) *Val = ConstantInt::getFalse(Context); 584 } 585 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) { 586 // If this isn't a switch on Cond, we can't handle it. 587 if (SI->getCondition() != Cond) return false; 588 589 // Check to see if a successor of the switch is guaranteed to go to the 590 // latch block or exit through a one exit block without having any 591 // side-effects. If so, determine the value of Cond that causes it to do 592 // this. 593 // Note that we can't trivially unswitch on the default case or 594 // on already unswitched cases. 595 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 596 i != e; ++i) { 597 BasicBlock *LoopExitCandidate; 598 if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop, 599 i.getCaseSuccessor()))) { 600 // Okay, we found a trivial case, remember the value that is trivial. 601 ConstantInt *CaseVal = i.getCaseValue(); 602 603 // Check that it was not unswitched before, since already unswitched 604 // trivial vals are looks trivial too. 605 if (BranchesInfo.isUnswitched(SI, CaseVal)) 606 continue; 607 LoopExitBB = LoopExitCandidate; 608 if (Val) *Val = CaseVal; 609 break; 610 } 611 } 612 } 613 614 // If we didn't find a single unique LoopExit block, or if the loop exit block 615 // contains phi nodes, this isn't trivial. 616 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin())) 617 return false; // Can't handle this. 618 619 if (LoopExit) *LoopExit = LoopExitBB; 620 621 // We already know that nothing uses any scalar values defined inside of this 622 // loop. As such, we just have to check to see if this loop will execute any 623 // side-effecting instructions (e.g. stores, calls, volatile loads) in the 624 // part of the loop that the code *would* execute. We already checked the 625 // tail, check the header now. 626 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I) 627 if (I->mayHaveSideEffects()) 628 return false; 629 return true; 630 } 631 632 /// UnswitchIfProfitable - We have found that we can unswitch currentLoop when 633 /// LoopCond == Val to simplify the loop. If we decide that this is profitable, 634 /// unswitch the loop, reprocess the pieces, then return true. 635 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) { 636 Function *F = loopHeader->getParent(); 637 Constant *CondVal = 0; 638 BasicBlock *ExitBlock = 0; 639 640 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) { 641 // If the condition is trivial, always unswitch. There is no code growth 642 // for this case. 643 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock); 644 return true; 645 } 646 647 // Check to see if it would be profitable to unswitch current loop. 648 649 // Do not do non-trivial unswitch while optimizing for size. 650 if (OptimizeForSize || 651 F->getAttributes().hasAttribute(AttributeSet::FunctionIndex, 652 Attribute::OptimizeForSize)) 653 return false; 654 655 UnswitchNontrivialCondition(LoopCond, Val, currentLoop); 656 return true; 657 } 658 659 /// CloneLoop - Recursively clone the specified loop and all of its children, 660 /// mapping the blocks with the specified map. 661 static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM, 662 LoopInfo *LI, LPPassManager *LPM) { 663 Loop *New = new Loop(); 664 LPM->insertLoop(New, PL); 665 666 // Add all of the blocks in L to the new loop. 667 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 668 I != E; ++I) 669 if (LI->getLoopFor(*I) == L) 670 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase()); 671 672 // Add all of the subloops to the new loop. 673 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) 674 CloneLoop(*I, New, VM, LI, LPM); 675 676 return New; 677 } 678 679 /// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values 680 /// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the 681 /// code immediately before InsertPt. 682 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, 683 BasicBlock *TrueDest, 684 BasicBlock *FalseDest, 685 Instruction *InsertPt) { 686 // Insert a conditional branch on LIC to the two preheaders. The original 687 // code is the true version and the new code is the false version. 688 Value *BranchVal = LIC; 689 if (!isa<ConstantInt>(Val) || 690 Val->getType() != Type::getInt1Ty(LIC->getContext())) 691 BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val); 692 else if (Val != ConstantInt::getTrue(Val->getContext())) 693 // We want to enter the new loop when the condition is true. 694 std::swap(TrueDest, FalseDest); 695 696 // Insert the new branch. 697 BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt); 698 699 // If either edge is critical, split it. This helps preserve LoopSimplify 700 // form for enclosing loops. 701 SplitCriticalEdge(BI, 0, this, false, false, true); 702 SplitCriticalEdge(BI, 1, this, false, false, true); 703 } 704 705 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable 706 /// condition in it (a cond branch from its header block to its latch block, 707 /// where the path through the loop that doesn't execute its body has no 708 /// side-effects), unswitch it. This doesn't involve any code duplication, just 709 /// moving the conditional branch outside of the loop and updating loop info. 710 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, 711 Constant *Val, 712 BasicBlock *ExitBlock) { 713 DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %" 714 << loopHeader->getName() << " [" << L->getBlocks().size() 715 << " blocks] in Function " << L->getHeader()->getParent()->getName() 716 << " on cond: " << *Val << " == " << *Cond << "\n"); 717 718 // First step, split the preheader, so that we know that there is a safe place 719 // to insert the conditional branch. We will change loopPreheader to have a 720 // conditional branch on Cond. 721 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this); 722 723 // Now that we have a place to insert the conditional branch, create a place 724 // to branch to: this is the exit block out of the loop that we should 725 // short-circuit to. 726 727 // Split this block now, so that the loop maintains its exit block, and so 728 // that the jump from the preheader can execute the contents of the exit block 729 // without actually branching to it (the exit block should be dominated by the 730 // loop header, not the preheader). 731 assert(!L->contains(ExitBlock) && "Exit block is in the loop?"); 732 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this); 733 734 // Okay, now we have a position to branch from and a position to branch to, 735 // insert the new conditional branch. 736 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH, 737 loopPreheader->getTerminator()); 738 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L); 739 loopPreheader->getTerminator()->eraseFromParent(); 740 741 // We need to reprocess this loop, it could be unswitched again. 742 redoLoop = true; 743 744 // Now that we know that the loop is never entered when this condition is a 745 // particular value, rewrite the loop with this info. We know that this will 746 // at least eliminate the old branch. 747 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false); 748 ++NumTrivial; 749 } 750 751 /// SplitExitEdges - Split all of the edges from inside the loop to their exit 752 /// blocks. Update the appropriate Phi nodes as we do so. 753 void LoopUnswitch::SplitExitEdges(Loop *L, 754 const SmallVectorImpl<BasicBlock *> &ExitBlocks){ 755 756 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 757 BasicBlock *ExitBlock = ExitBlocks[i]; 758 SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock), 759 pred_end(ExitBlock)); 760 761 // Although SplitBlockPredecessors doesn't preserve loop-simplify in 762 // general, if we call it on all predecessors of all exits then it does. 763 if (!ExitBlock->isLandingPad()) { 764 SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this); 765 } else { 766 SmallVector<BasicBlock*, 2> NewBBs; 767 SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa", 768 this, NewBBs); 769 } 770 } 771 } 772 773 /// UnswitchNontrivialCondition - We determined that the loop is profitable 774 /// to unswitch when LIC equal Val. Split it into loop versions and test the 775 /// condition outside of either loop. Return the loops created as Out1/Out2. 776 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, 777 Loop *L) { 778 Function *F = loopHeader->getParent(); 779 DEBUG(dbgs() << "loop-unswitch: Unswitching loop %" 780 << loopHeader->getName() << " [" << L->getBlocks().size() 781 << " blocks] in Function " << F->getName() 782 << " when '" << *Val << "' == " << *LIC << "\n"); 783 784 if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>()) 785 SE->forgetLoop(L); 786 787 LoopBlocks.clear(); 788 NewBlocks.clear(); 789 790 // First step, split the preheader and exit blocks, and add these blocks to 791 // the LoopBlocks list. 792 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this); 793 LoopBlocks.push_back(NewPreheader); 794 795 // We want the loop to come after the preheader, but before the exit blocks. 796 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end()); 797 798 SmallVector<BasicBlock*, 8> ExitBlocks; 799 L->getUniqueExitBlocks(ExitBlocks); 800 801 // Split all of the edges from inside the loop to their exit blocks. Update 802 // the appropriate Phi nodes as we do so. 803 SplitExitEdges(L, ExitBlocks); 804 805 // The exit blocks may have been changed due to edge splitting, recompute. 806 ExitBlocks.clear(); 807 L->getUniqueExitBlocks(ExitBlocks); 808 809 // Add exit blocks to the loop blocks. 810 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end()); 811 812 // Next step, clone all of the basic blocks that make up the loop (including 813 // the loop preheader and exit blocks), keeping track of the mapping between 814 // the instructions and blocks. 815 NewBlocks.reserve(LoopBlocks.size()); 816 ValueToValueMapTy VMap; 817 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { 818 BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F); 819 820 NewBlocks.push_back(NewBB); 821 VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping. 822 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L); 823 } 824 825 // Splice the newly inserted blocks into the function right before the 826 // original preheader. 827 F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(), 828 NewBlocks[0], F->end()); 829 830 // Now we create the new Loop object for the versioned loop. 831 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM); 832 833 // Recalculate unswitching quota, inherit simplified switches info for NewBB, 834 // Probably clone more loop-unswitch related loop properties. 835 BranchesInfo.cloneData(NewLoop, L, VMap); 836 837 Loop *ParentLoop = L->getParentLoop(); 838 if (ParentLoop) { 839 // Make sure to add the cloned preheader and exit blocks to the parent loop 840 // as well. 841 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase()); 842 } 843 844 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 845 BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]); 846 // The new exit block should be in the same loop as the old one. 847 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i])) 848 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase()); 849 850 assert(NewExit->getTerminator()->getNumSuccessors() == 1 && 851 "Exit block should have been split to have one successor!"); 852 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0); 853 854 // If the successor of the exit block had PHI nodes, add an entry for 855 // NewExit. 856 for (BasicBlock::iterator I = ExitSucc->begin(); 857 PHINode *PN = dyn_cast<PHINode>(I); ++I) { 858 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]); 859 ValueToValueMapTy::iterator It = VMap.find(V); 860 if (It != VMap.end()) V = It->second; 861 PN->addIncoming(V, NewExit); 862 } 863 864 if (LandingPadInst *LPad = NewExit->getLandingPadInst()) { 865 PHINode *PN = PHINode::Create(LPad->getType(), 0, "", 866 ExitSucc->getFirstInsertionPt()); 867 868 for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc); 869 I != E; ++I) { 870 BasicBlock *BB = *I; 871 LandingPadInst *LPI = BB->getLandingPadInst(); 872 LPI->replaceAllUsesWith(PN); 873 PN->addIncoming(LPI, BB); 874 } 875 } 876 } 877 878 // Rewrite the code to refer to itself. 879 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) 880 for (BasicBlock::iterator I = NewBlocks[i]->begin(), 881 E = NewBlocks[i]->end(); I != E; ++I) 882 RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries); 883 884 // Rewrite the original preheader to select between versions of the loop. 885 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator()); 886 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] && 887 "Preheader splitting did not work correctly!"); 888 889 // Emit the new branch that selects between the two versions of this loop. 890 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR); 891 LPM->deleteSimpleAnalysisValue(OldBR, L); 892 OldBR->eraseFromParent(); 893 894 LoopProcessWorklist.push_back(NewLoop); 895 redoLoop = true; 896 897 // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody 898 // deletes the instruction (for example by simplifying a PHI that feeds into 899 // the condition that we're unswitching on), we don't rewrite the second 900 // iteration. 901 WeakVH LICHandle(LIC); 902 903 // Now we rewrite the original code to know that the condition is true and the 904 // new code to know that the condition is false. 905 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false); 906 907 // It's possible that simplifying one loop could cause the other to be 908 // changed to another value or a constant. If its a constant, don't simplify 909 // it. 910 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop && 911 LICHandle && !isa<Constant>(LICHandle)) 912 RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true); 913 } 914 915 /// RemoveFromWorklist - Remove all instances of I from the worklist vector 916 /// specified. 917 static void RemoveFromWorklist(Instruction *I, 918 std::vector<Instruction*> &Worklist) { 919 920 Worklist.erase(std::remove(Worklist.begin(), Worklist.end(), I), 921 Worklist.end()); 922 } 923 924 /// ReplaceUsesOfWith - When we find that I really equals V, remove I from the 925 /// program, replacing all uses with V and update the worklist. 926 static void ReplaceUsesOfWith(Instruction *I, Value *V, 927 std::vector<Instruction*> &Worklist, 928 Loop *L, LPPassManager *LPM) { 929 DEBUG(dbgs() << "Replace with '" << *V << "': " << *I); 930 931 // Add uses to the worklist, which may be dead now. 932 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 933 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i))) 934 Worklist.push_back(Use); 935 936 // Add users to the worklist which may be simplified now. 937 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 938 UI != E; ++UI) 939 Worklist.push_back(cast<Instruction>(*UI)); 940 LPM->deleteSimpleAnalysisValue(I, L); 941 RemoveFromWorklist(I, Worklist); 942 I->replaceAllUsesWith(V); 943 I->eraseFromParent(); 944 ++NumSimplify; 945 } 946 947 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has 948 /// become unwrapped, either because the backedge was deleted, or because the 949 /// edge into the header was removed. If the edge into the header from the 950 /// latch block was removed, the loop is unwrapped but subloops are still alive, 951 /// so they just reparent loops. If the loops are actually dead, they will be 952 /// removed later. 953 void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) { 954 LPM->deleteLoopFromQueue(L); 955 RemoveLoopFromWorklist(L); 956 } 957 958 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has 959 // the value specified by Val in the specified loop, or we know it does NOT have 960 // that value. Rewrite any uses of LIC or of properties correlated to it. 961 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, 962 Constant *Val, 963 bool IsEqual) { 964 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?"); 965 966 // FIXME: Support correlated properties, like: 967 // for (...) 968 // if (li1 < li2) 969 // ... 970 // if (li1 > li2) 971 // ... 972 973 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches, 974 // selects, switches. 975 std::vector<Instruction*> Worklist; 976 LLVMContext &Context = Val->getContext(); 977 978 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC 979 // in the loop with the appropriate one directly. 980 if (IsEqual || (isa<ConstantInt>(Val) && 981 Val->getType()->isIntegerTy(1))) { 982 Value *Replacement; 983 if (IsEqual) 984 Replacement = Val; 985 else 986 Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()), 987 !cast<ConstantInt>(Val)->getZExtValue()); 988 989 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end(); 990 UI != E; ++UI) { 991 Instruction *U = dyn_cast<Instruction>(*UI); 992 if (!U || !L->contains(U)) 993 continue; 994 Worklist.push_back(U); 995 } 996 997 for (std::vector<Instruction*>::iterator UI = Worklist.begin(), 998 UE = Worklist.end(); UI != UE; ++UI) 999 (*UI)->replaceUsesOfWith(LIC, Replacement); 1000 1001 SimplifyCode(Worklist, L); 1002 return; 1003 } 1004 1005 // Otherwise, we don't know the precise value of LIC, but we do know that it 1006 // is certainly NOT "Val". As such, simplify any uses in the loop that we 1007 // can. This case occurs when we unswitch switch statements. 1008 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end(); 1009 UI != E; ++UI) { 1010 Instruction *U = dyn_cast<Instruction>(*UI); 1011 if (!U || !L->contains(U)) 1012 continue; 1013 1014 Worklist.push_back(U); 1015 1016 // TODO: We could do other simplifications, for example, turning 1017 // 'icmp eq LIC, Val' -> false. 1018 1019 // If we know that LIC is not Val, use this info to simplify code. 1020 SwitchInst *SI = dyn_cast<SwitchInst>(U); 1021 if (SI == 0 || !isa<ConstantInt>(Val)) continue; 1022 1023 SwitchInst::CaseIt DeadCase = SI->findCaseValue(cast<ConstantInt>(Val)); 1024 // Default case is live for multiple values. 1025 if (DeadCase == SI->case_default()) continue; 1026 1027 // Found a dead case value. Don't remove PHI nodes in the 1028 // successor if they become single-entry, those PHI nodes may 1029 // be in the Users list. 1030 1031 BasicBlock *Switch = SI->getParent(); 1032 BasicBlock *SISucc = DeadCase.getCaseSuccessor(); 1033 BasicBlock *Latch = L->getLoopLatch(); 1034 1035 BranchesInfo.setUnswitched(SI, Val); 1036 1037 if (!SI->findCaseDest(SISucc)) continue; // Edge is critical. 1038 // If the DeadCase successor dominates the loop latch, then the 1039 // transformation isn't safe since it will delete the sole predecessor edge 1040 // to the latch. 1041 if (Latch && DT->dominates(SISucc, Latch)) 1042 continue; 1043 1044 // FIXME: This is a hack. We need to keep the successor around 1045 // and hooked up so as to preserve the loop structure, because 1046 // trying to update it is complicated. So instead we preserve the 1047 // loop structure and put the block on a dead code path. 1048 SplitEdge(Switch, SISucc, this); 1049 // Compute the successors instead of relying on the return value 1050 // of SplitEdge, since it may have split the switch successor 1051 // after PHI nodes. 1052 BasicBlock *NewSISucc = DeadCase.getCaseSuccessor(); 1053 BasicBlock *OldSISucc = *succ_begin(NewSISucc); 1054 // Create an "unreachable" destination. 1055 BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable", 1056 Switch->getParent(), 1057 OldSISucc); 1058 new UnreachableInst(Context, Abort); 1059 // Force the new case destination to branch to the "unreachable" 1060 // block while maintaining a (dead) CFG edge to the old block. 1061 NewSISucc->getTerminator()->eraseFromParent(); 1062 BranchInst::Create(Abort, OldSISucc, 1063 ConstantInt::getTrue(Context), NewSISucc); 1064 // Release the PHI operands for this edge. 1065 for (BasicBlock::iterator II = NewSISucc->begin(); 1066 PHINode *PN = dyn_cast<PHINode>(II); ++II) 1067 PN->setIncomingValue(PN->getBasicBlockIndex(Switch), 1068 UndefValue::get(PN->getType())); 1069 // Tell the domtree about the new block. We don't fully update the 1070 // domtree here -- instead we force it to do a full recomputation 1071 // after the pass is complete -- but we do need to inform it of 1072 // new blocks. 1073 if (DT) 1074 DT->addNewBlock(Abort, NewSISucc); 1075 } 1076 1077 SimplifyCode(Worklist, L); 1078 } 1079 1080 /// SimplifyCode - Okay, now that we have simplified some instructions in the 1081 /// loop, walk over it and constant prop, dce, and fold control flow where 1082 /// possible. Note that this is effectively a very simple loop-structure-aware 1083 /// optimizer. During processing of this loop, L could very well be deleted, so 1084 /// it must not be used. 1085 /// 1086 /// FIXME: When the loop optimizer is more mature, separate this out to a new 1087 /// pass. 1088 /// 1089 void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) { 1090 while (!Worklist.empty()) { 1091 Instruction *I = Worklist.back(); 1092 Worklist.pop_back(); 1093 1094 // Simple DCE. 1095 if (isInstructionTriviallyDead(I)) { 1096 DEBUG(dbgs() << "Remove dead instruction '" << *I); 1097 1098 // Add uses to the worklist, which may be dead now. 1099 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 1100 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i))) 1101 Worklist.push_back(Use); 1102 LPM->deleteSimpleAnalysisValue(I, L); 1103 RemoveFromWorklist(I, Worklist); 1104 I->eraseFromParent(); 1105 ++NumSimplify; 1106 continue; 1107 } 1108 1109 // See if instruction simplification can hack this up. This is common for 1110 // things like "select false, X, Y" after unswitching made the condition be 1111 // 'false'. TODO: update the domtree properly so we can pass it here. 1112 if (Value *V = SimplifyInstruction(I)) 1113 if (LI->replacementPreservesLCSSAForm(I, V)) { 1114 ReplaceUsesOfWith(I, V, Worklist, L, LPM); 1115 continue; 1116 } 1117 1118 // Special case hacks that appear commonly in unswitched code. 1119 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1120 if (BI->isUnconditional()) { 1121 // If BI's parent is the only pred of the successor, fold the two blocks 1122 // together. 1123 BasicBlock *Pred = BI->getParent(); 1124 BasicBlock *Succ = BI->getSuccessor(0); 1125 BasicBlock *SinglePred = Succ->getSinglePredecessor(); 1126 if (!SinglePred) continue; // Nothing to do. 1127 assert(SinglePred == Pred && "CFG broken"); 1128 1129 DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- " 1130 << Succ->getName() << "\n"); 1131 1132 // Resolve any single entry PHI nodes in Succ. 1133 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin())) 1134 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM); 1135 1136 // If Succ has any successors with PHI nodes, update them to have 1137 // entries coming from Pred instead of Succ. 1138 Succ->replaceAllUsesWith(Pred); 1139 1140 // Move all of the successor contents from Succ to Pred. 1141 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(), 1142 Succ->end()); 1143 LPM->deleteSimpleAnalysisValue(BI, L); 1144 BI->eraseFromParent(); 1145 RemoveFromWorklist(BI, Worklist); 1146 1147 // Remove Succ from the loop tree. 1148 LI->removeBlock(Succ); 1149 LPM->deleteSimpleAnalysisValue(Succ, L); 1150 Succ->eraseFromParent(); 1151 ++NumSimplify; 1152 continue; 1153 } 1154 1155 continue; 1156 } 1157 } 1158 } 1159