SimplifyCFG.cpp revision a37029cd24105f645a694abbafbc9bf1212708b0
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/Analysis/InstructionSimplify.h" 23#include "llvm/Target/TargetData.h" 24#include "llvm/Transforms/Utils/BasicBlockUtils.h" 25#include "llvm/ADT/DenseMap.h" 26#include "llvm/ADT/SmallVector.h" 27#include "llvm/ADT/SmallPtrSet.h" 28#include "llvm/ADT/Statistic.h" 29#include "llvm/ADT/STLExtras.h" 30#include "llvm/Support/CFG.h" 31#include "llvm/Support/ConstantRange.h" 32#include "llvm/Support/Debug.h" 33#include "llvm/Support/raw_ostream.h" 34#include <algorithm> 35#include <set> 36#include <map> 37using namespace llvm; 38 39STATISTIC(NumSpeculations, "Number of speculative executed instructions"); 40 41namespace { 42class SimplifyCFGOpt { 43 const TargetData *const TD; 44 45 Value *isValueEqualityComparison(TerminatorInst *TI); 46 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI, 47 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases); 48 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 49 BasicBlock *Pred); 50 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI); 51 52 bool SimplifyReturn(ReturnInst *RI); 53 bool SimplifyUnwind(UnwindInst *UI); 54 bool SimplifyUnreachable(UnreachableInst *UI); 55 bool SimplifySwitch(SwitchInst *SI); 56 bool SimplifyIndirectBr(IndirectBrInst *IBI); 57 bool SimplifyUncondBranch(BranchInst *BI); 58 bool SimplifyCondBranch(BranchInst *BI); 59 60public: 61 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {} 62 bool run(BasicBlock *BB); 63}; 64} 65 66/// SafeToMergeTerminators - Return true if it is safe to merge these two 67/// terminator instructions together. 68/// 69static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) { 70 if (SI1 == SI2) return false; // Can't merge with self! 71 72 // It is not safe to merge these two switch instructions if they have a common 73 // successor, and if that successor has a PHI node, and if *that* PHI node has 74 // conflicting incoming values from the two switch blocks. 75 BasicBlock *SI1BB = SI1->getParent(); 76 BasicBlock *SI2BB = SI2->getParent(); 77 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); 78 79 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) 80 if (SI1Succs.count(*I)) 81 for (BasicBlock::iterator BBI = (*I)->begin(); 82 isa<PHINode>(BBI); ++BBI) { 83 PHINode *PN = cast<PHINode>(BBI); 84 if (PN->getIncomingValueForBlock(SI1BB) != 85 PN->getIncomingValueForBlock(SI2BB)) 86 return false; 87 } 88 89 return true; 90} 91 92/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will 93/// now be entries in it from the 'NewPred' block. The values that will be 94/// flowing into the PHI nodes will be the same as those coming in from 95/// ExistPred, an existing predecessor of Succ. 96static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, 97 BasicBlock *ExistPred) { 98 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do 99 100 PHINode *PN; 101 for (BasicBlock::iterator I = Succ->begin(); 102 (PN = dyn_cast<PHINode>(I)); ++I) 103 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred); 104} 105 106 107/// GetIfCondition - Given a basic block (BB) with two predecessors (and at 108/// least one PHI node in it), check to see if the merge at this block is due 109/// to an "if condition". If so, return the boolean condition that determines 110/// which entry into BB will be taken. Also, return by references the block 111/// that will be entered from if the condition is true, and the block that will 112/// be entered if the condition is false. 113/// 114/// This does no checking to see if the true/false blocks have large or unsavory 115/// instructions in them. 116static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 117 BasicBlock *&IfFalse) { 118 PHINode *SomePHI = cast<PHINode>(BB->begin()); 119 assert(SomePHI->getNumIncomingValues() == 2 && 120 "Function can only handle blocks with 2 predecessors!"); 121 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0); 122 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1); 123 124 // We can only handle branches. Other control flow will be lowered to 125 // branches if possible anyway. 126 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator()); 127 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator()); 128 if (Pred1Br == 0 || Pred2Br == 0) 129 return 0; 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 // The only thing we have to watch out for here is to make sure that Pred2 147 // doesn't have incoming edges from other blocks. If it does, the condition 148 // doesn't dominate BB. 149 if (Pred2->getSinglePredecessor() == 0) 150 return 0; 151 152 // If we found a conditional branch predecessor, make sure that it branches 153 // to BB and Pred2Br. If it doesn't, this isn't an "if statement". 154 if (Pred1Br->getSuccessor(0) == BB && 155 Pred1Br->getSuccessor(1) == Pred2) { 156 IfTrue = Pred1; 157 IfFalse = Pred2; 158 } else if (Pred1Br->getSuccessor(0) == Pred2 && 159 Pred1Br->getSuccessor(1) == BB) { 160 IfTrue = Pred2; 161 IfFalse = Pred1; 162 } else { 163 // We know that one arm of the conditional goes to BB, so the other must 164 // go somewhere unrelated, and this must not be an "if statement". 165 return 0; 166 } 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 BasicBlock *CommonPred = Pred1->getSinglePredecessor(); 175 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor()) 176 return 0; 177 178 // Otherwise, if this is a conditional branch, then we can use it! 179 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator()); 180 if (BI == 0) return 0; 181 182 assert(BI->isConditional() && "Two successors but not conditional?"); 183 if (BI->getSuccessor(0) == Pred1) { 184 IfTrue = Pred1; 185 IfFalse = Pred2; 186 } else { 187 IfTrue = Pred2; 188 IfFalse = Pred1; 189 } 190 return BI->getCondition(); 191} 192 193/// DominatesMergePoint - If we have a merge point of an "if condition" as 194/// accepted above, return true if the specified value dominates the block. We 195/// don't handle the true generality of domination here, just a special case 196/// which works well enough for us. 197/// 198/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to 199/// see if V (which must be an instruction) is cheap to compute and is 200/// non-trapping. If both are true, the instruction is inserted into the set 201/// and true is returned. 202static bool DominatesMergePoint(Value *V, BasicBlock *BB, 203 SmallPtrSet<Instruction*, 4> *AggressiveInsts) { 204 Instruction *I = dyn_cast<Instruction>(V); 205 if (!I) { 206 // Non-instructions all dominate instructions, but not all constantexprs 207 // can be executed unconditionally. 208 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V)) 209 if (C->canTrap()) 210 return false; 211 return true; 212 } 213 BasicBlock *PBB = I->getParent(); 214 215 // We don't want to allow weird loops that might have the "if condition" in 216 // the bottom of this block. 217 if (PBB == BB) return false; 218 219 // If this instruction is defined in a block that contains an unconditional 220 // branch to BB, then it must be in the 'conditional' part of the "if 221 // statement". If not, it definitely dominates the region. 222 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()); 223 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB) 224 return true; 225 226 // If we aren't allowing aggressive promotion anymore, then don't consider 227 // instructions in the 'if region'. 228 if (AggressiveInsts == 0) return false; 229 230 // Okay, it looks like the instruction IS in the "condition". Check to 231 // see if it's a cheap instruction to unconditionally compute, and if it 232 // only uses stuff defined outside of the condition. If so, hoist it out. 233 if (!I->isSafeToSpeculativelyExecute()) 234 return false; 235 236 switch (I->getOpcode()) { 237 default: return false; // Cannot hoist this out safely. 238 case Instruction::Load: 239 // We have to check to make sure there are no instructions before the 240 // load in its basic block, as we are going to hoist the load out to its 241 // predecessor. 242 if (PBB->getFirstNonPHIOrDbg() != I) 243 return false; 244 break; 245 case Instruction::Add: 246 case Instruction::Sub: 247 case Instruction::And: 248 case Instruction::Or: 249 case Instruction::Xor: 250 case Instruction::Shl: 251 case Instruction::LShr: 252 case Instruction::AShr: 253 case Instruction::ICmp: 254 break; // These are all cheap and non-trapping instructions. 255 } 256 257 // Okay, we can only really hoist these out if their operands are not 258 // defined in the conditional region. 259 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) 260 if (!DominatesMergePoint(*i, BB, 0)) 261 return false; 262 // Okay, it's safe to do this! Remember this instruction. 263 AggressiveInsts->insert(I); 264 return true; 265} 266 267/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr 268/// and PointerNullValue. Return NULL if value is not a constant int. 269static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) { 270 // Normal constant int. 271 ConstantInt *CI = dyn_cast<ConstantInt>(V); 272 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy()) 273 return CI; 274 275 // This is some kind of pointer constant. Turn it into a pointer-sized 276 // ConstantInt if possible. 277 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext()); 278 279 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*). 280 if (isa<ConstantPointerNull>(V)) 281 return ConstantInt::get(PtrTy, 0); 282 283 // IntToPtr const int. 284 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 285 if (CE->getOpcode() == Instruction::IntToPtr) 286 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) { 287 // The constant is very likely to have the right type already. 288 if (CI->getType() == PtrTy) 289 return CI; 290 else 291 return cast<ConstantInt> 292 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false)); 293 } 294 return 0; 295} 296 297/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together 298/// collection of icmp eq/ne instructions that compare a value against a 299/// constant, return the value being compared, and stick the constant into the 300/// Values vector. 301static Value * 302GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra, 303 const TargetData *TD, bool isEQ) { 304 Instruction *I = dyn_cast<Instruction>(V); 305 if (I == 0) return 0; 306 307 // If this is an icmp against a constant, handle this as one of the cases. 308 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) { 309 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) { 310 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) { 311 Vals.push_back(C); 312 return I->getOperand(0); 313 } 314 315 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to 316 // the set. 317 ConstantRange Span = 318 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue()); 319 320 // If this is an and/!= check then we want to optimize "x ugt 2" into 321 // x != 0 && x != 1. 322 if (!isEQ) 323 Span = Span.inverse(); 324 325 // If there are a ton of values, we don't want to make a ginormous switch. 326 if (Span.getSetSize().ugt(8) || Span.isEmptySet() || 327 // We don't handle wrapped sets yet. 328 Span.isWrappedSet()) 329 return 0; 330 331 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp) 332 Vals.push_back(ConstantInt::get(V->getContext(), Tmp)); 333 return I->getOperand(0); 334 } 335 return 0; 336 } 337 338 // Otherwise, we can only handle an | or &, depending on isEQ. 339 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And)) 340 return 0; 341 342 unsigned NumValsBeforeLHS = Vals.size(); 343 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD, 344 isEQ)) { 345 unsigned NumVals = Vals.size(); 346 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, 347 isEQ)) { 348 if (LHS == RHS) 349 return LHS; 350 Vals.resize(NumVals); 351 } 352 353 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet, 354 // set it and return success. 355 if (Extra == 0 || Extra == I->getOperand(1)) { 356 Extra = I->getOperand(1); 357 return LHS; 358 } 359 360 Vals.resize(NumValsBeforeLHS); 361 return 0; 362 } 363 364 // If the LHS can't be folded in, but Extra is available and RHS can, try to 365 // use LHS as Extra. 366 if (Extra == 0 || Extra == I->getOperand(0)) { 367 Value *OldExtra = Extra; 368 Extra = I->getOperand(0); 369 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, 370 isEQ)) 371 return RHS; 372 assert(Vals.size() == NumValsBeforeLHS); 373 Extra = OldExtra; 374 } 375 376 return 0; 377} 378 379static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) { 380 Instruction* Cond = 0; 381 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 382 Cond = dyn_cast<Instruction>(SI->getCondition()); 383 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 384 if (BI->isConditional()) 385 Cond = dyn_cast<Instruction>(BI->getCondition()); 386 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) { 387 Cond = dyn_cast<Instruction>(IBI->getAddress()); 388 } 389 390 TI->eraseFromParent(); 391 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond); 392} 393 394/// isValueEqualityComparison - Return true if the specified terminator checks 395/// to see if a value is equal to constant integer value. 396Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) { 397 Value *CV = 0; 398 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 399 // Do not permit merging of large switch instructions into their 400 // predecessors unless there is only one predecessor. 401 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()), 402 pred_end(SI->getParent())) <= 128) 403 CV = SI->getCondition(); 404 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) 405 if (BI->isConditional() && BI->getCondition()->hasOneUse()) 406 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) 407 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ || 408 ICI->getPredicate() == ICmpInst::ICMP_NE) && 409 GetConstantInt(ICI->getOperand(1), TD)) 410 CV = ICI->getOperand(0); 411 412 // Unwrap any lossless ptrtoint cast. 413 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext())) 414 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) 415 CV = PTII->getOperand(0); 416 return CV; 417} 418 419/// GetValueEqualityComparisonCases - Given a value comparison instruction, 420/// decode all of the 'cases' that it represents and return the 'default' block. 421BasicBlock *SimplifyCFGOpt:: 422GetValueEqualityComparisonCases(TerminatorInst *TI, 423 std::vector<std::pair<ConstantInt*, 424 BasicBlock*> > &Cases) { 425 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 426 Cases.reserve(SI->getNumCases()); 427 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 428 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i))); 429 return SI->getDefaultDest(); 430 } 431 432 BranchInst *BI = cast<BranchInst>(TI); 433 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); 434 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD), 435 BI->getSuccessor(ICI->getPredicate() == 436 ICmpInst::ICMP_NE))); 437 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ); 438} 439 440 441/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries 442/// in the list that match the specified block. 443static void EliminateBlockCases(BasicBlock *BB, 444 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) { 445 for (unsigned i = 0, e = Cases.size(); i != e; ++i) 446 if (Cases[i].second == BB) { 447 Cases.erase(Cases.begin()+i); 448 --i; --e; 449 } 450} 451 452/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as 453/// well. 454static bool 455ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1, 456 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) { 457 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2; 458 459 // Make V1 be smaller than V2. 460 if (V1->size() > V2->size()) 461 std::swap(V1, V2); 462 463 if (V1->size() == 0) return false; 464 if (V1->size() == 1) { 465 // Just scan V2. 466 ConstantInt *TheVal = (*V1)[0].first; 467 for (unsigned i = 0, e = V2->size(); i != e; ++i) 468 if (TheVal == (*V2)[i].first) 469 return true; 470 } 471 472 // Otherwise, just sort both lists and compare element by element. 473 array_pod_sort(V1->begin(), V1->end()); 474 array_pod_sort(V2->begin(), V2->end()); 475 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); 476 while (i1 != e1 && i2 != e2) { 477 if ((*V1)[i1].first == (*V2)[i2].first) 478 return true; 479 if ((*V1)[i1].first < (*V2)[i2].first) 480 ++i1; 481 else 482 ++i2; 483 } 484 return false; 485} 486 487/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a 488/// terminator instruction and its block is known to only have a single 489/// predecessor block, check to see if that predecessor is also a value 490/// comparison with the same value, and if that comparison determines the 491/// outcome of this comparison. If so, simplify TI. This does a very limited 492/// form of jump threading. 493bool SimplifyCFGOpt:: 494SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 495 BasicBlock *Pred) { 496 Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); 497 if (!PredVal) return false; // Not a value comparison in predecessor. 498 499 Value *ThisVal = isValueEqualityComparison(TI); 500 assert(ThisVal && "This isn't a value comparison!!"); 501 if (ThisVal != PredVal) return false; // Different predicates. 502 503 // Find out information about when control will move from Pred to TI's block. 504 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; 505 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), 506 PredCases); 507 EliminateBlockCases(PredDef, PredCases); // Remove default from cases. 508 509 // Find information about how control leaves this block. 510 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases; 511 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); 512 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. 513 514 // If TI's block is the default block from Pred's comparison, potentially 515 // simplify TI based on this knowledge. 516 if (PredDef == TI->getParent()) { 517 // If we are here, we know that the value is none of those cases listed in 518 // PredCases. If there are any cases in ThisCases that are in PredCases, we 519 // can simplify TI. 520 if (!ValuesOverlap(PredCases, ThisCases)) 521 return false; 522 523 if (isa<BranchInst>(TI)) { 524 // Okay, one of the successors of this condbr is dead. Convert it to a 525 // uncond br. 526 assert(ThisCases.size() == 1 && "Branch can only have one case!"); 527 // Insert the new branch. 528 Instruction *NI = BranchInst::Create(ThisDef, TI); 529 (void) NI; 530 531 // Remove PHI node entries for the dead edge. 532 ThisCases[0].second->removePredecessor(TI->getParent()); 533 534 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 535 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 536 537 EraseTerminatorInstAndDCECond(TI); 538 return true; 539 } 540 541 SwitchInst *SI = cast<SwitchInst>(TI); 542 // Okay, TI has cases that are statically dead, prune them away. 543 SmallPtrSet<Constant*, 16> DeadCases; 544 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 545 DeadCases.insert(PredCases[i].first); 546 547 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 548 << "Through successor TI: " << *TI); 549 550 for (unsigned i = SI->getNumCases()-1; i != 0; --i) 551 if (DeadCases.count(SI->getCaseValue(i))) { 552 SI->getSuccessor(i)->removePredecessor(TI->getParent()); 553 SI->removeCase(i); 554 } 555 556 DEBUG(dbgs() << "Leaving: " << *TI << "\n"); 557 return true; 558 } 559 560 // Otherwise, TI's block must correspond to some matched value. Find out 561 // which value (or set of values) this is. 562 ConstantInt *TIV = 0; 563 BasicBlock *TIBB = TI->getParent(); 564 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 565 if (PredCases[i].second == TIBB) { 566 if (TIV != 0) 567 return false; // Cannot handle multiple values coming to this block. 568 TIV = PredCases[i].first; 569 } 570 assert(TIV && "No edge from pred to succ?"); 571 572 // Okay, we found the one constant that our value can be if we get into TI's 573 // BB. Find out which successor will unconditionally be branched to. 574 BasicBlock *TheRealDest = 0; 575 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) 576 if (ThisCases[i].first == TIV) { 577 TheRealDest = ThisCases[i].second; 578 break; 579 } 580 581 // If not handled by any explicit cases, it is handled by the default case. 582 if (TheRealDest == 0) TheRealDest = ThisDef; 583 584 // Remove PHI node entries for dead edges. 585 BasicBlock *CheckEdge = TheRealDest; 586 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI) 587 if (*SI != CheckEdge) 588 (*SI)->removePredecessor(TIBB); 589 else 590 CheckEdge = 0; 591 592 // Insert the new branch. 593 Instruction *NI = BranchInst::Create(TheRealDest, TI); 594 (void) NI; 595 596 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 597 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 598 599 EraseTerminatorInstAndDCECond(TI); 600 return true; 601} 602 603namespace { 604 /// ConstantIntOrdering - This class implements a stable ordering of constant 605 /// integers that does not depend on their address. This is important for 606 /// applications that sort ConstantInt's to ensure uniqueness. 607 struct ConstantIntOrdering { 608 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { 609 return LHS->getValue().ult(RHS->getValue()); 610 } 611 }; 612} 613 614static int ConstantIntSortPredicate(const void *P1, const void *P2) { 615 const ConstantInt *LHS = *(const ConstantInt**)P1; 616 const ConstantInt *RHS = *(const ConstantInt**)P2; 617 if (LHS->getValue().ult(RHS->getValue())) 618 return 1; 619 if (LHS->getValue() == RHS->getValue()) 620 return 0; 621 return -1; 622} 623 624/// FoldValueComparisonIntoPredecessors - The specified terminator is a value 625/// equality comparison instruction (either a switch or a branch on "X == c"). 626/// See if any of the predecessors of the terminator block are value comparisons 627/// on the same value. If so, and if safe to do so, fold them together. 628bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) { 629 BasicBlock *BB = TI->getParent(); 630 Value *CV = isValueEqualityComparison(TI); // CondVal 631 assert(CV && "Not a comparison?"); 632 bool Changed = false; 633 634 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); 635 while (!Preds.empty()) { 636 BasicBlock *Pred = Preds.pop_back_val(); 637 638 // See if the predecessor is a comparison with the same value. 639 TerminatorInst *PTI = Pred->getTerminator(); 640 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal 641 642 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) { 643 // Figure out which 'cases' to copy from SI to PSI. 644 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases; 645 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); 646 647 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; 648 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); 649 650 // Based on whether the default edge from PTI goes to BB or not, fill in 651 // PredCases and PredDefault with the new switch cases we would like to 652 // build. 653 SmallVector<BasicBlock*, 8> NewSuccessors; 654 655 if (PredDefault == BB) { 656 // If this is the default destination from PTI, only the edges in TI 657 // that don't occur in PTI, or that branch to BB will be activated. 658 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 659 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 660 if (PredCases[i].second != BB) 661 PTIHandled.insert(PredCases[i].first); 662 else { 663 // The default destination is BB, we don't need explicit targets. 664 std::swap(PredCases[i], PredCases.back()); 665 PredCases.pop_back(); 666 --i; --e; 667 } 668 669 // Reconstruct the new switch statement we will be building. 670 if (PredDefault != BBDefault) { 671 PredDefault->removePredecessor(Pred); 672 PredDefault = BBDefault; 673 NewSuccessors.push_back(BBDefault); 674 } 675 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 676 if (!PTIHandled.count(BBCases[i].first) && 677 BBCases[i].second != BBDefault) { 678 PredCases.push_back(BBCases[i]); 679 NewSuccessors.push_back(BBCases[i].second); 680 } 681 682 } else { 683 // If this is not the default destination from PSI, only the edges 684 // in SI that occur in PSI with a destination of BB will be 685 // activated. 686 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 687 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 688 if (PredCases[i].second == BB) { 689 PTIHandled.insert(PredCases[i].first); 690 std::swap(PredCases[i], PredCases.back()); 691 PredCases.pop_back(); 692 --i; --e; 693 } 694 695 // Okay, now we know which constants were sent to BB from the 696 // predecessor. Figure out where they will all go now. 697 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 698 if (PTIHandled.count(BBCases[i].first)) { 699 // If this is one we are capable of getting... 700 PredCases.push_back(BBCases[i]); 701 NewSuccessors.push_back(BBCases[i].second); 702 PTIHandled.erase(BBCases[i].first);// This constant is taken care of 703 } 704 705 // If there are any constants vectored to BB that TI doesn't handle, 706 // they must go to the default destination of TI. 707 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I = 708 PTIHandled.begin(), 709 E = PTIHandled.end(); I != E; ++I) { 710 PredCases.push_back(std::make_pair(*I, BBDefault)); 711 NewSuccessors.push_back(BBDefault); 712 } 713 } 714 715 // Okay, at this point, we know which new successor Pred will get. Make 716 // sure we update the number of entries in the PHI nodes for these 717 // successors. 718 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i) 719 AddPredecessorToBlock(NewSuccessors[i], Pred, BB); 720 721 // Convert pointer to int before we switch. 722 if (CV->getType()->isPointerTy()) { 723 assert(TD && "Cannot switch on pointer without TargetData"); 724 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()), 725 "magicptr", PTI); 726 } 727 728 // Now that the successors are updated, create the new Switch instruction. 729 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault, 730 PredCases.size(), PTI); 731 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 732 NewSI->addCase(PredCases[i].first, PredCases[i].second); 733 734 EraseTerminatorInstAndDCECond(PTI); 735 736 // Okay, last check. If BB is still a successor of PSI, then we must 737 // have an infinite loop case. If so, add an infinitely looping block 738 // to handle the case to preserve the behavior of the code. 739 BasicBlock *InfLoopBlock = 0; 740 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) 741 if (NewSI->getSuccessor(i) == BB) { 742 if (InfLoopBlock == 0) { 743 // Insert it at the end of the function, because it's either code, 744 // or it won't matter if it's hot. :) 745 InfLoopBlock = BasicBlock::Create(BB->getContext(), 746 "infloop", BB->getParent()); 747 BranchInst::Create(InfLoopBlock, InfLoopBlock); 748 } 749 NewSI->setSuccessor(i, InfLoopBlock); 750 } 751 752 Changed = true; 753 } 754 } 755 return Changed; 756} 757 758// isSafeToHoistInvoke - If we would need to insert a select that uses the 759// value of this invoke (comments in HoistThenElseCodeToIf explain why we 760// would need to do this), we can't hoist the invoke, as there is nowhere 761// to put the select in this case. 762static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2, 763 Instruction *I1, Instruction *I2) { 764 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 765 PHINode *PN; 766 for (BasicBlock::iterator BBI = SI->begin(); 767 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 768 Value *BB1V = PN->getIncomingValueForBlock(BB1); 769 Value *BB2V = PN->getIncomingValueForBlock(BB2); 770 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) { 771 return false; 772 } 773 } 774 } 775 return true; 776} 777 778/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and 779/// BB2, hoist any common code in the two blocks up into the branch block. The 780/// caller of this function guarantees that BI's block dominates BB1 and BB2. 781static bool HoistThenElseCodeToIf(BranchInst *BI) { 782 // This does very trivial matching, with limited scanning, to find identical 783 // instructions in the two blocks. In particular, we don't want to get into 784 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As 785 // such, we currently just scan for obviously identical instructions in an 786 // identical order. 787 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. 788 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination 789 790 BasicBlock::iterator BB1_Itr = BB1->begin(); 791 BasicBlock::iterator BB2_Itr = BB2->begin(); 792 793 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++; 794 while (isa<DbgInfoIntrinsic>(I1)) 795 I1 = BB1_Itr++; 796 while (isa<DbgInfoIntrinsic>(I2)) 797 I2 = BB2_Itr++; 798 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) || 799 !I1->isIdenticalToWhenDefined(I2) || 800 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))) 801 return false; 802 803 // If we get here, we can hoist at least one instruction. 804 BasicBlock *BIParent = BI->getParent(); 805 806 do { 807 // If we are hoisting the terminator instruction, don't move one (making a 808 // broken BB), instead clone it, and remove BI. 809 if (isa<TerminatorInst>(I1)) 810 goto HoistTerminator; 811 812 // For a normal instruction, we just move one to right before the branch, 813 // then replace all uses of the other with the first. Finally, we remove 814 // the now redundant second instruction. 815 BIParent->getInstList().splice(BI, BB1->getInstList(), I1); 816 if (!I2->use_empty()) 817 I2->replaceAllUsesWith(I1); 818 I1->intersectOptionalDataWith(I2); 819 I2->eraseFromParent(); 820 821 I1 = BB1_Itr++; 822 while (isa<DbgInfoIntrinsic>(I1)) 823 I1 = BB1_Itr++; 824 I2 = BB2_Itr++; 825 while (isa<DbgInfoIntrinsic>(I2)) 826 I2 = BB2_Itr++; 827 } while (I1->getOpcode() == I2->getOpcode() && 828 I1->isIdenticalToWhenDefined(I2)); 829 830 return true; 831 832HoistTerminator: 833 // It may not be possible to hoist an invoke. 834 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) 835 return true; 836 837 // Okay, it is safe to hoist the terminator. 838 Instruction *NT = I1->clone(); 839 BIParent->getInstList().insert(BI, NT); 840 if (!NT->getType()->isVoidTy()) { 841 I1->replaceAllUsesWith(NT); 842 I2->replaceAllUsesWith(NT); 843 NT->takeName(I1); 844 } 845 846 // Hoisting one of the terminators from our successor is a great thing. 847 // Unfortunately, the successors of the if/else blocks may have PHI nodes in 848 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI 849 // nodes, so we insert select instruction to compute the final result. 850 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects; 851 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 852 PHINode *PN; 853 for (BasicBlock::iterator BBI = SI->begin(); 854 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 855 Value *BB1V = PN->getIncomingValueForBlock(BB1); 856 Value *BB2V = PN->getIncomingValueForBlock(BB2); 857 if (BB1V == BB2V) continue; 858 859 // These values do not agree. Insert a select instruction before NT 860 // that determines the right value. 861 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; 862 if (SI == 0) 863 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V, 864 BB1V->getName()+"."+BB2V->getName(), NT); 865 // Make the PHI node use the select for all incoming values for BB1/BB2 866 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 867 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2) 868 PN->setIncomingValue(i, SI); 869 } 870 } 871 872 // Update any PHI nodes in our new successors. 873 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) 874 AddPredecessorToBlock(*SI, BIParent, BB1); 875 876 EraseTerminatorInstAndDCECond(BI); 877 return true; 878} 879 880/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1 881/// and an BB2 and the only successor of BB1 is BB2, hoist simple code 882/// (for now, restricted to a single instruction that's side effect free) from 883/// the BB1 into the branch block to speculatively execute it. 884static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) { 885 // Only speculatively execution a single instruction (not counting the 886 // terminator) for now. 887 Instruction *HInst = NULL; 888 Instruction *Term = BB1->getTerminator(); 889 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); 890 BBI != BBE; ++BBI) { 891 Instruction *I = BBI; 892 // Skip debug info. 893 if (isa<DbgInfoIntrinsic>(I)) continue; 894 if (I == Term) break; 895 896 if (HInst) 897 return false; 898 HInst = I; 899 } 900 if (!HInst) 901 return false; 902 903 // Be conservative for now. FP select instruction can often be expensive. 904 Value *BrCond = BI->getCondition(); 905 if (isa<FCmpInst>(BrCond)) 906 return false; 907 908 // If BB1 is actually on the false edge of the conditional branch, remember 909 // to swap the select operands later. 910 bool Invert = false; 911 if (BB1 != BI->getSuccessor(0)) { 912 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?"); 913 Invert = true; 914 } 915 916 // Turn 917 // BB: 918 // %t1 = icmp 919 // br i1 %t1, label %BB1, label %BB2 920 // BB1: 921 // %t3 = add %t2, c 922 // br label BB2 923 // BB2: 924 // => 925 // BB: 926 // %t1 = icmp 927 // %t4 = add %t2, c 928 // %t3 = select i1 %t1, %t2, %t3 929 switch (HInst->getOpcode()) { 930 default: return false; // Not safe / profitable to hoist. 931 case Instruction::Add: 932 case Instruction::Sub: 933 // Not worth doing for vector ops. 934 if (HInst->getType()->isVectorTy()) 935 return false; 936 break; 937 case Instruction::And: 938 case Instruction::Or: 939 case Instruction::Xor: 940 case Instruction::Shl: 941 case Instruction::LShr: 942 case Instruction::AShr: 943 // Don't mess with vector operations. 944 if (HInst->getType()->isVectorTy()) 945 return false; 946 break; // These are all cheap and non-trapping instructions. 947 } 948 949 // If the instruction is obviously dead, don't try to predicate it. 950 if (HInst->use_empty()) { 951 HInst->eraseFromParent(); 952 return true; 953 } 954 955 // Can we speculatively execute the instruction? And what is the value 956 // if the condition is false? Consider the phi uses, if the incoming value 957 // from the "if" block are all the same V, then V is the value of the 958 // select if the condition is false. 959 BasicBlock *BIParent = BI->getParent(); 960 SmallVector<PHINode*, 4> PHIUses; 961 Value *FalseV = NULL; 962 963 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0); 964 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end(); 965 UI != E; ++UI) { 966 // Ignore any user that is not a PHI node in BB2. These can only occur in 967 // unreachable blocks, because they would not be dominated by the instr. 968 PHINode *PN = dyn_cast<PHINode>(*UI); 969 if (!PN || PN->getParent() != BB2) 970 return false; 971 PHIUses.push_back(PN); 972 973 Value *PHIV = PN->getIncomingValueForBlock(BIParent); 974 if (!FalseV) 975 FalseV = PHIV; 976 else if (FalseV != PHIV) 977 return false; // Inconsistent value when condition is false. 978 } 979 980 assert(FalseV && "Must have at least one user, and it must be a PHI"); 981 982 // Do not hoist the instruction if any of its operands are defined but not 983 // used in this BB. The transformation will prevent the operand from 984 // being sunk into the use block. 985 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end(); 986 i != e; ++i) { 987 Instruction *OpI = dyn_cast<Instruction>(*i); 988 if (OpI && OpI->getParent() == BIParent && 989 !OpI->isUsedInBasicBlock(BIParent)) 990 return false; 991 } 992 993 // If we get here, we can hoist the instruction. Try to place it 994 // before the icmp instruction preceding the conditional branch. 995 BasicBlock::iterator InsertPos = BI; 996 if (InsertPos != BIParent->begin()) 997 --InsertPos; 998 // Skip debug info between condition and branch. 999 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos)) 1000 --InsertPos; 1001 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) { 1002 SmallPtrSet<Instruction *, 4> BB1Insns; 1003 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end(); 1004 BB1I != BB1E; ++BB1I) 1005 BB1Insns.insert(BB1I); 1006 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end(); 1007 UI != UE; ++UI) { 1008 Instruction *Use = cast<Instruction>(*UI); 1009 if (!BB1Insns.count(Use)) continue; 1010 1011 // If BrCond uses the instruction that place it just before 1012 // branch instruction. 1013 InsertPos = BI; 1014 break; 1015 } 1016 } else 1017 InsertPos = BI; 1018 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst); 1019 1020 // Create a select whose true value is the speculatively executed value and 1021 // false value is the previously determined FalseV. 1022 SelectInst *SI; 1023 if (Invert) 1024 SI = SelectInst::Create(BrCond, FalseV, HInst, 1025 FalseV->getName() + "." + HInst->getName(), BI); 1026 else 1027 SI = SelectInst::Create(BrCond, HInst, FalseV, 1028 HInst->getName() + "." + FalseV->getName(), BI); 1029 1030 // Make the PHI node use the select for all incoming values for "then" and 1031 // "if" blocks. 1032 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) { 1033 PHINode *PN = PHIUses[i]; 1034 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j) 1035 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent) 1036 PN->setIncomingValue(j, SI); 1037 } 1038 1039 ++NumSpeculations; 1040 return true; 1041} 1042 1043/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch 1044/// across this block. 1045static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) { 1046 BranchInst *BI = cast<BranchInst>(BB->getTerminator()); 1047 unsigned Size = 0; 1048 1049 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1050 if (isa<DbgInfoIntrinsic>(BBI)) 1051 continue; 1052 if (Size > 10) return false; // Don't clone large BB's. 1053 ++Size; 1054 1055 // We can only support instructions that do not define values that are 1056 // live outside of the current basic block. 1057 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 1058 UI != E; ++UI) { 1059 Instruction *U = cast<Instruction>(*UI); 1060 if (U->getParent() != BB || isa<PHINode>(U)) return false; 1061 } 1062 1063 // Looks ok, continue checking. 1064 } 1065 1066 return true; 1067} 1068 1069/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value 1070/// that is defined in the same block as the branch and if any PHI entries are 1071/// constants, thread edges corresponding to that entry to be branches to their 1072/// ultimate destination. 1073static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) { 1074 BasicBlock *BB = BI->getParent(); 1075 PHINode *PN = dyn_cast<PHINode>(BI->getCondition()); 1076 // NOTE: we currently cannot transform this case if the PHI node is used 1077 // outside of the block. 1078 if (!PN || PN->getParent() != BB || !PN->hasOneUse()) 1079 return false; 1080 1081 // Degenerate case of a single entry PHI. 1082 if (PN->getNumIncomingValues() == 1) { 1083 FoldSingleEntryPHINodes(PN->getParent()); 1084 return true; 1085 } 1086 1087 // Now we know that this block has multiple preds and two succs. 1088 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false; 1089 1090 // Okay, this is a simple enough basic block. See if any phi values are 1091 // constants. 1092 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1093 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i)); 1094 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue; 1095 1096 // Okay, we now know that all edges from PredBB should be revectored to 1097 // branch to RealDest. 1098 BasicBlock *PredBB = PN->getIncomingBlock(i); 1099 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue()); 1100 1101 if (RealDest == BB) continue; // Skip self loops. 1102 1103 // The dest block might have PHI nodes, other predecessors and other 1104 // difficult cases. Instead of being smart about this, just insert a new 1105 // block that jumps to the destination block, effectively splitting 1106 // the edge we are about to create. 1107 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(), 1108 RealDest->getName()+".critedge", 1109 RealDest->getParent(), RealDest); 1110 BranchInst::Create(RealDest, EdgeBB); 1111 1112 // Update PHI nodes. 1113 AddPredecessorToBlock(RealDest, EdgeBB, BB); 1114 1115 // BB may have instructions that are being threaded over. Clone these 1116 // instructions into EdgeBB. We know that there will be no uses of the 1117 // cloned instructions outside of EdgeBB. 1118 BasicBlock::iterator InsertPt = EdgeBB->begin(); 1119 DenseMap<Value*, Value*> TranslateMap; // Track translated values. 1120 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1121 if (PHINode *PN = dyn_cast<PHINode>(BBI)) { 1122 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB); 1123 continue; 1124 } 1125 // Clone the instruction. 1126 Instruction *N = BBI->clone(); 1127 if (BBI->hasName()) N->setName(BBI->getName()+".c"); 1128 1129 // Update operands due to translation. 1130 for (User::op_iterator i = N->op_begin(), e = N->op_end(); 1131 i != e; ++i) { 1132 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i); 1133 if (PI != TranslateMap.end()) 1134 *i = PI->second; 1135 } 1136 1137 // Check for trivial simplification. 1138 if (Value *V = SimplifyInstruction(N, TD)) { 1139 TranslateMap[BBI] = V; 1140 delete N; // Instruction folded away, don't need actual inst 1141 } else { 1142 // Insert the new instruction into its new home. 1143 EdgeBB->getInstList().insert(InsertPt, N); 1144 if (!BBI->use_empty()) 1145 TranslateMap[BBI] = N; 1146 } 1147 } 1148 1149 // Loop over all of the edges from PredBB to BB, changing them to branch 1150 // to EdgeBB instead. 1151 TerminatorInst *PredBBTI = PredBB->getTerminator(); 1152 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i) 1153 if (PredBBTI->getSuccessor(i) == BB) { 1154 BB->removePredecessor(PredBB); 1155 PredBBTI->setSuccessor(i, EdgeBB); 1156 } 1157 1158 // Recurse, simplifying any other constants. 1159 return FoldCondBranchOnPHI(BI, TD) | true; 1160 } 1161 1162 return false; 1163} 1164 1165/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry 1166/// PHI node, see if we can eliminate it. 1167static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) { 1168 // Ok, this is a two entry PHI node. Check to see if this is a simple "if 1169 // statement", which has a very simple dominance structure. Basically, we 1170 // are trying to find the condition that is being branched on, which 1171 // subsequently causes this merge to happen. We really want control 1172 // dependence information for this check, but simplifycfg can't keep it up 1173 // to date, and this catches most of the cases we care about anyway. 1174 BasicBlock *BB = PN->getParent(); 1175 BasicBlock *IfTrue, *IfFalse; 1176 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse); 1177 if (!IfCond || 1178 // Don't bother if the branch will be constant folded trivially. 1179 isa<ConstantInt>(IfCond)) 1180 return false; 1181 1182 // Okay, we found that we can merge this two-entry phi node into a select. 1183 // Doing so would require us to fold *all* two entry phi nodes in this block. 1184 // At some point this becomes non-profitable (particularly if the target 1185 // doesn't support cmov's). Only do this transformation if there are two or 1186 // fewer PHI nodes in this block. 1187 unsigned NumPhis = 0; 1188 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I) 1189 if (NumPhis > 2) 1190 return false; 1191 1192 // Loop over the PHI's seeing if we can promote them all to select 1193 // instructions. While we are at it, keep track of the instructions 1194 // that need to be moved to the dominating block. 1195 SmallPtrSet<Instruction*, 4> AggressiveInsts; 1196 1197 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) { 1198 PHINode *PN = cast<PHINode>(II++); 1199 if (Value *V = SimplifyInstruction(PN, TD)) { 1200 PN->replaceAllUsesWith(V); 1201 PN->eraseFromParent(); 1202 continue; 1203 } 1204 1205 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts) || 1206 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts)) 1207 return false; 1208 } 1209 1210 // If we folded the the first phi, PN dangles at this point. Refresh it. If 1211 // we ran out of PHIs then we simplified them all. 1212 PN = dyn_cast<PHINode>(BB->begin()); 1213 if (PN == 0) return true; 1214 1215 // Don't fold i1 branches on PHIs which contain binary operators. These can 1216 // often be turned into switches and other things. 1217 if (PN->getType()->isIntegerTy(1) && 1218 (isa<BinaryOperator>(PN->getIncomingValue(0)) || 1219 isa<BinaryOperator>(PN->getIncomingValue(1)) || 1220 isa<BinaryOperator>(IfCond))) 1221 return false; 1222 1223 // If we all PHI nodes are promotable, check to make sure that all 1224 // instructions in the predecessor blocks can be promoted as well. If 1225 // not, we won't be able to get rid of the control flow, so it's not 1226 // worth promoting to select instructions. 1227 BasicBlock *DomBlock = 0; 1228 BasicBlock *IfBlock1 = PN->getIncomingBlock(0); 1229 BasicBlock *IfBlock2 = PN->getIncomingBlock(1); 1230 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) { 1231 IfBlock1 = 0; 1232 } else { 1233 DomBlock = *pred_begin(IfBlock1); 1234 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I) 1235 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1236 // This is not an aggressive instruction that we can promote. 1237 // Because of this, we won't be able to get rid of the control 1238 // flow, so the xform is not worth it. 1239 return false; 1240 } 1241 } 1242 1243 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) { 1244 IfBlock2 = 0; 1245 } else { 1246 DomBlock = *pred_begin(IfBlock2); 1247 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I) 1248 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1249 // This is not an aggressive instruction that we can promote. 1250 // Because of this, we won't be able to get rid of the control 1251 // flow, so the xform is not worth it. 1252 return false; 1253 } 1254 } 1255 1256 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: " 1257 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"); 1258 1259 // If we can still promote the PHI nodes after this gauntlet of tests, 1260 // do all of the PHI's now. 1261 Instruction *InsertPt = DomBlock->getTerminator(); 1262 1263 // Move all 'aggressive' instructions, which are defined in the 1264 // conditional parts of the if's up to the dominating block. 1265 if (IfBlock1) 1266 DomBlock->getInstList().splice(InsertPt, 1267 IfBlock1->getInstList(), IfBlock1->begin(), 1268 IfBlock1->getTerminator()); 1269 if (IfBlock2) 1270 DomBlock->getInstList().splice(InsertPt, 1271 IfBlock2->getInstList(), IfBlock2->begin(), 1272 IfBlock2->getTerminator()); 1273 1274 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 1275 // Change the PHI node into a select instruction. 1276 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); 1277 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); 1278 1279 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", InsertPt); 1280 PN->replaceAllUsesWith(NV); 1281 NV->takeName(PN); 1282 PN->eraseFromParent(); 1283 } 1284 1285 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement 1286 // has been flattened. Change DomBlock to jump directly to our new block to 1287 // avoid other simplifycfg's kicking in on the diamond. 1288 TerminatorInst *OldTI = DomBlock->getTerminator(); 1289 BranchInst::Create(BB, OldTI); 1290 OldTI->eraseFromParent(); 1291 return true; 1292} 1293 1294/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes 1295/// to two returning blocks, try to merge them together into one return, 1296/// introducing a select if the return values disagree. 1297static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) { 1298 assert(BI->isConditional() && "Must be a conditional branch"); 1299 BasicBlock *TrueSucc = BI->getSuccessor(0); 1300 BasicBlock *FalseSucc = BI->getSuccessor(1); 1301 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator()); 1302 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator()); 1303 1304 // Check to ensure both blocks are empty (just a return) or optionally empty 1305 // with PHI nodes. If there are other instructions, merging would cause extra 1306 // computation on one path or the other. 1307 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator()) 1308 return false; 1309 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator()) 1310 return false; 1311 1312 // Okay, we found a branch that is going to two return nodes. If 1313 // there is no return value for this function, just change the 1314 // branch into a return. 1315 if (FalseRet->getNumOperands() == 0) { 1316 TrueSucc->removePredecessor(BI->getParent()); 1317 FalseSucc->removePredecessor(BI->getParent()); 1318 ReturnInst::Create(BI->getContext(), 0, BI); 1319 EraseTerminatorInstAndDCECond(BI); 1320 return true; 1321 } 1322 1323 // Otherwise, figure out what the true and false return values are 1324 // so we can insert a new select instruction. 1325 Value *TrueValue = TrueRet->getReturnValue(); 1326 Value *FalseValue = FalseRet->getReturnValue(); 1327 1328 // Unwrap any PHI nodes in the return blocks. 1329 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue)) 1330 if (TVPN->getParent() == TrueSucc) 1331 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); 1332 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue)) 1333 if (FVPN->getParent() == FalseSucc) 1334 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); 1335 1336 // In order for this transformation to be safe, we must be able to 1337 // unconditionally execute both operands to the return. This is 1338 // normally the case, but we could have a potentially-trapping 1339 // constant expression that prevents this transformation from being 1340 // safe. 1341 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue)) 1342 if (TCV->canTrap()) 1343 return false; 1344 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue)) 1345 if (FCV->canTrap()) 1346 return false; 1347 1348 // Okay, we collected all the mapped values and checked them for sanity, and 1349 // defined to really do this transformation. First, update the CFG. 1350 TrueSucc->removePredecessor(BI->getParent()); 1351 FalseSucc->removePredecessor(BI->getParent()); 1352 1353 // Insert select instructions where needed. 1354 Value *BrCond = BI->getCondition(); 1355 if (TrueValue) { 1356 // Insert a select if the results differ. 1357 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) { 1358 } else if (isa<UndefValue>(TrueValue)) { 1359 TrueValue = FalseValue; 1360 } else { 1361 TrueValue = SelectInst::Create(BrCond, TrueValue, 1362 FalseValue, "retval", BI); 1363 } 1364 } 1365 1366 Value *RI = !TrueValue ? 1367 ReturnInst::Create(BI->getContext(), BI) : 1368 ReturnInst::Create(BI->getContext(), TrueValue, BI); 1369 (void) RI; 1370 1371 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" 1372 << "\n " << *BI << "NewRet = " << *RI 1373 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc); 1374 1375 EraseTerminatorInstAndDCECond(BI); 1376 1377 return true; 1378} 1379 1380/// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch, 1381/// and if a predecessor branches to us and one of our successors, fold the 1382/// setcc into the predecessor and use logical operations to pick the right 1383/// destination. 1384bool llvm::FoldBranchToCommonDest(BranchInst *BI) { 1385 BasicBlock *BB = BI->getParent(); 1386 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 1387 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) || 1388 Cond->getParent() != BB || !Cond->hasOneUse()) 1389 return false; 1390 1391 // Only allow this if the condition is a simple instruction that can be 1392 // executed unconditionally. It must be in the same block as the branch, and 1393 // must be at the front of the block. 1394 BasicBlock::iterator FrontIt = BB->front(); 1395 // Ignore dbg intrinsics. 1396 while (isa<DbgInfoIntrinsic>(FrontIt)) 1397 ++FrontIt; 1398 1399 // Allow a single instruction to be hoisted in addition to the compare 1400 // that feeds the branch. We later ensure that any values that _it_ uses 1401 // were also live in the predecessor, so that we don't unnecessarily create 1402 // register pressure or inhibit out-of-order execution. 1403 Instruction *BonusInst = 0; 1404 if (&*FrontIt != Cond && 1405 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond && 1406 FrontIt->isSafeToSpeculativelyExecute()) { 1407 BonusInst = &*FrontIt; 1408 ++FrontIt; 1409 } 1410 1411 // Only a single bonus inst is allowed. 1412 if (&*FrontIt != Cond) 1413 return false; 1414 1415 // Make sure the instruction after the condition is the cond branch. 1416 BasicBlock::iterator CondIt = Cond; ++CondIt; 1417 // Ingore dbg intrinsics. 1418 while(isa<DbgInfoIntrinsic>(CondIt)) 1419 ++CondIt; 1420 if (&*CondIt != BI) { 1421 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!"); 1422 return false; 1423 } 1424 1425 // Cond is known to be a compare or binary operator. Check to make sure that 1426 // neither operand is a potentially-trapping constant expression. 1427 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0))) 1428 if (CE->canTrap()) 1429 return false; 1430 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1))) 1431 if (CE->canTrap()) 1432 return false; 1433 1434 1435 // Finally, don't infinitely unroll conditional loops. 1436 BasicBlock *TrueDest = BI->getSuccessor(0); 1437 BasicBlock *FalseDest = BI->getSuccessor(1); 1438 if (TrueDest == BB || FalseDest == BB) 1439 return false; 1440 1441 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1442 BasicBlock *PredBlock = *PI; 1443 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); 1444 1445 // Check that we have two conditional branches. If there is a PHI node in 1446 // the common successor, verify that the same value flows in from both 1447 // blocks. 1448 if (PBI == 0 || PBI->isUnconditional() || 1449 !SafeToMergeTerminators(BI, PBI)) 1450 continue; 1451 1452 // Ensure that any values used in the bonus instruction are also used 1453 // by the terminator of the predecessor. This means that those values 1454 // must already have been resolved, so we won't be inhibiting the 1455 // out-of-order core by speculating them earlier. 1456 if (BonusInst) { 1457 // Collect the values used by the bonus inst 1458 SmallPtrSet<Value*, 4> UsedValues; 1459 for (Instruction::op_iterator OI = BonusInst->op_begin(), 1460 OE = BonusInst->op_end(); OI != OE; ++OI) { 1461 Value* V = *OI; 1462 if (!isa<Constant>(V)) 1463 UsedValues.insert(V); 1464 } 1465 1466 SmallVector<std::pair<Value*, unsigned>, 4> Worklist; 1467 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0)); 1468 1469 // Walk up to four levels back up the use-def chain of the predecessor's 1470 // terminator to see if all those values were used. The choice of four 1471 // levels is arbitrary, to provide a compile-time-cost bound. 1472 while (!Worklist.empty()) { 1473 std::pair<Value*, unsigned> Pair = Worklist.back(); 1474 Worklist.pop_back(); 1475 1476 if (Pair.second >= 4) continue; 1477 UsedValues.erase(Pair.first); 1478 if (UsedValues.empty()) break; 1479 1480 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) { 1481 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 1482 OI != OE; ++OI) 1483 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1)); 1484 } 1485 } 1486 1487 if (!UsedValues.empty()) return false; 1488 } 1489 1490 Instruction::BinaryOps Opc; 1491 bool InvertPredCond = false; 1492 1493 if (PBI->getSuccessor(0) == TrueDest) 1494 Opc = Instruction::Or; 1495 else if (PBI->getSuccessor(1) == FalseDest) 1496 Opc = Instruction::And; 1497 else if (PBI->getSuccessor(0) == FalseDest) 1498 Opc = Instruction::And, InvertPredCond = true; 1499 else if (PBI->getSuccessor(1) == TrueDest) 1500 Opc = Instruction::Or, InvertPredCond = true; 1501 else 1502 continue; 1503 1504 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB); 1505 1506 // If we need to invert the condition in the pred block to match, do so now. 1507 if (InvertPredCond) { 1508 Value *NewCond = PBI->getCondition(); 1509 1510 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) { 1511 CmpInst *CI = cast<CmpInst>(NewCond); 1512 CI->setPredicate(CI->getInversePredicate()); 1513 } else { 1514 NewCond = BinaryOperator::CreateNot(NewCond, 1515 PBI->getCondition()->getName()+".not", PBI); 1516 } 1517 1518 PBI->setCondition(NewCond); 1519 BasicBlock *OldTrue = PBI->getSuccessor(0); 1520 BasicBlock *OldFalse = PBI->getSuccessor(1); 1521 PBI->setSuccessor(0, OldFalse); 1522 PBI->setSuccessor(1, OldTrue); 1523 } 1524 1525 // If we have a bonus inst, clone it into the predecessor block. 1526 Instruction *NewBonus = 0; 1527 if (BonusInst) { 1528 NewBonus = BonusInst->clone(); 1529 PredBlock->getInstList().insert(PBI, NewBonus); 1530 NewBonus->takeName(BonusInst); 1531 BonusInst->setName(BonusInst->getName()+".old"); 1532 } 1533 1534 // Clone Cond into the predecessor basic block, and or/and the 1535 // two conditions together. 1536 Instruction *New = Cond->clone(); 1537 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus); 1538 PredBlock->getInstList().insert(PBI, New); 1539 New->takeName(Cond); 1540 Cond->setName(New->getName()+".old"); 1541 1542 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(), 1543 New, "or.cond", PBI); 1544 PBI->setCondition(NewCond); 1545 if (PBI->getSuccessor(0) == BB) { 1546 AddPredecessorToBlock(TrueDest, PredBlock, BB); 1547 PBI->setSuccessor(0, TrueDest); 1548 } 1549 if (PBI->getSuccessor(1) == BB) { 1550 AddPredecessorToBlock(FalseDest, PredBlock, BB); 1551 PBI->setSuccessor(1, FalseDest); 1552 } 1553 return true; 1554 } 1555 return false; 1556} 1557 1558/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a 1559/// predecessor of another block, this function tries to simplify it. We know 1560/// that PBI and BI are both conditional branches, and BI is in one of the 1561/// successor blocks of PBI - PBI branches to BI. 1562static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) { 1563 assert(PBI->isConditional() && BI->isConditional()); 1564 BasicBlock *BB = BI->getParent(); 1565 1566 // If this block ends with a branch instruction, and if there is a 1567 // predecessor that ends on a branch of the same condition, make 1568 // this conditional branch redundant. 1569 if (PBI->getCondition() == BI->getCondition() && 1570 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 1571 // Okay, the outcome of this conditional branch is statically 1572 // knowable. If this block had a single pred, handle specially. 1573 if (BB->getSinglePredecessor()) { 1574 // Turn this into a branch on constant. 1575 bool CondIsTrue = PBI->getSuccessor(0) == BB; 1576 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 1577 CondIsTrue)); 1578 return true; // Nuke the branch on constant. 1579 } 1580 1581 // Otherwise, if there are multiple predecessors, insert a PHI that merges 1582 // in the constant and simplify the block result. Subsequent passes of 1583 // simplifycfg will thread the block. 1584 if (BlockIsSimpleEnoughToThreadThrough(BB)) { 1585 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()), 1586 BI->getCondition()->getName() + ".pr", 1587 BB->begin()); 1588 // Okay, we're going to insert the PHI node. Since PBI is not the only 1589 // predecessor, compute the PHI'd conditional value for all of the preds. 1590 // Any predecessor where the condition is not computable we keep symbolic. 1591 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1592 BasicBlock *P = *PI; 1593 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && 1594 PBI != BI && PBI->isConditional() && 1595 PBI->getCondition() == BI->getCondition() && 1596 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 1597 bool CondIsTrue = PBI->getSuccessor(0) == BB; 1598 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 1599 CondIsTrue), P); 1600 } else { 1601 NewPN->addIncoming(BI->getCondition(), P); 1602 } 1603 } 1604 1605 BI->setCondition(NewPN); 1606 return true; 1607 } 1608 } 1609 1610 // If this is a conditional branch in an empty block, and if any 1611 // predecessors is a conditional branch to one of our destinations, 1612 // fold the conditions into logical ops and one cond br. 1613 BasicBlock::iterator BBI = BB->begin(); 1614 // Ignore dbg intrinsics. 1615 while (isa<DbgInfoIntrinsic>(BBI)) 1616 ++BBI; 1617 if (&*BBI != BI) 1618 return false; 1619 1620 1621 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition())) 1622 if (CE->canTrap()) 1623 return false; 1624 1625 int PBIOp, BIOp; 1626 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) 1627 PBIOp = BIOp = 0; 1628 else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) 1629 PBIOp = 0, BIOp = 1; 1630 else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) 1631 PBIOp = 1, BIOp = 0; 1632 else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) 1633 PBIOp = BIOp = 1; 1634 else 1635 return false; 1636 1637 // Check to make sure that the other destination of this branch 1638 // isn't BB itself. If so, this is an infinite loop that will 1639 // keep getting unwound. 1640 if (PBI->getSuccessor(PBIOp) == BB) 1641 return false; 1642 1643 // Do not perform this transformation if it would require 1644 // insertion of a large number of select instructions. For targets 1645 // without predication/cmovs, this is a big pessimization. 1646 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); 1647 1648 unsigned NumPhis = 0; 1649 for (BasicBlock::iterator II = CommonDest->begin(); 1650 isa<PHINode>(II); ++II, ++NumPhis) 1651 if (NumPhis > 2) // Disable this xform. 1652 return false; 1653 1654 // Finally, if everything is ok, fold the branches to logical ops. 1655 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); 1656 1657 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent() 1658 << "AND: " << *BI->getParent()); 1659 1660 1661 // If OtherDest *is* BB, then BB is a basic block with a single conditional 1662 // branch in it, where one edge (OtherDest) goes back to itself but the other 1663 // exits. We don't *know* that the program avoids the infinite loop 1664 // (even though that seems likely). If we do this xform naively, we'll end up 1665 // recursively unpeeling the loop. Since we know that (after the xform is 1666 // done) that the block *is* infinite if reached, we just make it an obviously 1667 // infinite loop with no cond branch. 1668 if (OtherDest == BB) { 1669 // Insert it at the end of the function, because it's either code, 1670 // or it won't matter if it's hot. :) 1671 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(), 1672 "infloop", BB->getParent()); 1673 BranchInst::Create(InfLoopBlock, InfLoopBlock); 1674 OtherDest = InfLoopBlock; 1675 } 1676 1677 DEBUG(dbgs() << *PBI->getParent()->getParent()); 1678 1679 // BI may have other predecessors. Because of this, we leave 1680 // it alone, but modify PBI. 1681 1682 // Make sure we get to CommonDest on True&True directions. 1683 Value *PBICond = PBI->getCondition(); 1684 if (PBIOp) 1685 PBICond = BinaryOperator::CreateNot(PBICond, 1686 PBICond->getName()+".not", 1687 PBI); 1688 Value *BICond = BI->getCondition(); 1689 if (BIOp) 1690 BICond = BinaryOperator::CreateNot(BICond, 1691 BICond->getName()+".not", 1692 PBI); 1693 // Merge the conditions. 1694 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI); 1695 1696 // Modify PBI to branch on the new condition to the new dests. 1697 PBI->setCondition(Cond); 1698 PBI->setSuccessor(0, CommonDest); 1699 PBI->setSuccessor(1, OtherDest); 1700 1701 // OtherDest may have phi nodes. If so, add an entry from PBI's 1702 // block that are identical to the entries for BI's block. 1703 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB); 1704 1705 // We know that the CommonDest already had an edge from PBI to 1706 // it. If it has PHIs though, the PHIs may have different 1707 // entries for BB and PBI's BB. If so, insert a select to make 1708 // them agree. 1709 PHINode *PN; 1710 for (BasicBlock::iterator II = CommonDest->begin(); 1711 (PN = dyn_cast<PHINode>(II)); ++II) { 1712 Value *BIV = PN->getIncomingValueForBlock(BB); 1713 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent()); 1714 Value *PBIV = PN->getIncomingValue(PBBIdx); 1715 if (BIV != PBIV) { 1716 // Insert a select in PBI to pick the right value. 1717 Value *NV = SelectInst::Create(PBICond, PBIV, BIV, 1718 PBIV->getName()+".mux", PBI); 1719 PN->setIncomingValue(PBBIdx, NV); 1720 } 1721 } 1722 1723 DEBUG(dbgs() << "INTO: " << *PBI->getParent()); 1724 DEBUG(dbgs() << *PBI->getParent()->getParent()); 1725 1726 // This basic block is probably dead. We know it has at least 1727 // one fewer predecessor. 1728 return true; 1729} 1730 1731// SimplifyIndirectBrOnSelect - Replaces 1732// (indirectbr (select cond, blockaddress(@fn, BlockA), 1733// blockaddress(@fn, BlockB))) 1734// with 1735// (br cond, BlockA, BlockB). 1736static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) { 1737 // Check that both operands of the select are block addresses. 1738 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue()); 1739 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue()); 1740 if (!TBA || !FBA) 1741 return false; 1742 1743 // Extract the actual blocks. 1744 BasicBlock *TrueBB = TBA->getBasicBlock(); 1745 BasicBlock *FalseBB = FBA->getBasicBlock(); 1746 1747 // Remove any superfluous successor edges from the CFG. 1748 // First, figure out which successors to preserve. 1749 // If TrueBB and FalseBB are equal, only try to preserve one copy of that 1750 // successor. 1751 BasicBlock *KeepEdge1 = TrueBB; 1752 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0; 1753 1754 // Then remove the rest. 1755 for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) { 1756 BasicBlock *Succ = IBI->getSuccessor(I); 1757 // Make sure only to keep exactly one copy of each edge. 1758 if (Succ == KeepEdge1) 1759 KeepEdge1 = 0; 1760 else if (Succ == KeepEdge2) 1761 KeepEdge2 = 0; 1762 else 1763 Succ->removePredecessor(IBI->getParent()); 1764 } 1765 1766 // Insert an appropriate new terminator. 1767 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) { 1768 if (TrueBB == FalseBB) 1769 // We were only looking for one successor, and it was present. 1770 // Create an unconditional branch to it. 1771 BranchInst::Create(TrueBB, IBI); 1772 else 1773 // We found both of the successors we were looking for. 1774 // Create a conditional branch sharing the condition of the select. 1775 BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI); 1776 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) { 1777 // Neither of the selected blocks were successors, so this 1778 // indirectbr must be unreachable. 1779 new UnreachableInst(IBI->getContext(), IBI); 1780 } else { 1781 // One of the selected values was a successor, but the other wasn't. 1782 // Insert an unconditional branch to the one that was found; 1783 // the edge to the one that wasn't must be unreachable. 1784 if (KeepEdge1 == 0) 1785 // Only TrueBB was found. 1786 BranchInst::Create(TrueBB, IBI); 1787 else 1788 // Only FalseBB was found. 1789 BranchInst::Create(FalseBB, IBI); 1790 } 1791 1792 EraseTerminatorInstAndDCECond(IBI); 1793 return true; 1794} 1795 1796/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp 1797/// instruction (a seteq/setne with a constant) as the only instruction in a 1798/// block that ends with an uncond branch. We are looking for a very specific 1799/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In 1800/// this case, we merge the first two "or's of icmp" into a switch, but then the 1801/// default value goes to an uncond block with a seteq in it, we get something 1802/// like: 1803/// 1804/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ] 1805/// DEFAULT: 1806/// %tmp = icmp eq i8 %A, 92 1807/// br label %end 1808/// end: 1809/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ] 1810/// 1811/// We prefer to split the edge to 'end' so that there is a true/false entry to 1812/// the PHI, merging the third icmp into the switch. 1813static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI, 1814 const TargetData *TD) { 1815 BasicBlock *BB = ICI->getParent(); 1816 // If the block has any PHIs in it or the icmp has multiple uses, it is too 1817 // complex. 1818 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false; 1819 1820 Value *V = ICI->getOperand(0); 1821 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1)); 1822 1823 // The pattern we're looking for is where our only predecessor is a switch on 1824 // 'V' and this block is the default case for the switch. In this case we can 1825 // fold the compared value into the switch to simplify things. 1826 BasicBlock *Pred = BB->getSinglePredecessor(); 1827 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false; 1828 1829 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator()); 1830 if (SI->getCondition() != V) 1831 return false; 1832 1833 // If BB is reachable on a non-default case, then we simply know the value of 1834 // V in this block. Substitute it and constant fold the icmp instruction 1835 // away. 1836 if (SI->getDefaultDest() != BB) { 1837 ConstantInt *VVal = SI->findCaseDest(BB); 1838 assert(VVal && "Should have a unique destination value"); 1839 ICI->setOperand(0, VVal); 1840 1841 if (Value *V = SimplifyInstruction(ICI, TD)) { 1842 ICI->replaceAllUsesWith(V); 1843 ICI->eraseFromParent(); 1844 } 1845 // BB is now empty, so it is likely to simplify away. 1846 return SimplifyCFG(BB) | true; 1847 } 1848 1849 // Ok, the block is reachable from the default dest. If the constant we're 1850 // comparing exists in one of the other edges, then we can constant fold ICI 1851 // and zap it. 1852 if (SI->findCaseValue(Cst) != 0) { 1853 Value *V; 1854 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 1855 V = ConstantInt::getFalse(BB->getContext()); 1856 else 1857 V = ConstantInt::getTrue(BB->getContext()); 1858 1859 ICI->replaceAllUsesWith(V); 1860 ICI->eraseFromParent(); 1861 // BB is now empty, so it is likely to simplify away. 1862 return SimplifyCFG(BB) | true; 1863 } 1864 1865 // The use of the icmp has to be in the 'end' block, by the only PHI node in 1866 // the block. 1867 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0); 1868 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back()); 1869 if (PHIUse == 0 || PHIUse != &SuccBlock->front() || 1870 isa<PHINode>(++BasicBlock::iterator(PHIUse))) 1871 return false; 1872 1873 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets 1874 // true in the PHI. 1875 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext()); 1876 Constant *NewCst = ConstantInt::getFalse(BB->getContext()); 1877 1878 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 1879 std::swap(DefaultCst, NewCst); 1880 1881 // Replace ICI (which is used by the PHI for the default value) with true or 1882 // false depending on if it is EQ or NE. 1883 ICI->replaceAllUsesWith(DefaultCst); 1884 ICI->eraseFromParent(); 1885 1886 // Okay, the switch goes to this block on a default value. Add an edge from 1887 // the switch to the merge point on the compared value. 1888 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge", 1889 BB->getParent(), BB); 1890 SI->addCase(Cst, NewBB); 1891 1892 // NewBB branches to the phi block, add the uncond branch and the phi entry. 1893 BranchInst::Create(SuccBlock, NewBB); 1894 PHIUse->addIncoming(NewCst, NewBB); 1895 return true; 1896} 1897 1898/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch. 1899/// Check to see if it is branching on an or/and chain of icmp instructions, and 1900/// fold it into a switch instruction if so. 1901static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) { 1902 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 1903 if (Cond == 0) return false; 1904 1905 1906 // Change br (X == 0 | X == 1), T, F into a switch instruction. 1907 // If this is a bunch of seteq's or'd together, or if it's a bunch of 1908 // 'setne's and'ed together, collect them. 1909 Value *CompVal = 0; 1910 std::vector<ConstantInt*> Values; 1911 bool TrueWhenEqual = true; 1912 Value *ExtraCase = 0; 1913 1914 if (Cond->getOpcode() == Instruction::Or) { 1915 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true); 1916 } else if (Cond->getOpcode() == Instruction::And) { 1917 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false); 1918 TrueWhenEqual = false; 1919 } 1920 1921 // If we didn't have a multiply compared value, fail. 1922 if (CompVal == 0) return false; 1923 1924 // There might be duplicate constants in the list, which the switch 1925 // instruction can't handle, remove them now. 1926 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate); 1927 Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); 1928 1929 // If Extra was used, we require at least two switch values to do the 1930 // transformation. A switch with one value is just an cond branch. 1931 if (ExtraCase && Values.size() < 2) return false; 1932 1933 // Figure out which block is which destination. 1934 BasicBlock *DefaultBB = BI->getSuccessor(1); 1935 BasicBlock *EdgeBB = BI->getSuccessor(0); 1936 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); 1937 1938 BasicBlock *BB = BI->getParent(); 1939 1940 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size() 1941 << " cases into SWITCH. BB is:\n" << *BB); 1942 1943 // If there are any extra values that couldn't be folded into the switch 1944 // then we evaluate them with an explicit branch first. Split the block 1945 // right before the condbr to handle it. 1946 if (ExtraCase) { 1947 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test"); 1948 // Remove the uncond branch added to the old block. 1949 TerminatorInst *OldTI = BB->getTerminator(); 1950 1951 if (TrueWhenEqual) 1952 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI); 1953 else 1954 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI); 1955 1956 OldTI->eraseFromParent(); 1957 1958 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them 1959 // for the edge we just added. 1960 AddPredecessorToBlock(EdgeBB, BB, NewBB); 1961 1962 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase 1963 << "\nEXTRABB = " << *BB); 1964 BB = NewBB; 1965 } 1966 1967 // Convert pointer to int before we switch. 1968 if (CompVal->getType()->isPointerTy()) { 1969 assert(TD && "Cannot switch on pointer without TargetData"); 1970 CompVal = new PtrToIntInst(CompVal, 1971 TD->getIntPtrType(CompVal->getContext()), 1972 "magicptr", BI); 1973 } 1974 1975 // Create the new switch instruction now. 1976 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI); 1977 1978 // Add all of the 'cases' to the switch instruction. 1979 for (unsigned i = 0, e = Values.size(); i != e; ++i) 1980 New->addCase(Values[i], EdgeBB); 1981 1982 // We added edges from PI to the EdgeBB. As such, if there were any 1983 // PHI nodes in EdgeBB, they need entries to be added corresponding to 1984 // the number of edges added. 1985 for (BasicBlock::iterator BBI = EdgeBB->begin(); 1986 isa<PHINode>(BBI); ++BBI) { 1987 PHINode *PN = cast<PHINode>(BBI); 1988 Value *InVal = PN->getIncomingValueForBlock(BB); 1989 for (unsigned i = 0, e = Values.size()-1; i != e; ++i) 1990 PN->addIncoming(InVal, BB); 1991 } 1992 1993 // Erase the old branch instruction. 1994 EraseTerminatorInstAndDCECond(BI); 1995 1996 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n'); 1997 return true; 1998} 1999 2000bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) { 2001 BasicBlock *BB = RI->getParent(); 2002 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; 2003 2004 // Find predecessors that end with branches. 2005 SmallVector<BasicBlock*, 8> UncondBranchPreds; 2006 SmallVector<BranchInst*, 8> CondBranchPreds; 2007 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 2008 BasicBlock *P = *PI; 2009 TerminatorInst *PTI = P->getTerminator(); 2010 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) { 2011 if (BI->isUnconditional()) 2012 UncondBranchPreds.push_back(P); 2013 else 2014 CondBranchPreds.push_back(BI); 2015 } 2016 } 2017 2018 // If we found some, do the transformation! 2019 if (!UncondBranchPreds.empty()) { 2020 while (!UncondBranchPreds.empty()) { 2021 BasicBlock *Pred = UncondBranchPreds.pop_back_val(); 2022 DEBUG(dbgs() << "FOLDING: " << *BB 2023 << "INTO UNCOND BRANCH PRED: " << *Pred); 2024 Instruction *UncondBranch = Pred->getTerminator(); 2025 // Clone the return and add it to the end of the predecessor. 2026 Instruction *NewRet = RI->clone(); 2027 Pred->getInstList().push_back(NewRet); 2028 2029 // If the return instruction returns a value, and if the value was a 2030 // PHI node in "BB", propagate the right value into the return. 2031 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end(); 2032 i != e; ++i) 2033 if (PHINode *PN = dyn_cast<PHINode>(*i)) 2034 if (PN->getParent() == BB) 2035 *i = PN->getIncomingValueForBlock(Pred); 2036 2037 // Update any PHI nodes in the returning block to realize that we no 2038 // longer branch to them. 2039 BB->removePredecessor(Pred); 2040 UncondBranch->eraseFromParent(); 2041 } 2042 2043 // If we eliminated all predecessors of the block, delete the block now. 2044 if (pred_begin(BB) == pred_end(BB)) 2045 // We know there are no successors, so just nuke the block. 2046 BB->eraseFromParent(); 2047 2048 return true; 2049 } 2050 2051 // Check out all of the conditional branches going to this return 2052 // instruction. If any of them just select between returns, change the 2053 // branch itself into a select/return pair. 2054 while (!CondBranchPreds.empty()) { 2055 BranchInst *BI = CondBranchPreds.pop_back_val(); 2056 2057 // Check to see if the non-BB successor is also a return block. 2058 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) && 2059 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) && 2060 SimplifyCondBranchToTwoReturns(BI)) 2061 return true; 2062 } 2063 return false; 2064} 2065 2066bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) { 2067 // Check to see if the first instruction in this block is just an unwind. 2068 // If so, replace any invoke instructions which use this as an exception 2069 // destination with call instructions. 2070 BasicBlock *BB = UI->getParent(); 2071 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; 2072 2073 bool Changed = false; 2074 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 2075 while (!Preds.empty()) { 2076 BasicBlock *Pred = Preds.back(); 2077 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()); 2078 if (II && II->getUnwindDest() == BB) { 2079 // Insert a new branch instruction before the invoke, because this 2080 // is now a fall through. 2081 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II); 2082 Pred->getInstList().remove(II); // Take out of symbol table 2083 2084 // Insert the call now. 2085 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3); 2086 CallInst *CI = CallInst::Create(II->getCalledValue(), 2087 Args.begin(), Args.end(), 2088 II->getName(), BI); 2089 CI->setCallingConv(II->getCallingConv()); 2090 CI->setAttributes(II->getAttributes()); 2091 // If the invoke produced a value, the Call now does instead. 2092 II->replaceAllUsesWith(CI); 2093 delete II; 2094 Changed = true; 2095 } 2096 2097 Preds.pop_back(); 2098 } 2099 2100 // If this block is now dead (and isn't the entry block), remove it. 2101 if (pred_begin(BB) == pred_end(BB) && 2102 BB != &BB->getParent()->getEntryBlock()) { 2103 // We know there are no successors, so just nuke the block. 2104 BB->eraseFromParent(); 2105 return true; 2106 } 2107 2108 return Changed; 2109} 2110 2111bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) { 2112 BasicBlock *BB = UI->getParent(); 2113 2114 bool Changed = false; 2115 2116 // If there are any instructions immediately before the unreachable that can 2117 // be removed, do so. 2118 while (UI != BB->begin()) { 2119 BasicBlock::iterator BBI = UI; 2120 --BBI; 2121 // Do not delete instructions that can have side effects, like calls 2122 // (which may never return) and volatile loads and stores. 2123 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break; 2124 2125 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) 2126 if (SI->isVolatile()) 2127 break; 2128 2129 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) 2130 if (LI->isVolatile()) 2131 break; 2132 2133 // Delete this instruction 2134 BBI->eraseFromParent(); 2135 Changed = true; 2136 } 2137 2138 // If the unreachable instruction is the first in the block, take a gander 2139 // at all of the predecessors of this instruction, and simplify them. 2140 if (&BB->front() != UI) return Changed; 2141 2142 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 2143 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 2144 TerminatorInst *TI = Preds[i]->getTerminator(); 2145 2146 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 2147 if (BI->isUnconditional()) { 2148 if (BI->getSuccessor(0) == BB) { 2149 new UnreachableInst(TI->getContext(), TI); 2150 TI->eraseFromParent(); 2151 Changed = true; 2152 } 2153 } else { 2154 if (BI->getSuccessor(0) == BB) { 2155 BranchInst::Create(BI->getSuccessor(1), BI); 2156 EraseTerminatorInstAndDCECond(BI); 2157 } else if (BI->getSuccessor(1) == BB) { 2158 BranchInst::Create(BI->getSuccessor(0), BI); 2159 EraseTerminatorInstAndDCECond(BI); 2160 Changed = true; 2161 } 2162 } 2163 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 2164 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2165 if (SI->getSuccessor(i) == BB) { 2166 BB->removePredecessor(SI->getParent()); 2167 SI->removeCase(i); 2168 --i; --e; 2169 Changed = true; 2170 } 2171 // If the default value is unreachable, figure out the most popular 2172 // destination and make it the default. 2173 if (SI->getSuccessor(0) == BB) { 2174 std::map<BasicBlock*, unsigned> Popularity; 2175 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2176 Popularity[SI->getSuccessor(i)]++; 2177 2178 // Find the most popular block. 2179 unsigned MaxPop = 0; 2180 BasicBlock *MaxBlock = 0; 2181 for (std::map<BasicBlock*, unsigned>::iterator 2182 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { 2183 if (I->second > MaxPop) { 2184 MaxPop = I->second; 2185 MaxBlock = I->first; 2186 } 2187 } 2188 if (MaxBlock) { 2189 // Make this the new default, allowing us to delete any explicit 2190 // edges to it. 2191 SI->setSuccessor(0, MaxBlock); 2192 Changed = true; 2193 2194 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from 2195 // it. 2196 if (isa<PHINode>(MaxBlock->begin())) 2197 for (unsigned i = 0; i != MaxPop-1; ++i) 2198 MaxBlock->removePredecessor(SI->getParent()); 2199 2200 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2201 if (SI->getSuccessor(i) == MaxBlock) { 2202 SI->removeCase(i); 2203 --i; --e; 2204 } 2205 } 2206 } 2207 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) { 2208 if (II->getUnwindDest() == BB) { 2209 // Convert the invoke to a call instruction. This would be a good 2210 // place to note that the call does not throw though. 2211 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II); 2212 II->removeFromParent(); // Take out of symbol table 2213 2214 // Insert the call now... 2215 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3); 2216 CallInst *CI = CallInst::Create(II->getCalledValue(), 2217 Args.begin(), Args.end(), 2218 II->getName(), BI); 2219 CI->setCallingConv(II->getCallingConv()); 2220 CI->setAttributes(II->getAttributes()); 2221 // If the invoke produced a value, the call does now instead. 2222 II->replaceAllUsesWith(CI); 2223 delete II; 2224 Changed = true; 2225 } 2226 } 2227 } 2228 2229 // If this block is now dead, remove it. 2230 if (pred_begin(BB) == pred_end(BB) && 2231 BB != &BB->getParent()->getEntryBlock()) { 2232 // We know there are no successors, so just nuke the block. 2233 BB->eraseFromParent(); 2234 return true; 2235 } 2236 2237 return Changed; 2238} 2239 2240 2241bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) { 2242 // If this switch is too complex to want to look at, ignore it. 2243 if (!isValueEqualityComparison(SI)) 2244 return false; 2245 2246 BasicBlock *BB = SI->getParent(); 2247 2248 // If we only have one predecessor, and if it is a branch on this value, 2249 // see if that predecessor totally determines the outcome of this switch. 2250 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 2251 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred)) 2252 return SimplifyCFG(BB) | true; 2253 2254 // If the block only contains the switch, see if we can fold the block 2255 // away into any preds. 2256 BasicBlock::iterator BBI = BB->begin(); 2257 // Ignore dbg intrinsics. 2258 while (isa<DbgInfoIntrinsic>(BBI)) 2259 ++BBI; 2260 if (SI == &*BBI) 2261 if (FoldValueComparisonIntoPredecessors(SI)) 2262 return SimplifyCFG(BB) | true; 2263 2264 return false; 2265} 2266 2267bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) { 2268 BasicBlock *BB = IBI->getParent(); 2269 bool Changed = false; 2270 2271 // Eliminate redundant destinations. 2272 SmallPtrSet<Value *, 8> Succs; 2273 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 2274 BasicBlock *Dest = IBI->getDestination(i); 2275 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) { 2276 Dest->removePredecessor(BB); 2277 IBI->removeDestination(i); 2278 --i; --e; 2279 Changed = true; 2280 } 2281 } 2282 2283 if (IBI->getNumDestinations() == 0) { 2284 // If the indirectbr has no successors, change it to unreachable. 2285 new UnreachableInst(IBI->getContext(), IBI); 2286 EraseTerminatorInstAndDCECond(IBI); 2287 return true; 2288 } 2289 2290 if (IBI->getNumDestinations() == 1) { 2291 // If the indirectbr has one successor, change it to a direct branch. 2292 BranchInst::Create(IBI->getDestination(0), IBI); 2293 EraseTerminatorInstAndDCECond(IBI); 2294 return true; 2295 } 2296 2297 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) { 2298 if (SimplifyIndirectBrOnSelect(IBI, SI)) 2299 return SimplifyCFG(BB) | true; 2300 } 2301 return Changed; 2302} 2303 2304bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) { 2305 BasicBlock *BB = BI->getParent(); 2306 2307 // If the Terminator is the only non-phi instruction, simplify the block. 2308 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg(); 2309 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() && 2310 TryToSimplifyUncondBranchFromEmptyBlock(BB)) 2311 return true; 2312 2313 // If the only instruction in the block is a seteq/setne comparison 2314 // against a constant, try to simplify the block. 2315 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) 2316 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) { 2317 for (++I; isa<DbgInfoIntrinsic>(I); ++I) 2318 ; 2319 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD)) 2320 return true; 2321 } 2322 2323 return false; 2324} 2325 2326 2327bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) { 2328 BasicBlock *BB = BI->getParent(); 2329 2330 // Conditional branch 2331 if (isValueEqualityComparison(BI)) { 2332 // If we only have one predecessor, and if it is a branch on this value, 2333 // see if that predecessor totally determines the outcome of this 2334 // switch. 2335 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 2336 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred)) 2337 return SimplifyCFG(BB) | true; 2338 2339 // This block must be empty, except for the setcond inst, if it exists. 2340 // Ignore dbg intrinsics. 2341 BasicBlock::iterator I = BB->begin(); 2342 // Ignore dbg intrinsics. 2343 while (isa<DbgInfoIntrinsic>(I)) 2344 ++I; 2345 if (&*I == BI) { 2346 if (FoldValueComparisonIntoPredecessors(BI)) 2347 return SimplifyCFG(BB) | true; 2348 } else if (&*I == cast<Instruction>(BI->getCondition())){ 2349 ++I; 2350 // Ignore dbg intrinsics. 2351 while (isa<DbgInfoIntrinsic>(I)) 2352 ++I; 2353 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI)) 2354 return SimplifyCFG(BB) | true; 2355 } 2356 } 2357 2358 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction. 2359 if (SimplifyBranchOnICmpChain(BI, TD)) 2360 return true; 2361 2362 // We have a conditional branch to two blocks that are only reachable 2363 // from BI. We know that the condbr dominates the two blocks, so see if 2364 // there is any identical code in the "then" and "else" blocks. If so, we 2365 // can hoist it up to the branching block. 2366 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) { 2367 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 2368 if (HoistThenElseCodeToIf(BI)) 2369 return SimplifyCFG(BB) | true; 2370 } else { 2371 // If Successor #1 has multiple preds, we may be able to conditionally 2372 // execute Successor #0 if it branches to successor #1. 2373 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator(); 2374 if (Succ0TI->getNumSuccessors() == 1 && 2375 Succ0TI->getSuccessor(0) == BI->getSuccessor(1)) 2376 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0))) 2377 return SimplifyCFG(BB) | true; 2378 } 2379 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 2380 // If Successor #0 has multiple preds, we may be able to conditionally 2381 // execute Successor #1 if it branches to successor #0. 2382 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator(); 2383 if (Succ1TI->getNumSuccessors() == 1 && 2384 Succ1TI->getSuccessor(0) == BI->getSuccessor(0)) 2385 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1))) 2386 return SimplifyCFG(BB) | true; 2387 } 2388 2389 // If this is a branch on a phi node in the current block, thread control 2390 // through this block if any PHI node entries are constants. 2391 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition())) 2392 if (PN->getParent() == BI->getParent()) 2393 if (FoldCondBranchOnPHI(BI, TD)) 2394 return SimplifyCFG(BB) | true; 2395 2396 // If this basic block is ONLY a setcc and a branch, and if a predecessor 2397 // branches to us and one of our successors, fold the setcc into the 2398 // predecessor and use logical operations to pick the right destination. 2399 if (FoldBranchToCommonDest(BI)) 2400 return SimplifyCFG(BB) | true; 2401 2402 // Scan predecessor blocks for conditional branches. 2403 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 2404 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) 2405 if (PBI != BI && PBI->isConditional()) 2406 if (SimplifyCondBranchToCondBranch(PBI, BI)) 2407 return SimplifyCFG(BB) | true; 2408 2409 return false; 2410} 2411 2412bool SimplifyCFGOpt::run(BasicBlock *BB) { 2413 bool Changed = false; 2414 2415 assert(BB && BB->getParent() && "Block not embedded in function!"); 2416 assert(BB->getTerminator() && "Degenerate basic block encountered!"); 2417 2418 // Remove basic blocks that have no predecessors (except the entry block)... 2419 // or that just have themself as a predecessor. These are unreachable. 2420 if ((pred_begin(BB) == pred_end(BB) && 2421 BB != &BB->getParent()->getEntryBlock()) || 2422 BB->getSinglePredecessor() == BB) { 2423 DEBUG(dbgs() << "Removing BB: \n" << *BB); 2424 DeleteDeadBlock(BB); 2425 return true; 2426 } 2427 2428 // Check to see if we can constant propagate this terminator instruction 2429 // away... 2430 Changed |= ConstantFoldTerminator(BB); 2431 2432 // Check for and eliminate duplicate PHI nodes in this block. 2433 Changed |= EliminateDuplicatePHINodes(BB); 2434 2435 // Merge basic blocks into their predecessor if there is only one distinct 2436 // pred, and if there is only one distinct successor of the predecessor, and 2437 // if there are no PHI nodes. 2438 // 2439 if (MergeBlockIntoPredecessor(BB)) 2440 return true; 2441 2442 // If there is a trivial two-entry PHI node in this basic block, and we can 2443 // eliminate it, do so now. 2444 if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) 2445 if (PN->getNumIncomingValues() == 2) 2446 Changed |= FoldTwoEntryPHINode(PN, TD); 2447 2448 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { 2449 if (BI->isUnconditional()) { 2450 if (SimplifyUncondBranch(BI)) return true; 2451 } else { 2452 if (SimplifyCondBranch(BI)) return true; 2453 } 2454 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 2455 if (SimplifyReturn(RI)) return true; 2456 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { 2457 if (SimplifySwitch(SI)) return true; 2458 } else if (UnreachableInst *UI = 2459 dyn_cast<UnreachableInst>(BB->getTerminator())) { 2460 if (SimplifyUnreachable(UI)) return true; 2461 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) { 2462 if (SimplifyUnwind(UI)) return true; 2463 } else if (IndirectBrInst *IBI = 2464 dyn_cast<IndirectBrInst>(BB->getTerminator())) { 2465 if (SimplifyIndirectBr(IBI)) return true; 2466 } 2467 2468 return Changed; 2469} 2470 2471/// SimplifyCFG - This function is used to do simplification of a CFG. For 2472/// example, it adjusts branches to branches to eliminate the extra hop, it 2473/// eliminates unreachable basic blocks, and does other "peephole" optimization 2474/// of the CFG. It returns true if a modification was made. 2475/// 2476bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) { 2477 return SimplifyCFGOpt(TD).run(BB); 2478} 2479