LoopUnswitch.cpp revision c2bbfc18e9adbbdcf5b3375d8d25e2452f7df7f1
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 bool redoLoop; 74 public: 75 static char ID; // Pass ID, replacement for typeid 76 explicit LoopUnswitch(bool Os = false) : 77 LoopPass((intptr_t)&ID), OptimizeForSize(Os), redoLoop(false) {} 78 79 bool runOnLoop(Loop *L, LPPassManager &LPM); 80 bool processLoop(Loop *L); 81 82 /// This transformation requires natural loop information & requires that 83 /// loop preheaders be inserted into the CFG... 84 /// 85 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 86 AU.addRequiredID(LoopSimplifyID); 87 AU.addPreservedID(LoopSimplifyID); 88 AU.addRequired<LoopInfo>(); 89 AU.addPreserved<LoopInfo>(); 90 AU.addRequiredID(LCSSAID); 91 AU.addPreservedID(LCSSAID); 92 AU.addPreserved<DominatorTree>(); 93 AU.addPreserved<DominanceFrontier>(); 94 } 95 96 private: 97 98 /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist, 99 /// remove it. 100 void RemoveLoopFromWorklist(Loop *L) { 101 std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(), 102 LoopProcessWorklist.end(), L); 103 if (I != LoopProcessWorklist.end()) 104 LoopProcessWorklist.erase(I); 105 } 106 107 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L); 108 unsigned getLoopUnswitchCost(Loop *L, Value *LIC); 109 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, 110 BasicBlock *ExitBlock); 111 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L); 112 113 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, 114 Constant *Val, bool isEqual); 115 116 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, 117 BasicBlock *TrueDest, 118 BasicBlock *FalseDest, 119 Instruction *InsertPt); 120 121 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L); 122 void RemoveBlockIfDead(BasicBlock *BB, 123 std::vector<Instruction*> &Worklist, Loop *l); 124 void RemoveLoopFromHierarchy(Loop *L); 125 }; 126 char LoopUnswitch::ID = 0; 127 RegisterPass<LoopUnswitch> X("loop-unswitch", "Unswitch loops"); 128} 129 130LoopPass *llvm::createLoopUnswitchPass(bool Os) { 131 return new LoopUnswitch(Os); 132} 133 134/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is 135/// invariant in the loop, or has an invariant piece, return the invariant. 136/// Otherwise, return null. 137static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) { 138 // Constants should be folded, not unswitched on! 139 if (isa<Constant>(Cond)) return false; 140 141 // TODO: Handle: br (VARIANT|INVARIANT). 142 // TODO: Hoist simple expressions out of loops. 143 if (L->isLoopInvariant(Cond)) return Cond; 144 145 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond)) 146 if (BO->getOpcode() == Instruction::And || 147 BO->getOpcode() == Instruction::Or) { 148 // If either the left or right side is invariant, we can unswitch on this, 149 // which will cause the branch to go away in one loop and the condition to 150 // simplify in the other one. 151 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed)) 152 return LHS; 153 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed)) 154 return RHS; 155 } 156 157 return 0; 158} 159 160bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { 161 LI = &getAnalysis<LoopInfo>(); 162 LPM = &LPM_Ref; 163 bool Changed = false; 164 165 do { 166 redoLoop = false; 167 Changed |= processLoop(L); 168 } while(redoLoop); 169 170 return Changed; 171} 172 173/// processLoop - Do actual work and unswitch loop if possible and profitable. 174bool LoopUnswitch::processLoop(Loop *L) { 175 assert(L->isLCSSAForm()); 176 bool Changed = false; 177 178 // Loop over all of the basic blocks in the loop. If we find an interior 179 // block that is branching on a loop-invariant condition, we can unswitch this 180 // loop. 181 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 182 I != E; ++I) { 183 TerminatorInst *TI = (*I)->getTerminator(); 184 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 185 // If this isn't branching on an invariant condition, we can't unswitch 186 // it. 187 if (BI->isConditional()) { 188 // See if this, or some part of it, is loop invariant. If so, we can 189 // unswitch on it if we desire. 190 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed); 191 if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(), 192 L)) { 193 ++NumBranches; 194 return true; 195 } 196 } 197 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 198 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed); 199 if (LoopCond && SI->getNumCases() > 1) { 200 // Find a value to unswitch on: 201 // FIXME: this should chose the most expensive case! 202 Constant *UnswitchVal = SI->getCaseValue(1); 203 // Do not process same value again and again. 204 if (!UnswitchedVals.insert(UnswitchVal)) 205 continue; 206 207 if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) { 208 ++NumSwitches; 209 return true; 210 } 211 } 212 } 213 214 // Scan the instructions to check for unswitchable values. 215 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end(); 216 BBI != E; ++BBI) 217 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) { 218 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed); 219 if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(), 220 L)) { 221 ++NumSelects; 222 return true; 223 } 224 } 225 } 226 227 assert(L->isLCSSAForm()); 228 229 return Changed; 230} 231 232/// isTrivialLoopExitBlock - Check to see if all paths from BB either: 233/// 1. Exit the loop with no side effects. 234/// 2. Branch to the latch block with no side-effects. 235/// 236/// If these conditions are true, we return true and set ExitBB to the block we 237/// exit through. 238/// 239static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB, 240 BasicBlock *&ExitBB, 241 std::set<BasicBlock*> &Visited) { 242 if (!Visited.insert(BB).second) { 243 // Already visited and Ok, end of recursion. 244 return true; 245 } else if (!L->contains(BB)) { 246 // Otherwise, this is a loop exit, this is fine so long as this is the 247 // first exit. 248 if (ExitBB != 0) return false; 249 ExitBB = BB; 250 return true; 251 } 252 253 // Otherwise, this is an unvisited intra-loop node. Check all successors. 254 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) { 255 // Check to see if the successor is a trivial loop exit. 256 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited)) 257 return false; 258 } 259 260 // Okay, everything after this looks good, check to make sure that this block 261 // doesn't include any side effects. 262 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 263 if (I->mayWriteToMemory()) 264 return false; 265 266 return true; 267} 268 269/// isTrivialLoopExitBlock - Return true if the specified block unconditionally 270/// leads to an exit from the specified loop, and has no side-effects in the 271/// process. If so, return the block that is exited to, otherwise return null. 272static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { 273 std::set<BasicBlock*> Visited; 274 Visited.insert(L->getHeader()); // Branches to header are ok. 275 BasicBlock *ExitBB = 0; 276 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited)) 277 return ExitBB; 278 return 0; 279} 280 281/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is 282/// trivial: that is, that the condition controls whether or not the loop does 283/// anything at all. If this is a trivial condition, unswitching produces no 284/// code duplications (equivalently, it produces a simpler loop and a new empty 285/// loop, which gets deleted). 286/// 287/// If this is a trivial condition, return true, otherwise return false. When 288/// returning true, this sets Cond and Val to the condition that controls the 289/// trivial condition: when Cond dynamically equals Val, the loop is known to 290/// exit. Finally, this sets LoopExit to the BB that the loop exits to when 291/// Cond == Val. 292/// 293static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, Constant **Val = 0, 294 BasicBlock **LoopExit = 0) { 295 BasicBlock *Header = L->getHeader(); 296 TerminatorInst *HeaderTerm = Header->getTerminator(); 297 298 BasicBlock *LoopExitBB = 0; 299 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) { 300 // If the header block doesn't end with a conditional branch on Cond, we 301 // can't handle it. 302 if (!BI->isConditional() || BI->getCondition() != Cond) 303 return false; 304 305 // Check to see if a successor of the branch is guaranteed to go to the 306 // latch block or exit through a one exit block without having any 307 // side-effects. If so, determine the value of Cond that causes it to do 308 // this. 309 if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) { 310 if (Val) *Val = ConstantInt::getTrue(); 311 } else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) { 312 if (Val) *Val = ConstantInt::getFalse(); 313 } 314 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) { 315 // If this isn't a switch on Cond, we can't handle it. 316 if (SI->getCondition() != Cond) return false; 317 318 // Check to see if a successor of the switch is guaranteed to go to the 319 // latch block or exit through a one exit block without having any 320 // side-effects. If so, determine the value of Cond that causes it to do 321 // this. Note that we can't trivially unswitch on the default case. 322 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) 323 if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) { 324 // Okay, we found a trivial case, remember the value that is trivial. 325 if (Val) *Val = SI->getCaseValue(i); 326 break; 327 } 328 } 329 330 // If we didn't find a single unique LoopExit block, or if the loop exit block 331 // contains phi nodes, this isn't trivial. 332 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin())) 333 return false; // Can't handle this. 334 335 if (LoopExit) *LoopExit = LoopExitBB; 336 337 // We already know that nothing uses any scalar values defined inside of this 338 // loop. As such, we just have to check to see if this loop will execute any 339 // side-effecting instructions (e.g. stores, calls, volatile loads) in the 340 // part of the loop that the code *would* execute. We already checked the 341 // tail, check the header now. 342 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I) 343 if (I->mayWriteToMemory()) 344 return false; 345 return true; 346} 347 348/// getLoopUnswitchCost - Return the cost (code size growth) that will happen if 349/// we choose to unswitch the specified loop on the specified value. 350/// 351unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) { 352 // If the condition is trivial, always unswitch. There is no code growth for 353 // this case. 354 if (IsTrivialUnswitchCondition(L, LIC)) 355 return 0; 356 357 // FIXME: This is really overly conservative. However, more liberal 358 // estimations have thus far resulted in excessive unswitching, which is bad 359 // both in compile time and in code size. This should be replaced once 360 // someone figures out how a good estimation. 361 return L->getBlocks().size(); 362 363 unsigned Cost = 0; 364 // FIXME: this is brain dead. It should take into consideration code 365 // shrinkage. 366 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 367 I != E; ++I) { 368 BasicBlock *BB = *I; 369 // Do not include empty blocks in the cost calculation. This happen due to 370 // loop canonicalization and will be removed. 371 if (BB->begin() == BasicBlock::iterator(BB->getTerminator())) 372 continue; 373 374 // Count basic blocks. 375 ++Cost; 376 } 377 378 return Cost; 379} 380 381/// UnswitchIfProfitable - We have found that we can unswitch L when 382/// LoopCond == Val to simplify the loop. If we decide that this is profitable, 383/// unswitch the loop, reprocess the pieces, then return true. 384bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){ 385 // Check to see if it would be profitable to unswitch this loop. 386 unsigned Cost = getLoopUnswitchCost(L, LoopCond); 387 388 // Do not do non-trivial unswitch while optimizing for size. 389 if (Cost && OptimizeForSize) 390 return false; 391 392 if (Cost > Threshold) { 393 // FIXME: this should estimate growth by the amount of code shared by the 394 // resultant unswitched loops. 395 // 396 DOUT << "NOT unswitching loop %" 397 << L->getHeader()->getName() << ", cost too high: " 398 << L->getBlocks().size() << "\n"; 399 return false; 400 } 401 402 // If this is a trivial condition to unswitch (which results in no code 403 // duplication), do it now. 404 Constant *CondVal; 405 BasicBlock *ExitBlock; 406 if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal, &ExitBlock)) { 407 UnswitchTrivialCondition(L, LoopCond, CondVal, ExitBlock); 408 } else { 409 UnswitchNontrivialCondition(LoopCond, Val, L); 410 } 411 412 return true; 413} 414 415// RemapInstruction - Convert the instruction operands from referencing the 416// current values into those specified by ValueMap. 417// 418static inline void RemapInstruction(Instruction *I, 419 DenseMap<const Value *, Value*> &ValueMap) { 420 for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { 421 Value *Op = I->getOperand(op); 422 DenseMap<const Value *, Value*>::iterator It = ValueMap.find(Op); 423 if (It != ValueMap.end()) Op = It->second; 424 I->setOperand(op, Op); 425 } 426} 427 428// CloneDomInfo - NewBB is cloned from Orig basic block. Now clone Dominator Info. 429// 430// If Orig block's immediate dominator is mapped in VM then use corresponding 431// immediate dominator from the map. Otherwise Orig block's dominator is also 432// NewBB's dominator. 433// 434// OrigPreheader is loop pre-header before this pass started 435// updating CFG. NewPrehader is loops new pre-header. However, after CFG 436// manipulation, loop L may not exist. So rely on input parameter NewPreheader. 437void CloneDomInfo(BasicBlock *NewBB, BasicBlock *Orig, 438 BasicBlock *NewPreheader, BasicBlock *OrigPreheader, 439 BasicBlock *OrigHeader, 440 DominatorTree *DT, DominanceFrontier *DF, 441 DenseMap<const Value*, Value*> &VM) { 442 443 // If NewBB alreay has found its place in domiantor tree then no need to do 444 // anything. 445 if (DT->getNode(NewBB)) 446 return; 447 448 // If Orig does not have any immediate domiantor then its clone, NewBB, does 449 // not need any immediate dominator. 450 DomTreeNode *OrigNode = DT->getNode(Orig); 451 if (!OrigNode) 452 return; 453 DomTreeNode *OrigIDomNode = OrigNode->getIDom(); 454 if (!OrigIDomNode) 455 return; 456 457 BasicBlock *OrigIDom = NULL; 458 459 // If Orig is original loop header then its immediate dominator is 460 // NewPreheader. 461 if (Orig == OrigHeader) 462 OrigIDom = NewPreheader; 463 464 // If Orig is new pre-header then its immediate dominator is 465 // original pre-header. 466 else if (Orig == NewPreheader) 467 OrigIDom = OrigPreheader; 468 469 // Other as DT to find Orig's immediate dominator. 470 else 471 OrigIDom = OrigIDomNode->getBlock(); 472 473 // Initially use Orig's immediate dominator as NewBB's immediate dominator. 474 BasicBlock *NewIDom = OrigIDom; 475 DenseMap<const Value*, Value*>::iterator I = VM.find(OrigIDom); 476 if (I != VM.end()) { 477 NewIDom = cast<BasicBlock>(I->second); 478 479 // If NewIDom does not have corresponding dominatore tree node then 480 // get one. 481 if (!DT->getNode(NewIDom)) 482 CloneDomInfo(NewIDom, OrigIDom, NewPreheader, OrigPreheader, 483 OrigHeader, DT, DF, VM); 484 } 485 486 DT->addNewBlock(NewBB, NewIDom); 487 488 // Copy cloned dominance frontiner set 489 DominanceFrontier::DomSetType NewDFSet; 490 if (DF) { 491 DominanceFrontier::iterator DFI = DF->find(Orig); 492 if ( DFI != DF->end()) { 493 DominanceFrontier::DomSetType S = DFI->second; 494 for (DominanceFrontier::DomSetType::iterator I = S.begin(), E = S.end(); 495 I != E; ++I) { 496 BasicBlock *BB = *I; 497 DenseMap<const Value*, Value*>::iterator IDM = VM.find(BB); 498 if (IDM != VM.end()) 499 NewDFSet.insert(cast<BasicBlock>(IDM->second)); 500 else 501 NewDFSet.insert(BB); 502 } 503 } 504 DF->addBasicBlock(NewBB, NewDFSet); 505 } 506} 507 508/// CloneLoop - Recursively clone the specified loop and all of its children, 509/// mapping the blocks with the specified map. 510static Loop *CloneLoop(Loop *L, Loop *PL, DenseMap<const Value*, Value*> &VM, 511 LoopInfo *LI, LPPassManager *LPM) { 512 Loop *New = new Loop(); 513 514 LPM->insertLoop(New, PL); 515 516 // Add all of the blocks in L to the new loop. 517 for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 518 I != E; ++I) 519 if (LI->getLoopFor(*I) == L) 520 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI); 521 522 // Add all of the subloops to the new loop. 523 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) 524 CloneLoop(*I, New, VM, LI, LPM); 525 526 return New; 527} 528 529/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values 530/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the 531/// code immediately before InsertPt. 532void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, 533 BasicBlock *TrueDest, 534 BasicBlock *FalseDest, 535 Instruction *InsertPt) { 536 // Insert a conditional branch on LIC to the two preheaders. The original 537 // code is the true version and the new code is the false version. 538 Value *BranchVal = LIC; 539 if (!isa<ConstantInt>(Val) || Val->getType() != Type::Int1Ty) 540 BranchVal = new ICmpInst(ICmpInst::ICMP_EQ, LIC, Val, "tmp", InsertPt); 541 else if (Val != ConstantInt::getTrue()) 542 // We want to enter the new loop when the condition is true. 543 std::swap(TrueDest, FalseDest); 544 545 // Insert the new branch. 546 BranchInst *BRI = new BranchInst(TrueDest, FalseDest, BranchVal, InsertPt); 547 548 // Update dominator info. 549 // BranchVal is a new preheader so it dominates true and false destination 550 // loop headers. 551 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) { 552 DT->changeImmediateDominator(TrueDest, BRI->getParent()); 553 DT->changeImmediateDominator(FalseDest, BRI->getParent()); 554 } 555 // No need to update DominanceFrontier. BRI->getParent() dominated TrueDest 556 // and FalseDest anyway. Now it immediately dominates them. 557} 558 559 560/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable 561/// condition in it (a cond branch from its header block to its latch block, 562/// where the path through the loop that doesn't execute its body has no 563/// side-effects), unswitch it. This doesn't involve any code duplication, just 564/// moving the conditional branch outside of the loop and updating loop info. 565void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, 566 Constant *Val, 567 BasicBlock *ExitBlock) { 568 DOUT << "loop-unswitch: Trivial-Unswitch loop %" 569 << L->getHeader()->getName() << " [" << L->getBlocks().size() 570 << " blocks] in Function " << L->getHeader()->getParent()->getName() 571 << " on cond: " << *Val << " == " << *Cond << "\n"; 572 573 // First step, split the preheader, so that we know that there is a safe place 574 // to insert the conditional branch. We will change 'OrigPH' to have a 575 // conditional branch on Cond. 576 BasicBlock *OrigPH = L->getLoopPreheader(); 577 BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader(), this); 578 579 // Now that we have a place to insert the conditional branch, create a place 580 // to branch to: this is the exit block out of the loop that we should 581 // short-circuit to. 582 583 // Split this block now, so that the loop maintains its exit block, and so 584 // that the jump from the preheader can execute the contents of the exit block 585 // without actually branching to it (the exit block should be dominated by the 586 // loop header, not the preheader). 587 assert(!L->contains(ExitBlock) && "Exit block is in the loop?"); 588 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this); 589 590 // Okay, now we have a position to branch from and a position to branch to, 591 // insert the new conditional branch. 592 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH, 593 OrigPH->getTerminator()); 594 OrigPH->getTerminator()->eraseFromParent(); 595 LPM->deleteSimpleAnalysisValue(OrigPH->getTerminator(), L); 596 597 // We need to reprocess this loop, it could be unswitched again. 598 redoLoop = true; 599 600 // Now that we know that the loop is never entered when this condition is a 601 // particular value, rewrite the loop with this info. We know that this will 602 // at least eliminate the old branch. 603 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false); 604 ++NumTrivial; 605} 606 607/// VersionLoop - We determined that the loop is profitable to unswitch when LIC 608/// equal Val. Split it into loop versions and test the condition outside of 609/// either loop. Return the loops created as Out1/Out2. 610void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, 611 Loop *L) { 612 Function *F = L->getHeader()->getParent(); 613 DOUT << "loop-unswitch: Unswitching loop %" 614 << L->getHeader()->getName() << " [" << L->getBlocks().size() 615 << " blocks] in Function " << F->getName() 616 << " when '" << *Val << "' == " << *LIC << "\n"; 617 618 // LoopBlocks contains all of the basic blocks of the loop, including the 619 // preheader of the loop, the body of the loop, and the exit blocks of the 620 // loop, in that order. 621 std::vector<BasicBlock*> LoopBlocks; 622 623 // First step, split the preheader and exit blocks, and add these blocks to 624 // the LoopBlocks list. 625 BasicBlock *OrigHeader = L->getHeader(); 626 BasicBlock *OrigPreheader = L->getLoopPreheader(); 627 BasicBlock *NewPreheader = SplitEdge(OrigPreheader, L->getHeader(), this); 628 LoopBlocks.push_back(NewPreheader); 629 630 // We want the loop to come after the preheader, but before the exit blocks. 631 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end()); 632 633 std::vector<BasicBlock*> ExitBlocks; 634 L->getUniqueExitBlocks(ExitBlocks); 635 636 // Split all of the edges from inside the loop to their exit blocks. Update 637 // the appropriate Phi nodes as we do so. 638 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 639 BasicBlock *ExitBlock = ExitBlocks[i]; 640 std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock)); 641 642 for (unsigned j = 0, e = Preds.size(); j != e; ++j) { 643 BasicBlock* MiddleBlock = SplitEdge(Preds[j], ExitBlock, this); 644 BasicBlock* StartBlock = Preds[j]; 645 BasicBlock* EndBlock; 646 if (MiddleBlock->getSinglePredecessor() == ExitBlock) { 647 EndBlock = MiddleBlock; 648 MiddleBlock = EndBlock->getSinglePredecessor();; 649 } else { 650 EndBlock = ExitBlock; 651 } 652 653 std::set<PHINode*> InsertedPHIs; 654 PHINode* OldLCSSA = 0; 655 for (BasicBlock::iterator I = EndBlock->begin(); 656 (OldLCSSA = dyn_cast<PHINode>(I)); ++I) { 657 Value* OldValue = OldLCSSA->getIncomingValueForBlock(MiddleBlock); 658 PHINode* NewLCSSA = new PHINode(OldLCSSA->getType(), 659 OldLCSSA->getName() + ".us-lcssa", 660 MiddleBlock->getTerminator()); 661 NewLCSSA->addIncoming(OldValue, StartBlock); 662 OldLCSSA->setIncomingValue(OldLCSSA->getBasicBlockIndex(MiddleBlock), 663 NewLCSSA); 664 InsertedPHIs.insert(NewLCSSA); 665 } 666 667 BasicBlock::iterator InsertPt = EndBlock->begin(); 668 while (dyn_cast<PHINode>(InsertPt)) ++InsertPt; 669 for (BasicBlock::iterator I = MiddleBlock->begin(); 670 (OldLCSSA = dyn_cast<PHINode>(I)) && InsertedPHIs.count(OldLCSSA) == 0; 671 ++I) { 672 PHINode *NewLCSSA = new PHINode(OldLCSSA->getType(), 673 OldLCSSA->getName() + ".us-lcssa", 674 InsertPt); 675 OldLCSSA->replaceAllUsesWith(NewLCSSA); 676 NewLCSSA->addIncoming(OldLCSSA, MiddleBlock); 677 } 678 } 679 } 680 681 // The exit blocks may have been changed due to edge splitting, recompute. 682 ExitBlocks.clear(); 683 L->getUniqueExitBlocks(ExitBlocks); 684 685 // Add exit blocks to the loop blocks. 686 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end()); 687 688 // Next step, clone all of the basic blocks that make up the loop (including 689 // the loop preheader and exit blocks), keeping track of the mapping between 690 // the instructions and blocks. 691 std::vector<BasicBlock*> NewBlocks; 692 NewBlocks.reserve(LoopBlocks.size()); 693 DenseMap<const Value*, Value*> ValueMap; 694 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { 695 BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F); 696 NewBlocks.push_back(New); 697 ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping. 698 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], New, L); 699 } 700 701 // Update dominator info 702 DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>(); 703 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) 704 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { 705 BasicBlock *LBB = LoopBlocks[i]; 706 BasicBlock *NBB = NewBlocks[i]; 707 CloneDomInfo(NBB, LBB, NewPreheader, OrigPreheader, 708 OrigHeader, DT, DF, ValueMap); 709 } 710 711 // Splice the newly inserted blocks into the function right before the 712 // original preheader. 713 F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(), 714 NewBlocks[0], F->end()); 715 716 // Now we create the new Loop object for the versioned loop. 717 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI, LPM); 718 Loop *ParentLoop = L->getParentLoop(); 719 if (ParentLoop) { 720 // Make sure to add the cloned preheader and exit blocks to the parent loop 721 // as well. 722 ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI); 723 } 724 725 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 726 BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]); 727 // The new exit block should be in the same loop as the old one. 728 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i])) 729 ExitBBLoop->addBasicBlockToLoop(NewExit, *LI); 730 731 assert(NewExit->getTerminator()->getNumSuccessors() == 1 && 732 "Exit block should have been split to have one successor!"); 733 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0); 734 735 // If the successor of the exit block had PHI nodes, add an entry for 736 // NewExit. 737 PHINode *PN; 738 for (BasicBlock::iterator I = ExitSucc->begin(); 739 (PN = dyn_cast<PHINode>(I)); ++I) { 740 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]); 741 DenseMap<const Value *, Value*>::iterator It = ValueMap.find(V); 742 if (It != ValueMap.end()) V = It->second; 743 PN->addIncoming(V, NewExit); 744 } 745 } 746 747 // Rewrite the code to refer to itself. 748 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) 749 for (BasicBlock::iterator I = NewBlocks[i]->begin(), 750 E = NewBlocks[i]->end(); I != E; ++I) 751 RemapInstruction(I, ValueMap); 752 753 // Rewrite the original preheader to select between versions of the loop. 754 BranchInst *OldBR = cast<BranchInst>(OrigPreheader->getTerminator()); 755 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] && 756 "Preheader splitting did not work correctly!"); 757 758 // Emit the new branch that selects between the two versions of this loop. 759 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR); 760 OldBR->eraseFromParent(); 761 LPM->deleteSimpleAnalysisValue(OldBR, L); 762 763 LoopProcessWorklist.push_back(NewLoop); 764 redoLoop = true; 765 766 // Now we rewrite the original code to know that the condition is true and the 767 // new code to know that the condition is false. 768 RewriteLoopBodyWithConditionConstant(L , LIC, Val, false); 769 770 // It's possible that simplifying one loop could cause the other to be 771 // deleted. If so, don't simplify it. 772 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop) 773 RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true); 774} 775 776/// RemoveFromWorklist - Remove all instances of I from the worklist vector 777/// specified. 778static void RemoveFromWorklist(Instruction *I, 779 std::vector<Instruction*> &Worklist) { 780 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(), 781 Worklist.end(), I); 782 while (WI != Worklist.end()) { 783 unsigned Offset = WI-Worklist.begin(); 784 Worklist.erase(WI); 785 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I); 786 } 787} 788 789/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the 790/// program, replacing all uses with V and update the worklist. 791static void ReplaceUsesOfWith(Instruction *I, Value *V, 792 std::vector<Instruction*> &Worklist, 793 Loop *L, LPPassManager *LPM) { 794 DOUT << "Replace with '" << *V << "': " << *I; 795 796 // Add uses to the worklist, which may be dead now. 797 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 798 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i))) 799 Worklist.push_back(Use); 800 801 // Add users to the worklist which may be simplified now. 802 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 803 UI != E; ++UI) 804 Worklist.push_back(cast<Instruction>(*UI)); 805 I->replaceAllUsesWith(V); 806 I->eraseFromParent(); 807 LPM->deleteSimpleAnalysisValue(I, L); 808 RemoveFromWorklist(I, Worklist); 809 ++NumSimplify; 810} 811 812/// RemoveBlockIfDead - If the specified block is dead, remove it, update loop 813/// information, and remove any dead successors it has. 814/// 815void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB, 816 std::vector<Instruction*> &Worklist, 817 Loop *L) { 818 if (pred_begin(BB) != pred_end(BB)) { 819 // This block isn't dead, since an edge to BB was just removed, see if there 820 // are any easy simplifications we can do now. 821 if (BasicBlock *Pred = BB->getSinglePredecessor()) { 822 // If it has one pred, fold phi nodes in BB. 823 while (isa<PHINode>(BB->begin())) 824 ReplaceUsesOfWith(BB->begin(), 825 cast<PHINode>(BB->begin())->getIncomingValue(0), 826 Worklist, L, LPM); 827 828 // If this is the header of a loop and the only pred is the latch, we now 829 // have an unreachable loop. 830 if (Loop *L = LI->getLoopFor(BB)) 831 if (L->getHeader() == BB && L->contains(Pred)) { 832 // Remove the branch from the latch to the header block, this makes 833 // the header dead, which will make the latch dead (because the header 834 // dominates the latch). 835 Pred->getTerminator()->eraseFromParent(); 836 LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L); 837 new UnreachableInst(Pred); 838 839 // The loop is now broken, remove it from LI. 840 RemoveLoopFromHierarchy(L); 841 842 // Reprocess the header, which now IS dead. 843 RemoveBlockIfDead(BB, Worklist, L); 844 return; 845 } 846 847 // If pred ends in a uncond branch, add uncond branch to worklist so that 848 // the two blocks will get merged. 849 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) 850 if (BI->isUnconditional()) 851 Worklist.push_back(BI); 852 } 853 return; 854 } 855 856 DOUT << "Nuking dead block: " << *BB; 857 858 // Remove the instructions in the basic block from the worklist. 859 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 860 RemoveFromWorklist(I, Worklist); 861 862 // Anything that uses the instructions in this basic block should have their 863 // uses replaced with undefs. 864 if (!I->use_empty()) 865 I->replaceAllUsesWith(UndefValue::get(I->getType())); 866 } 867 868 // If this is the edge to the header block for a loop, remove the loop and 869 // promote all subloops. 870 if (Loop *BBLoop = LI->getLoopFor(BB)) { 871 if (BBLoop->getLoopLatch() == BB) 872 RemoveLoopFromHierarchy(BBLoop); 873 } 874 875 // Remove the block from the loop info, which removes it from any loops it 876 // was in. 877 LI->removeBlock(BB); 878 879 880 // Remove phi node entries in successors for this block. 881 TerminatorInst *TI = BB->getTerminator(); 882 std::vector<BasicBlock*> Succs; 883 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { 884 Succs.push_back(TI->getSuccessor(i)); 885 TI->getSuccessor(i)->removePredecessor(BB); 886 } 887 888 // Unique the successors, remove anything with multiple uses. 889 std::sort(Succs.begin(), Succs.end()); 890 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end()); 891 892 // Remove the basic block, including all of the instructions contained in it. 893 BB->eraseFromParent(); 894 LPM->deleteSimpleAnalysisValue(BB, L); 895 // Remove successor blocks here that are not dead, so that we know we only 896 // have dead blocks in this list. Nondead blocks have a way of becoming dead, 897 // then getting removed before we revisit them, which is badness. 898 // 899 for (unsigned i = 0; i != Succs.size(); ++i) 900 if (pred_begin(Succs[i]) != pred_end(Succs[i])) { 901 // One exception is loop headers. If this block was the preheader for a 902 // loop, then we DO want to visit the loop so the loop gets deleted. 903 // We know that if the successor is a loop header, that this loop had to 904 // be the preheader: the case where this was the latch block was handled 905 // above and headers can only have two predecessors. 906 if (!LI->isLoopHeader(Succs[i])) { 907 Succs.erase(Succs.begin()+i); 908 --i; 909 } 910 } 911 912 for (unsigned i = 0, e = Succs.size(); i != e; ++i) 913 RemoveBlockIfDead(Succs[i], Worklist, L); 914} 915 916/// RemoveLoopFromHierarchy - We have discovered that the specified loop has 917/// become unwrapped, either because the backedge was deleted, or because the 918/// edge into the header was removed. If the edge into the header from the 919/// latch block was removed, the loop is unwrapped but subloops are still alive, 920/// so they just reparent loops. If the loops are actually dead, they will be 921/// removed later. 922void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) { 923 LPM->deleteLoopFromQueue(L); 924 RemoveLoopFromWorklist(L); 925} 926 927 928 929// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has 930// the value specified by Val in the specified loop, or we know it does NOT have 931// that value. Rewrite any uses of LIC or of properties correlated to it. 932void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, 933 Constant *Val, 934 bool IsEqual) { 935 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?"); 936 937 // FIXME: Support correlated properties, like: 938 // for (...) 939 // if (li1 < li2) 940 // ... 941 // if (li1 > li2) 942 // ... 943 944 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches, 945 // selects, switches. 946 std::vector<User*> Users(LIC->use_begin(), LIC->use_end()); 947 std::vector<Instruction*> Worklist; 948 949 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC 950 // in the loop with the appropriate one directly. 951 if (IsEqual || (isa<ConstantInt>(Val) && Val->getType() == Type::Int1Ty)) { 952 Value *Replacement; 953 if (IsEqual) 954 Replacement = Val; 955 else 956 Replacement = ConstantInt::get(Type::Int1Ty, 957 !cast<ConstantInt>(Val)->getZExtValue()); 958 959 for (unsigned i = 0, e = Users.size(); i != e; ++i) 960 if (Instruction *U = cast<Instruction>(Users[i])) { 961 if (!L->contains(U->getParent())) 962 continue; 963 U->replaceUsesOfWith(LIC, Replacement); 964 Worklist.push_back(U); 965 } 966 } else { 967 // Otherwise, we don't know the precise value of LIC, but we do know that it 968 // is certainly NOT "Val". As such, simplify any uses in the loop that we 969 // can. This case occurs when we unswitch switch statements. 970 for (unsigned i = 0, e = Users.size(); i != e; ++i) 971 if (Instruction *U = cast<Instruction>(Users[i])) { 972 if (!L->contains(U->getParent())) 973 continue; 974 975 Worklist.push_back(U); 976 977 // If we know that LIC is not Val, use this info to simplify code. 978 if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) { 979 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) { 980 if (SI->getCaseValue(i) == Val) { 981 // Found a dead case value. Don't remove PHI nodes in the 982 // successor if they become single-entry, those PHI nodes may 983 // be in the Users list. 984 985 // FIXME: This is a hack. We need to keep the successor around 986 // and hooked up so as to preserve the loop structure, because 987 // trying to update it is complicated. So instead we preserve the 988 // loop structure and put the block on an dead code path. 989 990 BasicBlock* Old = SI->getParent(); 991 BasicBlock* Split = SplitBlock(Old, SI, this); 992 993 Instruction* OldTerm = Old->getTerminator(); 994 new BranchInst(Split, SI->getSuccessor(i), 995 ConstantInt::getTrue(), OldTerm); 996 997 Old->getTerminator()->eraseFromParent(); 998 999 1000 PHINode *PN; 1001 for (BasicBlock::iterator II = SI->getSuccessor(i)->begin(); 1002 (PN = dyn_cast<PHINode>(II)); ++II) { 1003 Value *InVal = PN->removeIncomingValue(Split, false); 1004 PN->addIncoming(InVal, Old); 1005 } 1006 1007 SI->removeCase(i); 1008 break; 1009 } 1010 } 1011 } 1012 1013 // TODO: We could do other simplifications, for example, turning 1014 // LIC == Val -> false. 1015 } 1016 } 1017 1018 SimplifyCode(Worklist, L); 1019} 1020 1021/// SimplifyCode - Okay, now that we have simplified some instructions in the 1022/// loop, walk over it and constant prop, dce, and fold control flow where 1023/// possible. Note that this is effectively a very simple loop-structure-aware 1024/// optimizer. During processing of this loop, L could very well be deleted, so 1025/// it must not be used. 1026/// 1027/// FIXME: When the loop optimizer is more mature, separate this out to a new 1028/// pass. 1029/// 1030void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) { 1031 while (!Worklist.empty()) { 1032 Instruction *I = Worklist.back(); 1033 Worklist.pop_back(); 1034 1035 // Simple constant folding. 1036 if (Constant *C = ConstantFoldInstruction(I)) { 1037 ReplaceUsesOfWith(I, C, Worklist, L, LPM); 1038 continue; 1039 } 1040 1041 // Simple DCE. 1042 if (isInstructionTriviallyDead(I)) { 1043 DOUT << "Remove dead instruction '" << *I; 1044 1045 // Add uses to the worklist, which may be dead now. 1046 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 1047 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i))) 1048 Worklist.push_back(Use); 1049 I->eraseFromParent(); 1050 LPM->deleteSimpleAnalysisValue(I, L); 1051 RemoveFromWorklist(I, Worklist); 1052 ++NumSimplify; 1053 continue; 1054 } 1055 1056 // Special case hacks that appear commonly in unswitched code. 1057 switch (I->getOpcode()) { 1058 case Instruction::Select: 1059 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(0))) { 1060 ReplaceUsesOfWith(I, I->getOperand(!CB->getZExtValue()+1), Worklist, L, LPM); 1061 continue; 1062 } 1063 break; 1064 case Instruction::And: 1065 if (isa<ConstantInt>(I->getOperand(0)) && 1066 I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS 1067 cast<BinaryOperator>(I)->swapOperands(); 1068 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1))) 1069 if (CB->getType() == Type::Int1Ty) { 1070 if (CB->isOne()) // X & 1 -> X 1071 ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM); 1072 else // X & 0 -> 0 1073 ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM); 1074 continue; 1075 } 1076 break; 1077 case Instruction::Or: 1078 if (isa<ConstantInt>(I->getOperand(0)) && 1079 I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS 1080 cast<BinaryOperator>(I)->swapOperands(); 1081 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1))) 1082 if (CB->getType() == Type::Int1Ty) { 1083 if (CB->isOne()) // X | 1 -> 1 1084 ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM); 1085 else // X | 0 -> X 1086 ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM); 1087 continue; 1088 } 1089 break; 1090 case Instruction::Br: { 1091 BranchInst *BI = cast<BranchInst>(I); 1092 if (BI->isUnconditional()) { 1093 // If BI's parent is the only pred of the successor, fold the two blocks 1094 // together. 1095 BasicBlock *Pred = BI->getParent(); 1096 BasicBlock *Succ = BI->getSuccessor(0); 1097 BasicBlock *SinglePred = Succ->getSinglePredecessor(); 1098 if (!SinglePred) continue; // Nothing to do. 1099 assert(SinglePred == Pred && "CFG broken"); 1100 1101 DOUT << "Merging blocks: " << Pred->getName() << " <- " 1102 << Succ->getName() << "\n"; 1103 1104 // Resolve any single entry PHI nodes in Succ. 1105 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin())) 1106 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM); 1107 1108 // Move all of the successor contents from Succ to Pred. 1109 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(), 1110 Succ->end()); 1111 BI->eraseFromParent(); 1112 LPM->deleteSimpleAnalysisValue(BI, L); 1113 RemoveFromWorklist(BI, Worklist); 1114 1115 // If Succ has any successors with PHI nodes, update them to have 1116 // entries coming from Pred instead of Succ. 1117 Succ->replaceAllUsesWith(Pred); 1118 1119 // Remove Succ from the loop tree. 1120 LI->removeBlock(Succ); 1121 Succ->eraseFromParent(); 1122 LPM->deleteSimpleAnalysisValue(Succ, L); 1123 ++NumSimplify; 1124 } else if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){ 1125 // Conditional branch. Turn it into an unconditional branch, then 1126 // remove dead blocks. 1127 break; // FIXME: Enable. 1128 1129 DOUT << "Folded branch: " << *BI; 1130 BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue()); 1131 BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue()); 1132 DeadSucc->removePredecessor(BI->getParent(), true); 1133 Worklist.push_back(new BranchInst(LiveSucc, BI)); 1134 BI->eraseFromParent(); 1135 LPM->deleteSimpleAnalysisValue(BI, L); 1136 RemoveFromWorklist(BI, Worklist); 1137 ++NumSimplify; 1138 1139 RemoveBlockIfDead(DeadSucc, Worklist, L); 1140 } 1141 break; 1142 } 1143 } 1144 } 1145} 1146