LoopUnswitch.cpp revision df5cf2074c336fb4de7e5b77e7b3bbbf21948a53
1//===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source 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/Constants.h" 32#include "llvm/DerivedTypes.h" 33#include "llvm/Function.h" 34#include "llvm/Instructions.h" 35#include "llvm/Analysis/ConstantFolding.h" 36#include "llvm/Analysis/LoopInfo.h" 37#include "llvm/Analysis/LoopPass.h" 38#include "llvm/Analysis/Dominators.h" 39#include "llvm/Transforms/Utils/Cloning.h" 40#include "llvm/Transforms/Utils/Local.h" 41#include "llvm/Transforms/Utils/BasicBlockUtils.h" 42#include "llvm/ADT/Statistic.h" 43#include "llvm/ADT/SmallPtrSet.h" 44#include "llvm/ADT/PostOrderIterator.h" 45#include "llvm/Support/CommandLine.h" 46#include "llvm/Support/Compiler.h" 47#include "llvm/Support/Debug.h" 48#include <algorithm> 49#include <set> 50using namespace llvm; 51 52STATISTIC(NumBranches, "Number of branches unswitched"); 53STATISTIC(NumSwitches, "Number of switches unswitched"); 54STATISTIC(NumSelects , "Number of selects unswitched"); 55STATISTIC(NumTrivial , "Number of unswitches that are trivial"); 56STATISTIC(NumSimplify, "Number of simplifications of unswitched code"); 57 58namespace { 59 cl::opt<unsigned> 60 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), 61 cl::init(10), cl::Hidden); 62 63 class VISIBILITY_HIDDEN LoopUnswitch : public LoopPass { 64 LoopInfo *LI; // Loop information 65 LPPassManager *LPM; 66 67 // LoopProcessWorklist - Used to check if second loop needs processing 68 // after RewriteLoopBodyWithConditionConstant rewrites first loop. 69 std::vector<Loop*> LoopProcessWorklist; 70 SmallPtrSet<Value *,8> UnswitchedVals; 71 72 bool OptimizeForSize; 73 public: 74 static char ID; // Pass ID, replacement for typeid 75 LoopUnswitch(bool Os = false) : 76 LoopPass((intptr_t)&ID), OptimizeForSize(Os) {} 77 78 bool runOnLoop(Loop *L, LPPassManager &LPM); 79 80 /// This transformation requires natural loop information & requires that 81 /// loop preheaders be inserted into the CFG... 82 /// 83 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 84 AU.addRequiredID(LoopSimplifyID); 85 AU.addPreservedID(LoopSimplifyID); 86 AU.addRequired<LoopInfo>(); 87 AU.addPreserved<LoopInfo>(); 88 AU.addRequiredID(LCSSAID); 89 } 90 91 private: 92 /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist, 93 /// remove it. 94 void RemoveLoopFromWorklist(Loop *L) { 95 std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(), 96 LoopProcessWorklist.end(), L); 97 if (I != LoopProcessWorklist.end()) 98 LoopProcessWorklist.erase(I); 99 } 100 101 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L); 102 unsigned getLoopUnswitchCost(Loop *L, Value *LIC); 103 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, 104 BasicBlock *ExitBlock); 105 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L); 106 107 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, 108 Constant *Val, bool isEqual); 109 110 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, 111 BasicBlock *TrueDest, 112 BasicBlock *FalseDest, 113 Instruction *InsertPt); 114 115 void SimplifyCode(std::vector<Instruction*> &Worklist); 116 void RemoveBlockIfDead(BasicBlock *BB, 117 std::vector<Instruction*> &Worklist); 118 void RemoveLoopFromHierarchy(Loop *L); 119 }; 120 char LoopUnswitch::ID = 0; 121 RegisterPass<LoopUnswitch> X("loop-unswitch", "Unswitch loops"); 122} 123 124LoopPass *llvm::createLoopUnswitchPass(bool Os) { 125 return new LoopUnswitch(Os); 126} 127 128/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is 129/// invariant in the loop, or has an invariant piece, return the invariant. 130/// Otherwise, return null. 131static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) { 132 // Constants should be folded, not unswitched on! 133 if (isa<Constant>(Cond)) return false; 134 135 // TODO: Handle: br (VARIANT|INVARIANT). 136 // TODO: Hoist simple expressions out of loops. 137 if (L->isLoopInvariant(Cond)) return Cond; 138 139 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond)) 140 if (BO->getOpcode() == Instruction::And || 141 BO->getOpcode() == Instruction::Or) { 142 // If either the left or right side is invariant, we can unswitch on this, 143 // which will cause the branch to go away in one loop and the condition to 144 // simplify in the other one. 145 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed)) 146 return LHS; 147 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed)) 148 return RHS; 149 } 150 151 return 0; 152} 153 154bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { 155 assert(L->isLCSSAForm()); 156 LI = &getAnalysis<LoopInfo>(); 157 LPM = &LPM_Ref; 158 bool Changed = false; 159 160 // Loop over all of the basic blocks in the loop. If we find an interior 161 // block that is branching on a loop-invariant condition, we can unswitch this 162 // loop. 163 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 164 I != E; ++I) { 165 TerminatorInst *TI = (*I)->getTerminator(); 166 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 167 // If this isn't branching on an invariant condition, we can't unswitch 168 // it. 169 if (BI->isConditional()) { 170 // See if this, or some part of it, is loop invariant. If so, we can 171 // unswitch on it if we desire. 172 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed); 173 if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(), 174 L)) { 175 ++NumBranches; 176 return true; 177 } 178 } 179 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 180 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed); 181 if (LoopCond && SI->getNumCases() > 1) { 182 // Find a value to unswitch on: 183 // FIXME: this should chose the most expensive case! 184 Constant *UnswitchVal = SI->getCaseValue(1); 185 // Do not process same value again and again. 186 if (!UnswitchedVals.insert(UnswitchVal)) 187 continue; 188 189 if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) { 190 ++NumSwitches; 191 return true; 192 } 193 } 194 } 195 196 // Scan the instructions to check for unswitchable values. 197 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end(); 198 BBI != E; ++BBI) 199 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) { 200 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed); 201 if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(), 202 L)) { 203 ++NumSelects; 204 return true; 205 } 206 } 207 } 208 209 assert(L->isLCSSAForm()); 210 211 return Changed; 212} 213 214/// isTrivialLoopExitBlock - Check to see if all paths from BB either: 215/// 1. Exit the loop with no side effects. 216/// 2. Branch to the latch block with no side-effects. 217/// 218/// If these conditions are true, we return true and set ExitBB to the block we 219/// exit through. 220/// 221static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB, 222 BasicBlock *&ExitBB, 223 std::set<BasicBlock*> &Visited) { 224 if (!Visited.insert(BB).second) { 225 // Already visited and Ok, end of recursion. 226 return true; 227 } else if (!L->contains(BB)) { 228 // Otherwise, this is a loop exit, this is fine so long as this is the 229 // first exit. 230 if (ExitBB != 0) return false; 231 ExitBB = BB; 232 return true; 233 } 234 235 // Otherwise, this is an unvisited intra-loop node. Check all successors. 236 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) { 237 // Check to see if the successor is a trivial loop exit. 238 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited)) 239 return false; 240 } 241 242 // Okay, everything after this looks good, check to make sure that this block 243 // doesn't include any side effects. 244 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 245 if (I->mayWriteToMemory()) 246 return false; 247 248 return true; 249} 250 251/// isTrivialLoopExitBlock - Return true if the specified block unconditionally 252/// leads to an exit from the specified loop, and has no side-effects in the 253/// process. If so, return the block that is exited to, otherwise return null. 254static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { 255 std::set<BasicBlock*> Visited; 256 Visited.insert(L->getHeader()); // Branches to header are ok. 257 BasicBlock *ExitBB = 0; 258 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited)) 259 return ExitBB; 260 return 0; 261} 262 263/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is 264/// trivial: that is, that the condition controls whether or not the loop does 265/// anything at all. If this is a trivial condition, unswitching produces no 266/// code duplications (equivalently, it produces a simpler loop and a new empty 267/// loop, which gets deleted). 268/// 269/// If this is a trivial condition, return true, otherwise return false. When 270/// returning true, this sets Cond and Val to the condition that controls the 271/// trivial condition: when Cond dynamically equals Val, the loop is known to 272/// exit. Finally, this sets LoopExit to the BB that the loop exits to when 273/// Cond == Val. 274/// 275static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, Constant **Val = 0, 276 BasicBlock **LoopExit = 0) { 277 BasicBlock *Header = L->getHeader(); 278 TerminatorInst *HeaderTerm = Header->getTerminator(); 279 280 BasicBlock *LoopExitBB = 0; 281 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) { 282 // If the header block doesn't end with a conditional branch on Cond, we 283 // can't handle it. 284 if (!BI->isConditional() || BI->getCondition() != Cond) 285 return false; 286 287 // Check to see if a successor of the branch is guaranteed to go to the 288 // latch block or exit through a one exit block without having any 289 // side-effects. If so, determine the value of Cond that causes it to do 290 // this. 291 if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) { 292 if (Val) *Val = ConstantInt::getTrue(); 293 } else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) { 294 if (Val) *Val = ConstantInt::getFalse(); 295 } 296 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) { 297 // If this isn't a switch on Cond, we can't handle it. 298 if (SI->getCondition() != Cond) return false; 299 300 // Check to see if a successor of the switch is guaranteed to go to the 301 // latch block or exit through a one exit block without having any 302 // side-effects. If so, determine the value of Cond that causes it to do 303 // this. Note that we can't trivially unswitch on the default case. 304 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) 305 if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) { 306 // Okay, we found a trivial case, remember the value that is trivial. 307 if (Val) *Val = SI->getCaseValue(i); 308 break; 309 } 310 } 311 312 // If we didn't find a single unique LoopExit block, or if the loop exit block 313 // contains phi nodes, this isn't trivial. 314 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin())) 315 return false; // Can't handle this. 316 317 if (LoopExit) *LoopExit = LoopExitBB; 318 319 // We already know that nothing uses any scalar values defined inside of this 320 // loop. As such, we just have to check to see if this loop will execute any 321 // side-effecting instructions (e.g. stores, calls, volatile loads) in the 322 // part of the loop that the code *would* execute. We already checked the 323 // tail, check the header now. 324 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I) 325 if (I->mayWriteToMemory()) 326 return false; 327 return true; 328} 329 330/// getLoopUnswitchCost - Return the cost (code size growth) that will happen if 331/// we choose to unswitch the specified loop on the specified value. 332/// 333unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) { 334 // If the condition is trivial, always unswitch. There is no code growth for 335 // this case. 336 if (IsTrivialUnswitchCondition(L, LIC)) 337 return 0; 338 339 // FIXME: This is really overly conservative. However, more liberal 340 // estimations have thus far resulted in excessive unswitching, which is bad 341 // both in compile time and in code size. This should be replaced once 342 // someone figures out how a good estimation. 343 return L->getBlocks().size(); 344 345 unsigned Cost = 0; 346 // FIXME: this is brain dead. It should take into consideration code 347 // shrinkage. 348 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 349 I != E; ++I) { 350 BasicBlock *BB = *I; 351 // Do not include empty blocks in the cost calculation. This happen due to 352 // loop canonicalization and will be removed. 353 if (BB->begin() == BasicBlock::iterator(BB->getTerminator())) 354 continue; 355 356 // Count basic blocks. 357 ++Cost; 358 } 359 360 return Cost; 361} 362 363/// UnswitchIfProfitable - We have found that we can unswitch L when 364/// LoopCond == Val to simplify the loop. If we decide that this is profitable, 365/// unswitch the loop, reprocess the pieces, then return true. 366bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){ 367 // Check to see if it would be profitable to unswitch this loop. 368 unsigned Cost = getLoopUnswitchCost(L, LoopCond); 369 370 // Do not do non-trivial unswitch while optimizing for size. 371 if (Cost && OptimizeForSize) 372 return false; 373 374 if (Cost > Threshold) { 375 // FIXME: this should estimate growth by the amount of code shared by the 376 // resultant unswitched loops. 377 // 378 DOUT << "NOT unswitching loop %" 379 << L->getHeader()->getName() << ", cost too high: " 380 << L->getBlocks().size() << "\n"; 381 return false; 382 } 383 384 // If this is a trivial condition to unswitch (which results in no code 385 // duplication), do it now. 386 Constant *CondVal; 387 BasicBlock *ExitBlock; 388 if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal, &ExitBlock)) { 389 UnswitchTrivialCondition(L, LoopCond, CondVal, ExitBlock); 390 } else { 391 UnswitchNontrivialCondition(LoopCond, Val, L); 392 } 393 394 return true; 395} 396 397// RemapInstruction - Convert the instruction operands from referencing the 398// current values into those specified by ValueMap. 399// 400static inline void RemapInstruction(Instruction *I, 401 DenseMap<const Value *, Value*> &ValueMap) { 402 for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { 403 Value *Op = I->getOperand(op); 404 DenseMap<const Value *, Value*>::iterator It = ValueMap.find(Op); 405 if (It != ValueMap.end()) Op = It->second; 406 I->setOperand(op, Op); 407 } 408} 409 410// CloneDomInfo - NewBB is cloned from Orig basic block. Now clone Dominator Info. 411// 412// If Orig block's immediate dominator is mapped in VM then use corresponding 413// immediate dominator from the map. Otherwise Orig block's dominator is also 414// NewBB's dominator. 415// 416// OrigPreheader is loop pre-header before this pass started 417// updating CFG. NewPrehader is loops new pre-header. However, after CFG 418// manipulation, loop L may not exist. So rely on input parameter NewPreheader. 419void CloneDomInfo(BasicBlock *NewBB, BasicBlock *Orig, 420 BasicBlock *NewPreheader, BasicBlock *OrigPreheader, 421 BasicBlock *OrigHeader, 422 DominatorTree *DT, DominanceFrontier *DF, 423 DenseMap<const Value*, Value*> &VM) { 424 425 // If NewBB alreay has found its place in domiantor tree then no need to do 426 // anything. 427 if (DT->getNode(NewBB)) 428 return; 429 430 // If Orig does not have any immediate domiantor then its clone, NewBB, does 431 // not need any immediate dominator. 432 DomTreeNode *OrigNode = DT->getNode(Orig); 433 if (!OrigNode) 434 return; 435 DomTreeNode *OrigIDomNode = OrigNode->getIDom(); 436 if (!OrigIDomNode) 437 return; 438 439 BasicBlock *OrigIDom = NULL; 440 441 // If Orig is original loop header then its immediate dominator is 442 // NewPreheader. 443 if (Orig == OrigHeader) 444 OrigIDom = NewPreheader; 445 446 // If Orig is new pre-header then its immediate dominator is 447 // original pre-header. 448 else if (Orig == NewPreheader) 449 OrigIDom = OrigPreheader; 450 451 // Other as DT to find Orig's immediate dominator. 452 else 453 OrigIDom = OrigIDomNode->getBlock(); 454 455 // Initially use Orig's immediate dominator as NewBB's immediate dominator. 456 BasicBlock *NewIDom = OrigIDom; 457 DenseMap<const Value*, Value*>::iterator I = VM.find(OrigIDom); 458 if (I != VM.end()) { 459 NewIDom = cast<BasicBlock>(I->second); 460 461 // If NewIDom does not have corresponding dominatore tree node then 462 // get one. 463 if (!DT->getNode(NewIDom)) 464 CloneDomInfo(NewIDom, OrigIDom, NewPreheader, OrigPreheader, 465 OrigHeader, DT, DF, VM); 466 } 467 468 DT->addNewBlock(NewBB, NewIDom); 469 470 // Copy cloned dominance frontiner set 471 DominanceFrontier::DomSetType NewDFSet; 472 if (DF) { 473 DominanceFrontier::iterator DFI = DF->find(Orig); 474 if ( DFI != DF->end()) { 475 DominanceFrontier::DomSetType S = DFI->second; 476 for (DominanceFrontier::DomSetType::iterator I = S.begin(), E = S.end(); 477 I != E; ++I) { 478 BasicBlock *BB = *I; 479 DenseMap<const Value*, Value*>::iterator IDM = VM.find(BB); 480 if (IDM != VM.end()) 481 NewDFSet.insert(cast<BasicBlock>(IDM->second)); 482 else 483 NewDFSet.insert(BB); 484 } 485 } 486 DF->addBasicBlock(NewBB, NewDFSet); 487 } 488} 489 490/// CloneLoop - Recursively clone the specified loop and all of its children, 491/// mapping the blocks with the specified map. 492static Loop *CloneLoop(Loop *L, Loop *PL, DenseMap<const Value*, Value*> &VM, 493 LoopInfo *LI, LPPassManager *LPM) { 494 Loop *New = new Loop(); 495 496 LPM->insertLoop(New, PL); 497 498 // Add all of the blocks in L to the new loop. 499 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 500 I != E; ++I) 501 if (LI->getLoopFor(*I) == L) 502 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI); 503 504 // Add all of the subloops to the new loop. 505 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) 506 CloneLoop(*I, New, VM, LI, LPM); 507 508 return New; 509} 510 511/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values 512/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the 513/// code immediately before InsertPt. 514void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, 515 BasicBlock *TrueDest, 516 BasicBlock *FalseDest, 517 Instruction *InsertPt) { 518 // Insert a conditional branch on LIC to the two preheaders. The original 519 // code is the true version and the new code is the false version. 520 Value *BranchVal = LIC; 521 if (!isa<ConstantInt>(Val) || Val->getType() != Type::Int1Ty) 522 BranchVal = new ICmpInst(ICmpInst::ICMP_EQ, LIC, Val, "tmp", InsertPt); 523 else if (Val != ConstantInt::getTrue()) 524 // We want to enter the new loop when the condition is true. 525 std::swap(TrueDest, FalseDest); 526 527 // Insert the new branch. 528 BranchInst *BRI = new BranchInst(TrueDest, FalseDest, BranchVal, InsertPt); 529 530 // Update dominator info. 531 // BranchVal is a new preheader so it dominates true and false destination 532 // loop headers. 533 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) { 534 DT->changeImmediateDominator(TrueDest, BRI->getParent()); 535 DT->changeImmediateDominator(FalseDest, BRI->getParent()); 536 } 537 // No need to update DominanceFrontier. BRI->getParent() dominated TrueDest 538 // and FalseDest anyway. Now it immediately dominates them. 539} 540 541 542/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable 543/// condition in it (a cond branch from its header block to its latch block, 544/// where the path through the loop that doesn't execute its body has no 545/// side-effects), unswitch it. This doesn't involve any code duplication, just 546/// moving the conditional branch outside of the loop and updating loop info. 547void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, 548 Constant *Val, 549 BasicBlock *ExitBlock) { 550 DOUT << "loop-unswitch: Trivial-Unswitch loop %" 551 << L->getHeader()->getName() << " [" << L->getBlocks().size() 552 << " blocks] in Function " << L->getHeader()->getParent()->getName() 553 << " on cond: " << *Val << " == " << *Cond << "\n"; 554 555 // First step, split the preheader, so that we know that there is a safe place 556 // to insert the conditional branch. We will change 'OrigPH' to have a 557 // conditional branch on Cond. 558 BasicBlock *OrigPH = L->getLoopPreheader(); 559 BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader(), this); 560 561 // Now that we have a place to insert the conditional branch, create a place 562 // to branch to: this is the exit block out of the loop that we should 563 // short-circuit to. 564 565 // Split this block now, so that the loop maintains its exit block, and so 566 // that the jump from the preheader can execute the contents of the exit block 567 // without actually branching to it (the exit block should be dominated by the 568 // loop header, not the preheader). 569 assert(!L->contains(ExitBlock) && "Exit block is in the loop?"); 570 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this); 571 572 // Okay, now we have a position to branch from and a position to branch to, 573 // insert the new conditional branch. 574 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH, 575 OrigPH->getTerminator()); 576 OrigPH->getTerminator()->eraseFromParent(); 577 578 // We need to reprocess this loop, it could be unswitched again. 579 LPM->redoLoop(L); 580 581 // Now that we know that the loop is never entered when this condition is a 582 // particular value, rewrite the loop with this info. We know that this will 583 // at least eliminate the old branch. 584 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false); 585 ++NumTrivial; 586} 587 588/// VersionLoop - We determined that the loop is profitable to unswitch when LIC 589/// equal Val. Split it into loop versions and test the condition outside of 590/// either loop. Return the loops created as Out1/Out2. 591void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, 592 Loop *L) { 593 Function *F = L->getHeader()->getParent(); 594 DOUT << "loop-unswitch: Unswitching loop %" 595 << L->getHeader()->getName() << " [" << L->getBlocks().size() 596 << " blocks] in Function " << F->getName() 597 << " when '" << *Val << "' == " << *LIC << "\n"; 598 599 // LoopBlocks contains all of the basic blocks of the loop, including the 600 // preheader of the loop, the body of the loop, and the exit blocks of the 601 // loop, in that order. 602 std::vector<BasicBlock*> LoopBlocks; 603 604 // First step, split the preheader and exit blocks, and add these blocks to 605 // the LoopBlocks list. 606 BasicBlock *OrigHeader = L->getHeader(); 607 BasicBlock *OrigPreheader = L->getLoopPreheader(); 608 BasicBlock *NewPreheader = SplitEdge(OrigPreheader, L->getHeader(), this); 609 LoopBlocks.push_back(NewPreheader); 610 611 // We want the loop to come after the preheader, but before the exit blocks. 612 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end()); 613 614 std::vector<BasicBlock*> ExitBlocks; 615 L->getUniqueExitBlocks(ExitBlocks); 616 617 // Split all of the edges from inside the loop to their exit blocks. Update 618 // the appropriate Phi nodes as we do so. 619 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 620 BasicBlock *ExitBlock = ExitBlocks[i]; 621 std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock)); 622 623 for (unsigned j = 0, e = Preds.size(); j != e; ++j) { 624 BasicBlock* MiddleBlock = SplitEdge(Preds[j], ExitBlock, this); 625 BasicBlock* StartBlock = Preds[j]; 626 BasicBlock* EndBlock; 627 if (MiddleBlock->getSinglePredecessor() == ExitBlock) { 628 EndBlock = MiddleBlock; 629 MiddleBlock = EndBlock->getSinglePredecessor();; 630 } else { 631 EndBlock = ExitBlock; 632 } 633 634 std::set<PHINode*> InsertedPHIs; 635 PHINode* OldLCSSA = 0; 636 for (BasicBlock::iterator I = EndBlock->begin(); 637 (OldLCSSA = dyn_cast<PHINode>(I)); ++I) { 638 Value* OldValue = OldLCSSA->getIncomingValueForBlock(MiddleBlock); 639 PHINode* NewLCSSA = new PHINode(OldLCSSA->getType(), 640 OldLCSSA->getName() + ".us-lcssa", 641 MiddleBlock->getTerminator()); 642 NewLCSSA->addIncoming(OldValue, StartBlock); 643 OldLCSSA->setIncomingValue(OldLCSSA->getBasicBlockIndex(MiddleBlock), 644 NewLCSSA); 645 InsertedPHIs.insert(NewLCSSA); 646 } 647 648 BasicBlock::iterator InsertPt = EndBlock->begin(); 649 while (dyn_cast<PHINode>(InsertPt)) ++InsertPt; 650 for (BasicBlock::iterator I = MiddleBlock->begin(); 651 (OldLCSSA = dyn_cast<PHINode>(I)) && InsertedPHIs.count(OldLCSSA) == 0; 652 ++I) { 653 PHINode *NewLCSSA = new PHINode(OldLCSSA->getType(), 654 OldLCSSA->getName() + ".us-lcssa", 655 InsertPt); 656 OldLCSSA->replaceAllUsesWith(NewLCSSA); 657 NewLCSSA->addIncoming(OldLCSSA, MiddleBlock); 658 } 659 } 660 } 661 662 // The exit blocks may have been changed due to edge splitting, recompute. 663 ExitBlocks.clear(); 664 L->getUniqueExitBlocks(ExitBlocks); 665 666 // Add exit blocks to the loop blocks. 667 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end()); 668 669 // Next step, clone all of the basic blocks that make up the loop (including 670 // the loop preheader and exit blocks), keeping track of the mapping between 671 // the instructions and blocks. 672 std::vector<BasicBlock*> NewBlocks; 673 NewBlocks.reserve(LoopBlocks.size()); 674 DenseMap<const Value*, Value*> ValueMap; 675 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { 676 BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F); 677 NewBlocks.push_back(New); 678 ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping. 679 } 680 681 // Update dominator info 682 DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>(); 683 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) 684 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { 685 BasicBlock *LBB = LoopBlocks[i]; 686 BasicBlock *NBB = NewBlocks[i]; 687 CloneDomInfo(NBB, LBB, NewPreheader, OrigPreheader, 688 OrigHeader, DT, DF, ValueMap); 689 } 690 691 // Splice the newly inserted blocks into the function right before the 692 // original preheader. 693 F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(), 694 NewBlocks[0], F->end()); 695 696 // Now we create the new Loop object for the versioned loop. 697 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI, LPM); 698 Loop *ParentLoop = L->getParentLoop(); 699 if (ParentLoop) { 700 // Make sure to add the cloned preheader and exit blocks to the parent loop 701 // as well. 702 ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI); 703 } 704 705 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 706 BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]); 707 // The new exit block should be in the same loop as the old one. 708 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i])) 709 ExitBBLoop->addBasicBlockToLoop(NewExit, *LI); 710 711 assert(NewExit->getTerminator()->getNumSuccessors() == 1 && 712 "Exit block should have been split to have one successor!"); 713 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0); 714 715 // If the successor of the exit block had PHI nodes, add an entry for 716 // NewExit. 717 PHINode *PN; 718 for (BasicBlock::iterator I = ExitSucc->begin(); 719 (PN = dyn_cast<PHINode>(I)); ++I) { 720 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]); 721 DenseMap<const Value *, Value*>::iterator It = ValueMap.find(V); 722 if (It != ValueMap.end()) V = It->second; 723 PN->addIncoming(V, NewExit); 724 } 725 } 726 727 // Rewrite the code to refer to itself. 728 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) 729 for (BasicBlock::iterator I = NewBlocks[i]->begin(), 730 E = NewBlocks[i]->end(); I != E; ++I) 731 RemapInstruction(I, ValueMap); 732 733 // Rewrite the original preheader to select between versions of the loop. 734 BranchInst *OldBR = cast<BranchInst>(OrigPreheader->getTerminator()); 735 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] && 736 "Preheader splitting did not work correctly!"); 737 738 // Emit the new branch that selects between the two versions of this loop. 739 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR); 740 OldBR->eraseFromParent(); 741 742 LoopProcessWorklist.push_back(NewLoop); 743 LPM->redoLoop(L); 744 745 // Now we rewrite the original code to know that the condition is true and the 746 // new code to know that the condition is false. 747 RewriteLoopBodyWithConditionConstant(L , LIC, Val, false); 748 749 // It's possible that simplifying one loop could cause the other to be 750 // deleted. If so, don't simplify it. 751 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop) 752 RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true); 753} 754 755/// RemoveFromWorklist - Remove all instances of I from the worklist vector 756/// specified. 757static void RemoveFromWorklist(Instruction *I, 758 std::vector<Instruction*> &Worklist) { 759 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(), 760 Worklist.end(), I); 761 while (WI != Worklist.end()) { 762 unsigned Offset = WI-Worklist.begin(); 763 Worklist.erase(WI); 764 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I); 765 } 766} 767 768/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the 769/// program, replacing all uses with V and update the worklist. 770static void ReplaceUsesOfWith(Instruction *I, Value *V, 771 std::vector<Instruction*> &Worklist) { 772 DOUT << "Replace with '" << *V << "': " << *I; 773 774 // Add uses to the worklist, which may be dead now. 775 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 776 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i))) 777 Worklist.push_back(Use); 778 779 // Add users to the worklist which may be simplified now. 780 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 781 UI != E; ++UI) 782 Worklist.push_back(cast<Instruction>(*UI)); 783 I->replaceAllUsesWith(V); 784 I->eraseFromParent(); 785 RemoveFromWorklist(I, Worklist); 786 ++NumSimplify; 787} 788 789/// RemoveBlockIfDead - If the specified block is dead, remove it, update loop 790/// information, and remove any dead successors it has. 791/// 792void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB, 793 std::vector<Instruction*> &Worklist) { 794 if (pred_begin(BB) != pred_end(BB)) { 795 // This block isn't dead, since an edge to BB was just removed, see if there 796 // are any easy simplifications we can do now. 797 if (BasicBlock *Pred = BB->getSinglePredecessor()) { 798 // If it has one pred, fold phi nodes in BB. 799 while (isa<PHINode>(BB->begin())) 800 ReplaceUsesOfWith(BB->begin(), 801 cast<PHINode>(BB->begin())->getIncomingValue(0), 802 Worklist); 803 804 // If this is the header of a loop and the only pred is the latch, we now 805 // have an unreachable loop. 806 if (Loop *L = LI->getLoopFor(BB)) 807 if (L->getHeader() == BB && L->contains(Pred)) { 808 // Remove the branch from the latch to the header block, this makes 809 // the header dead, which will make the latch dead (because the header 810 // dominates the latch). 811 Pred->getTerminator()->eraseFromParent(); 812 new UnreachableInst(Pred); 813 814 // The loop is now broken, remove it from LI. 815 RemoveLoopFromHierarchy(L); 816 817 // Reprocess the header, which now IS dead. 818 RemoveBlockIfDead(BB, Worklist); 819 return; 820 } 821 822 // If pred ends in a uncond branch, add uncond branch to worklist so that 823 // the two blocks will get merged. 824 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) 825 if (BI->isUnconditional()) 826 Worklist.push_back(BI); 827 } 828 return; 829 } 830 831 DOUT << "Nuking dead block: " << *BB; 832 833 // Remove the instructions in the basic block from the worklist. 834 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 835 RemoveFromWorklist(I, Worklist); 836 837 // Anything that uses the instructions in this basic block should have their 838 // uses replaced with undefs. 839 if (!I->use_empty()) 840 I->replaceAllUsesWith(UndefValue::get(I->getType())); 841 } 842 843 // If this is the edge to the header block for a loop, remove the loop and 844 // promote all subloops. 845 if (Loop *BBLoop = LI->getLoopFor(BB)) { 846 if (BBLoop->getLoopLatch() == BB) 847 RemoveLoopFromHierarchy(BBLoop); 848 } 849 850 // Remove the block from the loop info, which removes it from any loops it 851 // was in. 852 LI->removeBlock(BB); 853 854 855 // Remove phi node entries in successors for this block. 856 TerminatorInst *TI = BB->getTerminator(); 857 std::vector<BasicBlock*> Succs; 858 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { 859 Succs.push_back(TI->getSuccessor(i)); 860 TI->getSuccessor(i)->removePredecessor(BB); 861 } 862 863 // Unique the successors, remove anything with multiple uses. 864 std::sort(Succs.begin(), Succs.end()); 865 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end()); 866 867 // Remove the basic block, including all of the instructions contained in it. 868 BB->eraseFromParent(); 869 870 // Remove successor blocks here that are not dead, so that we know we only 871 // have dead blocks in this list. Nondead blocks have a way of becoming dead, 872 // then getting removed before we revisit them, which is badness. 873 // 874 for (unsigned i = 0; i != Succs.size(); ++i) 875 if (pred_begin(Succs[i]) != pred_end(Succs[i])) { 876 // One exception is loop headers. If this block was the preheader for a 877 // loop, then we DO want to visit the loop so the loop gets deleted. 878 // We know that if the successor is a loop header, that this loop had to 879 // be the preheader: the case where this was the latch block was handled 880 // above and headers can only have two predecessors. 881 if (!LI->isLoopHeader(Succs[i])) { 882 Succs.erase(Succs.begin()+i); 883 --i; 884 } 885 } 886 887 for (unsigned i = 0, e = Succs.size(); i != e; ++i) 888 RemoveBlockIfDead(Succs[i], Worklist); 889} 890 891/// RemoveLoopFromHierarchy - We have discovered that the specified loop has 892/// become unwrapped, either because the backedge was deleted, or because the 893/// edge into the header was removed. If the edge into the header from the 894/// latch block was removed, the loop is unwrapped but subloops are still alive, 895/// so they just reparent loops. If the loops are actually dead, they will be 896/// removed later. 897void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) { 898 LPM->deleteLoopFromQueue(L); 899 RemoveLoopFromWorklist(L); 900} 901 902 903 904// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has 905// the value specified by Val in the specified loop, or we know it does NOT have 906// that value. Rewrite any uses of LIC or of properties correlated to it. 907void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, 908 Constant *Val, 909 bool IsEqual) { 910 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?"); 911 912 // FIXME: Support correlated properties, like: 913 // for (...) 914 // if (li1 < li2) 915 // ... 916 // if (li1 > li2) 917 // ... 918 919 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches, 920 // selects, switches. 921 std::vector<User*> Users(LIC->use_begin(), LIC->use_end()); 922 std::vector<Instruction*> Worklist; 923 924 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC 925 // in the loop with the appropriate one directly. 926 if (IsEqual || (isa<ConstantInt>(Val) && Val->getType() == Type::Int1Ty)) { 927 Value *Replacement; 928 if (IsEqual) 929 Replacement = Val; 930 else 931 Replacement = ConstantInt::get(Type::Int1Ty, 932 !cast<ConstantInt>(Val)->getZExtValue()); 933 934 for (unsigned i = 0, e = Users.size(); i != e; ++i) 935 if (Instruction *U = cast<Instruction>(Users[i])) { 936 if (!L->contains(U->getParent())) 937 continue; 938 U->replaceUsesOfWith(LIC, Replacement); 939 Worklist.push_back(U); 940 } 941 } else { 942 // Otherwise, we don't know the precise value of LIC, but we do know that it 943 // is certainly NOT "Val". As such, simplify any uses in the loop that we 944 // can. This case occurs when we unswitch switch statements. 945 for (unsigned i = 0, e = Users.size(); i != e; ++i) 946 if (Instruction *U = cast<Instruction>(Users[i])) { 947 if (!L->contains(U->getParent())) 948 continue; 949 950 Worklist.push_back(U); 951 952 // If we know that LIC is not Val, use this info to simplify code. 953 if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) { 954 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) { 955 if (SI->getCaseValue(i) == Val) { 956 // Found a dead case value. Don't remove PHI nodes in the 957 // successor if they become single-entry, those PHI nodes may 958 // be in the Users list. 959 960 // FIXME: This is a hack. We need to keep the successor around 961 // and hooked up so as to preserve the loop structure, because 962 // trying to update it is complicated. So instead we preserve the 963 // loop structure and put the block on an dead code path. 964 965 BasicBlock* Old = SI->getParent(); 966 BasicBlock* Split = SplitBlock(Old, SI, this); 967 968 Instruction* OldTerm = Old->getTerminator(); 969 new BranchInst(Split, SI->getSuccessor(i), 970 ConstantInt::getTrue(), OldTerm); 971 972 Old->getTerminator()->eraseFromParent(); 973 974 975 PHINode *PN; 976 for (BasicBlock::iterator II = SI->getSuccessor(i)->begin(); 977 (PN = dyn_cast<PHINode>(II)); ++II) { 978 Value *InVal = PN->removeIncomingValue(Split, false); 979 PN->addIncoming(InVal, Old); 980 } 981 982 SI->removeCase(i); 983 break; 984 } 985 } 986 } 987 988 // TODO: We could do other simplifications, for example, turning 989 // LIC == Val -> false. 990 } 991 } 992 993 SimplifyCode(Worklist); 994} 995 996/// SimplifyCode - Okay, now that we have simplified some instructions in the 997/// loop, walk over it and constant prop, dce, and fold control flow where 998/// possible. Note that this is effectively a very simple loop-structure-aware 999/// optimizer. During processing of this loop, L could very well be deleted, so 1000/// it must not be used. 1001/// 1002/// FIXME: When the loop optimizer is more mature, separate this out to a new 1003/// pass. 1004/// 1005void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist) { 1006 while (!Worklist.empty()) { 1007 Instruction *I = Worklist.back(); 1008 Worklist.pop_back(); 1009 1010 // Simple constant folding. 1011 if (Constant *C = ConstantFoldInstruction(I)) { 1012 ReplaceUsesOfWith(I, C, Worklist); 1013 continue; 1014 } 1015 1016 // Simple DCE. 1017 if (isInstructionTriviallyDead(I)) { 1018 DOUT << "Remove dead instruction '" << *I; 1019 1020 // Add uses to the worklist, which may be dead now. 1021 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 1022 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i))) 1023 Worklist.push_back(Use); 1024 I->eraseFromParent(); 1025 RemoveFromWorklist(I, Worklist); 1026 ++NumSimplify; 1027 continue; 1028 } 1029 1030 // Special case hacks that appear commonly in unswitched code. 1031 switch (I->getOpcode()) { 1032 case Instruction::Select: 1033 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(0))) { 1034 ReplaceUsesOfWith(I, I->getOperand(!CB->getZExtValue()+1), Worklist); 1035 continue; 1036 } 1037 break; 1038 case Instruction::And: 1039 if (isa<ConstantInt>(I->getOperand(0)) && 1040 I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS 1041 cast<BinaryOperator>(I)->swapOperands(); 1042 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1))) 1043 if (CB->getType() == Type::Int1Ty) { 1044 if (CB->isOne()) // X & 1 -> X 1045 ReplaceUsesOfWith(I, I->getOperand(0), Worklist); 1046 else // X & 0 -> 0 1047 ReplaceUsesOfWith(I, I->getOperand(1), Worklist); 1048 continue; 1049 } 1050 break; 1051 case Instruction::Or: 1052 if (isa<ConstantInt>(I->getOperand(0)) && 1053 I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS 1054 cast<BinaryOperator>(I)->swapOperands(); 1055 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1))) 1056 if (CB->getType() == Type::Int1Ty) { 1057 if (CB->isOne()) // X | 1 -> 1 1058 ReplaceUsesOfWith(I, I->getOperand(1), Worklist); 1059 else // X | 0 -> X 1060 ReplaceUsesOfWith(I, I->getOperand(0), Worklist); 1061 continue; 1062 } 1063 break; 1064 case Instruction::Br: { 1065 BranchInst *BI = cast<BranchInst>(I); 1066 if (BI->isUnconditional()) { 1067 // If BI's parent is the only pred of the successor, fold the two blocks 1068 // together. 1069 BasicBlock *Pred = BI->getParent(); 1070 BasicBlock *Succ = BI->getSuccessor(0); 1071 BasicBlock *SinglePred = Succ->getSinglePredecessor(); 1072 if (!SinglePred) continue; // Nothing to do. 1073 assert(SinglePred == Pred && "CFG broken"); 1074 1075 DOUT << "Merging blocks: " << Pred->getName() << " <- " 1076 << Succ->getName() << "\n"; 1077 1078 // Resolve any single entry PHI nodes in Succ. 1079 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin())) 1080 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist); 1081 1082 // Move all of the successor contents from Succ to Pred. 1083 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(), 1084 Succ->end()); 1085 BI->eraseFromParent(); 1086 RemoveFromWorklist(BI, Worklist); 1087 1088 // If Succ has any successors with PHI nodes, update them to have 1089 // entries coming from Pred instead of Succ. 1090 Succ->replaceAllUsesWith(Pred); 1091 1092 // Remove Succ from the loop tree. 1093 LI->removeBlock(Succ); 1094 Succ->eraseFromParent(); 1095 ++NumSimplify; 1096 } else if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){ 1097 // Conditional branch. Turn it into an unconditional branch, then 1098 // remove dead blocks. 1099 break; // FIXME: Enable. 1100 1101 DOUT << "Folded branch: " << *BI; 1102 BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue()); 1103 BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue()); 1104 DeadSucc->removePredecessor(BI->getParent(), true); 1105 Worklist.push_back(new BranchInst(LiveSucc, BI)); 1106 BI->eraseFromParent(); 1107 RemoveFromWorklist(BI, Worklist); 1108 ++NumSimplify; 1109 1110 RemoveBlockIfDead(DeadSucc, Worklist); 1111 } 1112 break; 1113 } 1114 } 1115 } 1116} 1117