Local.cpp revision 940267e7f208751fdc48dbb7d6b5d86b6310ce7c
1//===-- Local.cpp - Functions to perform local transformations ------------===// 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// This family of functions perform various local transformations to the 11// program. 12// 13//===----------------------------------------------------------------------===// 14 15#include "llvm/Transforms/Utils/Local.h" 16#include "llvm/ADT/DenseMap.h" 17#include "llvm/ADT/STLExtras.h" 18#include "llvm/ADT/SmallPtrSet.h" 19#include "llvm/ADT/Statistic.h" 20#include "llvm/Analysis/Dominators.h" 21#include "llvm/Analysis/InstructionSimplify.h" 22#include "llvm/Analysis/MemoryBuiltins.h" 23#include "llvm/Analysis/ValueTracking.h" 24#include "llvm/DIBuilder.h" 25#include "llvm/DebugInfo.h" 26#include "llvm/IR/Constants.h" 27#include "llvm/IR/DataLayout.h" 28#include "llvm/IR/DerivedTypes.h" 29#include "llvm/IR/GlobalAlias.h" 30#include "llvm/IR/GlobalVariable.h" 31#include "llvm/IR/IRBuilder.h" 32#include "llvm/IR/Instructions.h" 33#include "llvm/IR/IntrinsicInst.h" 34#include "llvm/IR/Intrinsics.h" 35#include "llvm/IR/MDBuilder.h" 36#include "llvm/IR/Metadata.h" 37#include "llvm/IR/Operator.h" 38#include "llvm/Support/CFG.h" 39#include "llvm/Support/Debug.h" 40#include "llvm/Support/GetElementPtrTypeIterator.h" 41#include "llvm/Support/MathExtras.h" 42#include "llvm/Support/ValueHandle.h" 43#include "llvm/Support/raw_ostream.h" 44using namespace llvm; 45 46STATISTIC(NumRemoved, "Number of unreachable basic blocks removed"); 47 48//===----------------------------------------------------------------------===// 49// Local constant propagation. 50// 51 52/// ConstantFoldTerminator - If a terminator instruction is predicated on a 53/// constant value, convert it into an unconditional branch to the constant 54/// destination. This is a nontrivial operation because the successors of this 55/// basic block must have their PHI nodes updated. 56/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch 57/// conditions and indirectbr addresses this might make dead if 58/// DeleteDeadConditions is true. 59bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions, 60 const TargetLibraryInfo *TLI) { 61 TerminatorInst *T = BB->getTerminator(); 62 IRBuilder<> Builder(T); 63 64 // Branch - See if we are conditional jumping on constant 65 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 66 if (BI->isUnconditional()) return false; // Can't optimize uncond branch 67 BasicBlock *Dest1 = BI->getSuccessor(0); 68 BasicBlock *Dest2 = BI->getSuccessor(1); 69 70 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { 71 // Are we branching on constant? 72 // YES. Change to unconditional branch... 73 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; 74 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; 75 76 //cerr << "Function: " << T->getParent()->getParent() 77 // << "\nRemoving branch from " << T->getParent() 78 // << "\n\nTo: " << OldDest << endl; 79 80 // Let the basic block know that we are letting go of it. Based on this, 81 // it will adjust it's PHI nodes. 82 OldDest->removePredecessor(BB); 83 84 // Replace the conditional branch with an unconditional one. 85 Builder.CreateBr(Destination); 86 BI->eraseFromParent(); 87 return true; 88 } 89 90 if (Dest2 == Dest1) { // Conditional branch to same location? 91 // This branch matches something like this: 92 // br bool %cond, label %Dest, label %Dest 93 // and changes it into: br label %Dest 94 95 // Let the basic block know that we are letting go of one copy of it. 96 assert(BI->getParent() && "Terminator not inserted in block!"); 97 Dest1->removePredecessor(BI->getParent()); 98 99 // Replace the conditional branch with an unconditional one. 100 Builder.CreateBr(Dest1); 101 Value *Cond = BI->getCondition(); 102 BI->eraseFromParent(); 103 if (DeleteDeadConditions) 104 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); 105 return true; 106 } 107 return false; 108 } 109 110 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { 111 // If we are switching on a constant, we can convert the switch into a 112 // single branch instruction! 113 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); 114 BasicBlock *TheOnlyDest = SI->getDefaultDest(); 115 BasicBlock *DefaultDest = TheOnlyDest; 116 117 // Figure out which case it goes to. 118 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 119 i != e; ++i) { 120 // Found case matching a constant operand? 121 if (i.getCaseValue() == CI) { 122 TheOnlyDest = i.getCaseSuccessor(); 123 break; 124 } 125 126 // Check to see if this branch is going to the same place as the default 127 // dest. If so, eliminate it as an explicit compare. 128 if (i.getCaseSuccessor() == DefaultDest) { 129 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof); 130 // MD should have 2 + NumCases operands. 131 if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) { 132 // Collect branch weights into a vector. 133 SmallVector<uint32_t, 8> Weights; 134 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e; 135 ++MD_i) { 136 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i)); 137 assert(CI); 138 Weights.push_back(CI->getValue().getZExtValue()); 139 } 140 // Merge weight of this case to the default weight. 141 unsigned idx = i.getCaseIndex(); 142 Weights[0] += Weights[idx+1]; 143 // Remove weight for this case. 144 std::swap(Weights[idx+1], Weights.back()); 145 Weights.pop_back(); 146 SI->setMetadata(LLVMContext::MD_prof, 147 MDBuilder(BB->getContext()). 148 createBranchWeights(Weights)); 149 } 150 // Remove this entry. 151 DefaultDest->removePredecessor(SI->getParent()); 152 SI->removeCase(i); 153 --i; --e; 154 continue; 155 } 156 157 // Otherwise, check to see if the switch only branches to one destination. 158 // We do this by reseting "TheOnlyDest" to null when we find two non-equal 159 // destinations. 160 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = 0; 161 } 162 163 if (CI && !TheOnlyDest) { 164 // Branching on a constant, but not any of the cases, go to the default 165 // successor. 166 TheOnlyDest = SI->getDefaultDest(); 167 } 168 169 // If we found a single destination that we can fold the switch into, do so 170 // now. 171 if (TheOnlyDest) { 172 // Insert the new branch. 173 Builder.CreateBr(TheOnlyDest); 174 BasicBlock *BB = SI->getParent(); 175 176 // Remove entries from PHI nodes which we no longer branch to... 177 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) { 178 // Found case matching a constant operand? 179 BasicBlock *Succ = SI->getSuccessor(i); 180 if (Succ == TheOnlyDest) 181 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest 182 else 183 Succ->removePredecessor(BB); 184 } 185 186 // Delete the old switch. 187 Value *Cond = SI->getCondition(); 188 SI->eraseFromParent(); 189 if (DeleteDeadConditions) 190 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); 191 return true; 192 } 193 194 if (SI->getNumCases() == 1) { 195 // Otherwise, we can fold this switch into a conditional branch 196 // instruction if it has only one non-default destination. 197 SwitchInst::CaseIt FirstCase = SI->case_begin(); 198 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), 199 FirstCase.getCaseValue(), "cond"); 200 201 // Insert the new branch. 202 BranchInst *NewBr = Builder.CreateCondBr(Cond, 203 FirstCase.getCaseSuccessor(), 204 SI->getDefaultDest()); 205 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof); 206 if (MD && MD->getNumOperands() == 3) { 207 ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2)); 208 ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1)); 209 assert(SICase && SIDef); 210 // The TrueWeight should be the weight for the single case of SI. 211 NewBr->setMetadata(LLVMContext::MD_prof, 212 MDBuilder(BB->getContext()). 213 createBranchWeights(SICase->getValue().getZExtValue(), 214 SIDef->getValue().getZExtValue())); 215 } 216 217 // Delete the old switch. 218 SI->eraseFromParent(); 219 return true; 220 } 221 return false; 222 } 223 224 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 225 // indirectbr blockaddress(@F, @BB) -> br label @BB 226 if (BlockAddress *BA = 227 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 228 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 229 // Insert the new branch. 230 Builder.CreateBr(TheOnlyDest); 231 232 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 233 if (IBI->getDestination(i) == TheOnlyDest) 234 TheOnlyDest = 0; 235 else 236 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 237 } 238 Value *Address = IBI->getAddress(); 239 IBI->eraseFromParent(); 240 if (DeleteDeadConditions) 241 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI); 242 243 // If we didn't find our destination in the IBI successor list, then we 244 // have undefined behavior. Replace the unconditional branch with an 245 // 'unreachable' instruction. 246 if (TheOnlyDest) { 247 BB->getTerminator()->eraseFromParent(); 248 new UnreachableInst(BB->getContext(), BB); 249 } 250 251 return true; 252 } 253 } 254 255 return false; 256} 257 258 259//===----------------------------------------------------------------------===// 260// Local dead code elimination. 261// 262 263/// isInstructionTriviallyDead - Return true if the result produced by the 264/// instruction is not used, and the instruction has no side effects. 265/// 266bool llvm::isInstructionTriviallyDead(Instruction *I, 267 const TargetLibraryInfo *TLI) { 268 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 269 270 // We don't want the landingpad instruction removed by anything this general. 271 if (isa<LandingPadInst>(I)) 272 return false; 273 274 // We don't want debug info removed by anything this general, unless 275 // debug info is empty. 276 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 277 if (DDI->getAddress()) 278 return false; 279 return true; 280 } 281 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 282 if (DVI->getValue()) 283 return false; 284 return true; 285 } 286 287 if (!I->mayHaveSideEffects()) return true; 288 289 // Special case intrinsics that "may have side effects" but can be deleted 290 // when dead. 291 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 292 // Safe to delete llvm.stacksave if dead. 293 if (II->getIntrinsicID() == Intrinsic::stacksave) 294 return true; 295 296 // Lifetime intrinsics are dead when their right-hand is undef. 297 if (II->getIntrinsicID() == Intrinsic::lifetime_start || 298 II->getIntrinsicID() == Intrinsic::lifetime_end) 299 return isa<UndefValue>(II->getArgOperand(1)); 300 } 301 302 if (isAllocLikeFn(I, TLI)) return true; 303 304 if (CallInst *CI = isFreeCall(I, TLI)) 305 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0))) 306 return C->isNullValue() || isa<UndefValue>(C); 307 308 return false; 309} 310 311/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 312/// trivially dead instruction, delete it. If that makes any of its operands 313/// trivially dead, delete them too, recursively. Return true if any 314/// instructions were deleted. 315bool 316llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V, 317 const TargetLibraryInfo *TLI) { 318 Instruction *I = dyn_cast<Instruction>(V); 319 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI)) 320 return false; 321 322 SmallVector<Instruction*, 16> DeadInsts; 323 DeadInsts.push_back(I); 324 325 do { 326 I = DeadInsts.pop_back_val(); 327 328 // Null out all of the instruction's operands to see if any operand becomes 329 // dead as we go. 330 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 331 Value *OpV = I->getOperand(i); 332 I->setOperand(i, 0); 333 334 if (!OpV->use_empty()) continue; 335 336 // If the operand is an instruction that became dead as we nulled out the 337 // operand, and if it is 'trivially' dead, delete it in a future loop 338 // iteration. 339 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 340 if (isInstructionTriviallyDead(OpI, TLI)) 341 DeadInsts.push_back(OpI); 342 } 343 344 I->eraseFromParent(); 345 } while (!DeadInsts.empty()); 346 347 return true; 348} 349 350/// areAllUsesEqual - Check whether the uses of a value are all the same. 351/// This is similar to Instruction::hasOneUse() except this will also return 352/// true when there are no uses or multiple uses that all refer to the same 353/// value. 354static bool areAllUsesEqual(Instruction *I) { 355 Value::use_iterator UI = I->use_begin(); 356 Value::use_iterator UE = I->use_end(); 357 if (UI == UE) 358 return true; 359 360 User *TheUse = *UI; 361 for (++UI; UI != UE; ++UI) { 362 if (*UI != TheUse) 363 return false; 364 } 365 return true; 366} 367 368/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 369/// dead PHI node, due to being a def-use chain of single-use nodes that 370/// either forms a cycle or is terminated by a trivially dead instruction, 371/// delete it. If that makes any of its operands trivially dead, delete them 372/// too, recursively. Return true if a change was made. 373bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN, 374 const TargetLibraryInfo *TLI) { 375 SmallPtrSet<Instruction*, 4> Visited; 376 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 377 I = cast<Instruction>(*I->use_begin())) { 378 if (I->use_empty()) 379 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 380 381 // If we find an instruction more than once, we're on a cycle that 382 // won't prove fruitful. 383 if (!Visited.insert(I)) { 384 // Break the cycle and delete the instruction and its operands. 385 I->replaceAllUsesWith(UndefValue::get(I->getType())); 386 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 387 return true; 388 } 389 } 390 return false; 391} 392 393/// SimplifyInstructionsInBlock - Scan the specified basic block and try to 394/// simplify any instructions in it and recursively delete dead instructions. 395/// 396/// This returns true if it changed the code, note that it can delete 397/// instructions in other blocks as well in this block. 398bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD, 399 const TargetLibraryInfo *TLI) { 400 bool MadeChange = false; 401 402#ifndef NDEBUG 403 // In debug builds, ensure that the terminator of the block is never replaced 404 // or deleted by these simplifications. The idea of simplification is that it 405 // cannot introduce new instructions, and there is no way to replace the 406 // terminator of a block without introducing a new instruction. 407 AssertingVH<Instruction> TerminatorVH(--BB->end()); 408#endif 409 410 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) { 411 assert(!BI->isTerminator()); 412 Instruction *Inst = BI++; 413 414 WeakVH BIHandle(BI); 415 if (recursivelySimplifyInstruction(Inst, TD, TLI)) { 416 MadeChange = true; 417 if (BIHandle != BI) 418 BI = BB->begin(); 419 continue; 420 } 421 422 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI); 423 if (BIHandle != BI) 424 BI = BB->begin(); 425 } 426 return MadeChange; 427} 428 429//===----------------------------------------------------------------------===// 430// Control Flow Graph Restructuring. 431// 432 433 434/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 435/// method is called when we're about to delete Pred as a predecessor of BB. If 436/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 437/// 438/// Unlike the removePredecessor method, this attempts to simplify uses of PHI 439/// nodes that collapse into identity values. For example, if we have: 440/// x = phi(1, 0, 0, 0) 441/// y = and x, z 442/// 443/// .. and delete the predecessor corresponding to the '1', this will attempt to 444/// recursively fold the and to 0. 445void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 446 DataLayout *TD) { 447 // This only adjusts blocks with PHI nodes. 448 if (!isa<PHINode>(BB->begin())) 449 return; 450 451 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 452 // them down. This will leave us with single entry phi nodes and other phis 453 // that can be removed. 454 BB->removePredecessor(Pred, true); 455 456 WeakVH PhiIt = &BB->front(); 457 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 458 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 459 Value *OldPhiIt = PhiIt; 460 461 if (!recursivelySimplifyInstruction(PN, TD)) 462 continue; 463 464 // If recursive simplification ended up deleting the next PHI node we would 465 // iterate to, then our iterator is invalid, restart scanning from the top 466 // of the block. 467 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 468 } 469} 470 471 472/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 473/// predecessor is known to have one successor (DestBB!). Eliminate the edge 474/// between them, moving the instructions in the predecessor into DestBB and 475/// deleting the predecessor block. 476/// 477void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 478 // If BB has single-entry PHI nodes, fold them. 479 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 480 Value *NewVal = PN->getIncomingValue(0); 481 // Replace self referencing PHI with undef, it must be dead. 482 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 483 PN->replaceAllUsesWith(NewVal); 484 PN->eraseFromParent(); 485 } 486 487 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 488 assert(PredBB && "Block doesn't have a single predecessor!"); 489 490 // Zap anything that took the address of DestBB. Not doing this will give the 491 // address an invalid value. 492 if (DestBB->hasAddressTaken()) { 493 BlockAddress *BA = BlockAddress::get(DestBB); 494 Constant *Replacement = 495 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 496 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 497 BA->getType())); 498 BA->destroyConstant(); 499 } 500 501 // Anything that branched to PredBB now branches to DestBB. 502 PredBB->replaceAllUsesWith(DestBB); 503 504 // Splice all the instructions from PredBB to DestBB. 505 PredBB->getTerminator()->eraseFromParent(); 506 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 507 508 if (P) { 509 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 510 if (DT) { 511 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 512 DT->changeImmediateDominator(DestBB, PredBBIDom); 513 DT->eraseNode(PredBB); 514 } 515 } 516 // Nuke BB. 517 PredBB->eraseFromParent(); 518} 519 520/// CanMergeValues - Return true if we can choose one of these values to use 521/// in place of the other. Note that we will always choose the non-undef 522/// value to keep. 523static bool CanMergeValues(Value *First, Value *Second) { 524 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second); 525} 526 527/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 528/// almost-empty BB ending in an unconditional branch to Succ, into Succ. 529/// 530/// Assumption: Succ is the single successor for BB. 531/// 532static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 533 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 534 535 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 536 << Succ->getName() << "\n"); 537 // Shortcut, if there is only a single predecessor it must be BB and merging 538 // is always safe 539 if (Succ->getSinglePredecessor()) return true; 540 541 // Make a list of the predecessors of BB 542 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 543 544 // Look at all the phi nodes in Succ, to see if they present a conflict when 545 // merging these blocks 546 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 547 PHINode *PN = cast<PHINode>(I); 548 549 // If the incoming value from BB is again a PHINode in 550 // BB which has the same incoming value for *PI as PN does, we can 551 // merge the phi nodes and then the blocks can still be merged 552 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 553 if (BBPN && BBPN->getParent() == BB) { 554 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 555 BasicBlock *IBB = PN->getIncomingBlock(PI); 556 if (BBPreds.count(IBB) && 557 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB), 558 PN->getIncomingValue(PI))) { 559 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 560 << Succ->getName() << " is conflicting with " 561 << BBPN->getName() << " with regard to common predecessor " 562 << IBB->getName() << "\n"); 563 return false; 564 } 565 } 566 } else { 567 Value* Val = PN->getIncomingValueForBlock(BB); 568 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 569 // See if the incoming value for the common predecessor is equal to the 570 // one for BB, in which case this phi node will not prevent the merging 571 // of the block. 572 BasicBlock *IBB = PN->getIncomingBlock(PI); 573 if (BBPreds.count(IBB) && 574 !CanMergeValues(Val, PN->getIncomingValue(PI))) { 575 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 576 << Succ->getName() << " is conflicting with regard to common " 577 << "predecessor " << IBB->getName() << "\n"); 578 return false; 579 } 580 } 581 } 582 } 583 584 return true; 585} 586 587typedef SmallVector<BasicBlock *, 16> PredBlockVector; 588typedef DenseMap<BasicBlock *, Value *> IncomingValueMap; 589 590/// \brief Determines the value to use as the phi node input for a block. 591/// 592/// Select between \p OldVal any value that we know flows from \p BB 593/// to a particular phi on the basis of which one (if either) is not 594/// undef. Update IncomingValues based on the selected value. 595/// 596/// \param OldVal The value we are considering selecting. 597/// \param BB The block that the value flows in from. 598/// \param IncomingValues A map from block-to-value for other phi inputs 599/// that we have examined. 600/// 601/// \returns the selected value. 602static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB, 603 IncomingValueMap &IncomingValues) { 604 if (!isa<UndefValue>(OldVal)) { 605 assert((!IncomingValues.count(BB) || 606 IncomingValues.find(BB)->second == OldVal) && 607 "Expected OldVal to match incoming value from BB!"); 608 609 IncomingValues.insert(std::make_pair(BB, OldVal)); 610 return OldVal; 611 } 612 613 IncomingValueMap::const_iterator It = IncomingValues.find(BB); 614 if (It != IncomingValues.end()) return It->second; 615 616 return OldVal; 617} 618 619/// \brief Create a map from block to value for the operands of a 620/// given phi. 621/// 622/// Create a map from block to value for each non-undef value flowing 623/// into \p PN. 624/// 625/// \param PN The phi we are collecting the map for. 626/// \param IncomingValues [out] The map from block to value for this phi. 627static void gatherIncomingValuesToPhi(PHINode *PN, 628 IncomingValueMap &IncomingValues) { 629 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 630 BasicBlock *BB = PN->getIncomingBlock(i); 631 Value *V = PN->getIncomingValue(i); 632 633 if (!isa<UndefValue>(V)) 634 IncomingValues.insert(std::make_pair(BB, V)); 635 } 636} 637 638/// \brief Replace the incoming undef values to a phi with the values 639/// from a block-to-value map. 640/// 641/// \param PN The phi we are replacing the undefs in. 642/// \param IncomingValues A map from block to value. 643static void replaceUndefValuesInPhi(PHINode *PN, 644 const IncomingValueMap &IncomingValues) { 645 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 646 Value *V = PN->getIncomingValue(i); 647 648 if (!isa<UndefValue>(V)) continue; 649 650 BasicBlock *BB = PN->getIncomingBlock(i); 651 IncomingValueMap::const_iterator It = IncomingValues.find(BB); 652 if (It == IncomingValues.end()) continue; 653 654 PN->setIncomingValue(i, It->second); 655 } 656} 657 658/// \brief Replace a value flowing from a block to a phi with 659/// potentially multiple instances of that value flowing from the 660/// block's predecessors to the phi. 661/// 662/// \param BB The block with the value flowing into the phi. 663/// \param BBPreds The predecessors of BB. 664/// \param PN The phi that we are updating. 665static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB, 666 const PredBlockVector &BBPreds, 667 PHINode *PN) { 668 Value *OldVal = PN->removeIncomingValue(BB, false); 669 assert(OldVal && "No entry in PHI for Pred BB!"); 670 671 IncomingValueMap IncomingValues; 672 673 // We are merging two blocks - BB, and the block containing PN - and 674 // as a result we need to redirect edges from the predecessors of BB 675 // to go to the block containing PN, and update PN 676 // accordingly. Since we allow merging blocks in the case where the 677 // predecessor and successor blocks both share some predecessors, 678 // and where some of those common predecessors might have undef 679 // values flowing into PN, we want to rewrite those values to be 680 // consistent with the non-undef values. 681 682 gatherIncomingValuesToPhi(PN, IncomingValues); 683 684 // If this incoming value is one of the PHI nodes in BB, the new entries 685 // in the PHI node are the entries from the old PHI. 686 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 687 PHINode *OldValPN = cast<PHINode>(OldVal); 688 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) { 689 // Note that, since we are merging phi nodes and BB and Succ might 690 // have common predecessors, we could end up with a phi node with 691 // identical incoming branches. This will be cleaned up later (and 692 // will trigger asserts if we try to clean it up now, without also 693 // simplifying the corresponding conditional branch). 694 BasicBlock *PredBB = OldValPN->getIncomingBlock(i); 695 Value *PredVal = OldValPN->getIncomingValue(i); 696 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB, 697 IncomingValues); 698 699 // And add a new incoming value for this predecessor for the 700 // newly retargeted branch. 701 PN->addIncoming(Selected, PredBB); 702 } 703 } else { 704 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) { 705 // Update existing incoming values in PN for this 706 // predecessor of BB. 707 BasicBlock *PredBB = BBPreds[i]; 708 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB, 709 IncomingValues); 710 711 // And add a new incoming value for this predecessor for the 712 // newly retargeted branch. 713 PN->addIncoming(Selected, PredBB); 714 } 715 } 716 717 replaceUndefValuesInPhi(PN, IncomingValues); 718} 719 720/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 721/// unconditional branch, and contains no instructions other than PHI nodes, 722/// potential side-effect free intrinsics and the branch. If possible, 723/// eliminate BB by rewriting all the predecessors to branch to the successor 724/// block and return true. If we can't transform, return false. 725bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 726 assert(BB != &BB->getParent()->getEntryBlock() && 727 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 728 729 // We can't eliminate infinite loops. 730 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 731 if (BB == Succ) return false; 732 733 // Check to see if merging these blocks would cause conflicts for any of the 734 // phi nodes in BB or Succ. If not, we can safely merge. 735 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 736 737 // Check for cases where Succ has multiple predecessors and a PHI node in BB 738 // has uses which will not disappear when the PHI nodes are merged. It is 739 // possible to handle such cases, but difficult: it requires checking whether 740 // BB dominates Succ, which is non-trivial to calculate in the case where 741 // Succ has multiple predecessors. Also, it requires checking whether 742 // constructing the necessary self-referential PHI node doesn't introduce any 743 // conflicts; this isn't too difficult, but the previous code for doing this 744 // was incorrect. 745 // 746 // Note that if this check finds a live use, BB dominates Succ, so BB is 747 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 748 // folding the branch isn't profitable in that case anyway. 749 if (!Succ->getSinglePredecessor()) { 750 BasicBlock::iterator BBI = BB->begin(); 751 while (isa<PHINode>(*BBI)) { 752 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 753 UI != E; ++UI) { 754 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 755 if (PN->getIncomingBlock(UI) != BB) 756 return false; 757 } else { 758 return false; 759 } 760 } 761 ++BBI; 762 } 763 } 764 765 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 766 767 if (isa<PHINode>(Succ->begin())) { 768 // If there is more than one pred of succ, and there are PHI nodes in 769 // the successor, then we need to add incoming edges for the PHI nodes 770 // 771 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB)); 772 773 // Loop over all of the PHI nodes in the successor of BB. 774 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 775 PHINode *PN = cast<PHINode>(I); 776 777 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN); 778 } 779 } 780 781 if (Succ->getSinglePredecessor()) { 782 // BB is the only predecessor of Succ, so Succ will end up with exactly 783 // the same predecessors BB had. 784 785 // Copy over any phi, debug or lifetime instruction. 786 BB->getTerminator()->eraseFromParent(); 787 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList()); 788 } else { 789 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 790 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 791 assert(PN->use_empty() && "There shouldn't be any uses here!"); 792 PN->eraseFromParent(); 793 } 794 } 795 796 // Everything that jumped to BB now goes to Succ. 797 BB->replaceAllUsesWith(Succ); 798 if (!Succ->hasName()) Succ->takeName(BB); 799 BB->eraseFromParent(); // Delete the old basic block. 800 return true; 801} 802 803/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 804/// nodes in this block. This doesn't try to be clever about PHI nodes 805/// which differ only in the order of the incoming values, but instcombine 806/// orders them so it usually won't matter. 807/// 808bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 809 bool Changed = false; 810 811 // This implementation doesn't currently consider undef operands 812 // specially. Theoretically, two phis which are identical except for 813 // one having an undef where the other doesn't could be collapsed. 814 815 // Map from PHI hash values to PHI nodes. If multiple PHIs have 816 // the same hash value, the element is the first PHI in the 817 // linked list in CollisionMap. 818 DenseMap<uintptr_t, PHINode *> HashMap; 819 820 // Maintain linked lists of PHI nodes with common hash values. 821 DenseMap<PHINode *, PHINode *> CollisionMap; 822 823 // Examine each PHI. 824 for (BasicBlock::iterator I = BB->begin(); 825 PHINode *PN = dyn_cast<PHINode>(I++); ) { 826 // Compute a hash value on the operands. Instcombine will likely have sorted 827 // them, which helps expose duplicates, but we have to check all the 828 // operands to be safe in case instcombine hasn't run. 829 uintptr_t Hash = 0; 830 // This hash algorithm is quite weak as hash functions go, but it seems 831 // to do a good enough job for this particular purpose, and is very quick. 832 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 833 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 834 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 835 } 836 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end(); 837 I != E; ++I) { 838 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I)); 839 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 840 } 841 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 842 Hash >>= 1; 843 // If we've never seen this hash value before, it's a unique PHI. 844 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 845 HashMap.insert(std::make_pair(Hash, PN)); 846 if (Pair.second) continue; 847 // Otherwise it's either a duplicate or a hash collision. 848 for (PHINode *OtherPN = Pair.first->second; ; ) { 849 if (OtherPN->isIdenticalTo(PN)) { 850 // A duplicate. Replace this PHI with its duplicate. 851 PN->replaceAllUsesWith(OtherPN); 852 PN->eraseFromParent(); 853 Changed = true; 854 break; 855 } 856 // A non-duplicate hash collision. 857 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 858 if (I == CollisionMap.end()) { 859 // Set this PHI to be the head of the linked list of colliding PHIs. 860 PHINode *Old = Pair.first->second; 861 Pair.first->second = PN; 862 CollisionMap[PN] = Old; 863 break; 864 } 865 // Proceed to the next PHI in the list. 866 OtherPN = I->second; 867 } 868 } 869 870 return Changed; 871} 872 873/// enforceKnownAlignment - If the specified pointer points to an object that 874/// we control, modify the object's alignment to PrefAlign. This isn't 875/// often possible though. If alignment is important, a more reliable approach 876/// is to simply align all global variables and allocation instructions to 877/// their preferred alignment from the beginning. 878/// 879static unsigned enforceKnownAlignment(Value *V, unsigned Align, 880 unsigned PrefAlign, const DataLayout *TD) { 881 V = V->stripPointerCasts(); 882 883 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 884 // If the preferred alignment is greater than the natural stack alignment 885 // then don't round up. This avoids dynamic stack realignment. 886 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign)) 887 return Align; 888 // If there is a requested alignment and if this is an alloca, round up. 889 if (AI->getAlignment() >= PrefAlign) 890 return AI->getAlignment(); 891 AI->setAlignment(PrefAlign); 892 return PrefAlign; 893 } 894 895 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 896 // If there is a large requested alignment and we can, bump up the alignment 897 // of the global. 898 if (GV->isDeclaration()) return Align; 899 // If the memory we set aside for the global may not be the memory used by 900 // the final program then it is impossible for us to reliably enforce the 901 // preferred alignment. 902 if (GV->isWeakForLinker()) return Align; 903 904 if (GV->getAlignment() >= PrefAlign) 905 return GV->getAlignment(); 906 // We can only increase the alignment of the global if it has no alignment 907 // specified or if it is not assigned a section. If it is assigned a 908 // section, the global could be densely packed with other objects in the 909 // section, increasing the alignment could cause padding issues. 910 if (!GV->hasSection() || GV->getAlignment() == 0) 911 GV->setAlignment(PrefAlign); 912 return GV->getAlignment(); 913 } 914 915 return Align; 916} 917 918/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 919/// we can determine, return it, otherwise return 0. If PrefAlign is specified, 920/// and it is more than the alignment of the ultimate object, see if we can 921/// increase the alignment of the ultimate object, making this check succeed. 922unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 923 const DataLayout *DL) { 924 assert(V->getType()->isPointerTy() && 925 "getOrEnforceKnownAlignment expects a pointer!"); 926 unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(V->getType()) : 64; 927 928 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 929 ComputeMaskedBits(V, KnownZero, KnownOne, DL); 930 unsigned TrailZ = KnownZero.countTrailingOnes(); 931 932 // Avoid trouble with ridiculously large TrailZ values, such as 933 // those computed from a null pointer. 934 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 935 936 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 937 938 // LLVM doesn't support alignments larger than this currently. 939 Align = std::min(Align, +Value::MaximumAlignment); 940 941 if (PrefAlign > Align) 942 Align = enforceKnownAlignment(V, Align, PrefAlign, DL); 943 944 // We don't need to make any adjustment. 945 return Align; 946} 947 948///===---------------------------------------------------------------------===// 949/// Dbg Intrinsic utilities 950/// 951 952/// See if there is a dbg.value intrinsic for DIVar before I. 953static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) { 954 // Since we can't guarantee that the original dbg.declare instrinsic 955 // is removed by LowerDbgDeclare(), we need to make sure that we are 956 // not inserting the same dbg.value intrinsic over and over. 957 llvm::BasicBlock::InstListType::iterator PrevI(I); 958 if (PrevI != I->getParent()->getInstList().begin()) { 959 --PrevI; 960 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI)) 961 if (DVI->getValue() == I->getOperand(0) && 962 DVI->getOffset() == 0 && 963 DVI->getVariable() == DIVar) 964 return true; 965 } 966 return false; 967} 968 969/// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value 970/// that has an associated llvm.dbg.decl intrinsic. 971bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 972 StoreInst *SI, DIBuilder &Builder) { 973 DIVariable DIVar(DDI->getVariable()); 974 assert((!DIVar || DIVar.isVariable()) && 975 "Variable in DbgDeclareInst should be either null or a DIVariable."); 976 if (!DIVar) 977 return false; 978 979 if (LdStHasDebugValue(DIVar, SI)) 980 return true; 981 982 Instruction *DbgVal = NULL; 983 // If an argument is zero extended then use argument directly. The ZExt 984 // may be zapped by an optimization pass in future. 985 Argument *ExtendedArg = NULL; 986 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) 987 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); 988 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) 989 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); 990 if (ExtendedArg) 991 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI); 992 else 993 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI); 994 995 // Propagate any debug metadata from the store onto the dbg.value. 996 DebugLoc SIDL = SI->getDebugLoc(); 997 if (!SIDL.isUnknown()) 998 DbgVal->setDebugLoc(SIDL); 999 // Otherwise propagate debug metadata from dbg.declare. 1000 else 1001 DbgVal->setDebugLoc(DDI->getDebugLoc()); 1002 return true; 1003} 1004 1005/// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value 1006/// that has an associated llvm.dbg.decl intrinsic. 1007bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 1008 LoadInst *LI, DIBuilder &Builder) { 1009 DIVariable DIVar(DDI->getVariable()); 1010 assert((!DIVar || DIVar.isVariable()) && 1011 "Variable in DbgDeclareInst should be either null or a DIVariable."); 1012 if (!DIVar) 1013 return false; 1014 1015 if (LdStHasDebugValue(DIVar, LI)) 1016 return true; 1017 1018 Instruction *DbgVal = 1019 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 1020 DIVar, LI); 1021 1022 // Propagate any debug metadata from the store onto the dbg.value. 1023 DebugLoc LIDL = LI->getDebugLoc(); 1024 if (!LIDL.isUnknown()) 1025 DbgVal->setDebugLoc(LIDL); 1026 // Otherwise propagate debug metadata from dbg.declare. 1027 else 1028 DbgVal->setDebugLoc(DDI->getDebugLoc()); 1029 return true; 1030} 1031 1032/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 1033/// of llvm.dbg.value intrinsics. 1034bool llvm::LowerDbgDeclare(Function &F) { 1035 DIBuilder DIB(*F.getParent()); 1036 SmallVector<DbgDeclareInst *, 4> Dbgs; 1037 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 1038 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 1039 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 1040 Dbgs.push_back(DDI); 1041 } 1042 if (Dbgs.empty()) 1043 return false; 1044 1045 for (SmallVectorImpl<DbgDeclareInst *>::iterator I = Dbgs.begin(), 1046 E = Dbgs.end(); I != E; ++I) { 1047 DbgDeclareInst *DDI = *I; 1048 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress()); 1049 // If this is an alloca for a scalar variable, insert a dbg.value 1050 // at each load and store to the alloca and erase the dbg.declare. 1051 if (AI && !AI->isArrayAllocation()) { 1052 1053 // We only remove the dbg.declare intrinsic if all uses are 1054 // converted to dbg.value intrinsics. 1055 bool RemoveDDI = true; 1056 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 1057 UI != E; ++UI) 1058 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 1059 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 1060 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 1061 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 1062 else 1063 RemoveDDI = false; 1064 if (RemoveDDI) 1065 DDI->eraseFromParent(); 1066 } 1067 } 1068 return true; 1069} 1070 1071/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the 1072/// alloca 'V', if any. 1073DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { 1074 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V)) 1075 for (Value::use_iterator UI = DebugNode->use_begin(), 1076 E = DebugNode->use_end(); UI != E; ++UI) 1077 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI)) 1078 return DDI; 1079 1080 return 0; 1081} 1082 1083bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress, 1084 DIBuilder &Builder) { 1085 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI); 1086 if (!DDI) 1087 return false; 1088 DIVariable DIVar(DDI->getVariable()); 1089 assert((!DIVar || DIVar.isVariable()) && 1090 "Variable in DbgDeclareInst should be either null or a DIVariable."); 1091 if (!DIVar) 1092 return false; 1093 1094 // Create a copy of the original DIDescriptor for user variable, appending 1095 // "deref" operation to a list of address elements, as new llvm.dbg.declare 1096 // will take a value storing address of the memory for variable, not 1097 // alloca itself. 1098 Type *Int64Ty = Type::getInt64Ty(AI->getContext()); 1099 SmallVector<Value*, 4> NewDIVarAddress; 1100 if (DIVar.hasComplexAddress()) { 1101 for (unsigned i = 0, n = DIVar.getNumAddrElements(); i < n; ++i) { 1102 NewDIVarAddress.push_back( 1103 ConstantInt::get(Int64Ty, DIVar.getAddrElement(i))); 1104 } 1105 } 1106 NewDIVarAddress.push_back(ConstantInt::get(Int64Ty, DIBuilder::OpDeref)); 1107 DIVariable NewDIVar = Builder.createComplexVariable( 1108 DIVar.getTag(), DIVar.getContext(), DIVar.getName(), 1109 DIVar.getFile(), DIVar.getLineNumber(), DIVar.getType(), 1110 NewDIVarAddress, DIVar.getArgNumber()); 1111 1112 // Insert llvm.dbg.declare in the same basic block as the original alloca, 1113 // and remove old llvm.dbg.declare. 1114 BasicBlock *BB = AI->getParent(); 1115 Builder.insertDeclare(NewAllocaAddress, NewDIVar, BB); 1116 DDI->eraseFromParent(); 1117 return true; 1118} 1119 1120/// changeToUnreachable - Insert an unreachable instruction before the specified 1121/// instruction, making it and the rest of the code in the block dead. 1122static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) { 1123 BasicBlock *BB = I->getParent(); 1124 // Loop over all of the successors, removing BB's entry from any PHI 1125 // nodes. 1126 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) 1127 (*SI)->removePredecessor(BB); 1128 1129 // Insert a call to llvm.trap right before this. This turns the undefined 1130 // behavior into a hard fail instead of falling through into random code. 1131 if (UseLLVMTrap) { 1132 Function *TrapFn = 1133 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap); 1134 CallInst *CallTrap = CallInst::Create(TrapFn, "", I); 1135 CallTrap->setDebugLoc(I->getDebugLoc()); 1136 } 1137 new UnreachableInst(I->getContext(), I); 1138 1139 // All instructions after this are dead. 1140 BasicBlock::iterator BBI = I, BBE = BB->end(); 1141 while (BBI != BBE) { 1142 if (!BBI->use_empty()) 1143 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType())); 1144 BB->getInstList().erase(BBI++); 1145 } 1146} 1147 1148/// changeToCall - Convert the specified invoke into a normal call. 1149static void changeToCall(InvokeInst *II) { 1150 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3); 1151 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II); 1152 NewCall->takeName(II); 1153 NewCall->setCallingConv(II->getCallingConv()); 1154 NewCall->setAttributes(II->getAttributes()); 1155 NewCall->setDebugLoc(II->getDebugLoc()); 1156 II->replaceAllUsesWith(NewCall); 1157 1158 // Follow the call by a branch to the normal destination. 1159 BranchInst::Create(II->getNormalDest(), II); 1160 1161 // Update PHI nodes in the unwind destination 1162 II->getUnwindDest()->removePredecessor(II->getParent()); 1163 II->eraseFromParent(); 1164} 1165 1166static bool markAliveBlocks(BasicBlock *BB, 1167 SmallPtrSet<BasicBlock*, 128> &Reachable) { 1168 1169 SmallVector<BasicBlock*, 128> Worklist; 1170 Worklist.push_back(BB); 1171 Reachable.insert(BB); 1172 bool Changed = false; 1173 do { 1174 BB = Worklist.pop_back_val(); 1175 1176 // Do a quick scan of the basic block, turning any obviously unreachable 1177 // instructions into LLVM unreachable insts. The instruction combining pass 1178 // canonicalizes unreachable insts into stores to null or undef. 1179 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){ 1180 if (CallInst *CI = dyn_cast<CallInst>(BBI)) { 1181 if (CI->doesNotReturn()) { 1182 // If we found a call to a no-return function, insert an unreachable 1183 // instruction after it. Make sure there isn't *already* one there 1184 // though. 1185 ++BBI; 1186 if (!isa<UnreachableInst>(BBI)) { 1187 // Don't insert a call to llvm.trap right before the unreachable. 1188 changeToUnreachable(BBI, false); 1189 Changed = true; 1190 } 1191 break; 1192 } 1193 } 1194 1195 // Store to undef and store to null are undefined and used to signal that 1196 // they should be changed to unreachable by passes that can't modify the 1197 // CFG. 1198 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) { 1199 // Don't touch volatile stores. 1200 if (SI->isVolatile()) continue; 1201 1202 Value *Ptr = SI->getOperand(1); 1203 1204 if (isa<UndefValue>(Ptr) || 1205 (isa<ConstantPointerNull>(Ptr) && 1206 SI->getPointerAddressSpace() == 0)) { 1207 changeToUnreachable(SI, true); 1208 Changed = true; 1209 break; 1210 } 1211 } 1212 } 1213 1214 // Turn invokes that call 'nounwind' functions into ordinary calls. 1215 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) { 1216 Value *Callee = II->getCalledValue(); 1217 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) { 1218 changeToUnreachable(II, true); 1219 Changed = true; 1220 } else if (II->doesNotThrow()) { 1221 if (II->use_empty() && II->onlyReadsMemory()) { 1222 // jump to the normal destination branch. 1223 BranchInst::Create(II->getNormalDest(), II); 1224 II->getUnwindDest()->removePredecessor(II->getParent()); 1225 II->eraseFromParent(); 1226 } else 1227 changeToCall(II); 1228 Changed = true; 1229 } 1230 } 1231 1232 Changed |= ConstantFoldTerminator(BB, true); 1233 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) 1234 if (Reachable.insert(*SI)) 1235 Worklist.push_back(*SI); 1236 } while (!Worklist.empty()); 1237 return Changed; 1238} 1239 1240/// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even 1241/// if they are in a dead cycle. Return true if a change was made, false 1242/// otherwise. 1243bool llvm::removeUnreachableBlocks(Function &F) { 1244 SmallPtrSet<BasicBlock*, 128> Reachable; 1245 bool Changed = markAliveBlocks(F.begin(), Reachable); 1246 1247 // If there are unreachable blocks in the CFG... 1248 if (Reachable.size() == F.size()) 1249 return Changed; 1250 1251 assert(Reachable.size() < F.size()); 1252 NumRemoved += F.size()-Reachable.size(); 1253 1254 // Loop over all of the basic blocks that are not reachable, dropping all of 1255 // their internal references... 1256 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) { 1257 if (Reachable.count(BB)) 1258 continue; 1259 1260 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) 1261 if (Reachable.count(*SI)) 1262 (*SI)->removePredecessor(BB); 1263 BB->dropAllReferences(); 1264 } 1265 1266 for (Function::iterator I = ++F.begin(); I != F.end();) 1267 if (!Reachable.count(I)) 1268 I = F.getBasicBlockList().erase(I); 1269 else 1270 ++I; 1271 1272 return true; 1273} 1274