SimplifyCFG.cpp revision d3a1788da15311781f661c1cbfe48cd5f98ae778
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/Analysis/ValueTracking.h" 24#include "llvm/Target/TargetData.h" 25#include "llvm/Transforms/Utils/BasicBlockUtils.h" 26#include "llvm/ADT/DenseMap.h" 27#include "llvm/ADT/SmallVector.h" 28#include "llvm/ADT/SmallPtrSet.h" 29#include "llvm/ADT/Statistic.h" 30#include "llvm/ADT/STLExtras.h" 31#include "llvm/Support/CFG.h" 32#include "llvm/Support/CommandLine.h" 33#include "llvm/Support/ConstantRange.h" 34#include "llvm/Support/Debug.h" 35#include "llvm/Support/IRBuilder.h" 36#include "llvm/Support/NoFolder.h" 37#include "llvm/Support/raw_ostream.h" 38#include <algorithm> 39#include <set> 40#include <map> 41using namespace llvm; 42 43static cl::opt<unsigned> 44PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1), 45 cl::desc("Control the amount of phi node folding to perform (default = 1)")); 46 47static cl::opt<bool> 48DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false), 49 cl::desc("Duplicate return instructions into unconditional branches")); 50 51STATISTIC(NumSpeculations, "Number of speculative executed instructions"); 52 53namespace { 54class SimplifyCFGOpt { 55 const TargetData *const TD; 56 57 Value *isValueEqualityComparison(TerminatorInst *TI); 58 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI, 59 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases); 60 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 61 BasicBlock *Pred, 62 IRBuilder<> &Builder); 63 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI, 64 IRBuilder<> &Builder); 65 66 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder); 67 bool SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder); 68 bool SimplifyUnreachable(UnreachableInst *UI); 69 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder); 70 bool SimplifyIndirectBr(IndirectBrInst *IBI); 71 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder); 72 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder); 73 74public: 75 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {} 76 bool run(BasicBlock *BB); 77}; 78} 79 80/// SafeToMergeTerminators - Return true if it is safe to merge these two 81/// terminator instructions together. 82/// 83static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) { 84 if (SI1 == SI2) return false; // Can't merge with self! 85 86 // It is not safe to merge these two switch instructions if they have a common 87 // successor, and if that successor has a PHI node, and if *that* PHI node has 88 // conflicting incoming values from the two switch blocks. 89 BasicBlock *SI1BB = SI1->getParent(); 90 BasicBlock *SI2BB = SI2->getParent(); 91 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); 92 93 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) 94 if (SI1Succs.count(*I)) 95 for (BasicBlock::iterator BBI = (*I)->begin(); 96 isa<PHINode>(BBI); ++BBI) { 97 PHINode *PN = cast<PHINode>(BBI); 98 if (PN->getIncomingValueForBlock(SI1BB) != 99 PN->getIncomingValueForBlock(SI2BB)) 100 return false; 101 } 102 103 return true; 104} 105 106/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will 107/// now be entries in it from the 'NewPred' block. The values that will be 108/// flowing into the PHI nodes will be the same as those coming in from 109/// ExistPred, an existing predecessor of Succ. 110static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, 111 BasicBlock *ExistPred) { 112 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do 113 114 PHINode *PN; 115 for (BasicBlock::iterator I = Succ->begin(); 116 (PN = dyn_cast<PHINode>(I)); ++I) 117 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred); 118} 119 120 121/// GetIfCondition - Given a basic block (BB) with two predecessors (and at 122/// least one PHI node in it), check to see if the merge at this block is due 123/// to an "if condition". If so, return the boolean condition that determines 124/// which entry into BB will be taken. Also, return by references the block 125/// that will be entered from if the condition is true, and the block that will 126/// be entered if the condition is false. 127/// 128/// This does no checking to see if the true/false blocks have large or unsavory 129/// instructions in them. 130static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 131 BasicBlock *&IfFalse) { 132 PHINode *SomePHI = cast<PHINode>(BB->begin()); 133 assert(SomePHI->getNumIncomingValues() == 2 && 134 "Function can only handle blocks with 2 predecessors!"); 135 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0); 136 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1); 137 138 // We can only handle branches. Other control flow will be lowered to 139 // branches if possible anyway. 140 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator()); 141 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator()); 142 if (Pred1Br == 0 || Pred2Br == 0) 143 return 0; 144 145 // Eliminate code duplication by ensuring that Pred1Br is conditional if 146 // either are. 147 if (Pred2Br->isConditional()) { 148 // If both branches are conditional, we don't have an "if statement". In 149 // reality, we could transform this case, but since the condition will be 150 // required anyway, we stand no chance of eliminating it, so the xform is 151 // probably not profitable. 152 if (Pred1Br->isConditional()) 153 return 0; 154 155 std::swap(Pred1, Pred2); 156 std::swap(Pred1Br, Pred2Br); 157 } 158 159 if (Pred1Br->isConditional()) { 160 // The only thing we have to watch out for here is to make sure that Pred2 161 // doesn't have incoming edges from other blocks. If it does, the condition 162 // doesn't dominate BB. 163 if (Pred2->getSinglePredecessor() == 0) 164 return 0; 165 166 // If we found a conditional branch predecessor, make sure that it branches 167 // to BB and Pred2Br. If it doesn't, this isn't an "if statement". 168 if (Pred1Br->getSuccessor(0) == BB && 169 Pred1Br->getSuccessor(1) == Pred2) { 170 IfTrue = Pred1; 171 IfFalse = Pred2; 172 } else if (Pred1Br->getSuccessor(0) == Pred2 && 173 Pred1Br->getSuccessor(1) == BB) { 174 IfTrue = Pred2; 175 IfFalse = Pred1; 176 } else { 177 // We know that one arm of the conditional goes to BB, so the other must 178 // go somewhere unrelated, and this must not be an "if statement". 179 return 0; 180 } 181 182 return Pred1Br->getCondition(); 183 } 184 185 // Ok, if we got here, both predecessors end with an unconditional branch to 186 // BB. Don't panic! If both blocks only have a single (identical) 187 // predecessor, and THAT is a conditional branch, then we're all ok! 188 BasicBlock *CommonPred = Pred1->getSinglePredecessor(); 189 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor()) 190 return 0; 191 192 // Otherwise, if this is a conditional branch, then we can use it! 193 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator()); 194 if (BI == 0) return 0; 195 196 assert(BI->isConditional() && "Two successors but not conditional?"); 197 if (BI->getSuccessor(0) == Pred1) { 198 IfTrue = Pred1; 199 IfFalse = Pred2; 200 } else { 201 IfTrue = Pred2; 202 IfFalse = Pred1; 203 } 204 return BI->getCondition(); 205} 206 207/// DominatesMergePoint - If we have a merge point of an "if condition" as 208/// accepted above, return true if the specified value dominates the block. We 209/// don't handle the true generality of domination here, just a special case 210/// which works well enough for us. 211/// 212/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to 213/// see if V (which must be an instruction) and its recursive operands 214/// that do not dominate BB have a combined cost lower than CostRemaining and 215/// are non-trapping. If both are true, the instruction is inserted into the 216/// set and true is returned. 217/// 218/// The cost for most non-trapping instructions is defined as 1 except for 219/// Select whose cost is 2. 220/// 221/// After this function returns, CostRemaining is decreased by the cost of 222/// V plus its non-dominating operands. If that cost is greater than 223/// CostRemaining, false is returned and CostRemaining is undefined. 224static bool DominatesMergePoint(Value *V, BasicBlock *BB, 225 SmallPtrSet<Instruction*, 4> *AggressiveInsts, 226 unsigned &CostRemaining) { 227 Instruction *I = dyn_cast<Instruction>(V); 228 if (!I) { 229 // Non-instructions all dominate instructions, but not all constantexprs 230 // can be executed unconditionally. 231 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V)) 232 if (C->canTrap()) 233 return false; 234 return true; 235 } 236 BasicBlock *PBB = I->getParent(); 237 238 // We don't want to allow weird loops that might have the "if condition" in 239 // the bottom of this block. 240 if (PBB == BB) return false; 241 242 // If this instruction is defined in a block that contains an unconditional 243 // branch to BB, then it must be in the 'conditional' part of the "if 244 // statement". If not, it definitely dominates the region. 245 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()); 246 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB) 247 return true; 248 249 // If we aren't allowing aggressive promotion anymore, then don't consider 250 // instructions in the 'if region'. 251 if (AggressiveInsts == 0) return false; 252 253 // If we have seen this instruction before, don't count it again. 254 if (AggressiveInsts->count(I)) return true; 255 256 // Okay, it looks like the instruction IS in the "condition". Check to 257 // see if it's a cheap instruction to unconditionally compute, and if it 258 // only uses stuff defined outside of the condition. If so, hoist it out. 259 if (!I->isSafeToSpeculativelyExecute()) 260 return false; 261 262 unsigned Cost = 0; 263 264 switch (I->getOpcode()) { 265 default: return false; // Cannot hoist this out safely. 266 case Instruction::Load: 267 // We have to check to make sure there are no instructions before the 268 // load in its basic block, as we are going to hoist the load out to its 269 // predecessor. 270 if (PBB->getFirstNonPHIOrDbg() != I) 271 return false; 272 Cost = 1; 273 break; 274 case Instruction::GetElementPtr: 275 // GEPs are cheap if all indices are constant. 276 if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices()) 277 return false; 278 Cost = 1; 279 break; 280 case Instruction::Add: 281 case Instruction::Sub: 282 case Instruction::And: 283 case Instruction::Or: 284 case Instruction::Xor: 285 case Instruction::Shl: 286 case Instruction::LShr: 287 case Instruction::AShr: 288 case Instruction::ICmp: 289 case Instruction::Trunc: 290 case Instruction::ZExt: 291 case Instruction::SExt: 292 Cost = 1; 293 break; // These are all cheap and non-trapping instructions. 294 295 case Instruction::Select: 296 Cost = 2; 297 break; 298 } 299 300 if (Cost > CostRemaining) 301 return false; 302 303 CostRemaining -= Cost; 304 305 // Okay, we can only really hoist these out if their operands do 306 // not take us over the cost threshold. 307 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) 308 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining)) 309 return false; 310 // Okay, it's safe to do this! Remember this instruction. 311 AggressiveInsts->insert(I); 312 return true; 313} 314 315/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr 316/// and PointerNullValue. Return NULL if value is not a constant int. 317static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) { 318 // Normal constant int. 319 ConstantInt *CI = dyn_cast<ConstantInt>(V); 320 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy()) 321 return CI; 322 323 // This is some kind of pointer constant. Turn it into a pointer-sized 324 // ConstantInt if possible. 325 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext()); 326 327 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*). 328 if (isa<ConstantPointerNull>(V)) 329 return ConstantInt::get(PtrTy, 0); 330 331 // IntToPtr const int. 332 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 333 if (CE->getOpcode() == Instruction::IntToPtr) 334 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) { 335 // The constant is very likely to have the right type already. 336 if (CI->getType() == PtrTy) 337 return CI; 338 else 339 return cast<ConstantInt> 340 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false)); 341 } 342 return 0; 343} 344 345/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together 346/// collection of icmp eq/ne instructions that compare a value against a 347/// constant, return the value being compared, and stick the constant into the 348/// Values vector. 349static Value * 350GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra, 351 const TargetData *TD, bool isEQ, unsigned &UsedICmps) { 352 Instruction *I = dyn_cast<Instruction>(V); 353 if (I == 0) return 0; 354 355 // If this is an icmp against a constant, handle this as one of the cases. 356 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) { 357 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) { 358 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) { 359 UsedICmps++; 360 Vals.push_back(C); 361 return I->getOperand(0); 362 } 363 364 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to 365 // the set. 366 ConstantRange Span = 367 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue()); 368 369 // If this is an and/!= check then we want to optimize "x ugt 2" into 370 // x != 0 && x != 1. 371 if (!isEQ) 372 Span = Span.inverse(); 373 374 // If there are a ton of values, we don't want to make a ginormous switch. 375 if (Span.getSetSize().ugt(8) || Span.isEmptySet() || 376 // We don't handle wrapped sets yet. 377 Span.isWrappedSet()) 378 return 0; 379 380 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp) 381 Vals.push_back(ConstantInt::get(V->getContext(), Tmp)); 382 UsedICmps++; 383 return I->getOperand(0); 384 } 385 return 0; 386 } 387 388 // Otherwise, we can only handle an | or &, depending on isEQ. 389 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And)) 390 return 0; 391 392 unsigned NumValsBeforeLHS = Vals.size(); 393 unsigned UsedICmpsBeforeLHS = UsedICmps; 394 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD, 395 isEQ, UsedICmps)) { 396 unsigned NumVals = Vals.size(); 397 unsigned UsedICmpsBeforeRHS = UsedICmps; 398 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, 399 isEQ, UsedICmps)) { 400 if (LHS == RHS) 401 return LHS; 402 Vals.resize(NumVals); 403 UsedICmps = UsedICmpsBeforeRHS; 404 } 405 406 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet, 407 // set it and return success. 408 if (Extra == 0 || Extra == I->getOperand(1)) { 409 Extra = I->getOperand(1); 410 return LHS; 411 } 412 413 Vals.resize(NumValsBeforeLHS); 414 UsedICmps = UsedICmpsBeforeLHS; 415 return 0; 416 } 417 418 // If the LHS can't be folded in, but Extra is available and RHS can, try to 419 // use LHS as Extra. 420 if (Extra == 0 || Extra == I->getOperand(0)) { 421 Value *OldExtra = Extra; 422 Extra = I->getOperand(0); 423 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, 424 isEQ, UsedICmps)) 425 return RHS; 426 assert(Vals.size() == NumValsBeforeLHS); 427 Extra = OldExtra; 428 } 429 430 return 0; 431} 432 433static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) { 434 Instruction* Cond = 0; 435 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 436 Cond = dyn_cast<Instruction>(SI->getCondition()); 437 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 438 if (BI->isConditional()) 439 Cond = dyn_cast<Instruction>(BI->getCondition()); 440 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) { 441 Cond = dyn_cast<Instruction>(IBI->getAddress()); 442 } 443 444 TI->eraseFromParent(); 445 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond); 446} 447 448/// isValueEqualityComparison - Return true if the specified terminator checks 449/// to see if a value is equal to constant integer value. 450Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) { 451 Value *CV = 0; 452 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 453 // Do not permit merging of large switch instructions into their 454 // predecessors unless there is only one predecessor. 455 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()), 456 pred_end(SI->getParent())) <= 128) 457 CV = SI->getCondition(); 458 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) 459 if (BI->isConditional() && BI->getCondition()->hasOneUse()) 460 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) 461 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ || 462 ICI->getPredicate() == ICmpInst::ICMP_NE) && 463 GetConstantInt(ICI->getOperand(1), TD)) 464 CV = ICI->getOperand(0); 465 466 // Unwrap any lossless ptrtoint cast. 467 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext())) 468 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) 469 CV = PTII->getOperand(0); 470 return CV; 471} 472 473/// GetValueEqualityComparisonCases - Given a value comparison instruction, 474/// decode all of the 'cases' that it represents and return the 'default' block. 475BasicBlock *SimplifyCFGOpt:: 476GetValueEqualityComparisonCases(TerminatorInst *TI, 477 std::vector<std::pair<ConstantInt*, 478 BasicBlock*> > &Cases) { 479 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 480 Cases.reserve(SI->getNumCases()); 481 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 482 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i))); 483 return SI->getDefaultDest(); 484 } 485 486 BranchInst *BI = cast<BranchInst>(TI); 487 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); 488 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD), 489 BI->getSuccessor(ICI->getPredicate() == 490 ICmpInst::ICMP_NE))); 491 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ); 492} 493 494 495/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries 496/// in the list that match the specified block. 497static void EliminateBlockCases(BasicBlock *BB, 498 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) { 499 for (unsigned i = 0, e = Cases.size(); i != e; ++i) 500 if (Cases[i].second == BB) { 501 Cases.erase(Cases.begin()+i); 502 --i; --e; 503 } 504} 505 506/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as 507/// well. 508static bool 509ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1, 510 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) { 511 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2; 512 513 // Make V1 be smaller than V2. 514 if (V1->size() > V2->size()) 515 std::swap(V1, V2); 516 517 if (V1->size() == 0) return false; 518 if (V1->size() == 1) { 519 // Just scan V2. 520 ConstantInt *TheVal = (*V1)[0].first; 521 for (unsigned i = 0, e = V2->size(); i != e; ++i) 522 if (TheVal == (*V2)[i].first) 523 return true; 524 } 525 526 // Otherwise, just sort both lists and compare element by element. 527 array_pod_sort(V1->begin(), V1->end()); 528 array_pod_sort(V2->begin(), V2->end()); 529 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); 530 while (i1 != e1 && i2 != e2) { 531 if ((*V1)[i1].first == (*V2)[i2].first) 532 return true; 533 if ((*V1)[i1].first < (*V2)[i2].first) 534 ++i1; 535 else 536 ++i2; 537 } 538 return false; 539} 540 541/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a 542/// terminator instruction and its block is known to only have a single 543/// predecessor block, check to see if that predecessor is also a value 544/// comparison with the same value, and if that comparison determines the 545/// outcome of this comparison. If so, simplify TI. This does a very limited 546/// form of jump threading. 547bool SimplifyCFGOpt:: 548SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 549 BasicBlock *Pred, 550 IRBuilder<> &Builder) { 551 Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); 552 if (!PredVal) return false; // Not a value comparison in predecessor. 553 554 Value *ThisVal = isValueEqualityComparison(TI); 555 assert(ThisVal && "This isn't a value comparison!!"); 556 if (ThisVal != PredVal) return false; // Different predicates. 557 558 // Find out information about when control will move from Pred to TI's block. 559 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; 560 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), 561 PredCases); 562 EliminateBlockCases(PredDef, PredCases); // Remove default from cases. 563 564 // Find information about how control leaves this block. 565 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases; 566 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); 567 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. 568 569 // If TI's block is the default block from Pred's comparison, potentially 570 // simplify TI based on this knowledge. 571 if (PredDef == TI->getParent()) { 572 // If we are here, we know that the value is none of those cases listed in 573 // PredCases. If there are any cases in ThisCases that are in PredCases, we 574 // can simplify TI. 575 if (!ValuesOverlap(PredCases, ThisCases)) 576 return false; 577 578 if (isa<BranchInst>(TI)) { 579 // Okay, one of the successors of this condbr is dead. Convert it to a 580 // uncond br. 581 assert(ThisCases.size() == 1 && "Branch can only have one case!"); 582 // Insert the new branch. 583 Instruction *NI = Builder.CreateBr(ThisDef); 584 (void) NI; 585 586 // Remove PHI node entries for the dead edge. 587 ThisCases[0].second->removePredecessor(TI->getParent()); 588 589 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 590 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 591 592 EraseTerminatorInstAndDCECond(TI); 593 return true; 594 } 595 596 SwitchInst *SI = cast<SwitchInst>(TI); 597 // Okay, TI has cases that are statically dead, prune them away. 598 SmallPtrSet<Constant*, 16> DeadCases; 599 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 600 DeadCases.insert(PredCases[i].first); 601 602 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 603 << "Through successor TI: " << *TI); 604 605 for (unsigned i = SI->getNumCases()-1; i != 0; --i) 606 if (DeadCases.count(SI->getCaseValue(i))) { 607 SI->getSuccessor(i)->removePredecessor(TI->getParent()); 608 SI->removeCase(i); 609 } 610 611 DEBUG(dbgs() << "Leaving: " << *TI << "\n"); 612 return true; 613 } 614 615 // Otherwise, TI's block must correspond to some matched value. Find out 616 // which value (or set of values) this is. 617 ConstantInt *TIV = 0; 618 BasicBlock *TIBB = TI->getParent(); 619 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 620 if (PredCases[i].second == TIBB) { 621 if (TIV != 0) 622 return false; // Cannot handle multiple values coming to this block. 623 TIV = PredCases[i].first; 624 } 625 assert(TIV && "No edge from pred to succ?"); 626 627 // Okay, we found the one constant that our value can be if we get into TI's 628 // BB. Find out which successor will unconditionally be branched to. 629 BasicBlock *TheRealDest = 0; 630 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) 631 if (ThisCases[i].first == TIV) { 632 TheRealDest = ThisCases[i].second; 633 break; 634 } 635 636 // If not handled by any explicit cases, it is handled by the default case. 637 if (TheRealDest == 0) TheRealDest = ThisDef; 638 639 // Remove PHI node entries for dead edges. 640 BasicBlock *CheckEdge = TheRealDest; 641 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI) 642 if (*SI != CheckEdge) 643 (*SI)->removePredecessor(TIBB); 644 else 645 CheckEdge = 0; 646 647 // Insert the new branch. 648 Instruction *NI = Builder.CreateBr(TheRealDest); 649 (void) NI; 650 651 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 652 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 653 654 EraseTerminatorInstAndDCECond(TI); 655 return true; 656} 657 658namespace { 659 /// ConstantIntOrdering - This class implements a stable ordering of constant 660 /// integers that does not depend on their address. This is important for 661 /// applications that sort ConstantInt's to ensure uniqueness. 662 struct ConstantIntOrdering { 663 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { 664 return LHS->getValue().ult(RHS->getValue()); 665 } 666 }; 667} 668 669static int ConstantIntSortPredicate(const void *P1, const void *P2) { 670 const ConstantInt *LHS = *(const ConstantInt**)P1; 671 const ConstantInt *RHS = *(const ConstantInt**)P2; 672 if (LHS->getValue().ult(RHS->getValue())) 673 return 1; 674 if (LHS->getValue() == RHS->getValue()) 675 return 0; 676 return -1; 677} 678 679/// FoldValueComparisonIntoPredecessors - The specified terminator is a value 680/// equality comparison instruction (either a switch or a branch on "X == c"). 681/// See if any of the predecessors of the terminator block are value comparisons 682/// on the same value. If so, and if safe to do so, fold them together. 683bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI, 684 IRBuilder<> &Builder) { 685 BasicBlock *BB = TI->getParent(); 686 Value *CV = isValueEqualityComparison(TI); // CondVal 687 assert(CV && "Not a comparison?"); 688 bool Changed = false; 689 690 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); 691 while (!Preds.empty()) { 692 BasicBlock *Pred = Preds.pop_back_val(); 693 694 // See if the predecessor is a comparison with the same value. 695 TerminatorInst *PTI = Pred->getTerminator(); 696 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal 697 698 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) { 699 // Figure out which 'cases' to copy from SI to PSI. 700 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases; 701 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); 702 703 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; 704 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); 705 706 // Based on whether the default edge from PTI goes to BB or not, fill in 707 // PredCases and PredDefault with the new switch cases we would like to 708 // build. 709 SmallVector<BasicBlock*, 8> NewSuccessors; 710 711 if (PredDefault == BB) { 712 // If this is the default destination from PTI, only the edges in TI 713 // that don't occur in PTI, or that branch to BB will be activated. 714 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 715 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 716 if (PredCases[i].second != BB) 717 PTIHandled.insert(PredCases[i].first); 718 else { 719 // The default destination is BB, we don't need explicit targets. 720 std::swap(PredCases[i], PredCases.back()); 721 PredCases.pop_back(); 722 --i; --e; 723 } 724 725 // Reconstruct the new switch statement we will be building. 726 if (PredDefault != BBDefault) { 727 PredDefault->removePredecessor(Pred); 728 PredDefault = BBDefault; 729 NewSuccessors.push_back(BBDefault); 730 } 731 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 732 if (!PTIHandled.count(BBCases[i].first) && 733 BBCases[i].second != BBDefault) { 734 PredCases.push_back(BBCases[i]); 735 NewSuccessors.push_back(BBCases[i].second); 736 } 737 738 } else { 739 // If this is not the default destination from PSI, only the edges 740 // in SI that occur in PSI with a destination of BB will be 741 // activated. 742 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 743 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 744 if (PredCases[i].second == BB) { 745 PTIHandled.insert(PredCases[i].first); 746 std::swap(PredCases[i], PredCases.back()); 747 PredCases.pop_back(); 748 --i; --e; 749 } 750 751 // Okay, now we know which constants were sent to BB from the 752 // predecessor. Figure out where they will all go now. 753 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 754 if (PTIHandled.count(BBCases[i].first)) { 755 // If this is one we are capable of getting... 756 PredCases.push_back(BBCases[i]); 757 NewSuccessors.push_back(BBCases[i].second); 758 PTIHandled.erase(BBCases[i].first);// This constant is taken care of 759 } 760 761 // If there are any constants vectored to BB that TI doesn't handle, 762 // they must go to the default destination of TI. 763 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I = 764 PTIHandled.begin(), 765 E = PTIHandled.end(); I != E; ++I) { 766 PredCases.push_back(std::make_pair(*I, BBDefault)); 767 NewSuccessors.push_back(BBDefault); 768 } 769 } 770 771 // Okay, at this point, we know which new successor Pred will get. Make 772 // sure we update the number of entries in the PHI nodes for these 773 // successors. 774 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i) 775 AddPredecessorToBlock(NewSuccessors[i], Pred, BB); 776 777 Builder.SetInsertPoint(PTI); 778 // Convert pointer to int before we switch. 779 if (CV->getType()->isPointerTy()) { 780 assert(TD && "Cannot switch on pointer without TargetData"); 781 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()), 782 "magicptr"); 783 } 784 785 // Now that the successors are updated, create the new Switch instruction. 786 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault, 787 PredCases.size()); 788 NewSI->setDebugLoc(PTI->getDebugLoc()); 789 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 790 NewSI->addCase(PredCases[i].first, PredCases[i].second); 791 792 EraseTerminatorInstAndDCECond(PTI); 793 794 // Okay, last check. If BB is still a successor of PSI, then we must 795 // have an infinite loop case. If so, add an infinitely looping block 796 // to handle the case to preserve the behavior of the code. 797 BasicBlock *InfLoopBlock = 0; 798 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) 799 if (NewSI->getSuccessor(i) == BB) { 800 if (InfLoopBlock == 0) { 801 // Insert it at the end of the function, because it's either code, 802 // or it won't matter if it's hot. :) 803 InfLoopBlock = BasicBlock::Create(BB->getContext(), 804 "infloop", BB->getParent()); 805 BranchInst::Create(InfLoopBlock, InfLoopBlock); 806 } 807 NewSI->setSuccessor(i, InfLoopBlock); 808 } 809 810 Changed = true; 811 } 812 } 813 return Changed; 814} 815 816// isSafeToHoistInvoke - If we would need to insert a select that uses the 817// value of this invoke (comments in HoistThenElseCodeToIf explain why we 818// would need to do this), we can't hoist the invoke, as there is nowhere 819// to put the select in this case. 820static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2, 821 Instruction *I1, Instruction *I2) { 822 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 823 PHINode *PN; 824 for (BasicBlock::iterator BBI = SI->begin(); 825 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 826 Value *BB1V = PN->getIncomingValueForBlock(BB1); 827 Value *BB2V = PN->getIncomingValueForBlock(BB2); 828 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) { 829 return false; 830 } 831 } 832 } 833 return true; 834} 835 836/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and 837/// BB2, hoist any common code in the two blocks up into the branch block. The 838/// caller of this function guarantees that BI's block dominates BB1 and BB2. 839static bool HoistThenElseCodeToIf(BranchInst *BI) { 840 // This does very trivial matching, with limited scanning, to find identical 841 // instructions in the two blocks. In particular, we don't want to get into 842 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As 843 // such, we currently just scan for obviously identical instructions in an 844 // identical order. 845 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. 846 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination 847 848 BasicBlock::iterator BB1_Itr = BB1->begin(); 849 BasicBlock::iterator BB2_Itr = BB2->begin(); 850 851 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++; 852 // Skip debug info if it is not identical. 853 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); 854 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); 855 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { 856 while (isa<DbgInfoIntrinsic>(I1)) 857 I1 = BB1_Itr++; 858 while (isa<DbgInfoIntrinsic>(I2)) 859 I2 = BB2_Itr++; 860 } 861 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) || 862 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))) 863 return false; 864 865 // If we get here, we can hoist at least one instruction. 866 BasicBlock *BIParent = BI->getParent(); 867 868 do { 869 // If we are hoisting the terminator instruction, don't move one (making a 870 // broken BB), instead clone it, and remove BI. 871 if (isa<TerminatorInst>(I1)) 872 goto HoistTerminator; 873 874 // For a normal instruction, we just move one to right before the branch, 875 // then replace all uses of the other with the first. Finally, we remove 876 // the now redundant second instruction. 877 BIParent->getInstList().splice(BI, BB1->getInstList(), I1); 878 if (!I2->use_empty()) 879 I2->replaceAllUsesWith(I1); 880 I1->intersectOptionalDataWith(I2); 881 I2->eraseFromParent(); 882 883 I1 = BB1_Itr++; 884 I2 = BB2_Itr++; 885 // Skip debug info if it is not identical. 886 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); 887 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); 888 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { 889 while (isa<DbgInfoIntrinsic>(I1)) 890 I1 = BB1_Itr++; 891 while (isa<DbgInfoIntrinsic>(I2)) 892 I2 = BB2_Itr++; 893 } 894 } while (I1->isIdenticalToWhenDefined(I2)); 895 896 return true; 897 898HoistTerminator: 899 // It may not be possible to hoist an invoke. 900 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) 901 return true; 902 903 // Okay, it is safe to hoist the terminator. 904 Instruction *NT = I1->clone(); 905 BIParent->getInstList().insert(BI, NT); 906 if (!NT->getType()->isVoidTy()) { 907 I1->replaceAllUsesWith(NT); 908 I2->replaceAllUsesWith(NT); 909 NT->takeName(I1); 910 } 911 912 IRBuilder<true, NoFolder> Builder(NT); 913 // Hoisting one of the terminators from our successor is a great thing. 914 // Unfortunately, the successors of the if/else blocks may have PHI nodes in 915 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI 916 // nodes, so we insert select instruction to compute the final result. 917 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects; 918 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 919 PHINode *PN; 920 for (BasicBlock::iterator BBI = SI->begin(); 921 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 922 Value *BB1V = PN->getIncomingValueForBlock(BB1); 923 Value *BB2V = PN->getIncomingValueForBlock(BB2); 924 if (BB1V == BB2V) continue; 925 926 // These values do not agree. Insert a select instruction before NT 927 // that determines the right value. 928 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; 929 if (SI == 0) 930 SI = cast<SelectInst> 931 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V, 932 BB1V->getName()+"."+BB2V->getName())); 933 934 // Make the PHI node use the select for all incoming values for BB1/BB2 935 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 936 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2) 937 PN->setIncomingValue(i, SI); 938 } 939 } 940 941 // Update any PHI nodes in our new successors. 942 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) 943 AddPredecessorToBlock(*SI, BIParent, BB1); 944 945 EraseTerminatorInstAndDCECond(BI); 946 return true; 947} 948 949/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1 950/// and an BB2 and the only successor of BB1 is BB2, hoist simple code 951/// (for now, restricted to a single instruction that's side effect free) from 952/// the BB1 into the branch block to speculatively execute it. 953static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) { 954 // Only speculatively execution a single instruction (not counting the 955 // terminator) for now. 956 Instruction *HInst = NULL; 957 Instruction *Term = BB1->getTerminator(); 958 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); 959 BBI != BBE; ++BBI) { 960 Instruction *I = BBI; 961 // Skip debug info. 962 if (isa<DbgInfoIntrinsic>(I)) continue; 963 if (I == Term) break; 964 965 if (HInst) 966 return false; 967 HInst = I; 968 } 969 if (!HInst) 970 return false; 971 972 // Be conservative for now. FP select instruction can often be expensive. 973 Value *BrCond = BI->getCondition(); 974 if (isa<FCmpInst>(BrCond)) 975 return false; 976 977 // If BB1 is actually on the false edge of the conditional branch, remember 978 // to swap the select operands later. 979 bool Invert = false; 980 if (BB1 != BI->getSuccessor(0)) { 981 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?"); 982 Invert = true; 983 } 984 985 // Turn 986 // BB: 987 // %t1 = icmp 988 // br i1 %t1, label %BB1, label %BB2 989 // BB1: 990 // %t3 = add %t2, c 991 // br label BB2 992 // BB2: 993 // => 994 // BB: 995 // %t1 = icmp 996 // %t4 = add %t2, c 997 // %t3 = select i1 %t1, %t2, %t3 998 switch (HInst->getOpcode()) { 999 default: return false; // Not safe / profitable to hoist. 1000 case Instruction::Add: 1001 case Instruction::Sub: 1002 // Not worth doing for vector ops. 1003 if (HInst->getType()->isVectorTy()) 1004 return false; 1005 break; 1006 case Instruction::And: 1007 case Instruction::Or: 1008 case Instruction::Xor: 1009 case Instruction::Shl: 1010 case Instruction::LShr: 1011 case Instruction::AShr: 1012 // Don't mess with vector operations. 1013 if (HInst->getType()->isVectorTy()) 1014 return false; 1015 break; // These are all cheap and non-trapping instructions. 1016 } 1017 1018 // If the instruction is obviously dead, don't try to predicate it. 1019 if (HInst->use_empty()) { 1020 HInst->eraseFromParent(); 1021 return true; 1022 } 1023 1024 // Can we speculatively execute the instruction? And what is the value 1025 // if the condition is false? Consider the phi uses, if the incoming value 1026 // from the "if" block are all the same V, then V is the value of the 1027 // select if the condition is false. 1028 BasicBlock *BIParent = BI->getParent(); 1029 SmallVector<PHINode*, 4> PHIUses; 1030 Value *FalseV = NULL; 1031 1032 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0); 1033 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end(); 1034 UI != E; ++UI) { 1035 // Ignore any user that is not a PHI node in BB2. These can only occur in 1036 // unreachable blocks, because they would not be dominated by the instr. 1037 PHINode *PN = dyn_cast<PHINode>(*UI); 1038 if (!PN || PN->getParent() != BB2) 1039 return false; 1040 PHIUses.push_back(PN); 1041 1042 Value *PHIV = PN->getIncomingValueForBlock(BIParent); 1043 if (!FalseV) 1044 FalseV = PHIV; 1045 else if (FalseV != PHIV) 1046 return false; // Inconsistent value when condition is false. 1047 } 1048 1049 assert(FalseV && "Must have at least one user, and it must be a PHI"); 1050 1051 // Do not hoist the instruction if any of its operands are defined but not 1052 // used in this BB. The transformation will prevent the operand from 1053 // being sunk into the use block. 1054 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end(); 1055 i != e; ++i) { 1056 Instruction *OpI = dyn_cast<Instruction>(*i); 1057 if (OpI && OpI->getParent() == BIParent && 1058 !OpI->isUsedInBasicBlock(BIParent)) 1059 return false; 1060 } 1061 1062 // If we get here, we can hoist the instruction. Try to place it 1063 // before the icmp instruction preceding the conditional branch. 1064 BasicBlock::iterator InsertPos = BI; 1065 if (InsertPos != BIParent->begin()) 1066 --InsertPos; 1067 // Skip debug info between condition and branch. 1068 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos)) 1069 --InsertPos; 1070 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) { 1071 SmallPtrSet<Instruction *, 4> BB1Insns; 1072 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end(); 1073 BB1I != BB1E; ++BB1I) 1074 BB1Insns.insert(BB1I); 1075 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end(); 1076 UI != UE; ++UI) { 1077 Instruction *Use = cast<Instruction>(*UI); 1078 if (!BB1Insns.count(Use)) continue; 1079 1080 // If BrCond uses the instruction that place it just before 1081 // branch instruction. 1082 InsertPos = BI; 1083 break; 1084 } 1085 } else 1086 InsertPos = BI; 1087 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst); 1088 1089 // Create a select whose true value is the speculatively executed value and 1090 // false value is the previously determined FalseV. 1091 IRBuilder<true, NoFolder> Builder(BI); 1092 SelectInst *SI; 1093 if (Invert) 1094 SI = cast<SelectInst> 1095 (Builder.CreateSelect(BrCond, FalseV, HInst, 1096 FalseV->getName() + "." + HInst->getName())); 1097 else 1098 SI = cast<SelectInst> 1099 (Builder.CreateSelect(BrCond, HInst, FalseV, 1100 HInst->getName() + "." + FalseV->getName())); 1101 1102 // Make the PHI node use the select for all incoming values for "then" and 1103 // "if" blocks. 1104 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) { 1105 PHINode *PN = PHIUses[i]; 1106 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j) 1107 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent) 1108 PN->setIncomingValue(j, SI); 1109 } 1110 1111 ++NumSpeculations; 1112 return true; 1113} 1114 1115/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch 1116/// across this block. 1117static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) { 1118 BranchInst *BI = cast<BranchInst>(BB->getTerminator()); 1119 unsigned Size = 0; 1120 1121 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1122 if (isa<DbgInfoIntrinsic>(BBI)) 1123 continue; 1124 if (Size > 10) return false; // Don't clone large BB's. 1125 ++Size; 1126 1127 // We can only support instructions that do not define values that are 1128 // live outside of the current basic block. 1129 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 1130 UI != E; ++UI) { 1131 Instruction *U = cast<Instruction>(*UI); 1132 if (U->getParent() != BB || isa<PHINode>(U)) return false; 1133 } 1134 1135 // Looks ok, continue checking. 1136 } 1137 1138 return true; 1139} 1140 1141/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value 1142/// that is defined in the same block as the branch and if any PHI entries are 1143/// constants, thread edges corresponding to that entry to be branches to their 1144/// ultimate destination. 1145static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) { 1146 BasicBlock *BB = BI->getParent(); 1147 PHINode *PN = dyn_cast<PHINode>(BI->getCondition()); 1148 // NOTE: we currently cannot transform this case if the PHI node is used 1149 // outside of the block. 1150 if (!PN || PN->getParent() != BB || !PN->hasOneUse()) 1151 return false; 1152 1153 // Degenerate case of a single entry PHI. 1154 if (PN->getNumIncomingValues() == 1) { 1155 FoldSingleEntryPHINodes(PN->getParent()); 1156 return true; 1157 } 1158 1159 // Now we know that this block has multiple preds and two succs. 1160 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false; 1161 1162 // Okay, this is a simple enough basic block. See if any phi values are 1163 // constants. 1164 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1165 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i)); 1166 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue; 1167 1168 // Okay, we now know that all edges from PredBB should be revectored to 1169 // branch to RealDest. 1170 BasicBlock *PredBB = PN->getIncomingBlock(i); 1171 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue()); 1172 1173 if (RealDest == BB) continue; // Skip self loops. 1174 1175 // The dest block might have PHI nodes, other predecessors and other 1176 // difficult cases. Instead of being smart about this, just insert a new 1177 // block that jumps to the destination block, effectively splitting 1178 // the edge we are about to create. 1179 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(), 1180 RealDest->getName()+".critedge", 1181 RealDest->getParent(), RealDest); 1182 BranchInst::Create(RealDest, EdgeBB); 1183 1184 // Update PHI nodes. 1185 AddPredecessorToBlock(RealDest, EdgeBB, BB); 1186 1187 // BB may have instructions that are being threaded over. Clone these 1188 // instructions into EdgeBB. We know that there will be no uses of the 1189 // cloned instructions outside of EdgeBB. 1190 BasicBlock::iterator InsertPt = EdgeBB->begin(); 1191 DenseMap<Value*, Value*> TranslateMap; // Track translated values. 1192 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1193 if (PHINode *PN = dyn_cast<PHINode>(BBI)) { 1194 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB); 1195 continue; 1196 } 1197 // Clone the instruction. 1198 Instruction *N = BBI->clone(); 1199 if (BBI->hasName()) N->setName(BBI->getName()+".c"); 1200 1201 // Update operands due to translation. 1202 for (User::op_iterator i = N->op_begin(), e = N->op_end(); 1203 i != e; ++i) { 1204 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i); 1205 if (PI != TranslateMap.end()) 1206 *i = PI->second; 1207 } 1208 1209 // Check for trivial simplification. 1210 if (Value *V = SimplifyInstruction(N, TD)) { 1211 TranslateMap[BBI] = V; 1212 delete N; // Instruction folded away, don't need actual inst 1213 } else { 1214 // Insert the new instruction into its new home. 1215 EdgeBB->getInstList().insert(InsertPt, N); 1216 if (!BBI->use_empty()) 1217 TranslateMap[BBI] = N; 1218 } 1219 } 1220 1221 // Loop over all of the edges from PredBB to BB, changing them to branch 1222 // to EdgeBB instead. 1223 TerminatorInst *PredBBTI = PredBB->getTerminator(); 1224 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i) 1225 if (PredBBTI->getSuccessor(i) == BB) { 1226 BB->removePredecessor(PredBB); 1227 PredBBTI->setSuccessor(i, EdgeBB); 1228 } 1229 1230 // Recurse, simplifying any other constants. 1231 return FoldCondBranchOnPHI(BI, TD) | true; 1232 } 1233 1234 return false; 1235} 1236 1237/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry 1238/// PHI node, see if we can eliminate it. 1239static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) { 1240 // Ok, this is a two entry PHI node. Check to see if this is a simple "if 1241 // statement", which has a very simple dominance structure. Basically, we 1242 // are trying to find the condition that is being branched on, which 1243 // subsequently causes this merge to happen. We really want control 1244 // dependence information for this check, but simplifycfg can't keep it up 1245 // to date, and this catches most of the cases we care about anyway. 1246 BasicBlock *BB = PN->getParent(); 1247 BasicBlock *IfTrue, *IfFalse; 1248 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse); 1249 if (!IfCond || 1250 // Don't bother if the branch will be constant folded trivially. 1251 isa<ConstantInt>(IfCond)) 1252 return false; 1253 1254 // Okay, we found that we can merge this two-entry phi node into a select. 1255 // Doing so would require us to fold *all* two entry phi nodes in this block. 1256 // At some point this becomes non-profitable (particularly if the target 1257 // doesn't support cmov's). Only do this transformation if there are two or 1258 // fewer PHI nodes in this block. 1259 unsigned NumPhis = 0; 1260 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I) 1261 if (NumPhis > 2) 1262 return false; 1263 1264 // Loop over the PHI's seeing if we can promote them all to select 1265 // instructions. While we are at it, keep track of the instructions 1266 // that need to be moved to the dominating block. 1267 SmallPtrSet<Instruction*, 4> AggressiveInsts; 1268 unsigned MaxCostVal0 = PHINodeFoldingThreshold, 1269 MaxCostVal1 = PHINodeFoldingThreshold; 1270 1271 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) { 1272 PHINode *PN = cast<PHINode>(II++); 1273 if (Value *V = SimplifyInstruction(PN, TD)) { 1274 PN->replaceAllUsesWith(V); 1275 PN->eraseFromParent(); 1276 continue; 1277 } 1278 1279 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts, 1280 MaxCostVal0) || 1281 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts, 1282 MaxCostVal1)) 1283 return false; 1284 } 1285 1286 // If we folded the the first phi, PN dangles at this point. Refresh it. If 1287 // we ran out of PHIs then we simplified them all. 1288 PN = dyn_cast<PHINode>(BB->begin()); 1289 if (PN == 0) return true; 1290 1291 // Don't fold i1 branches on PHIs which contain binary operators. These can 1292 // often be turned into switches and other things. 1293 if (PN->getType()->isIntegerTy(1) && 1294 (isa<BinaryOperator>(PN->getIncomingValue(0)) || 1295 isa<BinaryOperator>(PN->getIncomingValue(1)) || 1296 isa<BinaryOperator>(IfCond))) 1297 return false; 1298 1299 // If we all PHI nodes are promotable, check to make sure that all 1300 // instructions in the predecessor blocks can be promoted as well. If 1301 // not, we won't be able to get rid of the control flow, so it's not 1302 // worth promoting to select instructions. 1303 BasicBlock *DomBlock = 0; 1304 BasicBlock *IfBlock1 = PN->getIncomingBlock(0); 1305 BasicBlock *IfBlock2 = PN->getIncomingBlock(1); 1306 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) { 1307 IfBlock1 = 0; 1308 } else { 1309 DomBlock = *pred_begin(IfBlock1); 1310 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I) 1311 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1312 // This is not an aggressive instruction that we can promote. 1313 // Because of this, we won't be able to get rid of the control 1314 // flow, so the xform is not worth it. 1315 return false; 1316 } 1317 } 1318 1319 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) { 1320 IfBlock2 = 0; 1321 } else { 1322 DomBlock = *pred_begin(IfBlock2); 1323 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I) 1324 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1325 // This is not an aggressive instruction that we can promote. 1326 // Because of this, we won't be able to get rid of the control 1327 // flow, so the xform is not worth it. 1328 return false; 1329 } 1330 } 1331 1332 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: " 1333 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"); 1334 1335 // If we can still promote the PHI nodes after this gauntlet of tests, 1336 // do all of the PHI's now. 1337 Instruction *InsertPt = DomBlock->getTerminator(); 1338 IRBuilder<true, NoFolder> Builder(InsertPt); 1339 1340 // Move all 'aggressive' instructions, which are defined in the 1341 // conditional parts of the if's up to the dominating block. 1342 if (IfBlock1) 1343 DomBlock->getInstList().splice(InsertPt, 1344 IfBlock1->getInstList(), IfBlock1->begin(), 1345 IfBlock1->getTerminator()); 1346 if (IfBlock2) 1347 DomBlock->getInstList().splice(InsertPt, 1348 IfBlock2->getInstList(), IfBlock2->begin(), 1349 IfBlock2->getTerminator()); 1350 1351 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 1352 // Change the PHI node into a select instruction. 1353 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); 1354 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); 1355 1356 SelectInst *NV = 1357 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, "")); 1358 PN->replaceAllUsesWith(NV); 1359 NV->takeName(PN); 1360 PN->eraseFromParent(); 1361 } 1362 1363 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement 1364 // has been flattened. Change DomBlock to jump directly to our new block to 1365 // avoid other simplifycfg's kicking in on the diamond. 1366 TerminatorInst *OldTI = DomBlock->getTerminator(); 1367 Builder.SetInsertPoint(OldTI); 1368 Builder.CreateBr(BB); 1369 OldTI->eraseFromParent(); 1370 return true; 1371} 1372 1373/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes 1374/// to two returning blocks, try to merge them together into one return, 1375/// introducing a select if the return values disagree. 1376static bool SimplifyCondBranchToTwoReturns(BranchInst *BI, 1377 IRBuilder<> &Builder) { 1378 assert(BI->isConditional() && "Must be a conditional branch"); 1379 BasicBlock *TrueSucc = BI->getSuccessor(0); 1380 BasicBlock *FalseSucc = BI->getSuccessor(1); 1381 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator()); 1382 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator()); 1383 1384 // Check to ensure both blocks are empty (just a return) or optionally empty 1385 // with PHI nodes. If there are other instructions, merging would cause extra 1386 // computation on one path or the other. 1387 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator()) 1388 return false; 1389 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator()) 1390 return false; 1391 1392 Builder.SetInsertPoint(BI); 1393 // Okay, we found a branch that is going to two return nodes. If 1394 // there is no return value for this function, just change the 1395 // branch into a return. 1396 if (FalseRet->getNumOperands() == 0) { 1397 TrueSucc->removePredecessor(BI->getParent()); 1398 FalseSucc->removePredecessor(BI->getParent()); 1399 Builder.CreateRetVoid(); 1400 EraseTerminatorInstAndDCECond(BI); 1401 return true; 1402 } 1403 1404 // Otherwise, figure out what the true and false return values are 1405 // so we can insert a new select instruction. 1406 Value *TrueValue = TrueRet->getReturnValue(); 1407 Value *FalseValue = FalseRet->getReturnValue(); 1408 1409 // Unwrap any PHI nodes in the return blocks. 1410 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue)) 1411 if (TVPN->getParent() == TrueSucc) 1412 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); 1413 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue)) 1414 if (FVPN->getParent() == FalseSucc) 1415 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); 1416 1417 // In order for this transformation to be safe, we must be able to 1418 // unconditionally execute both operands to the return. This is 1419 // normally the case, but we could have a potentially-trapping 1420 // constant expression that prevents this transformation from being 1421 // safe. 1422 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue)) 1423 if (TCV->canTrap()) 1424 return false; 1425 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue)) 1426 if (FCV->canTrap()) 1427 return false; 1428 1429 // Okay, we collected all the mapped values and checked them for sanity, and 1430 // defined to really do this transformation. First, update the CFG. 1431 TrueSucc->removePredecessor(BI->getParent()); 1432 FalseSucc->removePredecessor(BI->getParent()); 1433 1434 // Insert select instructions where needed. 1435 Value *BrCond = BI->getCondition(); 1436 if (TrueValue) { 1437 // Insert a select if the results differ. 1438 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) { 1439 } else if (isa<UndefValue>(TrueValue)) { 1440 TrueValue = FalseValue; 1441 } else { 1442 TrueValue = Builder.CreateSelect(BrCond, TrueValue, 1443 FalseValue, "retval"); 1444 } 1445 } 1446 1447 Value *RI = !TrueValue ? 1448 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue); 1449 1450 (void) RI; 1451 1452 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" 1453 << "\n " << *BI << "NewRet = " << *RI 1454 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc); 1455 1456 EraseTerminatorInstAndDCECond(BI); 1457 1458 return true; 1459} 1460 1461/// FoldBranchToCommonDest - If this basic block is simple enough, and if a 1462/// predecessor branches to us and one of our successors, fold the block into 1463/// the predecessor and use logical operations to pick the right destination. 1464bool llvm::FoldBranchToCommonDest(BranchInst *BI) { 1465 BasicBlock *BB = BI->getParent(); 1466 1467 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 1468 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) || 1469 Cond->getParent() != BB || !Cond->hasOneUse()) 1470 return false; 1471 1472 // Only allow this if the condition is a simple instruction that can be 1473 // executed unconditionally. It must be in the same block as the branch, and 1474 // must be at the front of the block. 1475 BasicBlock::iterator FrontIt = BB->front(); 1476 1477 // Ignore dbg intrinsics. 1478 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt; 1479 1480 // Allow a single instruction to be hoisted in addition to the compare 1481 // that feeds the branch. We later ensure that any values that _it_ uses 1482 // were also live in the predecessor, so that we don't unnecessarily create 1483 // register pressure or inhibit out-of-order execution. 1484 Instruction *BonusInst = 0; 1485 if (&*FrontIt != Cond && 1486 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond && 1487 FrontIt->isSafeToSpeculativelyExecute()) { 1488 BonusInst = &*FrontIt; 1489 ++FrontIt; 1490 1491 // Ignore dbg intrinsics. 1492 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt; 1493 } 1494 1495 // Only a single bonus inst is allowed. 1496 if (&*FrontIt != Cond) 1497 return false; 1498 1499 // Make sure the instruction after the condition is the cond branch. 1500 BasicBlock::iterator CondIt = Cond; ++CondIt; 1501 1502 // Ingore dbg intrinsics. 1503 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt; 1504 1505 if (&*CondIt != BI) 1506 return false; 1507 1508 // Cond is known to be a compare or binary operator. Check to make sure that 1509 // neither operand is a potentially-trapping constant expression. 1510 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0))) 1511 if (CE->canTrap()) 1512 return false; 1513 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1))) 1514 if (CE->canTrap()) 1515 return false; 1516 1517 // Finally, don't infinitely unroll conditional loops. 1518 BasicBlock *TrueDest = BI->getSuccessor(0); 1519 BasicBlock *FalseDest = BI->getSuccessor(1); 1520 if (TrueDest == BB || FalseDest == BB) 1521 return false; 1522 1523 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1524 BasicBlock *PredBlock = *PI; 1525 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); 1526 1527 // Check that we have two conditional branches. If there is a PHI node in 1528 // the common successor, verify that the same value flows in from both 1529 // blocks. 1530 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI)) 1531 continue; 1532 1533 // Determine if the two branches share a common destination. 1534 Instruction::BinaryOps Opc; 1535 bool InvertPredCond = false; 1536 1537 if (PBI->getSuccessor(0) == TrueDest) 1538 Opc = Instruction::Or; 1539 else if (PBI->getSuccessor(1) == FalseDest) 1540 Opc = Instruction::And; 1541 else if (PBI->getSuccessor(0) == FalseDest) 1542 Opc = Instruction::And, InvertPredCond = true; 1543 else if (PBI->getSuccessor(1) == TrueDest) 1544 Opc = Instruction::Or, InvertPredCond = true; 1545 else 1546 continue; 1547 1548 // Ensure that any values used in the bonus instruction are also used 1549 // by the terminator of the predecessor. This means that those values 1550 // must already have been resolved, so we won't be inhibiting the 1551 // out-of-order core by speculating them earlier. 1552 if (BonusInst) { 1553 // Collect the values used by the bonus inst 1554 SmallPtrSet<Value*, 4> UsedValues; 1555 for (Instruction::op_iterator OI = BonusInst->op_begin(), 1556 OE = BonusInst->op_end(); OI != OE; ++OI) { 1557 Value* V = *OI; 1558 if (!isa<Constant>(V)) 1559 UsedValues.insert(V); 1560 } 1561 1562 SmallVector<std::pair<Value*, unsigned>, 4> Worklist; 1563 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0)); 1564 1565 // Walk up to four levels back up the use-def chain of the predecessor's 1566 // terminator to see if all those values were used. The choice of four 1567 // levels is arbitrary, to provide a compile-time-cost bound. 1568 while (!Worklist.empty()) { 1569 std::pair<Value*, unsigned> Pair = Worklist.back(); 1570 Worklist.pop_back(); 1571 1572 if (Pair.second >= 4) continue; 1573 UsedValues.erase(Pair.first); 1574 if (UsedValues.empty()) break; 1575 1576 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) { 1577 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 1578 OI != OE; ++OI) 1579 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1)); 1580 } 1581 } 1582 1583 if (!UsedValues.empty()) return false; 1584 } 1585 1586 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB); 1587 IRBuilder<> Builder(PBI); 1588 1589 // If we need to invert the condition in the pred block to match, do so now. 1590 if (InvertPredCond) { 1591 Value *NewCond = PBI->getCondition(); 1592 1593 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) { 1594 CmpInst *CI = cast<CmpInst>(NewCond); 1595 CI->setPredicate(CI->getInversePredicate()); 1596 } else { 1597 NewCond = Builder.CreateNot(NewCond, 1598 PBI->getCondition()->getName()+".not"); 1599 } 1600 1601 PBI->setCondition(NewCond); 1602 BasicBlock *OldTrue = PBI->getSuccessor(0); 1603 BasicBlock *OldFalse = PBI->getSuccessor(1); 1604 PBI->setSuccessor(0, OldFalse); 1605 PBI->setSuccessor(1, OldTrue); 1606 } 1607 1608 // If we have a bonus inst, clone it into the predecessor block. 1609 Instruction *NewBonus = 0; 1610 if (BonusInst) { 1611 NewBonus = BonusInst->clone(); 1612 PredBlock->getInstList().insert(PBI, NewBonus); 1613 NewBonus->takeName(BonusInst); 1614 BonusInst->setName(BonusInst->getName()+".old"); 1615 } 1616 1617 // Clone Cond into the predecessor basic block, and or/and the 1618 // two conditions together. 1619 Instruction *New = Cond->clone(); 1620 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus); 1621 PredBlock->getInstList().insert(PBI, New); 1622 New->takeName(Cond); 1623 Cond->setName(New->getName()+".old"); 1624 1625 Instruction *NewCond = 1626 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(), 1627 New, "or.cond")); 1628 PBI->setCondition(NewCond); 1629 if (PBI->getSuccessor(0) == BB) { 1630 AddPredecessorToBlock(TrueDest, PredBlock, BB); 1631 PBI->setSuccessor(0, TrueDest); 1632 } 1633 if (PBI->getSuccessor(1) == BB) { 1634 AddPredecessorToBlock(FalseDest, PredBlock, BB); 1635 PBI->setSuccessor(1, FalseDest); 1636 } 1637 1638 // Copy any debug value intrinsics into the end of PredBlock. 1639 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 1640 if (isa<DbgInfoIntrinsic>(*I)) 1641 I->clone()->insertBefore(PBI); 1642 1643 return true; 1644 } 1645 return false; 1646} 1647 1648/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a 1649/// predecessor of another block, this function tries to simplify it. We know 1650/// that PBI and BI are both conditional branches, and BI is in one of the 1651/// successor blocks of PBI - PBI branches to BI. 1652static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) { 1653 assert(PBI->isConditional() && BI->isConditional()); 1654 BasicBlock *BB = BI->getParent(); 1655 1656 // If this block ends with a branch instruction, and if there is a 1657 // predecessor that ends on a branch of the same condition, make 1658 // this conditional branch redundant. 1659 if (PBI->getCondition() == BI->getCondition() && 1660 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 1661 // Okay, the outcome of this conditional branch is statically 1662 // knowable. If this block had a single pred, handle specially. 1663 if (BB->getSinglePredecessor()) { 1664 // Turn this into a branch on constant. 1665 bool CondIsTrue = PBI->getSuccessor(0) == BB; 1666 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 1667 CondIsTrue)); 1668 return true; // Nuke the branch on constant. 1669 } 1670 1671 // Otherwise, if there are multiple predecessors, insert a PHI that merges 1672 // in the constant and simplify the block result. Subsequent passes of 1673 // simplifycfg will thread the block. 1674 if (BlockIsSimpleEnoughToThreadThrough(BB)) { 1675 pred_iterator PB = pred_begin(BB), PE = pred_end(BB); 1676 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()), 1677 std::distance(PB, PE), 1678 BI->getCondition()->getName() + ".pr", 1679 BB->begin()); 1680 // Okay, we're going to insert the PHI node. Since PBI is not the only 1681 // predecessor, compute the PHI'd conditional value for all of the preds. 1682 // Any predecessor where the condition is not computable we keep symbolic. 1683 for (pred_iterator PI = PB; PI != PE; ++PI) { 1684 BasicBlock *P = *PI; 1685 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && 1686 PBI != BI && PBI->isConditional() && 1687 PBI->getCondition() == BI->getCondition() && 1688 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 1689 bool CondIsTrue = PBI->getSuccessor(0) == BB; 1690 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 1691 CondIsTrue), P); 1692 } else { 1693 NewPN->addIncoming(BI->getCondition(), P); 1694 } 1695 } 1696 1697 BI->setCondition(NewPN); 1698 return true; 1699 } 1700 } 1701 1702 // If this is a conditional branch in an empty block, and if any 1703 // predecessors is a conditional branch to one of our destinations, 1704 // fold the conditions into logical ops and one cond br. 1705 BasicBlock::iterator BBI = BB->begin(); 1706 // Ignore dbg intrinsics. 1707 while (isa<DbgInfoIntrinsic>(BBI)) 1708 ++BBI; 1709 if (&*BBI != BI) 1710 return false; 1711 1712 1713 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition())) 1714 if (CE->canTrap()) 1715 return false; 1716 1717 int PBIOp, BIOp; 1718 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) 1719 PBIOp = BIOp = 0; 1720 else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) 1721 PBIOp = 0, BIOp = 1; 1722 else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) 1723 PBIOp = 1, BIOp = 0; 1724 else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) 1725 PBIOp = BIOp = 1; 1726 else 1727 return false; 1728 1729 // Check to make sure that the other destination of this branch 1730 // isn't BB itself. If so, this is an infinite loop that will 1731 // keep getting unwound. 1732 if (PBI->getSuccessor(PBIOp) == BB) 1733 return false; 1734 1735 // Do not perform this transformation if it would require 1736 // insertion of a large number of select instructions. For targets 1737 // without predication/cmovs, this is a big pessimization. 1738 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); 1739 1740 unsigned NumPhis = 0; 1741 for (BasicBlock::iterator II = CommonDest->begin(); 1742 isa<PHINode>(II); ++II, ++NumPhis) 1743 if (NumPhis > 2) // Disable this xform. 1744 return false; 1745 1746 // Finally, if everything is ok, fold the branches to logical ops. 1747 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); 1748 1749 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent() 1750 << "AND: " << *BI->getParent()); 1751 1752 1753 // If OtherDest *is* BB, then BB is a basic block with a single conditional 1754 // branch in it, where one edge (OtherDest) goes back to itself but the other 1755 // exits. We don't *know* that the program avoids the infinite loop 1756 // (even though that seems likely). If we do this xform naively, we'll end up 1757 // recursively unpeeling the loop. Since we know that (after the xform is 1758 // done) that the block *is* infinite if reached, we just make it an obviously 1759 // infinite loop with no cond branch. 1760 if (OtherDest == BB) { 1761 // Insert it at the end of the function, because it's either code, 1762 // or it won't matter if it's hot. :) 1763 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(), 1764 "infloop", BB->getParent()); 1765 BranchInst::Create(InfLoopBlock, InfLoopBlock); 1766 OtherDest = InfLoopBlock; 1767 } 1768 1769 DEBUG(dbgs() << *PBI->getParent()->getParent()); 1770 1771 // BI may have other predecessors. Because of this, we leave 1772 // it alone, but modify PBI. 1773 1774 // Make sure we get to CommonDest on True&True directions. 1775 Value *PBICond = PBI->getCondition(); 1776 IRBuilder<true, NoFolder> Builder(PBI); 1777 if (PBIOp) 1778 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not"); 1779 1780 Value *BICond = BI->getCondition(); 1781 if (BIOp) 1782 BICond = Builder.CreateNot(BICond, BICond->getName()+".not"); 1783 1784 // Merge the conditions. 1785 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge"); 1786 1787 // Modify PBI to branch on the new condition to the new dests. 1788 PBI->setCondition(Cond); 1789 PBI->setSuccessor(0, CommonDest); 1790 PBI->setSuccessor(1, OtherDest); 1791 1792 // OtherDest may have phi nodes. If so, add an entry from PBI's 1793 // block that are identical to the entries for BI's block. 1794 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB); 1795 1796 // We know that the CommonDest already had an edge from PBI to 1797 // it. If it has PHIs though, the PHIs may have different 1798 // entries for BB and PBI's BB. If so, insert a select to make 1799 // them agree. 1800 PHINode *PN; 1801 for (BasicBlock::iterator II = CommonDest->begin(); 1802 (PN = dyn_cast<PHINode>(II)); ++II) { 1803 Value *BIV = PN->getIncomingValueForBlock(BB); 1804 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent()); 1805 Value *PBIV = PN->getIncomingValue(PBBIdx); 1806 if (BIV != PBIV) { 1807 // Insert a select in PBI to pick the right value. 1808 Value *NV = cast<SelectInst> 1809 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux")); 1810 PN->setIncomingValue(PBBIdx, NV); 1811 } 1812 } 1813 1814 DEBUG(dbgs() << "INTO: " << *PBI->getParent()); 1815 DEBUG(dbgs() << *PBI->getParent()->getParent()); 1816 1817 // This basic block is probably dead. We know it has at least 1818 // one fewer predecessor. 1819 return true; 1820} 1821 1822// SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a 1823// branch to TrueBB if Cond is true or to FalseBB if Cond is false. 1824// Takes care of updating the successors and removing the old terminator. 1825// Also makes sure not to introduce new successors by assuming that edges to 1826// non-successor TrueBBs and FalseBBs aren't reachable. 1827static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond, 1828 BasicBlock *TrueBB, BasicBlock *FalseBB){ 1829 // Remove any superfluous successor edges from the CFG. 1830 // First, figure out which successors to preserve. 1831 // If TrueBB and FalseBB are equal, only try to preserve one copy of that 1832 // successor. 1833 BasicBlock *KeepEdge1 = TrueBB; 1834 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0; 1835 1836 // Then remove the rest. 1837 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) { 1838 BasicBlock *Succ = OldTerm->getSuccessor(I); 1839 // Make sure only to keep exactly one copy of each edge. 1840 if (Succ == KeepEdge1) 1841 KeepEdge1 = 0; 1842 else if (Succ == KeepEdge2) 1843 KeepEdge2 = 0; 1844 else 1845 Succ->removePredecessor(OldTerm->getParent()); 1846 } 1847 1848 IRBuilder<> Builder(OldTerm); 1849 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc()); 1850 1851 // Insert an appropriate new terminator. 1852 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) { 1853 if (TrueBB == FalseBB) 1854 // We were only looking for one successor, and it was present. 1855 // Create an unconditional branch to it. 1856 Builder.CreateBr(TrueBB); 1857 else 1858 // We found both of the successors we were looking for. 1859 // Create a conditional branch sharing the condition of the select. 1860 Builder.CreateCondBr(Cond, TrueBB, FalseBB); 1861 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) { 1862 // Neither of the selected blocks were successors, so this 1863 // terminator must be unreachable. 1864 new UnreachableInst(OldTerm->getContext(), OldTerm); 1865 } else { 1866 // One of the selected values was a successor, but the other wasn't. 1867 // Insert an unconditional branch to the one that was found; 1868 // the edge to the one that wasn't must be unreachable. 1869 if (KeepEdge1 == 0) 1870 // Only TrueBB was found. 1871 Builder.CreateBr(TrueBB); 1872 else 1873 // Only FalseBB was found. 1874 Builder.CreateBr(FalseBB); 1875 } 1876 1877 EraseTerminatorInstAndDCECond(OldTerm); 1878 return true; 1879} 1880 1881// SimplifySwitchOnSelect - Replaces 1882// (switch (select cond, X, Y)) on constant X, Y 1883// with a branch - conditional if X and Y lead to distinct BBs, 1884// unconditional otherwise. 1885static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) { 1886 // Check for constant integer values in the select. 1887 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue()); 1888 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue()); 1889 if (!TrueVal || !FalseVal) 1890 return false; 1891 1892 // Find the relevant condition and destinations. 1893 Value *Condition = Select->getCondition(); 1894 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal)); 1895 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal)); 1896 1897 // Perform the actual simplification. 1898 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB); 1899} 1900 1901// SimplifyIndirectBrOnSelect - Replaces 1902// (indirectbr (select cond, blockaddress(@fn, BlockA), 1903// blockaddress(@fn, BlockB))) 1904// with 1905// (br cond, BlockA, BlockB). 1906static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) { 1907 // Check that both operands of the select are block addresses. 1908 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue()); 1909 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue()); 1910 if (!TBA || !FBA) 1911 return false; 1912 1913 // Extract the actual blocks. 1914 BasicBlock *TrueBB = TBA->getBasicBlock(); 1915 BasicBlock *FalseBB = FBA->getBasicBlock(); 1916 1917 // Perform the actual simplification. 1918 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB); 1919} 1920 1921/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp 1922/// instruction (a seteq/setne with a constant) as the only instruction in a 1923/// block that ends with an uncond branch. We are looking for a very specific 1924/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In 1925/// this case, we merge the first two "or's of icmp" into a switch, but then the 1926/// default value goes to an uncond block with a seteq in it, we get something 1927/// like: 1928/// 1929/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ] 1930/// DEFAULT: 1931/// %tmp = icmp eq i8 %A, 92 1932/// br label %end 1933/// end: 1934/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ] 1935/// 1936/// We prefer to split the edge to 'end' so that there is a true/false entry to 1937/// the PHI, merging the third icmp into the switch. 1938static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI, 1939 const TargetData *TD, 1940 IRBuilder<> &Builder) { 1941 BasicBlock *BB = ICI->getParent(); 1942 1943 // If the block has any PHIs in it or the icmp has multiple uses, it is too 1944 // complex. 1945 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false; 1946 1947 Value *V = ICI->getOperand(0); 1948 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1)); 1949 1950 // The pattern we're looking for is where our only predecessor is a switch on 1951 // 'V' and this block is the default case for the switch. In this case we can 1952 // fold the compared value into the switch to simplify things. 1953 BasicBlock *Pred = BB->getSinglePredecessor(); 1954 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false; 1955 1956 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator()); 1957 if (SI->getCondition() != V) 1958 return false; 1959 1960 // If BB is reachable on a non-default case, then we simply know the value of 1961 // V in this block. Substitute it and constant fold the icmp instruction 1962 // away. 1963 if (SI->getDefaultDest() != BB) { 1964 ConstantInt *VVal = SI->findCaseDest(BB); 1965 assert(VVal && "Should have a unique destination value"); 1966 ICI->setOperand(0, VVal); 1967 1968 if (Value *V = SimplifyInstruction(ICI, TD)) { 1969 ICI->replaceAllUsesWith(V); 1970 ICI->eraseFromParent(); 1971 } 1972 // BB is now empty, so it is likely to simplify away. 1973 return SimplifyCFG(BB) | true; 1974 } 1975 1976 // Ok, the block is reachable from the default dest. If the constant we're 1977 // comparing exists in one of the other edges, then we can constant fold ICI 1978 // and zap it. 1979 if (SI->findCaseValue(Cst) != 0) { 1980 Value *V; 1981 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 1982 V = ConstantInt::getFalse(BB->getContext()); 1983 else 1984 V = ConstantInt::getTrue(BB->getContext()); 1985 1986 ICI->replaceAllUsesWith(V); 1987 ICI->eraseFromParent(); 1988 // BB is now empty, so it is likely to simplify away. 1989 return SimplifyCFG(BB) | true; 1990 } 1991 1992 // The use of the icmp has to be in the 'end' block, by the only PHI node in 1993 // the block. 1994 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0); 1995 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back()); 1996 if (PHIUse == 0 || PHIUse != &SuccBlock->front() || 1997 isa<PHINode>(++BasicBlock::iterator(PHIUse))) 1998 return false; 1999 2000 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets 2001 // true in the PHI. 2002 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext()); 2003 Constant *NewCst = ConstantInt::getFalse(BB->getContext()); 2004 2005 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 2006 std::swap(DefaultCst, NewCst); 2007 2008 // Replace ICI (which is used by the PHI for the default value) with true or 2009 // false depending on if it is EQ or NE. 2010 ICI->replaceAllUsesWith(DefaultCst); 2011 ICI->eraseFromParent(); 2012 2013 // Okay, the switch goes to this block on a default value. Add an edge from 2014 // the switch to the merge point on the compared value. 2015 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge", 2016 BB->getParent(), BB); 2017 SI->addCase(Cst, NewBB); 2018 2019 // NewBB branches to the phi block, add the uncond branch and the phi entry. 2020 Builder.SetInsertPoint(NewBB); 2021 Builder.SetCurrentDebugLocation(SI->getDebugLoc()); 2022 Builder.CreateBr(SuccBlock); 2023 PHIUse->addIncoming(NewCst, NewBB); 2024 return true; 2025} 2026 2027/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch. 2028/// Check to see if it is branching on an or/and chain of icmp instructions, and 2029/// fold it into a switch instruction if so. 2030static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD, 2031 IRBuilder<> &Builder) { 2032 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 2033 if (Cond == 0) return false; 2034 2035 2036 // Change br (X == 0 | X == 1), T, F into a switch instruction. 2037 // If this is a bunch of seteq's or'd together, or if it's a bunch of 2038 // 'setne's and'ed together, collect them. 2039 Value *CompVal = 0; 2040 std::vector<ConstantInt*> Values; 2041 bool TrueWhenEqual = true; 2042 Value *ExtraCase = 0; 2043 unsigned UsedICmps = 0; 2044 2045 if (Cond->getOpcode() == Instruction::Or) { 2046 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true, 2047 UsedICmps); 2048 } else if (Cond->getOpcode() == Instruction::And) { 2049 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false, 2050 UsedICmps); 2051 TrueWhenEqual = false; 2052 } 2053 2054 // If we didn't have a multiply compared value, fail. 2055 if (CompVal == 0) return false; 2056 2057 // Avoid turning single icmps into a switch. 2058 if (UsedICmps <= 1) 2059 return false; 2060 2061 // There might be duplicate constants in the list, which the switch 2062 // instruction can't handle, remove them now. 2063 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate); 2064 Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); 2065 2066 // If Extra was used, we require at least two switch values to do the 2067 // transformation. A switch with one value is just an cond branch. 2068 if (ExtraCase && Values.size() < 2) return false; 2069 2070 // Figure out which block is which destination. 2071 BasicBlock *DefaultBB = BI->getSuccessor(1); 2072 BasicBlock *EdgeBB = BI->getSuccessor(0); 2073 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); 2074 2075 BasicBlock *BB = BI->getParent(); 2076 2077 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size() 2078 << " cases into SWITCH. BB is:\n" << *BB); 2079 2080 // If there are any extra values that couldn't be folded into the switch 2081 // then we evaluate them with an explicit branch first. Split the block 2082 // right before the condbr to handle it. 2083 if (ExtraCase) { 2084 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test"); 2085 // Remove the uncond branch added to the old block. 2086 TerminatorInst *OldTI = BB->getTerminator(); 2087 Builder.SetInsertPoint(OldTI); 2088 2089 if (TrueWhenEqual) 2090 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB); 2091 else 2092 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB); 2093 2094 OldTI->eraseFromParent(); 2095 2096 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them 2097 // for the edge we just added. 2098 AddPredecessorToBlock(EdgeBB, BB, NewBB); 2099 2100 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase 2101 << "\nEXTRABB = " << *BB); 2102 BB = NewBB; 2103 } 2104 2105 Builder.SetInsertPoint(BI); 2106 // Convert pointer to int before we switch. 2107 if (CompVal->getType()->isPointerTy()) { 2108 assert(TD && "Cannot switch on pointer without TargetData"); 2109 CompVal = Builder.CreatePtrToInt(CompVal, 2110 TD->getIntPtrType(CompVal->getContext()), 2111 "magicptr"); 2112 } 2113 2114 // Create the new switch instruction now. 2115 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size()); 2116 2117 // Add all of the 'cases' to the switch instruction. 2118 for (unsigned i = 0, e = Values.size(); i != e; ++i) 2119 New->addCase(Values[i], EdgeBB); 2120 2121 // We added edges from PI to the EdgeBB. As such, if there were any 2122 // PHI nodes in EdgeBB, they need entries to be added corresponding to 2123 // the number of edges added. 2124 for (BasicBlock::iterator BBI = EdgeBB->begin(); 2125 isa<PHINode>(BBI); ++BBI) { 2126 PHINode *PN = cast<PHINode>(BBI); 2127 Value *InVal = PN->getIncomingValueForBlock(BB); 2128 for (unsigned i = 0, e = Values.size()-1; i != e; ++i) 2129 PN->addIncoming(InVal, BB); 2130 } 2131 2132 // Erase the old branch instruction. 2133 EraseTerminatorInstAndDCECond(BI); 2134 2135 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n'); 2136 return true; 2137} 2138 2139bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) { 2140 BasicBlock *BB = RI->getParent(); 2141 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; 2142 2143 // Find predecessors that end with branches. 2144 SmallVector<BasicBlock*, 8> UncondBranchPreds; 2145 SmallVector<BranchInst*, 8> CondBranchPreds; 2146 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 2147 BasicBlock *P = *PI; 2148 TerminatorInst *PTI = P->getTerminator(); 2149 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) { 2150 if (BI->isUnconditional()) 2151 UncondBranchPreds.push_back(P); 2152 else 2153 CondBranchPreds.push_back(BI); 2154 } 2155 } 2156 2157 // If we found some, do the transformation! 2158 if (!UncondBranchPreds.empty() && DupRet) { 2159 while (!UncondBranchPreds.empty()) { 2160 BasicBlock *Pred = UncondBranchPreds.pop_back_val(); 2161 DEBUG(dbgs() << "FOLDING: " << *BB 2162 << "INTO UNCOND BRANCH PRED: " << *Pred); 2163 (void)FoldReturnIntoUncondBranch(RI, BB, Pred); 2164 } 2165 2166 // If we eliminated all predecessors of the block, delete the block now. 2167 if (pred_begin(BB) == pred_end(BB)) 2168 // We know there are no successors, so just nuke the block. 2169 BB->eraseFromParent(); 2170 2171 return true; 2172 } 2173 2174 // Check out all of the conditional branches going to this return 2175 // instruction. If any of them just select between returns, change the 2176 // branch itself into a select/return pair. 2177 while (!CondBranchPreds.empty()) { 2178 BranchInst *BI = CondBranchPreds.pop_back_val(); 2179 2180 // Check to see if the non-BB successor is also a return block. 2181 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) && 2182 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) && 2183 SimplifyCondBranchToTwoReturns(BI, Builder)) 2184 return true; 2185 } 2186 return false; 2187} 2188 2189bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder) { 2190 // Check to see if the first instruction in this block is just an unwind. 2191 // If so, replace any invoke instructions which use this as an exception 2192 // destination with call instructions. 2193 BasicBlock *BB = UI->getParent(); 2194 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; 2195 2196 bool Changed = false; 2197 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 2198 while (!Preds.empty()) { 2199 BasicBlock *Pred = Preds.back(); 2200 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()); 2201 if (II && II->getUnwindDest() == BB) { 2202 // Insert a new branch instruction before the invoke, because this 2203 // is now a fall through. 2204 Builder.SetInsertPoint(II); 2205 BranchInst *BI = Builder.CreateBr(II->getNormalDest()); 2206 Pred->getInstList().remove(II); // Take out of symbol table 2207 2208 // Insert the call now. 2209 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3); 2210 Builder.SetInsertPoint(BI); 2211 CallInst *CI = Builder.CreateCall(II->getCalledValue(), 2212 Args.begin(), Args.end(), 2213 II->getName()); 2214 CI->setCallingConv(II->getCallingConv()); 2215 CI->setAttributes(II->getAttributes()); 2216 // If the invoke produced a value, the Call now does instead. 2217 II->replaceAllUsesWith(CI); 2218 delete II; 2219 Changed = true; 2220 } 2221 2222 Preds.pop_back(); 2223 } 2224 2225 // If this block is now dead (and isn't the entry block), remove it. 2226 if (pred_begin(BB) == pred_end(BB) && 2227 BB != &BB->getParent()->getEntryBlock()) { 2228 // We know there are no successors, so just nuke the block. 2229 BB->eraseFromParent(); 2230 return true; 2231 } 2232 2233 return Changed; 2234} 2235 2236bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) { 2237 BasicBlock *BB = UI->getParent(); 2238 2239 bool Changed = false; 2240 2241 // If there are any instructions immediately before the unreachable that can 2242 // be removed, do so. 2243 while (UI != BB->begin()) { 2244 BasicBlock::iterator BBI = UI; 2245 --BBI; 2246 // Do not delete instructions that can have side effects, like calls 2247 // (which may never return) and volatile loads and stores. 2248 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break; 2249 2250 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) 2251 if (SI->isVolatile()) 2252 break; 2253 2254 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) 2255 if (LI->isVolatile()) 2256 break; 2257 2258 // Delete this instruction (any uses are guaranteed to be dead) 2259 if (!BBI->use_empty()) 2260 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType())); 2261 BBI->eraseFromParent(); 2262 Changed = true; 2263 } 2264 2265 // If the unreachable instruction is the first in the block, take a gander 2266 // at all of the predecessors of this instruction, and simplify them. 2267 if (&BB->front() != UI) return Changed; 2268 2269 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 2270 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 2271 TerminatorInst *TI = Preds[i]->getTerminator(); 2272 IRBuilder<> Builder(TI); 2273 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 2274 if (BI->isUnconditional()) { 2275 if (BI->getSuccessor(0) == BB) { 2276 new UnreachableInst(TI->getContext(), TI); 2277 TI->eraseFromParent(); 2278 Changed = true; 2279 } 2280 } else { 2281 if (BI->getSuccessor(0) == BB) { 2282 Builder.CreateBr(BI->getSuccessor(1)); 2283 EraseTerminatorInstAndDCECond(BI); 2284 } else if (BI->getSuccessor(1) == BB) { 2285 Builder.CreateBr(BI->getSuccessor(0)); 2286 EraseTerminatorInstAndDCECond(BI); 2287 Changed = true; 2288 } 2289 } 2290 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 2291 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2292 if (SI->getSuccessor(i) == BB) { 2293 BB->removePredecessor(SI->getParent()); 2294 SI->removeCase(i); 2295 --i; --e; 2296 Changed = true; 2297 } 2298 // If the default value is unreachable, figure out the most popular 2299 // destination and make it the default. 2300 if (SI->getSuccessor(0) == BB) { 2301 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity; 2302 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) { 2303 std::pair<unsigned, unsigned>& entry = 2304 Popularity[SI->getSuccessor(i)]; 2305 if (entry.first == 0) { 2306 entry.first = 1; 2307 entry.second = i; 2308 } else { 2309 entry.first++; 2310 } 2311 } 2312 2313 // Find the most popular block. 2314 unsigned MaxPop = 0; 2315 unsigned MaxIndex = 0; 2316 BasicBlock *MaxBlock = 0; 2317 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator 2318 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { 2319 if (I->second.first > MaxPop || 2320 (I->second.first == MaxPop && MaxIndex > I->second.second)) { 2321 MaxPop = I->second.first; 2322 MaxIndex = I->second.second; 2323 MaxBlock = I->first; 2324 } 2325 } 2326 if (MaxBlock) { 2327 // Make this the new default, allowing us to delete any explicit 2328 // edges to it. 2329 SI->setSuccessor(0, MaxBlock); 2330 Changed = true; 2331 2332 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from 2333 // it. 2334 if (isa<PHINode>(MaxBlock->begin())) 2335 for (unsigned i = 0; i != MaxPop-1; ++i) 2336 MaxBlock->removePredecessor(SI->getParent()); 2337 2338 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) 2339 if (SI->getSuccessor(i) == MaxBlock) { 2340 SI->removeCase(i); 2341 --i; --e; 2342 } 2343 } 2344 } 2345 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) { 2346 if (II->getUnwindDest() == BB) { 2347 // Convert the invoke to a call instruction. This would be a good 2348 // place to note that the call does not throw though. 2349 BranchInst *BI = Builder.CreateBr(II->getNormalDest()); 2350 II->removeFromParent(); // Take out of symbol table 2351 2352 // Insert the call now... 2353 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3); 2354 Builder.SetInsertPoint(BI); 2355 CallInst *CI = Builder.CreateCall(II->getCalledValue(), 2356 Args.begin(), Args.end(), 2357 II->getName()); 2358 CI->setCallingConv(II->getCallingConv()); 2359 CI->setAttributes(II->getAttributes()); 2360 // If the invoke produced a value, the call does now instead. 2361 II->replaceAllUsesWith(CI); 2362 delete II; 2363 Changed = true; 2364 } 2365 } 2366 } 2367 2368 // If this block is now dead, remove it. 2369 if (pred_begin(BB) == pred_end(BB) && 2370 BB != &BB->getParent()->getEntryBlock()) { 2371 // We know there are no successors, so just nuke the block. 2372 BB->eraseFromParent(); 2373 return true; 2374 } 2375 2376 return Changed; 2377} 2378 2379/// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a 2380/// integer range comparison into a sub, an icmp and a branch. 2381static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) { 2382 assert(SI->getNumCases() > 2 && "Degenerate switch?"); 2383 2384 // Make sure all cases point to the same destination and gather the values. 2385 SmallVector<ConstantInt *, 16> Cases; 2386 Cases.push_back(SI->getCaseValue(1)); 2387 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) { 2388 if (SI->getSuccessor(I-1) != SI->getSuccessor(I)) 2389 return false; 2390 Cases.push_back(SI->getCaseValue(I)); 2391 } 2392 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered"); 2393 2394 // Sort the case values, then check if they form a range we can transform. 2395 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate); 2396 for (unsigned I = 1, E = Cases.size(); I != E; ++I) { 2397 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1) 2398 return false; 2399 } 2400 2401 Constant *Offset = ConstantExpr::getNeg(Cases.back()); 2402 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1); 2403 2404 Value *Sub = SI->getCondition(); 2405 if (!Offset->isNullValue()) 2406 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off"); 2407 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch"); 2408 Builder.CreateCondBr(Cmp, SI->getSuccessor(1), SI->getDefaultDest()); 2409 2410 // Prune obsolete incoming values off the successor's PHI nodes. 2411 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin(); 2412 isa<PHINode>(BBI); ++BBI) { 2413 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I) 2414 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent()); 2415 } 2416 SI->eraseFromParent(); 2417 2418 return true; 2419} 2420 2421/// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch 2422/// and use it to remove dead cases. 2423static bool EliminateDeadSwitchCases(SwitchInst *SI) { 2424 Value *Cond = SI->getCondition(); 2425 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth(); 2426 APInt KnownZero(Bits, 0), KnownOne(Bits, 0); 2427 ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne); 2428 2429 // Gather dead cases. 2430 SmallVector<ConstantInt*, 8> DeadCases; 2431 for (unsigned I = 1, E = SI->getNumCases(); I != E; ++I) { 2432 if ((SI->getCaseValue(I)->getValue() & KnownZero) != 0 || 2433 (SI->getCaseValue(I)->getValue() & KnownOne) != KnownOne) { 2434 DeadCases.push_back(SI->getCaseValue(I)); 2435 DEBUG(dbgs() << "SimplifyCFG: switch case '" 2436 << SI->getCaseValue(I)->getValue() << "' is dead.\n"); 2437 } 2438 } 2439 2440 // Remove dead cases from the switch. 2441 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) { 2442 unsigned Case = SI->findCaseValue(DeadCases[I]); 2443 // Prune unused values from PHI nodes. 2444 SI->getSuccessor(Case)->removePredecessor(SI->getParent()); 2445 SI->removeCase(Case); 2446 } 2447 2448 return !DeadCases.empty(); 2449} 2450 2451bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) { 2452 // If this switch is too complex to want to look at, ignore it. 2453 if (!isValueEqualityComparison(SI)) 2454 return false; 2455 2456 BasicBlock *BB = SI->getParent(); 2457 2458 // If we only have one predecessor, and if it is a branch on this value, 2459 // see if that predecessor totally determines the outcome of this switch. 2460 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 2461 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder)) 2462 return SimplifyCFG(BB) | true; 2463 2464 Value *Cond = SI->getCondition(); 2465 if (SelectInst *Select = dyn_cast<SelectInst>(Cond)) 2466 if (SimplifySwitchOnSelect(SI, Select)) 2467 return SimplifyCFG(BB) | true; 2468 2469 // If the block only contains the switch, see if we can fold the block 2470 // away into any preds. 2471 BasicBlock::iterator BBI = BB->begin(); 2472 // Ignore dbg intrinsics. 2473 while (isa<DbgInfoIntrinsic>(BBI)) 2474 ++BBI; 2475 if (SI == &*BBI) 2476 if (FoldValueComparisonIntoPredecessors(SI, Builder)) 2477 return SimplifyCFG(BB) | true; 2478 2479 // Try to transform the switch into an icmp and a branch. 2480 if (TurnSwitchRangeIntoICmp(SI, Builder)) 2481 return SimplifyCFG(BB) | true; 2482 2483 // Remove unreachable cases. 2484 if (EliminateDeadSwitchCases(SI)) 2485 return SimplifyCFG(BB) | true; 2486 2487 return false; 2488} 2489 2490bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) { 2491 BasicBlock *BB = IBI->getParent(); 2492 bool Changed = false; 2493 2494 // Eliminate redundant destinations. 2495 SmallPtrSet<Value *, 8> Succs; 2496 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 2497 BasicBlock *Dest = IBI->getDestination(i); 2498 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) { 2499 Dest->removePredecessor(BB); 2500 IBI->removeDestination(i); 2501 --i; --e; 2502 Changed = true; 2503 } 2504 } 2505 2506 if (IBI->getNumDestinations() == 0) { 2507 // If the indirectbr has no successors, change it to unreachable. 2508 new UnreachableInst(IBI->getContext(), IBI); 2509 EraseTerminatorInstAndDCECond(IBI); 2510 return true; 2511 } 2512 2513 if (IBI->getNumDestinations() == 1) { 2514 // If the indirectbr has one successor, change it to a direct branch. 2515 BranchInst::Create(IBI->getDestination(0), IBI); 2516 EraseTerminatorInstAndDCECond(IBI); 2517 return true; 2518 } 2519 2520 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) { 2521 if (SimplifyIndirectBrOnSelect(IBI, SI)) 2522 return SimplifyCFG(BB) | true; 2523 } 2524 return Changed; 2525} 2526 2527bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){ 2528 BasicBlock *BB = BI->getParent(); 2529 2530 // If the Terminator is the only non-phi instruction, simplify the block. 2531 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg(); 2532 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() && 2533 TryToSimplifyUncondBranchFromEmptyBlock(BB)) 2534 return true; 2535 2536 // If the only instruction in the block is a seteq/setne comparison 2537 // against a constant, try to simplify the block. 2538 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) 2539 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) { 2540 for (++I; isa<DbgInfoIntrinsic>(I); ++I) 2541 ; 2542 if (I->isTerminator() 2543 && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder)) 2544 return true; 2545 } 2546 2547 return false; 2548} 2549 2550 2551bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) { 2552 BasicBlock *BB = BI->getParent(); 2553 2554 // Conditional branch 2555 if (isValueEqualityComparison(BI)) { 2556 // If we only have one predecessor, and if it is a branch on this value, 2557 // see if that predecessor totally determines the outcome of this 2558 // switch. 2559 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 2560 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder)) 2561 return SimplifyCFG(BB) | true; 2562 2563 // This block must be empty, except for the setcond inst, if it exists. 2564 // Ignore dbg intrinsics. 2565 BasicBlock::iterator I = BB->begin(); 2566 // Ignore dbg intrinsics. 2567 while (isa<DbgInfoIntrinsic>(I)) 2568 ++I; 2569 if (&*I == BI) { 2570 if (FoldValueComparisonIntoPredecessors(BI, Builder)) 2571 return SimplifyCFG(BB) | true; 2572 } else if (&*I == cast<Instruction>(BI->getCondition())){ 2573 ++I; 2574 // Ignore dbg intrinsics. 2575 while (isa<DbgInfoIntrinsic>(I)) 2576 ++I; 2577 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder)) 2578 return SimplifyCFG(BB) | true; 2579 } 2580 } 2581 2582 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction. 2583 if (SimplifyBranchOnICmpChain(BI, TD, Builder)) 2584 return true; 2585 2586 // We have a conditional branch to two blocks that are only reachable 2587 // from BI. We know that the condbr dominates the two blocks, so see if 2588 // there is any identical code in the "then" and "else" blocks. If so, we 2589 // can hoist it up to the branching block. 2590 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) { 2591 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 2592 if (HoistThenElseCodeToIf(BI)) 2593 return SimplifyCFG(BB) | true; 2594 } else { 2595 // If Successor #1 has multiple preds, we may be able to conditionally 2596 // execute Successor #0 if it branches to successor #1. 2597 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator(); 2598 if (Succ0TI->getNumSuccessors() == 1 && 2599 Succ0TI->getSuccessor(0) == BI->getSuccessor(1)) 2600 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0))) 2601 return SimplifyCFG(BB) | true; 2602 } 2603 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 2604 // If Successor #0 has multiple preds, we may be able to conditionally 2605 // execute Successor #1 if it branches to successor #0. 2606 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator(); 2607 if (Succ1TI->getNumSuccessors() == 1 && 2608 Succ1TI->getSuccessor(0) == BI->getSuccessor(0)) 2609 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1))) 2610 return SimplifyCFG(BB) | true; 2611 } 2612 2613 // If this is a branch on a phi node in the current block, thread control 2614 // through this block if any PHI node entries are constants. 2615 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition())) 2616 if (PN->getParent() == BI->getParent()) 2617 if (FoldCondBranchOnPHI(BI, TD)) 2618 return SimplifyCFG(BB) | true; 2619 2620 // If this basic block is ONLY a setcc and a branch, and if a predecessor 2621 // branches to us and one of our successors, fold the setcc into the 2622 // predecessor and use logical operations to pick the right destination. 2623 if (FoldBranchToCommonDest(BI)) 2624 return SimplifyCFG(BB) | true; 2625 2626 // Scan predecessor blocks for conditional branches. 2627 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 2628 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) 2629 if (PBI != BI && PBI->isConditional()) 2630 if (SimplifyCondBranchToCondBranch(PBI, BI)) 2631 return SimplifyCFG(BB) | true; 2632 2633 return false; 2634} 2635 2636bool SimplifyCFGOpt::run(BasicBlock *BB) { 2637 bool Changed = false; 2638 2639 assert(BB && BB->getParent() && "Block not embedded in function!"); 2640 assert(BB->getTerminator() && "Degenerate basic block encountered!"); 2641 2642 // Remove basic blocks that have no predecessors (except the entry block)... 2643 // or that just have themself as a predecessor. These are unreachable. 2644 if ((pred_begin(BB) == pred_end(BB) && 2645 BB != &BB->getParent()->getEntryBlock()) || 2646 BB->getSinglePredecessor() == BB) { 2647 DEBUG(dbgs() << "Removing BB: \n" << *BB); 2648 DeleteDeadBlock(BB); 2649 return true; 2650 } 2651 2652 // Check to see if we can constant propagate this terminator instruction 2653 // away... 2654 Changed |= ConstantFoldTerminator(BB); 2655 2656 // Check for and eliminate duplicate PHI nodes in this block. 2657 Changed |= EliminateDuplicatePHINodes(BB); 2658 2659 // Merge basic blocks into their predecessor if there is only one distinct 2660 // pred, and if there is only one distinct successor of the predecessor, and 2661 // if there are no PHI nodes. 2662 // 2663 if (MergeBlockIntoPredecessor(BB)) 2664 return true; 2665 2666 IRBuilder<> Builder(BB); 2667 2668 // If there is a trivial two-entry PHI node in this basic block, and we can 2669 // eliminate it, do so now. 2670 if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) 2671 if (PN->getNumIncomingValues() == 2) 2672 Changed |= FoldTwoEntryPHINode(PN, TD); 2673 2674 Builder.SetInsertPoint(BB->getTerminator()); 2675 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { 2676 if (BI->isUnconditional()) { 2677 if (SimplifyUncondBranch(BI, Builder)) return true; 2678 } else { 2679 if (SimplifyCondBranch(BI, Builder)) return true; 2680 } 2681 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 2682 if (SimplifyReturn(RI, Builder)) return true; 2683 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { 2684 if (SimplifySwitch(SI, Builder)) return true; 2685 } else if (UnreachableInst *UI = 2686 dyn_cast<UnreachableInst>(BB->getTerminator())) { 2687 if (SimplifyUnreachable(UI)) return true; 2688 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) { 2689 if (SimplifyUnwind(UI, Builder)) return true; 2690 } else if (IndirectBrInst *IBI = 2691 dyn_cast<IndirectBrInst>(BB->getTerminator())) { 2692 if (SimplifyIndirectBr(IBI)) return true; 2693 } 2694 2695 return Changed; 2696} 2697 2698/// SimplifyCFG - This function is used to do simplification of a CFG. For 2699/// example, it adjusts branches to branches to eliminate the extra hop, it 2700/// eliminates unreachable basic blocks, and does other "peephole" optimization 2701/// of the CFG. It returns true if a modification was made. 2702/// 2703bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) { 2704 return SimplifyCFGOpt(TD).run(BB); 2705} 2706