Local.cpp revision ad2890760f9661fb6a3dfa3ca863a87f6aea4139
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/Constants.h" 17#include "llvm/DIBuilder.h" 18#include "llvm/DebugInfo.h" 19#include "llvm/DerivedTypes.h" 20#include "llvm/GlobalAlias.h" 21#include "llvm/GlobalVariable.h" 22#include "llvm/IRBuilder.h" 23#include "llvm/Instructions.h" 24#include "llvm/IntrinsicInst.h" 25#include "llvm/Intrinsics.h" 26#include "llvm/MDBuilder.h" 27#include "llvm/Metadata.h" 28#include "llvm/Operator.h" 29#include "llvm/ADT/DenseMap.h" 30#include "llvm/ADT/SmallPtrSet.h" 31#include "llvm/Analysis/Dominators.h" 32#include "llvm/Analysis/InstructionSimplify.h" 33#include "llvm/Analysis/MemoryBuiltins.h" 34#include "llvm/Analysis/ProfileInfo.h" 35#include "llvm/Analysis/ValueTracking.h" 36#include "llvm/Support/CFG.h" 37#include "llvm/Support/Debug.h" 38#include "llvm/Support/GetElementPtrTypeIterator.h" 39#include "llvm/Support/MathExtras.h" 40#include "llvm/Support/ValueHandle.h" 41#include "llvm/Support/raw_ostream.h" 42#include "llvm/Target/TargetData.h" 43using namespace llvm; 44 45//===----------------------------------------------------------------------===// 46// Local constant propagation. 47// 48 49/// ConstantFoldTerminator - If a terminator instruction is predicated on a 50/// constant value, convert it into an unconditional branch to the constant 51/// destination. This is a nontrivial operation because the successors of this 52/// basic block must have their PHI nodes updated. 53/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch 54/// conditions and indirectbr addresses this might make dead if 55/// DeleteDeadConditions is true. 56bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions, 57 const TargetLibraryInfo *TLI) { 58 TerminatorInst *T = BB->getTerminator(); 59 IRBuilder<> Builder(T); 60 61 // Branch - See if we are conditional jumping on constant 62 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 63 if (BI->isUnconditional()) return false; // Can't optimize uncond branch 64 BasicBlock *Dest1 = BI->getSuccessor(0); 65 BasicBlock *Dest2 = BI->getSuccessor(1); 66 67 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { 68 // Are we branching on constant? 69 // YES. Change to unconditional branch... 70 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; 71 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; 72 73 //cerr << "Function: " << T->getParent()->getParent() 74 // << "\nRemoving branch from " << T->getParent() 75 // << "\n\nTo: " << OldDest << endl; 76 77 // Let the basic block know that we are letting go of it. Based on this, 78 // it will adjust it's PHI nodes. 79 OldDest->removePredecessor(BB); 80 81 // Replace the conditional branch with an unconditional one. 82 Builder.CreateBr(Destination); 83 BI->eraseFromParent(); 84 return true; 85 } 86 87 if (Dest2 == Dest1) { // Conditional branch to same location? 88 // This branch matches something like this: 89 // br bool %cond, label %Dest, label %Dest 90 // and changes it into: br label %Dest 91 92 // Let the basic block know that we are letting go of one copy of it. 93 assert(BI->getParent() && "Terminator not inserted in block!"); 94 Dest1->removePredecessor(BI->getParent()); 95 96 // Replace the conditional branch with an unconditional one. 97 Builder.CreateBr(Dest1); 98 Value *Cond = BI->getCondition(); 99 BI->eraseFromParent(); 100 if (DeleteDeadConditions) 101 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); 102 return true; 103 } 104 return false; 105 } 106 107 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { 108 // If we are switching on a constant, we can convert the switch into a 109 // single branch instruction! 110 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); 111 BasicBlock *TheOnlyDest = SI->getDefaultDest(); 112 BasicBlock *DefaultDest = TheOnlyDest; 113 114 // Figure out which case it goes to. 115 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 116 i != e; ++i) { 117 // Found case matching a constant operand? 118 if (i.getCaseValue() == CI) { 119 TheOnlyDest = i.getCaseSuccessor(); 120 break; 121 } 122 123 // Check to see if this branch is going to the same place as the default 124 // dest. If so, eliminate it as an explicit compare. 125 if (i.getCaseSuccessor() == DefaultDest) { 126 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof); 127 // MD should have 2 + NumCases operands. 128 if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) { 129 // Collect branch weights into a vector. 130 SmallVector<uint32_t, 8> Weights; 131 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e; 132 ++MD_i) { 133 ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i)); 134 assert(CI); 135 Weights.push_back(CI->getValue().getZExtValue()); 136 } 137 // Merge weight of this case to the default weight. 138 unsigned idx = i.getCaseIndex(); 139 Weights[0] += Weights[idx+1]; 140 // Remove weight for this case. 141 std::swap(Weights[idx+1], Weights.back()); 142 Weights.pop_back(); 143 SI->setMetadata(LLVMContext::MD_prof, 144 MDBuilder(BB->getContext()). 145 createBranchWeights(Weights)); 146 } 147 // Remove this entry. 148 DefaultDest->removePredecessor(SI->getParent()); 149 SI->removeCase(i); 150 --i; --e; 151 continue; 152 } 153 154 // Otherwise, check to see if the switch only branches to one destination. 155 // We do this by reseting "TheOnlyDest" to null when we find two non-equal 156 // destinations. 157 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = 0; 158 } 159 160 if (CI && !TheOnlyDest) { 161 // Branching on a constant, but not any of the cases, go to the default 162 // successor. 163 TheOnlyDest = SI->getDefaultDest(); 164 } 165 166 // If we found a single destination that we can fold the switch into, do so 167 // now. 168 if (TheOnlyDest) { 169 // Insert the new branch. 170 Builder.CreateBr(TheOnlyDest); 171 BasicBlock *BB = SI->getParent(); 172 173 // Remove entries from PHI nodes which we no longer branch to... 174 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) { 175 // Found case matching a constant operand? 176 BasicBlock *Succ = SI->getSuccessor(i); 177 if (Succ == TheOnlyDest) 178 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest 179 else 180 Succ->removePredecessor(BB); 181 } 182 183 // Delete the old switch. 184 Value *Cond = SI->getCondition(); 185 SI->eraseFromParent(); 186 if (DeleteDeadConditions) 187 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); 188 return true; 189 } 190 191 if (SI->getNumCases() == 1) { 192 // Otherwise, we can fold this switch into a conditional branch 193 // instruction if it has only one non-default destination. 194 SwitchInst::CaseIt FirstCase = SI->case_begin(); 195 IntegersSubset& Case = FirstCase.getCaseValueEx(); 196 if (Case.isSingleNumber()) { 197 // FIXME: Currently work with ConstantInt based numbers. 198 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), 199 Case.getSingleNumber(0).toConstantInt(), 200 "cond"); 201 202 // Insert the new branch. 203 BranchInst *NewBr = Builder.CreateCondBr(Cond, 204 FirstCase.getCaseSuccessor(), 205 SI->getDefaultDest()); 206 MDNode* MD = SI->getMetadata(LLVMContext::MD_prof); 207 if (MD && MD->getNumOperands() == 3) { 208 ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2)); 209 ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1)); 210 assert(SICase && SIDef); 211 // The TrueWeight should be the weight for the single case of SI. 212 NewBr->setMetadata(LLVMContext::MD_prof, 213 MDBuilder(BB->getContext()). 214 createBranchWeights(SICase->getValue().getZExtValue(), 215 SIDef->getValue().getZExtValue())); 216 } 217 218 // Delete the old switch. 219 SI->eraseFromParent(); 220 return true; 221 } 222 } 223 return false; 224 } 225 226 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 227 // indirectbr blockaddress(@F, @BB) -> br label @BB 228 if (BlockAddress *BA = 229 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 230 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 231 // Insert the new branch. 232 Builder.CreateBr(TheOnlyDest); 233 234 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 235 if (IBI->getDestination(i) == TheOnlyDest) 236 TheOnlyDest = 0; 237 else 238 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 239 } 240 Value *Address = IBI->getAddress(); 241 IBI->eraseFromParent(); 242 if (DeleteDeadConditions) 243 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI); 244 245 // If we didn't find our destination in the IBI successor list, then we 246 // have undefined behavior. Replace the unconditional branch with an 247 // 'unreachable' instruction. 248 if (TheOnlyDest) { 249 BB->getTerminator()->eraseFromParent(); 250 new UnreachableInst(BB->getContext(), BB); 251 } 252 253 return true; 254 } 255 } 256 257 return false; 258} 259 260 261//===----------------------------------------------------------------------===// 262// Local dead code elimination. 263// 264 265/// isInstructionTriviallyDead - Return true if the result produced by the 266/// instruction is not used, and the instruction has no side effects. 267/// 268bool llvm::isInstructionTriviallyDead(Instruction *I, 269 const TargetLibraryInfo *TLI) { 270 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 271 272 // We don't want the landingpad instruction removed by anything this general. 273 if (isa<LandingPadInst>(I)) 274 return false; 275 276 // We don't want debug info removed by anything this general, unless 277 // debug info is empty. 278 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 279 if (DDI->getAddress()) 280 return false; 281 return true; 282 } 283 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 284 if (DVI->getValue()) 285 return false; 286 return true; 287 } 288 289 if (!I->mayHaveSideEffects()) return true; 290 291 // Special case intrinsics that "may have side effects" but can be deleted 292 // when dead. 293 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 294 // Safe to delete llvm.stacksave if dead. 295 if (II->getIntrinsicID() == Intrinsic::stacksave) 296 return true; 297 298 // Lifetime intrinsics are dead when their right-hand is undef. 299 if (II->getIntrinsicID() == Intrinsic::lifetime_start || 300 II->getIntrinsicID() == Intrinsic::lifetime_end) 301 return isa<UndefValue>(II->getArgOperand(1)); 302 } 303 304 if (isAllocLikeFn(I, TLI)) return true; 305 306 if (CallInst *CI = isFreeCall(I, TLI)) 307 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0))) 308 return C->isNullValue() || isa<UndefValue>(C); 309 310 return false; 311} 312 313/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 314/// trivially dead instruction, delete it. If that makes any of its operands 315/// trivially dead, delete them too, recursively. Return true if any 316/// instructions were deleted. 317bool 318llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V, 319 const TargetLibraryInfo *TLI) { 320 Instruction *I = dyn_cast<Instruction>(V); 321 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI)) 322 return false; 323 324 SmallVector<Instruction*, 16> DeadInsts; 325 DeadInsts.push_back(I); 326 327 do { 328 I = DeadInsts.pop_back_val(); 329 330 // Null out all of the instruction's operands to see if any operand becomes 331 // dead as we go. 332 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 333 Value *OpV = I->getOperand(i); 334 I->setOperand(i, 0); 335 336 if (!OpV->use_empty()) continue; 337 338 // If the operand is an instruction that became dead as we nulled out the 339 // operand, and if it is 'trivially' dead, delete it in a future loop 340 // iteration. 341 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 342 if (isInstructionTriviallyDead(OpI, TLI)) 343 DeadInsts.push_back(OpI); 344 } 345 346 I->eraseFromParent(); 347 } while (!DeadInsts.empty()); 348 349 return true; 350} 351 352/// areAllUsesEqual - Check whether the uses of a value are all the same. 353/// This is similar to Instruction::hasOneUse() except this will also return 354/// true when there are no uses or multiple uses that all refer to the same 355/// value. 356static bool areAllUsesEqual(Instruction *I) { 357 Value::use_iterator UI = I->use_begin(); 358 Value::use_iterator UE = I->use_end(); 359 if (UI == UE) 360 return true; 361 362 User *TheUse = *UI; 363 for (++UI; UI != UE; ++UI) { 364 if (*UI != TheUse) 365 return false; 366 } 367 return true; 368} 369 370/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 371/// dead PHI node, due to being a def-use chain of single-use nodes that 372/// either forms a cycle or is terminated by a trivially dead instruction, 373/// delete it. If that makes any of its operands trivially dead, delete them 374/// too, recursively. Return true if a change was made. 375bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN, 376 const TargetLibraryInfo *TLI) { 377 SmallPtrSet<Instruction*, 4> Visited; 378 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 379 I = cast<Instruction>(*I->use_begin())) { 380 if (I->use_empty()) 381 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 382 383 // If we find an instruction more than once, we're on a cycle that 384 // won't prove fruitful. 385 if (!Visited.insert(I)) { 386 // Break the cycle and delete the instruction and its operands. 387 I->replaceAllUsesWith(UndefValue::get(I->getType())); 388 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 389 return true; 390 } 391 } 392 return false; 393} 394 395/// SimplifyInstructionsInBlock - Scan the specified basic block and try to 396/// simplify any instructions in it and recursively delete dead instructions. 397/// 398/// This returns true if it changed the code, note that it can delete 399/// instructions in other blocks as well in this block. 400bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD, 401 const TargetLibraryInfo *TLI) { 402 bool MadeChange = false; 403 404#ifndef NDEBUG 405 // In debug builds, ensure that the terminator of the block is never replaced 406 // or deleted by these simplifications. The idea of simplification is that it 407 // cannot introduce new instructions, and there is no way to replace the 408 // terminator of a block without introducing a new instruction. 409 AssertingVH<Instruction> TerminatorVH(--BB->end()); 410#endif 411 412 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) { 413 assert(!BI->isTerminator()); 414 Instruction *Inst = BI++; 415 416 WeakVH BIHandle(BI); 417 if (recursivelySimplifyInstruction(Inst, TD)) { 418 MadeChange = true; 419 if (BIHandle != BI) 420 BI = BB->begin(); 421 continue; 422 } 423 424 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI); 425 if (BIHandle != BI) 426 BI = BB->begin(); 427 } 428 return MadeChange; 429} 430 431//===----------------------------------------------------------------------===// 432// Control Flow Graph Restructuring. 433// 434 435 436/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 437/// method is called when we're about to delete Pred as a predecessor of BB. If 438/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 439/// 440/// Unlike the removePredecessor method, this attempts to simplify uses of PHI 441/// nodes that collapse into identity values. For example, if we have: 442/// x = phi(1, 0, 0, 0) 443/// y = and x, z 444/// 445/// .. and delete the predecessor corresponding to the '1', this will attempt to 446/// recursively fold the and to 0. 447void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 448 TargetData *TD) { 449 // This only adjusts blocks with PHI nodes. 450 if (!isa<PHINode>(BB->begin())) 451 return; 452 453 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 454 // them down. This will leave us with single entry phi nodes and other phis 455 // that can be removed. 456 BB->removePredecessor(Pred, true); 457 458 WeakVH PhiIt = &BB->front(); 459 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 460 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 461 Value *OldPhiIt = PhiIt; 462 463 if (!recursivelySimplifyInstruction(PN, TD)) 464 continue; 465 466 // If recursive simplification ended up deleting the next PHI node we would 467 // iterate to, then our iterator is invalid, restart scanning from the top 468 // of the block. 469 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 470 } 471} 472 473 474/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 475/// predecessor is known to have one successor (DestBB!). Eliminate the edge 476/// between them, moving the instructions in the predecessor into DestBB and 477/// deleting the predecessor block. 478/// 479void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 480 // If BB has single-entry PHI nodes, fold them. 481 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 482 Value *NewVal = PN->getIncomingValue(0); 483 // Replace self referencing PHI with undef, it must be dead. 484 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 485 PN->replaceAllUsesWith(NewVal); 486 PN->eraseFromParent(); 487 } 488 489 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 490 assert(PredBB && "Block doesn't have a single predecessor!"); 491 492 // Zap anything that took the address of DestBB. Not doing this will give the 493 // address an invalid value. 494 if (DestBB->hasAddressTaken()) { 495 BlockAddress *BA = BlockAddress::get(DestBB); 496 Constant *Replacement = 497 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 498 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 499 BA->getType())); 500 BA->destroyConstant(); 501 } 502 503 // Anything that branched to PredBB now branches to DestBB. 504 PredBB->replaceAllUsesWith(DestBB); 505 506 // Splice all the instructions from PredBB to DestBB. 507 PredBB->getTerminator()->eraseFromParent(); 508 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 509 510 if (P) { 511 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 512 if (DT) { 513 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 514 DT->changeImmediateDominator(DestBB, PredBBIDom); 515 DT->eraseNode(PredBB); 516 } 517 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 518 if (PI) { 519 PI->replaceAllUses(PredBB, DestBB); 520 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 521 } 522 } 523 // Nuke BB. 524 PredBB->eraseFromParent(); 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 BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) { 558 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 559 << Succ->getName() << " is conflicting with " 560 << BBPN->getName() << " with regard to common predecessor " 561 << IBB->getName() << "\n"); 562 return false; 563 } 564 } 565 } else { 566 Value* Val = PN->getIncomingValueForBlock(BB); 567 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 568 // See if the incoming value for the common predecessor is equal to the 569 // one for BB, in which case this phi node will not prevent the merging 570 // of the block. 571 BasicBlock *IBB = PN->getIncomingBlock(PI); 572 if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) { 573 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 574 << Succ->getName() << " is conflicting with regard to common " 575 << "predecessor " << IBB->getName() << "\n"); 576 return false; 577 } 578 } 579 } 580 } 581 582 return true; 583} 584 585/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 586/// unconditional branch, and contains no instructions other than PHI nodes, 587/// potential side-effect free intrinsics and the branch. If possible, 588/// eliminate BB by rewriting all the predecessors to branch to the successor 589/// block and return true. If we can't transform, return false. 590bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 591 assert(BB != &BB->getParent()->getEntryBlock() && 592 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 593 594 // We can't eliminate infinite loops. 595 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 596 if (BB == Succ) return false; 597 598 // Check to see if merging these blocks would cause conflicts for any of the 599 // phi nodes in BB or Succ. If not, we can safely merge. 600 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 601 602 // Check for cases where Succ has multiple predecessors and a PHI node in BB 603 // has uses which will not disappear when the PHI nodes are merged. It is 604 // possible to handle such cases, but difficult: it requires checking whether 605 // BB dominates Succ, which is non-trivial to calculate in the case where 606 // Succ has multiple predecessors. Also, it requires checking whether 607 // constructing the necessary self-referential PHI node doesn't intoduce any 608 // conflicts; this isn't too difficult, but the previous code for doing this 609 // was incorrect. 610 // 611 // Note that if this check finds a live use, BB dominates Succ, so BB is 612 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 613 // folding the branch isn't profitable in that case anyway. 614 if (!Succ->getSinglePredecessor()) { 615 BasicBlock::iterator BBI = BB->begin(); 616 while (isa<PHINode>(*BBI)) { 617 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 618 UI != E; ++UI) { 619 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 620 if (PN->getIncomingBlock(UI) != BB) 621 return false; 622 } else { 623 return false; 624 } 625 } 626 ++BBI; 627 } 628 } 629 630 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 631 632 if (isa<PHINode>(Succ->begin())) { 633 // If there is more than one pred of succ, and there are PHI nodes in 634 // the successor, then we need to add incoming edges for the PHI nodes 635 // 636 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 637 638 // Loop over all of the PHI nodes in the successor of BB. 639 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 640 PHINode *PN = cast<PHINode>(I); 641 Value *OldVal = PN->removeIncomingValue(BB, false); 642 assert(OldVal && "No entry in PHI for Pred BB!"); 643 644 // If this incoming value is one of the PHI nodes in BB, the new entries 645 // in the PHI node are the entries from the old PHI. 646 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 647 PHINode *OldValPN = cast<PHINode>(OldVal); 648 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 649 // Note that, since we are merging phi nodes and BB and Succ might 650 // have common predecessors, we could end up with a phi node with 651 // identical incoming branches. This will be cleaned up later (and 652 // will trigger asserts if we try to clean it up now, without also 653 // simplifying the corresponding conditional branch). 654 PN->addIncoming(OldValPN->getIncomingValue(i), 655 OldValPN->getIncomingBlock(i)); 656 } else { 657 // Add an incoming value for each of the new incoming values. 658 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 659 PN->addIncoming(OldVal, BBPreds[i]); 660 } 661 } 662 } 663 664 if (Succ->getSinglePredecessor()) { 665 // BB is the only predecessor of Succ, so Succ will end up with exactly 666 // the same predecessors BB had. 667 668 // Copy over any phi, debug or lifetime instruction. 669 BB->getTerminator()->eraseFromParent(); 670 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList()); 671 } else { 672 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 673 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 674 assert(PN->use_empty() && "There shouldn't be any uses here!"); 675 PN->eraseFromParent(); 676 } 677 } 678 679 // Everything that jumped to BB now goes to Succ. 680 BB->replaceAllUsesWith(Succ); 681 if (!Succ->hasName()) Succ->takeName(BB); 682 BB->eraseFromParent(); // Delete the old basic block. 683 return true; 684} 685 686/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 687/// nodes in this block. This doesn't try to be clever about PHI nodes 688/// which differ only in the order of the incoming values, but instcombine 689/// orders them so it usually won't matter. 690/// 691bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 692 bool Changed = false; 693 694 // This implementation doesn't currently consider undef operands 695 // specially. Theoretically, two phis which are identical except for 696 // one having an undef where the other doesn't could be collapsed. 697 698 // Map from PHI hash values to PHI nodes. If multiple PHIs have 699 // the same hash value, the element is the first PHI in the 700 // linked list in CollisionMap. 701 DenseMap<uintptr_t, PHINode *> HashMap; 702 703 // Maintain linked lists of PHI nodes with common hash values. 704 DenseMap<PHINode *, PHINode *> CollisionMap; 705 706 // Examine each PHI. 707 for (BasicBlock::iterator I = BB->begin(); 708 PHINode *PN = dyn_cast<PHINode>(I++); ) { 709 // Compute a hash value on the operands. Instcombine will likely have sorted 710 // them, which helps expose duplicates, but we have to check all the 711 // operands to be safe in case instcombine hasn't run. 712 uintptr_t Hash = 0; 713 // This hash algorithm is quite weak as hash functions go, but it seems 714 // to do a good enough job for this particular purpose, and is very quick. 715 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 716 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 717 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 718 } 719 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end(); 720 I != E; ++I) { 721 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I)); 722 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 723 } 724 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 725 Hash >>= 1; 726 // If we've never seen this hash value before, it's a unique PHI. 727 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 728 HashMap.insert(std::make_pair(Hash, PN)); 729 if (Pair.second) continue; 730 // Otherwise it's either a duplicate or a hash collision. 731 for (PHINode *OtherPN = Pair.first->second; ; ) { 732 if (OtherPN->isIdenticalTo(PN)) { 733 // A duplicate. Replace this PHI with its duplicate. 734 PN->replaceAllUsesWith(OtherPN); 735 PN->eraseFromParent(); 736 Changed = true; 737 break; 738 } 739 // A non-duplicate hash collision. 740 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 741 if (I == CollisionMap.end()) { 742 // Set this PHI to be the head of the linked list of colliding PHIs. 743 PHINode *Old = Pair.first->second; 744 Pair.first->second = PN; 745 CollisionMap[PN] = Old; 746 break; 747 } 748 // Proceed to the next PHI in the list. 749 OtherPN = I->second; 750 } 751 } 752 753 return Changed; 754} 755 756/// enforceKnownAlignment - If the specified pointer points to an object that 757/// we control, modify the object's alignment to PrefAlign. This isn't 758/// often possible though. If alignment is important, a more reliable approach 759/// is to simply align all global variables and allocation instructions to 760/// their preferred alignment from the beginning. 761/// 762static unsigned enforceKnownAlignment(Value *V, unsigned Align, 763 unsigned PrefAlign, const TargetData *TD) { 764 V = V->stripPointerCasts(); 765 766 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 767 // If the preferred alignment is greater than the natural stack alignment 768 // then don't round up. This avoids dynamic stack realignment. 769 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign)) 770 return Align; 771 // If there is a requested alignment and if this is an alloca, round up. 772 if (AI->getAlignment() >= PrefAlign) 773 return AI->getAlignment(); 774 AI->setAlignment(PrefAlign); 775 return PrefAlign; 776 } 777 778 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 779 // If there is a large requested alignment and we can, bump up the alignment 780 // of the global. 781 if (GV->isDeclaration()) return Align; 782 // If the memory we set aside for the global may not be the memory used by 783 // the final program then it is impossible for us to reliably enforce the 784 // preferred alignment. 785 if (GV->isWeakForLinker()) return Align; 786 787 if (GV->getAlignment() >= PrefAlign) 788 return GV->getAlignment(); 789 // We can only increase the alignment of the global if it has no alignment 790 // specified or if it is not assigned a section. If it is assigned a 791 // section, the global could be densely packed with other objects in the 792 // section, increasing the alignment could cause padding issues. 793 if (!GV->hasSection() || GV->getAlignment() == 0) 794 GV->setAlignment(PrefAlign); 795 return GV->getAlignment(); 796 } 797 798 return Align; 799} 800 801/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 802/// we can determine, return it, otherwise return 0. If PrefAlign is specified, 803/// and it is more than the alignment of the ultimate object, see if we can 804/// increase the alignment of the ultimate object, making this check succeed. 805unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 806 const TargetData *TD) { 807 assert(V->getType()->isPointerTy() && 808 "getOrEnforceKnownAlignment expects a pointer!"); 809 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 810 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 811 ComputeMaskedBits(V, KnownZero, KnownOne, TD); 812 unsigned TrailZ = KnownZero.countTrailingOnes(); 813 814 // Avoid trouble with rediculously large TrailZ values, such as 815 // those computed from a null pointer. 816 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 817 818 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 819 820 // LLVM doesn't support alignments larger than this currently. 821 Align = std::min(Align, +Value::MaximumAlignment); 822 823 if (PrefAlign > Align) 824 Align = enforceKnownAlignment(V, Align, PrefAlign, TD); 825 826 // We don't need to make any adjustment. 827 return Align; 828} 829 830///===---------------------------------------------------------------------===// 831/// Dbg Intrinsic utilities 832/// 833 834/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 835/// that has an associated llvm.dbg.decl intrinsic. 836bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 837 StoreInst *SI, DIBuilder &Builder) { 838 DIVariable DIVar(DDI->getVariable()); 839 if (!DIVar.Verify()) 840 return false; 841 842 Instruction *DbgVal = NULL; 843 // If an argument is zero extended then use argument directly. The ZExt 844 // may be zapped by an optimization pass in future. 845 Argument *ExtendedArg = NULL; 846 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) 847 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); 848 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) 849 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); 850 if (ExtendedArg) 851 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI); 852 else 853 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI); 854 855 // Propagate any debug metadata from the store onto the dbg.value. 856 DebugLoc SIDL = SI->getDebugLoc(); 857 if (!SIDL.isUnknown()) 858 DbgVal->setDebugLoc(SIDL); 859 // Otherwise propagate debug metadata from dbg.declare. 860 else 861 DbgVal->setDebugLoc(DDI->getDebugLoc()); 862 return true; 863} 864 865/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 866/// that has an associated llvm.dbg.decl intrinsic. 867bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 868 LoadInst *LI, DIBuilder &Builder) { 869 DIVariable DIVar(DDI->getVariable()); 870 if (!DIVar.Verify()) 871 return false; 872 873 Instruction *DbgVal = 874 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 875 DIVar, LI); 876 877 // Propagate any debug metadata from the store onto the dbg.value. 878 DebugLoc LIDL = LI->getDebugLoc(); 879 if (!LIDL.isUnknown()) 880 DbgVal->setDebugLoc(LIDL); 881 // Otherwise propagate debug metadata from dbg.declare. 882 else 883 DbgVal->setDebugLoc(DDI->getDebugLoc()); 884 return true; 885} 886 887/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 888/// of llvm.dbg.value intrinsics. 889bool llvm::LowerDbgDeclare(Function &F) { 890 DIBuilder DIB(*F.getParent()); 891 SmallVector<DbgDeclareInst *, 4> Dbgs; 892 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 893 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 894 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 895 Dbgs.push_back(DDI); 896 } 897 if (Dbgs.empty()) 898 return false; 899 900 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(), 901 E = Dbgs.end(); I != E; ++I) { 902 DbgDeclareInst *DDI = *I; 903 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) { 904 bool RemoveDDI = true; 905 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 906 UI != E; ++UI) 907 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 908 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 909 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 910 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 911 else 912 RemoveDDI = false; 913 if (RemoveDDI) 914 DDI->eraseFromParent(); 915 } 916 } 917 return true; 918} 919 920/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the 921/// alloca 'V', if any. 922DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { 923 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V)) 924 for (Value::use_iterator UI = DebugNode->use_begin(), 925 E = DebugNode->use_end(); UI != E; ++UI) 926 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI)) 927 return DDI; 928 929 return 0; 930} 931