SimplifyCFG.cpp revision 2d9220e8f5b45390d64e943fa4eef1562b87f04b
1//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===// 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// Peephole optimize the CFG. 11// 12//===----------------------------------------------------------------------===// 13 14#define DEBUG_TYPE "simplifycfg" 15#include "llvm/Transforms/Utils/Local.h" 16#include "llvm/Constants.h" 17#include "llvm/Instructions.h" 18#include "llvm/IntrinsicInst.h" 19#include "llvm/Type.h" 20#include "llvm/DerivedTypes.h" 21#include "llvm/GlobalVariable.h" 22#include "llvm/Support/CFG.h" 23#include "llvm/Support/Debug.h" 24#include "llvm/Support/raw_ostream.h" 25#include "llvm/Analysis/ConstantFolding.h" 26#include "llvm/Target/TargetData.h" 27#include "llvm/Transforms/Utils/BasicBlockUtils.h" 28#include "llvm/ADT/DenseMap.h" 29#include "llvm/ADT/SmallVector.h" 30#include "llvm/ADT/SmallPtrSet.h" 31#include "llvm/ADT/Statistic.h" 32#include "llvm/ADT/STLExtras.h" 33#include <algorithm> 34#include <set> 35#include <map> 36using namespace llvm; 37 38STATISTIC(NumSpeculations, "Number of speculative executed instructions"); 39 40namespace { 41class SimplifyCFGOpt { 42 const TargetData *const TD; 43 44 Value *isValueEqualityComparison(TerminatorInst *TI); 45 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI, 46 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases); 47 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 48 BasicBlock *Pred); 49 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI); 50 51 bool SimplifyReturn(ReturnInst *RI); 52 bool SimplifyUnwind(UnwindInst *UI); 53 bool SimplifyUnreachable(UnreachableInst *UI); 54 bool SimplifySwitch(SwitchInst *SI); 55 bool SimplifyIndirectBr(IndirectBrInst *IBI); 56 bool SimplifyUncondBranch(BranchInst *BI); 57 bool SimplifyCondBranch(BranchInst *BI); 58 59public: 60 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {} 61 bool run(BasicBlock *BB); 62}; 63} 64 65/// SafeToMergeTerminators - Return true if it is safe to merge these two 66/// terminator instructions together. 67/// 68static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) { 69 if (SI1 == SI2) return false; // Can't merge with self! 70 71 // It is not safe to merge these two switch instructions if they have a common 72 // successor, and if that successor has a PHI node, and if *that* PHI node has 73 // conflicting incoming values from the two switch blocks. 74 BasicBlock *SI1BB = SI1->getParent(); 75 BasicBlock *SI2BB = SI2->getParent(); 76 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); 77 78 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) 79 if (SI1Succs.count(*I)) 80 for (BasicBlock::iterator BBI = (*I)->begin(); 81 isa<PHINode>(BBI); ++BBI) { 82 PHINode *PN = cast<PHINode>(BBI); 83 if (PN->getIncomingValueForBlock(SI1BB) != 84 PN->getIncomingValueForBlock(SI2BB)) 85 return false; 86 } 87 88 return true; 89} 90 91/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will 92/// now be entries in it from the 'NewPred' block. The values that will be 93/// flowing into the PHI nodes will be the same as those coming in from 94/// ExistPred, an existing predecessor of Succ. 95static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, 96 BasicBlock *ExistPred) { 97 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) != 98 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!"); 99 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do 100 101 PHINode *PN; 102 for (BasicBlock::iterator I = Succ->begin(); 103 (PN = dyn_cast<PHINode>(I)); ++I) 104 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred); 105} 106 107 108/// GetIfCondition - Given a basic block (BB) with two predecessors (and 109/// presumably PHI nodes in it), check to see if the merge at this block is due 110/// to an "if condition". If so, return the boolean condition that determines 111/// which entry into BB will be taken. Also, return by references the block 112/// that will be entered from if the condition is true, and the block that will 113/// be entered if the condition is false. 114/// 115/// 116static Value *GetIfCondition(BasicBlock *BB, 117 BasicBlock *&IfTrue, BasicBlock *&IfFalse) { 118 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 && 119 "Function can only handle blocks with 2 predecessors!"); 120 BasicBlock *Pred1 = *pred_begin(BB); 121 BasicBlock *Pred2 = *++pred_begin(BB); 122 123 // We can only handle branches. Other control flow will be lowered to 124 // branches if possible anyway. 125 if (!isa<BranchInst>(Pred1->getTerminator()) || 126 !isa<BranchInst>(Pred2->getTerminator())) 127 return 0; 128 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator()); 129 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator()); 130 131 // Eliminate code duplication by ensuring that Pred1Br is conditional if 132 // either are. 133 if (Pred2Br->isConditional()) { 134 // If both branches are conditional, we don't have an "if statement". In 135 // reality, we could transform this case, but since the condition will be 136 // required anyway, we stand no chance of eliminating it, so the xform is 137 // probably not profitable. 138 if (Pred1Br->isConditional()) 139 return 0; 140 141 std::swap(Pred1, Pred2); 142 std::swap(Pred1Br, Pred2Br); 143 } 144 145 if (Pred1Br->isConditional()) { 146 // If we found a conditional branch predecessor, make sure that it branches 147 // to BB and Pred2Br. If it doesn't, this isn't an "if statement". 148 if (Pred1Br->getSuccessor(0) == BB && 149 Pred1Br->getSuccessor(1) == Pred2) { 150 IfTrue = Pred1; 151 IfFalse = Pred2; 152 } else if (Pred1Br->getSuccessor(0) == Pred2 && 153 Pred1Br->getSuccessor(1) == BB) { 154 IfTrue = Pred2; 155 IfFalse = Pred1; 156 } else { 157 // We know that one arm of the conditional goes to BB, so the other must 158 // go somewhere unrelated, and this must not be an "if statement". 159 return 0; 160 } 161 162 // The only thing we have to watch out for here is to make sure that Pred2 163 // doesn't have incoming edges from other blocks. If it does, the condition 164 // doesn't dominate BB. 165 if (++pred_begin(Pred2) != pred_end(Pred2)) 166 return 0; 167 168 return Pred1Br->getCondition(); 169 } 170 171 // Ok, if we got here, both predecessors end with an unconditional branch to 172 // BB. Don't panic! If both blocks only have a single (identical) 173 // predecessor, and THAT is a conditional branch, then we're all ok! 174 if (pred_begin(Pred1) == pred_end(Pred1) || 175 ++pred_begin(Pred1) != pred_end(Pred1) || 176 pred_begin(Pred2) == pred_end(Pred2) || 177 ++pred_begin(Pred2) != pred_end(Pred2) || 178 *pred_begin(Pred1) != *pred_begin(Pred2)) 179 return 0; 180 181 // Otherwise, if this is a conditional branch, then we can use it! 182 BasicBlock *CommonPred = *pred_begin(Pred1); 183 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) { 184 assert(BI->isConditional() && "Two successors but not conditional?"); 185 if (BI->getSuccessor(0) == Pred1) { 186 IfTrue = Pred1; 187 IfFalse = Pred2; 188 } else { 189 IfTrue = Pred2; 190 IfFalse = Pred1; 191 } 192 return BI->getCondition(); 193 } 194 return 0; 195} 196 197/// DominatesMergePoint - If we have a merge point of an "if condition" as 198/// accepted above, return true if the specified value dominates the block. We 199/// don't handle the true generality of domination here, just a special case 200/// which works well enough for us. 201/// 202/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to 203/// see if V (which must be an instruction) is cheap to compute and is 204/// non-trapping. If both are true, the instruction is inserted into the set 205/// and true is returned. 206static bool DominatesMergePoint(Value *V, BasicBlock *BB, 207 std::set<Instruction*> *AggressiveInsts) { 208 Instruction *I = dyn_cast<Instruction>(V); 209 if (!I) { 210 // Non-instructions all dominate instructions, but not all constantexprs 211 // can be executed unconditionally. 212 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V)) 213 if (C->canTrap()) 214 return false; 215 return true; 216 } 217 BasicBlock *PBB = I->getParent(); 218 219 // We don't want to allow weird loops that might have the "if condition" in 220 // the bottom of this block. 221 if (PBB == BB) return false; 222 223 // If this instruction is defined in a block that contains an unconditional 224 // branch to BB, then it must be in the 'conditional' part of the "if 225 // statement". 226 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator())) 227 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) { 228 if (!AggressiveInsts) return false; 229 // Okay, it looks like the instruction IS in the "condition". Check to 230 // see if it's a cheap instruction to unconditionally compute, and if it 231 // only uses stuff defined outside of the condition. If so, hoist it out. 232 if (!I->isSafeToSpeculativelyExecute()) 233 return false; 234 235 switch (I->getOpcode()) { 236 default: return false; // Cannot hoist this out safely. 237 case Instruction::Load: { 238 // We have to check to make sure there are no instructions before the 239 // load in its basic block, as we are going to hoist the loop out to 240 // its predecessor. 241 BasicBlock::iterator IP = PBB->begin(); 242 while (isa<DbgInfoIntrinsic>(IP)) 243 IP++; 244 if (IP != BasicBlock::iterator(I)) 245 return false; 246 break; 247 } 248 case Instruction::Add: 249 case Instruction::Sub: 250 case Instruction::And: 251 case Instruction::Or: 252 case Instruction::Xor: 253 case Instruction::Shl: 254 case Instruction::LShr: 255 case Instruction::AShr: 256 case Instruction::ICmp: 257 break; // These are all cheap and non-trapping instructions. 258 } 259 260 // Okay, we can only really hoist these out if their operands are not 261 // defined in the conditional region. 262 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) 263 if (!DominatesMergePoint(*i, BB, 0)) 264 return false; 265 // Okay, it's safe to do this! Remember this instruction. 266 AggressiveInsts->insert(I); 267 } 268 269 return true; 270} 271 272/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr 273/// and PointerNullValue. Return NULL if value is not a constant int. 274static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) { 275 // Normal constant int. 276 ConstantInt *CI = dyn_cast<ConstantInt>(V); 277 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy()) 278 return CI; 279 280 // This is some kind of pointer constant. Turn it into a pointer-sized 281 // ConstantInt if possible. 282 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext()); 283 284 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*). 285 if (isa<ConstantPointerNull>(V)) 286 return ConstantInt::get(PtrTy, 0); 287 288 // IntToPtr const int. 289 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 290 if (CE->getOpcode() == Instruction::IntToPtr) 291 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) { 292 // The constant is very likely to have the right type already. 293 if (CI->getType() == PtrTy) 294 return CI; 295 else 296 return cast<ConstantInt> 297 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false)); 298 } 299 return 0; 300} 301 302/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together 303/// collection of icmp eq/ne instructions that compare a value against a 304/// constant, return the value being compared, and stick the constant into the 305/// Values vector. 306static Value * 307GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra, 308 const TargetData *TD, bool isEQ) { 309 Instruction *I = dyn_cast<Instruction>(V); 310 if (I == 0) return 0; 311 312 // If this is an icmp against a constant, handle this as one of the cases. 313 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) { 314 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE)) 315 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) { 316 Vals.push_back(C); 317 return I->getOperand(0); 318 } 319 return 0; 320 } 321 322 // Otherwise, we can only handle an | or &, depending on isEQ. 323 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And)) 324 return 0; 325 326 unsigned NumValsBeforeLHS = Vals.size(); 327 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD, 328 isEQ)) { 329 unsigned NumVals = Vals.size(); 330 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, 331 isEQ)) { 332 if (LHS == RHS) 333 return LHS; 334 Vals.resize(NumVals); 335 } 336 337 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet, 338 // set it and return success. 339 if (Extra == 0 || Extra == I->getOperand(1)) { 340 Extra = I->getOperand(1); 341 return LHS; 342 } 343 344 Vals.resize(NumValsBeforeLHS); 345 return 0; 346 } 347 348 // If the LHS can't be folded in, but Extra is available and RHS can, try to 349 // use LHS as Extra. 350 if (Extra == 0 || Extra == I->getOperand(0)) { 351 Value *OldExtra = Extra; 352 Extra = I->getOperand(0); 353 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, 354 isEQ)) 355 return RHS; 356 assert(Vals.size() == NumValsBeforeLHS); 357 Extra = OldExtra; 358 } 359 360 return 0; 361} 362 363static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) { 364 Instruction* Cond = 0; 365 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 366 Cond = dyn_cast<Instruction>(SI->getCondition()); 367 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 368 if (BI->isConditional()) 369 Cond = dyn_cast<Instruction>(BI->getCondition()); 370 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) { 371 Cond = dyn_cast<Instruction>(IBI->getAddress()); 372 } 373 374 TI->eraseFromParent(); 375 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond); 376} 377 378/// isValueEqualityComparison - Return true if the specified terminator checks 379/// to see if a value is equal to constant integer value. 380Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) { 381 Value *CV = 0; 382 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 383 // Do not permit merging of large switch instructions into their 384 // predecessors unless there is only one predecessor. 385 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()), 386 pred_end(SI->getParent())) <= 128) 387 CV = SI->getCondition(); 388 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) 389 if (BI->isConditional() && BI->getCondition()->hasOneUse()) 390 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) 391 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ || 392 ICI->getPredicate() == ICmpInst::ICMP_NE) && 393 GetConstantInt(ICI->getOperand(1), TD)) 394 CV = ICI->getOperand(0); 395 396 // Unwrap any lossless ptrtoint cast. 397 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext())) 398 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) 399 CV = PTII->getOperand(0); 400 return CV; 401} 402 403/// GetValueEqualityComparisonCases - Given a value comparison instruction, 404/// decode all of the 'cases' that it represents and return the 'default' block. 405BasicBlock *SimplifyCFGOpt:: 406GetValueEqualityComparisonCases(TerminatorInst *TI, 407 std::vector<std::pair<ConstantInt*, 408 BasicBlock*> > &Cases) { 409 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 410 Cases.reserve(SI->getNumCases()); 411 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 412 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i))); 413 return SI->getDefaultDest(); 414 } 415 416 BranchInst *BI = cast<BranchInst>(TI); 417 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); 418 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD), 419 BI->getSuccessor(ICI->getPredicate() == 420 ICmpInst::ICMP_NE))); 421 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ); 422} 423 424 425/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries 426/// in the list that match the specified block. 427static void EliminateBlockCases(BasicBlock *BB, 428 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) { 429 for (unsigned i = 0, e = Cases.size(); i != e; ++i) 430 if (Cases[i].second == BB) { 431 Cases.erase(Cases.begin()+i); 432 --i; --e; 433 } 434} 435 436/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as 437/// well. 438static bool 439ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1, 440 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) { 441 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2; 442 443 // Make V1 be smaller than V2. 444 if (V1->size() > V2->size()) 445 std::swap(V1, V2); 446 447 if (V1->size() == 0) return false; 448 if (V1->size() == 1) { 449 // Just scan V2. 450 ConstantInt *TheVal = (*V1)[0].first; 451 for (unsigned i = 0, e = V2->size(); i != e; ++i) 452 if (TheVal == (*V2)[i].first) 453 return true; 454 } 455 456 // Otherwise, just sort both lists and compare element by element. 457 array_pod_sort(V1->begin(), V1->end()); 458 array_pod_sort(V2->begin(), V2->end()); 459 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); 460 while (i1 != e1 && i2 != e2) { 461 if ((*V1)[i1].first == (*V2)[i2].first) 462 return true; 463 if ((*V1)[i1].first < (*V2)[i2].first) 464 ++i1; 465 else 466 ++i2; 467 } 468 return false; 469} 470 471/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a 472/// terminator instruction and its block is known to only have a single 473/// predecessor block, check to see if that predecessor is also a value 474/// comparison with the same value, and if that comparison determines the 475/// outcome of this comparison. If so, simplify TI. This does a very limited 476/// form of jump threading. 477bool SimplifyCFGOpt:: 478SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 479 BasicBlock *Pred) { 480 Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); 481 if (!PredVal) return false; // Not a value comparison in predecessor. 482 483 Value *ThisVal = isValueEqualityComparison(TI); 484 assert(ThisVal && "This isn't a value comparison!!"); 485 if (ThisVal != PredVal) return false; // Different predicates. 486 487 // Find out information about when control will move from Pred to TI's block. 488 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; 489 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), 490 PredCases); 491 EliminateBlockCases(PredDef, PredCases); // Remove default from cases. 492 493 // Find information about how control leaves this block. 494 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases; 495 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); 496 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. 497 498 // If TI's block is the default block from Pred's comparison, potentially 499 // simplify TI based on this knowledge. 500 if (PredDef == TI->getParent()) { 501 // If we are here, we know that the value is none of those cases listed in 502 // PredCases. If there are any cases in ThisCases that are in PredCases, we 503 // can simplify TI. 504 if (!ValuesOverlap(PredCases, ThisCases)) 505 return false; 506 507 if (isa<BranchInst>(TI)) { 508 // Okay, one of the successors of this condbr is dead. Convert it to a 509 // uncond br. 510 assert(ThisCases.size() == 1 && "Branch can only have one case!"); 511 // Insert the new branch. 512 Instruction *NI = BranchInst::Create(ThisDef, TI); 513 (void) NI; 514 515 // Remove PHI node entries for the dead edge. 516 ThisCases[0].second->removePredecessor(TI->getParent()); 517 518 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 519 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 520 521 EraseTerminatorInstAndDCECond(TI); 522 return true; 523 } 524 525 SwitchInst *SI = cast<SwitchInst>(TI); 526 // Okay, TI has cases that are statically dead, prune them away. 527 SmallPtrSet<Constant*, 16> DeadCases; 528 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 529 DeadCases.insert(PredCases[i].first); 530 531 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 532 << "Through successor TI: " << *TI); 533 534 for (unsigned i = SI->getNumCases()-1; i != 0; --i) 535 if (DeadCases.count(SI->getCaseValue(i))) { 536 SI->getSuccessor(i)->removePredecessor(TI->getParent()); 537 SI->removeCase(i); 538 } 539 540 DEBUG(dbgs() << "Leaving: " << *TI << "\n"); 541 return true; 542 } 543 544 // Otherwise, TI's block must correspond to some matched value. Find out 545 // which value (or set of values) this is. 546 ConstantInt *TIV = 0; 547 BasicBlock *TIBB = TI->getParent(); 548 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 549 if (PredCases[i].second == TIBB) { 550 if (TIV != 0) 551 return false; // Cannot handle multiple values coming to this block. 552 TIV = PredCases[i].first; 553 } 554 assert(TIV && "No edge from pred to succ?"); 555 556 // Okay, we found the one constant that our value can be if we get into TI's 557 // BB. Find out which successor will unconditionally be branched to. 558 BasicBlock *TheRealDest = 0; 559 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) 560 if (ThisCases[i].first == TIV) { 561 TheRealDest = ThisCases[i].second; 562 break; 563 } 564 565 // If not handled by any explicit cases, it is handled by the default case. 566 if (TheRealDest == 0) TheRealDest = ThisDef; 567 568 // Remove PHI node entries for dead edges. 569 BasicBlock *CheckEdge = TheRealDest; 570 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI) 571 if (*SI != CheckEdge) 572 (*SI)->removePredecessor(TIBB); 573 else 574 CheckEdge = 0; 575 576 // Insert the new branch. 577 Instruction *NI = BranchInst::Create(TheRealDest, TI); 578 (void) NI; 579 580 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 581 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 582 583 EraseTerminatorInstAndDCECond(TI); 584 return true; 585} 586 587namespace { 588 /// ConstantIntOrdering - This class implements a stable ordering of constant 589 /// integers that does not depend on their address. This is important for 590 /// applications that sort ConstantInt's to ensure uniqueness. 591 struct ConstantIntOrdering { 592 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { 593 return LHS->getValue().ult(RHS->getValue()); 594 } 595 }; 596} 597 598static int ConstantIntSortPredicate(const void *P1, const void *P2) { 599 const ConstantInt *LHS = *(const ConstantInt**)P1; 600 const ConstantInt *RHS = *(const ConstantInt**)P2; 601 return LHS->getValue().ult(RHS->getValue()) ? 1 : -1; 602} 603 604/// FoldValueComparisonIntoPredecessors - The specified terminator is a value 605/// equality comparison instruction (either a switch or a branch on "X == c"). 606/// See if any of the predecessors of the terminator block are value comparisons 607/// on the same value. If so, and if safe to do so, fold them together. 608bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) { 609 BasicBlock *BB = TI->getParent(); 610 Value *CV = isValueEqualityComparison(TI); // CondVal 611 assert(CV && "Not a comparison?"); 612 bool Changed = false; 613 614 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); 615 while (!Preds.empty()) { 616 BasicBlock *Pred = Preds.pop_back_val(); 617 618 // See if the predecessor is a comparison with the same value. 619 TerminatorInst *PTI = Pred->getTerminator(); 620 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal 621 622 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) { 623 // Figure out which 'cases' to copy from SI to PSI. 624 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases; 625 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); 626 627 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; 628 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); 629 630 // Based on whether the default edge from PTI goes to BB or not, fill in 631 // PredCases and PredDefault with the new switch cases we would like to 632 // build. 633 SmallVector<BasicBlock*, 8> NewSuccessors; 634 635 if (PredDefault == BB) { 636 // If this is the default destination from PTI, only the edges in TI 637 // that don't occur in PTI, or that branch to BB will be activated. 638 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 639 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 640 if (PredCases[i].second != BB) 641 PTIHandled.insert(PredCases[i].first); 642 else { 643 // The default destination is BB, we don't need explicit targets. 644 std::swap(PredCases[i], PredCases.back()); 645 PredCases.pop_back(); 646 --i; --e; 647 } 648 649 // Reconstruct the new switch statement we will be building. 650 if (PredDefault != BBDefault) { 651 PredDefault->removePredecessor(Pred); 652 PredDefault = BBDefault; 653 NewSuccessors.push_back(BBDefault); 654 } 655 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 656 if (!PTIHandled.count(BBCases[i].first) && 657 BBCases[i].second != BBDefault) { 658 PredCases.push_back(BBCases[i]); 659 NewSuccessors.push_back(BBCases[i].second); 660 } 661 662 } else { 663 // If this is not the default destination from PSI, only the edges 664 // in SI that occur in PSI with a destination of BB will be 665 // activated. 666 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 667 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 668 if (PredCases[i].second == BB) { 669 PTIHandled.insert(PredCases[i].first); 670 std::swap(PredCases[i], PredCases.back()); 671 PredCases.pop_back(); 672 --i; --e; 673 } 674 675 // Okay, now we know which constants were sent to BB from the 676 // predecessor. Figure out where they will all go now. 677 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 678 if (PTIHandled.count(BBCases[i].first)) { 679 // If this is one we are capable of getting... 680 PredCases.push_back(BBCases[i]); 681 NewSuccessors.push_back(BBCases[i].second); 682 PTIHandled.erase(BBCases[i].first);// This constant is taken care of 683 } 684 685 // If there are any constants vectored to BB that TI doesn't handle, 686 // they must go to the default destination of TI. 687 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I = 688 PTIHandled.begin(), 689 E = PTIHandled.end(); I != E; ++I) { 690 PredCases.push_back(std::make_pair(*I, BBDefault)); 691 NewSuccessors.push_back(BBDefault); 692 } 693 } 694 695 // Okay, at this point, we know which new successor Pred will get. Make 696 // sure we update the number of entries in the PHI nodes for these 697 // successors. 698 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i) 699 AddPredecessorToBlock(NewSuccessors[i], Pred, BB); 700 701 // Convert pointer to int before we switch. 702 if (CV->getType()->isPointerTy()) { 703 assert(TD && "Cannot switch on pointer without TargetData"); 704 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()), 705 "magicptr", PTI); 706 } 707 708 // Now that the successors are updated, create the new Switch instruction. 709 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault, 710 PredCases.size(), PTI); 711 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 712 NewSI->addCase(PredCases[i].first, PredCases[i].second); 713 714 EraseTerminatorInstAndDCECond(PTI); 715 716 // Okay, last check. If BB is still a successor of PSI, then we must 717 // have an infinite loop case. If so, add an infinitely looping block 718 // to handle the case to preserve the behavior of the code. 719 BasicBlock *InfLoopBlock = 0; 720 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) 721 if (NewSI->getSuccessor(i) == BB) { 722 if (InfLoopBlock == 0) { 723 // Insert it at the end of the function, because it's either code, 724 // or it won't matter if it's hot. :) 725 InfLoopBlock = BasicBlock::Create(BB->getContext(), 726 "infloop", BB->getParent()); 727 BranchInst::Create(InfLoopBlock, InfLoopBlock); 728 } 729 NewSI->setSuccessor(i, InfLoopBlock); 730 } 731 732 Changed = true; 733 } 734 } 735 return Changed; 736} 737 738// isSafeToHoistInvoke - If we would need to insert a select that uses the 739// value of this invoke (comments in HoistThenElseCodeToIf explain why we 740// would need to do this), we can't hoist the invoke, as there is nowhere 741// to put the select in this case. 742static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2, 743 Instruction *I1, Instruction *I2) { 744 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 745 PHINode *PN; 746 for (BasicBlock::iterator BBI = SI->begin(); 747 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 748 Value *BB1V = PN->getIncomingValueForBlock(BB1); 749 Value *BB2V = PN->getIncomingValueForBlock(BB2); 750 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) { 751 return false; 752 } 753 } 754 } 755 return true; 756} 757 758/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and 759/// BB2, hoist any common code in the two blocks up into the branch block. The 760/// caller of this function guarantees that BI's block dominates BB1 and BB2. 761static bool HoistThenElseCodeToIf(BranchInst *BI) { 762 // This does very trivial matching, with limited scanning, to find identical 763 // instructions in the two blocks. In particular, we don't want to get into 764 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As 765 // such, we currently just scan for obviously identical instructions in an 766 // identical order. 767 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. 768 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination 769 770 BasicBlock::iterator BB1_Itr = BB1->begin(); 771 BasicBlock::iterator BB2_Itr = BB2->begin(); 772 773 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++; 774 while (isa<DbgInfoIntrinsic>(I1)) 775 I1 = BB1_Itr++; 776 while (isa<DbgInfoIntrinsic>(I2)) 777 I2 = BB2_Itr++; 778 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) || 779 !I1->isIdenticalToWhenDefined(I2) || 780 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))) 781 return false; 782 783 // If we get here, we can hoist at least one instruction. 784 BasicBlock *BIParent = BI->getParent(); 785 786 do { 787 // If we are hoisting the terminator instruction, don't move one (making a 788 // broken BB), instead clone it, and remove BI. 789 if (isa<TerminatorInst>(I1)) 790 goto HoistTerminator; 791 792 // For a normal instruction, we just move one to right before the branch, 793 // then replace all uses of the other with the first. Finally, we remove 794 // the now redundant second instruction. 795 BIParent->getInstList().splice(BI, BB1->getInstList(), I1); 796 if (!I2->use_empty()) 797 I2->replaceAllUsesWith(I1); 798 I1->intersectOptionalDataWith(I2); 799 BB2->getInstList().erase(I2); 800 801 I1 = BB1_Itr++; 802 while (isa<DbgInfoIntrinsic>(I1)) 803 I1 = BB1_Itr++; 804 I2 = BB2_Itr++; 805 while (isa<DbgInfoIntrinsic>(I2)) 806 I2 = BB2_Itr++; 807 } while (I1->getOpcode() == I2->getOpcode() && 808 I1->isIdenticalToWhenDefined(I2)); 809 810 return true; 811 812HoistTerminator: 813 // It may not be possible to hoist an invoke. 814 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) 815 return true; 816 817 // Okay, it is safe to hoist the terminator. 818 Instruction *NT = I1->clone(); 819 BIParent->getInstList().insert(BI, NT); 820 if (!NT->getType()->isVoidTy()) { 821 I1->replaceAllUsesWith(NT); 822 I2->replaceAllUsesWith(NT); 823 NT->takeName(I1); 824 } 825 826 // Hoisting one of the terminators from our successor is a great thing. 827 // Unfortunately, the successors of the if/else blocks may have PHI nodes in 828 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI 829 // nodes, so we insert select instruction to compute the final result. 830 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects; 831 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 832 PHINode *PN; 833 for (BasicBlock::iterator BBI = SI->begin(); 834 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 835 Value *BB1V = PN->getIncomingValueForBlock(BB1); 836 Value *BB2V = PN->getIncomingValueForBlock(BB2); 837 if (BB1V == BB2V) continue; 838 839 // These values do not agree. Insert a select instruction before NT 840 // that determines the right value. 841 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; 842 if (SI == 0) 843 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V, 844 BB1V->getName()+"."+BB2V->getName(), NT); 845 // Make the PHI node use the select for all incoming values for BB1/BB2 846 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 847 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2) 848 PN->setIncomingValue(i, SI); 849 } 850 } 851 852 // Update any PHI nodes in our new successors. 853 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) 854 AddPredecessorToBlock(*SI, BIParent, BB1); 855 856 EraseTerminatorInstAndDCECond(BI); 857 return true; 858} 859 860/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1 861/// and an BB2 and the only successor of BB1 is BB2, hoist simple code 862/// (for now, restricted to a single instruction that's side effect free) from 863/// the BB1 into the branch block to speculatively execute it. 864static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) { 865 // Only speculatively execution a single instruction (not counting the 866 // terminator) for now. 867 Instruction *HInst = NULL; 868 Instruction *Term = BB1->getTerminator(); 869 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); 870 BBI != BBE; ++BBI) { 871 Instruction *I = BBI; 872 // Skip debug info. 873 if (isa<DbgInfoIntrinsic>(I)) continue; 874 if (I == Term) break; 875 876 if (HInst) 877 return false; 878 HInst = I; 879 } 880 if (!HInst) 881 return false; 882 883 // Be conservative for now. FP select instruction can often be expensive. 884 Value *BrCond = BI->getCondition(); 885 if (isa<FCmpInst>(BrCond)) 886 return false; 887 888 // If BB1 is actually on the false edge of the conditional branch, remember 889 // to swap the select operands later. 890 bool Invert = false; 891 if (BB1 != BI->getSuccessor(0)) { 892 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?"); 893 Invert = true; 894 } 895 896 // Turn 897 // BB: 898 // %t1 = icmp 899 // br i1 %t1, label %BB1, label %BB2 900 // BB1: 901 // %t3 = add %t2, c 902 // br label BB2 903 // BB2: 904 // => 905 // BB: 906 // %t1 = icmp 907 // %t4 = add %t2, c 908 // %t3 = select i1 %t1, %t2, %t3 909 switch (HInst->getOpcode()) { 910 default: return false; // Not safe / profitable to hoist. 911 case Instruction::Add: 912 case Instruction::Sub: 913 // Not worth doing for vector ops. 914 if (HInst->getType()->isVectorTy()) 915 return false; 916 break; 917 case Instruction::And: 918 case Instruction::Or: 919 case Instruction::Xor: 920 case Instruction::Shl: 921 case Instruction::LShr: 922 case Instruction::AShr: 923 // Don't mess with vector operations. 924 if (HInst->getType()->isVectorTy()) 925 return false; 926 break; // These are all cheap and non-trapping instructions. 927 } 928 929 // If the instruction is obviously dead, don't try to predicate it. 930 if (HInst->use_empty()) { 931 HInst->eraseFromParent(); 932 return true; 933 } 934 935 // Can we speculatively execute the instruction? And what is the value 936 // if the condition is false? Consider the phi uses, if the incoming value 937 // from the "if" block are all the same V, then V is the value of the 938 // select if the condition is false. 939 BasicBlock *BIParent = BI->getParent(); 940 SmallVector<PHINode*, 4> PHIUses; 941 Value *FalseV = NULL; 942 943 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0); 944 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end(); 945 UI != E; ++UI) { 946 // Ignore any user that is not a PHI node in BB2. These can only occur in 947 // unreachable blocks, because they would not be dominated by the instr. 948 PHINode *PN = dyn_cast<PHINode>(*UI); 949 if (!PN || PN->getParent() != BB2) 950 return false; 951 PHIUses.push_back(PN); 952 953 Value *PHIV = PN->getIncomingValueForBlock(BIParent); 954 if (!FalseV) 955 FalseV = PHIV; 956 else if (FalseV != PHIV) 957 return false; // Inconsistent value when condition is false. 958 } 959 960 assert(FalseV && "Must have at least one user, and it must be a PHI"); 961 962 // Do not hoist the instruction if any of its operands are defined but not 963 // used in this BB. The transformation will prevent the operand from 964 // being sunk into the use block. 965 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end(); 966 i != e; ++i) { 967 Instruction *OpI = dyn_cast<Instruction>(*i); 968 if (OpI && OpI->getParent() == BIParent && 969 !OpI->isUsedInBasicBlock(BIParent)) 970 return false; 971 } 972 973 // If we get here, we can hoist the instruction. Try to place it 974 // before the icmp instruction preceding the conditional branch. 975 BasicBlock::iterator InsertPos = BI; 976 if (InsertPos != BIParent->begin()) 977 --InsertPos; 978 // Skip debug info between condition and branch. 979 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos)) 980 --InsertPos; 981 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) { 982 SmallPtrSet<Instruction *, 4> BB1Insns; 983 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end(); 984 BB1I != BB1E; ++BB1I) 985 BB1Insns.insert(BB1I); 986 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end(); 987 UI != UE; ++UI) { 988 Instruction *Use = cast<Instruction>(*UI); 989 if (!BB1Insns.count(Use)) continue; 990 991 // If BrCond uses the instruction that place it just before 992 // branch instruction. 993 InsertPos = BI; 994 break; 995 } 996 } else 997 InsertPos = BI; 998 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst); 999 1000 // Create a select whose true value is the speculatively executed value and 1001 // false value is the previously determined FalseV. 1002 SelectInst *SI; 1003 if (Invert) 1004 SI = SelectInst::Create(BrCond, FalseV, HInst, 1005 FalseV->getName() + "." + HInst->getName(), BI); 1006 else 1007 SI = SelectInst::Create(BrCond, HInst, FalseV, 1008 HInst->getName() + "." + FalseV->getName(), BI); 1009 1010 // Make the PHI node use the select for all incoming values for "then" and 1011 // "if" blocks. 1012 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) { 1013 PHINode *PN = PHIUses[i]; 1014 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j) 1015 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent) 1016 PN->setIncomingValue(j, SI); 1017 } 1018 1019 ++NumSpeculations; 1020 return true; 1021} 1022 1023/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch 1024/// across this block. 1025static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) { 1026 BranchInst *BI = cast<BranchInst>(BB->getTerminator()); 1027 unsigned Size = 0; 1028 1029 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1030 if (isa<DbgInfoIntrinsic>(BBI)) 1031 continue; 1032 if (Size > 10) return false; // Don't clone large BB's. 1033 ++Size; 1034 1035 // We can only support instructions that do not define values that are 1036 // live outside of the current basic block. 1037 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 1038 UI != E; ++UI) { 1039 Instruction *U = cast<Instruction>(*UI); 1040 if (U->getParent() != BB || isa<PHINode>(U)) return false; 1041 } 1042 1043 // Looks ok, continue checking. 1044 } 1045 1046 return true; 1047} 1048 1049/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value 1050/// that is defined in the same block as the branch and if any PHI entries are 1051/// constants, thread edges corresponding to that entry to be branches to their 1052/// ultimate destination. 1053static bool FoldCondBranchOnPHI(BranchInst *BI) { 1054 BasicBlock *BB = BI->getParent(); 1055 PHINode *PN = dyn_cast<PHINode>(BI->getCondition()); 1056 // NOTE: we currently cannot transform this case if the PHI node is used 1057 // outside of the block. 1058 if (!PN || PN->getParent() != BB || !PN->hasOneUse()) 1059 return false; 1060 1061 // Degenerate case of a single entry PHI. 1062 if (PN->getNumIncomingValues() == 1) { 1063 FoldSingleEntryPHINodes(PN->getParent()); 1064 return true; 1065 } 1066 1067 // Now we know that this block has multiple preds and two succs. 1068 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false; 1069 1070 // Okay, this is a simple enough basic block. See if any phi values are 1071 // constants. 1072 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1073 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i)); 1074 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue; 1075 1076 // Okay, we now know that all edges from PredBB should be revectored to 1077 // branch to RealDest. 1078 BasicBlock *PredBB = PN->getIncomingBlock(i); 1079 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue()); 1080 1081 if (RealDest == BB) continue; // Skip self loops. 1082 1083 // The dest block might have PHI nodes, other predecessors and other 1084 // difficult cases. Instead of being smart about this, just insert a new 1085 // block that jumps to the destination block, effectively splitting 1086 // the edge we are about to create. 1087 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(), 1088 RealDest->getName()+".critedge", 1089 RealDest->getParent(), RealDest); 1090 BranchInst::Create(RealDest, EdgeBB); 1091 PHINode *PN; 1092 for (BasicBlock::iterator BBI = RealDest->begin(); 1093 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 1094 Value *V = PN->getIncomingValueForBlock(BB); 1095 PN->addIncoming(V, EdgeBB); 1096 } 1097 1098 // BB may have instructions that are being threaded over. Clone these 1099 // instructions into EdgeBB. We know that there will be no uses of the 1100 // cloned instructions outside of EdgeBB. 1101 BasicBlock::iterator InsertPt = EdgeBB->begin(); 1102 DenseMap<Value*, Value*> TranslateMap; // Track translated values. 1103 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1104 if (PHINode *PN = dyn_cast<PHINode>(BBI)) { 1105 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB); 1106 continue; 1107 } 1108 // Clone the instruction. 1109 Instruction *N = BBI->clone(); 1110 if (BBI->hasName()) N->setName(BBI->getName()+".c"); 1111 1112 // Update operands due to translation. 1113 for (User::op_iterator i = N->op_begin(), e = N->op_end(); 1114 i != e; ++i) { 1115 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i); 1116 if (PI != TranslateMap.end()) 1117 *i = PI->second; 1118 } 1119 1120 // Check for trivial simplification. 1121 if (Constant *C = ConstantFoldInstruction(N)) { 1122 TranslateMap[BBI] = C; 1123 delete N; // Constant folded away, don't need actual inst 1124 } else { 1125 // Insert the new instruction into its new home. 1126 EdgeBB->getInstList().insert(InsertPt, N); 1127 if (!BBI->use_empty()) 1128 TranslateMap[BBI] = N; 1129 } 1130 } 1131 1132 // Loop over all of the edges from PredBB to BB, changing them to branch 1133 // to EdgeBB instead. 1134 TerminatorInst *PredBBTI = PredBB->getTerminator(); 1135 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i) 1136 if (PredBBTI->getSuccessor(i) == BB) { 1137 BB->removePredecessor(PredBB); 1138 PredBBTI->setSuccessor(i, EdgeBB); 1139 } 1140 1141 // Recurse, simplifying any other constants. 1142 return FoldCondBranchOnPHI(BI) | true; 1143 } 1144 1145 return false; 1146} 1147 1148/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry 1149/// PHI node, see if we can eliminate it. 1150static bool FoldTwoEntryPHINode(PHINode *PN) { 1151 // Ok, this is a two entry PHI node. Check to see if this is a simple "if 1152 // statement", which has a very simple dominance structure. Basically, we 1153 // are trying to find the condition that is being branched on, which 1154 // subsequently causes this merge to happen. We really want control 1155 // dependence information for this check, but simplifycfg can't keep it up 1156 // to date, and this catches most of the cases we care about anyway. 1157 // 1158 BasicBlock *BB = PN->getParent(); 1159 BasicBlock *IfTrue, *IfFalse; 1160 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse); 1161 if (!IfCond) return false; 1162 1163 // Okay, we found that we can merge this two-entry phi node into a select. 1164 // Doing so would require us to fold *all* two entry phi nodes in this block. 1165 // At some point this becomes non-profitable (particularly if the target 1166 // doesn't support cmov's). Only do this transformation if there are two or 1167 // fewer PHI nodes in this block. 1168 unsigned NumPhis = 0; 1169 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I) 1170 if (NumPhis > 2) 1171 return false; 1172 1173 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: " 1174 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"); 1175 1176 // Loop over the PHI's seeing if we can promote them all to select 1177 // instructions. While we are at it, keep track of the instructions 1178 // that need to be moved to the dominating block. 1179 std::set<Instruction*> AggressiveInsts; 1180 1181 BasicBlock::iterator AfterPHIIt = BB->begin(); 1182 while (isa<PHINode>(AfterPHIIt)) { 1183 PHINode *PN = cast<PHINode>(AfterPHIIt++); 1184 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) { 1185 if (PN->getIncomingValue(0) != PN) 1186 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 1187 else 1188 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 1189 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB, 1190 &AggressiveInsts) || 1191 !DominatesMergePoint(PN->getIncomingValue(1), BB, 1192 &AggressiveInsts)) { 1193 return false; 1194 } 1195 } 1196 1197 // If we all PHI nodes are promotable, check to make sure that all 1198 // instructions in the predecessor blocks can be promoted as well. If 1199 // not, we won't be able to get rid of the control flow, so it's not 1200 // worth promoting to select instructions. 1201 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0; 1202 PN = cast<PHINode>(BB->begin()); 1203 BasicBlock *Pred = PN->getIncomingBlock(0); 1204 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) { 1205 IfBlock1 = Pred; 1206 DomBlock = *pred_begin(Pred); 1207 for (BasicBlock::iterator I = Pred->begin(); 1208 !isa<TerminatorInst>(I); ++I) 1209 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1210 // This is not an aggressive instruction that we can promote. 1211 // Because of this, we won't be able to get rid of the control 1212 // flow, so the xform is not worth it. 1213 return false; 1214 } 1215 } 1216 1217 Pred = PN->getIncomingBlock(1); 1218 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) { 1219 IfBlock2 = Pred; 1220 DomBlock = *pred_begin(Pred); 1221 for (BasicBlock::iterator I = Pred->begin(); 1222 !isa<TerminatorInst>(I); ++I) 1223 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1224 // This is not an aggressive instruction that we can promote. 1225 // Because of this, we won't be able to get rid of the control 1226 // flow, so the xform is not worth it. 1227 return false; 1228 } 1229 } 1230 1231 // If we can still promote the PHI nodes after this gauntlet of tests, 1232 // do all of the PHI's now. 1233 1234 // Move all 'aggressive' instructions, which are defined in the 1235 // conditional parts of the if's up to the dominating block. 1236 if (IfBlock1) 1237 DomBlock->getInstList().splice(DomBlock->getTerminator(), 1238 IfBlock1->getInstList(), IfBlock1->begin(), 1239 IfBlock1->getTerminator()); 1240 if (IfBlock2) 1241 DomBlock->getInstList().splice(DomBlock->getTerminator(), 1242 IfBlock2->getInstList(), IfBlock2->begin(), 1243 IfBlock2->getTerminator()); 1244 1245 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 1246 // Change the PHI node into a select instruction. 1247 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); 1248 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); 1249 1250 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt); 1251 PN->replaceAllUsesWith(NV); 1252 NV->takeName(PN); 1253 1254 BB->getInstList().erase(PN); 1255 } 1256 return true; 1257} 1258 1259/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes 1260/// to two returning blocks, try to merge them together into one return, 1261/// introducing a select if the return values disagree. 1262static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) { 1263 assert(BI->isConditional() && "Must be a conditional branch"); 1264 BasicBlock *TrueSucc = BI->getSuccessor(0); 1265 BasicBlock *FalseSucc = BI->getSuccessor(1); 1266 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator()); 1267 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator()); 1268 1269 // Check to ensure both blocks are empty (just a return) or optionally empty 1270 // with PHI nodes. If there are other instructions, merging would cause extra 1271 // computation on one path or the other. 1272 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator()) 1273 return false; 1274 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator()) 1275 return false; 1276 1277 // Okay, we found a branch that is going to two return nodes. If 1278 // there is no return value for this function, just change the 1279 // branch into a return. 1280 if (FalseRet->getNumOperands() == 0) { 1281 TrueSucc->removePredecessor(BI->getParent()); 1282 FalseSucc->removePredecessor(BI->getParent()); 1283 ReturnInst::Create(BI->getContext(), 0, BI); 1284 EraseTerminatorInstAndDCECond(BI); 1285 return true; 1286 } 1287 1288 // Otherwise, figure out what the true and false return values are 1289 // so we can insert a new select instruction. 1290 Value *TrueValue = TrueRet->getReturnValue(); 1291 Value *FalseValue = FalseRet->getReturnValue(); 1292 1293 // Unwrap any PHI nodes in the return blocks. 1294 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue)) 1295 if (TVPN->getParent() == TrueSucc) 1296 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); 1297 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue)) 1298 if (FVPN->getParent() == FalseSucc) 1299 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); 1300 1301 // In order for this transformation to be safe, we must be able to 1302 // unconditionally execute both operands to the return. This is 1303 // normally the case, but we could have a potentially-trapping 1304 // constant expression that prevents this transformation from being 1305 // safe. 1306 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue)) 1307 if (TCV->canTrap()) 1308 return false; 1309 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue)) 1310 if (FCV->canTrap()) 1311 return false; 1312 1313 // Okay, we collected all the mapped values and checked them for sanity, and 1314 // defined to really do this transformation. First, update the CFG. 1315 TrueSucc->removePredecessor(BI->getParent()); 1316 FalseSucc->removePredecessor(BI->getParent()); 1317 1318 // Insert select instructions where needed. 1319 Value *BrCond = BI->getCondition(); 1320 if (TrueValue) { 1321 // Insert a select if the results differ. 1322 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) { 1323 } else if (isa<UndefValue>(TrueValue)) { 1324 TrueValue = FalseValue; 1325 } else { 1326 TrueValue = SelectInst::Create(BrCond, TrueValue, 1327 FalseValue, "retval", BI); 1328 } 1329 } 1330 1331 Value *RI = !TrueValue ? 1332 ReturnInst::Create(BI->getContext(), BI) : 1333 ReturnInst::Create(BI->getContext(), TrueValue, BI); 1334 (void) RI; 1335 1336 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" 1337 << "\n " << *BI << "NewRet = " << *RI 1338 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc); 1339 1340 EraseTerminatorInstAndDCECond(BI); 1341 1342 return true; 1343} 1344 1345/// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch, 1346/// and if a predecessor branches to us and one of our successors, fold the 1347/// setcc into the predecessor and use logical operations to pick the right 1348/// destination. 1349bool llvm::FoldBranchToCommonDest(BranchInst *BI) { 1350 BasicBlock *BB = BI->getParent(); 1351 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 1352 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) || 1353 Cond->getParent() != BB || !Cond->hasOneUse()) 1354 return false; 1355 1356 // Only allow this if the condition is a simple instruction that can be 1357 // executed unconditionally. It must be in the same block as the branch, and 1358 // must be at the front of the block. 1359 BasicBlock::iterator FrontIt = BB->front(); 1360 // Ignore dbg intrinsics. 1361 while (isa<DbgInfoIntrinsic>(FrontIt)) 1362 ++FrontIt; 1363 1364 // Allow a single instruction to be hoisted in addition to the compare 1365 // that feeds the branch. We later ensure that any values that _it_ uses 1366 // were also live in the predecessor, so that we don't unnecessarily create 1367 // register pressure or inhibit out-of-order execution. 1368 Instruction *BonusInst = 0; 1369 if (&*FrontIt != Cond && 1370 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond && 1371 FrontIt->isSafeToSpeculativelyExecute()) { 1372 BonusInst = &*FrontIt; 1373 ++FrontIt; 1374 } 1375 1376 // Only a single bonus inst is allowed. 1377 if (&*FrontIt != Cond) 1378 return false; 1379 1380 // Make sure the instruction after the condition is the cond branch. 1381 BasicBlock::iterator CondIt = Cond; ++CondIt; 1382 // Ingore dbg intrinsics. 1383 while(isa<DbgInfoIntrinsic>(CondIt)) 1384 ++CondIt; 1385 if (&*CondIt != BI) { 1386 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!"); 1387 return false; 1388 } 1389 1390 // Cond is known to be a compare or binary operator. Check to make sure that 1391 // neither operand is a potentially-trapping constant expression. 1392 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0))) 1393 if (CE->canTrap()) 1394 return false; 1395 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1))) 1396 if (CE->canTrap()) 1397 return false; 1398 1399 1400 // Finally, don't infinitely unroll conditional loops. 1401 BasicBlock *TrueDest = BI->getSuccessor(0); 1402 BasicBlock *FalseDest = BI->getSuccessor(1); 1403 if (TrueDest == BB || FalseDest == BB) 1404 return false; 1405 1406 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1407 BasicBlock *PredBlock = *PI; 1408 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); 1409 1410 // Check that we have two conditional branches. If there is a PHI node in 1411 // the common successor, verify that the same value flows in from both 1412 // blocks. 1413 if (PBI == 0 || PBI->isUnconditional() || 1414 !SafeToMergeTerminators(BI, PBI)) 1415 continue; 1416 1417 // Ensure that any values used in the bonus instruction are also used 1418 // by the terminator of the predecessor. This means that those values 1419 // must already have been resolved, so we won't be inhibiting the 1420 // out-of-order core by speculating them earlier. 1421 if (BonusInst) { 1422 // Collect the values used by the bonus inst 1423 SmallPtrSet<Value*, 4> UsedValues; 1424 for (Instruction::op_iterator OI = BonusInst->op_begin(), 1425 OE = BonusInst->op_end(); OI != OE; ++OI) { 1426 Value* V = *OI; 1427 if (!isa<Constant>(V)) 1428 UsedValues.insert(V); 1429 } 1430 1431 SmallVector<std::pair<Value*, unsigned>, 4> Worklist; 1432 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0)); 1433 1434 // Walk up to four levels back up the use-def chain of the predecessor's 1435 // terminator to see if all those values were used. The choice of four 1436 // levels is arbitrary, to provide a compile-time-cost bound. 1437 while (!Worklist.empty()) { 1438 std::pair<Value*, unsigned> Pair = Worklist.back(); 1439 Worklist.pop_back(); 1440 1441 if (Pair.second >= 4) continue; 1442 UsedValues.erase(Pair.first); 1443 if (UsedValues.empty()) break; 1444 1445 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) { 1446 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 1447 OI != OE; ++OI) 1448 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1)); 1449 } 1450 } 1451 1452 if (!UsedValues.empty()) return false; 1453 } 1454 1455 Instruction::BinaryOps Opc; 1456 bool InvertPredCond = false; 1457 1458 if (PBI->getSuccessor(0) == TrueDest) 1459 Opc = Instruction::Or; 1460 else if (PBI->getSuccessor(1) == FalseDest) 1461 Opc = Instruction::And; 1462 else if (PBI->getSuccessor(0) == FalseDest) 1463 Opc = Instruction::And, InvertPredCond = true; 1464 else if (PBI->getSuccessor(1) == TrueDest) 1465 Opc = Instruction::Or, InvertPredCond = true; 1466 else 1467 continue; 1468 1469 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB); 1470 1471 // If we need to invert the condition in the pred block to match, do so now. 1472 if (InvertPredCond) { 1473 Value *NewCond = PBI->getCondition(); 1474 1475 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) { 1476 CmpInst *CI = cast<CmpInst>(NewCond); 1477 CI->setPredicate(CI->getInversePredicate()); 1478 } else { 1479 NewCond = BinaryOperator::CreateNot(NewCond, 1480 PBI->getCondition()->getName()+".not", PBI); 1481 } 1482 1483 PBI->setCondition(NewCond); 1484 BasicBlock *OldTrue = PBI->getSuccessor(0); 1485 BasicBlock *OldFalse = PBI->getSuccessor(1); 1486 PBI->setSuccessor(0, OldFalse); 1487 PBI->setSuccessor(1, OldTrue); 1488 } 1489 1490 // If we have a bonus inst, clone it into the predecessor block. 1491 Instruction *NewBonus = 0; 1492 if (BonusInst) { 1493 NewBonus = BonusInst->clone(); 1494 PredBlock->getInstList().insert(PBI, NewBonus); 1495 NewBonus->takeName(BonusInst); 1496 BonusInst->setName(BonusInst->getName()+".old"); 1497 } 1498 1499 // Clone Cond into the predecessor basic block, and or/and the 1500 // two conditions together. 1501 Instruction *New = Cond->clone(); 1502 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus); 1503 PredBlock->getInstList().insert(PBI, New); 1504 New->takeName(Cond); 1505 Cond->setName(New->getName()+".old"); 1506 1507 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(), 1508 New, "or.cond", PBI); 1509 PBI->setCondition(NewCond); 1510 if (PBI->getSuccessor(0) == BB) { 1511 AddPredecessorToBlock(TrueDest, PredBlock, BB); 1512 PBI->setSuccessor(0, TrueDest); 1513 } 1514 if (PBI->getSuccessor(1) == BB) { 1515 AddPredecessorToBlock(FalseDest, PredBlock, BB); 1516 PBI->setSuccessor(1, FalseDest); 1517 } 1518 return SimplifyCFG(PBI->getParent()) | true; 1519 } 1520 return false; 1521} 1522 1523/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a 1524/// predecessor of another block, this function tries to simplify it. We know 1525/// that PBI and BI are both conditional branches, and BI is in one of the 1526/// successor blocks of PBI - PBI branches to BI. 1527static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) { 1528 assert(PBI->isConditional() && BI->isConditional()); 1529 BasicBlock *BB = BI->getParent(); 1530 1531 // If this block ends with a branch instruction, and if there is a 1532 // predecessor that ends on a branch of the same condition, make 1533 // this conditional branch redundant. 1534 if (PBI->getCondition() == BI->getCondition() && 1535 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 1536 // Okay, the outcome of this conditional branch is statically 1537 // knowable. If this block had a single pred, handle specially. 1538 if (BB->getSinglePredecessor()) { 1539 // Turn this into a branch on constant. 1540 bool CondIsTrue = PBI->getSuccessor(0) == BB; 1541 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 1542 CondIsTrue)); 1543 return true; // Nuke the branch on constant. 1544 } 1545 1546 // Otherwise, if there are multiple predecessors, insert a PHI that merges 1547 // in the constant and simplify the block result. Subsequent passes of 1548 // simplifycfg will thread the block. 1549 if (BlockIsSimpleEnoughToThreadThrough(BB)) { 1550 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()), 1551 BI->getCondition()->getName() + ".pr", 1552 BB->begin()); 1553 // Okay, we're going to insert the PHI node. Since PBI is not the only 1554 // predecessor, compute the PHI'd conditional value for all of the preds. 1555 // Any predecessor where the condition is not computable we keep symbolic. 1556 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1557 BasicBlock *P = *PI; 1558 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && 1559 PBI != BI && PBI->isConditional() && 1560 PBI->getCondition() == BI->getCondition() && 1561 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 1562 bool CondIsTrue = PBI->getSuccessor(0) == BB; 1563 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 1564 CondIsTrue), P); 1565 } else { 1566 NewPN->addIncoming(BI->getCondition(), P); 1567 } 1568 } 1569 1570 BI->setCondition(NewPN); 1571 return true; 1572 } 1573 } 1574 1575 // If this is a conditional branch in an empty block, and if any 1576 // predecessors is a conditional branch to one of our destinations, 1577 // fold the conditions into logical ops and one cond br. 1578 BasicBlock::iterator BBI = BB->begin(); 1579 // Ignore dbg intrinsics. 1580 while (isa<DbgInfoIntrinsic>(BBI)) 1581 ++BBI; 1582 if (&*BBI != BI) 1583 return false; 1584 1585 1586 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition())) 1587 if (CE->canTrap()) 1588 return false; 1589 1590 int PBIOp, BIOp; 1591 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) 1592 PBIOp = BIOp = 0; 1593 else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) 1594 PBIOp = 0, BIOp = 1; 1595 else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) 1596 PBIOp = 1, BIOp = 0; 1597 else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) 1598 PBIOp = BIOp = 1; 1599 else 1600 return false; 1601 1602 // Check to make sure that the other destination of this branch 1603 // isn't BB itself. If so, this is an infinite loop that will 1604 // keep getting unwound. 1605 if (PBI->getSuccessor(PBIOp) == BB) 1606 return false; 1607 1608 // Do not perform this transformation if it would require 1609 // insertion of a large number of select instructions. For targets 1610 // without predication/cmovs, this is a big pessimization. 1611 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); 1612 1613 unsigned NumPhis = 0; 1614 for (BasicBlock::iterator II = CommonDest->begin(); 1615 isa<PHINode>(II); ++II, ++NumPhis) 1616 if (NumPhis > 2) // Disable this xform. 1617 return false; 1618 1619 // Finally, if everything is ok, fold the branches to logical ops. 1620 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); 1621 1622 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent() 1623 << "AND: " << *BI->getParent()); 1624 1625 1626 // If OtherDest *is* BB, then BB is a basic block with a single conditional 1627 // branch in it, where one edge (OtherDest) goes back to itself but the other 1628 // exits. We don't *know* that the program avoids the infinite loop 1629 // (even though that seems likely). If we do this xform naively, we'll end up 1630 // recursively unpeeling the loop. Since we know that (after the xform is 1631 // done) that the block *is* infinite if reached, we just make it an obviously 1632 // infinite loop with no cond branch. 1633 if (OtherDest == BB) { 1634 // Insert it at the end of the function, because it's either code, 1635 // or it won't matter if it's hot. :) 1636 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(), 1637 "infloop", BB->getParent()); 1638 BranchInst::Create(InfLoopBlock, InfLoopBlock); 1639 OtherDest = InfLoopBlock; 1640 } 1641 1642 DEBUG(dbgs() << *PBI->getParent()->getParent()); 1643 1644 // BI may have other predecessors. Because of this, we leave 1645 // it alone, but modify PBI. 1646 1647 // Make sure we get to CommonDest on True&True directions. 1648 Value *PBICond = PBI->getCondition(); 1649 if (PBIOp) 1650 PBICond = BinaryOperator::CreateNot(PBICond, 1651 PBICond->getName()+".not", 1652 PBI); 1653 Value *BICond = BI->getCondition(); 1654 if (BIOp) 1655 BICond = BinaryOperator::CreateNot(BICond, 1656 BICond->getName()+".not", 1657 PBI); 1658 // Merge the conditions. 1659 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI); 1660 1661 // Modify PBI to branch on the new condition to the new dests. 1662 PBI->setCondition(Cond); 1663 PBI->setSuccessor(0, CommonDest); 1664 PBI->setSuccessor(1, OtherDest); 1665 1666 // OtherDest may have phi nodes. If so, add an entry from PBI's 1667 // block that are identical to the entries for BI's block. 1668 PHINode *PN; 1669 for (BasicBlock::iterator II = OtherDest->begin(); 1670 (PN = dyn_cast<PHINode>(II)); ++II) { 1671 Value *V = PN->getIncomingValueForBlock(BB); 1672 PN->addIncoming(V, PBI->getParent()); 1673 } 1674 1675 // We know that the CommonDest already had an edge from PBI to 1676 // it. If it has PHIs though, the PHIs may have different 1677 // entries for BB and PBI's BB. If so, insert a select to make 1678 // them agree. 1679 for (BasicBlock::iterator II = CommonDest->begin(); 1680 (PN = dyn_cast<PHINode>(II)); ++II) { 1681 Value *BIV = PN->getIncomingValueForBlock(BB); 1682 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent()); 1683 Value *PBIV = PN->getIncomingValue(PBBIdx); 1684 if (BIV != PBIV) { 1685 // Insert a select in PBI to pick the right value. 1686 Value *NV = SelectInst::Create(PBICond, PBIV, BIV, 1687 PBIV->getName()+".mux", PBI); 1688 PN->setIncomingValue(PBBIdx, NV); 1689 } 1690 } 1691 1692 DEBUG(dbgs() << "INTO: " << *PBI->getParent()); 1693 DEBUG(dbgs() << *PBI->getParent()->getParent()); 1694 1695 // This basic block is probably dead. We know it has at least 1696 // one fewer predecessor. 1697 return true; 1698} 1699 1700// SimplifyIndirectBrOnSelect - Replaces 1701// (indirectbr (select cond, blockaddress(@fn, BlockA), 1702// blockaddress(@fn, BlockB))) 1703// with 1704// (br cond, BlockA, BlockB). 1705static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) { 1706 // Check that both operands of the select are block addresses. 1707 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue()); 1708 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue()); 1709 if (!TBA || !FBA) 1710 return false; 1711 1712 // Extract the actual blocks. 1713 BasicBlock *TrueBB = TBA->getBasicBlock(); 1714 BasicBlock *FalseBB = FBA->getBasicBlock(); 1715 1716 // Remove any superfluous successor edges from the CFG. 1717 // First, figure out which successors to preserve. 1718 // If TrueBB and FalseBB are equal, only try to preserve one copy of that 1719 // successor. 1720 BasicBlock *KeepEdge1 = TrueBB; 1721 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0; 1722 1723 // Then remove the rest. 1724 for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) { 1725 BasicBlock *Succ = IBI->getSuccessor(I); 1726 // Make sure only to keep exactly one copy of each edge. 1727 if (Succ == KeepEdge1) 1728 KeepEdge1 = 0; 1729 else if (Succ == KeepEdge2) 1730 KeepEdge2 = 0; 1731 else 1732 Succ->removePredecessor(IBI->getParent()); 1733 } 1734 1735 // Insert an appropriate new terminator. 1736 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) { 1737 if (TrueBB == FalseBB) 1738 // We were only looking for one successor, and it was present. 1739 // Create an unconditional branch to it. 1740 BranchInst::Create(TrueBB, IBI); 1741 else 1742 // We found both of the successors we were looking for. 1743 // Create a conditional branch sharing the condition of the select. 1744 BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI); 1745 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) { 1746 // Neither of the selected blocks were successors, so this 1747 // indirectbr must be unreachable. 1748 new UnreachableInst(IBI->getContext(), IBI); 1749 } else { 1750 // One of the selected values was a successor, but the other wasn't. 1751 // Insert an unconditional branch to the one that was found; 1752 // the edge to the one that wasn't must be unreachable. 1753 if (KeepEdge1 == 0) 1754 // Only TrueBB was found. 1755 BranchInst::Create(TrueBB, IBI); 1756 else 1757 // Only FalseBB was found. 1758 BranchInst::Create(FalseBB, IBI); 1759 } 1760 1761 EraseTerminatorInstAndDCECond(IBI); 1762 return true; 1763} 1764 1765/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp 1766/// instruction (a seteq/setne with a constant) as the only instruction in a 1767/// block that ends with an uncond branch. We are looking for a very specific 1768/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In 1769/// this case, we merge the first two "or's of icmp" into a switch, but then the 1770/// default value goes to an uncond block with a seteq in it, we get something 1771/// like: 1772/// 1773/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ] 1774/// DEFAULT: 1775/// %tmp = icmp eq i8 %A, 92 1776/// br label %end 1777/// end: 1778/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ] 1779/// 1780/// We prefer to split the edge to 'end' so that there is a true/false entry to 1781/// the PHI, merging the third icmp into the switch. 1782static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI) { 1783 BasicBlock *BB = ICI->getParent(); 1784 // If the block has any PHIs in it or the icmp has multiple uses, it is too 1785 // complex. 1786 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false; 1787 1788 Value *V = ICI->getOperand(0); 1789 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1)); 1790 1791 // The pattern we're looking for is where our only predecessor is a switch on 1792 // 'V' and this block is the default case for the switch. In this case we can 1793 // fold the compared value into the switch to simplify things. 1794 BasicBlock *Pred = BB->getSinglePredecessor(); 1795 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false; 1796 1797 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator()); 1798 if (SI->getCondition() != V) 1799 return false; 1800 1801 // If BB is reachable on a non-default case, then we simply know the value of 1802 // V in this block. Substitute it and constant fold the icmp instruction 1803 // away. 1804 if (SI->getDefaultDest() != BB) { 1805 ConstantInt *VVal = SI->findCaseDest(BB); 1806 assert(VVal && "Should have a unique destination value"); 1807 ICI->setOperand(0, VVal); 1808 1809 if (Constant *C = ConstantFoldInstruction(ICI)) { 1810 ICI->replaceAllUsesWith(C); 1811 ICI->eraseFromParent(); 1812 } 1813 // BB is now empty, so it is likely to simplify away. 1814 return SimplifyCFG(BB) | true; 1815 } 1816 1817 // Ok, the block is reachable from the default dest. If the constant we're 1818 // comparing exists in one of the other edges, then we can constant fold ICI 1819 // and zap it. 1820 if (SI->findCaseValue(Cst) != 0) { 1821 Value *V; 1822 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 1823 V = ConstantInt::getFalse(BB->getContext()); 1824 else 1825 V = ConstantInt::getTrue(BB->getContext()); 1826 1827 ICI->replaceAllUsesWith(V); 1828 ICI->eraseFromParent(); 1829 // BB is now empty, so it is likely to simplify away. 1830 return SimplifyCFG(BB) | true; 1831 } 1832 1833 // The use of the icmp has to be in the 'end' block, by the only PHI node in 1834 // the block. 1835 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0); 1836 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back()); 1837 if (PHIUse == 0 || PHIUse != &SuccBlock->front() || 1838 isa<PHINode>(++BasicBlock::iterator(PHIUse))) 1839 return false; 1840 1841 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets 1842 // true in the PHI. 1843 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext()); 1844 Constant *NewCst = ConstantInt::getFalse(BB->getContext()); 1845 1846 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 1847 std::swap(DefaultCst, NewCst); 1848 1849 // Replace ICI (which is used by the PHI for the default value) with true or 1850 // false depending on if it is EQ or NE. 1851 ICI->replaceAllUsesWith(DefaultCst); 1852 ICI->eraseFromParent(); 1853 1854 // Okay, the switch goes to this block on a default value. Add an edge from 1855 // the switch to the merge point on the compared value. 1856 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge", 1857 BB->getParent(), BB); 1858 SI->addCase(Cst, NewBB); 1859 1860 // NewBB branches to the phi block, add the uncond branch and the phi entry. 1861 BranchInst::Create(SuccBlock, NewBB); 1862 PHIUse->addIncoming(NewCst, NewBB); 1863 return true; 1864} 1865 1866/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch. 1867/// Check to see if it is branching on an or/and chain of icmp instructions, and 1868/// fold it into a switch instruction if so. 1869static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) { 1870 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 1871 if (Cond == 0) return false; 1872 1873 1874 // Change br (X == 0 | X == 1), T, F into a switch instruction. 1875 // If this is a bunch of seteq's or'd together, or if it's a bunch of 1876 // 'setne's and'ed together, collect them. 1877 Value *CompVal = 0; 1878 std::vector<ConstantInt*> Values; 1879 bool TrueWhenEqual = true; 1880 Value *ExtraCase = 0; 1881 1882 if (Cond->getOpcode() == Instruction::Or) { 1883 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true); 1884 } else if (Cond->getOpcode() == Instruction::And) { 1885 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false); 1886 TrueWhenEqual = false; 1887 } 1888 1889 // If we didn't have a multiply compared value, fail. 1890 if (CompVal == 0) return false; 1891 1892 // There might be duplicate constants in the list, which the switch 1893 // instruction can't handle, remove them now. 1894 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate); 1895 Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); 1896 1897 // If Extra was used, we require at least two switch values to do the 1898 // transformation. A switch with one value is just an cond branch. 1899 if (ExtraCase && Values.size() < 2) return false; 1900 1901 // Figure out which block is which destination. 1902 BasicBlock *DefaultBB = BI->getSuccessor(1); 1903 BasicBlock *EdgeBB = BI->getSuccessor(0); 1904 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); 1905 1906 BasicBlock *BB = BI->getParent(); 1907 1908 // If there are any extra values that couldn't be folded into the switch 1909 // then we evaluate them with an explicit branch first. Split the block 1910 // right before the condbr to handle it. 1911 if (ExtraCase) { 1912 return false; 1913 1914 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test"); 1915 // Remove the uncond branch added to the old block. 1916 TerminatorInst *OldTI = BB->getTerminator(); 1917 1918 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI); 1919 OldTI->eraseFromParent(); 1920 1921 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them 1922 // for the edge we just added. 1923 for (BasicBlock::iterator I = EdgeBB->begin(); isa<PHINode>(I); ++I) { 1924 PHINode *PN = cast<PHINode>(I); 1925 PN->addIncoming(PN->getIncomingValueForBlock(NewBB), BB); 1926 } 1927 BB = NewBB; 1928 } 1929 1930 // Convert pointer to int before we switch. 1931 if (CompVal->getType()->isPointerTy()) { 1932 assert(TD && "Cannot switch on pointer without TargetData"); 1933 CompVal = new PtrToIntInst(CompVal, 1934 TD->getIntPtrType(CompVal->getContext()), 1935 "magicptr", BI); 1936 } 1937 1938 // Create the new switch instruction now. 1939 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI); 1940 1941 // Add all of the 'cases' to the switch instruction. 1942 for (unsigned i = 0, e = Values.size(); i != e; ++i) 1943 New->addCase(Values[i], EdgeBB); 1944 1945 // We added edges from PI to the EdgeBB. As such, if there were any 1946 // PHI nodes in EdgeBB, they need entries to be added corresponding to 1947 // the number of edges added. 1948 for (BasicBlock::iterator BBI = EdgeBB->begin(); 1949 isa<PHINode>(BBI); ++BBI) { 1950 PHINode *PN = cast<PHINode>(BBI); 1951 Value *InVal = PN->getIncomingValueForBlock(BB); 1952 for (unsigned i = 0, e = Values.size()-1; i != e; ++i) 1953 PN->addIncoming(InVal, BB); 1954 } 1955 1956 // Erase the old branch instruction. 1957 EraseTerminatorInstAndDCECond(BI); 1958 return true; 1959} 1960 1961bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) { 1962 BasicBlock *BB = RI->getParent(); 1963 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; 1964 1965 // Find predecessors that end with branches. 1966 SmallVector<BasicBlock*, 8> UncondBranchPreds; 1967 SmallVector<BranchInst*, 8> CondBranchPreds; 1968 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1969 BasicBlock *P = *PI; 1970 TerminatorInst *PTI = P->getTerminator(); 1971 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) { 1972 if (BI->isUnconditional()) 1973 UncondBranchPreds.push_back(P); 1974 else 1975 CondBranchPreds.push_back(BI); 1976 } 1977 } 1978 1979 // If we found some, do the transformation! 1980 if (!UncondBranchPreds.empty()) { 1981 while (!UncondBranchPreds.empty()) { 1982 BasicBlock *Pred = UncondBranchPreds.pop_back_val(); 1983 DEBUG(dbgs() << "FOLDING: " << *BB 1984 << "INTO UNCOND BRANCH PRED: " << *Pred); 1985 Instruction *UncondBranch = Pred->getTerminator(); 1986 // Clone the return and add it to the end of the predecessor. 1987 Instruction *NewRet = RI->clone(); 1988 Pred->getInstList().push_back(NewRet); 1989 1990 // If the return instruction returns a value, and if the value was a 1991 // PHI node in "BB", propagate the right value into the return. 1992 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end(); 1993 i != e; ++i) 1994 if (PHINode *PN = dyn_cast<PHINode>(*i)) 1995 if (PN->getParent() == BB) 1996 *i = PN->getIncomingValueForBlock(Pred); 1997 1998 // Update any PHI nodes in the returning block to realize that we no 1999 // longer branch to them. 2000 BB->removePredecessor(Pred); 2001 Pred->getInstList().erase(UncondBranch); 2002 } 2003 2004 // If we eliminated all predecessors of the block, delete the block now. 2005 if (pred_begin(BB) == pred_end(BB)) 2006 // We know there are no successors, so just nuke the block. 2007 BB->eraseFromParent(); 2008 2009 return true; 2010 } 2011 2012 // Check out all of the conditional branches going to this return 2013 // instruction. If any of them just select between returns, change the 2014 // branch itself into a select/return pair. 2015 while (!CondBranchPreds.empty()) { 2016 BranchInst *BI = CondBranchPreds.pop_back_val(); 2017 2018 // Check to see if the non-BB successor is also a return block. 2019 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) && 2020 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) && 2021 SimplifyCondBranchToTwoReturns(BI)) 2022 return true; 2023 } 2024 return false; 2025} 2026 2027bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) { 2028 // Check to see if the first instruction in this block is just an unwind. 2029 // If so, replace any invoke instructions which use this as an exception 2030 // destination with call instructions. 2031 BasicBlock *BB = UI->getParent(); 2032 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; 2033 2034 bool Changed = false; 2035 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 2036 while (!Preds.empty()) { 2037 BasicBlock *Pred = Preds.back(); 2038 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()); 2039 if (II && II->getUnwindDest() == BB) { 2040 // Insert a new branch instruction before the invoke, because this 2041 // is now a fall through. 2042 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II); 2043 Pred->getInstList().remove(II); // Take out of symbol table 2044 2045 // Insert the call now. 2046 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3); 2047 CallInst *CI = CallInst::Create(II->getCalledValue(), 2048 Args.begin(), Args.end(), 2049 II->getName(), BI); 2050 CI->setCallingConv(II->getCallingConv()); 2051 CI->setAttributes(II->getAttributes()); 2052 // If the invoke produced a value, the Call now does instead. 2053 II->replaceAllUsesWith(CI); 2054 delete II; 2055 Changed = true; 2056 } 2057 2058 Preds.pop_back(); 2059 } 2060 2061 // If this block is now dead (and isn't the entry block), remove it. 2062 if (pred_begin(BB) == pred_end(BB) && 2063 BB != &BB->getParent()->getEntryBlock()) { 2064 // We know there are no successors, so just nuke the block. 2065 BB->eraseFromParent(); 2066 return true; 2067 } 2068 2069 return Changed; 2070} 2071 2072bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) { 2073 BasicBlock *BB = UI->getParent(); 2074 2075 bool Changed = false; 2076 2077 // If there are any instructions immediately before the unreachable that can 2078 // be removed, do so. 2079 while (UI != BB->begin()) { 2080 BasicBlock::iterator BBI = UI; 2081 --BBI; 2082 // Do not delete instructions that can have side effects, like calls 2083 // (which may never return) and volatile loads and stores. 2084 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break; 2085 2086 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) 2087 if (SI->isVolatile()) 2088 break; 2089 2090 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) 2091 if (LI->isVolatile()) 2092 break; 2093 2094 // Delete this instruction 2095 BB->getInstList().erase(BBI); 2096 Changed = true; 2097 } 2098 2099 // If the unreachable instruction is the first in the block, take a gander 2100 // at all of the predecessors of this instruction, and simplify them. 2101 if (&BB->front() != UI) return Changed; 2102 2103 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 2104 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 2105 TerminatorInst *TI = Preds[i]->getTerminator(); 2106 2107 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 2108 if (BI->isUnconditional()) { 2109 if (BI->getSuccessor(0) == BB) { 2110 new UnreachableInst(TI->getContext(), TI); 2111 TI->eraseFromParent(); 2112 Changed = true; 2113 } 2114 } else { 2115 if (BI->getSuccessor(0) == BB) { 2116 BranchInst::Create(BI->getSuccessor(1), BI); 2117 EraseTerminatorInstAndDCECond(BI); 2118 } else if (BI->getSuccessor(1) == BB) { 2119 BranchInst::Create(BI->getSuccessor(0), BI); 2120 EraseTerminatorInstAndDCECond(BI); 2121 Changed = true; 2122 } 2123 } 2124 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 2125 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2126 if (SI->getSuccessor(i) == BB) { 2127 BB->removePredecessor(SI->getParent()); 2128 SI->removeCase(i); 2129 --i; --e; 2130 Changed = true; 2131 } 2132 // If the default value is unreachable, figure out the most popular 2133 // destination and make it the default. 2134 if (SI->getSuccessor(0) == BB) { 2135 std::map<BasicBlock*, unsigned> Popularity; 2136 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2137 Popularity[SI->getSuccessor(i)]++; 2138 2139 // Find the most popular block. 2140 unsigned MaxPop = 0; 2141 BasicBlock *MaxBlock = 0; 2142 for (std::map<BasicBlock*, unsigned>::iterator 2143 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { 2144 if (I->second > MaxPop) { 2145 MaxPop = I->second; 2146 MaxBlock = I->first; 2147 } 2148 } 2149 if (MaxBlock) { 2150 // Make this the new default, allowing us to delete any explicit 2151 // edges to it. 2152 SI->setSuccessor(0, MaxBlock); 2153 Changed = true; 2154 2155 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from 2156 // it. 2157 if (isa<PHINode>(MaxBlock->begin())) 2158 for (unsigned i = 0; i != MaxPop-1; ++i) 2159 MaxBlock->removePredecessor(SI->getParent()); 2160 2161 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2162 if (SI->getSuccessor(i) == MaxBlock) { 2163 SI->removeCase(i); 2164 --i; --e; 2165 } 2166 } 2167 } 2168 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) { 2169 if (II->getUnwindDest() == BB) { 2170 // Convert the invoke to a call instruction. This would be a good 2171 // place to note that the call does not throw though. 2172 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II); 2173 II->removeFromParent(); // Take out of symbol table 2174 2175 // Insert the call now... 2176 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3); 2177 CallInst *CI = CallInst::Create(II->getCalledValue(), 2178 Args.begin(), Args.end(), 2179 II->getName(), BI); 2180 CI->setCallingConv(II->getCallingConv()); 2181 CI->setAttributes(II->getAttributes()); 2182 // If the invoke produced a value, the call does now instead. 2183 II->replaceAllUsesWith(CI); 2184 delete II; 2185 Changed = true; 2186 } 2187 } 2188 } 2189 2190 // If this block is now dead, remove it. 2191 if (pred_begin(BB) == pred_end(BB) && 2192 BB != &BB->getParent()->getEntryBlock()) { 2193 // We know there are no successors, so just nuke the block. 2194 BB->eraseFromParent(); 2195 return true; 2196 } 2197 2198 return Changed; 2199} 2200 2201 2202bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) { 2203 // If this switch is too complex to want to look at, ignore it. 2204 if (!isValueEqualityComparison(SI)) 2205 return false; 2206 2207 BasicBlock *BB = SI->getParent(); 2208 2209 // If we only have one predecessor, and if it is a branch on this value, 2210 // see if that predecessor totally determines the outcome of this switch. 2211 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 2212 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred)) 2213 return SimplifyCFG(BB) | true; 2214 2215 // If the block only contains the switch, see if we can fold the block 2216 // away into any preds. 2217 BasicBlock::iterator BBI = BB->begin(); 2218 // Ignore dbg intrinsics. 2219 while (isa<DbgInfoIntrinsic>(BBI)) 2220 ++BBI; 2221 if (SI == &*BBI) 2222 if (FoldValueComparisonIntoPredecessors(SI)) 2223 return SimplifyCFG(BB) | true; 2224 2225 return false; 2226} 2227 2228bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) { 2229 BasicBlock *BB = IBI->getParent(); 2230 bool Changed = false; 2231 2232 // Eliminate redundant destinations. 2233 SmallPtrSet<Value *, 8> Succs; 2234 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 2235 BasicBlock *Dest = IBI->getDestination(i); 2236 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) { 2237 Dest->removePredecessor(BB); 2238 IBI->removeDestination(i); 2239 --i; --e; 2240 Changed = true; 2241 } 2242 } 2243 2244 if (IBI->getNumDestinations() == 0) { 2245 // If the indirectbr has no successors, change it to unreachable. 2246 new UnreachableInst(IBI->getContext(), IBI); 2247 EraseTerminatorInstAndDCECond(IBI); 2248 return true; 2249 } 2250 2251 if (IBI->getNumDestinations() == 1) { 2252 // If the indirectbr has one successor, change it to a direct branch. 2253 BranchInst::Create(IBI->getDestination(0), IBI); 2254 EraseTerminatorInstAndDCECond(IBI); 2255 return true; 2256 } 2257 2258 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) { 2259 if (SimplifyIndirectBrOnSelect(IBI, SI)) 2260 return SimplifyCFG(BB) | true; 2261 } 2262 return Changed; 2263} 2264 2265bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) { 2266 BasicBlock *BB = BI->getParent(); 2267 2268 // If the Terminator is the only non-phi instruction, simplify the block. 2269 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg(); 2270 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() && 2271 TryToSimplifyUncondBranchFromEmptyBlock(BB)) 2272 return true; 2273 2274 // If the only instruction in the block is a seteq/setne comparison 2275 // against a constant, try to simplify the block. 2276 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) 2277 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) { 2278 for (++I; isa<DbgInfoIntrinsic>(I); ++I) 2279 ; 2280 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI)) 2281 return true; 2282 } 2283 2284 return false; 2285} 2286 2287 2288bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) { 2289 BasicBlock *BB = BI->getParent(); 2290 2291 // Conditional branch 2292 if (isValueEqualityComparison(BI)) { 2293 // If we only have one predecessor, and if it is a branch on this value, 2294 // see if that predecessor totally determines the outcome of this 2295 // switch. 2296 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 2297 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred)) 2298 return SimplifyCFG(BB) | true; 2299 2300 // This block must be empty, except for the setcond inst, if it exists. 2301 // Ignore dbg intrinsics. 2302 BasicBlock::iterator I = BB->begin(); 2303 // Ignore dbg intrinsics. 2304 while (isa<DbgInfoIntrinsic>(I)) 2305 ++I; 2306 if (&*I == BI) { 2307 if (FoldValueComparisonIntoPredecessors(BI)) 2308 return SimplifyCFG(BB) | true; 2309 } else if (&*I == cast<Instruction>(BI->getCondition())){ 2310 ++I; 2311 // Ignore dbg intrinsics. 2312 while (isa<DbgInfoIntrinsic>(I)) 2313 ++I; 2314 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI)) 2315 return SimplifyCFG(BB) | true; 2316 } 2317 } 2318 2319 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction. 2320 if (SimplifyBranchOnICmpChain(BI, TD)) 2321 return true; 2322 2323 // We have a conditional branch to two blocks that are only reachable 2324 // from BI. We know that the condbr dominates the two blocks, so see if 2325 // there is any identical code in the "then" and "else" blocks. If so, we 2326 // can hoist it up to the branching block. 2327 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) { 2328 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 2329 if (HoistThenElseCodeToIf(BI)) 2330 return SimplifyCFG(BB) | true; 2331 } else { 2332 // If Successor #1 has multiple preds, we may be able to conditionally 2333 // execute Successor #0 if it branches to successor #1. 2334 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator(); 2335 if (Succ0TI->getNumSuccessors() == 1 && 2336 Succ0TI->getSuccessor(0) == BI->getSuccessor(1)) 2337 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0))) 2338 return SimplifyCFG(BB) | true; 2339 } 2340 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 2341 // If Successor #0 has multiple preds, we may be able to conditionally 2342 // execute Successor #1 if it branches to successor #0. 2343 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator(); 2344 if (Succ1TI->getNumSuccessors() == 1 && 2345 Succ1TI->getSuccessor(0) == BI->getSuccessor(0)) 2346 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1))) 2347 return SimplifyCFG(BB) | true; 2348 } 2349 2350 // If this is a branch on a phi node in the current block, thread control 2351 // through this block if any PHI node entries are constants. 2352 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition())) 2353 if (PN->getParent() == BI->getParent()) 2354 if (FoldCondBranchOnPHI(BI)) 2355 return SimplifyCFG(BB) | true; 2356 2357 // If this basic block is ONLY a setcc and a branch, and if a predecessor 2358 // branches to us and one of our successors, fold the setcc into the 2359 // predecessor and use logical operations to pick the right destination. 2360 if (FoldBranchToCommonDest(BI)) 2361 return SimplifyCFG(BB) | true; 2362 2363 // Scan predecessor blocks for conditional branches. 2364 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 2365 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) 2366 if (PBI != BI && PBI->isConditional()) 2367 if (SimplifyCondBranchToCondBranch(PBI, BI)) 2368 return SimplifyCFG(BB) | true; 2369 2370 return false; 2371} 2372 2373bool SimplifyCFGOpt::run(BasicBlock *BB) { 2374 bool Changed = false; 2375 Function *Fn = BB->getParent(); 2376 2377 assert(BB && Fn && "Block not embedded in function!"); 2378 assert(BB->getTerminator() && "Degenerate basic block encountered!"); 2379 2380 // Remove basic blocks that have no predecessors (except the entry block)... 2381 // or that just have themself as a predecessor. These are unreachable. 2382 if ((pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) || 2383 BB->getSinglePredecessor() == BB) { 2384 DEBUG(dbgs() << "Removing BB: \n" << *BB); 2385 DeleteDeadBlock(BB); 2386 return true; 2387 } 2388 2389 // Check to see if we can constant propagate this terminator instruction 2390 // away... 2391 Changed |= ConstantFoldTerminator(BB); 2392 2393 // Check for and eliminate duplicate PHI nodes in this block. 2394 Changed |= EliminateDuplicatePHINodes(BB); 2395 2396 // Merge basic blocks into their predecessor if there is only one distinct 2397 // pred, and if there is only one distinct successor of the predecessor, and 2398 // if there are no PHI nodes. 2399 // 2400 if (MergeBlockIntoPredecessor(BB)) 2401 return true; 2402 2403 // If there is a trivial two-entry PHI node in this basic block, and we can 2404 // eliminate it, do so now. 2405 if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) 2406 if (PN->getNumIncomingValues() == 2) 2407 Changed |= FoldTwoEntryPHINode(PN); 2408 2409 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { 2410 if (BI->isUnconditional()) { 2411 if (SimplifyUncondBranch(BI)) return true; 2412 } else { 2413 if (SimplifyCondBranch(BI)) 2414 return true; 2415 } 2416 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 2417 if (SimplifyReturn(RI)) return true; 2418 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { 2419 if (SimplifySwitch(SI)) return true; 2420 } else if (UnreachableInst *UI = 2421 dyn_cast<UnreachableInst>(BB->getTerminator())) { 2422 if (SimplifyUnreachable(UI)) return true; 2423 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) { 2424 if (SimplifyUnwind(UI)) return true; 2425 } else if (IndirectBrInst *IBI = 2426 dyn_cast<IndirectBrInst>(BB->getTerminator())) { 2427 if (SimplifyIndirectBr(IBI)) return true; 2428 } 2429 2430 return Changed; 2431} 2432 2433/// SimplifyCFG - This function is used to do simplification of a CFG. For 2434/// example, it adjusts branches to branches to eliminate the extra hop, it 2435/// eliminates unreachable basic blocks, and does other "peephole" optimization 2436/// of the CFG. It returns true if a modification was made. 2437/// 2438bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) { 2439 return SimplifyCFGOpt(TD).run(BB); 2440} 2441