SimplifyCFG.cpp revision 9e620952617b90992e50dcf9bca8078c535cbaef
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/ADT/DenseMap.h" 17#include "llvm/ADT/STLExtras.h" 18#include "llvm/ADT/SetVector.h" 19#include "llvm/ADT/SmallPtrSet.h" 20#include "llvm/ADT/SmallVector.h" 21#include "llvm/ADT/Statistic.h" 22#include "llvm/Analysis/InstructionSimplify.h" 23#include "llvm/Analysis/TargetTransformInfo.h" 24#include "llvm/Analysis/ValueTracking.h" 25#include "llvm/IR/Constants.h" 26#include "llvm/IR/DataLayout.h" 27#include "llvm/IR/DerivedTypes.h" 28#include "llvm/IR/GlobalVariable.h" 29#include "llvm/IR/IRBuilder.h" 30#include "llvm/IR/Instructions.h" 31#include "llvm/IR/IntrinsicInst.h" 32#include "llvm/IR/LLVMContext.h" 33#include "llvm/IR/MDBuilder.h" 34#include "llvm/IR/Metadata.h" 35#include "llvm/IR/Module.h" 36#include "llvm/IR/Operator.h" 37#include "llvm/IR/Type.h" 38#include "llvm/Support/CFG.h" 39#include "llvm/Support/CommandLine.h" 40#include "llvm/Support/ConstantRange.h" 41#include "llvm/Support/Debug.h" 42#include "llvm/Support/NoFolder.h" 43#include "llvm/Support/raw_ostream.h" 44#include "llvm/Transforms/Utils/BasicBlockUtils.h" 45#include <algorithm> 46#include <map> 47#include <set> 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 TargetTransformInfo &TTI; 86 const DataLayout *const TD; 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 TargetTransformInfo &TTI, const DataLayout *TD) 107 : TTI(TTI), TD(TD) {} 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 && CV->getType() == TD->getIntPtrType(CV->getContext())) 539 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) 540 CV = PTII->getOperand(0); 541 return CV; 542} 543 544/// GetValueEqualityComparisonCases - Given a value comparison instruction, 545/// decode all of the 'cases' that it represents and return the 'default' block. 546BasicBlock *SimplifyCFGOpt:: 547GetValueEqualityComparisonCases(TerminatorInst *TI, 548 std::vector<ValueEqualityComparisonCase> 549 &Cases) { 550 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 551 Cases.reserve(SI->getNumCases()); 552 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i) 553 Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(), 554 i.getCaseSuccessor())); 555 return SI->getDefaultDest(); 556 } 557 558 BranchInst *BI = cast<BranchInst>(TI); 559 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); 560 BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE); 561 Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1), 562 TD), 563 Succ)); 564 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ); 565} 566 567 568/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries 569/// in the list that match the specified block. 570static void EliminateBlockCases(BasicBlock *BB, 571 std::vector<ValueEqualityComparisonCase> &Cases) { 572 Cases.erase(std::remove(Cases.begin(), Cases.end(), BB), Cases.end()); 573} 574 575/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as 576/// well. 577static bool 578ValuesOverlap(std::vector<ValueEqualityComparisonCase> &C1, 579 std::vector<ValueEqualityComparisonCase > &C2) { 580 std::vector<ValueEqualityComparisonCase> *V1 = &C1, *V2 = &C2; 581 582 // Make V1 be smaller than V2. 583 if (V1->size() > V2->size()) 584 std::swap(V1, V2); 585 586 if (V1->size() == 0) return false; 587 if (V1->size() == 1) { 588 // Just scan V2. 589 ConstantInt *TheVal = (*V1)[0].Value; 590 for (unsigned i = 0, e = V2->size(); i != e; ++i) 591 if (TheVal == (*V2)[i].Value) 592 return true; 593 } 594 595 // Otherwise, just sort both lists and compare element by element. 596 array_pod_sort(V1->begin(), V1->end()); 597 array_pod_sort(V2->begin(), V2->end()); 598 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); 599 while (i1 != e1 && i2 != e2) { 600 if ((*V1)[i1].Value == (*V2)[i2].Value) 601 return true; 602 if ((*V1)[i1].Value < (*V2)[i2].Value) 603 ++i1; 604 else 605 ++i2; 606 } 607 return false; 608} 609 610/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a 611/// terminator instruction and its block is known to only have a single 612/// predecessor block, check to see if that predecessor is also a value 613/// comparison with the same value, and if that comparison determines the 614/// outcome of this comparison. If so, simplify TI. This does a very limited 615/// form of jump threading. 616bool SimplifyCFGOpt:: 617SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, 618 BasicBlock *Pred, 619 IRBuilder<> &Builder) { 620 Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); 621 if (!PredVal) return false; // Not a value comparison in predecessor. 622 623 Value *ThisVal = isValueEqualityComparison(TI); 624 assert(ThisVal && "This isn't a value comparison!!"); 625 if (ThisVal != PredVal) return false; // Different predicates. 626 627 // TODO: Preserve branch weight metadata, similarly to how 628 // FoldValueComparisonIntoPredecessors preserves it. 629 630 // Find out information about when control will move from Pred to TI's block. 631 std::vector<ValueEqualityComparisonCase> PredCases; 632 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), 633 PredCases); 634 EliminateBlockCases(PredDef, PredCases); // Remove default from cases. 635 636 // Find information about how control leaves this block. 637 std::vector<ValueEqualityComparisonCase> ThisCases; 638 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); 639 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. 640 641 // If TI's block is the default block from Pred's comparison, potentially 642 // simplify TI based on this knowledge. 643 if (PredDef == TI->getParent()) { 644 // If we are here, we know that the value is none of those cases listed in 645 // PredCases. If there are any cases in ThisCases that are in PredCases, we 646 // can simplify TI. 647 if (!ValuesOverlap(PredCases, ThisCases)) 648 return false; 649 650 if (isa<BranchInst>(TI)) { 651 // Okay, one of the successors of this condbr is dead. Convert it to a 652 // uncond br. 653 assert(ThisCases.size() == 1 && "Branch can only have one case!"); 654 // Insert the new branch. 655 Instruction *NI = Builder.CreateBr(ThisDef); 656 (void) NI; 657 658 // Remove PHI node entries for the dead edge. 659 ThisCases[0].Dest->removePredecessor(TI->getParent()); 660 661 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 662 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 663 664 EraseTerminatorInstAndDCECond(TI); 665 return true; 666 } 667 668 SwitchInst *SI = cast<SwitchInst>(TI); 669 // Okay, TI has cases that are statically dead, prune them away. 670 SmallPtrSet<Constant*, 16> DeadCases; 671 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 672 DeadCases.insert(PredCases[i].Value); 673 674 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 675 << "Through successor TI: " << *TI); 676 677 // Collect branch weights into a vector. 678 SmallVector<uint32_t, 8> Weights; 679 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof); 680 bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases()); 681 if (HasWeight) 682 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e; 683 ++MD_i) { 684 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i)); 685 assert(CI); 686 Weights.push_back(CI->getValue().getZExtValue()); 687 } 688 for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) { 689 --i; 690 if (DeadCases.count(i.getCaseValue())) { 691 if (HasWeight) { 692 std::swap(Weights[i.getCaseIndex()+1], Weights.back()); 693 Weights.pop_back(); 694 } 695 i.getCaseSuccessor()->removePredecessor(TI->getParent()); 696 SI->removeCase(i); 697 } 698 } 699 if (HasWeight && Weights.size() >= 2) 700 SI->setMetadata(LLVMContext::MD_prof, 701 MDBuilder(SI->getParent()->getContext()). 702 createBranchWeights(Weights)); 703 704 DEBUG(dbgs() << "Leaving: " << *TI << "\n"); 705 return true; 706 } 707 708 // Otherwise, TI's block must correspond to some matched value. Find out 709 // which value (or set of values) this is. 710 ConstantInt *TIV = 0; 711 BasicBlock *TIBB = TI->getParent(); 712 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 713 if (PredCases[i].Dest == TIBB) { 714 if (TIV != 0) 715 return false; // Cannot handle multiple values coming to this block. 716 TIV = PredCases[i].Value; 717 } 718 assert(TIV && "No edge from pred to succ?"); 719 720 // Okay, we found the one constant that our value can be if we get into TI's 721 // BB. Find out which successor will unconditionally be branched to. 722 BasicBlock *TheRealDest = 0; 723 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) 724 if (ThisCases[i].Value == TIV) { 725 TheRealDest = ThisCases[i].Dest; 726 break; 727 } 728 729 // If not handled by any explicit cases, it is handled by the default case. 730 if (TheRealDest == 0) TheRealDest = ThisDef; 731 732 // Remove PHI node entries for dead edges. 733 BasicBlock *CheckEdge = TheRealDest; 734 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI) 735 if (*SI != CheckEdge) 736 (*SI)->removePredecessor(TIBB); 737 else 738 CheckEdge = 0; 739 740 // Insert the new branch. 741 Instruction *NI = Builder.CreateBr(TheRealDest); 742 (void) NI; 743 744 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() 745 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); 746 747 EraseTerminatorInstAndDCECond(TI); 748 return true; 749} 750 751namespace { 752 /// ConstantIntOrdering - This class implements a stable ordering of constant 753 /// integers that does not depend on their address. This is important for 754 /// applications that sort ConstantInt's to ensure uniqueness. 755 struct ConstantIntOrdering { 756 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { 757 return LHS->getValue().ult(RHS->getValue()); 758 } 759 }; 760} 761 762static int ConstantIntSortPredicate(const void *P1, const void *P2) { 763 const ConstantInt *LHS = *(const ConstantInt*const*)P1; 764 const ConstantInt *RHS = *(const ConstantInt*const*)P2; 765 if (LHS->getValue().ult(RHS->getValue())) 766 return 1; 767 if (LHS->getValue() == RHS->getValue()) 768 return 0; 769 return -1; 770} 771 772static inline bool HasBranchWeights(const Instruction* I) { 773 MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof); 774 if (ProfMD && ProfMD->getOperand(0)) 775 if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0))) 776 return MDS->getString().equals("branch_weights"); 777 778 return false; 779} 780 781/// Get Weights of a given TerminatorInst, the default weight is at the front 782/// of the vector. If TI is a conditional eq, we need to swap the branch-weight 783/// metadata. 784static void GetBranchWeights(TerminatorInst *TI, 785 SmallVectorImpl<uint64_t> &Weights) { 786 MDNode* MD = TI->getMetadata(LLVMContext::MD_prof); 787 assert(MD); 788 for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) { 789 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i)); 790 assert(CI); 791 Weights.push_back(CI->getValue().getZExtValue()); 792 } 793 794 // If TI is a conditional eq, the default case is the false case, 795 // and the corresponding branch-weight data is at index 2. We swap the 796 // default weight to be the first entry. 797 if (BranchInst* BI = dyn_cast<BranchInst>(TI)) { 798 assert(Weights.size() == 2); 799 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); 800 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 801 std::swap(Weights.front(), Weights.back()); 802 } 803} 804 805/// Sees if any of the weights are too big for a uint32_t, and halves all the 806/// weights if any are. 807static void FitWeights(MutableArrayRef<uint64_t> Weights) { 808 bool Halve = false; 809 for (unsigned i = 0; i < Weights.size(); ++i) 810 if (Weights[i] > UINT_MAX) { 811 Halve = true; 812 break; 813 } 814 815 if (! Halve) 816 return; 817 818 for (unsigned i = 0; i < Weights.size(); ++i) 819 Weights[i] /= 2; 820} 821 822/// FoldValueComparisonIntoPredecessors - The specified terminator is a value 823/// equality comparison instruction (either a switch or a branch on "X == c"). 824/// See if any of the predecessors of the terminator block are value comparisons 825/// on the same value. If so, and if safe to do so, fold them together. 826bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI, 827 IRBuilder<> &Builder) { 828 BasicBlock *BB = TI->getParent(); 829 Value *CV = isValueEqualityComparison(TI); // CondVal 830 assert(CV && "Not a comparison?"); 831 bool Changed = false; 832 833 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); 834 while (!Preds.empty()) { 835 BasicBlock *Pred = Preds.pop_back_val(); 836 837 // See if the predecessor is a comparison with the same value. 838 TerminatorInst *PTI = Pred->getTerminator(); 839 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal 840 841 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) { 842 // Figure out which 'cases' to copy from SI to PSI. 843 std::vector<ValueEqualityComparisonCase> BBCases; 844 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); 845 846 std::vector<ValueEqualityComparisonCase> PredCases; 847 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); 848 849 // Based on whether the default edge from PTI goes to BB or not, fill in 850 // PredCases and PredDefault with the new switch cases we would like to 851 // build. 852 SmallVector<BasicBlock*, 8> NewSuccessors; 853 854 // Update the branch weight metadata along the way 855 SmallVector<uint64_t, 8> Weights; 856 bool PredHasWeights = HasBranchWeights(PTI); 857 bool SuccHasWeights = HasBranchWeights(TI); 858 859 if (PredHasWeights) { 860 GetBranchWeights(PTI, Weights); 861 // branch-weight metadata is inconsistent here. 862 if (Weights.size() != 1 + PredCases.size()) 863 PredHasWeights = SuccHasWeights = false; 864 } else if (SuccHasWeights) 865 // If there are no predecessor weights but there are successor weights, 866 // populate Weights with 1, which will later be scaled to the sum of 867 // successor's weights 868 Weights.assign(1 + PredCases.size(), 1); 869 870 SmallVector<uint64_t, 8> SuccWeights; 871 if (SuccHasWeights) { 872 GetBranchWeights(TI, SuccWeights); 873 // branch-weight metadata is inconsistent here. 874 if (SuccWeights.size() != 1 + BBCases.size()) 875 PredHasWeights = SuccHasWeights = false; 876 } else if (PredHasWeights) 877 SuccWeights.assign(1 + BBCases.size(), 1); 878 879 if (PredDefault == BB) { 880 // If this is the default destination from PTI, only the edges in TI 881 // that don't occur in PTI, or that branch to BB will be activated. 882 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 883 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 884 if (PredCases[i].Dest != BB) 885 PTIHandled.insert(PredCases[i].Value); 886 else { 887 // The default destination is BB, we don't need explicit targets. 888 std::swap(PredCases[i], PredCases.back()); 889 890 if (PredHasWeights || SuccHasWeights) { 891 // Increase weight for the default case. 892 Weights[0] += Weights[i+1]; 893 std::swap(Weights[i+1], Weights.back()); 894 Weights.pop_back(); 895 } 896 897 PredCases.pop_back(); 898 --i; --e; 899 } 900 901 // Reconstruct the new switch statement we will be building. 902 if (PredDefault != BBDefault) { 903 PredDefault->removePredecessor(Pred); 904 PredDefault = BBDefault; 905 NewSuccessors.push_back(BBDefault); 906 } 907 908 unsigned CasesFromPred = Weights.size(); 909 uint64_t ValidTotalSuccWeight = 0; 910 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 911 if (!PTIHandled.count(BBCases[i].Value) && 912 BBCases[i].Dest != BBDefault) { 913 PredCases.push_back(BBCases[i]); 914 NewSuccessors.push_back(BBCases[i].Dest); 915 if (SuccHasWeights || PredHasWeights) { 916 // The default weight is at index 0, so weight for the ith case 917 // should be at index i+1. Scale the cases from successor by 918 // PredDefaultWeight (Weights[0]). 919 Weights.push_back(Weights[0] * SuccWeights[i+1]); 920 ValidTotalSuccWeight += SuccWeights[i+1]; 921 } 922 } 923 924 if (SuccHasWeights || PredHasWeights) { 925 ValidTotalSuccWeight += SuccWeights[0]; 926 // Scale the cases from predecessor by ValidTotalSuccWeight. 927 for (unsigned i = 1; i < CasesFromPred; ++i) 928 Weights[i] *= ValidTotalSuccWeight; 929 // Scale the default weight by SuccDefaultWeight (SuccWeights[0]). 930 Weights[0] *= SuccWeights[0]; 931 } 932 } else { 933 // If this is not the default destination from PSI, only the edges 934 // in SI that occur in PSI with a destination of BB will be 935 // activated. 936 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled; 937 std::map<ConstantInt*, uint64_t> WeightsForHandled; 938 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 939 if (PredCases[i].Dest == BB) { 940 PTIHandled.insert(PredCases[i].Value); 941 942 if (PredHasWeights || SuccHasWeights) { 943 WeightsForHandled[PredCases[i].Value] = Weights[i+1]; 944 std::swap(Weights[i+1], Weights.back()); 945 Weights.pop_back(); 946 } 947 948 std::swap(PredCases[i], PredCases.back()); 949 PredCases.pop_back(); 950 --i; --e; 951 } 952 953 // Okay, now we know which constants were sent to BB from the 954 // predecessor. Figure out where they will all go now. 955 for (unsigned i = 0, e = BBCases.size(); i != e; ++i) 956 if (PTIHandled.count(BBCases[i].Value)) { 957 // If this is one we are capable of getting... 958 if (PredHasWeights || SuccHasWeights) 959 Weights.push_back(WeightsForHandled[BBCases[i].Value]); 960 PredCases.push_back(BBCases[i]); 961 NewSuccessors.push_back(BBCases[i].Dest); 962 PTIHandled.erase(BBCases[i].Value);// This constant is taken care of 963 } 964 965 // If there are any constants vectored to BB that TI doesn't handle, 966 // they must go to the default destination of TI. 967 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I = 968 PTIHandled.begin(), 969 E = PTIHandled.end(); I != E; ++I) { 970 if (PredHasWeights || SuccHasWeights) 971 Weights.push_back(WeightsForHandled[*I]); 972 PredCases.push_back(ValueEqualityComparisonCase(*I, BBDefault)); 973 NewSuccessors.push_back(BBDefault); 974 } 975 } 976 977 // Okay, at this point, we know which new successor Pred will get. Make 978 // sure we update the number of entries in the PHI nodes for these 979 // successors. 980 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i) 981 AddPredecessorToBlock(NewSuccessors[i], Pred, BB); 982 983 Builder.SetInsertPoint(PTI); 984 // Convert pointer to int before we switch. 985 if (CV->getType()->isPointerTy()) { 986 assert(TD && "Cannot switch on pointer without DataLayout"); 987 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()), 988 "magicptr"); 989 } 990 991 // Now that the successors are updated, create the new Switch instruction. 992 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault, 993 PredCases.size()); 994 NewSI->setDebugLoc(PTI->getDebugLoc()); 995 for (unsigned i = 0, e = PredCases.size(); i != e; ++i) 996 NewSI->addCase(PredCases[i].Value, PredCases[i].Dest); 997 998 if (PredHasWeights || SuccHasWeights) { 999 // Halve the weights if any of them cannot fit in an uint32_t 1000 FitWeights(Weights); 1001 1002 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end()); 1003 1004 NewSI->setMetadata(LLVMContext::MD_prof, 1005 MDBuilder(BB->getContext()). 1006 createBranchWeights(MDWeights)); 1007 } 1008 1009 EraseTerminatorInstAndDCECond(PTI); 1010 1011 // Okay, last check. If BB is still a successor of PSI, then we must 1012 // have an infinite loop case. If so, add an infinitely looping block 1013 // to handle the case to preserve the behavior of the code. 1014 BasicBlock *InfLoopBlock = 0; 1015 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) 1016 if (NewSI->getSuccessor(i) == BB) { 1017 if (InfLoopBlock == 0) { 1018 // Insert it at the end of the function, because it's either code, 1019 // or it won't matter if it's hot. :) 1020 InfLoopBlock = BasicBlock::Create(BB->getContext(), 1021 "infloop", BB->getParent()); 1022 BranchInst::Create(InfLoopBlock, InfLoopBlock); 1023 } 1024 NewSI->setSuccessor(i, InfLoopBlock); 1025 } 1026 1027 Changed = true; 1028 } 1029 } 1030 return Changed; 1031} 1032 1033// isSafeToHoistInvoke - If we would need to insert a select that uses the 1034// value of this invoke (comments in HoistThenElseCodeToIf explain why we 1035// would need to do this), we can't hoist the invoke, as there is nowhere 1036// to put the select in this case. 1037static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2, 1038 Instruction *I1, Instruction *I2) { 1039 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 1040 PHINode *PN; 1041 for (BasicBlock::iterator BBI = SI->begin(); 1042 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 1043 Value *BB1V = PN->getIncomingValueForBlock(BB1); 1044 Value *BB2V = PN->getIncomingValueForBlock(BB2); 1045 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) { 1046 return false; 1047 } 1048 } 1049 } 1050 return true; 1051} 1052 1053/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and 1054/// BB2, hoist any common code in the two blocks up into the branch block. The 1055/// caller of this function guarantees that BI's block dominates BB1 and BB2. 1056static bool HoistThenElseCodeToIf(BranchInst *BI) { 1057 // This does very trivial matching, with limited scanning, to find identical 1058 // instructions in the two blocks. In particular, we don't want to get into 1059 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As 1060 // such, we currently just scan for obviously identical instructions in an 1061 // identical order. 1062 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. 1063 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination 1064 1065 BasicBlock::iterator BB1_Itr = BB1->begin(); 1066 BasicBlock::iterator BB2_Itr = BB2->begin(); 1067 1068 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++; 1069 // Skip debug info if it is not identical. 1070 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); 1071 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); 1072 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { 1073 while (isa<DbgInfoIntrinsic>(I1)) 1074 I1 = BB1_Itr++; 1075 while (isa<DbgInfoIntrinsic>(I2)) 1076 I2 = BB2_Itr++; 1077 } 1078 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) || 1079 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))) 1080 return false; 1081 1082 // If we get here, we can hoist at least one instruction. 1083 BasicBlock *BIParent = BI->getParent(); 1084 1085 do { 1086 // If we are hoisting the terminator instruction, don't move one (making a 1087 // broken BB), instead clone it, and remove BI. 1088 if (isa<TerminatorInst>(I1)) 1089 goto HoistTerminator; 1090 1091 // For a normal instruction, we just move one to right before the branch, 1092 // then replace all uses of the other with the first. Finally, we remove 1093 // the now redundant second instruction. 1094 BIParent->getInstList().splice(BI, BB1->getInstList(), I1); 1095 if (!I2->use_empty()) 1096 I2->replaceAllUsesWith(I1); 1097 I1->intersectOptionalDataWith(I2); 1098 I2->eraseFromParent(); 1099 1100 I1 = BB1_Itr++; 1101 I2 = BB2_Itr++; 1102 // Skip debug info if it is not identical. 1103 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); 1104 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); 1105 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { 1106 while (isa<DbgInfoIntrinsic>(I1)) 1107 I1 = BB1_Itr++; 1108 while (isa<DbgInfoIntrinsic>(I2)) 1109 I2 = BB2_Itr++; 1110 } 1111 } while (I1->isIdenticalToWhenDefined(I2)); 1112 1113 return true; 1114 1115HoistTerminator: 1116 // It may not be possible to hoist an invoke. 1117 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) 1118 return true; 1119 1120 // Okay, it is safe to hoist the terminator. 1121 Instruction *NT = I1->clone(); 1122 BIParent->getInstList().insert(BI, NT); 1123 if (!NT->getType()->isVoidTy()) { 1124 I1->replaceAllUsesWith(NT); 1125 I2->replaceAllUsesWith(NT); 1126 NT->takeName(I1); 1127 } 1128 1129 IRBuilder<true, NoFolder> Builder(NT); 1130 // Hoisting one of the terminators from our successor is a great thing. 1131 // Unfortunately, the successors of the if/else blocks may have PHI nodes in 1132 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI 1133 // nodes, so we insert select instruction to compute the final result. 1134 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects; 1135 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { 1136 PHINode *PN; 1137 for (BasicBlock::iterator BBI = SI->begin(); 1138 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 1139 Value *BB1V = PN->getIncomingValueForBlock(BB1); 1140 Value *BB2V = PN->getIncomingValueForBlock(BB2); 1141 if (BB1V == BB2V) continue; 1142 1143 // These values do not agree. Insert a select instruction before NT 1144 // that determines the right value. 1145 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; 1146 if (SI == 0) 1147 SI = cast<SelectInst> 1148 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V, 1149 BB1V->getName()+"."+BB2V->getName())); 1150 1151 // Make the PHI node use the select for all incoming values for BB1/BB2 1152 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 1153 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2) 1154 PN->setIncomingValue(i, SI); 1155 } 1156 } 1157 1158 // Update any PHI nodes in our new successors. 1159 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) 1160 AddPredecessorToBlock(*SI, BIParent, BB1); 1161 1162 EraseTerminatorInstAndDCECond(BI); 1163 return true; 1164} 1165 1166/// SinkThenElseCodeToEnd - Given an unconditional branch that goes to BBEnd, 1167/// check whether BBEnd has only two predecessors and the other predecessor 1168/// ends with an unconditional branch. If it is true, sink any common code 1169/// in the two predecessors to BBEnd. 1170static bool SinkThenElseCodeToEnd(BranchInst *BI1) { 1171 assert(BI1->isUnconditional()); 1172 BasicBlock *BB1 = BI1->getParent(); 1173 BasicBlock *BBEnd = BI1->getSuccessor(0); 1174 1175 // Check that BBEnd has two predecessors and the other predecessor ends with 1176 // an unconditional branch. 1177 pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd); 1178 BasicBlock *Pred0 = *PI++; 1179 if (PI == PE) // Only one predecessor. 1180 return false; 1181 BasicBlock *Pred1 = *PI++; 1182 if (PI != PE) // More than two predecessors. 1183 return false; 1184 BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0; 1185 BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator()); 1186 if (!BI2 || !BI2->isUnconditional()) 1187 return false; 1188 1189 // Gather the PHI nodes in BBEnd. 1190 std::map<Value*, std::pair<Value*, PHINode*> > MapValueFromBB1ToBB2; 1191 Instruction *FirstNonPhiInBBEnd = 0; 1192 for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end(); 1193 I != E; ++I) { 1194 if (PHINode *PN = dyn_cast<PHINode>(I)) { 1195 Value *BB1V = PN->getIncomingValueForBlock(BB1); 1196 Value *BB2V = PN->getIncomingValueForBlock(BB2); 1197 MapValueFromBB1ToBB2[BB1V] = std::make_pair(BB2V, PN); 1198 } else { 1199 FirstNonPhiInBBEnd = &*I; 1200 break; 1201 } 1202 } 1203 if (!FirstNonPhiInBBEnd) 1204 return false; 1205 1206 1207 // This does very trivial matching, with limited scanning, to find identical 1208 // instructions in the two blocks. We scan backward for obviously identical 1209 // instructions in an identical order. 1210 BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(), 1211 RE1 = BB1->getInstList().rend(), RI2 = BB2->getInstList().rbegin(), 1212 RE2 = BB2->getInstList().rend(); 1213 // Skip debug info. 1214 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1; 1215 if (RI1 == RE1) 1216 return false; 1217 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2; 1218 if (RI2 == RE2) 1219 return false; 1220 // Skip the unconditional branches. 1221 ++RI1; 1222 ++RI2; 1223 1224 bool Changed = false; 1225 while (RI1 != RE1 && RI2 != RE2) { 1226 // Skip debug info. 1227 while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1)) ++RI1; 1228 if (RI1 == RE1) 1229 return Changed; 1230 while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2)) ++RI2; 1231 if (RI2 == RE2) 1232 return Changed; 1233 1234 Instruction *I1 = &*RI1, *I2 = &*RI2; 1235 // I1 and I2 should have a single use in the same PHI node, and they 1236 // perform the same operation. 1237 // Cannot move control-flow-involving, volatile loads, vaarg, etc. 1238 if (isa<PHINode>(I1) || isa<PHINode>(I2) || 1239 isa<TerminatorInst>(I1) || isa<TerminatorInst>(I2) || 1240 isa<LandingPadInst>(I1) || isa<LandingPadInst>(I2) || 1241 isa<AllocaInst>(I1) || isa<AllocaInst>(I2) || 1242 I1->mayHaveSideEffects() || I2->mayHaveSideEffects() || 1243 I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() || 1244 !I1->hasOneUse() || !I2->hasOneUse() || 1245 MapValueFromBB1ToBB2.find(I1) == MapValueFromBB1ToBB2.end() || 1246 MapValueFromBB1ToBB2[I1].first != I2) 1247 return Changed; 1248 1249 // Check whether we should swap the operands of ICmpInst. 1250 ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2); 1251 bool SwapOpnds = false; 1252 if (ICmp1 && ICmp2 && 1253 ICmp1->getOperand(0) != ICmp2->getOperand(0) && 1254 ICmp1->getOperand(1) != ICmp2->getOperand(1) && 1255 (ICmp1->getOperand(0) == ICmp2->getOperand(1) || 1256 ICmp1->getOperand(1) == ICmp2->getOperand(0))) { 1257 ICmp2->swapOperands(); 1258 SwapOpnds = true; 1259 } 1260 if (!I1->isSameOperationAs(I2)) { 1261 if (SwapOpnds) 1262 ICmp2->swapOperands(); 1263 return Changed; 1264 } 1265 1266 // The operands should be either the same or they need to be generated 1267 // with a PHI node after sinking. We only handle the case where there is 1268 // a single pair of different operands. 1269 Value *DifferentOp1 = 0, *DifferentOp2 = 0; 1270 unsigned Op1Idx = 0; 1271 for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) { 1272 if (I1->getOperand(I) == I2->getOperand(I)) 1273 continue; 1274 // Early exit if we have more-than one pair of different operands or 1275 // the different operand is already in MapValueFromBB1ToBB2. 1276 // Early exit if we need a PHI node to replace a constant. 1277 if (DifferentOp1 || 1278 MapValueFromBB1ToBB2.find(I1->getOperand(I)) != 1279 MapValueFromBB1ToBB2.end() || 1280 isa<Constant>(I1->getOperand(I)) || 1281 isa<Constant>(I2->getOperand(I))) { 1282 // If we can't sink the instructions, undo the swapping. 1283 if (SwapOpnds) 1284 ICmp2->swapOperands(); 1285 return Changed; 1286 } 1287 DifferentOp1 = I1->getOperand(I); 1288 Op1Idx = I; 1289 DifferentOp2 = I2->getOperand(I); 1290 } 1291 1292 // We insert the pair of different operands to MapValueFromBB1ToBB2 and 1293 // remove (I1, I2) from MapValueFromBB1ToBB2. 1294 if (DifferentOp1) { 1295 PHINode *NewPN = PHINode::Create(DifferentOp1->getType(), 2, 1296 DifferentOp1->getName() + ".sink", 1297 BBEnd->begin()); 1298 MapValueFromBB1ToBB2[DifferentOp1] = std::make_pair(DifferentOp2, NewPN); 1299 // I1 should use NewPN instead of DifferentOp1. 1300 I1->setOperand(Op1Idx, NewPN); 1301 NewPN->addIncoming(DifferentOp1, BB1); 1302 NewPN->addIncoming(DifferentOp2, BB2); 1303 DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";); 1304 } 1305 PHINode *OldPN = MapValueFromBB1ToBB2[I1].second; 1306 MapValueFromBB1ToBB2.erase(I1); 1307 1308 DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n";); 1309 DEBUG(dbgs() << " " << *I2 << "\n";); 1310 // We need to update RE1 and RE2 if we are going to sink the first 1311 // instruction in the basic block down. 1312 bool UpdateRE1 = (I1 == BB1->begin()), UpdateRE2 = (I2 == BB2->begin()); 1313 // Sink the instruction. 1314 BBEnd->getInstList().splice(FirstNonPhiInBBEnd, BB1->getInstList(), I1); 1315 if (!OldPN->use_empty()) 1316 OldPN->replaceAllUsesWith(I1); 1317 OldPN->eraseFromParent(); 1318 1319 if (!I2->use_empty()) 1320 I2->replaceAllUsesWith(I1); 1321 I1->intersectOptionalDataWith(I2); 1322 I2->eraseFromParent(); 1323 1324 if (UpdateRE1) 1325 RE1 = BB1->getInstList().rend(); 1326 if (UpdateRE2) 1327 RE2 = BB2->getInstList().rend(); 1328 FirstNonPhiInBBEnd = I1; 1329 NumSinkCommons++; 1330 Changed = true; 1331 } 1332 return Changed; 1333} 1334 1335/// \brief Speculate a conditional basic block flattening the CFG. 1336/// 1337/// Note that this is a very risky transform currently. Speculating 1338/// instructions like this is most often not desirable. Instead, there is an MI 1339/// pass which can do it with full awareness of the resource constraints. 1340/// However, some cases are "obvious" and we should do directly. An example of 1341/// this is speculating a single, reasonably cheap instruction. 1342/// 1343/// There is only one distinct advantage to flattening the CFG at the IR level: 1344/// it makes very common but simplistic optimizations such as are common in 1345/// instcombine and the DAG combiner more powerful by removing CFG edges and 1346/// modeling their effects with easier to reason about SSA value graphs. 1347/// 1348/// 1349/// An illustration of this transform is turning this IR: 1350/// \code 1351/// BB: 1352/// %cmp = icmp ult %x, %y 1353/// br i1 %cmp, label %EndBB, label %ThenBB 1354/// ThenBB: 1355/// %sub = sub %x, %y 1356/// br label BB2 1357/// EndBB: 1358/// %phi = phi [ %sub, %ThenBB ], [ 0, %EndBB ] 1359/// ... 1360/// \endcode 1361/// 1362/// Into this IR: 1363/// \code 1364/// BB: 1365/// %cmp = icmp ult %x, %y 1366/// %sub = sub %x, %y 1367/// %cond = select i1 %cmp, 0, %sub 1368/// ... 1369/// \endcode 1370/// 1371/// \returns true if the conditional block is removed. 1372static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) { 1373 // Be conservative for now. FP select instruction can often be expensive. 1374 Value *BrCond = BI->getCondition(); 1375 if (isa<FCmpInst>(BrCond)) 1376 return false; 1377 1378 // Only speculatively execution a single instruction (not counting the 1379 // terminator) for now. 1380 Instruction *HInst = NULL; 1381 Instruction *Term = BB1->getTerminator(); 1382 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); 1383 BBI != BBE; ++BBI) { 1384 Instruction *I = BBI; 1385 // Skip debug info. 1386 if (isa<DbgInfoIntrinsic>(I)) continue; 1387 if (I == Term) break; 1388 1389 if (HInst) 1390 return false; 1391 HInst = I; 1392 } 1393 1394 BasicBlock *BIParent = BI->getParent(); 1395 1396 // Check the instruction to be hoisted, if there is one. 1397 if (HInst) { 1398 // Don't hoist the instruction if it's unsafe or expensive. 1399 if (!isSafeToSpeculativelyExecute(HInst)) 1400 return false; 1401 if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold) 1402 return false; 1403 1404 // Do not hoist the instruction if any of its operands are defined but not 1405 // used in this BB. The transformation will prevent the operand from 1406 // being sunk into the use block. 1407 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end(); 1408 i != e; ++i) { 1409 Instruction *OpI = dyn_cast<Instruction>(*i); 1410 if (OpI && OpI->getParent() == BIParent && 1411 !OpI->mayHaveSideEffects() && 1412 !OpI->isUsedInBasicBlock(BIParent)) 1413 return false; 1414 } 1415 } 1416 1417 // If BB1 is actually on the false edge of the conditional branch, remember 1418 // to swap the select operands later. 1419 bool Invert = false; 1420 if (BB1 != BI->getSuccessor(0)) { 1421 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?"); 1422 Invert = true; 1423 } 1424 1425 // Collect interesting PHIs, and scan for hazards. 1426 SmallSetVector<std::pair<Value *, Value *>, 4> PHIs; 1427 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0); 1428 for (BasicBlock::iterator I = BB2->begin(); 1429 PHINode *PN = dyn_cast<PHINode>(I); ++I) { 1430 Value *BB1V = PN->getIncomingValueForBlock(BB1); 1431 Value *BIParentV = PN->getIncomingValueForBlock(BIParent); 1432 1433 // Skip PHIs which are trivial. 1434 if (BB1V == BIParentV) 1435 continue; 1436 1437 // Check for safety. 1438 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) { 1439 // An unfolded ConstantExpr could end up getting expanded into 1440 // Instructions. Don't speculate this and another instruction at 1441 // the same time. 1442 if (HInst) 1443 return false; 1444 if (!isSafeToSpeculativelyExecute(CE)) 1445 return false; 1446 if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold) 1447 return false; 1448 } 1449 1450 // Ok, we may insert a select for this PHI. 1451 PHIs.insert(std::make_pair(BB1V, BIParentV)); 1452 } 1453 1454 // If there are no PHIs to process, bail early. This helps ensure idempotence 1455 // as well. 1456 if (PHIs.empty()) 1457 return false; 1458 1459 // If we get here, we can hoist the instruction and if-convert. 1460 DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";); 1461 1462 // Hoist the instruction. 1463 if (HInst) 1464 BIParent->getInstList().splice(BI, BB1->getInstList(), HInst); 1465 1466 // Insert selects and rewrite the PHI operands. 1467 IRBuilder<true, NoFolder> Builder(BI); 1468 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) { 1469 Value *TrueV = PHIs[i].first; 1470 Value *FalseV = PHIs[i].second; 1471 1472 // Create a select whose true value is the speculatively executed value and 1473 // false value is the previously determined FalseV. 1474 SelectInst *SI; 1475 if (Invert) 1476 SI = cast<SelectInst> 1477 (Builder.CreateSelect(BrCond, FalseV, TrueV, 1478 FalseV->getName() + "." + TrueV->getName())); 1479 else 1480 SI = cast<SelectInst> 1481 (Builder.CreateSelect(BrCond, TrueV, FalseV, 1482 TrueV->getName() + "." + FalseV->getName())); 1483 1484 // Make the PHI node use the select for all incoming values for "then" and 1485 // "if" blocks. 1486 for (BasicBlock::iterator I = BB2->begin(); 1487 PHINode *PN = dyn_cast<PHINode>(I); ++I) { 1488 unsigned BB1I = PN->getBasicBlockIndex(BB1); 1489 unsigned BIParentI = PN->getBasicBlockIndex(BIParent); 1490 Value *BB1V = PN->getIncomingValue(BB1I); 1491 Value *BIParentV = PN->getIncomingValue(BIParentI); 1492 if (TrueV == BB1V && FalseV == BIParentV) { 1493 PN->setIncomingValue(BB1I, SI); 1494 PN->setIncomingValue(BIParentI, SI); 1495 } 1496 } 1497 } 1498 1499 ++NumSpeculations; 1500 return true; 1501} 1502 1503/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch 1504/// across this block. 1505static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) { 1506 BranchInst *BI = cast<BranchInst>(BB->getTerminator()); 1507 unsigned Size = 0; 1508 1509 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1510 if (isa<DbgInfoIntrinsic>(BBI)) 1511 continue; 1512 if (Size > 10) return false; // Don't clone large BB's. 1513 ++Size; 1514 1515 // We can only support instructions that do not define values that are 1516 // live outside of the current basic block. 1517 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 1518 UI != E; ++UI) { 1519 Instruction *U = cast<Instruction>(*UI); 1520 if (U->getParent() != BB || isa<PHINode>(U)) return false; 1521 } 1522 1523 // Looks ok, continue checking. 1524 } 1525 1526 return true; 1527} 1528 1529/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value 1530/// that is defined in the same block as the branch and if any PHI entries are 1531/// constants, thread edges corresponding to that entry to be branches to their 1532/// ultimate destination. 1533static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout *TD) { 1534 BasicBlock *BB = BI->getParent(); 1535 PHINode *PN = dyn_cast<PHINode>(BI->getCondition()); 1536 // NOTE: we currently cannot transform this case if the PHI node is used 1537 // outside of the block. 1538 if (!PN || PN->getParent() != BB || !PN->hasOneUse()) 1539 return false; 1540 1541 // Degenerate case of a single entry PHI. 1542 if (PN->getNumIncomingValues() == 1) { 1543 FoldSingleEntryPHINodes(PN->getParent()); 1544 return true; 1545 } 1546 1547 // Now we know that this block has multiple preds and two succs. 1548 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false; 1549 1550 // Okay, this is a simple enough basic block. See if any phi values are 1551 // constants. 1552 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1553 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i)); 1554 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue; 1555 1556 // Okay, we now know that all edges from PredBB should be revectored to 1557 // branch to RealDest. 1558 BasicBlock *PredBB = PN->getIncomingBlock(i); 1559 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue()); 1560 1561 if (RealDest == BB) continue; // Skip self loops. 1562 // Skip if the predecessor's terminator is an indirect branch. 1563 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue; 1564 1565 // The dest block might have PHI nodes, other predecessors and other 1566 // difficult cases. Instead of being smart about this, just insert a new 1567 // block that jumps to the destination block, effectively splitting 1568 // the edge we are about to create. 1569 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(), 1570 RealDest->getName()+".critedge", 1571 RealDest->getParent(), RealDest); 1572 BranchInst::Create(RealDest, EdgeBB); 1573 1574 // Update PHI nodes. 1575 AddPredecessorToBlock(RealDest, EdgeBB, BB); 1576 1577 // BB may have instructions that are being threaded over. Clone these 1578 // instructions into EdgeBB. We know that there will be no uses of the 1579 // cloned instructions outside of EdgeBB. 1580 BasicBlock::iterator InsertPt = EdgeBB->begin(); 1581 DenseMap<Value*, Value*> TranslateMap; // Track translated values. 1582 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { 1583 if (PHINode *PN = dyn_cast<PHINode>(BBI)) { 1584 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB); 1585 continue; 1586 } 1587 // Clone the instruction. 1588 Instruction *N = BBI->clone(); 1589 if (BBI->hasName()) N->setName(BBI->getName()+".c"); 1590 1591 // Update operands due to translation. 1592 for (User::op_iterator i = N->op_begin(), e = N->op_end(); 1593 i != e; ++i) { 1594 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i); 1595 if (PI != TranslateMap.end()) 1596 *i = PI->second; 1597 } 1598 1599 // Check for trivial simplification. 1600 if (Value *V = SimplifyInstruction(N, TD)) { 1601 TranslateMap[BBI] = V; 1602 delete N; // Instruction folded away, don't need actual inst 1603 } else { 1604 // Insert the new instruction into its new home. 1605 EdgeBB->getInstList().insert(InsertPt, N); 1606 if (!BBI->use_empty()) 1607 TranslateMap[BBI] = N; 1608 } 1609 } 1610 1611 // Loop over all of the edges from PredBB to BB, changing them to branch 1612 // to EdgeBB instead. 1613 TerminatorInst *PredBBTI = PredBB->getTerminator(); 1614 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i) 1615 if (PredBBTI->getSuccessor(i) == BB) { 1616 BB->removePredecessor(PredBB); 1617 PredBBTI->setSuccessor(i, EdgeBB); 1618 } 1619 1620 // Recurse, simplifying any other constants. 1621 return FoldCondBranchOnPHI(BI, TD) | true; 1622 } 1623 1624 return false; 1625} 1626 1627/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry 1628/// PHI node, see if we can eliminate it. 1629static bool FoldTwoEntryPHINode(PHINode *PN, const DataLayout *TD) { 1630 // Ok, this is a two entry PHI node. Check to see if this is a simple "if 1631 // statement", which has a very simple dominance structure. Basically, we 1632 // are trying to find the condition that is being branched on, which 1633 // subsequently causes this merge to happen. We really want control 1634 // dependence information for this check, but simplifycfg can't keep it up 1635 // to date, and this catches most of the cases we care about anyway. 1636 BasicBlock *BB = PN->getParent(); 1637 BasicBlock *IfTrue, *IfFalse; 1638 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse); 1639 if (!IfCond || 1640 // Don't bother if the branch will be constant folded trivially. 1641 isa<ConstantInt>(IfCond)) 1642 return false; 1643 1644 // Okay, we found that we can merge this two-entry phi node into a select. 1645 // Doing so would require us to fold *all* two entry phi nodes in this block. 1646 // At some point this becomes non-profitable (particularly if the target 1647 // doesn't support cmov's). Only do this transformation if there are two or 1648 // fewer PHI nodes in this block. 1649 unsigned NumPhis = 0; 1650 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I) 1651 if (NumPhis > 2) 1652 return false; 1653 1654 // Loop over the PHI's seeing if we can promote them all to select 1655 // instructions. While we are at it, keep track of the instructions 1656 // that need to be moved to the dominating block. 1657 SmallPtrSet<Instruction*, 4> AggressiveInsts; 1658 unsigned MaxCostVal0 = PHINodeFoldingThreshold, 1659 MaxCostVal1 = PHINodeFoldingThreshold; 1660 1661 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) { 1662 PHINode *PN = cast<PHINode>(II++); 1663 if (Value *V = SimplifyInstruction(PN, TD)) { 1664 PN->replaceAllUsesWith(V); 1665 PN->eraseFromParent(); 1666 continue; 1667 } 1668 1669 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts, 1670 MaxCostVal0) || 1671 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts, 1672 MaxCostVal1)) 1673 return false; 1674 } 1675 1676 // If we folded the first phi, PN dangles at this point. Refresh it. If 1677 // we ran out of PHIs then we simplified them all. 1678 PN = dyn_cast<PHINode>(BB->begin()); 1679 if (PN == 0) return true; 1680 1681 // Don't fold i1 branches on PHIs which contain binary operators. These can 1682 // often be turned into switches and other things. 1683 if (PN->getType()->isIntegerTy(1) && 1684 (isa<BinaryOperator>(PN->getIncomingValue(0)) || 1685 isa<BinaryOperator>(PN->getIncomingValue(1)) || 1686 isa<BinaryOperator>(IfCond))) 1687 return false; 1688 1689 // If we all PHI nodes are promotable, check to make sure that all 1690 // instructions in the predecessor blocks can be promoted as well. If 1691 // not, we won't be able to get rid of the control flow, so it's not 1692 // worth promoting to select instructions. 1693 BasicBlock *DomBlock = 0; 1694 BasicBlock *IfBlock1 = PN->getIncomingBlock(0); 1695 BasicBlock *IfBlock2 = PN->getIncomingBlock(1); 1696 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) { 1697 IfBlock1 = 0; 1698 } else { 1699 DomBlock = *pred_begin(IfBlock1); 1700 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I) 1701 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1702 // This is not an aggressive instruction that we can promote. 1703 // Because of this, we won't be able to get rid of the control 1704 // flow, so the xform is not worth it. 1705 return false; 1706 } 1707 } 1708 1709 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) { 1710 IfBlock2 = 0; 1711 } else { 1712 DomBlock = *pred_begin(IfBlock2); 1713 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I) 1714 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) { 1715 // This is not an aggressive instruction that we can promote. 1716 // Because of this, we won't be able to get rid of the control 1717 // flow, so the xform is not worth it. 1718 return false; 1719 } 1720 } 1721 1722 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: " 1723 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"); 1724 1725 // If we can still promote the PHI nodes after this gauntlet of tests, 1726 // do all of the PHI's now. 1727 Instruction *InsertPt = DomBlock->getTerminator(); 1728 IRBuilder<true, NoFolder> Builder(InsertPt); 1729 1730 // Move all 'aggressive' instructions, which are defined in the 1731 // conditional parts of the if's up to the dominating block. 1732 if (IfBlock1) 1733 DomBlock->getInstList().splice(InsertPt, 1734 IfBlock1->getInstList(), IfBlock1->begin(), 1735 IfBlock1->getTerminator()); 1736 if (IfBlock2) 1737 DomBlock->getInstList().splice(InsertPt, 1738 IfBlock2->getInstList(), IfBlock2->begin(), 1739 IfBlock2->getTerminator()); 1740 1741 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 1742 // Change the PHI node into a select instruction. 1743 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); 1744 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); 1745 1746 SelectInst *NV = 1747 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, "")); 1748 PN->replaceAllUsesWith(NV); 1749 NV->takeName(PN); 1750 PN->eraseFromParent(); 1751 } 1752 1753 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement 1754 // has been flattened. Change DomBlock to jump directly to our new block to 1755 // avoid other simplifycfg's kicking in on the diamond. 1756 TerminatorInst *OldTI = DomBlock->getTerminator(); 1757 Builder.SetInsertPoint(OldTI); 1758 Builder.CreateBr(BB); 1759 OldTI->eraseFromParent(); 1760 return true; 1761} 1762 1763/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes 1764/// to two returning blocks, try to merge them together into one return, 1765/// introducing a select if the return values disagree. 1766static bool SimplifyCondBranchToTwoReturns(BranchInst *BI, 1767 IRBuilder<> &Builder) { 1768 assert(BI->isConditional() && "Must be a conditional branch"); 1769 BasicBlock *TrueSucc = BI->getSuccessor(0); 1770 BasicBlock *FalseSucc = BI->getSuccessor(1); 1771 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator()); 1772 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator()); 1773 1774 // Check to ensure both blocks are empty (just a return) or optionally empty 1775 // with PHI nodes. If there are other instructions, merging would cause extra 1776 // computation on one path or the other. 1777 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator()) 1778 return false; 1779 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator()) 1780 return false; 1781 1782 Builder.SetInsertPoint(BI); 1783 // Okay, we found a branch that is going to two return nodes. If 1784 // there is no return value for this function, just change the 1785 // branch into a return. 1786 if (FalseRet->getNumOperands() == 0) { 1787 TrueSucc->removePredecessor(BI->getParent()); 1788 FalseSucc->removePredecessor(BI->getParent()); 1789 Builder.CreateRetVoid(); 1790 EraseTerminatorInstAndDCECond(BI); 1791 return true; 1792 } 1793 1794 // Otherwise, figure out what the true and false return values are 1795 // so we can insert a new select instruction. 1796 Value *TrueValue = TrueRet->getReturnValue(); 1797 Value *FalseValue = FalseRet->getReturnValue(); 1798 1799 // Unwrap any PHI nodes in the return blocks. 1800 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue)) 1801 if (TVPN->getParent() == TrueSucc) 1802 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); 1803 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue)) 1804 if (FVPN->getParent() == FalseSucc) 1805 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); 1806 1807 // In order for this transformation to be safe, we must be able to 1808 // unconditionally execute both operands to the return. This is 1809 // normally the case, but we could have a potentially-trapping 1810 // constant expression that prevents this transformation from being 1811 // safe. 1812 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue)) 1813 if (TCV->canTrap()) 1814 return false; 1815 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue)) 1816 if (FCV->canTrap()) 1817 return false; 1818 1819 // Okay, we collected all the mapped values and checked them for sanity, and 1820 // defined to really do this transformation. First, update the CFG. 1821 TrueSucc->removePredecessor(BI->getParent()); 1822 FalseSucc->removePredecessor(BI->getParent()); 1823 1824 // Insert select instructions where needed. 1825 Value *BrCond = BI->getCondition(); 1826 if (TrueValue) { 1827 // Insert a select if the results differ. 1828 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) { 1829 } else if (isa<UndefValue>(TrueValue)) { 1830 TrueValue = FalseValue; 1831 } else { 1832 TrueValue = Builder.CreateSelect(BrCond, TrueValue, 1833 FalseValue, "retval"); 1834 } 1835 } 1836 1837 Value *RI = !TrueValue ? 1838 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue); 1839 1840 (void) RI; 1841 1842 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" 1843 << "\n " << *BI << "NewRet = " << *RI 1844 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc); 1845 1846 EraseTerminatorInstAndDCECond(BI); 1847 1848 return true; 1849} 1850 1851/// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the 1852/// probabilities of the branch taking each edge. Fills in the two APInt 1853/// parameters and return true, or returns false if no or invalid metadata was 1854/// found. 1855static bool ExtractBranchMetadata(BranchInst *BI, 1856 uint64_t &ProbTrue, uint64_t &ProbFalse) { 1857 assert(BI->isConditional() && 1858 "Looking for probabilities on unconditional branch?"); 1859 MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof); 1860 if (!ProfileData || ProfileData->getNumOperands() != 3) return false; 1861 ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1)); 1862 ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2)); 1863 if (!CITrue || !CIFalse) return false; 1864 ProbTrue = CITrue->getValue().getZExtValue(); 1865 ProbFalse = CIFalse->getValue().getZExtValue(); 1866 return true; 1867} 1868 1869/// checkCSEInPredecessor - Return true if the given instruction is available 1870/// in its predecessor block. If yes, the instruction will be removed. 1871/// 1872static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) { 1873 if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst)) 1874 return false; 1875 for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) { 1876 Instruction *PBI = &*I; 1877 // Check whether Inst and PBI generate the same value. 1878 if (Inst->isIdenticalTo(PBI)) { 1879 Inst->replaceAllUsesWith(PBI); 1880 Inst->eraseFromParent(); 1881 return true; 1882 } 1883 } 1884 return false; 1885} 1886 1887/// FoldBranchToCommonDest - If this basic block is simple enough, and if a 1888/// predecessor branches to us and one of our successors, fold the block into 1889/// the predecessor and use logical operations to pick the right destination. 1890bool llvm::FoldBranchToCommonDest(BranchInst *BI) { 1891 BasicBlock *BB = BI->getParent(); 1892 1893 Instruction *Cond = 0; 1894 if (BI->isConditional()) 1895 Cond = dyn_cast<Instruction>(BI->getCondition()); 1896 else { 1897 // For unconditional branch, check for a simple CFG pattern, where 1898 // BB has a single predecessor and BB's successor is also its predecessor's 1899 // successor. If such pattern exisits, check for CSE between BB and its 1900 // predecessor. 1901 if (BasicBlock *PB = BB->getSinglePredecessor()) 1902 if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator())) 1903 if (PBI->isConditional() && 1904 (BI->getSuccessor(0) == PBI->getSuccessor(0) || 1905 BI->getSuccessor(0) == PBI->getSuccessor(1))) { 1906 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); 1907 I != E; ) { 1908 Instruction *Curr = I++; 1909 if (isa<CmpInst>(Curr)) { 1910 Cond = Curr; 1911 break; 1912 } 1913 // Quit if we can't remove this instruction. 1914 if (!checkCSEInPredecessor(Curr, PB)) 1915 return false; 1916 } 1917 } 1918 1919 if (Cond == 0) 1920 return false; 1921 } 1922 1923 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) || 1924 Cond->getParent() != BB || !Cond->hasOneUse()) 1925 return false; 1926 1927 // Only allow this if the condition is a simple instruction that can be 1928 // executed unconditionally. It must be in the same block as the branch, and 1929 // must be at the front of the block. 1930 BasicBlock::iterator FrontIt = BB->front(); 1931 1932 // Ignore dbg intrinsics. 1933 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt; 1934 1935 // Allow a single instruction to be hoisted in addition to the compare 1936 // that feeds the branch. We later ensure that any values that _it_ uses 1937 // were also live in the predecessor, so that we don't unnecessarily create 1938 // register pressure or inhibit out-of-order execution. 1939 Instruction *BonusInst = 0; 1940 if (&*FrontIt != Cond && 1941 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond && 1942 isSafeToSpeculativelyExecute(FrontIt)) { 1943 BonusInst = &*FrontIt; 1944 ++FrontIt; 1945 1946 // Ignore dbg intrinsics. 1947 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt; 1948 } 1949 1950 // Only a single bonus inst is allowed. 1951 if (&*FrontIt != Cond) 1952 return false; 1953 1954 // Make sure the instruction after the condition is the cond branch. 1955 BasicBlock::iterator CondIt = Cond; ++CondIt; 1956 1957 // Ingore dbg intrinsics. 1958 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt; 1959 1960 if (&*CondIt != BI) 1961 return false; 1962 1963 // Cond is known to be a compare or binary operator. Check to make sure that 1964 // neither operand is a potentially-trapping constant expression. 1965 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0))) 1966 if (CE->canTrap()) 1967 return false; 1968 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1))) 1969 if (CE->canTrap()) 1970 return false; 1971 1972 // Finally, don't infinitely unroll conditional loops. 1973 BasicBlock *TrueDest = BI->getSuccessor(0); 1974 BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0; 1975 if (TrueDest == BB || FalseDest == BB) 1976 return false; 1977 1978 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 1979 BasicBlock *PredBlock = *PI; 1980 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); 1981 1982 // Check that we have two conditional branches. If there is a PHI node in 1983 // the common successor, verify that the same value flows in from both 1984 // blocks. 1985 SmallVector<PHINode*, 4> PHIs; 1986 if (PBI == 0 || PBI->isUnconditional() || 1987 (BI->isConditional() && 1988 !SafeToMergeTerminators(BI, PBI)) || 1989 (!BI->isConditional() && 1990 !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs))) 1991 continue; 1992 1993 // Determine if the two branches share a common destination. 1994 Instruction::BinaryOps Opc = Instruction::BinaryOpsEnd; 1995 bool InvertPredCond = false; 1996 1997 if (BI->isConditional()) { 1998 if (PBI->getSuccessor(0) == TrueDest) 1999 Opc = Instruction::Or; 2000 else if (PBI->getSuccessor(1) == FalseDest) 2001 Opc = Instruction::And; 2002 else if (PBI->getSuccessor(0) == FalseDest) 2003 Opc = Instruction::And, InvertPredCond = true; 2004 else if (PBI->getSuccessor(1) == TrueDest) 2005 Opc = Instruction::Or, InvertPredCond = true; 2006 else 2007 continue; 2008 } else { 2009 if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest) 2010 continue; 2011 } 2012 2013 // Ensure that any values used in the bonus instruction are also used 2014 // by the terminator of the predecessor. This means that those values 2015 // must already have been resolved, so we won't be inhibiting the 2016 // out-of-order core by speculating them earlier. 2017 if (BonusInst) { 2018 // Collect the values used by the bonus inst 2019 SmallPtrSet<Value*, 4> UsedValues; 2020 for (Instruction::op_iterator OI = BonusInst->op_begin(), 2021 OE = BonusInst->op_end(); OI != OE; ++OI) { 2022 Value *V = *OI; 2023 if (!isa<Constant>(V)) 2024 UsedValues.insert(V); 2025 } 2026 2027 SmallVector<std::pair<Value*, unsigned>, 4> Worklist; 2028 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0)); 2029 2030 // Walk up to four levels back up the use-def chain of the predecessor's 2031 // terminator to see if all those values were used. The choice of four 2032 // levels is arbitrary, to provide a compile-time-cost bound. 2033 while (!Worklist.empty()) { 2034 std::pair<Value*, unsigned> Pair = Worklist.back(); 2035 Worklist.pop_back(); 2036 2037 if (Pair.second >= 4) continue; 2038 UsedValues.erase(Pair.first); 2039 if (UsedValues.empty()) break; 2040 2041 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) { 2042 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 2043 OI != OE; ++OI) 2044 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1)); 2045 } 2046 } 2047 2048 if (!UsedValues.empty()) return false; 2049 } 2050 2051 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB); 2052 IRBuilder<> Builder(PBI); 2053 2054 // If we need to invert the condition in the pred block to match, do so now. 2055 if (InvertPredCond) { 2056 Value *NewCond = PBI->getCondition(); 2057 2058 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) { 2059 CmpInst *CI = cast<CmpInst>(NewCond); 2060 CI->setPredicate(CI->getInversePredicate()); 2061 } else { 2062 NewCond = Builder.CreateNot(NewCond, 2063 PBI->getCondition()->getName()+".not"); 2064 } 2065 2066 PBI->setCondition(NewCond); 2067 PBI->swapSuccessors(); 2068 } 2069 2070 // If we have a bonus inst, clone it into the predecessor block. 2071 Instruction *NewBonus = 0; 2072 if (BonusInst) { 2073 NewBonus = BonusInst->clone(); 2074 PredBlock->getInstList().insert(PBI, NewBonus); 2075 NewBonus->takeName(BonusInst); 2076 BonusInst->setName(BonusInst->getName()+".old"); 2077 } 2078 2079 // Clone Cond into the predecessor basic block, and or/and the 2080 // two conditions together. 2081 Instruction *New = Cond->clone(); 2082 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus); 2083 PredBlock->getInstList().insert(PBI, New); 2084 New->takeName(Cond); 2085 Cond->setName(New->getName()+".old"); 2086 2087 if (BI->isConditional()) { 2088 Instruction *NewCond = 2089 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(), 2090 New, "or.cond")); 2091 PBI->setCondition(NewCond); 2092 2093 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight; 2094 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight, 2095 PredFalseWeight); 2096 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight, 2097 SuccFalseWeight); 2098 SmallVector<uint64_t, 8> NewWeights; 2099 2100 if (PBI->getSuccessor(0) == BB) { 2101 if (PredHasWeights && SuccHasWeights) { 2102 // PBI: br i1 %x, BB, FalseDest 2103 // BI: br i1 %y, TrueDest, FalseDest 2104 //TrueWeight is TrueWeight for PBI * TrueWeight for BI. 2105 NewWeights.push_back(PredTrueWeight * SuccTrueWeight); 2106 //FalseWeight is FalseWeight for PBI * TotalWeight for BI + 2107 // TrueWeight for PBI * FalseWeight for BI. 2108 // We assume that total weights of a BranchInst can fit into 32 bits. 2109 // Therefore, we will not have overflow using 64-bit arithmetic. 2110 NewWeights.push_back(PredFalseWeight * (SuccFalseWeight + 2111 SuccTrueWeight) + PredTrueWeight * SuccFalseWeight); 2112 } 2113 AddPredecessorToBlock(TrueDest, PredBlock, BB); 2114 PBI->setSuccessor(0, TrueDest); 2115 } 2116 if (PBI->getSuccessor(1) == BB) { 2117 if (PredHasWeights && SuccHasWeights) { 2118 // PBI: br i1 %x, TrueDest, BB 2119 // BI: br i1 %y, TrueDest, FalseDest 2120 //TrueWeight is TrueWeight for PBI * TotalWeight for BI + 2121 // FalseWeight for PBI * TrueWeight for BI. 2122 NewWeights.push_back(PredTrueWeight * (SuccFalseWeight + 2123 SuccTrueWeight) + PredFalseWeight * SuccTrueWeight); 2124 //FalseWeight is FalseWeight for PBI * FalseWeight for BI. 2125 NewWeights.push_back(PredFalseWeight * SuccFalseWeight); 2126 } 2127 AddPredecessorToBlock(FalseDest, PredBlock, BB); 2128 PBI->setSuccessor(1, FalseDest); 2129 } 2130 if (NewWeights.size() == 2) { 2131 // Halve the weights if any of them cannot fit in an uint32_t 2132 FitWeights(NewWeights); 2133 2134 SmallVector<uint32_t, 8> MDWeights(NewWeights.begin(),NewWeights.end()); 2135 PBI->setMetadata(LLVMContext::MD_prof, 2136 MDBuilder(BI->getContext()). 2137 createBranchWeights(MDWeights)); 2138 } else 2139 PBI->setMetadata(LLVMContext::MD_prof, NULL); 2140 } else { 2141 // Update PHI nodes in the common successors. 2142 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) { 2143 ConstantInt *PBI_C = cast<ConstantInt>( 2144 PHIs[i]->getIncomingValueForBlock(PBI->getParent())); 2145 assert(PBI_C->getType()->isIntegerTy(1)); 2146 Instruction *MergedCond = 0; 2147 if (PBI->getSuccessor(0) == TrueDest) { 2148 // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value) 2149 // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value) 2150 // is false: !PBI_Cond and BI_Value 2151 Instruction *NotCond = 2152 cast<Instruction>(Builder.CreateNot(PBI->getCondition(), 2153 "not.cond")); 2154 MergedCond = 2155 cast<Instruction>(Builder.CreateBinOp(Instruction::And, 2156 NotCond, New, 2157 "and.cond")); 2158 if (PBI_C->isOne()) 2159 MergedCond = 2160 cast<Instruction>(Builder.CreateBinOp(Instruction::Or, 2161 PBI->getCondition(), MergedCond, 2162 "or.cond")); 2163 } else { 2164 // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C) 2165 // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond) 2166 // is false: PBI_Cond and BI_Value 2167 MergedCond = 2168 cast<Instruction>(Builder.CreateBinOp(Instruction::And, 2169 PBI->getCondition(), New, 2170 "and.cond")); 2171 if (PBI_C->isOne()) { 2172 Instruction *NotCond = 2173 cast<Instruction>(Builder.CreateNot(PBI->getCondition(), 2174 "not.cond")); 2175 MergedCond = 2176 cast<Instruction>(Builder.CreateBinOp(Instruction::Or, 2177 NotCond, MergedCond, 2178 "or.cond")); 2179 } 2180 } 2181 // Update PHI Node. 2182 PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()), 2183 MergedCond); 2184 } 2185 // Change PBI from Conditional to Unconditional. 2186 BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI); 2187 EraseTerminatorInstAndDCECond(PBI); 2188 PBI = New_PBI; 2189 } 2190 2191 // TODO: If BB is reachable from all paths through PredBlock, then we 2192 // could replace PBI's branch probabilities with BI's. 2193 2194 // Copy any debug value intrinsics into the end of PredBlock. 2195 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 2196 if (isa<DbgInfoIntrinsic>(*I)) 2197 I->clone()->insertBefore(PBI); 2198 2199 return true; 2200 } 2201 return false; 2202} 2203 2204/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a 2205/// predecessor of another block, this function tries to simplify it. We know 2206/// that PBI and BI are both conditional branches, and BI is in one of the 2207/// successor blocks of PBI - PBI branches to BI. 2208static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) { 2209 assert(PBI->isConditional() && BI->isConditional()); 2210 BasicBlock *BB = BI->getParent(); 2211 2212 // If this block ends with a branch instruction, and if there is a 2213 // predecessor that ends on a branch of the same condition, make 2214 // this conditional branch redundant. 2215 if (PBI->getCondition() == BI->getCondition() && 2216 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 2217 // Okay, the outcome of this conditional branch is statically 2218 // knowable. If this block had a single pred, handle specially. 2219 if (BB->getSinglePredecessor()) { 2220 // Turn this into a branch on constant. 2221 bool CondIsTrue = PBI->getSuccessor(0) == BB; 2222 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 2223 CondIsTrue)); 2224 return true; // Nuke the branch on constant. 2225 } 2226 2227 // Otherwise, if there are multiple predecessors, insert a PHI that merges 2228 // in the constant and simplify the block result. Subsequent passes of 2229 // simplifycfg will thread the block. 2230 if (BlockIsSimpleEnoughToThreadThrough(BB)) { 2231 pred_iterator PB = pred_begin(BB), PE = pred_end(BB); 2232 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()), 2233 std::distance(PB, PE), 2234 BI->getCondition()->getName() + ".pr", 2235 BB->begin()); 2236 // Okay, we're going to insert the PHI node. Since PBI is not the only 2237 // predecessor, compute the PHI'd conditional value for all of the preds. 2238 // Any predecessor where the condition is not computable we keep symbolic. 2239 for (pred_iterator PI = PB; PI != PE; ++PI) { 2240 BasicBlock *P = *PI; 2241 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && 2242 PBI != BI && PBI->isConditional() && 2243 PBI->getCondition() == BI->getCondition() && 2244 PBI->getSuccessor(0) != PBI->getSuccessor(1)) { 2245 bool CondIsTrue = PBI->getSuccessor(0) == BB; 2246 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()), 2247 CondIsTrue), P); 2248 } else { 2249 NewPN->addIncoming(BI->getCondition(), P); 2250 } 2251 } 2252 2253 BI->setCondition(NewPN); 2254 return true; 2255 } 2256 } 2257 2258 // If this is a conditional branch in an empty block, and if any 2259 // predecessors is a conditional branch to one of our destinations, 2260 // fold the conditions into logical ops and one cond br. 2261 BasicBlock::iterator BBI = BB->begin(); 2262 // Ignore dbg intrinsics. 2263 while (isa<DbgInfoIntrinsic>(BBI)) 2264 ++BBI; 2265 if (&*BBI != BI) 2266 return false; 2267 2268 2269 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition())) 2270 if (CE->canTrap()) 2271 return false; 2272 2273 int PBIOp, BIOp; 2274 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) 2275 PBIOp = BIOp = 0; 2276 else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) 2277 PBIOp = 0, BIOp = 1; 2278 else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) 2279 PBIOp = 1, BIOp = 0; 2280 else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) 2281 PBIOp = BIOp = 1; 2282 else 2283 return false; 2284 2285 // Check to make sure that the other destination of this branch 2286 // isn't BB itself. If so, this is an infinite loop that will 2287 // keep getting unwound. 2288 if (PBI->getSuccessor(PBIOp) == BB) 2289 return false; 2290 2291 // Do not perform this transformation if it would require 2292 // insertion of a large number of select instructions. For targets 2293 // without predication/cmovs, this is a big pessimization. 2294 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); 2295 2296 unsigned NumPhis = 0; 2297 for (BasicBlock::iterator II = CommonDest->begin(); 2298 isa<PHINode>(II); ++II, ++NumPhis) 2299 if (NumPhis > 2) // Disable this xform. 2300 return false; 2301 2302 // Finally, if everything is ok, fold the branches to logical ops. 2303 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); 2304 2305 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent() 2306 << "AND: " << *BI->getParent()); 2307 2308 2309 // If OtherDest *is* BB, then BB is a basic block with a single conditional 2310 // branch in it, where one edge (OtherDest) goes back to itself but the other 2311 // exits. We don't *know* that the program avoids the infinite loop 2312 // (even though that seems likely). If we do this xform naively, we'll end up 2313 // recursively unpeeling the loop. Since we know that (after the xform is 2314 // done) that the block *is* infinite if reached, we just make it an obviously 2315 // infinite loop with no cond branch. 2316 if (OtherDest == BB) { 2317 // Insert it at the end of the function, because it's either code, 2318 // or it won't matter if it's hot. :) 2319 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(), 2320 "infloop", BB->getParent()); 2321 BranchInst::Create(InfLoopBlock, InfLoopBlock); 2322 OtherDest = InfLoopBlock; 2323 } 2324 2325 DEBUG(dbgs() << *PBI->getParent()->getParent()); 2326 2327 // BI may have other predecessors. Because of this, we leave 2328 // it alone, but modify PBI. 2329 2330 // Make sure we get to CommonDest on True&True directions. 2331 Value *PBICond = PBI->getCondition(); 2332 IRBuilder<true, NoFolder> Builder(PBI); 2333 if (PBIOp) 2334 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not"); 2335 2336 Value *BICond = BI->getCondition(); 2337 if (BIOp) 2338 BICond = Builder.CreateNot(BICond, BICond->getName()+".not"); 2339 2340 // Merge the conditions. 2341 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge"); 2342 2343 // Modify PBI to branch on the new condition to the new dests. 2344 PBI->setCondition(Cond); 2345 PBI->setSuccessor(0, CommonDest); 2346 PBI->setSuccessor(1, OtherDest); 2347 2348 // Update branch weight for PBI. 2349 uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight; 2350 bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight, 2351 PredFalseWeight); 2352 bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight, 2353 SuccFalseWeight); 2354 if (PredHasWeights && SuccHasWeights) { 2355 uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight; 2356 uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight; 2357 uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight; 2358 uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight; 2359 // The weight to CommonDest should be PredCommon * SuccTotal + 2360 // PredOther * SuccCommon. 2361 // The weight to OtherDest should be PredOther * SuccOther. 2362 SmallVector<uint64_t, 2> NewWeights; 2363 NewWeights.push_back(PredCommon * (SuccCommon + SuccOther) + 2364 PredOther * SuccCommon); 2365 NewWeights.push_back(PredOther * SuccOther); 2366 // Halve the weights if any of them cannot fit in an uint32_t 2367 FitWeights(NewWeights); 2368 2369 SmallVector<uint32_t, 2> MDWeights(NewWeights.begin(),NewWeights.end()); 2370 PBI->setMetadata(LLVMContext::MD_prof, 2371 MDBuilder(BI->getContext()). 2372 createBranchWeights(MDWeights)); 2373 } 2374 2375 // OtherDest may have phi nodes. If so, add an entry from PBI's 2376 // block that are identical to the entries for BI's block. 2377 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB); 2378 2379 // We know that the CommonDest already had an edge from PBI to 2380 // it. If it has PHIs though, the PHIs may have different 2381 // entries for BB and PBI's BB. If so, insert a select to make 2382 // them agree. 2383 PHINode *PN; 2384 for (BasicBlock::iterator II = CommonDest->begin(); 2385 (PN = dyn_cast<PHINode>(II)); ++II) { 2386 Value *BIV = PN->getIncomingValueForBlock(BB); 2387 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent()); 2388 Value *PBIV = PN->getIncomingValue(PBBIdx); 2389 if (BIV != PBIV) { 2390 // Insert a select in PBI to pick the right value. 2391 Value *NV = cast<SelectInst> 2392 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux")); 2393 PN->setIncomingValue(PBBIdx, NV); 2394 } 2395 } 2396 2397 DEBUG(dbgs() << "INTO: " << *PBI->getParent()); 2398 DEBUG(dbgs() << *PBI->getParent()->getParent()); 2399 2400 // This basic block is probably dead. We know it has at least 2401 // one fewer predecessor. 2402 return true; 2403} 2404 2405// SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a 2406// branch to TrueBB if Cond is true or to FalseBB if Cond is false. 2407// Takes care of updating the successors and removing the old terminator. 2408// Also makes sure not to introduce new successors by assuming that edges to 2409// non-successor TrueBBs and FalseBBs aren't reachable. 2410static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond, 2411 BasicBlock *TrueBB, BasicBlock *FalseBB, 2412 uint32_t TrueWeight, 2413 uint32_t FalseWeight){ 2414 // Remove any superfluous successor edges from the CFG. 2415 // First, figure out which successors to preserve. 2416 // If TrueBB and FalseBB are equal, only try to preserve one copy of that 2417 // successor. 2418 BasicBlock *KeepEdge1 = TrueBB; 2419 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0; 2420 2421 // Then remove the rest. 2422 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) { 2423 BasicBlock *Succ = OldTerm->getSuccessor(I); 2424 // Make sure only to keep exactly one copy of each edge. 2425 if (Succ == KeepEdge1) 2426 KeepEdge1 = 0; 2427 else if (Succ == KeepEdge2) 2428 KeepEdge2 = 0; 2429 else 2430 Succ->removePredecessor(OldTerm->getParent()); 2431 } 2432 2433 IRBuilder<> Builder(OldTerm); 2434 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc()); 2435 2436 // Insert an appropriate new terminator. 2437 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) { 2438 if (TrueBB == FalseBB) 2439 // We were only looking for one successor, and it was present. 2440 // Create an unconditional branch to it. 2441 Builder.CreateBr(TrueBB); 2442 else { 2443 // We found both of the successors we were looking for. 2444 // Create a conditional branch sharing the condition of the select. 2445 BranchInst *NewBI = Builder.CreateCondBr(Cond, TrueBB, FalseBB); 2446 if (TrueWeight != FalseWeight) 2447 NewBI->setMetadata(LLVMContext::MD_prof, 2448 MDBuilder(OldTerm->getContext()). 2449 createBranchWeights(TrueWeight, FalseWeight)); 2450 } 2451 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) { 2452 // Neither of the selected blocks were successors, so this 2453 // terminator must be unreachable. 2454 new UnreachableInst(OldTerm->getContext(), OldTerm); 2455 } else { 2456 // One of the selected values was a successor, but the other wasn't. 2457 // Insert an unconditional branch to the one that was found; 2458 // the edge to the one that wasn't must be unreachable. 2459 if (KeepEdge1 == 0) 2460 // Only TrueBB was found. 2461 Builder.CreateBr(TrueBB); 2462 else 2463 // Only FalseBB was found. 2464 Builder.CreateBr(FalseBB); 2465 } 2466 2467 EraseTerminatorInstAndDCECond(OldTerm); 2468 return true; 2469} 2470 2471// SimplifySwitchOnSelect - Replaces 2472// (switch (select cond, X, Y)) on constant X, Y 2473// with a branch - conditional if X and Y lead to distinct BBs, 2474// unconditional otherwise. 2475static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) { 2476 // Check for constant integer values in the select. 2477 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue()); 2478 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue()); 2479 if (!TrueVal || !FalseVal) 2480 return false; 2481 2482 // Find the relevant condition and destinations. 2483 Value *Condition = Select->getCondition(); 2484 BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor(); 2485 BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor(); 2486 2487 // Get weight for TrueBB and FalseBB. 2488 uint32_t TrueWeight = 0, FalseWeight = 0; 2489 SmallVector<uint64_t, 8> Weights; 2490 bool HasWeights = HasBranchWeights(SI); 2491 if (HasWeights) { 2492 GetBranchWeights(SI, Weights); 2493 if (Weights.size() == 1 + SI->getNumCases()) { 2494 TrueWeight = (uint32_t)Weights[SI->findCaseValue(TrueVal). 2495 getSuccessorIndex()]; 2496 FalseWeight = (uint32_t)Weights[SI->findCaseValue(FalseVal). 2497 getSuccessorIndex()]; 2498 } 2499 } 2500 2501 // Perform the actual simplification. 2502 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB, 2503 TrueWeight, FalseWeight); 2504} 2505 2506// SimplifyIndirectBrOnSelect - Replaces 2507// (indirectbr (select cond, blockaddress(@fn, BlockA), 2508// blockaddress(@fn, BlockB))) 2509// with 2510// (br cond, BlockA, BlockB). 2511static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) { 2512 // Check that both operands of the select are block addresses. 2513 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue()); 2514 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue()); 2515 if (!TBA || !FBA) 2516 return false; 2517 2518 // Extract the actual blocks. 2519 BasicBlock *TrueBB = TBA->getBasicBlock(); 2520 BasicBlock *FalseBB = FBA->getBasicBlock(); 2521 2522 // Perform the actual simplification. 2523 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB, 2524 0, 0); 2525} 2526 2527/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp 2528/// instruction (a seteq/setne with a constant) as the only instruction in a 2529/// block that ends with an uncond branch. We are looking for a very specific 2530/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In 2531/// this case, we merge the first two "or's of icmp" into a switch, but then the 2532/// default value goes to an uncond block with a seteq in it, we get something 2533/// like: 2534/// 2535/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ] 2536/// DEFAULT: 2537/// %tmp = icmp eq i8 %A, 92 2538/// br label %end 2539/// end: 2540/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ] 2541/// 2542/// We prefer to split the edge to 'end' so that there is a true/false entry to 2543/// the PHI, merging the third icmp into the switch. 2544static bool TryToSimplifyUncondBranchWithICmpInIt( 2545 ICmpInst *ICI, IRBuilder<> &Builder, const TargetTransformInfo &TTI, 2546 const DataLayout *TD) { 2547 BasicBlock *BB = ICI->getParent(); 2548 2549 // If the block has any PHIs in it or the icmp has multiple uses, it is too 2550 // complex. 2551 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false; 2552 2553 Value *V = ICI->getOperand(0); 2554 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1)); 2555 2556 // The pattern we're looking for is where our only predecessor is a switch on 2557 // 'V' and this block is the default case for the switch. In this case we can 2558 // fold the compared value into the switch to simplify things. 2559 BasicBlock *Pred = BB->getSinglePredecessor(); 2560 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false; 2561 2562 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator()); 2563 if (SI->getCondition() != V) 2564 return false; 2565 2566 // If BB is reachable on a non-default case, then we simply know the value of 2567 // V in this block. Substitute it and constant fold the icmp instruction 2568 // away. 2569 if (SI->getDefaultDest() != BB) { 2570 ConstantInt *VVal = SI->findCaseDest(BB); 2571 assert(VVal && "Should have a unique destination value"); 2572 ICI->setOperand(0, VVal); 2573 2574 if (Value *V = SimplifyInstruction(ICI, TD)) { 2575 ICI->replaceAllUsesWith(V); 2576 ICI->eraseFromParent(); 2577 } 2578 // BB is now empty, so it is likely to simplify away. 2579 return SimplifyCFG(BB, TTI, TD) | true; 2580 } 2581 2582 // Ok, the block is reachable from the default dest. If the constant we're 2583 // comparing exists in one of the other edges, then we can constant fold ICI 2584 // and zap it. 2585 if (SI->findCaseValue(Cst) != SI->case_default()) { 2586 Value *V; 2587 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 2588 V = ConstantInt::getFalse(BB->getContext()); 2589 else 2590 V = ConstantInt::getTrue(BB->getContext()); 2591 2592 ICI->replaceAllUsesWith(V); 2593 ICI->eraseFromParent(); 2594 // BB is now empty, so it is likely to simplify away. 2595 return SimplifyCFG(BB, TTI, TD) | true; 2596 } 2597 2598 // The use of the icmp has to be in the 'end' block, by the only PHI node in 2599 // the block. 2600 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0); 2601 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back()); 2602 if (PHIUse == 0 || PHIUse != &SuccBlock->front() || 2603 isa<PHINode>(++BasicBlock::iterator(PHIUse))) 2604 return false; 2605 2606 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets 2607 // true in the PHI. 2608 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext()); 2609 Constant *NewCst = ConstantInt::getFalse(BB->getContext()); 2610 2611 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 2612 std::swap(DefaultCst, NewCst); 2613 2614 // Replace ICI (which is used by the PHI for the default value) with true or 2615 // false depending on if it is EQ or NE. 2616 ICI->replaceAllUsesWith(DefaultCst); 2617 ICI->eraseFromParent(); 2618 2619 // Okay, the switch goes to this block on a default value. Add an edge from 2620 // the switch to the merge point on the compared value. 2621 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge", 2622 BB->getParent(), BB); 2623 SmallVector<uint64_t, 8> Weights; 2624 bool HasWeights = HasBranchWeights(SI); 2625 if (HasWeights) { 2626 GetBranchWeights(SI, Weights); 2627 if (Weights.size() == 1 + SI->getNumCases()) { 2628 // Split weight for default case to case for "Cst". 2629 Weights[0] = (Weights[0]+1) >> 1; 2630 Weights.push_back(Weights[0]); 2631 2632 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end()); 2633 SI->setMetadata(LLVMContext::MD_prof, 2634 MDBuilder(SI->getContext()). 2635 createBranchWeights(MDWeights)); 2636 } 2637 } 2638 SI->addCase(Cst, NewBB); 2639 2640 // NewBB branches to the phi block, add the uncond branch and the phi entry. 2641 Builder.SetInsertPoint(NewBB); 2642 Builder.SetCurrentDebugLocation(SI->getDebugLoc()); 2643 Builder.CreateBr(SuccBlock); 2644 PHIUse->addIncoming(NewCst, NewBB); 2645 return true; 2646} 2647 2648/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch. 2649/// Check to see if it is branching on an or/and chain of icmp instructions, and 2650/// fold it into a switch instruction if so. 2651static bool SimplifyBranchOnICmpChain(BranchInst *BI, const DataLayout *TD, 2652 IRBuilder<> &Builder) { 2653 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); 2654 if (Cond == 0) return false; 2655 2656 2657 // Change br (X == 0 | X == 1), T, F into a switch instruction. 2658 // If this is a bunch of seteq's or'd together, or if it's a bunch of 2659 // 'setne's and'ed together, collect them. 2660 Value *CompVal = 0; 2661 std::vector<ConstantInt*> Values; 2662 bool TrueWhenEqual = true; 2663 Value *ExtraCase = 0; 2664 unsigned UsedICmps = 0; 2665 2666 if (Cond->getOpcode() == Instruction::Or) { 2667 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true, 2668 UsedICmps); 2669 } else if (Cond->getOpcode() == Instruction::And) { 2670 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false, 2671 UsedICmps); 2672 TrueWhenEqual = false; 2673 } 2674 2675 // If we didn't have a multiply compared value, fail. 2676 if (CompVal == 0) return false; 2677 2678 // Avoid turning single icmps into a switch. 2679 if (UsedICmps <= 1) 2680 return false; 2681 2682 // There might be duplicate constants in the list, which the switch 2683 // instruction can't handle, remove them now. 2684 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate); 2685 Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); 2686 2687 // If Extra was used, we require at least two switch values to do the 2688 // transformation. A switch with one value is just an cond branch. 2689 if (ExtraCase && Values.size() < 2) return false; 2690 2691 // TODO: Preserve branch weight metadata, similarly to how 2692 // FoldValueComparisonIntoPredecessors preserves it. 2693 2694 // Figure out which block is which destination. 2695 BasicBlock *DefaultBB = BI->getSuccessor(1); 2696 BasicBlock *EdgeBB = BI->getSuccessor(0); 2697 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); 2698 2699 BasicBlock *BB = BI->getParent(); 2700 2701 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size() 2702 << " cases into SWITCH. BB is:\n" << *BB); 2703 2704 // If there are any extra values that couldn't be folded into the switch 2705 // then we evaluate them with an explicit branch first. Split the block 2706 // right before the condbr to handle it. 2707 if (ExtraCase) { 2708 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test"); 2709 // Remove the uncond branch added to the old block. 2710 TerminatorInst *OldTI = BB->getTerminator(); 2711 Builder.SetInsertPoint(OldTI); 2712 2713 if (TrueWhenEqual) 2714 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB); 2715 else 2716 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB); 2717 2718 OldTI->eraseFromParent(); 2719 2720 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them 2721 // for the edge we just added. 2722 AddPredecessorToBlock(EdgeBB, BB, NewBB); 2723 2724 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase 2725 << "\nEXTRABB = " << *BB); 2726 BB = NewBB; 2727 } 2728 2729 Builder.SetInsertPoint(BI); 2730 // Convert pointer to int before we switch. 2731 if (CompVal->getType()->isPointerTy()) { 2732 assert(TD && "Cannot switch on pointer without DataLayout"); 2733 CompVal = Builder.CreatePtrToInt(CompVal, 2734 TD->getIntPtrType(CompVal->getContext()), 2735 "magicptr"); 2736 } 2737 2738 // Create the new switch instruction now. 2739 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size()); 2740 2741 // Add all of the 'cases' to the switch instruction. 2742 for (unsigned i = 0, e = Values.size(); i != e; ++i) 2743 New->addCase(Values[i], EdgeBB); 2744 2745 // We added edges from PI to the EdgeBB. As such, if there were any 2746 // PHI nodes in EdgeBB, they need entries to be added corresponding to 2747 // the number of edges added. 2748 for (BasicBlock::iterator BBI = EdgeBB->begin(); 2749 isa<PHINode>(BBI); ++BBI) { 2750 PHINode *PN = cast<PHINode>(BBI); 2751 Value *InVal = PN->getIncomingValueForBlock(BB); 2752 for (unsigned i = 0, e = Values.size()-1; i != e; ++i) 2753 PN->addIncoming(InVal, BB); 2754 } 2755 2756 // Erase the old branch instruction. 2757 EraseTerminatorInstAndDCECond(BI); 2758 2759 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n'); 2760 return true; 2761} 2762 2763bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) { 2764 // If this is a trivial landing pad that just continues unwinding the caught 2765 // exception then zap the landing pad, turning its invokes into calls. 2766 BasicBlock *BB = RI->getParent(); 2767 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI()); 2768 if (RI->getValue() != LPInst) 2769 // Not a landing pad, or the resume is not unwinding the exception that 2770 // caused control to branch here. 2771 return false; 2772 2773 // Check that there are no other instructions except for debug intrinsics. 2774 BasicBlock::iterator I = LPInst, E = RI; 2775 while (++I != E) 2776 if (!isa<DbgInfoIntrinsic>(I)) 2777 return false; 2778 2779 // Turn all invokes that unwind here into calls and delete the basic block. 2780 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) { 2781 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator()); 2782 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3); 2783 // Insert a call instruction before the invoke. 2784 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II); 2785 Call->takeName(II); 2786 Call->setCallingConv(II->getCallingConv()); 2787 Call->setAttributes(II->getAttributes()); 2788 Call->setDebugLoc(II->getDebugLoc()); 2789 2790 // Anything that used the value produced by the invoke instruction now uses 2791 // the value produced by the call instruction. Note that we do this even 2792 // for void functions and calls with no uses so that the callgraph edge is 2793 // updated. 2794 II->replaceAllUsesWith(Call); 2795 BB->removePredecessor(II->getParent()); 2796 2797 // Insert a branch to the normal destination right before the invoke. 2798 BranchInst::Create(II->getNormalDest(), II); 2799 2800 // Finally, delete the invoke instruction! 2801 II->eraseFromParent(); 2802 } 2803 2804 // The landingpad is now unreachable. Zap it. 2805 BB->eraseFromParent(); 2806 return true; 2807} 2808 2809bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) { 2810 BasicBlock *BB = RI->getParent(); 2811 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; 2812 2813 // Find predecessors that end with branches. 2814 SmallVector<BasicBlock*, 8> UncondBranchPreds; 2815 SmallVector<BranchInst*, 8> CondBranchPreds; 2816 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 2817 BasicBlock *P = *PI; 2818 TerminatorInst *PTI = P->getTerminator(); 2819 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) { 2820 if (BI->isUnconditional()) 2821 UncondBranchPreds.push_back(P); 2822 else 2823 CondBranchPreds.push_back(BI); 2824 } 2825 } 2826 2827 // If we found some, do the transformation! 2828 if (!UncondBranchPreds.empty() && DupRet) { 2829 while (!UncondBranchPreds.empty()) { 2830 BasicBlock *Pred = UncondBranchPreds.pop_back_val(); 2831 DEBUG(dbgs() << "FOLDING: " << *BB 2832 << "INTO UNCOND BRANCH PRED: " << *Pred); 2833 (void)FoldReturnIntoUncondBranch(RI, BB, Pred); 2834 } 2835 2836 // If we eliminated all predecessors of the block, delete the block now. 2837 if (pred_begin(BB) == pred_end(BB)) 2838 // We know there are no successors, so just nuke the block. 2839 BB->eraseFromParent(); 2840 2841 return true; 2842 } 2843 2844 // Check out all of the conditional branches going to this return 2845 // instruction. If any of them just select between returns, change the 2846 // branch itself into a select/return pair. 2847 while (!CondBranchPreds.empty()) { 2848 BranchInst *BI = CondBranchPreds.pop_back_val(); 2849 2850 // Check to see if the non-BB successor is also a return block. 2851 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) && 2852 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) && 2853 SimplifyCondBranchToTwoReturns(BI, Builder)) 2854 return true; 2855 } 2856 return false; 2857} 2858 2859bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) { 2860 BasicBlock *BB = UI->getParent(); 2861 2862 bool Changed = false; 2863 2864 // If there are any instructions immediately before the unreachable that can 2865 // be removed, do so. 2866 while (UI != BB->begin()) { 2867 BasicBlock::iterator BBI = UI; 2868 --BBI; 2869 // Do not delete instructions that can have side effects which might cause 2870 // the unreachable to not be reachable; specifically, calls and volatile 2871 // operations may have this effect. 2872 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break; 2873 2874 if (BBI->mayHaveSideEffects()) { 2875 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) { 2876 if (SI->isVolatile()) 2877 break; 2878 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) { 2879 if (LI->isVolatile()) 2880 break; 2881 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) { 2882 if (RMWI->isVolatile()) 2883 break; 2884 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) { 2885 if (CXI->isVolatile()) 2886 break; 2887 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) && 2888 !isa<LandingPadInst>(BBI)) { 2889 break; 2890 } 2891 // Note that deleting LandingPad's here is in fact okay, although it 2892 // involves a bit of subtle reasoning. If this inst is a LandingPad, 2893 // all the predecessors of this block will be the unwind edges of Invokes, 2894 // and we can therefore guarantee this block will be erased. 2895 } 2896 2897 // Delete this instruction (any uses are guaranteed to be dead) 2898 if (!BBI->use_empty()) 2899 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType())); 2900 BBI->eraseFromParent(); 2901 Changed = true; 2902 } 2903 2904 // If the unreachable instruction is the first in the block, take a gander 2905 // at all of the predecessors of this instruction, and simplify them. 2906 if (&BB->front() != UI) return Changed; 2907 2908 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); 2909 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 2910 TerminatorInst *TI = Preds[i]->getTerminator(); 2911 IRBuilder<> Builder(TI); 2912 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { 2913 if (BI->isUnconditional()) { 2914 if (BI->getSuccessor(0) == BB) { 2915 new UnreachableInst(TI->getContext(), TI); 2916 TI->eraseFromParent(); 2917 Changed = true; 2918 } 2919 } else { 2920 if (BI->getSuccessor(0) == BB) { 2921 Builder.CreateBr(BI->getSuccessor(1)); 2922 EraseTerminatorInstAndDCECond(BI); 2923 } else if (BI->getSuccessor(1) == BB) { 2924 Builder.CreateBr(BI->getSuccessor(0)); 2925 EraseTerminatorInstAndDCECond(BI); 2926 Changed = true; 2927 } 2928 } 2929 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { 2930 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 2931 i != e; ++i) 2932 if (i.getCaseSuccessor() == BB) { 2933 BB->removePredecessor(SI->getParent()); 2934 SI->removeCase(i); 2935 --i; --e; 2936 Changed = true; 2937 } 2938 // If the default value is unreachable, figure out the most popular 2939 // destination and make it the default. 2940 if (SI->getDefaultDest() == BB) { 2941 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity; 2942 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 2943 i != e; ++i) { 2944 std::pair<unsigned, unsigned> &entry = 2945 Popularity[i.getCaseSuccessor()]; 2946 if (entry.first == 0) { 2947 entry.first = 1; 2948 entry.second = i.getCaseIndex(); 2949 } else { 2950 entry.first++; 2951 } 2952 } 2953 2954 // Find the most popular block. 2955 unsigned MaxPop = 0; 2956 unsigned MaxIndex = 0; 2957 BasicBlock *MaxBlock = 0; 2958 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator 2959 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { 2960 if (I->second.first > MaxPop || 2961 (I->second.first == MaxPop && MaxIndex > I->second.second)) { 2962 MaxPop = I->second.first; 2963 MaxIndex = I->second.second; 2964 MaxBlock = I->first; 2965 } 2966 } 2967 if (MaxBlock) { 2968 // Make this the new default, allowing us to delete any explicit 2969 // edges to it. 2970 SI->setDefaultDest(MaxBlock); 2971 Changed = true; 2972 2973 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from 2974 // it. 2975 if (isa<PHINode>(MaxBlock->begin())) 2976 for (unsigned i = 0; i != MaxPop-1; ++i) 2977 MaxBlock->removePredecessor(SI->getParent()); 2978 2979 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 2980 i != e; ++i) 2981 if (i.getCaseSuccessor() == MaxBlock) { 2982 SI->removeCase(i); 2983 --i; --e; 2984 } 2985 } 2986 } 2987 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) { 2988 if (II->getUnwindDest() == BB) { 2989 // Convert the invoke to a call instruction. This would be a good 2990 // place to note that the call does not throw though. 2991 BranchInst *BI = Builder.CreateBr(II->getNormalDest()); 2992 II->removeFromParent(); // Take out of symbol table 2993 2994 // Insert the call now... 2995 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3); 2996 Builder.SetInsertPoint(BI); 2997 CallInst *CI = Builder.CreateCall(II->getCalledValue(), 2998 Args, II->getName()); 2999 CI->setCallingConv(II->getCallingConv()); 3000 CI->setAttributes(II->getAttributes()); 3001 // If the invoke produced a value, the call does now instead. 3002 II->replaceAllUsesWith(CI); 3003 delete II; 3004 Changed = true; 3005 } 3006 } 3007 } 3008 3009 // If this block is now dead, remove it. 3010 if (pred_begin(BB) == pred_end(BB) && 3011 BB != &BB->getParent()->getEntryBlock()) { 3012 // We know there are no successors, so just nuke the block. 3013 BB->eraseFromParent(); 3014 return true; 3015 } 3016 3017 return Changed; 3018} 3019 3020/// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a 3021/// integer range comparison into a sub, an icmp and a branch. 3022static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) { 3023 assert(SI->getNumCases() > 1 && "Degenerate switch?"); 3024 3025 // Make sure all cases point to the same destination and gather the values. 3026 SmallVector<ConstantInt *, 16> Cases; 3027 SwitchInst::CaseIt I = SI->case_begin(); 3028 Cases.push_back(I.getCaseValue()); 3029 SwitchInst::CaseIt PrevI = I++; 3030 for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) { 3031 if (PrevI.getCaseSuccessor() != I.getCaseSuccessor()) 3032 return false; 3033 Cases.push_back(I.getCaseValue()); 3034 } 3035 assert(Cases.size() == SI->getNumCases() && "Not all cases gathered"); 3036 3037 // Sort the case values, then check if they form a range we can transform. 3038 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate); 3039 for (unsigned I = 1, E = Cases.size(); I != E; ++I) { 3040 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1) 3041 return false; 3042 } 3043 3044 Constant *Offset = ConstantExpr::getNeg(Cases.back()); 3045 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()); 3046 3047 Value *Sub = SI->getCondition(); 3048 if (!Offset->isNullValue()) 3049 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off"); 3050 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch"); 3051 BranchInst *NewBI = Builder.CreateCondBr( 3052 Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest()); 3053 3054 // Update weight for the newly-created conditional branch. 3055 SmallVector<uint64_t, 8> Weights; 3056 bool HasWeights = HasBranchWeights(SI); 3057 if (HasWeights) { 3058 GetBranchWeights(SI, Weights); 3059 if (Weights.size() == 1 + SI->getNumCases()) { 3060 // Combine all weights for the cases to be the true weight of NewBI. 3061 // We assume that the sum of all weights for a Terminator can fit into 32 3062 // bits. 3063 uint32_t NewTrueWeight = 0; 3064 for (unsigned I = 1, E = Weights.size(); I != E; ++I) 3065 NewTrueWeight += (uint32_t)Weights[I]; 3066 NewBI->setMetadata(LLVMContext::MD_prof, 3067 MDBuilder(SI->getContext()). 3068 createBranchWeights(NewTrueWeight, 3069 (uint32_t)Weights[0])); 3070 } 3071 } 3072 3073 // Prune obsolete incoming values off the successor's PHI nodes. 3074 for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin(); 3075 isa<PHINode>(BBI); ++BBI) { 3076 for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I) 3077 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent()); 3078 } 3079 SI->eraseFromParent(); 3080 3081 return true; 3082} 3083 3084/// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch 3085/// and use it to remove dead cases. 3086static bool EliminateDeadSwitchCases(SwitchInst *SI) { 3087 Value *Cond = SI->getCondition(); 3088 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth(); 3089 APInt KnownZero(Bits, 0), KnownOne(Bits, 0); 3090 ComputeMaskedBits(Cond, KnownZero, KnownOne); 3091 3092 // Gather dead cases. 3093 SmallVector<ConstantInt*, 8> DeadCases; 3094 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) { 3095 if ((I.getCaseValue()->getValue() & KnownZero) != 0 || 3096 (I.getCaseValue()->getValue() & KnownOne) != KnownOne) { 3097 DeadCases.push_back(I.getCaseValue()); 3098 DEBUG(dbgs() << "SimplifyCFG: switch case '" 3099 << I.getCaseValue() << "' is dead.\n"); 3100 } 3101 } 3102 3103 SmallVector<uint64_t, 8> Weights; 3104 bool HasWeight = HasBranchWeights(SI); 3105 if (HasWeight) { 3106 GetBranchWeights(SI, Weights); 3107 HasWeight = (Weights.size() == 1 + SI->getNumCases()); 3108 } 3109 3110 // Remove dead cases from the switch. 3111 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) { 3112 SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]); 3113 assert(Case != SI->case_default() && 3114 "Case was not found. Probably mistake in DeadCases forming."); 3115 if (HasWeight) { 3116 std::swap(Weights[Case.getCaseIndex()+1], Weights.back()); 3117 Weights.pop_back(); 3118 } 3119 3120 // Prune unused values from PHI nodes. 3121 Case.getCaseSuccessor()->removePredecessor(SI->getParent()); 3122 SI->removeCase(Case); 3123 } 3124 if (HasWeight) { 3125 SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end()); 3126 SI->setMetadata(LLVMContext::MD_prof, 3127 MDBuilder(SI->getParent()->getContext()). 3128 createBranchWeights(MDWeights)); 3129 } 3130 3131 return !DeadCases.empty(); 3132} 3133 3134/// FindPHIForConditionForwarding - If BB would be eligible for simplification 3135/// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated 3136/// by an unconditional branch), look at the phi node for BB in the successor 3137/// block and see if the incoming value is equal to CaseValue. If so, return 3138/// the phi node, and set PhiIndex to BB's index in the phi node. 3139static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue, 3140 BasicBlock *BB, 3141 int *PhiIndex) { 3142 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator()) 3143 return NULL; // BB must be empty to be a candidate for simplification. 3144 if (!BB->getSinglePredecessor()) 3145 return NULL; // BB must be dominated by the switch. 3146 3147 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator()); 3148 if (!Branch || !Branch->isUnconditional()) 3149 return NULL; // Terminator must be unconditional branch. 3150 3151 BasicBlock *Succ = Branch->getSuccessor(0); 3152 3153 BasicBlock::iterator I = Succ->begin(); 3154 while (PHINode *PHI = dyn_cast<PHINode>(I++)) { 3155 int Idx = PHI->getBasicBlockIndex(BB); 3156 assert(Idx >= 0 && "PHI has no entry for predecessor?"); 3157 3158 Value *InValue = PHI->getIncomingValue(Idx); 3159 if (InValue != CaseValue) continue; 3160 3161 *PhiIndex = Idx; 3162 return PHI; 3163 } 3164 3165 return NULL; 3166} 3167 3168/// ForwardSwitchConditionToPHI - Try to forward the condition of a switch 3169/// instruction to a phi node dominated by the switch, if that would mean that 3170/// some of the destination blocks of the switch can be folded away. 3171/// Returns true if a change is made. 3172static bool ForwardSwitchConditionToPHI(SwitchInst *SI) { 3173 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap; 3174 ForwardingNodesMap ForwardingNodes; 3175 3176 for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) { 3177 ConstantInt *CaseValue = I.getCaseValue(); 3178 BasicBlock *CaseDest = I.getCaseSuccessor(); 3179 3180 int PhiIndex; 3181 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest, 3182 &PhiIndex); 3183 if (!PHI) continue; 3184 3185 ForwardingNodes[PHI].push_back(PhiIndex); 3186 } 3187 3188 bool Changed = false; 3189 3190 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(), 3191 E = ForwardingNodes.end(); I != E; ++I) { 3192 PHINode *Phi = I->first; 3193 SmallVector<int,4> &Indexes = I->second; 3194 3195 if (Indexes.size() < 2) continue; 3196 3197 for (size_t I = 0, E = Indexes.size(); I != E; ++I) 3198 Phi->setIncomingValue(Indexes[I], SI->getCondition()); 3199 Changed = true; 3200 } 3201 3202 return Changed; 3203} 3204 3205/// ValidLookupTableConstant - Return true if the backend will be able to handle 3206/// initializing an array of constants like C. 3207static bool ValidLookupTableConstant(Constant *C) { 3208 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 3209 return CE->isGEPWithNoNotionalOverIndexing(); 3210 3211 return isa<ConstantFP>(C) || 3212 isa<ConstantInt>(C) || 3213 isa<ConstantPointerNull>(C) || 3214 isa<GlobalValue>(C) || 3215 isa<UndefValue>(C); 3216} 3217 3218/// LookupConstant - If V is a Constant, return it. Otherwise, try to look up 3219/// its constant value in ConstantPool, returning 0 if it's not there. 3220static Constant *LookupConstant(Value *V, 3221 const SmallDenseMap<Value*, Constant*>& ConstantPool) { 3222 if (Constant *C = dyn_cast<Constant>(V)) 3223 return C; 3224 return ConstantPool.lookup(V); 3225} 3226 3227/// ConstantFold - Try to fold instruction I into a constant. This works for 3228/// simple instructions such as binary operations where both operands are 3229/// constant or can be replaced by constants from the ConstantPool. Returns the 3230/// resulting constant on success, 0 otherwise. 3231static Constant *ConstantFold(Instruction *I, 3232 const SmallDenseMap<Value*, Constant*>& ConstantPool) { 3233 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) { 3234 Constant *A = LookupConstant(BO->getOperand(0), ConstantPool); 3235 if (!A) 3236 return 0; 3237 Constant *B = LookupConstant(BO->getOperand(1), ConstantPool); 3238 if (!B) 3239 return 0; 3240 return ConstantExpr::get(BO->getOpcode(), A, B); 3241 } 3242 3243 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) { 3244 Constant *A = LookupConstant(I->getOperand(0), ConstantPool); 3245 if (!A) 3246 return 0; 3247 Constant *B = LookupConstant(I->getOperand(1), ConstantPool); 3248 if (!B) 3249 return 0; 3250 return ConstantExpr::getCompare(Cmp->getPredicate(), A, B); 3251 } 3252 3253 if (SelectInst *Select = dyn_cast<SelectInst>(I)) { 3254 Constant *A = LookupConstant(Select->getCondition(), ConstantPool); 3255 if (!A) 3256 return 0; 3257 if (A->isAllOnesValue()) 3258 return LookupConstant(Select->getTrueValue(), ConstantPool); 3259 if (A->isNullValue()) 3260 return LookupConstant(Select->getFalseValue(), ConstantPool); 3261 return 0; 3262 } 3263 3264 if (CastInst *Cast = dyn_cast<CastInst>(I)) { 3265 Constant *A = LookupConstant(I->getOperand(0), ConstantPool); 3266 if (!A) 3267 return 0; 3268 return ConstantExpr::getCast(Cast->getOpcode(), A, Cast->getDestTy()); 3269 } 3270 3271 return 0; 3272} 3273 3274/// GetCaseResults - Try to determine the resulting constant values in phi nodes 3275/// at the common destination basic block, *CommonDest, for one of the case 3276/// destionations CaseDest corresponding to value CaseVal (0 for the default 3277/// case), of a switch instruction SI. 3278static bool GetCaseResults(SwitchInst *SI, 3279 ConstantInt *CaseVal, 3280 BasicBlock *CaseDest, 3281 BasicBlock **CommonDest, 3282 SmallVector<std::pair<PHINode*,Constant*>, 4> &Res) { 3283 // The block from which we enter the common destination. 3284 BasicBlock *Pred = SI->getParent(); 3285 3286 // If CaseDest is empty except for some side-effect free instructions through 3287 // which we can constant-propagate the CaseVal, continue to its successor. 3288 SmallDenseMap<Value*, Constant*> ConstantPool; 3289 ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal)); 3290 for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E; 3291 ++I) { 3292 if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) { 3293 // If the terminator is a simple branch, continue to the next block. 3294 if (T->getNumSuccessors() != 1) 3295 return false; 3296 Pred = CaseDest; 3297 CaseDest = T->getSuccessor(0); 3298 } else if (isa<DbgInfoIntrinsic>(I)) { 3299 // Skip debug intrinsic. 3300 continue; 3301 } else if (Constant *C = ConstantFold(I, ConstantPool)) { 3302 // Instruction is side-effect free and constant. 3303 ConstantPool.insert(std::make_pair(I, C)); 3304 } else { 3305 break; 3306 } 3307 } 3308 3309 // If we did not have a CommonDest before, use the current one. 3310 if (!*CommonDest) 3311 *CommonDest = CaseDest; 3312 // If the destination isn't the common one, abort. 3313 if (CaseDest != *CommonDest) 3314 return false; 3315 3316 // Get the values for this case from phi nodes in the destination block. 3317 BasicBlock::iterator I = (*CommonDest)->begin(); 3318 while (PHINode *PHI = dyn_cast<PHINode>(I++)) { 3319 int Idx = PHI->getBasicBlockIndex(Pred); 3320 if (Idx == -1) 3321 continue; 3322 3323 Constant *ConstVal = LookupConstant(PHI->getIncomingValue(Idx), 3324 ConstantPool); 3325 if (!ConstVal) 3326 return false; 3327 3328 // Note: If the constant comes from constant-propagating the case value 3329 // through the CaseDest basic block, it will be safe to remove the 3330 // instructions in that block. They cannot be used (except in the phi nodes 3331 // we visit) outside CaseDest, because that block does not dominate its 3332 // successor. If it did, we would not be in this phi node. 3333 3334 // Be conservative about which kinds of constants we support. 3335 if (!ValidLookupTableConstant(ConstVal)) 3336 return false; 3337 3338 Res.push_back(std::make_pair(PHI, ConstVal)); 3339 } 3340 3341 return true; 3342} 3343 3344namespace { 3345 /// SwitchLookupTable - This class represents a lookup table that can be used 3346 /// to replace a switch. 3347 class SwitchLookupTable { 3348 public: 3349 /// SwitchLookupTable - Create a lookup table to use as a switch replacement 3350 /// with the contents of Values, using DefaultValue to fill any holes in the 3351 /// table. 3352 SwitchLookupTable(Module &M, 3353 uint64_t TableSize, 3354 ConstantInt *Offset, 3355 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values, 3356 Constant *DefaultValue, 3357 const DataLayout *TD); 3358 3359 /// BuildLookup - Build instructions with Builder to retrieve the value at 3360 /// the position given by Index in the lookup table. 3361 Value *BuildLookup(Value *Index, IRBuilder<> &Builder); 3362 3363 /// WouldFitInRegister - Return true if a table with TableSize elements of 3364 /// type ElementType would fit in a target-legal register. 3365 static bool WouldFitInRegister(const DataLayout *TD, 3366 uint64_t TableSize, 3367 const Type *ElementType); 3368 3369 private: 3370 // Depending on the contents of the table, it can be represented in 3371 // different ways. 3372 enum { 3373 // For tables where each element contains the same value, we just have to 3374 // store that single value and return it for each lookup. 3375 SingleValueKind, 3376 3377 // For small tables with integer elements, we can pack them into a bitmap 3378 // that fits into a target-legal register. Values are retrieved by 3379 // shift and mask operations. 3380 BitMapKind, 3381 3382 // The table is stored as an array of values. Values are retrieved by load 3383 // instructions from the table. 3384 ArrayKind 3385 } Kind; 3386 3387 // For SingleValueKind, this is the single value. 3388 Constant *SingleValue; 3389 3390 // For BitMapKind, this is the bitmap. 3391 ConstantInt *BitMap; 3392 IntegerType *BitMapElementTy; 3393 3394 // For ArrayKind, this is the array. 3395 GlobalVariable *Array; 3396 }; 3397} 3398 3399SwitchLookupTable::SwitchLookupTable(Module &M, 3400 uint64_t TableSize, 3401 ConstantInt *Offset, 3402 const SmallVector<std::pair<ConstantInt*, Constant*>, 4>& Values, 3403 Constant *DefaultValue, 3404 const DataLayout *TD) 3405 : SingleValue(0), BitMap(0), BitMapElementTy(0), Array(0) { 3406 assert(Values.size() && "Can't build lookup table without values!"); 3407 assert(TableSize >= Values.size() && "Can't fit values in table!"); 3408 3409 // If all values in the table are equal, this is that value. 3410 SingleValue = Values.begin()->second; 3411 3412 // Build up the table contents. 3413 SmallVector<Constant*, 64> TableContents(TableSize); 3414 for (size_t I = 0, E = Values.size(); I != E; ++I) { 3415 ConstantInt *CaseVal = Values[I].first; 3416 Constant *CaseRes = Values[I].second; 3417 assert(CaseRes->getType() == DefaultValue->getType()); 3418 3419 uint64_t Idx = (CaseVal->getValue() - Offset->getValue()) 3420 .getLimitedValue(); 3421 TableContents[Idx] = CaseRes; 3422 3423 if (CaseRes != SingleValue) 3424 SingleValue = 0; 3425 } 3426 3427 // Fill in any holes in the table with the default result. 3428 if (Values.size() < TableSize) { 3429 for (uint64_t I = 0; I < TableSize; ++I) { 3430 if (!TableContents[I]) 3431 TableContents[I] = DefaultValue; 3432 } 3433 3434 if (DefaultValue != SingleValue) 3435 SingleValue = 0; 3436 } 3437 3438 // If each element in the table contains the same value, we only need to store 3439 // that single value. 3440 if (SingleValue) { 3441 Kind = SingleValueKind; 3442 return; 3443 } 3444 3445 // If the type is integer and the table fits in a register, build a bitmap. 3446 if (WouldFitInRegister(TD, TableSize, DefaultValue->getType())) { 3447 IntegerType *IT = cast<IntegerType>(DefaultValue->getType()); 3448 APInt TableInt(TableSize * IT->getBitWidth(), 0); 3449 for (uint64_t I = TableSize; I > 0; --I) { 3450 TableInt <<= IT->getBitWidth(); 3451 // Insert values into the bitmap. Undef values are set to zero. 3452 if (!isa<UndefValue>(TableContents[I - 1])) { 3453 ConstantInt *Val = cast<ConstantInt>(TableContents[I - 1]); 3454 TableInt |= Val->getValue().zext(TableInt.getBitWidth()); 3455 } 3456 } 3457 BitMap = ConstantInt::get(M.getContext(), TableInt); 3458 BitMapElementTy = IT; 3459 Kind = BitMapKind; 3460 ++NumBitMaps; 3461 return; 3462 } 3463 3464 // Store the table in an array. 3465 ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize); 3466 Constant *Initializer = ConstantArray::get(ArrayTy, TableContents); 3467 3468 Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true, 3469 GlobalVariable::PrivateLinkage, 3470 Initializer, 3471 "switch.table"); 3472 Array->setUnnamedAddr(true); 3473 Kind = ArrayKind; 3474} 3475 3476Value *SwitchLookupTable::BuildLookup(Value *Index, IRBuilder<> &Builder) { 3477 switch (Kind) { 3478 case SingleValueKind: 3479 return SingleValue; 3480 case BitMapKind: { 3481 // Type of the bitmap (e.g. i59). 3482 IntegerType *MapTy = BitMap->getType(); 3483 3484 // Cast Index to the same type as the bitmap. 3485 // Note: The Index is <= the number of elements in the table, so 3486 // truncating it to the width of the bitmask is safe. 3487 Value *ShiftAmt = Builder.CreateZExtOrTrunc(Index, MapTy, "switch.cast"); 3488 3489 // Multiply the shift amount by the element width. 3490 ShiftAmt = Builder.CreateMul(ShiftAmt, 3491 ConstantInt::get(MapTy, BitMapElementTy->getBitWidth()), 3492 "switch.shiftamt"); 3493 3494 // Shift down. 3495 Value *DownShifted = Builder.CreateLShr(BitMap, ShiftAmt, 3496 "switch.downshift"); 3497 // Mask off. 3498 return Builder.CreateTrunc(DownShifted, BitMapElementTy, 3499 "switch.masked"); 3500 } 3501 case ArrayKind: { 3502 Value *GEPIndices[] = { Builder.getInt32(0), Index }; 3503 Value *GEP = Builder.CreateInBoundsGEP(Array, GEPIndices, 3504 "switch.gep"); 3505 return Builder.CreateLoad(GEP, "switch.load"); 3506 } 3507 } 3508 llvm_unreachable("Unknown lookup table kind!"); 3509} 3510 3511bool SwitchLookupTable::WouldFitInRegister(const DataLayout *TD, 3512 uint64_t TableSize, 3513 const Type *ElementType) { 3514 if (!TD) 3515 return false; 3516 const IntegerType *IT = dyn_cast<IntegerType>(ElementType); 3517 if (!IT) 3518 return false; 3519 // FIXME: If the type is wider than it needs to be, e.g. i8 but all values 3520 // are <= 15, we could try to narrow the type. 3521 3522 // Avoid overflow, fitsInLegalInteger uses unsigned int for the width. 3523 if (TableSize >= UINT_MAX/IT->getBitWidth()) 3524 return false; 3525 return TD->fitsInLegalInteger(TableSize * IT->getBitWidth()); 3526} 3527 3528/// ShouldBuildLookupTable - Determine whether a lookup table should be built 3529/// for this switch, based on the number of caes, size of the table and the 3530/// types of the results. 3531static bool ShouldBuildLookupTable(SwitchInst *SI, 3532 uint64_t TableSize, 3533 const TargetTransformInfo &TTI, 3534 const DataLayout *TD, 3535 const SmallDenseMap<PHINode*, Type*>& ResultTypes) { 3536 if (SI->getNumCases() > TableSize || TableSize >= UINT64_MAX / 10) 3537 return false; // TableSize overflowed, or mul below might overflow. 3538 3539 bool AllTablesFitInRegister = true; 3540 bool HasIllegalType = false; 3541 for (SmallDenseMap<PHINode*, Type*>::const_iterator I = ResultTypes.begin(), 3542 E = ResultTypes.end(); I != E; ++I) { 3543 Type *Ty = I->second; 3544 3545 // Saturate this flag to true. 3546 HasIllegalType = HasIllegalType || !TTI.isTypeLegal(Ty); 3547 3548 // Saturate this flag to false. 3549 AllTablesFitInRegister = AllTablesFitInRegister && 3550 SwitchLookupTable::WouldFitInRegister(TD, TableSize, Ty); 3551 3552 // If both flags saturate, we're done. NOTE: This *only* works with 3553 // saturating flags, and all flags have to saturate first due to the 3554 // non-deterministic behavior of iterating over a dense map. 3555 if (HasIllegalType && !AllTablesFitInRegister) 3556 break; 3557 } 3558 3559 // If each table would fit in a register, we should build it anyway. 3560 if (AllTablesFitInRegister) 3561 return true; 3562 3563 // Don't build a table that doesn't fit in-register if it has illegal types. 3564 if (HasIllegalType) 3565 return false; 3566 3567 // The table density should be at least 40%. This is the same criterion as for 3568 // jump tables, see SelectionDAGBuilder::handleJTSwitchCase. 3569 // FIXME: Find the best cut-off. 3570 return SI->getNumCases() * 10 >= TableSize * 4; 3571} 3572 3573/// SwitchToLookupTable - If the switch is only used to initialize one or more 3574/// phi nodes in a common successor block with different constant values, 3575/// replace the switch with lookup tables. 3576static bool SwitchToLookupTable(SwitchInst *SI, 3577 IRBuilder<> &Builder, 3578 const TargetTransformInfo &TTI, 3579 const DataLayout* TD) { 3580 assert(SI->getNumCases() > 1 && "Degenerate switch?"); 3581 3582 // Only build lookup table when we have a target that supports it. 3583 if (!TTI.shouldBuildLookupTables()) 3584 return false; 3585 3586 // FIXME: If the switch is too sparse for a lookup table, perhaps we could 3587 // split off a dense part and build a lookup table for that. 3588 3589 // FIXME: This creates arrays of GEPs to constant strings, which means each 3590 // GEP needs a runtime relocation in PIC code. We should just build one big 3591 // string and lookup indices into that. 3592 3593 // Ignore the switch if the number of cases is too small. 3594 // This is similar to the check when building jump tables in 3595 // SelectionDAGBuilder::handleJTSwitchCase. 3596 // FIXME: Determine the best cut-off. 3597 if (SI->getNumCases() < 4) 3598 return false; 3599 3600 // Figure out the corresponding result for each case value and phi node in the 3601 // common destination, as well as the the min and max case values. 3602 assert(SI->case_begin() != SI->case_end()); 3603 SwitchInst::CaseIt CI = SI->case_begin(); 3604 ConstantInt *MinCaseVal = CI.getCaseValue(); 3605 ConstantInt *MaxCaseVal = CI.getCaseValue(); 3606 3607 BasicBlock *CommonDest = 0; 3608 typedef SmallVector<std::pair<ConstantInt*, Constant*>, 4> ResultListTy; 3609 SmallDenseMap<PHINode*, ResultListTy> ResultLists; 3610 SmallDenseMap<PHINode*, Constant*> DefaultResults; 3611 SmallDenseMap<PHINode*, Type*> ResultTypes; 3612 SmallVector<PHINode*, 4> PHIs; 3613 3614 for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) { 3615 ConstantInt *CaseVal = CI.getCaseValue(); 3616 if (CaseVal->getValue().slt(MinCaseVal->getValue())) 3617 MinCaseVal = CaseVal; 3618 if (CaseVal->getValue().sgt(MaxCaseVal->getValue())) 3619 MaxCaseVal = CaseVal; 3620 3621 // Resulting value at phi nodes for this case value. 3622 typedef SmallVector<std::pair<PHINode*, Constant*>, 4> ResultsTy; 3623 ResultsTy Results; 3624 if (!GetCaseResults(SI, CaseVal, CI.getCaseSuccessor(), &CommonDest, 3625 Results)) 3626 return false; 3627 3628 // Append the result from this case to the list for each phi. 3629 for (ResultsTy::iterator I = Results.begin(), E = Results.end(); I!=E; ++I) { 3630 if (!ResultLists.count(I->first)) 3631 PHIs.push_back(I->first); 3632 ResultLists[I->first].push_back(std::make_pair(CaseVal, I->second)); 3633 } 3634 } 3635 3636 // Get the resulting values for the default case. 3637 SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList; 3638 if (!GetCaseResults(SI, 0, SI->getDefaultDest(), &CommonDest, 3639 DefaultResultsList)) 3640 return false; 3641 for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) { 3642 PHINode *PHI = DefaultResultsList[I].first; 3643 Constant *Result = DefaultResultsList[I].second; 3644 DefaultResults[PHI] = Result; 3645 ResultTypes[PHI] = Result->getType(); 3646 } 3647 3648 APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue(); 3649 uint64_t TableSize = RangeSpread.getLimitedValue() + 1; 3650 if (!ShouldBuildLookupTable(SI, TableSize, TTI, TD, ResultTypes)) 3651 return false; 3652 3653 // Create the BB that does the lookups. 3654 Module &Mod = *CommonDest->getParent()->getParent(); 3655 BasicBlock *LookupBB = BasicBlock::Create(Mod.getContext(), 3656 "switch.lookup", 3657 CommonDest->getParent(), 3658 CommonDest); 3659 3660 // Check whether the condition value is within the case range, and branch to 3661 // the new BB. 3662 Builder.SetInsertPoint(SI); 3663 Value *TableIndex = Builder.CreateSub(SI->getCondition(), MinCaseVal, 3664 "switch.tableidx"); 3665 Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get( 3666 MinCaseVal->getType(), TableSize)); 3667 Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest()); 3668 3669 // Populate the BB that does the lookups. 3670 Builder.SetInsertPoint(LookupBB); 3671 bool ReturnedEarly = false; 3672 for (size_t I = 0, E = PHIs.size(); I != E; ++I) { 3673 PHINode *PHI = PHIs[I]; 3674 3675 SwitchLookupTable Table(Mod, TableSize, MinCaseVal, ResultLists[PHI], 3676 DefaultResults[PHI], TD); 3677 3678 Value *Result = Table.BuildLookup(TableIndex, Builder); 3679 3680 // If the result is used to return immediately from the function, we want to 3681 // do that right here. 3682 if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin()) && 3683 *PHI->use_begin() == CommonDest->getFirstNonPHIOrDbg()) { 3684 Builder.CreateRet(Result); 3685 ReturnedEarly = true; 3686 break; 3687 } 3688 3689 PHI->addIncoming(Result, LookupBB); 3690 } 3691 3692 if (!ReturnedEarly) 3693 Builder.CreateBr(CommonDest); 3694 3695 // Remove the switch. 3696 for (unsigned i = 0; i < SI->getNumSuccessors(); ++i) { 3697 BasicBlock *Succ = SI->getSuccessor(i); 3698 if (Succ == SI->getDefaultDest()) continue; 3699 Succ->removePredecessor(SI->getParent()); 3700 } 3701 SI->eraseFromParent(); 3702 3703 ++NumLookupTables; 3704 return true; 3705} 3706 3707bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) { 3708 BasicBlock *BB = SI->getParent(); 3709 3710 if (isValueEqualityComparison(SI)) { 3711 // If we only have one predecessor, and if it is a branch on this value, 3712 // see if that predecessor totally determines the outcome of this switch. 3713 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 3714 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder)) 3715 return SimplifyCFG(BB, TTI, TD) | true; 3716 3717 Value *Cond = SI->getCondition(); 3718 if (SelectInst *Select = dyn_cast<SelectInst>(Cond)) 3719 if (SimplifySwitchOnSelect(SI, Select)) 3720 return SimplifyCFG(BB, TTI, TD) | true; 3721 3722 // If the block only contains the switch, see if we can fold the block 3723 // away into any preds. 3724 BasicBlock::iterator BBI = BB->begin(); 3725 // Ignore dbg intrinsics. 3726 while (isa<DbgInfoIntrinsic>(BBI)) 3727 ++BBI; 3728 if (SI == &*BBI) 3729 if (FoldValueComparisonIntoPredecessors(SI, Builder)) 3730 return SimplifyCFG(BB, TTI, TD) | true; 3731 } 3732 3733 // Try to transform the switch into an icmp and a branch. 3734 if (TurnSwitchRangeIntoICmp(SI, Builder)) 3735 return SimplifyCFG(BB, TTI, TD) | true; 3736 3737 // Remove unreachable cases. 3738 if (EliminateDeadSwitchCases(SI)) 3739 return SimplifyCFG(BB, TTI, TD) | true; 3740 3741 if (ForwardSwitchConditionToPHI(SI)) 3742 return SimplifyCFG(BB, TTI, TD) | true; 3743 3744 if (SwitchToLookupTable(SI, Builder, TTI, TD)) 3745 return SimplifyCFG(BB, TTI, TD) | true; 3746 3747 return false; 3748} 3749 3750bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) { 3751 BasicBlock *BB = IBI->getParent(); 3752 bool Changed = false; 3753 3754 // Eliminate redundant destinations. 3755 SmallPtrSet<Value *, 8> Succs; 3756 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 3757 BasicBlock *Dest = IBI->getDestination(i); 3758 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) { 3759 Dest->removePredecessor(BB); 3760 IBI->removeDestination(i); 3761 --i; --e; 3762 Changed = true; 3763 } 3764 } 3765 3766 if (IBI->getNumDestinations() == 0) { 3767 // If the indirectbr has no successors, change it to unreachable. 3768 new UnreachableInst(IBI->getContext(), IBI); 3769 EraseTerminatorInstAndDCECond(IBI); 3770 return true; 3771 } 3772 3773 if (IBI->getNumDestinations() == 1) { 3774 // If the indirectbr has one successor, change it to a direct branch. 3775 BranchInst::Create(IBI->getDestination(0), IBI); 3776 EraseTerminatorInstAndDCECond(IBI); 3777 return true; 3778 } 3779 3780 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) { 3781 if (SimplifyIndirectBrOnSelect(IBI, SI)) 3782 return SimplifyCFG(BB, TTI, TD) | true; 3783 } 3784 return Changed; 3785} 3786 3787bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){ 3788 BasicBlock *BB = BI->getParent(); 3789 3790 if (SinkCommon && SinkThenElseCodeToEnd(BI)) 3791 return true; 3792 3793 // If the Terminator is the only non-phi instruction, simplify the block. 3794 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime(); 3795 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() && 3796 TryToSimplifyUncondBranchFromEmptyBlock(BB)) 3797 return true; 3798 3799 // If the only instruction in the block is a seteq/setne comparison 3800 // against a constant, try to simplify the block. 3801 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) 3802 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) { 3803 for (++I; isa<DbgInfoIntrinsic>(I); ++I) 3804 ; 3805 if (I->isTerminator() && 3806 TryToSimplifyUncondBranchWithICmpInIt(ICI, Builder, TTI, TD)) 3807 return true; 3808 } 3809 3810 // If this basic block is ONLY a compare and a branch, and if a predecessor 3811 // branches to us and our successor, fold the comparison into the 3812 // predecessor and use logical operations to update the incoming value 3813 // for PHI nodes in common successor. 3814 if (FoldBranchToCommonDest(BI)) 3815 return SimplifyCFG(BB, TTI, TD) | true; 3816 return false; 3817} 3818 3819 3820bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) { 3821 BasicBlock *BB = BI->getParent(); 3822 3823 // Conditional branch 3824 if (isValueEqualityComparison(BI)) { 3825 // If we only have one predecessor, and if it is a branch on this value, 3826 // see if that predecessor totally determines the outcome of this 3827 // switch. 3828 if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) 3829 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder)) 3830 return SimplifyCFG(BB, TTI, TD) | true; 3831 3832 // This block must be empty, except for the setcond inst, if it exists. 3833 // Ignore dbg intrinsics. 3834 BasicBlock::iterator I = BB->begin(); 3835 // Ignore dbg intrinsics. 3836 while (isa<DbgInfoIntrinsic>(I)) 3837 ++I; 3838 if (&*I == BI) { 3839 if (FoldValueComparisonIntoPredecessors(BI, Builder)) 3840 return SimplifyCFG(BB, TTI, TD) | true; 3841 } else if (&*I == cast<Instruction>(BI->getCondition())){ 3842 ++I; 3843 // Ignore dbg intrinsics. 3844 while (isa<DbgInfoIntrinsic>(I)) 3845 ++I; 3846 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder)) 3847 return SimplifyCFG(BB, TTI, TD) | true; 3848 } 3849 } 3850 3851 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction. 3852 if (SimplifyBranchOnICmpChain(BI, TD, Builder)) 3853 return true; 3854 3855 // If this basic block is ONLY a compare and a branch, and if a predecessor 3856 // branches to us and one of our successors, fold the comparison into the 3857 // predecessor and use logical operations to pick the right destination. 3858 if (FoldBranchToCommonDest(BI)) 3859 return SimplifyCFG(BB, TTI, TD) | true; 3860 3861 // We have a conditional branch to two blocks that are only reachable 3862 // from BI. We know that the condbr dominates the two blocks, so see if 3863 // there is any identical code in the "then" and "else" blocks. If so, we 3864 // can hoist it up to the branching block. 3865 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) { 3866 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 3867 if (HoistThenElseCodeToIf(BI)) 3868 return SimplifyCFG(BB, TTI, TD) | true; 3869 } else { 3870 // If Successor #1 has multiple preds, we may be able to conditionally 3871 // execute Successor #0 if it branches to successor #1. 3872 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator(); 3873 if (Succ0TI->getNumSuccessors() == 1 && 3874 Succ0TI->getSuccessor(0) == BI->getSuccessor(1)) 3875 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0))) 3876 return SimplifyCFG(BB, TTI, TD) | true; 3877 } 3878 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { 3879 // If Successor #0 has multiple preds, we may be able to conditionally 3880 // execute Successor #1 if it branches to successor #0. 3881 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator(); 3882 if (Succ1TI->getNumSuccessors() == 1 && 3883 Succ1TI->getSuccessor(0) == BI->getSuccessor(0)) 3884 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1))) 3885 return SimplifyCFG(BB, TTI, TD) | true; 3886 } 3887 3888 // If this is a branch on a phi node in the current block, thread control 3889 // through this block if any PHI node entries are constants. 3890 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition())) 3891 if (PN->getParent() == BI->getParent()) 3892 if (FoldCondBranchOnPHI(BI, TD)) 3893 return SimplifyCFG(BB, TTI, TD) | true; 3894 3895 // Scan predecessor blocks for conditional branches. 3896 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 3897 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) 3898 if (PBI != BI && PBI->isConditional()) 3899 if (SimplifyCondBranchToCondBranch(PBI, BI)) 3900 return SimplifyCFG(BB, TTI, TD) | true; 3901 3902 return false; 3903} 3904 3905/// Check if passing a value to an instruction will cause undefined behavior. 3906static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) { 3907 Constant *C = dyn_cast<Constant>(V); 3908 if (!C) 3909 return false; 3910 3911 if (I->use_empty()) 3912 return false; 3913 3914 if (C->isNullValue()) { 3915 // Only look at the first use, avoid hurting compile time with long uselists 3916 User *Use = *I->use_begin(); 3917 3918 // Now make sure that there are no instructions in between that can alter 3919 // control flow (eg. calls) 3920 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i) 3921 if (i == I->getParent()->end() || i->mayHaveSideEffects()) 3922 return false; 3923 3924 // Look through GEPs. A load from a GEP derived from NULL is still undefined 3925 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use)) 3926 if (GEP->getPointerOperand() == I) 3927 return passingValueIsAlwaysUndefined(V, GEP); 3928 3929 // Look through bitcasts. 3930 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use)) 3931 return passingValueIsAlwaysUndefined(V, BC); 3932 3933 // Load from null is undefined. 3934 if (LoadInst *LI = dyn_cast<LoadInst>(Use)) 3935 return LI->getPointerAddressSpace() == 0; 3936 3937 // Store to null is undefined. 3938 if (StoreInst *SI = dyn_cast<StoreInst>(Use)) 3939 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I; 3940 } 3941 return false; 3942} 3943 3944/// If BB has an incoming value that will always trigger undefined behavior 3945/// (eg. null pointer dereference), remove the branch leading here. 3946static bool removeUndefIntroducingPredecessor(BasicBlock *BB) { 3947 for (BasicBlock::iterator i = BB->begin(); 3948 PHINode *PHI = dyn_cast<PHINode>(i); ++i) 3949 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) 3950 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) { 3951 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator(); 3952 IRBuilder<> Builder(T); 3953 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 3954 BB->removePredecessor(PHI->getIncomingBlock(i)); 3955 // Turn uncoditional branches into unreachables and remove the dead 3956 // destination from conditional branches. 3957 if (BI->isUnconditional()) 3958 Builder.CreateUnreachable(); 3959 else 3960 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) : 3961 BI->getSuccessor(0)); 3962 BI->eraseFromParent(); 3963 return true; 3964 } 3965 // TODO: SwitchInst. 3966 } 3967 3968 return false; 3969} 3970 3971bool SimplifyCFGOpt::run(BasicBlock *BB) { 3972 bool Changed = false; 3973 3974 assert(BB && BB->getParent() && "Block not embedded in function!"); 3975 assert(BB->getTerminator() && "Degenerate basic block encountered!"); 3976 3977 // Remove basic blocks that have no predecessors (except the entry block)... 3978 // or that just have themself as a predecessor. These are unreachable. 3979 if ((pred_begin(BB) == pred_end(BB) && 3980 BB != &BB->getParent()->getEntryBlock()) || 3981 BB->getSinglePredecessor() == BB) { 3982 DEBUG(dbgs() << "Removing BB: \n" << *BB); 3983 DeleteDeadBlock(BB); 3984 return true; 3985 } 3986 3987 // Check to see if we can constant propagate this terminator instruction 3988 // away... 3989 Changed |= ConstantFoldTerminator(BB, true); 3990 3991 // Check for and eliminate duplicate PHI nodes in this block. 3992 Changed |= EliminateDuplicatePHINodes(BB); 3993 3994 // Check for and remove branches that will always cause undefined behavior. 3995 Changed |= removeUndefIntroducingPredecessor(BB); 3996 3997 // Merge basic blocks into their predecessor if there is only one distinct 3998 // pred, and if there is only one distinct successor of the predecessor, and 3999 // if there are no PHI nodes. 4000 // 4001 if (MergeBlockIntoPredecessor(BB)) 4002 return true; 4003 4004 IRBuilder<> Builder(BB); 4005 4006 // If there is a trivial two-entry PHI node in this basic block, and we can 4007 // eliminate it, do so now. 4008 if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) 4009 if (PN->getNumIncomingValues() == 2) 4010 Changed |= FoldTwoEntryPHINode(PN, TD); 4011 4012 Builder.SetInsertPoint(BB->getTerminator()); 4013 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { 4014 if (BI->isUnconditional()) { 4015 if (SimplifyUncondBranch(BI, Builder)) return true; 4016 } else { 4017 if (SimplifyCondBranch(BI, Builder)) return true; 4018 } 4019 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { 4020 if (SimplifyReturn(RI, Builder)) return true; 4021 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) { 4022 if (SimplifyResume(RI, Builder)) return true; 4023 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { 4024 if (SimplifySwitch(SI, Builder)) return true; 4025 } else if (UnreachableInst *UI = 4026 dyn_cast<UnreachableInst>(BB->getTerminator())) { 4027 if (SimplifyUnreachable(UI)) return true; 4028 } else if (IndirectBrInst *IBI = 4029 dyn_cast<IndirectBrInst>(BB->getTerminator())) { 4030 if (SimplifyIndirectBr(IBI)) return true; 4031 } 4032 4033 return Changed; 4034} 4035 4036/// SimplifyCFG - This function is used to do simplification of a CFG. For 4037/// example, it adjusts branches to branches to eliminate the extra hop, it 4038/// eliminates unreachable basic blocks, and does other "peephole" optimization 4039/// of the CFG. It returns true if a modification was made. 4040/// 4041bool llvm::SimplifyCFG(BasicBlock *BB, const TargetTransformInfo &TTI, 4042 const DataLayout *TD) { 4043 return SimplifyCFGOpt(TTI, TD).run(BB); 4044} 4045