SimplifyCFG.cpp revision daf4cfc8d890c7f17241ff7127b64c13ed2cb4d4
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/DataLayout.h" 18#include "llvm/DerivedTypes.h" 19#include "llvm/GlobalVariable.h" 20#include "llvm/IRBuilder.h" 21#include "llvm/Instructions.h" 22#include "llvm/IntrinsicInst.h" 23#include "llvm/LLVMContext.h" 24#include "llvm/MDBuilder.h" 25#include "llvm/Metadata.h" 26#include "llvm/Module.h" 27#include "llvm/Operator.h" 28#include "llvm/Type.h" 29#include "llvm/ADT/DenseMap.h" 30#include "llvm/ADT/STLExtras.h" 31#include "llvm/ADT/SetVector.h" 32#include "llvm/ADT/SmallPtrSet.h" 33#include "llvm/ADT/SmallVector.h" 34#include "llvm/ADT/Statistic.h" 35#include "llvm/Analysis/InstructionSimplify.h" 36#include "llvm/Analysis/ValueTracking.h" 37#include "llvm/Support/CFG.h" 38#include "llvm/Support/CommandLine.h" 39#include "llvm/Support/ConstantRange.h" 40#include "llvm/Support/Debug.h" 41#include "llvm/Support/NoFolder.h" 42#include "llvm/Support/raw_ostream.h" 43#include "llvm/TargetTransformInfo.h" 44#include "llvm/Transforms/Utils/BasicBlockUtils.h" 45#include <algorithm> 46#include <set> 47#include <map> 48using namespace llvm; 49 50static cl::opt<unsigned> 51PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1), 52 cl::desc("Control the amount of phi node folding to perform (default = 1)")); 53 54static cl::opt<bool> 55DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false), 56 cl::desc("Duplicate return instructions into unconditional branches")); 57 58static cl::opt<bool> 59SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true), 60 cl::desc("Sink common instructions down to the end block")); 61 62STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps"); 63STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables"); 64STATISTIC(NumSinkCommons, "Number of common instructions sunk down to the end block"); 65STATISTIC(NumSpeculations, "Number of speculative executed instructions"); 66 67namespace { 68 /// ValueEqualityComparisonCase - Represents a case of a switch. 69 struct ValueEqualityComparisonCase { 70 ConstantInt *Value; 71 BasicBlock *Dest; 72 73 ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest) 74 : Value(Value), Dest(Dest) {} 75 76 bool operator<(ValueEqualityComparisonCase RHS) const { 77 // Comparing pointers is ok as we only rely on the order for uniquing. 78 return Value < RHS.Value; 79 } 80 81 bool operator==(BasicBlock *RHSDest) const { return Dest == RHSDest; } 82 }; 83 84class SimplifyCFGOpt { 85 const DataLayout *const TD; 86 const TargetTransformInfo *const TTI; 87 88 Value *isValueEqualityComparison(TerminatorInst *TI); 89 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI, 90 std::vector<ValueEqualityComparisonCase> &Cases); 91 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 92 BasicBlock *Pred, 93 IRBuilder<> &Builder); 94 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI, 95 IRBuilder<> &Builder); 96 97 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder); 98 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder); 99 bool SimplifyUnreachable(UnreachableInst *UI); 100 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder); 101 bool SimplifyIndirectBr(IndirectBrInst *IBI); 102 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder); 103 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder); 104 105public: 106 SimplifyCFGOpt(const DataLayout *td, const TargetTransformInfo *tti) 107 : TD(td), TTI(tti) {} 108 bool run(BasicBlock *BB); 109}; 110} 111 112/// SafeToMergeTerminators - Return true if it is safe to merge these two 113/// terminator instructions together. 114/// 115static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) { 116 if (SI1 == SI2) return false; // Can't merge with self! 117 118 // It is not safe to merge these two switch instructions if they have a common 119 // successor, and if that successor has a PHI node, and if *that* PHI node has 120 // conflicting incoming values from the two switch blocks. 121 BasicBlock *SI1BB = SI1->getParent(); 122 BasicBlock *SI2BB = SI2->getParent(); 123 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); 124 125 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) 126 if (SI1Succs.count(*I)) 127 for (BasicBlock::iterator BBI = (*I)->begin(); 128 isa<PHINode>(BBI); ++BBI) { 129 PHINode *PN = cast<PHINode>(BBI); 130 if (PN->getIncomingValueForBlock(SI1BB) != 131 PN->getIncomingValueForBlock(SI2BB)) 132 return false; 133 } 134 135 return true; 136} 137 138/// isProfitableToFoldUnconditional - Return true if it is safe and profitable 139/// to merge these two terminator instructions together, where SI1 is an 140/// unconditional branch. PhiNodes will store all PHI nodes in common 141/// successors. 142/// 143static bool isProfitableToFoldUnconditional(BranchInst *SI1, 144 BranchInst *SI2, 145 Instruction *Cond, 146 SmallVectorImpl<PHINode*> &PhiNodes) { 147 if (SI1 == SI2) return false; // Can't merge with self! 148 assert(SI1->isUnconditional() && SI2->isConditional()); 149 150 // We fold the unconditional branch if we can easily update all PHI nodes in 151 // common successors: 152 // 1> We have a constant incoming value for the conditional branch; 153 // 2> We have "Cond" as the incoming value for the unconditional branch; 154 // 3> SI2->getCondition() and Cond have same operands. 155 CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition()); 156 if (!Ci2) return false; 157 if (!(Cond->getOperand(0) == Ci2->getOperand(0) && 158 Cond->getOperand(1) == Ci2->getOperand(1)) && 159 !(Cond->getOperand(0) == Ci2->getOperand(1) && 160 Cond->getOperand(1) == Ci2->getOperand(0))) 161 return false; 162 163 BasicBlock *SI1BB = SI1->getParent(); 164 BasicBlock *SI2BB = SI2->getParent(); 165 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); 166 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) 167 if (SI1Succs.count(*I)) 168 for (BasicBlock::iterator BBI = (*I)->begin(); 169 isa<PHINode>(BBI); ++BBI) { 170 PHINode *PN = cast<PHINode>(BBI); 171 if (PN->getIncomingValueForBlock(SI1BB) != Cond || 172 !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB))) 173 return false; 174 PhiNodes.push_back(PN); 175 } 176 return true; 177} 178 179/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will 180/// now be entries in it from the 'NewPred' block. The values that will be 181/// flowing into the PHI nodes will be the same as those coming in from 182/// ExistPred, an existing predecessor of Succ. 183static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, 184 BasicBlock *ExistPred) { 185 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do 186 187 PHINode *PN; 188 for (BasicBlock::iterator I = Succ->begin(); 189 (PN = dyn_cast<PHINode>(I)); ++I) 190 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred); 191} 192 193 194/// GetIfCondition - Given a basic block (BB) with two predecessors (and at 195/// least one PHI node in it), check to see if the merge at this block is due 196/// to an "if condition". If so, return the boolean condition that determines 197/// which entry into BB will be taken. Also, return by references the block 198/// that will be entered from if the condition is true, and the block that will 199/// be entered if the condition is false. 200/// 201/// This does no checking to see if the true/false blocks have large or unsavory 202/// instructions in them. 203static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 204 BasicBlock *&IfFalse) { 205 PHINode *SomePHI = cast<PHINode>(BB->begin()); 206 assert(SomePHI->getNumIncomingValues() == 2 && 207 "Function can only handle blocks with 2 predecessors!"); 208 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0); 209 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1); 210 211 // We can only handle branches. Other control flow will be lowered to 212 // branches if possible anyway. 213 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator()); 214 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator()); 215 if (Pred1Br == 0 || Pred2Br == 0) 216 return 0; 217 218 // Eliminate code duplication by ensuring that Pred1Br is conditional if 219 // either are. 220 if (Pred2Br->isConditional()) { 221 // If both branches are conditional, we don't have an "if statement". In 222 // reality, we could transform this case, but since the condition will be 223 // required anyway, we stand no chance of eliminating it, so the xform is 224 // probably not profitable. 225 if (Pred1Br->isConditional()) 226 return 0; 227 228 std::swap(Pred1, Pred2); 229 std::swap(Pred1Br, Pred2Br); 230 } 231 232 if (Pred1Br->isConditional()) { 233 // The only thing we have to watch out for here is to make sure that Pred2 234 // doesn't have incoming edges from other blocks. If it does, the condition 235 // doesn't dominate BB. 236 if (Pred2->getSinglePredecessor() == 0) 237 return 0; 238 239 // If we found a conditional branch predecessor, make sure that it branches 240 // to BB and Pred2Br. If it doesn't, this isn't an "if statement". 241 if (Pred1Br->getSuccessor(0) == BB && 242 Pred1Br->getSuccessor(1) == Pred2) { 243 IfTrue = Pred1; 244 IfFalse = Pred2; 245 } else if (Pred1Br->getSuccessor(0) == Pred2 && 246 Pred1Br->getSuccessor(1) == BB) { 247 IfTrue = Pred2; 248 IfFalse = Pred1; 249 } else { 250 // We know that one arm of the conditional goes to BB, so the other must 251 // go somewhere unrelated, and this must not be an "if statement". 252 return 0; 253 } 254 255 return Pred1Br->getCondition(); 256 } 257 258 // Ok, if we got here, both predecessors end with an unconditional branch to 259 // BB. Don't panic! If both blocks only have a single (identical) 260 // predecessor, and THAT is a conditional branch, then we're all ok! 261 BasicBlock *CommonPred = Pred1->getSinglePredecessor(); 262 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor()) 263 return 0; 264 265 // Otherwise, if this is a conditional branch, then we can use it! 266 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator()); 267 if (BI == 0) return 0; 268 269 assert(BI->isConditional() && "Two successors but not conditional?"); 270 if (BI->getSuccessor(0) == Pred1) { 271 IfTrue = Pred1; 272 IfFalse = Pred2; 273 } else { 274 IfTrue = Pred2; 275 IfFalse = Pred1; 276 } 277 return BI->getCondition(); 278} 279 280/// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the 281/// given instruction, which is assumed to be safe to speculate. 1 means 282/// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive. 283static unsigned ComputeSpeculationCost(const User *I) { 284 assert(isSafeToSpeculativelyExecute(I) && 285 "Instruction is not safe to speculatively execute!"); 286 switch (Operator::getOpcode(I)) { 287 default: 288 // In doubt, be conservative. 289 return UINT_MAX; 290 case Instruction::GetElementPtr: 291 // GEPs are cheap if all indices are constant. 292 if (!cast<GEPOperator>(I)->hasAllConstantIndices()) 293 return UINT_MAX; 294 return 1; 295 case Instruction::Load: 296 case Instruction::Add: 297 case Instruction::Sub: 298 case Instruction::And: 299 case Instruction::Or: 300 case Instruction::Xor: 301 case Instruction::Shl: 302 case Instruction::LShr: 303 case Instruction::AShr: 304 case Instruction::ICmp: 305 case Instruction::Trunc: 306 case Instruction::ZExt: 307 case Instruction::SExt: 308 return 1; // These are all cheap. 309 310 case Instruction::Call: 311 case Instruction::Select: 312 return 2; 313 } 314} 315 316/// DominatesMergePoint - If we have a merge point of an "if condition" as 317/// accepted above, return true if the specified value dominates the block. We 318/// don't handle the true generality of domination here, just a special case 319/// which works well enough for us. 320/// 321/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to 322/// see if V (which must be an instruction) and its recursive operands 323/// that do not dominate BB have a combined cost lower than CostRemaining and 324/// are non-trapping. If both are true, the instruction is inserted into the 325/// set and true is returned. 326/// 327/// The cost for most non-trapping instructions is defined as 1 except for 328/// Select whose cost is 2. 329/// 330/// After this function returns, CostRemaining is decreased by the cost of 331/// V plus its non-dominating operands. If that cost is greater than 332/// CostRemaining, false is returned and CostRemaining is undefined. 333static bool DominatesMergePoint(Value *V, BasicBlock *BB, 334 SmallPtrSet<Instruction*, 4> *AggressiveInsts, 335 unsigned &CostRemaining) { 336 Instruction *I = dyn_cast<Instruction>(V); 337 if (!I) { 338 // Non-instructions all dominate instructions, but not all constantexprs 339 // can be executed unconditionally. 340 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V)) 341 if (C->canTrap()) 342 return false; 343 return true; 344 } 345 BasicBlock *PBB = I->getParent(); 346 347 // We don't want to allow weird loops that might have the "if condition" in 348 // the bottom of this block. 349 if (PBB == BB) return false; 350 351 // If this instruction is defined in a block that contains an unconditional 352 // branch to BB, then it must be in the 'conditional' part of the "if 353 // statement". If not, it definitely dominates the region. 354 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()); 355 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB) 356 return true; 357 358 // If we aren't allowing aggressive promotion anymore, then don't consider 359 // instructions in the 'if region'. 360 if (AggressiveInsts == 0) return false; 361 362 // If we have seen this instruction before, don't count it again. 363 if (AggressiveInsts->count(I)) return true; 364 365 // Okay, it looks like the instruction IS in the "condition". Check to 366 // see if it's a cheap instruction to unconditionally compute, and if it 367 // only uses stuff defined outside of the condition. If so, hoist it out. 368 if (!isSafeToSpeculativelyExecute(I)) 369 return false; 370 371 unsigned Cost = ComputeSpeculationCost(I); 372 373 if (Cost > CostRemaining) 374 return false; 375 376 CostRemaining -= Cost; 377 378 // Okay, we can only really hoist these out if their operands do 379 // not take us over the cost threshold. 380 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) 381 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining)) 382 return false; 383 // Okay, it's safe to do this! Remember this instruction. 384 AggressiveInsts->insert(I); 385 return true; 386} 387 388/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr 389/// and PointerNullValue. Return NULL if value is not a constant int. 390static ConstantInt *GetConstantInt(Value *V, const DataLayout *TD) { 391 // Normal constant int. 392 ConstantInt *CI = dyn_cast<ConstantInt>(V); 393 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy()) 394 return CI; 395 396 // This is some kind of pointer constant. Turn it into a pointer-sized 397 // ConstantInt if possible. 398 IntegerType *PtrTy = cast<IntegerType>(TD->getIntPtrType(V->getType())); 399 400 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*). 401 if (isa<ConstantPointerNull>(V)) 402 return ConstantInt::get(PtrTy, 0); 403 404 // IntToPtr const int. 405 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 406 if (CE->getOpcode() == Instruction::IntToPtr) 407 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) { 408 // The constant is very likely to have the right type already. 409 if (CI->getType() == PtrTy) 410 return CI; 411 else 412 return cast<ConstantInt> 413 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false)); 414 } 415 return 0; 416} 417 418/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together 419/// collection of icmp eq/ne instructions that compare a value against a 420/// constant, return the value being compared, and stick the constant into the 421/// Values vector. 422static Value * 423GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra, 424 const DataLayout *TD, bool isEQ, unsigned &UsedICmps) { 425 Instruction *I = dyn_cast<Instruction>(V); 426 if (I == 0) return 0; 427 428 // If this is an icmp against a constant, handle this as one of the cases. 429 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) { 430 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) { 431 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) { 432 UsedICmps++; 433 Vals.push_back(C); 434 return I->getOperand(0); 435 } 436 437 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to 438 // the set. 439 ConstantRange Span = 440 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue()); 441 442 // If this is an and/!= check then we want to optimize "x ugt 2" into 443 // x != 0 && x != 1. 444 if (!isEQ) 445 Span = Span.inverse(); 446 447 // If there are a ton of values, we don't want to make a ginormous switch. 448 if (Span.getSetSize().ugt(8) || Span.isEmptySet()) 449 return 0; 450 451 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp) 452 Vals.push_back(ConstantInt::get(V->getContext(), Tmp)); 453 UsedICmps++; 454 return I->getOperand(0); 455 } 456 return 0; 457 } 458 459 // Otherwise, we can only handle an | or &, depending on isEQ. 460 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And)) 461 return 0; 462 463 unsigned NumValsBeforeLHS = Vals.size(); 464 unsigned UsedICmpsBeforeLHS = UsedICmps; 465 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD, 466 isEQ, UsedICmps)) { 467 unsigned NumVals = Vals.size(); 468 unsigned UsedICmpsBeforeRHS = UsedICmps; 469 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, 470 isEQ, UsedICmps)) { 471 if (LHS == RHS) 472 return LHS; 473 Vals.resize(NumVals); 474 UsedICmps = UsedICmpsBeforeRHS; 475 } 476 477 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet, 478 // set it and return success. 479 if (Extra == 0 || Extra == I->getOperand(1)) { 480 Extra = I->getOperand(1); 481 return LHS; 482 } 483 484 Vals.resize(NumValsBeforeLHS); 485 UsedICmps = UsedICmpsBeforeLHS; 486 return 0; 487 } 488 489 // If the LHS can't be folded in, but Extra is available and RHS can, try to 490 // use LHS as Extra. 491 if (Extra == 0 || Extra == I->getOperand(0)) { 492 Value *OldExtra = Extra; 493 Extra = I->getOperand(0); 494 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, 495 isEQ, UsedICmps)) 496 return RHS; 497 assert(Vals.size() == NumValsBeforeLHS); 498 Extra = OldExtra; 499 } 500 501 return 0; 502} 503 504static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) { 505 Instruction *Cond = 0; 506 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 507 Cond = dyn_cast<Instruction>(SI->getCondition()); 508 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 509 if (BI->isConditional()) 510 Cond = dyn_cast<Instruction>(BI->getCondition()); 511 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) { 512 Cond = dyn_cast<Instruction>(IBI->getAddress()); 513 } 514 515 TI->eraseFromParent(); 516 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond); 517} 518 519/// isValueEqualityComparison - Return true if the specified terminator checks 520/// to see if a value is equal to constant integer value. 521Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) { 522 Value *CV = 0; 523 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 524 // Do not permit merging of large switch instructions into their 525 // predecessors unless there is only one predecessor. 526 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()), 527 pred_end(SI->getParent())) <= 128) 528 CV = SI->getCondition(); 529 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) 530 if (BI->isConditional() && BI->getCondition()->hasOneUse()) 531 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) 532 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ || 533 ICI->getPredicate() == ICmpInst::ICMP_NE) && 534 GetConstantInt(ICI->getOperand(1), TD)) 535 CV = ICI->getOperand(0); 536 537 // Unwrap any lossless ptrtoint cast. 538 if (TD && CV) { 539 PtrToIntInst *PTII = NULL; 540 if ((PTII = dyn_cast<PtrToIntInst>(CV)) && 541 CV->getType() == TD->getIntPtrType(CV->getContext(), 542 PTII->getPointerAddressSpace())) 543 CV = PTII->getOperand(0); 544 } 545 return CV; 546} 547 548/// GetValueEqualityComparisonCases - Given a value comparison instruction, 549/// decode all of the 'cases' that it represents and return the 'default' block. 550BasicBlock *SimplifyCFGOpt:: 551GetValueEqualityComparisonCases(TerminatorInst *TI, 552 std::vector<ValueEqualityComparisonCase> 553 &Cases) { 554 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 555 Cases.reserve(SI->getNumCases()); 556 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i) 557 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(), 558 i.getCaseSuccessor())); 559 return SI->getDefaultDest(); 560 } 561 562 BranchInst *BI = cast<BranchInst>(TI); 563 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); 564 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE); 565 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1), 566 TD), 567 Succ)); 568 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ); 569} 570 571 572/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries 573/// in the list that match the specified block. 574static void EliminateBlockCases(BasicBlock *BB, 575 std::vector<ValueEqualityComparisonCase> &Cases) { 576 Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end()); 577} 578 579/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as 580/// well. 581static bool 582ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1, 583 std::vector<ValueEqualityComparisonCase > &C2) { 584 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2; 585 586 // Make V1 be smaller than V2. 587 if (V1->size() > V2->size()) 588 std::swap(V1, V2); 589 590 if (V1->size() == 0) return false; 591 if (V1->size() == 1) { 592 // Just scan V2. 593 ConstantInt *TheVal = (*V1)[0].Value; 594 for (unsigned i = 0, e = V2->size(); i != e; ++i) 595 if (TheVal == (*V2)[i].Value) 596 return true; 597 } 598 599 // Otherwise, just sort both lists and compare element by element. 600 array_pod_sort(V1->begin(), V1->end()); 601 array_pod_sort(V2->begin(), V2->end()); 602 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); 603 while (i1 != e1 && i2 != e2) { 604 if ((*V1)[i1].Value == (*V2)[i2].Value) 605 return true; 606 if ((*V1)[i1].Value < (*V2)[i2].Value) 607 ++i1; 608 else 609 ++i2; 610 } 611 return false; 612} 613 614/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a 615/// terminator instruction and its block is known to only have a single 616/// predecessor block, check to see if that predecessor is also a value 617/// comparison with the same value, and if that comparison determines the 618/// outcome of this comparison. If so, simplify TI. This does a very limited 619/// form of jump threading. 620bool SimplifyCFGOpt:: 621SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 622 BasicBlock *Pred, 623 IRBuilder<> &Builder) { 624 Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); 625 if (!PredVal) return false; // Not a value comparison in predecessor. 626 627 Value *ThisVal = isValueEqualityComparison(TI); 628 assert(ThisVal && "This isn't a value comparison!!"); 629 if (ThisVal != PredVal) return false; // Different predicates. 630 631 // TODO: Preserve branch weight metadata, similarly to how 632 // FoldValueComparisonIntoPredecessors preserves it. 633 634 // Find out information about when control will move from Pred to TI's block. 635 std::vector<ValueEqualityComparisonCase> PredCases; 636 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), 637 PredCases); 638 EliminateBlockCases(PredDef, PredCases); // Remove default from cases. 639 640 // Find information about how control leaves this block. 641 std::vector<ValueEqualityComparisonCase> ThisCases; 642 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); 643 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. 644 645 // If TI's block is the default block from Pred's comparison, potentially 646 // simplify TI based on this knowledge. 647 if (PredDef == TI->getParent()) { 648 // If we are here, we know that the value is none of those cases listed in 649 // PredCases. If there are any cases in ThisCases that are in PredCases, we 650 // can simplify TI. 651 if (!ValuesOverlap(PredCases, ThisCases)) 652 return false; 653 654 if (isa<BranchInst>(TI)) { 655 // Okay, one of the successors of this condbr is dead. Convert it to a 656 // uncond br. 657 assert(ThisCases.size() == 1 && "Branch can only have one case!"); 658 // Insert the new branch. 659 Instruction *NI = Builder.CreateBr(ThisDef); 660 (void) NI; 661 662 // Remove PHI node entries for the dead edge. 663 ThisCases[0].Dest->removePredecessor(TI->getParent()); 664 665 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 666 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 667 668 EraseTerminatorInstAndDCECond(TI); 669 return true; 670 } 671 672 SwitchInst *SI = cast<SwitchInst>(TI); 673 // Okay, TI has cases that are statically dead, prune them away. 674 SmallPtrSet<Constant*, 16> DeadCases; 675 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 676 DeadCases.insert(PredCases[i].Value); 677 678 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 679 << "Through successor TI: " << *TI); 680 681 // Collect branch weights into a vector. 682 SmallVector<uint32_t, 8> Weights; 683 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof); 684 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases()); 685 if (HasWeight) 686 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e; 687 ++MD_i) { 688 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i)); 689 assert(CI); 690 Weights.push_back(CI->getValue().getZExtValue()); 691 } 692 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) { 693 --i; 694 if (DeadCases.count(i.getCaseValue())) { 695 if (HasWeight) { 696 std::swap(Weights[i.getCaseIndex()+1], Weights.back()); 697 Weights.pop_back(); 698 } 699 i.getCaseSuccessor()->removePredecessor(TI->getParent()); 700 SI->removeCase(i); 701 } 702 } 703 if (HasWeight && Weights.size() >= 2) 704 SI->setMetadata(LLVMContext::MD_prof, 705 MDBuilder(SI->getParent()->getContext()). 706 createBranchWeights(Weights)); 707 708 DEBUG(dbgs() << "Leaving: " << *TI << "\n"); 709 return true; 710 } 711 712 // Otherwise, TI's block must correspond to some matched value. Find out 713 // which value (or set of values) this is. 714 ConstantInt *TIV = 0; 715 BasicBlock *TIBB = TI->getParent(); 716 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 717 if (PredCases[i].Dest == TIBB) { 718 if (TIV != 0) 719 return false; // Cannot handle multiple values coming to this block. 720 TIV = PredCases[i].Value; 721 } 722 assert(TIV && "No edge from pred to succ?"); 723 724 // Okay, we found the one constant that our value can be if we get into TI's 725 // BB. Find out which successor will unconditionally be branched to. 726 BasicBlock *TheRealDest = 0; 727 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) 728 if (ThisCases[i].Value == TIV) { 729 TheRealDest = ThisCases[i].Dest; 730 break; 731 } 732 733 // If not handled by any explicit cases, it is handled by the default case. 734 if (TheRealDest == 0) TheRealDest = ThisDef; 735 736 // Remove PHI node entries for dead edges. 737 BasicBlock *CheckEdge = TheRealDest; 738 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI) 739 if (*SI != CheckEdge) 740 (*SI)->removePredecessor(TIBB); 741 else 742 CheckEdge = 0; 743 744 // Insert the new branch. 745 Instruction *NI = Builder.CreateBr(TheRealDest); 746 (void) NI; 747 748 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 749 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 750 751 EraseTerminatorInstAndDCECond(TI); 752 return true; 753} 754 755namespace { 756 /// ConstantIntOrdering - This class implements a stable ordering of constant 757 /// integers that does not depend on their address. This is important for 758 /// applications that sort ConstantInt's to ensure uniqueness. 759 struct ConstantIntOrdering { 760 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { 761 return LHS->getValue().ult(RHS->getValue()); 762 } 763 }; 764} 765 766static int ConstantIntSortPredicate(const void *P1, const void *P2) { 767 const ConstantInt *LHS = *(const ConstantInt*const*)P1; 768 const ConstantInt *RHS = *(const ConstantInt*const*)P2; 769 if (LHS->getValue().ult(RHS->getValue())) 770 return 1; 771 if (LHS->getValue() == RHS->getValue()) 772 return 0; 773 return -1; 774} 775 776static inline bool HasBranchWeights(const Instruction* I) { 777 MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof); 778 if (ProfMD && ProfMD->getOperand(0)) 779 if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0))) 780 return MDS->getString().equals("branch_weights"); 781 782 return false; 783} 784 785/// Get Weights of a given TerminatorInst, the default weight is at the front 786/// of the vector. If TI is a conditional eq, we need to swap the branch-weight 787/// metadata. 788static void GetBranchWeights(TerminatorInst *TI, 789 SmallVectorImpl<uint64_t> &Weights) { 790 MDNode* MD = TI->getMetadata(LLVMContext::MD_prof); 791 assert(MD); 792 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) { 793 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i)); 794 assert(CI); 795 Weights.push_back(CI->getValue().getZExtValue()); 796 } 797 798 // If TI is a conditional eq, the default case is the false case, 799 // and the corresponding branch-weight data is at index 2. We swap the 800 // default weight to be the first entry. 801 if (BranchInst* BI = dyn_cast<BranchInst>(TI)) { 802 assert(Weights.size() == 2); 803 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); 804 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 805 std::swap(Weights.front(), Weights.back()); 806 } 807} 808 809/// Sees if any of the weights are too big for a uint32_t, and halves all the 810/// weights if any are. 811static void FitWeights(MutableArrayRef<uint64_t> Weights) { 812 bool Halve = false; 813 for (unsigned i = 0; i < Weights.size(); ++i) 814 if (Weights[i] > UINT_MAX) { 815 Halve = true; 816 break; 817 } 818 819 if (! Halve) 820 return; 821 822 for (unsigned i = 0; i < Weights.size(); ++i) 823 Weights[i] /= 2; 824} 825 826/// FoldValueComparisonIntoPredecessors - The specified terminator is a value 827/// equality comparison instruction (either a switch or a branch on "X == c"). 828/// See if any of the predecessors of the terminator block are value comparisons 829/// on the same value. If so, and if safe to do so, fold them together. 830bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI, 831 IRBuilder<> &Builder) { 832 BasicBlock *BB = TI->getParent(); 833 Value *CV = isValueEqualityComparison(TI); // CondVal 834 assert(CV && "Not a comparison?"); 835 bool Changed = false; 836 837 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); 838 while (!Preds.empty()) { 839 BasicBlock *Pred = Preds.pop_back_val(); 840 841 // See if the predecessor is a comparison with the same value. 842 TerminatorInst *PTI = Pred->getTerminator(); 843 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal 844 845 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) { 846 // Figure out which 'cases' to copy from SI to PSI. 847 std::vector<ValueEqualityComparisonCase> BBCases; 848 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); 849 850 std::vector<ValueEqualityComparisonCase> PredCases; 851 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); 852 853 // Based on whether the default edge from PTI goes to BB or not, fill in 854 // PredCases and PredDefault with the new switch cases we would like to 855 // build. 856 SmallVector<BasicBlock*, 8> NewSuccessors; 857 858 // Update the branch weight metadata along the way 859 SmallVector<uint64_t, 8> Weights; 860 bool PredHasWeights = HasBranchWeights(PTI); 861 bool SuccHasWeights = HasBranchWeights(TI); 862 863 if (PredHasWeights) { 864 GetBranchWeights(PTI, Weights); 865 // branch-weight metadata is inconsistant here. 866 if (Weights.size() != 1 + PredCases.size()) 867 PredHasWeights = SuccHasWeights = false; 868 } else if (SuccHasWeights) 869 // If there are no predecessor weights but there are successor weights, 870 // populate Weights with 1, which will later be scaled to the sum of 871 // successor's weights 872 Weights.assign(1 + PredCases.size(), 1); 873 874 SmallVector<uint64_t, 8> SuccWeights; 875 if (SuccHasWeights) { 876 GetBranchWeights(TI, SuccWeights); 877 // branch-weight metadata is inconsistant here. 878 if (SuccWeights.size() != 1 + BBCases.size()) 879 PredHasWeights = SuccHasWeights = false; 880 } else if (PredHasWeights) 881 SuccWeights.assign(1 + BBCases.size(), 1); 882 883 if (PredDefault == BB) { 884 // If this is the default destination from PTI, only the edges in TI 885 // that don't occur in PTI, or that branch to BB will be activated. 886 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 887 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 888 if (PredCases[i].Dest != BB) 889 PTIHandled.insert(PredCases[i].Value); 890 else { 891 // The default destination is BB, we don't need explicit targets. 892 std::swap(PredCases[i], PredCases.back()); 893 894 if (PredHasWeights || SuccHasWeights) { 895 // Increase weight for the default case. 896 Weights[0] += Weights[i+1]; 897 std::swap(Weights[i+1], Weights.back()); 898 Weights.pop_back(); 899 } 900 901 PredCases.pop_back(); 902 --i; --e; 903 } 904 905 // Reconstruct the new switch statement we will be building. 906 if (PredDefault != BBDefault) { 907 PredDefault->removePredecessor(Pred); 908 PredDefault = BBDefault; 909 NewSuccessors.push_back(BBDefault); 910 } 911 912 unsigned CasesFromPred = Weights.size(); 913 uint64_t ValidTotalSuccWeight = 0; 914 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 915 if (!PTIHandled.count(BBCases[i].Value) && 916 BBCases[i].Dest != BBDefault) { 917 PredCases.push_back(BBCases[i]); 918 NewSuccessors.push_back(BBCases[i].Dest); 919 if (SuccHasWeights || PredHasWeights) { 920 // The default weight is at index 0, so weight for the ith case 921 // should be at index i+1. Scale the cases from successor by 922 // PredDefaultWeight (Weights[0]). 923 Weights.push_back(Weights[0] * SuccWeights[i+1]); 924 ValidTotalSuccWeight += SuccWeights[i+1]; 925 } 926 } 927 928 if (SuccHasWeights || PredHasWeights) { 929 ValidTotalSuccWeight += SuccWeights[0]; 930 // Scale the cases from predecessor by ValidTotalSuccWeight. 931 for (unsigned i = 1; i < CasesFromPred; ++i) 932 Weights[i] *= ValidTotalSuccWeight; 933 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]). 934 Weights[0] *= SuccWeights[0]; 935 } 936 } else { 937 // If this is not the default destination from PSI, only the edges 938 // in SI that occur in PSI with a destination of BB will be 939 // activated. 940 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 941 std::map<ConstantInt*, uint64_t> WeightsForHandled; 942 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 943 if (PredCases[i].Dest == BB) { 944 PTIHandled.insert(PredCases[i].Value); 945 946 if (PredHasWeights || SuccHasWeights) { 947 WeightsForHandled[PredCases[i].Value] = Weights[i+1]; 948 std::swap(Weights[i+1], Weights.back()); 949 Weights.pop_back(); 950 } 951 952 std::swap(PredCases[i], PredCases.back()); 953 PredCases.pop_back(); 954 --i; --e; 955 } 956 957 // Okay, now we know which constants were sent to BB from the 958 // predecessor. Figure out where they will all go now. 959 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 960 if (PTIHandled.count(BBCases[i].Value)) { 961 // If this is one we are capable of getting... 962 if (PredHasWeights || SuccHasWeights) 963 Weights.push_back(WeightsForHandled[BBCases[i].Value]); 964 PredCases.push_back(BBCases[i]); 965 NewSuccessors.push_back(BBCases[i].Dest); 966 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of 967 } 968 969 // If there are any constants vectored to BB that TI doesn't handle, 970 // they must go to the default destination of TI. 971 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I = 972 PTIHandled.begin(), 973 E = PTIHandled.end(); I != E; ++I) { 974 if (PredHasWeights || SuccHasWeights) 975 Weights.push_back(WeightsForHandled[*I]); 976 PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault)); 977 NewSuccessors.push_back(BBDefault); 978 } 979 } 980 981 // Okay, at this point, we know which new successor Pred will get. Make 982 // sure we update the number of entries in the PHI nodes for these 983 // successors. 984 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i) 985 AddPredecessorToBlock(NewSuccessors[i], Pred, BB); 986 987 Builder.SetInsertPoint(PTI); 988 // Convert pointer to int before we switch. 989 if (CV->getType()->isPointerTy()) { 990 assert(TD && "Cannot switch on pointer without DataLayout"); 991 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getType()), 992 "magicptr"); 993 } 994 995 // Now that the successors are updated, create the new Switch instruction. 996 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault, 997 PredCases.size()); 998 NewSI->setDebugLoc(PTI->getDebugLoc()); 999 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 1000 NewSI->addCase(PredCases[i].Value, PredCases[i].Dest); 1001 1002 if (PredHasWeights || SuccHasWeights) { 1003 // Halve the weights if any of them cannot fit in an uint32_t 1004 FitWeights(Weights); 1005 1006 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end()); 1007 1008 NewSI->setMetadata(LLVMContext::MD_prof, 1009 MDBuilder(BB->getContext()). 1010 createBranchWeights(MDWeights)); 1011 } 1012 1013 EraseTerminatorInstAndDCECond(PTI); 1014 1015 // Okay, last check. If BB is still a successor of PSI, then we must 1016 // have an infinite loop case. If so, add an infinitely looping block 1017 // to handle the case to preserve the behavior of the code. 1018 BasicBlock *InfLoopBlock = 0; 1019 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) 1020 if (NewSI->getSuccessor(i) == BB) { 1021 if (InfLoopBlock == 0) { 1022 // Insert it at the end of the function, because it's either code, 1023 // or it won't matter if it's hot. :) 1024 InfLoopBlock = BasicBlock::Create(BB->getContext(), 1025 "infloop", BB->getParent()); 1026 BranchInst::Create(InfLoopBlock, InfLoopBlock); 1027 } 1028 NewSI->setSuccessor(i, InfLoopBlock); 1029 } 1030 1031 Changed = true; 1032 } 1033 } 1034 return Changed; 1035} 1036 1037// isSafeToHoistInvoke - If we would need to insert a select that uses the 1038// value of this invoke (comments in HoistThenElseCodeToIf explain why we 1039// would need to do this), we can't hoist the invoke, as there is nowhere 1040// to put the select in this case. 1041static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2, 1042 Instruction *I1, Instruction *I2) { 1043 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 1044 PHINode *PN; 1045 for (BasicBlock::iterator BBI = SI->begin(); 1046 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 1047 Value *BB1V = PN->getIncomingValueForBlock(BB1); 1048 Value *BB2V = PN->getIncomingValueForBlock(BB2); 1049 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) { 1050 return false; 1051 } 1052 } 1053 } 1054 return true; 1055} 1056 1057/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and 1058/// BB2, hoist any common code in the two blocks up into the branch block. The 1059/// caller of this function guarantees that BI's block dominates BB1 and BB2. 1060static bool HoistThenElseCodeToIf(BranchInst *BI) { 1061 // This does very trivial matching, with limited scanning, to find identical 1062 // instructions in the two blocks. In particular, we don't want to get into 1063 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As 1064 // such, we currently just scan for obviously identical instructions in an 1065 // identical order. 1066 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. 1067 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination 1068 1069 BasicBlock::iterator BB1_Itr = BB1->begin(); 1070 BasicBlock::iterator BB2_Itr = BB2->begin(); 1071 1072 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++; 1073 // Skip debug info if it is not identical. 1074 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); 1075 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); 1076 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { 1077 while (isa<DbgInfoIntrinsic>(I1)) 1078 I1 = BB1_Itr++; 1079 while (isa<DbgInfoIntrinsic>(I2)) 1080 I2 = BB2_Itr++; 1081 } 1082 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) || 1083 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))) 1084 return false; 1085 1086 // If we get here, we can hoist at least one instruction. 1087 BasicBlock *BIParent = BI->getParent(); 1088 1089 do { 1090 // If we are hoisting the terminator instruction, don't move one (making a 1091 // broken BB), instead clone it, and remove BI. 1092 if (isa<TerminatorInst>(I1)) 1093 goto HoistTerminator; 1094 1095 // For a normal instruction, we just move one to right before the branch, 1096 // then replace all uses of the other with the first. Finally, we remove 1097 // the now redundant second instruction. 1098 BIParent->getInstList().splice(BI, BB1->getInstList(), I1); 1099 if (!I2->use_empty()) 1100 I2->replaceAllUsesWith(I1); 1101 I1->intersectOptionalDataWith(I2); 1102 I2->eraseFromParent(); 1103 1104 I1 = BB1_Itr++; 1105 I2 = BB2_Itr++; 1106 // Skip debug info if it is not identical. 1107 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); 1108 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); 1109 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { 1110 while (isa<DbgInfoIntrinsic>(I1)) 1111 I1 = BB1_Itr++; 1112 while (isa<DbgInfoIntrinsic>(I2)) 1113 I2 = BB2_Itr++; 1114 } 1115 } while (I1->isIdenticalToWhenDefined(I2)); 1116 1117 return true; 1118 1119HoistTerminator: 1120 // It may not be possible to hoist an invoke. 1121 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) 1122 return true; 1123 1124 // Okay, it is safe to hoist the terminator. 1125 Instruction *NT = I1->clone(); 1126 BIParent->getInstList().insert(BI, NT); 1127 if (!NT->getType()->isVoidTy()) { 1128 I1->replaceAllUsesWith(NT); 1129 I2->replaceAllUsesWith(NT); 1130 NT->takeName(I1); 1131 } 1132 1133 IRBuilder<true, NoFolder> Builder(NT); 1134 // Hoisting one of the terminators from our successor is a great thing. 1135 // Unfortunately, the successors of the if/else blocks may have PHI nodes in 1136 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI 1137 // nodes, so we insert select instruction to compute the final result. 1138 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects; 1139 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 1140 PHINode *PN; 1141 for (BasicBlock::iterator BBI = SI->begin(); 1142 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 1143 Value *BB1V = PN->getIncomingValueForBlock(BB1); 1144 Value *BB2V = PN->getIncomingValueForBlock(BB2); 1145 if (BB1V == BB2V) continue; 1146 1147 // These values do not agree. Insert a select instruction before NT 1148 // that determines the right value. 1149 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; 1150 if (SI == 0) 1151 SI = cast<SelectInst> 1152 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V, 1153 BB1V->getName()+"."+BB2V->getName())); 1154 1155 // Make the PHI node use the select for all incoming values for BB1/BB2 1156 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 1157 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2) 1158 PN->setIncomingValue(i, SI); 1159 } 1160 } 1161 1162 // Update any PHI nodes in our new successors. 1163 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) 1164 AddPredecessorToBlock(*SI, BIParent, BB1); 1165 1166 EraseTerminatorInstAndDCECond(BI); 1167 return true; 1168} 1169 1170/// SinkThenElseCodeToEnd - Given an unconditional branch that goes to BBEnd, 1171/// check whether BBEnd has only two predecessors and the other predecessor 1172/// ends with an unconditional branch. If it is true, sink any common code 1173/// in the two predecessors to BBEnd. 1174static bool SinkThenElseCodeToEnd(BranchInst *BI1) { 1175 assert(BI1->isUnconditional()); 1176 BasicBlock *BB1 = BI1->getParent(); 1177 BasicBlock *BBEnd = BI1->getSuccessor(0); 1178 1179 // Check that BBEnd has two predecessors and the other predecessor ends with 1180 // an unconditional branch. 1181 pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd); 1182 BasicBlock *Pred0 = *PI++; 1183 if (PI == PE) // Only one predecessor. 1184 return false; 1185 BasicBlock *Pred1 = *PI++; 1186 if (PI != PE) // More than two predecessors. 1187 return false; 1188 BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0; 1189 BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator()); 1190 if (!BI2 || !BI2->isUnconditional()) 1191 return false; 1192 1193 // Gather the PHI nodes in BBEnd. 1194 std::map<Value*, std::pair<Value*, PHINode*> > MapValueFromBB1ToBB2; 1195 Instruction *FirstNonPhiInBBEnd = 0; 1196 for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end(); 1197 I != E; ++I) { 1198 if (PHINode *PN = dyn_cast<PHINode>(I)) { 1199 Value *BB1V = PN->getIncomingValueForBlock(BB1); 1200 Value *BB2V = PN->getIncomingValueForBlock(BB2); 1201 MapValueFromBB1ToBB2[BB1V] = std::make_pair(BB2V, PN); 1202 } else { 1203 FirstNonPhiInBBEnd = &*I; 1204 break; 1205 } 1206 } 1207 if (!FirstNonPhiInBBEnd) 1208 return false; 1209 1210 1211 // This does very trivial matching, with limited scanning, to find identical 1212 // instructions in the two blocks. We scan backward for obviously identical 1213 // instructions in an identical order. 1214 BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(), 1215 RE1 = BB1->getInstList().rend(), RI2 = BB2->getInstList().rbegin(), 1216 RE2 = BB2->getInstList().rend(); 1217 // Skip debug info. 1218 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1; 1219 if (RI1 == RE1) 1220 return false; 1221 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2; 1222 if (RI2 == RE2) 1223 return false; 1224 // Skip the unconditional branches. 1225 ++RI1; 1226 ++RI2; 1227 1228 bool Changed = false; 1229 while (RI1 != RE1 && RI2 != RE2) { 1230 // Skip debug info. 1231 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1; 1232 if (RI1 == RE1) 1233 return Changed; 1234 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2; 1235 if (RI2 == RE2) 1236 return Changed; 1237 1238 Instruction *I1 = &*RI1, *I2 = &*RI2; 1239 // I1 and I2 should have a single use in the same PHI node, and they 1240 // perform the same operation. 1241 // Cannot move control-flow-involving, volatile loads, vaarg, etc. 1242 if (isa<PHINode>(I1) || isa<PHINode>(I2) || 1243 isa<TerminatorInst>(I1) || isa<TerminatorInst>(I2) || 1244 isa<LandingPadInst>(I1) || isa<LandingPadInst>(I2) || 1245 isa<AllocaInst>(I1) || isa<AllocaInst>(I2) || 1246 I1->mayHaveSideEffects() || I2->mayHaveSideEffects() || 1247 I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() || 1248 !I1->hasOneUse() || !I2->hasOneUse() || 1249 MapValueFromBB1ToBB2.find(I1) == MapValueFromBB1ToBB2.end() || 1250 MapValueFromBB1ToBB2[I1].first != I2) 1251 return Changed; 1252 1253 // Check whether we should swap the operands of ICmpInst. 1254 ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2); 1255 bool SwapOpnds = false; 1256 if (ICmp1 && ICmp2 && 1257 ICmp1->getOperand(0) != ICmp2->getOperand(0) && 1258 ICmp1->getOperand(1) != ICmp2->getOperand(1) && 1259 (ICmp1->getOperand(0) == ICmp2->getOperand(1) || 1260 ICmp1->getOperand(1) == ICmp2->getOperand(0))) { 1261 ICmp2->swapOperands(); 1262 SwapOpnds = true; 1263 } 1264 if (!I1->isSameOperationAs(I2)) { 1265 if (SwapOpnds) 1266 ICmp2->swapOperands(); 1267 return Changed; 1268 } 1269 1270 // The operands should be either the same or they need to be generated 1271 // with a PHI node after sinking. We only handle the case where there is 1272 // a single pair of different operands. 1273 Value *DifferentOp1 = 0, *DifferentOp2 = 0; 1274 unsigned Op1Idx = 0; 1275 for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) { 1276 if (I1->getOperand(I) == I2->getOperand(I)) 1277 continue; 1278 // Early exit if we have more-than one pair of different operands or 1279 // the different operand is already in MapValueFromBB1ToBB2. 1280 // Early exit if we need a PHI node to replace a constant. 1281 if (DifferentOp1 || 1282 MapValueFromBB1ToBB2.find(I1->getOperand(I)) != 1283 MapValueFromBB1ToBB2.end() || 1284 isa<Constant>(I1->getOperand(I)) || 1285 isa<Constant>(I2->getOperand(I))) { 1286 // If we can't sink the instructions, undo the swapping. 1287 if (SwapOpnds) 1288 ICmp2->swapOperands(); 1289 return Changed; 1290 } 1291 DifferentOp1 = I1->getOperand(I); 1292 Op1Idx = I; 1293 DifferentOp2 = I2->getOperand(I); 1294 } 1295 1296 // We insert the pair of different operands to MapValueFromBB1ToBB2 and 1297 // remove (I1, I2) from MapValueFromBB1ToBB2. 1298 if (DifferentOp1) { 1299 PHINode *NewPN = PHINode::Create(DifferentOp1->getType(), 2, 1300 DifferentOp1->getName() + ".sink", 1301 BBEnd->begin()); 1302 MapValueFromBB1ToBB2[DifferentOp1] = std::make_pair(DifferentOp2, NewPN); 1303 // I1 should use NewPN instead of DifferentOp1. 1304 I1->setOperand(Op1Idx, NewPN); 1305 NewPN->addIncoming(DifferentOp1, BB1); 1306 NewPN->addIncoming(DifferentOp2, BB2); 1307 DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";); 1308 } 1309 PHINode *OldPN = MapValueFromBB1ToBB2[I1].second; 1310 MapValueFromBB1ToBB2.erase(I1); 1311 1312 DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n";); 1313 DEBUG(dbgs() << " " << *I2 << "\n";); 1314 // We need to update RE1 and RE2 if we are going to sink the first 1315 // instruction in the basic block down. 1316 bool UpdateRE1 = (I1 == BB1->begin()), UpdateRE2 = (I2 == BB2->begin()); 1317 // Sink the instruction. 1318 BBEnd->getInstList().splice(FirstNonPhiInBBEnd, BB1->getInstList(), I1); 1319 if (!OldPN->use_empty()) 1320 OldPN->replaceAllUsesWith(I1); 1321 OldPN->eraseFromParent(); 1322 1323 if (!I2->use_empty()) 1324 I2->replaceAllUsesWith(I1); 1325 I1->intersectOptionalDataWith(I2); 1326 I2->eraseFromParent(); 1327 1328 if (UpdateRE1) 1329 RE1 = BB1->getInstList().rend(); 1330 if (UpdateRE2) 1331 RE2 = BB2->getInstList().rend(); 1332 FirstNonPhiInBBEnd = I1; 1333 NumSinkCommons++; 1334 Changed = true; 1335 } 1336 return Changed; 1337} 1338 1339/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1 1340/// and an BB2 and the only successor of BB1 is BB2, hoist simple code 1341/// (for now, restricted to a single instruction that's side effect free) from 1342/// the BB1 into the branch block to speculatively execute it. 1343/// 1344/// Turn 1345/// BB: 1346/// %t1 = icmp 1347/// br i1 %t1, label %BB1, label %BB2 1348/// BB1: 1349/// %t3 = add %t2, c 1350/// br label BB2 1351/// BB2: 1352/// => 1353/// BB: 1354/// %t1 = icmp 1355/// %t4 = add %t2, c 1356/// %t3 = select i1 %t1, %t2, %t3 1357static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) { 1358 // Only speculatively execution a single instruction (not counting the 1359 // terminator) for now. 1360 Instruction *HInst = NULL; 1361 Instruction *Term = BB1->getTerminator(); 1362 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); 1363 BBI != BBE; ++BBI) { 1364 Instruction *I = BBI; 1365 // Skip debug info. 1366 if (isa<DbgInfoIntrinsic>(I)) continue; 1367 if (I == Term) break; 1368 1369 if (HInst) 1370 return false; 1371 HInst = I; 1372 } 1373 1374 BasicBlock *BIParent = BI->getParent(); 1375 1376 // Check the instruction to be hoisted, if there is one. 1377 if (HInst) { 1378 // Don't hoist the instruction if it's unsafe or expensive. 1379 if (!isSafeToSpeculativelyExecute(HInst)) 1380 return false; 1381 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold) 1382 return false; 1383 1384 // Do not hoist the instruction if any of its operands are defined but not 1385 // used in this BB. The transformation will prevent the operand from 1386 // being sunk into the use block. 1387 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end(); 1388 i != e; ++i) { 1389 Instruction *OpI = dyn_cast<Instruction>(*i); 1390 if (OpI && OpI->getParent() == BIParent && 1391 !OpI->mayHaveSideEffects() && 1392 !OpI->isUsedInBasicBlock(BIParent)) 1393 return false; 1394 } 1395 } 1396 1397 // Be conservative for now. FP select instruction can often be expensive. 1398 Value *BrCond = BI->getCondition(); 1399 if (isa<FCmpInst>(BrCond)) 1400 return false; 1401 1402 // If BB1 is actually on the false edge of the conditional branch, remember 1403 // to swap the select operands later. 1404 bool Invert = false; 1405 if (BB1 != BI->getSuccessor(0)) { 1406 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?"); 1407 Invert = true; 1408 } 1409 1410 // Collect interesting PHIs, and scan for hazards. 1411 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs; 1412 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0); 1413 for (BasicBlock::iterator I = BB2->begin(); 1414 PHINode *PN = dyn_cast<PHINode>(I); ++I) { 1415 Value *BB1V = PN->getIncomingValueForBlock(BB1); 1416 Value *BIParentV = PN->getIncomingValueForBlock(BIParent); 1417 1418 // Skip PHIs which are trivial. 1419 if (BB1V == BIParentV) 1420 continue; 1421 1422 // Check for saftey. 1423 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) { 1424 // An unfolded ConstantExpr could end up getting expanded into 1425 // Instructions. Don't speculate this and another instruction at 1426 // the same time. 1427 if (HInst) 1428 return false; 1429 if (!isSafeToSpeculativelyExecute(CE)) 1430 return false; 1431 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold) 1432 return false; 1433 } 1434 1435 // Ok, we may insert a select for this PHI. 1436 PHIs.insert(std::make_pair(BB1V, BIParentV)); 1437 } 1438 1439 // If there are no PHIs to process, bail early. This helps ensure idempotence 1440 // as well. 1441 if (PHIs.empty()) 1442 return false; 1443 1444 // If we get here, we can hoist the instruction and if-convert. 1445 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";); 1446 1447 // Hoist the instruction. 1448 if (HInst) 1449 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst); 1450 1451 // Insert selects and rewrite the PHI operands. 1452 IRBuilder<true, NoFolder> Builder(BI); 1453 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) { 1454 Value *TrueV = PHIs[i].first; 1455 Value *FalseV = PHIs[i].second; 1456 1457 // Create a select whose true value is the speculatively executed value and 1458 // false value is the previously determined FalseV. 1459 SelectInst *SI; 1460 if (Invert) 1461 SI = cast<SelectInst> 1462 (Builder.CreateSelect(BrCond, FalseV, TrueV, 1463 FalseV->getName() + "." + TrueV->getName())); 1464 else 1465 SI = cast<SelectInst> 1466 (Builder.CreateSelect(BrCond, TrueV, FalseV, 1467 TrueV->getName() + "." + FalseV->getName())); 1468 1469 // Make the PHI node use the select for all incoming values for "then" and 1470 // "if" blocks. 1471 for (BasicBlock::iterator I = BB2->begin(); 1472 PHINode *PN = dyn_cast<PHINode>(I); ++I) { 1473 unsigned BB1I = PN->getBasicBlockIndex(BB1); 1474 unsigned BIParentI = PN->getBasicBlockIndex(BIParent); 1475 Value *BB1V = PN->getIncomingValue(BB1I); 1476 Value *BIParentV = PN->getIncomingValue(BIParentI); 1477 if (TrueV == BB1V && FalseV == BIParentV) { 1478 PN->setIncomingValue(BB1I, SI); 1479 PN->setIncomingValue(BIParentI, SI); 1480 } 1481 } 1482 } 1483 1484 ++NumSpeculations; 1485 return true; 1486} 1487 1488/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch 1489/// across this block. 1490static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) { 1491 BranchInst *BI = cast<BranchInst>(BB->getTerminator()); 1492 unsigned Size = 0; 1493 1494 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1495 if (isa<DbgInfoIntrinsic>(BBI)) 1496 continue; 1497 if (Size > 10) return false; // Don't clone large BB's. 1498 ++Size; 1499 1500 // We can only support instructions that do not define values that are 1501 // live outside of the current basic block. 1502 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 1503 UI != E; ++UI) { 1504 Instruction *U = cast<Instruction>(*UI); 1505 if (U->getParent() != BB || isa<PHINode>(U)) return false; 1506 } 1507 1508 // Looks ok, continue checking. 1509 } 1510 1511 return true; 1512} 1513 1514/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value 1515/// that is defined in the same block as the branch and if any PHI entries are 1516/// constants, thread edges corresponding to that entry to be branches to their 1517/// ultimate destination. 1518static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout *TD) { 1519 BasicBlock *BB = BI->getParent(); 1520 PHINode *PN = dyn_cast<PHINode>(BI->getCondition()); 1521 // NOTE: we currently cannot transform this case if the PHI node is used 1522 // outside of the block. 1523 if (!PN || PN->getParent() != BB || !PN->hasOneUse()) 1524 return false; 1525 1526 // Degenerate case of a single entry PHI. 1527 if (PN->getNumIncomingValues() == 1) { 1528 FoldSingleEntryPHINodes(PN->getParent()); 1529 return true; 1530 } 1531 1532 // Now we know that this block has multiple preds and two succs. 1533 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false; 1534 1535 // Okay, this is a simple enough basic block. See if any phi values are 1536 // constants. 1537 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1538 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i)); 1539 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue; 1540 1541 // Okay, we now know that all edges from PredBB should be revectored to 1542 // branch to RealDest. 1543 BasicBlock *PredBB = PN->getIncomingBlock(i); 1544 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue()); 1545 1546 if (RealDest == BB) continue; // Skip self loops. 1547 // Skip if the predecessor's terminator is an indirect branch. 1548 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue; 1549 1550 // The dest block might have PHI nodes, other predecessors and other 1551 // difficult cases. Instead of being smart about this, just insert a new 1552 // block that jumps to the destination block, effectively splitting 1553 // the edge we are about to create. 1554 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(), 1555 RealDest->getName()+".critedge", 1556 RealDest->getParent(), RealDest); 1557 BranchInst::Create(RealDest, EdgeBB); 1558 1559 // Update PHI nodes. 1560 AddPredecessorToBlock(RealDest, EdgeBB, BB); 1561 1562 // BB may have instructions that are being threaded over. Clone these 1563 // instructions into EdgeBB. We know that there will be no uses of the 1564 // cloned instructions outside of EdgeBB. 1565 BasicBlock::iterator InsertPt = EdgeBB->begin(); 1566 DenseMap<Value*, Value*> TranslateMap; // Track translated values. 1567 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1568 if (PHINode *PN = dyn_cast<PHINode>(BBI)) { 1569 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB); 1570 continue; 1571 } 1572 // Clone the instruction. 1573 Instruction *N = BBI->clone(); 1574 if (BBI->hasName()) N->setName(BBI->getName()+".c"); 1575 1576 // Update operands due to translation. 1577 for (User::op_iterator i = N->op_begin(), e = N->op_end(); 1578 i != e; ++i) { 1579 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i); 1580 if (PI != TranslateMap.end()) 1581 *i = PI->second; 1582 } 1583 1584 // Check for trivial simplification. 1585 if (Value *V = SimplifyInstruction(N, TD)) { 1586 TranslateMap[BBI] = V; 1587 delete N; // Instruction folded away, don't need actual inst 1588 } else { 1589 // Insert the new instruction into its new home. 1590 EdgeBB->getInstList().insert(InsertPt, N); 1591 if (!BBI->use_empty()) 1592 TranslateMap[BBI] = N; 1593 } 1594 } 1595 1596 // Loop over all of the edges from PredBB to BB, changing them to branch 1597 // to EdgeBB instead. 1598 TerminatorInst *PredBBTI = PredBB->getTerminator(); 1599 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i) 1600 if (PredBBTI->getSuccessor(i) == BB) { 1601 BB->removePredecessor(PredBB); 1602 PredBBTI->setSuccessor(i, EdgeBB); 1603 } 1604 1605 // Recurse, simplifying any other constants. 1606 return FoldCondBranchOnPHI(BI, TD) | true; 1607 } 1608 1609 return false; 1610} 1611 1612/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry 1613/// PHI node, see if we can eliminate it. 1614static bool FoldTwoEntryPHINode(PHINode *PN, const DataLayout *TD) { 1615 // Ok, this is a two entry PHI node. Check to see if this is a simple "if 1616 // statement", which has a very simple dominance structure. Basically, we 1617 // are trying to find the condition that is being branched on, which 1618 // subsequently causes this merge to happen. We really want control 1619 // dependence information for this check, but simplifycfg can't keep it up 1620 // to date, and this catches most of the cases we care about anyway. 1621 BasicBlock *BB = PN->getParent(); 1622 BasicBlock *IfTrue, *IfFalse; 1623 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse); 1624 if (!IfCond || 1625 // Don't bother if the branch will be constant folded trivially. 1626 isa<ConstantInt>(IfCond)) 1627 return false; 1628 1629 // Okay, we found that we can merge this two-entry phi node into a select. 1630 // Doing so would require us to fold *all* two entry phi nodes in this block. 1631 // At some point this becomes non-profitable (particularly if the target 1632 // doesn't support cmov's). Only do this transformation if there are two or 1633 // fewer PHI nodes in this block. 1634 unsigned NumPhis = 0; 1635 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I) 1636 if (NumPhis > 2) 1637 return false; 1638 1639 // Loop over the PHI's seeing if we can promote them all to select 1640 // instructions. While we are at it, keep track of the instructions 1641 // that need to be moved to the dominating block. 1642 SmallPtrSet<Instruction*, 4> AggressiveInsts; 1643 unsigned MaxCostVal0 = PHINodeFoldingThreshold, 1644 MaxCostVal1 = PHINodeFoldingThreshold; 1645 1646 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) { 1647 PHINode *PN = cast<PHINode>(II++); 1648 if (Value *V = SimplifyInstruction(PN, TD)) { 1649 PN->replaceAllUsesWith(V); 1650 PN->eraseFromParent(); 1651 continue; 1652 } 1653 1654 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts, 1655 MaxCostVal0) || 1656 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts, 1657 MaxCostVal1)) 1658 return false; 1659 } 1660 1661 // If we folded the first phi, PN dangles at this point. Refresh it. If 1662 // we ran out of PHIs then we simplified them all. 1663 PN = dyn_cast<PHINode>(BB->begin()); 1664 if (PN == 0) return true; 1665 1666 // Don't fold i1 branches on PHIs which contain binary operators. These can 1667 // often be turned into switches and other things. 1668 if (PN->getType()->isIntegerTy(1) && 1669 (isa<BinaryOperator>(PN->getIncomingValue(0)) || 1670 isa<BinaryOperator>(PN->getIncomingValue(1)) || 1671 isa<BinaryOperator>(IfCond))) 1672 return false; 1673 1674 // If we all PHI nodes are promotable, check to make sure that all 1675 // instructions in the predecessor blocks can be promoted as well. If 1676 // not, we won't be able to get rid of the control flow, so it's not 1677 // worth promoting to select instructions. 1678 BasicBlock *DomBlock = 0; 1679 BasicBlock *IfBlock1 = PN->getIncomingBlock(0); 1680 BasicBlock *IfBlock2 = PN->getIncomingBlock(1); 1681 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) { 1682 IfBlock1 = 0; 1683 } else { 1684 DomBlock = *pred_begin(IfBlock1); 1685 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I) 1686 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1687 // This is not an aggressive instruction that we can promote. 1688 // Because of this, we won't be able to get rid of the control 1689 // flow, so the xform is not worth it. 1690 return false; 1691 } 1692 } 1693 1694 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) { 1695 IfBlock2 = 0; 1696 } else { 1697 DomBlock = *pred_begin(IfBlock2); 1698 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I) 1699 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1700 // This is not an aggressive instruction that we can promote. 1701 // Because of this, we won't be able to get rid of the control 1702 // flow, so the xform is not worth it. 1703 return false; 1704 } 1705 } 1706 1707 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: " 1708 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"); 1709 1710 // If we can still promote the PHI nodes after this gauntlet of tests, 1711 // do all of the PHI's now. 1712 Instruction *InsertPt = DomBlock->getTerminator(); 1713 IRBuilder<true, NoFolder> Builder(InsertPt); 1714 1715 // Move all 'aggressive' instructions, which are defined in the 1716 // conditional parts of the if's up to the dominating block. 1717 if (IfBlock1) 1718 DomBlock->getInstList().splice(InsertPt, 1719 IfBlock1->getInstList(), IfBlock1->begin(), 1720 IfBlock1->getTerminator()); 1721 if (IfBlock2) 1722 DomBlock->getInstList().splice(InsertPt, 1723 IfBlock2->getInstList(), IfBlock2->begin(), 1724 IfBlock2->getTerminator()); 1725 1726 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 1727 // Change the PHI node into a select instruction. 1728 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); 1729 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); 1730 1731 SelectInst *NV = 1732 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, "")); 1733 PN->replaceAllUsesWith(NV); 1734 NV->takeName(PN); 1735 PN->eraseFromParent(); 1736 } 1737 1738 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement 1739 // has been flattened. Change DomBlock to jump directly to our new block to 1740 // avoid other simplifycfg's kicking in on the diamond. 1741 TerminatorInst *OldTI = DomBlock->getTerminator(); 1742 Builder.SetInsertPoint(OldTI); 1743 Builder.CreateBr(BB); 1744 OldTI->eraseFromParent(); 1745 return true; 1746} 1747 1748/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes 1749/// to two returning blocks, try to merge them together into one return, 1750/// introducing a select if the return values disagree. 1751static bool SimplifyCondBranchToTwoReturns(BranchInst *BI, 1752 IRBuilder<> &Builder) { 1753 assert(BI->isConditional() && "Must be a conditional branch"); 1754 BasicBlock *TrueSucc = BI->getSuccessor(0); 1755 BasicBlock *FalseSucc = BI->getSuccessor(1); 1756 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator()); 1757 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator()); 1758 1759 // Check to ensure both blocks are empty (just a return) or optionally empty 1760 // with PHI nodes. If there are other instructions, merging would cause extra 1761 // computation on one path or the other. 1762 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator()) 1763 return false; 1764 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator()) 1765 return false; 1766 1767 Builder.SetInsertPoint(BI); 1768 // Okay, we found a branch that is going to two return nodes. If 1769 // there is no return value for this function, just change the 1770 // branch into a return. 1771 if (FalseRet->getNumOperands() == 0) { 1772 TrueSucc->removePredecessor(BI->getParent()); 1773 FalseSucc->removePredecessor(BI->getParent()); 1774 Builder.CreateRetVoid(); 1775 EraseTerminatorInstAndDCECond(BI); 1776 return true; 1777 } 1778 1779 // Otherwise, figure out what the true and false return values are 1780 // so we can insert a new select instruction. 1781 Value *TrueValue = TrueRet->getReturnValue(); 1782 Value *FalseValue = FalseRet->getReturnValue(); 1783 1784 // Unwrap any PHI nodes in the return blocks. 1785 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue)) 1786 if (TVPN->getParent() == TrueSucc) 1787 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); 1788 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue)) 1789 if (FVPN->getParent() == FalseSucc) 1790 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); 1791 1792 // In order for this transformation to be safe, we must be able to 1793 // unconditionally execute both operands to the return. This is 1794 // normally the case, but we could have a potentially-trapping 1795 // constant expression that prevents this transformation from being 1796 // safe. 1797 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue)) 1798 if (TCV->canTrap()) 1799 return false; 1800 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue)) 1801 if (FCV->canTrap()) 1802 return false; 1803 1804 // Okay, we collected all the mapped values and checked them for sanity, and 1805 // defined to really do this transformation. First, update the CFG. 1806 TrueSucc->removePredecessor(BI->getParent()); 1807 FalseSucc->removePredecessor(BI->getParent()); 1808 1809 // Insert select instructions where needed. 1810 Value *BrCond = BI->getCondition(); 1811 if (TrueValue) { 1812 // Insert a select if the results differ. 1813 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) { 1814 } else if (isa<UndefValue>(TrueValue)) { 1815 TrueValue = FalseValue; 1816 } else { 1817 TrueValue = Builder.CreateSelect(BrCond, TrueValue, 1818 FalseValue, "retval"); 1819 } 1820 } 1821 1822 Value *RI = !TrueValue ? 1823 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue); 1824 1825 (void) RI; 1826 1827 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" 1828 << "\n " << *BI << "NewRet = " << *RI 1829 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc); 1830 1831 EraseTerminatorInstAndDCECond(BI); 1832 1833 return true; 1834} 1835 1836/// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the 1837/// probabilities of the branch taking each edge. Fills in the two APInt 1838/// parameters and return true, or returns false if no or invalid metadata was 1839/// found. 1840static bool ExtractBranchMetadata(BranchInst *BI, 1841 uint64_t &ProbTrue, uint64_t &ProbFalse) { 1842 assert(BI->isConditional() && 1843 "Looking for probabilities on unconditional branch?"); 1844 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof); 1845 if (!ProfileData || ProfileData->getNumOperands() != 3) return false; 1846 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1)); 1847 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2)); 1848 if (!CITrue || !CIFalse) return false; 1849 ProbTrue = CITrue->getValue().getZExtValue(); 1850 ProbFalse = CIFalse->getValue().getZExtValue(); 1851 return true; 1852} 1853 1854/// checkCSEInPredecessor - Return true if the given instruction is available 1855/// in its predecessor block. If yes, the instruction will be removed. 1856/// 1857static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) { 1858 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst)) 1859 return false; 1860 for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) { 1861 Instruction *PBI = &*I; 1862 // Check whether Inst and PBI generate the same value. 1863 if (Inst->isIdenticalTo(PBI)) { 1864 Inst->replaceAllUsesWith(PBI); 1865 Inst->eraseFromParent(); 1866 return true; 1867 } 1868 } 1869 return false; 1870} 1871 1872/// FoldBranchToCommonDest - If this basic block is simple enough, and if a 1873/// predecessor branches to us and one of our successors, fold the block into 1874/// the predecessor and use logical operations to pick the right destination. 1875bool llvm::FoldBranchToCommonDest(BranchInst *BI) { 1876 BasicBlock *BB = BI->getParent(); 1877 1878 Instruction *Cond = 0; 1879 if (BI->isConditional()) 1880 Cond = dyn_cast<Instruction>(BI->getCondition()); 1881 else { 1882 // For unconditional branch, check for a simple CFG pattern, where 1883 // BB has a single predecessor and BB's successor is also its predecessor's 1884 // successor. If such pattern exisits, check for CSE between BB and its 1885 // predecessor. 1886 if (BasicBlock *PB = BB->getSinglePredecessor()) 1887 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator())) 1888 if (PBI->isConditional() && 1889 (BI->getSuccessor(0) == PBI->getSuccessor(0) || 1890 BI->getSuccessor(0) == PBI->getSuccessor(1))) { 1891 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); 1892 I != E; ) { 1893 Instruction *Curr = I++; 1894 if (isa<CmpInst>(Curr)) { 1895 Cond = Curr; 1896 break; 1897 } 1898 // Quit if we can't remove this instruction. 1899 if (!checkCSEInPredecessor(Curr, PB)) 1900 return false; 1901 } 1902 } 1903 1904 if (Cond == 0) 1905 return false; 1906 } 1907 1908 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) || 1909 Cond->getParent() != BB || !Cond->hasOneUse()) 1910 return false; 1911 1912 // Only allow this if the condition is a simple instruction that can be 1913 // executed unconditionally. It must be in the same block as the branch, and 1914 // must be at the front of the block. 1915 BasicBlock::iterator FrontIt = BB->front(); 1916 1917 // Ignore dbg intrinsics. 1918 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt; 1919 1920 // Allow a single instruction to be hoisted in addition to the compare 1921 // that feeds the branch. We later ensure that any values that _it_ uses 1922 // were also live in the predecessor, so that we don't unnecessarily create 1923 // register pressure or inhibit out-of-order execution. 1924 Instruction *BonusInst = 0; 1925 if (&*FrontIt != Cond && 1926 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond && 1927 isSafeToSpeculativelyExecute(FrontIt)) { 1928 BonusInst = &*FrontIt; 1929 ++FrontIt; 1930 1931 // Ignore dbg intrinsics. 1932 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt; 1933 } 1934 1935 // Only a single bonus inst is allowed. 1936 if (&*FrontIt != Cond) 1937 return false; 1938 1939 // Make sure the instruction after the condition is the cond branch. 1940 BasicBlock::iterator CondIt = Cond; ++CondIt; 1941 1942 // Ingore dbg intrinsics. 1943 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt; 1944 1945 if (&*CondIt != BI) 1946 return false; 1947 1948 // Cond is known to be a compare or binary operator. Check to make sure that 1949 // neither operand is a potentially-trapping constant expression. 1950 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0))) 1951 if (CE->canTrap()) 1952 return false; 1953 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1))) 1954 if (CE->canTrap()) 1955 return false; 1956 1957 // Finally, don't infinitely unroll conditional loops. 1958 BasicBlock *TrueDest = BI->getSuccessor(0); 1959 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0; 1960 if (TrueDest == BB || FalseDest == BB) 1961 return false; 1962 1963 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1964 BasicBlock *PredBlock = *PI; 1965 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); 1966 1967 // Check that we have two conditional branches. If there is a PHI node in 1968 // the common successor, verify that the same value flows in from both 1969 // blocks. 1970 SmallVector<PHINode*, 4> PHIs; 1971 if (PBI == 0 || PBI->isUnconditional() || 1972 (BI->isConditional() && 1973 !SafeToMergeTerminators(BI, PBI)) || 1974 (!BI->isConditional() && 1975 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs))) 1976 continue; 1977 1978 // Determine if the two branches share a common destination. 1979 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd; 1980 bool InvertPredCond = false; 1981 1982 if (BI->isConditional()) { 1983 if (PBI->getSuccessor(0) == TrueDest) 1984 Opc = Instruction::Or; 1985 else if (PBI->getSuccessor(1) == FalseDest) 1986 Opc = Instruction::And; 1987 else if (PBI->getSuccessor(0) == FalseDest) 1988 Opc = Instruction::And, InvertPredCond = true; 1989 else if (PBI->getSuccessor(1) == TrueDest) 1990 Opc = Instruction::Or, InvertPredCond = true; 1991 else 1992 continue; 1993 } else { 1994 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest) 1995 continue; 1996 } 1997 1998 // Ensure that any values used in the bonus instruction are also used 1999 // by the terminator of the predecessor. This means that those values 2000 // must already have been resolved, so we won't be inhibiting the 2001 // out-of-order core by speculating them earlier. 2002 if (BonusInst) { 2003 // Collect the values used by the bonus inst 2004 SmallPtrSet<Value*, 4> UsedValues; 2005 for (Instruction::op_iterator OI = BonusInst->op_begin(), 2006 OE = BonusInst->op_end(); OI != OE; ++OI) { 2007 Value *V = *OI; 2008 if (!isa<Constant>(V)) 2009 UsedValues.insert(V); 2010 } 2011 2012 SmallVector<std::pair<Value*, unsigned>, 4> Worklist; 2013 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0)); 2014 2015 // Walk up to four levels back up the use-def chain of the predecessor's 2016 // terminator to see if all those values were used. The choice of four 2017 // levels is arbitrary, to provide a compile-time-cost bound. 2018 while (!Worklist.empty()) { 2019 std::pair<Value*, unsigned> Pair = Worklist.back(); 2020 Worklist.pop_back(); 2021 2022 if (Pair.second >= 4) continue; 2023 UsedValues.erase(Pair.first); 2024 if (UsedValues.empty()) break; 2025 2026 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) { 2027 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 2028 OI != OE; ++OI) 2029 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1)); 2030 } 2031 } 2032 2033 if (!UsedValues.empty()) return false; 2034 } 2035 2036 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB); 2037 IRBuilder<> Builder(PBI); 2038 2039 // If we need to invert the condition in the pred block to match, do so now. 2040 if (InvertPredCond) { 2041 Value *NewCond = PBI->getCondition(); 2042 2043 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) { 2044 CmpInst *CI = cast<CmpInst>(NewCond); 2045 CI->setPredicate(CI->getInversePredicate()); 2046 } else { 2047 NewCond = Builder.CreateNot(NewCond, 2048 PBI->getCondition()->getName()+".not"); 2049 } 2050 2051 PBI->setCondition(NewCond); 2052 PBI->swapSuccessors(); 2053 } 2054 2055 // If we have a bonus inst, clone it into the predecessor block. 2056 Instruction *NewBonus = 0; 2057 if (BonusInst) { 2058 NewBonus = BonusInst->clone(); 2059 PredBlock->getInstList().insert(PBI, NewBonus); 2060 NewBonus->takeName(BonusInst); 2061 BonusInst->setName(BonusInst->getName()+".old"); 2062 } 2063 2064 // Clone Cond into the predecessor basic block, and or/and the 2065 // two conditions together. 2066 Instruction *New = Cond->clone(); 2067 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus); 2068 PredBlock->getInstList().insert(PBI, New); 2069 New->takeName(Cond); 2070 Cond->setName(New->getName()+".old"); 2071 2072 if (BI->isConditional()) { 2073 Instruction *NewCond = 2074 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(), 2075 New, "or.cond")); 2076 PBI->setCondition(NewCond); 2077 2078 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight; 2079 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight, 2080 PredFalseWeight); 2081 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight, 2082 SuccFalseWeight); 2083 SmallVector<uint64_t, 8> NewWeights; 2084 2085 if (PBI->getSuccessor(0) == BB) { 2086 if (PredHasWeights && SuccHasWeights) { 2087 // PBI: br i1 %x, BB, FalseDest 2088 // BI: br i1 %y, TrueDest, FalseDest 2089 //TrueWeight is TrueWeight for PBI * TrueWeight for BI. 2090 NewWeights.push_back(PredTrueWeight * SuccTrueWeight); 2091 //FalseWeight is FalseWeight for PBI * TotalWeight for BI + 2092 // TrueWeight for PBI * FalseWeight for BI. 2093 // We assume that total weights of a BranchInst can fit into 32 bits. 2094 // Therefore, we will not have overflow using 64-bit arithmetic. 2095 NewWeights.push_back(PredFalseWeight * (SuccFalseWeight + 2096 SuccTrueWeight) + PredTrueWeight * SuccFalseWeight); 2097 } 2098 AddPredecessorToBlock(TrueDest, PredBlock, BB); 2099 PBI->setSuccessor(0, TrueDest); 2100 } 2101 if (PBI->getSuccessor(1) == BB) { 2102 if (PredHasWeights && SuccHasWeights) { 2103 // PBI: br i1 %x, TrueDest, BB 2104 // BI: br i1 %y, TrueDest, FalseDest 2105 //TrueWeight is TrueWeight for PBI * TotalWeight for BI + 2106 // FalseWeight for PBI * TrueWeight for BI. 2107 NewWeights.push_back(PredTrueWeight * (SuccFalseWeight + 2108 SuccTrueWeight) + PredFalseWeight * SuccTrueWeight); 2109 //FalseWeight is FalseWeight for PBI * FalseWeight for BI. 2110 NewWeights.push_back(PredFalseWeight * SuccFalseWeight); 2111 } 2112 AddPredecessorToBlock(FalseDest, PredBlock, BB); 2113 PBI->setSuccessor(1, FalseDest); 2114 } 2115 if (NewWeights.size() == 2) { 2116 // Halve the weights if any of them cannot fit in an uint32_t 2117 FitWeights(NewWeights); 2118 2119 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),NewWeights.end()); 2120 PBI->setMetadata(LLVMContext::MD_prof, 2121 MDBuilder(BI->getContext()). 2122 createBranchWeights(MDWeights)); 2123 } else 2124 PBI->setMetadata(LLVMContext::MD_prof, NULL); 2125 } else { 2126 // Update PHI nodes in the common successors. 2127 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) { 2128 ConstantInt *PBI_C = cast<ConstantInt>( 2129 PHIs[i]->getIncomingValueForBlock(PBI->getParent())); 2130 assert(PBI_C->getType()->isIntegerTy(1)); 2131 Instruction *MergedCond = 0; 2132 if (PBI->getSuccessor(0) == TrueDest) { 2133 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value) 2134 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value) 2135 // is false: !PBI_Cond and BI_Value 2136 Instruction *NotCond = 2137 cast<Instruction>(Builder.CreateNot(PBI->getCondition(), 2138 "not.cond")); 2139 MergedCond = 2140 cast<Instruction>(Builder.CreateBinOp(Instruction::And, 2141 NotCond, New, 2142 "and.cond")); 2143 if (PBI_C->isOne()) 2144 MergedCond = 2145 cast<Instruction>(Builder.CreateBinOp(Instruction::Or, 2146 PBI->getCondition(), MergedCond, 2147 "or.cond")); 2148 } else { 2149 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C) 2150 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond) 2151 // is false: PBI_Cond and BI_Value 2152 MergedCond = 2153 cast<Instruction>(Builder.CreateBinOp(Instruction::And, 2154 PBI->getCondition(), New, 2155 "and.cond")); 2156 if (PBI_C->isOne()) { 2157 Instruction *NotCond = 2158 cast<Instruction>(Builder.CreateNot(PBI->getCondition(), 2159 "not.cond")); 2160 MergedCond = 2161 cast<Instruction>(Builder.CreateBinOp(Instruction::Or, 2162 NotCond, MergedCond, 2163 "or.cond")); 2164 } 2165 } 2166 // Update PHI Node. 2167 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()), 2168 MergedCond); 2169 } 2170 // Change PBI from Conditional to Unconditional. 2171 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI); 2172 EraseTerminatorInstAndDCECond(PBI); 2173 PBI = New_PBI; 2174 } 2175 2176 // TODO: If BB is reachable from all paths through PredBlock, then we 2177 // could replace PBI's branch probabilities with BI's. 2178 2179 // Copy any debug value intrinsics into the end of PredBlock. 2180 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 2181 if (isa<DbgInfoIntrinsic>(*I)) 2182 I->clone()->insertBefore(PBI); 2183 2184 return true; 2185 } 2186 return false; 2187} 2188 2189/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a 2190/// predecessor of another block, this function tries to simplify it. We know 2191/// that PBI and BI are both conditional branches, and BI is in one of the 2192/// successor blocks of PBI - PBI branches to BI. 2193static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) { 2194 assert(PBI->isConditional() && BI->isConditional()); 2195 BasicBlock *BB = BI->getParent(); 2196 2197 // If this block ends with a branch instruction, and if there is a 2198 // predecessor that ends on a branch of the same condition, make 2199 // this conditional branch redundant. 2200 if (PBI->getCondition() == BI->getCondition() && 2201 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 2202 // Okay, the outcome of this conditional branch is statically 2203 // knowable. If this block had a single pred, handle specially. 2204 if (BB->getSinglePredecessor()) { 2205 // Turn this into a branch on constant. 2206 bool CondIsTrue = PBI->getSuccessor(0) == BB; 2207 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 2208 CondIsTrue)); 2209 return true; // Nuke the branch on constant. 2210 } 2211 2212 // Otherwise, if there are multiple predecessors, insert a PHI that merges 2213 // in the constant and simplify the block result. Subsequent passes of 2214 // simplifycfg will thread the block. 2215 if (BlockIsSimpleEnoughToThreadThrough(BB)) { 2216 pred_iterator PB = pred_begin(BB), PE = pred_end(BB); 2217 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()), 2218 std::distance(PB, PE), 2219 BI->getCondition()->getName() + ".pr", 2220 BB->begin()); 2221 // Okay, we're going to insert the PHI node. Since PBI is not the only 2222 // predecessor, compute the PHI'd conditional value for all of the preds. 2223 // Any predecessor where the condition is not computable we keep symbolic. 2224 for (pred_iterator PI = PB; PI != PE; ++PI) { 2225 BasicBlock *P = *PI; 2226 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && 2227 PBI != BI && PBI->isConditional() && 2228 PBI->getCondition() == BI->getCondition() && 2229 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 2230 bool CondIsTrue = PBI->getSuccessor(0) == BB; 2231 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 2232 CondIsTrue), P); 2233 } else { 2234 NewPN->addIncoming(BI->getCondition(), P); 2235 } 2236 } 2237 2238 BI->setCondition(NewPN); 2239 return true; 2240 } 2241 } 2242 2243 // If this is a conditional branch in an empty block, and if any 2244 // predecessors is a conditional branch to one of our destinations, 2245 // fold the conditions into logical ops and one cond br. 2246 BasicBlock::iterator BBI = BB->begin(); 2247 // Ignore dbg intrinsics. 2248 while (isa<DbgInfoIntrinsic>(BBI)) 2249 ++BBI; 2250 if (&*BBI != BI) 2251 return false; 2252 2253 2254 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition())) 2255 if (CE->canTrap()) 2256 return false; 2257 2258 int PBIOp, BIOp; 2259 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) 2260 PBIOp = BIOp = 0; 2261 else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) 2262 PBIOp = 0, BIOp = 1; 2263 else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) 2264 PBIOp = 1, BIOp = 0; 2265 else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) 2266 PBIOp = BIOp = 1; 2267 else 2268 return false; 2269 2270 // Check to make sure that the other destination of this branch 2271 // isn't BB itself. If so, this is an infinite loop that will 2272 // keep getting unwound. 2273 if (PBI->getSuccessor(PBIOp) == BB) 2274 return false; 2275 2276 // Do not perform this transformation if it would require 2277 // insertion of a large number of select instructions. For targets 2278 // without predication/cmovs, this is a big pessimization. 2279 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); 2280 2281 unsigned NumPhis = 0; 2282 for (BasicBlock::iterator II = CommonDest->begin(); 2283 isa<PHINode>(II); ++II, ++NumPhis) 2284 if (NumPhis > 2) // Disable this xform. 2285 return false; 2286 2287 // Finally, if everything is ok, fold the branches to logical ops. 2288 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); 2289 2290 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent() 2291 << "AND: " << *BI->getParent()); 2292 2293 2294 // If OtherDest *is* BB, then BB is a basic block with a single conditional 2295 // branch in it, where one edge (OtherDest) goes back to itself but the other 2296 // exits. We don't *know* that the program avoids the infinite loop 2297 // (even though that seems likely). If we do this xform naively, we'll end up 2298 // recursively unpeeling the loop. Since we know that (after the xform is 2299 // done) that the block *is* infinite if reached, we just make it an obviously 2300 // infinite loop with no cond branch. 2301 if (OtherDest == BB) { 2302 // Insert it at the end of the function, because it's either code, 2303 // or it won't matter if it's hot. :) 2304 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(), 2305 "infloop", BB->getParent()); 2306 BranchInst::Create(InfLoopBlock, InfLoopBlock); 2307 OtherDest = InfLoopBlock; 2308 } 2309 2310 DEBUG(dbgs() << *PBI->getParent()->getParent()); 2311 2312 // BI may have other predecessors. Because of this, we leave 2313 // it alone, but modify PBI. 2314 2315 // Make sure we get to CommonDest on True&True directions. 2316 Value *PBICond = PBI->getCondition(); 2317 IRBuilder<true, NoFolder> Builder(PBI); 2318 if (PBIOp) 2319 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not"); 2320 2321 Value *BICond = BI->getCondition(); 2322 if (BIOp) 2323 BICond = Builder.CreateNot(BICond, BICond->getName()+".not"); 2324 2325 // Merge the conditions. 2326 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge"); 2327 2328 // Modify PBI to branch on the new condition to the new dests. 2329 PBI->setCondition(Cond); 2330 PBI->setSuccessor(0, CommonDest); 2331 PBI->setSuccessor(1, OtherDest); 2332 2333 // Update branch weight for PBI. 2334 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight; 2335 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight, 2336 PredFalseWeight); 2337 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight, 2338 SuccFalseWeight); 2339 if (PredHasWeights && SuccHasWeights) { 2340 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight; 2341 uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight; 2342 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight; 2343 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight; 2344 // The weight to CommonDest should be PredCommon * SuccTotal + 2345 // PredOther * SuccCommon. 2346 // The weight to OtherDest should be PredOther * SuccOther. 2347 SmallVector<uint64_t, 2> NewWeights; 2348 NewWeights.push_back(PredCommon * (SuccCommon + SuccOther) + 2349 PredOther * SuccCommon); 2350 NewWeights.push_back(PredOther * SuccOther); 2351 // Halve the weights if any of them cannot fit in an uint32_t 2352 FitWeights(NewWeights); 2353 2354 SmallVector<uint32_t, 2> MDWeights(NewWeights.begin(),NewWeights.end()); 2355 PBI->setMetadata(LLVMContext::MD_prof, 2356 MDBuilder(BI->getContext()). 2357 createBranchWeights(MDWeights)); 2358 } 2359 2360 // OtherDest may have phi nodes. If so, add an entry from PBI's 2361 // block that are identical to the entries for BI's block. 2362 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB); 2363 2364 // We know that the CommonDest already had an edge from PBI to 2365 // it. If it has PHIs though, the PHIs may have different 2366 // entries for BB and PBI's BB. If so, insert a select to make 2367 // them agree. 2368 PHINode *PN; 2369 for (BasicBlock::iterator II = CommonDest->begin(); 2370 (PN = dyn_cast<PHINode>(II)); ++II) { 2371 Value *BIV = PN->getIncomingValueForBlock(BB); 2372 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent()); 2373 Value *PBIV = PN->getIncomingValue(PBBIdx); 2374 if (BIV != PBIV) { 2375 // Insert a select in PBI to pick the right value. 2376 Value *NV = cast<SelectInst> 2377 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux")); 2378 PN->setIncomingValue(PBBIdx, NV); 2379 } 2380 } 2381 2382 DEBUG(dbgs() << "INTO: " << *PBI->getParent()); 2383 DEBUG(dbgs() << *PBI->getParent()->getParent()); 2384 2385 // This basic block is probably dead. We know it has at least 2386 // one fewer predecessor. 2387 return true; 2388} 2389 2390// SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a 2391// branch to TrueBB if Cond is true or to FalseBB if Cond is false. 2392// Takes care of updating the successors and removing the old terminator. 2393// Also makes sure not to introduce new successors by assuming that edges to 2394// non-successor TrueBBs and FalseBBs aren't reachable. 2395static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond, 2396 BasicBlock *TrueBB, BasicBlock *FalseBB, 2397 uint32_t TrueWeight, 2398 uint32_t FalseWeight){ 2399 // Remove any superfluous successor edges from the CFG. 2400 // First, figure out which successors to preserve. 2401 // If TrueBB and FalseBB are equal, only try to preserve one copy of that 2402 // successor. 2403 BasicBlock *KeepEdge1 = TrueBB; 2404 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0; 2405 2406 // Then remove the rest. 2407 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) { 2408 BasicBlock *Succ = OldTerm->getSuccessor(I); 2409 // Make sure only to keep exactly one copy of each edge. 2410 if (Succ == KeepEdge1) 2411 KeepEdge1 = 0; 2412 else if (Succ == KeepEdge2) 2413 KeepEdge2 = 0; 2414 else 2415 Succ->removePredecessor(OldTerm->getParent()); 2416 } 2417 2418 IRBuilder<> Builder(OldTerm); 2419 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc()); 2420 2421 // Insert an appropriate new terminator. 2422 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) { 2423 if (TrueBB == FalseBB) 2424 // We were only looking for one successor, and it was present. 2425 // Create an unconditional branch to it. 2426 Builder.CreateBr(TrueBB); 2427 else { 2428 // We found both of the successors we were looking for. 2429 // Create a conditional branch sharing the condition of the select. 2430 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB); 2431 if (TrueWeight != FalseWeight) 2432 NewBI->setMetadata(LLVMContext::MD_prof, 2433 MDBuilder(OldTerm->getContext()). 2434 createBranchWeights(TrueWeight, FalseWeight)); 2435 } 2436 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) { 2437 // Neither of the selected blocks were successors, so this 2438 // terminator must be unreachable. 2439 new UnreachableInst(OldTerm->getContext(), OldTerm); 2440 } else { 2441 // One of the selected values was a successor, but the other wasn't. 2442 // Insert an unconditional branch to the one that was found; 2443 // the edge to the one that wasn't must be unreachable. 2444 if (KeepEdge1 == 0) 2445 // Only TrueBB was found. 2446 Builder.CreateBr(TrueBB); 2447 else 2448 // Only FalseBB was found. 2449 Builder.CreateBr(FalseBB); 2450 } 2451 2452 EraseTerminatorInstAndDCECond(OldTerm); 2453 return true; 2454} 2455 2456// SimplifySwitchOnSelect - Replaces 2457// (switch (select cond, X, Y)) on constant X, Y 2458// with a branch - conditional if X and Y lead to distinct BBs, 2459// unconditional otherwise. 2460static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) { 2461 // Check for constant integer values in the select. 2462 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue()); 2463 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue()); 2464 if (!TrueVal || !FalseVal) 2465 return false; 2466 2467 // Find the relevant condition and destinations. 2468 Value *Condition = Select->getCondition(); 2469 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor(); 2470 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor(); 2471 2472 // Get weight for TrueBB and FalseBB. 2473 uint32_t TrueWeight = 0, FalseWeight = 0; 2474 SmallVector<uint64_t, 8> Weights; 2475 bool HasWeights = HasBranchWeights(SI); 2476 if (HasWeights) { 2477 GetBranchWeights(SI, Weights); 2478 if (Weights.size() == 1 + SI->getNumCases()) { 2479 TrueWeight = (uint32_t)Weights[SI->findCaseValue(TrueVal). 2480 getSuccessorIndex()]; 2481 FalseWeight = (uint32_t)Weights[SI->findCaseValue(FalseVal). 2482 getSuccessorIndex()]; 2483 } 2484 } 2485 2486 // Perform the actual simplification. 2487 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, 2488 TrueWeight, FalseWeight); 2489} 2490 2491// SimplifyIndirectBrOnSelect - Replaces 2492// (indirectbr (select cond, blockaddress(@fn, BlockA), 2493// blockaddress(@fn, BlockB))) 2494// with 2495// (br cond, BlockA, BlockB). 2496static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) { 2497 // Check that both operands of the select are block addresses. 2498 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue()); 2499 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue()); 2500 if (!TBA || !FBA) 2501 return false; 2502 2503 // Extract the actual blocks. 2504 BasicBlock *TrueBB = TBA->getBasicBlock(); 2505 BasicBlock *FalseBB = FBA->getBasicBlock(); 2506 2507 // Perform the actual simplification. 2508 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB, 2509 0, 0); 2510} 2511 2512/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp 2513/// instruction (a seteq/setne with a constant) as the only instruction in a 2514/// block that ends with an uncond branch. We are looking for a very specific 2515/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In 2516/// this case, we merge the first two "or's of icmp" into a switch, but then the 2517/// default value goes to an uncond block with a seteq in it, we get something 2518/// like: 2519/// 2520/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ] 2521/// DEFAULT: 2522/// %tmp = icmp eq i8 %A, 92 2523/// br label %end 2524/// end: 2525/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ] 2526/// 2527/// We prefer to split the edge to 'end' so that there is a true/false entry to 2528/// the PHI, merging the third icmp into the switch. 2529static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI, 2530 const DataLayout *TD, 2531 IRBuilder<> &Builder) { 2532 BasicBlock *BB = ICI->getParent(); 2533 2534 // If the block has any PHIs in it or the icmp has multiple uses, it is too 2535 // complex. 2536 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false; 2537 2538 Value *V = ICI->getOperand(0); 2539 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1)); 2540 2541 // The pattern we're looking for is where our only predecessor is a switch on 2542 // 'V' and this block is the default case for the switch. In this case we can 2543 // fold the compared value into the switch to simplify things. 2544 BasicBlock *Pred = BB->getSinglePredecessor(); 2545 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false; 2546 2547 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator()); 2548 if (SI->getCondition() != V) 2549 return false; 2550 2551 // If BB is reachable on a non-default case, then we simply know the value of 2552 // V in this block. Substitute it and constant fold the icmp instruction 2553 // away. 2554 if (SI->getDefaultDest() != BB) { 2555 ConstantInt *VVal = SI->findCaseDest(BB); 2556 assert(VVal && "Should have a unique destination value"); 2557 ICI->setOperand(0, VVal); 2558 2559 if (Value *V = SimplifyInstruction(ICI, TD)) { 2560 ICI->replaceAllUsesWith(V); 2561 ICI->eraseFromParent(); 2562 } 2563 // BB is now empty, so it is likely to simplify away. 2564 return SimplifyCFG(BB) | true; 2565 } 2566 2567 // Ok, the block is reachable from the default dest. If the constant we're 2568 // comparing exists in one of the other edges, then we can constant fold ICI 2569 // and zap it. 2570 if (SI->findCaseValue(Cst) != SI->case_default()) { 2571 Value *V; 2572 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 2573 V = ConstantInt::getFalse(BB->getContext()); 2574 else 2575 V = ConstantInt::getTrue(BB->getContext()); 2576 2577 ICI->replaceAllUsesWith(V); 2578 ICI->eraseFromParent(); 2579 // BB is now empty, so it is likely to simplify away. 2580 return SimplifyCFG(BB) | true; 2581 } 2582 2583 // The use of the icmp has to be in the 'end' block, by the only PHI node in 2584 // the block. 2585 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0); 2586 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back()); 2587 if (PHIUse == 0 || PHIUse != &SuccBlock->front() || 2588 isa<PHINode>(++BasicBlock::iterator(PHIUse))) 2589 return false; 2590 2591 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets 2592 // true in the PHI. 2593 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext()); 2594 Constant *NewCst = ConstantInt::getFalse(BB->getContext()); 2595 2596 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 2597 std::swap(DefaultCst, NewCst); 2598 2599 // Replace ICI (which is used by the PHI for the default value) with true or 2600 // false depending on if it is EQ or NE. 2601 ICI->replaceAllUsesWith(DefaultCst); 2602 ICI->eraseFromParent(); 2603 2604 // Okay, the switch goes to this block on a default value. Add an edge from 2605 // the switch to the merge point on the compared value. 2606 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge", 2607 BB->getParent(), BB); 2608 SmallVector<uint64_t, 8> Weights; 2609 bool HasWeights = HasBranchWeights(SI); 2610 if (HasWeights) { 2611 GetBranchWeights(SI, Weights); 2612 if (Weights.size() == 1 + SI->getNumCases()) { 2613 // Split weight for default case to case for "Cst". 2614 Weights[0] = (Weights[0]+1) >> 1; 2615 Weights.push_back(Weights[0]); 2616 2617 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end()); 2618 SI->setMetadata(LLVMContext::MD_prof, 2619 MDBuilder(SI->getContext()). 2620 createBranchWeights(MDWeights)); 2621 } 2622 } 2623 SI->addCase(Cst, NewBB); 2624 2625 // NewBB branches to the phi block, add the uncond branch and the phi entry. 2626 Builder.SetInsertPoint(NewBB); 2627 Builder.SetCurrentDebugLocation(SI->getDebugLoc()); 2628 Builder.CreateBr(SuccBlock); 2629 PHIUse->addIncoming(NewCst, NewBB); 2630 return true; 2631} 2632 2633/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch. 2634/// Check to see if it is branching on an or/and chain of icmp instructions, and 2635/// fold it into a switch instruction if so. 2636static bool SimplifyBranchOnICmpChain(BranchInst *BI, const DataLayout *TD, 2637 IRBuilder<> &Builder) { 2638 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 2639 if (Cond == 0) return false; 2640 2641 2642 // Change br (X == 0 | X == 1), T, F into a switch instruction. 2643 // If this is a bunch of seteq's or'd together, or if it's a bunch of 2644 // 'setne's and'ed together, collect them. 2645 Value *CompVal = 0; 2646 std::vector<ConstantInt*> Values; 2647 bool TrueWhenEqual = true; 2648 Value *ExtraCase = 0; 2649 unsigned UsedICmps = 0; 2650 2651 if (Cond->getOpcode() == Instruction::Or) { 2652 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true, 2653 UsedICmps); 2654 } else if (Cond->getOpcode() == Instruction::And) { 2655 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false, 2656 UsedICmps); 2657 TrueWhenEqual = false; 2658 } 2659 2660 // If we didn't have a multiply compared value, fail. 2661 if (CompVal == 0) return false; 2662 2663 // Avoid turning single icmps into a switch. 2664 if (UsedICmps <= 1) 2665 return false; 2666 2667 // There might be duplicate constants in the list, which the switch 2668 // instruction can't handle, remove them now. 2669 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate); 2670 Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); 2671 2672 // If Extra was used, we require at least two switch values to do the 2673 // transformation. A switch with one value is just an cond branch. 2674 if (ExtraCase && Values.size() < 2) return false; 2675 2676 // TODO: Preserve branch weight metadata, similarly to how 2677 // FoldValueComparisonIntoPredecessors preserves it. 2678 2679 // Figure out which block is which destination. 2680 BasicBlock *DefaultBB = BI->getSuccessor(1); 2681 BasicBlock *EdgeBB = BI->getSuccessor(0); 2682 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); 2683 2684 BasicBlock *BB = BI->getParent(); 2685 2686 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size() 2687 << " cases into SWITCH. BB is:\n" << *BB); 2688 2689 // If there are any extra values that couldn't be folded into the switch 2690 // then we evaluate them with an explicit branch first. Split the block 2691 // right before the condbr to handle it. 2692 if (ExtraCase) { 2693 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test"); 2694 // Remove the uncond branch added to the old block. 2695 TerminatorInst *OldTI = BB->getTerminator(); 2696 Builder.SetInsertPoint(OldTI); 2697 2698 if (TrueWhenEqual) 2699 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB); 2700 else 2701 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB); 2702 2703 OldTI->eraseFromParent(); 2704 2705 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them 2706 // for the edge we just added. 2707 AddPredecessorToBlock(EdgeBB, BB, NewBB); 2708 2709 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase 2710 << "\nEXTRABB = " << *BB); 2711 BB = NewBB; 2712 } 2713 2714 Builder.SetInsertPoint(BI); 2715 // Convert pointer to int before we switch. 2716 if (CompVal->getType()->isPointerTy()) { 2717 assert(TD && "Cannot switch on pointer without DataLayout"); 2718 CompVal = Builder.CreatePtrToInt(CompVal, 2719 TD->getIntPtrType(CompVal->getType()), 2720 "magicptr"); 2721 } 2722 2723 // Create the new switch instruction now. 2724 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size()); 2725 2726 // Add all of the 'cases' to the switch instruction. 2727 for (unsigned i = 0, e = Values.size(); i != e; ++i) 2728 New->addCase(Values[i], EdgeBB); 2729 2730 // We added edges from PI to the EdgeBB. As such, if there were any 2731 // PHI nodes in EdgeBB, they need entries to be added corresponding to 2732 // the number of edges added. 2733 for (BasicBlock::iterator BBI = EdgeBB->begin(); 2734 isa<PHINode>(BBI); ++BBI) { 2735 PHINode *PN = cast<PHINode>(BBI); 2736 Value *InVal = PN->getIncomingValueForBlock(BB); 2737 for (unsigned i = 0, e = Values.size()-1; i != e; ++i) 2738 PN->addIncoming(InVal, BB); 2739 } 2740 2741 // Erase the old branch instruction. 2742 EraseTerminatorInstAndDCECond(BI); 2743 2744 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n'); 2745 return true; 2746} 2747 2748bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) { 2749 // If this is a trivial landing pad that just continues unwinding the caught 2750 // exception then zap the landing pad, turning its invokes into calls. 2751 BasicBlock *BB = RI->getParent(); 2752 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI()); 2753 if (RI->getValue() != LPInst) 2754 // Not a landing pad, or the resume is not unwinding the exception that 2755 // caused control to branch here. 2756 return false; 2757 2758 // Check that there are no other instructions except for debug intrinsics. 2759 BasicBlock::iterator I = LPInst, E = RI; 2760 while (++I != E) 2761 if (!isa<DbgInfoIntrinsic>(I)) 2762 return false; 2763 2764 // Turn all invokes that unwind here into calls and delete the basic block. 2765 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) { 2766 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator()); 2767 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3); 2768 // Insert a call instruction before the invoke. 2769 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II); 2770 Call->takeName(II); 2771 Call->setCallingConv(II->getCallingConv()); 2772 Call->setAttributes(II->getAttributes()); 2773 Call->setDebugLoc(II->getDebugLoc()); 2774 2775 // Anything that used the value produced by the invoke instruction now uses 2776 // the value produced by the call instruction. Note that we do this even 2777 // for void functions and calls with no uses so that the callgraph edge is 2778 // updated. 2779 II->replaceAllUsesWith(Call); 2780 BB->removePredecessor(II->getParent()); 2781 2782 // Insert a branch to the normal destination right before the invoke. 2783 BranchInst::Create(II->getNormalDest(), II); 2784 2785 // Finally, delete the invoke instruction! 2786 II->eraseFromParent(); 2787 } 2788 2789 // The landingpad is now unreachable. Zap it. 2790 BB->eraseFromParent(); 2791 return true; 2792} 2793 2794bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) { 2795 BasicBlock *BB = RI->getParent(); 2796 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; 2797 2798 // Find predecessors that end with branches. 2799 SmallVector<BasicBlock*, 8> UncondBranchPreds; 2800 SmallVector<BranchInst*, 8> CondBranchPreds; 2801 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 2802 BasicBlock *P = *PI; 2803 TerminatorInst *PTI = P->getTerminator(); 2804 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) { 2805 if (BI->isUnconditional()) 2806 UncondBranchPreds.push_back(P); 2807 else 2808 CondBranchPreds.push_back(BI); 2809 } 2810 } 2811 2812 // If we found some, do the transformation! 2813 if (!UncondBranchPreds.empty() && DupRet) { 2814 while (!UncondBranchPreds.empty()) { 2815 BasicBlock *Pred = UncondBranchPreds.pop_back_val(); 2816 DEBUG(dbgs() << "FOLDING: " << *BB 2817 << "INTO UNCOND BRANCH PRED: " << *Pred); 2818 (void)FoldReturnIntoUncondBranch(RI, BB, Pred); 2819 } 2820 2821 // If we eliminated all predecessors of the block, delete the block now. 2822 if (pred_begin(BB) == pred_end(BB)) 2823 // We know there are no successors, so just nuke the block. 2824 BB->eraseFromParent(); 2825 2826 return true; 2827 } 2828 2829 // Check out all of the conditional branches going to this return 2830 // instruction. If any of them just select between returns, change the 2831 // branch itself into a select/return pair. 2832 while (!CondBranchPreds.empty()) { 2833 BranchInst *BI = CondBranchPreds.pop_back_val(); 2834 2835 // Check to see if the non-BB successor is also a return block. 2836 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) && 2837 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) && 2838 SimplifyCondBranchToTwoReturns(BI, Builder)) 2839 return true; 2840 } 2841 return false; 2842} 2843 2844bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) { 2845 BasicBlock *BB = UI->getParent(); 2846 2847 bool Changed = false; 2848 2849 // If there are any instructions immediately before the unreachable that can 2850 // be removed, do so. 2851 while (UI != BB->begin()) { 2852 BasicBlock::iterator BBI = UI; 2853 --BBI; 2854 // Do not delete instructions that can have side effects which might cause 2855 // the unreachable to not be reachable; specifically, calls and volatile 2856 // operations may have this effect. 2857 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break; 2858 2859 if (BBI->mayHaveSideEffects()) { 2860 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) { 2861 if (SI->isVolatile()) 2862 break; 2863 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) { 2864 if (LI->isVolatile()) 2865 break; 2866 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) { 2867 if (RMWI->isVolatile()) 2868 break; 2869 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) { 2870 if (CXI->isVolatile()) 2871 break; 2872 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) && 2873 !isa<LandingPadInst>(BBI)) { 2874 break; 2875 } 2876 // Note that deleting LandingPad's here is in fact okay, although it 2877 // involves a bit of subtle reasoning. If this inst is a LandingPad, 2878 // all the predecessors of this block will be the unwind edges of Invokes, 2879 // and we can therefore guarantee this block will be erased. 2880 } 2881 2882 // Delete this instruction (any uses are guaranteed to be dead) 2883 if (!BBI->use_empty()) 2884 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType())); 2885 BBI->eraseFromParent(); 2886 Changed = true; 2887 } 2888 2889 // If the unreachable instruction is the first in the block, take a gander 2890 // at all of the predecessors of this instruction, and simplify them. 2891 if (&BB->front() != UI) return Changed; 2892 2893 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 2894 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 2895 TerminatorInst *TI = Preds[i]->getTerminator(); 2896 IRBuilder<> Builder(TI); 2897 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 2898 if (BI->isUnconditional()) { 2899 if (BI->getSuccessor(0) == BB) { 2900 new UnreachableInst(TI->getContext(), TI); 2901 TI->eraseFromParent(); 2902 Changed = true; 2903 } 2904 } else { 2905 if (BI->getSuccessor(0) == BB) { 2906 Builder.CreateBr(BI->getSuccessor(1)); 2907 EraseTerminatorInstAndDCECond(BI); 2908 } else if (BI->getSuccessor(1) == BB) { 2909 Builder.CreateBr(BI->getSuccessor(0)); 2910 EraseTerminatorInstAndDCECond(BI); 2911 Changed = true; 2912 } 2913 } 2914 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 2915 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 2916 i != e; ++i) 2917 if (i.getCaseSuccessor() == BB) { 2918 BB->removePredecessor(SI->getParent()); 2919 SI->removeCase(i); 2920 --i; --e; 2921 Changed = true; 2922 } 2923 // If the default value is unreachable, figure out the most popular 2924 // destination and make it the default. 2925 if (SI->getDefaultDest() == BB) { 2926 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity; 2927 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 2928 i != e; ++i) { 2929 std::pair<unsigned, unsigned> &entry = 2930 Popularity[i.getCaseSuccessor()]; 2931 if (entry.first == 0) { 2932 entry.first = 1; 2933 entry.second = i.getCaseIndex(); 2934 } else { 2935 entry.first++; 2936 } 2937 } 2938 2939 // Find the most popular block. 2940 unsigned MaxPop = 0; 2941 unsigned MaxIndex = 0; 2942 BasicBlock *MaxBlock = 0; 2943 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator 2944 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { 2945 if (I->second.first > MaxPop || 2946 (I->second.first == MaxPop && MaxIndex > I->second.second)) { 2947 MaxPop = I->second.first; 2948 MaxIndex = I->second.second; 2949 MaxBlock = I->first; 2950 } 2951 } 2952 if (MaxBlock) { 2953 // Make this the new default, allowing us to delete any explicit 2954 // edges to it. 2955 SI->setDefaultDest(MaxBlock); 2956 Changed = true; 2957 2958 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from 2959 // it. 2960 if (isa<PHINode>(MaxBlock->begin())) 2961 for (unsigned i = 0; i != MaxPop-1; ++i) 2962 MaxBlock->removePredecessor(SI->getParent()); 2963 2964 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 2965 i != e; ++i) 2966 if (i.getCaseSuccessor() == MaxBlock) { 2967 SI->removeCase(i); 2968 --i; --e; 2969 } 2970 } 2971 } 2972 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) { 2973 if (II->getUnwindDest() == BB) { 2974 // Convert the invoke to a call instruction. This would be a good 2975 // place to note that the call does not throw though. 2976 BranchInst *BI = Builder.CreateBr(II->getNormalDest()); 2977 II->removeFromParent(); // Take out of symbol table 2978 2979 // Insert the call now... 2980 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3); 2981 Builder.SetInsertPoint(BI); 2982 CallInst *CI = Builder.CreateCall(II->getCalledValue(), 2983 Args, II->getName()); 2984 CI->setCallingConv(II->getCallingConv()); 2985 CI->setAttributes(II->getAttributes()); 2986 // If the invoke produced a value, the call does now instead. 2987 II->replaceAllUsesWith(CI); 2988 delete II; 2989 Changed = true; 2990 } 2991 } 2992 } 2993 2994 // If this block is now dead, remove it. 2995 if (pred_begin(BB) == pred_end(BB) && 2996 BB != &BB->getParent()->getEntryBlock()) { 2997 // We know there are no successors, so just nuke the block. 2998 BB->eraseFromParent(); 2999 return true; 3000 } 3001 3002 return Changed; 3003} 3004 3005/// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a 3006/// integer range comparison into a sub, an icmp and a branch. 3007static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) { 3008 assert(SI->getNumCases() > 1 && "Degenerate switch?"); 3009 3010 // Make sure all cases point to the same destination and gather the values. 3011 SmallVector<ConstantInt *, 16> Cases; 3012 SwitchInst::CaseIt I = SI->case_begin(); 3013 Cases.push_back(I.getCaseValue()); 3014 SwitchInst::CaseIt PrevI = I++; 3015 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) { 3016 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor()) 3017 return false; 3018 Cases.push_back(I.getCaseValue()); 3019 } 3020 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered"); 3021 3022 // Sort the case values, then check if they form a range we can transform. 3023 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate); 3024 for (unsigned I = 1, E = Cases.size(); I != E; ++I) { 3025 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1) 3026 return false; 3027 } 3028 3029 Constant *Offset = ConstantExpr::getNeg(Cases.back()); 3030 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()); 3031 3032 Value *Sub = SI->getCondition(); 3033 if (!Offset->isNullValue()) 3034 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off"); 3035 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch"); 3036 BranchInst *NewBI = Builder.CreateCondBr( 3037 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest()); 3038 3039 // Update weight for the newly-created conditional branch. 3040 SmallVector<uint64_t, 8> Weights; 3041 bool HasWeights = HasBranchWeights(SI); 3042 if (HasWeights) { 3043 GetBranchWeights(SI, Weights); 3044 if (Weights.size() == 1 + SI->getNumCases()) { 3045 // Combine all weights for the cases to be the true weight of NewBI. 3046 // We assume that the sum of all weights for a Terminator can fit into 32 3047 // bits. 3048 uint32_t NewTrueWeight = 0; 3049 for (unsigned I = 1, E = Weights.size(); I != E; ++I) 3050 NewTrueWeight += (uint32_t)Weights[I]; 3051 NewBI->setMetadata(LLVMContext::MD_prof, 3052 MDBuilder(SI->getContext()). 3053 createBranchWeights(NewTrueWeight, 3054 (uint32_t)Weights[0])); 3055 } 3056 } 3057 3058 // Prune obsolete incoming values off the successor's PHI nodes. 3059 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin(); 3060 isa<PHINode>(BBI); ++BBI) { 3061 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I) 3062 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent()); 3063 } 3064 SI->eraseFromParent(); 3065 3066 return true; 3067} 3068 3069/// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch 3070/// and use it to remove dead cases. 3071static bool EliminateDeadSwitchCases(SwitchInst *SI) { 3072 Value *Cond = SI->getCondition(); 3073 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth(); 3074 APInt KnownZero(Bits, 0), KnownOne(Bits, 0); 3075 ComputeMaskedBits(Cond, KnownZero, KnownOne); 3076 3077 // Gather dead cases. 3078 SmallVector<ConstantInt*, 8> DeadCases; 3079 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) { 3080 if ((I.getCaseValue()->getValue() & KnownZero) != 0 || 3081 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) { 3082 DeadCases.push_back(I.getCaseValue()); 3083 DEBUG(dbgs() << "SimplifyCFG: switch case '" 3084 << I.getCaseValue() << "' is dead.\n"); 3085 } 3086 } 3087 3088 SmallVector<uint64_t, 8> Weights; 3089 bool HasWeight = HasBranchWeights(SI); 3090 if (HasWeight) { 3091 GetBranchWeights(SI, Weights); 3092 HasWeight = (Weights.size() == 1 + SI->getNumCases()); 3093 } 3094 3095 // Remove dead cases from the switch. 3096 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) { 3097 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]); 3098 assert(Case != SI->case_default() && 3099 "Case was not found. Probably mistake in DeadCases forming."); 3100 if (HasWeight) { 3101 std::swap(Weights[Case.getCaseIndex()+1], Weights.back()); 3102 Weights.pop_back(); 3103 } 3104 3105 // Prune unused values from PHI nodes. 3106 Case.getCaseSuccessor()->removePredecessor(SI->getParent()); 3107 SI->removeCase(Case); 3108 } 3109 if (HasWeight) { 3110 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end()); 3111 SI->setMetadata(LLVMContext::MD_prof, 3112 MDBuilder(SI->getParent()->getContext()). 3113 createBranchWeights(MDWeights)); 3114 } 3115 3116 return !DeadCases.empty(); 3117} 3118 3119/// FindPHIForConditionForwarding - If BB would be eligible for simplification 3120/// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated 3121/// by an unconditional branch), look at the phi node for BB in the successor 3122/// block and see if the incoming value is equal to CaseValue. If so, return 3123/// the phi node, and set PhiIndex to BB's index in the phi node. 3124static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue, 3125 BasicBlock *BB, 3126 int *PhiIndex) { 3127 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator()) 3128 return NULL; // BB must be empty to be a candidate for simplification. 3129 if (!BB->getSinglePredecessor()) 3130 return NULL; // BB must be dominated by the switch. 3131 3132 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator()); 3133 if (!Branch || !Branch->isUnconditional()) 3134 return NULL; // Terminator must be unconditional branch. 3135 3136 BasicBlock *Succ = Branch->getSuccessor(0); 3137 3138 BasicBlock::iterator I = Succ->begin(); 3139 while (PHINode *PHI = dyn_cast<PHINode>(I++)) { 3140 int Idx = PHI->getBasicBlockIndex(BB); 3141 assert(Idx >= 0 && "PHI has no entry for predecessor?"); 3142 3143 Value *InValue = PHI->getIncomingValue(Idx); 3144 if (InValue != CaseValue) continue; 3145 3146 *PhiIndex = Idx; 3147 return PHI; 3148 } 3149 3150 return NULL; 3151} 3152 3153/// ForwardSwitchConditionToPHI - Try to forward the condition of a switch 3154/// instruction to a phi node dominated by the switch, if that would mean that 3155/// some of the destination blocks of the switch can be folded away. 3156/// Returns true if a change is made. 3157static bool ForwardSwitchConditionToPHI(SwitchInst *SI) { 3158 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap; 3159 ForwardingNodesMap ForwardingNodes; 3160 3161 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) { 3162 ConstantInt *CaseValue = I.getCaseValue(); 3163 BasicBlock *CaseDest = I.getCaseSuccessor(); 3164 3165 int PhiIndex; 3166 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest, 3167 &PhiIndex); 3168 if (!PHI) continue; 3169 3170 ForwardingNodes[PHI].push_back(PhiIndex); 3171 } 3172 3173 bool Changed = false; 3174 3175 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(), 3176 E = ForwardingNodes.end(); I != E; ++I) { 3177 PHINode *Phi = I->first; 3178 SmallVector<int,4> &Indexes = I->second; 3179 3180 if (Indexes.size() < 2) continue; 3181 3182 for (size_t I = 0, E = Indexes.size(); I != E; ++I) 3183 Phi->setIncomingValue(Indexes[I], SI->getCondition()); 3184 Changed = true; 3185 } 3186 3187 return Changed; 3188} 3189 3190/// ValidLookupTableConstant - Return true if the backend will be able to handle 3191/// initializing an array of constants like C. 3192static bool ValidLookupTableConstant(Constant *C) { 3193 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 3194 return CE->isGEPWithNoNotionalOverIndexing(); 3195 3196 return isa<ConstantFP>(C) || 3197 isa<ConstantInt>(C) || 3198 isa<ConstantPointerNull>(C) || 3199 isa<GlobalValue>(C) || 3200 isa<UndefValue>(C); 3201} 3202 3203/// LookupConstant - If V is a Constant, return it. Otherwise, try to look up 3204/// its constant value in ConstantPool, returning 0 if it's not there. 3205static Constant *LookupConstant(Value *V, 3206 const SmallDenseMap<Value*, Constant*>& ConstantPool) { 3207 if (Constant *C = dyn_cast<Constant>(V)) 3208 return C; 3209 return ConstantPool.lookup(V); 3210} 3211 3212/// ConstantFold - Try to fold instruction I into a constant. This works for 3213/// simple instructions such as binary operations where both operands are 3214/// constant or can be replaced by constants from the ConstantPool. Returns the 3215/// resulting constant on success, 0 otherwise. 3216static Constant *ConstantFold(Instruction *I, 3217 const SmallDenseMap<Value*, Constant*>& ConstantPool) { 3218 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) { 3219 Constant *A = LookupConstant(BO->getOperand(0), ConstantPool); 3220 if (!A) 3221 return 0; 3222 Constant *B = LookupConstant(BO->getOperand(1), ConstantPool); 3223 if (!B) 3224 return 0; 3225 return ConstantExpr::get(BO->getOpcode(), A, B); 3226 } 3227 3228 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) { 3229 Constant *A = LookupConstant(I->getOperand(0), ConstantPool); 3230 if (!A) 3231 return 0; 3232 Constant *B = LookupConstant(I->getOperand(1), ConstantPool); 3233 if (!B) 3234 return 0; 3235 return ConstantExpr::getCompare(Cmp->getPredicate(), A, B); 3236 } 3237 3238 if (SelectInst *Select = dyn_cast<SelectInst>(I)) { 3239 Constant *A = LookupConstant(Select->getCondition(), ConstantPool); 3240 if (!A) 3241 return 0; 3242 if (A->isAllOnesValue()) 3243 return LookupConstant(Select->getTrueValue(), ConstantPool); 3244 if (A->isNullValue()) 3245 return LookupConstant(Select->getFalseValue(), ConstantPool); 3246 return 0; 3247 } 3248 3249 if (CastInst *Cast = dyn_cast<CastInst>(I)) { 3250 Constant *A = LookupConstant(I->getOperand(0), ConstantPool); 3251 if (!A) 3252 return 0; 3253 return ConstantExpr::getCast(Cast->getOpcode(), A, Cast->getDestTy()); 3254 } 3255 3256 return 0; 3257} 3258 3259/// GetCaseResults - Try to determine the resulting constant values in phi nodes 3260/// at the common destination basic block, *CommonDest, for one of the case 3261/// destionations CaseDest corresponding to value CaseVal (0 for the default 3262/// case), of a switch instruction SI. 3263static bool GetCaseResults(SwitchInst *SI, 3264 ConstantInt *CaseVal, 3265 BasicBlock *CaseDest, 3266 BasicBlock **CommonDest, 3267 SmallVector<std::pair<PHINode*,Constant*>, 4> &Res) { 3268 // The block from which we enter the common destination. 3269 BasicBlock *Pred = SI->getParent(); 3270 3271 // If CaseDest is empty except for some side-effect free instructions through 3272 // which we can constant-propagate the CaseVal, continue to its successor. 3273 SmallDenseMap<Value*, Constant*> ConstantPool; 3274 ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal)); 3275 for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E; 3276 ++I) { 3277 if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) { 3278 // If the terminator is a simple branch, continue to the next block. 3279 if (T->getNumSuccessors() != 1) 3280 return false; 3281 Pred = CaseDest; 3282 CaseDest = T->getSuccessor(0); 3283 } else if (isa<DbgInfoIntrinsic>(I)) { 3284 // Skip debug intrinsic. 3285 continue; 3286 } else if (Constant *C = ConstantFold(I, ConstantPool)) { 3287 // Instruction is side-effect free and constant. 3288 ConstantPool.insert(std::make_pair(I, C)); 3289 } else { 3290 break; 3291 } 3292 } 3293 3294 // If we did not have a CommonDest before, use the current one. 3295 if (!*CommonDest) 3296 *CommonDest = CaseDest; 3297 // If the destination isn't the common one, abort. 3298 if (CaseDest != *CommonDest) 3299 return false; 3300 3301 // Get the values for this case from phi nodes in the destination block. 3302 BasicBlock::iterator I = (*CommonDest)->begin(); 3303 while (PHINode *PHI = dyn_cast<PHINode>(I++)) { 3304 int Idx = PHI->getBasicBlockIndex(Pred); 3305 if (Idx == -1) 3306 continue; 3307 3308 Constant *ConstVal = LookupConstant(PHI->getIncomingValue(Idx), 3309 ConstantPool); 3310 if (!ConstVal) 3311 return false; 3312 3313 // Note: If the constant comes from constant-propagating the case value 3314 // through the CaseDest basic block, it will be safe to remove the 3315 // instructions in that block. They cannot be used (except in the phi nodes 3316 // we visit) outside CaseDest, because that block does not dominate its 3317 // successor. If it did, we would not be in this phi node. 3318 3319 // Be conservative about which kinds of constants we support. 3320 if (!ValidLookupTableConstant(ConstVal)) 3321 return false; 3322 3323 Res.push_back(std::make_pair(PHI, ConstVal)); 3324 } 3325 3326 return true; 3327} 3328 3329namespace { 3330 /// SwitchLookupTable - This class represents a lookup table that can be used 3331 /// to replace a switch. 3332 class SwitchLookupTable { 3333 public: 3334 /// SwitchLookupTable - Create a lookup table to use as a switch replacement 3335 /// with the contents of Values, using DefaultValue to fill any holes in the 3336 /// table. 3337 SwitchLookupTable(Module &M, 3338 uint64_t TableSize, 3339 ConstantInt *Offset, 3340 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values, 3341 Constant *DefaultValue, 3342 const DataLayout *TD); 3343 3344 /// BuildLookup - Build instructions with Builder to retrieve the value at 3345 /// the position given by Index in the lookup table. 3346 Value *BuildLookup(Value *Index, IRBuilder<> &Builder); 3347 3348 /// WouldFitInRegister - Return true if a table with TableSize elements of 3349 /// type ElementType would fit in a target-legal register. 3350 static bool WouldFitInRegister(const DataLayout *TD, 3351 uint64_t TableSize, 3352 const Type *ElementType); 3353 3354 private: 3355 // Depending on the contents of the table, it can be represented in 3356 // different ways. 3357 enum { 3358 // For tables where each element contains the same value, we just have to 3359 // store that single value and return it for each lookup. 3360 SingleValueKind, 3361 3362 // For small tables with integer elements, we can pack them into a bitmap 3363 // that fits into a target-legal register. Values are retrieved by 3364 // shift and mask operations. 3365 BitMapKind, 3366 3367 // The table is stored as an array of values. Values are retrieved by load 3368 // instructions from the table. 3369 ArrayKind 3370 } Kind; 3371 3372 // For SingleValueKind, this is the single value. 3373 Constant *SingleValue; 3374 3375 // For BitMapKind, this is the bitmap. 3376 ConstantInt *BitMap; 3377 IntegerType *BitMapElementTy; 3378 3379 // For ArrayKind, this is the array. 3380 GlobalVariable *Array; 3381 }; 3382} 3383 3384SwitchLookupTable::SwitchLookupTable(Module &M, 3385 uint64_t TableSize, 3386 ConstantInt *Offset, 3387 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values, 3388 Constant *DefaultValue, 3389 const DataLayout *TD) { 3390 assert(Values.size() && "Can't build lookup table without values!"); 3391 assert(TableSize >= Values.size() && "Can't fit values in table!"); 3392 3393 // If all values in the table are equal, this is that value. 3394 SingleValue = Values.begin()->second; 3395 3396 // Build up the table contents. 3397 SmallVector<Constant*, 64> TableContents(TableSize); 3398 for (size_t I = 0, E = Values.size(); I != E; ++I) { 3399 ConstantInt *CaseVal = Values[I].first; 3400 Constant *CaseRes = Values[I].second; 3401 assert(CaseRes->getType() == DefaultValue->getType()); 3402 3403 uint64_t Idx = (CaseVal->getValue() - Offset->getValue()) 3404 .getLimitedValue(); 3405 TableContents[Idx] = CaseRes; 3406 3407 if (CaseRes != SingleValue) 3408 SingleValue = 0; 3409 } 3410 3411 // Fill in any holes in the table with the default result. 3412 if (Values.size() < TableSize) { 3413 for (uint64_t I = 0; I < TableSize; ++I) { 3414 if (!TableContents[I]) 3415 TableContents[I] = DefaultValue; 3416 } 3417 3418 if (DefaultValue != SingleValue) 3419 SingleValue = 0; 3420 } 3421 3422 // If each element in the table contains the same value, we only need to store 3423 // that single value. 3424 if (SingleValue) { 3425 Kind = SingleValueKind; 3426 return; 3427 } 3428 3429 // If the type is integer and the table fits in a register, build a bitmap. 3430 if (WouldFitInRegister(TD, TableSize, DefaultValue->getType())) { 3431 IntegerType *IT = cast<IntegerType>(DefaultValue->getType()); 3432 APInt TableInt(TableSize * IT->getBitWidth(), 0); 3433 for (uint64_t I = TableSize; I > 0; --I) { 3434 TableInt <<= IT->getBitWidth(); 3435 // Insert values into the bitmap. Undef values are set to zero. 3436 if (!isa<UndefValue>(TableContents[I - 1])) { 3437 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]); 3438 TableInt |= Val->getValue().zext(TableInt.getBitWidth()); 3439 } 3440 } 3441 BitMap = ConstantInt::get(M.getContext(), TableInt); 3442 BitMapElementTy = IT; 3443 Kind = BitMapKind; 3444 ++NumBitMaps; 3445 return; 3446 } 3447 3448 // Store the table in an array. 3449 ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize); 3450 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents); 3451 3452 Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true, 3453 GlobalVariable::PrivateLinkage, 3454 Initializer, 3455 "switch.table"); 3456 Array->setUnnamedAddr(true); 3457 Kind = ArrayKind; 3458} 3459 3460Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) { 3461 switch (Kind) { 3462 case SingleValueKind: 3463 return SingleValue; 3464 case BitMapKind: { 3465 // Type of the bitmap (e.g. i59). 3466 IntegerType *MapTy = BitMap->getType(); 3467 3468 // Cast Index to the same type as the bitmap. 3469 // Note: The Index is <= the number of elements in the table, so 3470 // truncating it to the width of the bitmask is safe. 3471 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast"); 3472 3473 // Multiply the shift amount by the element width. 3474 ShiftAmt = Builder.CreateMul(ShiftAmt, 3475 ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()), 3476 "switch.shiftamt"); 3477 3478 // Shift down. 3479 Value *DownShifted = Builder.CreateLShr(BitMap, ShiftAmt, 3480 "switch.downshift"); 3481 // Mask off. 3482 return Builder.CreateTrunc(DownShifted, BitMapElementTy, 3483 "switch.masked"); 3484 } 3485 case ArrayKind: { 3486 Value *GEPIndices[] = { Builder.getInt32(0), Index }; 3487 Value *GEP = Builder.CreateInBoundsGEP(Array, GEPIndices, 3488 "switch.gep"); 3489 return Builder.CreateLoad(GEP, "switch.load"); 3490 } 3491 } 3492 llvm_unreachable("Unknown lookup table kind!"); 3493} 3494 3495bool SwitchLookupTable::WouldFitInRegister(const DataLayout *TD, 3496 uint64_t TableSize, 3497 const Type *ElementType) { 3498 if (!TD) 3499 return false; 3500 const IntegerType *IT = dyn_cast<IntegerType>(ElementType); 3501 if (!IT) 3502 return false; 3503 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values 3504 // are <= 15, we could try to narrow the type. 3505 3506 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width. 3507 if (TableSize >= UINT_MAX/IT->getBitWidth()) 3508 return false; 3509 return TD->fitsInLegalInteger(TableSize * IT->getBitWidth()); 3510} 3511 3512/// ShouldBuildLookupTable - Determine whether a lookup table should be built 3513/// for this switch, based on the number of caes, size of the table and the 3514/// types of the results. 3515static bool ShouldBuildLookupTable(SwitchInst *SI, 3516 uint64_t TableSize, 3517 const DataLayout *TD, 3518 const SmallDenseMap<PHINode*, Type*>& ResultTypes) { 3519 // The table density should be at least 40%. This is the same criterion as for 3520 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase. 3521 // FIXME: Find the best cut-off. 3522 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10) 3523 return false; // TableSize overflowed, or mul below might overflow. 3524 if (SI->getNumCases() * 10 >= TableSize * 4) 3525 return true; 3526 3527 // If each table would fit in a register, we should build it anyway. 3528 for (SmallDenseMap<PHINode*, Type*>::const_iterator I = ResultTypes.begin(), 3529 E = ResultTypes.end(); I != E; ++I) { 3530 if (!SwitchLookupTable::WouldFitInRegister(TD, TableSize, I->second)) 3531 return false; 3532 } 3533 return true; 3534} 3535 3536/// SwitchToLookupTable - If the switch is only used to initialize one or more 3537/// phi nodes in a common successor block with different constant values, 3538/// replace the switch with lookup tables. 3539static bool SwitchToLookupTable(SwitchInst *SI, 3540 IRBuilder<> &Builder, 3541 const DataLayout* TD, 3542 const TargetTransformInfo *TTI) { 3543 assert(SI->getNumCases() > 1 && "Degenerate switch?"); 3544 3545 if (TTI && !TTI->getScalarTargetTransformInfo()->shouldBuildLookupTables()) 3546 return false; 3547 3548 // FIXME: Handle unreachable cases. 3549 3550 // FIXME: If the switch is too sparse for a lookup table, perhaps we could 3551 // split off a dense part and build a lookup table for that. 3552 3553 // FIXME: This creates arrays of GEPs to constant strings, which means each 3554 // GEP needs a runtime relocation in PIC code. We should just build one big 3555 // string and lookup indices into that. 3556 3557 // Ignore the switch if the number of cases is too small. 3558 // This is similar to the check when building jump tables in 3559 // SelectionDAGBuilder::handleJTSwitchCase. 3560 // FIXME: Determine the best cut-off. 3561 if (SI->getNumCases() < 4) 3562 return false; 3563 3564 // Figure out the corresponding result for each case value and phi node in the 3565 // common destination, as well as the the min and max case values. 3566 assert(SI->case_begin() != SI->case_end()); 3567 SwitchInst::CaseIt CI = SI->case_begin(); 3568 ConstantInt *MinCaseVal = CI.getCaseValue(); 3569 ConstantInt *MaxCaseVal = CI.getCaseValue(); 3570 3571 BasicBlock *CommonDest = 0; 3572 typedef SmallVector<std::pair<ConstantInt*, Constant*>, 4> ResultListTy; 3573 SmallDenseMap<PHINode*, ResultListTy> ResultLists; 3574 SmallDenseMap<PHINode*, Constant*> DefaultResults; 3575 SmallDenseMap<PHINode*, Type*> ResultTypes; 3576 SmallVector<PHINode*, 4> PHIs; 3577 3578 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) { 3579 ConstantInt *CaseVal = CI.getCaseValue(); 3580 if (CaseVal->getValue().slt(MinCaseVal->getValue())) 3581 MinCaseVal = CaseVal; 3582 if (CaseVal->getValue().sgt(MaxCaseVal->getValue())) 3583 MaxCaseVal = CaseVal; 3584 3585 // Resulting value at phi nodes for this case value. 3586 typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy; 3587 ResultsTy Results; 3588 if (!GetCaseResults(SI, CaseVal, CI.getCaseSuccessor(), &CommonDest, 3589 Results)) 3590 return false; 3591 3592 // Append the result from this case to the list for each phi. 3593 for (ResultsTy::iterator I = Results.begin(), E = Results.end(); I!=E; ++I) { 3594 if (!ResultLists.count(I->first)) 3595 PHIs.push_back(I->first); 3596 ResultLists[I->first].push_back(std::make_pair(CaseVal, I->second)); 3597 } 3598 } 3599 3600 // Get the resulting values for the default case. 3601 SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList; 3602 if (!GetCaseResults(SI, 0, SI->getDefaultDest(), &CommonDest, 3603 DefaultResultsList)) 3604 return false; 3605 for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) { 3606 PHINode *PHI = DefaultResultsList[I].first; 3607 Constant *Result = DefaultResultsList[I].second; 3608 DefaultResults[PHI] = Result; 3609 ResultTypes[PHI] = Result->getType(); 3610 } 3611 3612 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue(); 3613 uint64_t TableSize = RangeSpread.getLimitedValue() + 1; 3614 if (!ShouldBuildLookupTable(SI, TableSize, TD, ResultTypes)) 3615 return false; 3616 3617 // Create the BB that does the lookups. 3618 Module &Mod = *CommonDest->getParent()->getParent(); 3619 BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(), 3620 "switch.lookup", 3621 CommonDest->getParent(), 3622 CommonDest); 3623 3624 // Check whether the condition value is within the case range, and branch to 3625 // the new BB. 3626 Builder.SetInsertPoint(SI); 3627 Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal, 3628 "switch.tableidx"); 3629 Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get( 3630 MinCaseVal->getType(), TableSize)); 3631 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest()); 3632 3633 // Populate the BB that does the lookups. 3634 Builder.SetInsertPoint(LookupBB); 3635 bool ReturnedEarly = false; 3636 for (size_t I = 0, E = PHIs.size(); I != E; ++I) { 3637 PHINode *PHI = PHIs[I]; 3638 3639 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultLists[PHI], 3640 DefaultResults[PHI], TD); 3641 3642 Value *Result = Table.BuildLookup(TableIndex, Builder); 3643 3644 // If the result is used to return immediately from the function, we want to 3645 // do that right here. 3646 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin()) && 3647 *PHI->use_begin() == CommonDest->getFirstNonPHIOrDbg()) { 3648 Builder.CreateRet(Result); 3649 ReturnedEarly = true; 3650 break; 3651 } 3652 3653 PHI->addIncoming(Result, LookupBB); 3654 } 3655 3656 if (!ReturnedEarly) 3657 Builder.CreateBr(CommonDest); 3658 3659 // Remove the switch. 3660 for (unsigned i = 0; i < SI->getNumSuccessors(); ++i) { 3661 BasicBlock *Succ = SI->getSuccessor(i); 3662 if (Succ == SI->getDefaultDest()) continue; 3663 Succ->removePredecessor(SI->getParent()); 3664 } 3665 SI->eraseFromParent(); 3666 3667 ++NumLookupTables; 3668 return true; 3669} 3670 3671bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) { 3672 BasicBlock *BB = SI->getParent(); 3673 3674 if (isValueEqualityComparison(SI)) { 3675 // If we only have one predecessor, and if it is a branch on this value, 3676 // see if that predecessor totally determines the outcome of this switch. 3677 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 3678 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder)) 3679 return SimplifyCFG(BB) | true; 3680 3681 Value *Cond = SI->getCondition(); 3682 if (SelectInst *Select = dyn_cast<SelectInst>(Cond)) 3683 if (SimplifySwitchOnSelect(SI, Select)) 3684 return SimplifyCFG(BB) | true; 3685 3686 // If the block only contains the switch, see if we can fold the block 3687 // away into any preds. 3688 BasicBlock::iterator BBI = BB->begin(); 3689 // Ignore dbg intrinsics. 3690 while (isa<DbgInfoIntrinsic>(BBI)) 3691 ++BBI; 3692 if (SI == &*BBI) 3693 if (FoldValueComparisonIntoPredecessors(SI, Builder)) 3694 return SimplifyCFG(BB) | true; 3695 } 3696 3697 // Try to transform the switch into an icmp and a branch. 3698 if (TurnSwitchRangeIntoICmp(SI, Builder)) 3699 return SimplifyCFG(BB) | true; 3700 3701 // Remove unreachable cases. 3702 if (EliminateDeadSwitchCases(SI)) 3703 return SimplifyCFG(BB) | true; 3704 3705 if (ForwardSwitchConditionToPHI(SI)) 3706 return SimplifyCFG(BB) | true; 3707 3708 if (SwitchToLookupTable(SI, Builder, TD, TTI)) 3709 return SimplifyCFG(BB) | true; 3710 3711 return false; 3712} 3713 3714bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) { 3715 BasicBlock *BB = IBI->getParent(); 3716 bool Changed = false; 3717 3718 // Eliminate redundant destinations. 3719 SmallPtrSet<Value *, 8> Succs; 3720 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 3721 BasicBlock *Dest = IBI->getDestination(i); 3722 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) { 3723 Dest->removePredecessor(BB); 3724 IBI->removeDestination(i); 3725 --i; --e; 3726 Changed = true; 3727 } 3728 } 3729 3730 if (IBI->getNumDestinations() == 0) { 3731 // If the indirectbr has no successors, change it to unreachable. 3732 new UnreachableInst(IBI->getContext(), IBI); 3733 EraseTerminatorInstAndDCECond(IBI); 3734 return true; 3735 } 3736 3737 if (IBI->getNumDestinations() == 1) { 3738 // If the indirectbr has one successor, change it to a direct branch. 3739 BranchInst::Create(IBI->getDestination(0), IBI); 3740 EraseTerminatorInstAndDCECond(IBI); 3741 return true; 3742 } 3743 3744 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) { 3745 if (SimplifyIndirectBrOnSelect(IBI, SI)) 3746 return SimplifyCFG(BB) | true; 3747 } 3748 return Changed; 3749} 3750 3751bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){ 3752 BasicBlock *BB = BI->getParent(); 3753 3754 if (SinkCommon && SinkThenElseCodeToEnd(BI)) 3755 return true; 3756 3757 // If the Terminator is the only non-phi instruction, simplify the block. 3758 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime(); 3759 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() && 3760 TryToSimplifyUncondBranchFromEmptyBlock(BB)) 3761 return true; 3762 3763 // If the only instruction in the block is a seteq/setne comparison 3764 // against a constant, try to simplify the block. 3765 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) 3766 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) { 3767 for (++I; isa<DbgInfoIntrinsic>(I); ++I) 3768 ; 3769 if (I->isTerminator() && 3770 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder)) 3771 return true; 3772 } 3773 3774 // If this basic block is ONLY a compare and a branch, and if a predecessor 3775 // branches to us and our successor, fold the comparison into the 3776 // predecessor and use logical operations to update the incoming value 3777 // for PHI nodes in common successor. 3778 if (FoldBranchToCommonDest(BI)) 3779 return SimplifyCFG(BB) | true; 3780 return false; 3781} 3782 3783 3784bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) { 3785 BasicBlock *BB = BI->getParent(); 3786 3787 // Conditional branch 3788 if (isValueEqualityComparison(BI)) { 3789 // If we only have one predecessor, and if it is a branch on this value, 3790 // see if that predecessor totally determines the outcome of this 3791 // switch. 3792 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 3793 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder)) 3794 return SimplifyCFG(BB) | true; 3795 3796 // This block must be empty, except for the setcond inst, if it exists. 3797 // Ignore dbg intrinsics. 3798 BasicBlock::iterator I = BB->begin(); 3799 // Ignore dbg intrinsics. 3800 while (isa<DbgInfoIntrinsic>(I)) 3801 ++I; 3802 if (&*I == BI) { 3803 if (FoldValueComparisonIntoPredecessors(BI, Builder)) 3804 return SimplifyCFG(BB) | true; 3805 } else if (&*I == cast<Instruction>(BI->getCondition())){ 3806 ++I; 3807 // Ignore dbg intrinsics. 3808 while (isa<DbgInfoIntrinsic>(I)) 3809 ++I; 3810 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder)) 3811 return SimplifyCFG(BB) | true; 3812 } 3813 } 3814 3815 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction. 3816 if (SimplifyBranchOnICmpChain(BI, TD, Builder)) 3817 return true; 3818 3819 // If this basic block is ONLY a compare and a branch, and if a predecessor 3820 // branches to us and one of our successors, fold the comparison into the 3821 // predecessor and use logical operations to pick the right destination. 3822 if (FoldBranchToCommonDest(BI)) 3823 return SimplifyCFG(BB) | true; 3824 3825 // We have a conditional branch to two blocks that are only reachable 3826 // from BI. We know that the condbr dominates the two blocks, so see if 3827 // there is any identical code in the "then" and "else" blocks. If so, we 3828 // can hoist it up to the branching block. 3829 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) { 3830 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 3831 if (HoistThenElseCodeToIf(BI)) 3832 return SimplifyCFG(BB) | true; 3833 } else { 3834 // If Successor #1 has multiple preds, we may be able to conditionally 3835 // execute Successor #0 if it branches to successor #1. 3836 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator(); 3837 if (Succ0TI->getNumSuccessors() == 1 && 3838 Succ0TI->getSuccessor(0) == BI->getSuccessor(1)) 3839 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0))) 3840 return SimplifyCFG(BB) | true; 3841 } 3842 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 3843 // If Successor #0 has multiple preds, we may be able to conditionally 3844 // execute Successor #1 if it branches to successor #0. 3845 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator(); 3846 if (Succ1TI->getNumSuccessors() == 1 && 3847 Succ1TI->getSuccessor(0) == BI->getSuccessor(0)) 3848 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1))) 3849 return SimplifyCFG(BB) | true; 3850 } 3851 3852 // If this is a branch on a phi node in the current block, thread control 3853 // through this block if any PHI node entries are constants. 3854 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition())) 3855 if (PN->getParent() == BI->getParent()) 3856 if (FoldCondBranchOnPHI(BI, TD)) 3857 return SimplifyCFG(BB) | true; 3858 3859 // Scan predecessor blocks for conditional branches. 3860 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 3861 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) 3862 if (PBI != BI && PBI->isConditional()) 3863 if (SimplifyCondBranchToCondBranch(PBI, BI)) 3864 return SimplifyCFG(BB) | true; 3865 3866 return false; 3867} 3868 3869/// Check if passing a value to an instruction will cause undefined behavior. 3870static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) { 3871 Constant *C = dyn_cast<Constant>(V); 3872 if (!C) 3873 return false; 3874 3875 if (I->use_empty()) 3876 return false; 3877 3878 if (C->isNullValue()) { 3879 // Only look at the first use, avoid hurting compile time with long uselists 3880 User *Use = *I->use_begin(); 3881 3882 // Now make sure that there are no instructions in between that can alter 3883 // control flow (eg. calls) 3884 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i) 3885 if (i == I->getParent()->end() || i->mayHaveSideEffects()) 3886 return false; 3887 3888 // Look through GEPs. A load from a GEP derived from NULL is still undefined 3889 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use)) 3890 if (GEP->getPointerOperand() == I) 3891 return passingValueIsAlwaysUndefined(V, GEP); 3892 3893 // Look through bitcasts. 3894 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use)) 3895 return passingValueIsAlwaysUndefined(V, BC); 3896 3897 // Load from null is undefined. 3898 if (LoadInst *LI = dyn_cast<LoadInst>(Use)) 3899 return LI->getPointerAddressSpace() == 0; 3900 3901 // Store to null is undefined. 3902 if (StoreInst *SI = dyn_cast<StoreInst>(Use)) 3903 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I; 3904 } 3905 return false; 3906} 3907 3908/// If BB has an incoming value that will always trigger undefined behavior 3909/// (eg. null pointer dereference), remove the branch leading here. 3910static bool removeUndefIntroducingPredecessor(BasicBlock *BB) { 3911 for (BasicBlock::iterator i = BB->begin(); 3912 PHINode *PHI = dyn_cast<PHINode>(i); ++i) 3913 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) 3914 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) { 3915 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator(); 3916 IRBuilder<> Builder(T); 3917 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 3918 BB->removePredecessor(PHI->getIncomingBlock(i)); 3919 // Turn uncoditional branches into unreachables and remove the dead 3920 // destination from conditional branches. 3921 if (BI->isUnconditional()) 3922 Builder.CreateUnreachable(); 3923 else 3924 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) : 3925 BI->getSuccessor(0)); 3926 BI->eraseFromParent(); 3927 return true; 3928 } 3929 // TODO: SwitchInst. 3930 } 3931 3932 return false; 3933} 3934 3935bool SimplifyCFGOpt::run(BasicBlock *BB) { 3936 bool Changed = false; 3937 3938 assert(BB && BB->getParent() && "Block not embedded in function!"); 3939 assert(BB->getTerminator() && "Degenerate basic block encountered!"); 3940 3941 // Remove basic blocks that have no predecessors (except the entry block)... 3942 // or that just have themself as a predecessor. These are unreachable. 3943 if ((pred_begin(BB) == pred_end(BB) && 3944 BB != &BB->getParent()->getEntryBlock()) || 3945 BB->getSinglePredecessor() == BB) { 3946 DEBUG(dbgs() << "Removing BB: \n" << *BB); 3947 DeleteDeadBlock(BB); 3948 return true; 3949 } 3950 3951 // Check to see if we can constant propagate this terminator instruction 3952 // away... 3953 Changed |= ConstantFoldTerminator(BB, true); 3954 3955 // Check for and eliminate duplicate PHI nodes in this block. 3956 Changed |= EliminateDuplicatePHINodes(BB); 3957 3958 // Check for and remove branches that will always cause undefined behavior. 3959 Changed |= removeUndefIntroducingPredecessor(BB); 3960 3961 // Merge basic blocks into their predecessor if there is only one distinct 3962 // pred, and if there is only one distinct successor of the predecessor, and 3963 // if there are no PHI nodes. 3964 // 3965 if (MergeBlockIntoPredecessor(BB)) 3966 return true; 3967 3968 IRBuilder<> Builder(BB); 3969 3970 // If there is a trivial two-entry PHI node in this basic block, and we can 3971 // eliminate it, do so now. 3972 if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) 3973 if (PN->getNumIncomingValues() == 2) 3974 Changed |= FoldTwoEntryPHINode(PN, TD); 3975 3976 Builder.SetInsertPoint(BB->getTerminator()); 3977 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { 3978 if (BI->isUnconditional()) { 3979 if (SimplifyUncondBranch(BI, Builder)) return true; 3980 } else { 3981 if (SimplifyCondBranch(BI, Builder)) return true; 3982 } 3983 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 3984 if (SimplifyReturn(RI, Builder)) return true; 3985 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) { 3986 if (SimplifyResume(RI, Builder)) return true; 3987 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { 3988 if (SimplifySwitch(SI, Builder)) return true; 3989 } else if (UnreachableInst *UI = 3990 dyn_cast<UnreachableInst>(BB->getTerminator())) { 3991 if (SimplifyUnreachable(UI)) return true; 3992 } else if (IndirectBrInst *IBI = 3993 dyn_cast<IndirectBrInst>(BB->getTerminator())) { 3994 if (SimplifyIndirectBr(IBI)) return true; 3995 } 3996 3997 return Changed; 3998} 3999 4000/// SimplifyCFG - This function is used to do simplification of a CFG. For 4001/// example, it adjusts branches to branches to eliminate the extra hop, it 4002/// eliminates unreachable basic blocks, and does other "peephole" optimization 4003/// of the CFG. It returns true if a modification was made. 4004/// 4005bool llvm::SimplifyCFG(BasicBlock *BB, const DataLayout *TD, 4006 const TargetTransformInfo *TTI) { 4007 return SimplifyCFGOpt(TD, TTI).run(BB); 4008} 4009