Local.cpp revision 0aa32d5d0ff6cd65b6cff957858a79e2d2a614bd
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/GlobalAlias.h" 18#include "llvm/GlobalVariable.h" 19#include "llvm/DerivedTypes.h" 20#include "llvm/Instructions.h" 21#include "llvm/Intrinsics.h" 22#include "llvm/IntrinsicInst.h" 23#include "llvm/Metadata.h" 24#include "llvm/Operator.h" 25#include "llvm/ADT/DenseMap.h" 26#include "llvm/ADT/SmallPtrSet.h" 27#include "llvm/Analysis/DebugInfo.h" 28#include "llvm/Analysis/DIBuilder.h" 29#include "llvm/Analysis/Dominators.h" 30#include "llvm/Analysis/InstructionSimplify.h" 31#include "llvm/Analysis/MemoryBuiltins.h" 32#include "llvm/Analysis/ProfileInfo.h" 33#include "llvm/Analysis/ValueTracking.h" 34#include "llvm/Target/TargetData.h" 35#include "llvm/Support/CFG.h" 36#include "llvm/Support/Debug.h" 37#include "llvm/Support/GetElementPtrTypeIterator.h" 38#include "llvm/Support/IRBuilder.h" 39#include "llvm/Support/MathExtras.h" 40#include "llvm/Support/ValueHandle.h" 41#include "llvm/Support/raw_ostream.h" 42using namespace llvm; 43 44//===----------------------------------------------------------------------===// 45// Local constant propagation. 46// 47 48/// ConstantFoldTerminator - If a terminator instruction is predicated on a 49/// constant value, convert it into an unconditional branch to the constant 50/// destination. This is a nontrivial operation because the successors of this 51/// basic block must have their PHI nodes updated. 52/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch 53/// conditions and indirectbr addresses this might make dead if 54/// DeleteDeadConditions is true. 55bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions) { 56 TerminatorInst *T = BB->getTerminator(); 57 IRBuilder<> Builder(T); 58 59 // Branch - See if we are conditional jumping on constant 60 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 61 if (BI->isUnconditional()) return false; // Can't optimize uncond branch 62 BasicBlock *Dest1 = BI->getSuccessor(0); 63 BasicBlock *Dest2 = BI->getSuccessor(1); 64 65 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { 66 // Are we branching on constant? 67 // YES. Change to unconditional branch... 68 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; 69 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; 70 71 //cerr << "Function: " << T->getParent()->getParent() 72 // << "\nRemoving branch from " << T->getParent() 73 // << "\n\nTo: " << OldDest << endl; 74 75 // Let the basic block know that we are letting go of it. Based on this, 76 // it will adjust it's PHI nodes. 77 OldDest->removePredecessor(BB); 78 79 // Replace the conditional branch with an unconditional one. 80 Builder.CreateBr(Destination); 81 BI->eraseFromParent(); 82 return true; 83 } 84 85 if (Dest2 == Dest1) { // Conditional branch to same location? 86 // This branch matches something like this: 87 // br bool %cond, label %Dest, label %Dest 88 // and changes it into: br label %Dest 89 90 // Let the basic block know that we are letting go of one copy of it. 91 assert(BI->getParent() && "Terminator not inserted in block!"); 92 Dest1->removePredecessor(BI->getParent()); 93 94 // Replace the conditional branch with an unconditional one. 95 Builder.CreateBr(Dest1); 96 Value *Cond = BI->getCondition(); 97 BI->eraseFromParent(); 98 if (DeleteDeadConditions) 99 RecursivelyDeleteTriviallyDeadInstructions(Cond); 100 return true; 101 } 102 return false; 103 } 104 105 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { 106 // If we are switching on a constant, we can convert the switch into a 107 // single branch instruction! 108 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); 109 BasicBlock *TheOnlyDest = SI->getDefaultDest(); 110 BasicBlock *DefaultDest = TheOnlyDest; 111 112 // Figure out which case it goes to. 113 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 114 i != e; ++i) { 115 // Found case matching a constant operand? 116 if (i.getCaseValue() == CI) { 117 TheOnlyDest = i.getCaseSuccessor(); 118 break; 119 } 120 121 // Check to see if this branch is going to the same place as the default 122 // dest. If so, eliminate it as an explicit compare. 123 if (i.getCaseSuccessor() == DefaultDest) { 124 // Remove this entry. 125 DefaultDest->removePredecessor(SI->getParent()); 126 SI->removeCase(i); 127 --i; --e; 128 continue; 129 } 130 131 // Otherwise, check to see if the switch only branches to one destination. 132 // We do this by reseting "TheOnlyDest" to null when we find two non-equal 133 // destinations. 134 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = 0; 135 } 136 137 if (CI && !TheOnlyDest) { 138 // Branching on a constant, but not any of the cases, go to the default 139 // successor. 140 TheOnlyDest = SI->getDefaultDest(); 141 } 142 143 // If we found a single destination that we can fold the switch into, do so 144 // now. 145 if (TheOnlyDest) { 146 // Insert the new branch. 147 Builder.CreateBr(TheOnlyDest); 148 BasicBlock *BB = SI->getParent(); 149 150 // Remove entries from PHI nodes which we no longer branch to... 151 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) { 152 // Found case matching a constant operand? 153 BasicBlock *Succ = SI->getSuccessor(i); 154 if (Succ == TheOnlyDest) 155 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest 156 else 157 Succ->removePredecessor(BB); 158 } 159 160 // Delete the old switch. 161 Value *Cond = SI->getCondition(); 162 SI->eraseFromParent(); 163 if (DeleteDeadConditions) 164 RecursivelyDeleteTriviallyDeadInstructions(Cond); 165 return true; 166 } 167 168 if (SI->getNumCases() == 1) { 169 // Otherwise, we can fold this switch into a conditional branch 170 // instruction if it has only one non-default destination. 171 SwitchInst::CaseIt FirstCase = SI->case_begin(); 172 IntegersSubset CaseRanges = FirstCase.getCaseValueEx(); 173 if (CaseRanges.getNumItems() == 1 && CaseRanges.isSingleNumber(0)) { 174 // FIXME: Currently work with ConstantInt based numbers. 175 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), 176 CaseRanges.getItem(0).Low.toConstantInt(), 177 "cond"); 178 179 // Insert the new branch. 180 Builder.CreateCondBr(Cond, FirstCase.getCaseSuccessor(), 181 SI->getDefaultDest()); 182 183 // Delete the old switch. 184 SI->eraseFromParent(); 185 return true; 186 187 } 188 } 189 return false; 190 } 191 192 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 193 // indirectbr blockaddress(@F, @BB) -> br label @BB 194 if (BlockAddress *BA = 195 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 196 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 197 // Insert the new branch. 198 Builder.CreateBr(TheOnlyDest); 199 200 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 201 if (IBI->getDestination(i) == TheOnlyDest) 202 TheOnlyDest = 0; 203 else 204 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 205 } 206 Value *Address = IBI->getAddress(); 207 IBI->eraseFromParent(); 208 if (DeleteDeadConditions) 209 RecursivelyDeleteTriviallyDeadInstructions(Address); 210 211 // If we didn't find our destination in the IBI successor list, then we 212 // have undefined behavior. Replace the unconditional branch with an 213 // 'unreachable' instruction. 214 if (TheOnlyDest) { 215 BB->getTerminator()->eraseFromParent(); 216 new UnreachableInst(BB->getContext(), BB); 217 } 218 219 return true; 220 } 221 } 222 223 return false; 224} 225 226 227//===----------------------------------------------------------------------===// 228// Local dead code elimination. 229// 230 231/// isInstructionTriviallyDead - Return true if the result produced by the 232/// instruction is not used, and the instruction has no side effects. 233/// 234bool llvm::isInstructionTriviallyDead(Instruction *I) { 235 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 236 237 // We don't want the landingpad instruction removed by anything this general. 238 if (isa<LandingPadInst>(I)) 239 return false; 240 241 // We don't want debug info removed by anything this general, unless 242 // debug info is empty. 243 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 244 if (DDI->getAddress()) 245 return false; 246 return true; 247 } 248 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 249 if (DVI->getValue()) 250 return false; 251 return true; 252 } 253 254 if (!I->mayHaveSideEffects()) return true; 255 256 // Special case intrinsics that "may have side effects" but can be deleted 257 // when dead. 258 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 259 // Safe to delete llvm.stacksave if dead. 260 if (II->getIntrinsicID() == Intrinsic::stacksave) 261 return true; 262 263 // Lifetime intrinsics are dead when their right-hand is undef. 264 if (II->getIntrinsicID() == Intrinsic::lifetime_start || 265 II->getIntrinsicID() == Intrinsic::lifetime_end) 266 return isa<UndefValue>(II->getArgOperand(1)); 267 } 268 269 if (extractMallocCall(I) || extractCallocCall(I)) return true; 270 271 if (CallInst *CI = isFreeCall(I)) 272 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0))) 273 return C->isNullValue() || isa<UndefValue>(C); 274 275 return false; 276} 277 278/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 279/// trivially dead instruction, delete it. If that makes any of its operands 280/// trivially dead, delete them too, recursively. Return true if any 281/// instructions were deleted. 282bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) { 283 Instruction *I = dyn_cast<Instruction>(V); 284 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I)) 285 return false; 286 287 SmallVector<Instruction*, 16> DeadInsts; 288 DeadInsts.push_back(I); 289 290 do { 291 I = DeadInsts.pop_back_val(); 292 293 // Null out all of the instruction's operands to see if any operand becomes 294 // dead as we go. 295 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 296 Value *OpV = I->getOperand(i); 297 I->setOperand(i, 0); 298 299 if (!OpV->use_empty()) continue; 300 301 // If the operand is an instruction that became dead as we nulled out the 302 // operand, and if it is 'trivially' dead, delete it in a future loop 303 // iteration. 304 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 305 if (isInstructionTriviallyDead(OpI)) 306 DeadInsts.push_back(OpI); 307 } 308 309 I->eraseFromParent(); 310 } while (!DeadInsts.empty()); 311 312 return true; 313} 314 315/// areAllUsesEqual - Check whether the uses of a value are all the same. 316/// This is similar to Instruction::hasOneUse() except this will also return 317/// true when there are no uses or multiple uses that all refer to the same 318/// value. 319static bool areAllUsesEqual(Instruction *I) { 320 Value::use_iterator UI = I->use_begin(); 321 Value::use_iterator UE = I->use_end(); 322 if (UI == UE) 323 return true; 324 325 User *TheUse = *UI; 326 for (++UI; UI != UE; ++UI) { 327 if (*UI != TheUse) 328 return false; 329 } 330 return true; 331} 332 333/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 334/// dead PHI node, due to being a def-use chain of single-use nodes that 335/// either forms a cycle or is terminated by a trivially dead instruction, 336/// delete it. If that makes any of its operands trivially dead, delete them 337/// too, recursively. Return true if a change was made. 338bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) { 339 SmallPtrSet<Instruction*, 4> Visited; 340 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 341 I = cast<Instruction>(*I->use_begin())) { 342 if (I->use_empty()) 343 return RecursivelyDeleteTriviallyDeadInstructions(I); 344 345 // If we find an instruction more than once, we're on a cycle that 346 // won't prove fruitful. 347 if (!Visited.insert(I)) { 348 // Break the cycle and delete the instruction and its operands. 349 I->replaceAllUsesWith(UndefValue::get(I->getType())); 350 (void)RecursivelyDeleteTriviallyDeadInstructions(I); 351 return true; 352 } 353 } 354 return false; 355} 356 357/// SimplifyInstructionsInBlock - Scan the specified basic block and try to 358/// simplify any instructions in it and recursively delete dead instructions. 359/// 360/// This returns true if it changed the code, note that it can delete 361/// instructions in other blocks as well in this block. 362bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) { 363 bool MadeChange = false; 364 365#ifndef NDEBUG 366 // In debug builds, ensure that the terminator of the block is never replaced 367 // or deleted by these simplifications. The idea of simplification is that it 368 // cannot introduce new instructions, and there is no way to replace the 369 // terminator of a block without introducing a new instruction. 370 AssertingVH<Instruction> TerminatorVH(--BB->end()); 371#endif 372 373 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) { 374 assert(!BI->isTerminator()); 375 Instruction *Inst = BI++; 376 377 WeakVH BIHandle(BI); 378 if (recursivelySimplifyInstruction(Inst, TD)) { 379 MadeChange = true; 380 if (BIHandle != BI) 381 BI = BB->begin(); 382 continue; 383 } 384 385 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst); 386 if (BIHandle != BI) 387 BI = BB->begin(); 388 } 389 return MadeChange; 390} 391 392//===----------------------------------------------------------------------===// 393// Control Flow Graph Restructuring. 394// 395 396 397/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 398/// method is called when we're about to delete Pred as a predecessor of BB. If 399/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 400/// 401/// Unlike the removePredecessor method, this attempts to simplify uses of PHI 402/// nodes that collapse into identity values. For example, if we have: 403/// x = phi(1, 0, 0, 0) 404/// y = and x, z 405/// 406/// .. and delete the predecessor corresponding to the '1', this will attempt to 407/// recursively fold the and to 0. 408void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 409 TargetData *TD) { 410 // This only adjusts blocks with PHI nodes. 411 if (!isa<PHINode>(BB->begin())) 412 return; 413 414 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 415 // them down. This will leave us with single entry phi nodes and other phis 416 // that can be removed. 417 BB->removePredecessor(Pred, true); 418 419 WeakVH PhiIt = &BB->front(); 420 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 421 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 422 Value *OldPhiIt = PhiIt; 423 424 if (!recursivelySimplifyInstruction(PN, TD)) 425 continue; 426 427 // If recursive simplification ended up deleting the next PHI node we would 428 // iterate to, then our iterator is invalid, restart scanning from the top 429 // of the block. 430 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 431 } 432} 433 434 435/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 436/// predecessor is known to have one successor (DestBB!). Eliminate the edge 437/// between them, moving the instructions in the predecessor into DestBB and 438/// deleting the predecessor block. 439/// 440void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 441 // If BB has single-entry PHI nodes, fold them. 442 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 443 Value *NewVal = PN->getIncomingValue(0); 444 // Replace self referencing PHI with undef, it must be dead. 445 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 446 PN->replaceAllUsesWith(NewVal); 447 PN->eraseFromParent(); 448 } 449 450 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 451 assert(PredBB && "Block doesn't have a single predecessor!"); 452 453 // Zap anything that took the address of DestBB. Not doing this will give the 454 // address an invalid value. 455 if (DestBB->hasAddressTaken()) { 456 BlockAddress *BA = BlockAddress::get(DestBB); 457 Constant *Replacement = 458 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 459 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 460 BA->getType())); 461 BA->destroyConstant(); 462 } 463 464 // Anything that branched to PredBB now branches to DestBB. 465 PredBB->replaceAllUsesWith(DestBB); 466 467 // Splice all the instructions from PredBB to DestBB. 468 PredBB->getTerminator()->eraseFromParent(); 469 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 470 471 if (P) { 472 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 473 if (DT) { 474 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 475 DT->changeImmediateDominator(DestBB, PredBBIDom); 476 DT->eraseNode(PredBB); 477 } 478 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 479 if (PI) { 480 PI->replaceAllUses(PredBB, DestBB); 481 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 482 } 483 } 484 // Nuke BB. 485 PredBB->eraseFromParent(); 486} 487 488/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 489/// almost-empty BB ending in an unconditional branch to Succ, into succ. 490/// 491/// Assumption: Succ is the single successor for BB. 492/// 493static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 494 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 495 496 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 497 << Succ->getName() << "\n"); 498 // Shortcut, if there is only a single predecessor it must be BB and merging 499 // is always safe 500 if (Succ->getSinglePredecessor()) return true; 501 502 // Make a list of the predecessors of BB 503 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 504 505 // Look at all the phi nodes in Succ, to see if they present a conflict when 506 // merging these blocks 507 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 508 PHINode *PN = cast<PHINode>(I); 509 510 // If the incoming value from BB is again a PHINode in 511 // BB which has the same incoming value for *PI as PN does, we can 512 // merge the phi nodes and then the blocks can still be merged 513 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 514 if (BBPN && BBPN->getParent() == BB) { 515 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 516 BasicBlock *IBB = PN->getIncomingBlock(PI); 517 if (BBPreds.count(IBB) && 518 BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) { 519 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 520 << Succ->getName() << " is conflicting with " 521 << BBPN->getName() << " with regard to common predecessor " 522 << IBB->getName() << "\n"); 523 return false; 524 } 525 } 526 } else { 527 Value* Val = PN->getIncomingValueForBlock(BB); 528 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 529 // See if the incoming value for the common predecessor is equal to the 530 // one for BB, in which case this phi node will not prevent the merging 531 // of the block. 532 BasicBlock *IBB = PN->getIncomingBlock(PI); 533 if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) { 534 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 535 << Succ->getName() << " is conflicting with regard to common " 536 << "predecessor " << IBB->getName() << "\n"); 537 return false; 538 } 539 } 540 } 541 } 542 543 return true; 544} 545 546/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 547/// unconditional branch, and contains no instructions other than PHI nodes, 548/// potential side-effect free intrinsics and the branch. If possible, 549/// eliminate BB by rewriting all the predecessors to branch to the successor 550/// block and return true. If we can't transform, return false. 551bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 552 assert(BB != &BB->getParent()->getEntryBlock() && 553 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 554 555 // We can't eliminate infinite loops. 556 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 557 if (BB == Succ) return false; 558 559 // Check to see if merging these blocks would cause conflicts for any of the 560 // phi nodes in BB or Succ. If not, we can safely merge. 561 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 562 563 // Check for cases where Succ has multiple predecessors and a PHI node in BB 564 // has uses which will not disappear when the PHI nodes are merged. It is 565 // possible to handle such cases, but difficult: it requires checking whether 566 // BB dominates Succ, which is non-trivial to calculate in the case where 567 // Succ has multiple predecessors. Also, it requires checking whether 568 // constructing the necessary self-referential PHI node doesn't intoduce any 569 // conflicts; this isn't too difficult, but the previous code for doing this 570 // was incorrect. 571 // 572 // Note that if this check finds a live use, BB dominates Succ, so BB is 573 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 574 // folding the branch isn't profitable in that case anyway. 575 if (!Succ->getSinglePredecessor()) { 576 BasicBlock::iterator BBI = BB->begin(); 577 while (isa<PHINode>(*BBI)) { 578 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 579 UI != E; ++UI) { 580 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 581 if (PN->getIncomingBlock(UI) != BB) 582 return false; 583 } else { 584 return false; 585 } 586 } 587 ++BBI; 588 } 589 } 590 591 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 592 593 if (isa<PHINode>(Succ->begin())) { 594 // If there is more than one pred of succ, and there are PHI nodes in 595 // the successor, then we need to add incoming edges for the PHI nodes 596 // 597 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 598 599 // Loop over all of the PHI nodes in the successor of BB. 600 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 601 PHINode *PN = cast<PHINode>(I); 602 Value *OldVal = PN->removeIncomingValue(BB, false); 603 assert(OldVal && "No entry in PHI for Pred BB!"); 604 605 // If this incoming value is one of the PHI nodes in BB, the new entries 606 // in the PHI node are the entries from the old PHI. 607 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 608 PHINode *OldValPN = cast<PHINode>(OldVal); 609 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 610 // Note that, since we are merging phi nodes and BB and Succ might 611 // have common predecessors, we could end up with a phi node with 612 // identical incoming branches. This will be cleaned up later (and 613 // will trigger asserts if we try to clean it up now, without also 614 // simplifying the corresponding conditional branch). 615 PN->addIncoming(OldValPN->getIncomingValue(i), 616 OldValPN->getIncomingBlock(i)); 617 } else { 618 // Add an incoming value for each of the new incoming values. 619 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 620 PN->addIncoming(OldVal, BBPreds[i]); 621 } 622 } 623 } 624 625 if (Succ->getSinglePredecessor()) { 626 // BB is the only predecessor of Succ, so Succ will end up with exactly 627 // the same predecessors BB had. 628 629 // Copy over any phi, debug or lifetime instruction. 630 BB->getTerminator()->eraseFromParent(); 631 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList()); 632 } else { 633 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 634 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 635 assert(PN->use_empty() && "There shouldn't be any uses here!"); 636 PN->eraseFromParent(); 637 } 638 } 639 640 // Everything that jumped to BB now goes to Succ. 641 BB->replaceAllUsesWith(Succ); 642 if (!Succ->hasName()) Succ->takeName(BB); 643 BB->eraseFromParent(); // Delete the old basic block. 644 return true; 645} 646 647/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 648/// nodes in this block. This doesn't try to be clever about PHI nodes 649/// which differ only in the order of the incoming values, but instcombine 650/// orders them so it usually won't matter. 651/// 652bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 653 bool Changed = false; 654 655 // This implementation doesn't currently consider undef operands 656 // specially. Theoretically, two phis which are identical except for 657 // one having an undef where the other doesn't could be collapsed. 658 659 // Map from PHI hash values to PHI nodes. If multiple PHIs have 660 // the same hash value, the element is the first PHI in the 661 // linked list in CollisionMap. 662 DenseMap<uintptr_t, PHINode *> HashMap; 663 664 // Maintain linked lists of PHI nodes with common hash values. 665 DenseMap<PHINode *, PHINode *> CollisionMap; 666 667 // Examine each PHI. 668 for (BasicBlock::iterator I = BB->begin(); 669 PHINode *PN = dyn_cast<PHINode>(I++); ) { 670 // Compute a hash value on the operands. Instcombine will likely have sorted 671 // them, which helps expose duplicates, but we have to check all the 672 // operands to be safe in case instcombine hasn't run. 673 uintptr_t Hash = 0; 674 // This hash algorithm is quite weak as hash functions go, but it seems 675 // to do a good enough job for this particular purpose, and is very quick. 676 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 677 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 678 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 679 } 680 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end(); 681 I != E; ++I) { 682 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I)); 683 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 684 } 685 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 686 Hash >>= 1; 687 // If we've never seen this hash value before, it's a unique PHI. 688 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 689 HashMap.insert(std::make_pair(Hash, PN)); 690 if (Pair.second) continue; 691 // Otherwise it's either a duplicate or a hash collision. 692 for (PHINode *OtherPN = Pair.first->second; ; ) { 693 if (OtherPN->isIdenticalTo(PN)) { 694 // A duplicate. Replace this PHI with its duplicate. 695 PN->replaceAllUsesWith(OtherPN); 696 PN->eraseFromParent(); 697 Changed = true; 698 break; 699 } 700 // A non-duplicate hash collision. 701 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 702 if (I == CollisionMap.end()) { 703 // Set this PHI to be the head of the linked list of colliding PHIs. 704 PHINode *Old = Pair.first->second; 705 Pair.first->second = PN; 706 CollisionMap[PN] = Old; 707 break; 708 } 709 // Procede to the next PHI in the list. 710 OtherPN = I->second; 711 } 712 } 713 714 return Changed; 715} 716 717/// enforceKnownAlignment - If the specified pointer points to an object that 718/// we control, modify the object's alignment to PrefAlign. This isn't 719/// often possible though. If alignment is important, a more reliable approach 720/// is to simply align all global variables and allocation instructions to 721/// their preferred alignment from the beginning. 722/// 723static unsigned enforceKnownAlignment(Value *V, unsigned Align, 724 unsigned PrefAlign, const TargetData *TD) { 725 V = V->stripPointerCasts(); 726 727 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 728 // If the preferred alignment is greater than the natural stack alignment 729 // then don't round up. This avoids dynamic stack realignment. 730 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign)) 731 return Align; 732 // If there is a requested alignment and if this is an alloca, round up. 733 if (AI->getAlignment() >= PrefAlign) 734 return AI->getAlignment(); 735 AI->setAlignment(PrefAlign); 736 return PrefAlign; 737 } 738 739 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 740 // If there is a large requested alignment and we can, bump up the alignment 741 // of the global. 742 if (GV->isDeclaration()) return Align; 743 // If the memory we set aside for the global may not be the memory used by 744 // the final program then it is impossible for us to reliably enforce the 745 // preferred alignment. 746 if (GV->isWeakForLinker()) return Align; 747 748 if (GV->getAlignment() >= PrefAlign) 749 return GV->getAlignment(); 750 // We can only increase the alignment of the global if it has no alignment 751 // specified or if it is not assigned a section. If it is assigned a 752 // section, the global could be densely packed with other objects in the 753 // section, increasing the alignment could cause padding issues. 754 if (!GV->hasSection() || GV->getAlignment() == 0) 755 GV->setAlignment(PrefAlign); 756 return GV->getAlignment(); 757 } 758 759 return Align; 760} 761 762/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 763/// we can determine, return it, otherwise return 0. If PrefAlign is specified, 764/// and it is more than the alignment of the ultimate object, see if we can 765/// increase the alignment of the ultimate object, making this check succeed. 766unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 767 const TargetData *TD) { 768 assert(V->getType()->isPointerTy() && 769 "getOrEnforceKnownAlignment expects a pointer!"); 770 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 771 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 772 ComputeMaskedBits(V, KnownZero, KnownOne, TD); 773 unsigned TrailZ = KnownZero.countTrailingOnes(); 774 775 // Avoid trouble with rediculously large TrailZ values, such as 776 // those computed from a null pointer. 777 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 778 779 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 780 781 // LLVM doesn't support alignments larger than this currently. 782 Align = std::min(Align, +Value::MaximumAlignment); 783 784 if (PrefAlign > Align) 785 Align = enforceKnownAlignment(V, Align, PrefAlign, TD); 786 787 // We don't need to make any adjustment. 788 return Align; 789} 790 791///===---------------------------------------------------------------------===// 792/// Dbg Intrinsic utilities 793/// 794 795/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 796/// that has an associated llvm.dbg.decl intrinsic. 797bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 798 StoreInst *SI, DIBuilder &Builder) { 799 DIVariable DIVar(DDI->getVariable()); 800 if (!DIVar.Verify()) 801 return false; 802 803 Instruction *DbgVal = NULL; 804 // If an argument is zero extended then use argument directly. The ZExt 805 // may be zapped by an optimization pass in future. 806 Argument *ExtendedArg = NULL; 807 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) 808 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); 809 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) 810 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); 811 if (ExtendedArg) 812 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI); 813 else 814 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI); 815 816 // Propagate any debug metadata from the store onto the dbg.value. 817 DebugLoc SIDL = SI->getDebugLoc(); 818 if (!SIDL.isUnknown()) 819 DbgVal->setDebugLoc(SIDL); 820 // Otherwise propagate debug metadata from dbg.declare. 821 else 822 DbgVal->setDebugLoc(DDI->getDebugLoc()); 823 return true; 824} 825 826/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 827/// that has an associated llvm.dbg.decl intrinsic. 828bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 829 LoadInst *LI, DIBuilder &Builder) { 830 DIVariable DIVar(DDI->getVariable()); 831 if (!DIVar.Verify()) 832 return false; 833 834 Instruction *DbgVal = 835 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 836 DIVar, LI); 837 838 // Propagate any debug metadata from the store onto the dbg.value. 839 DebugLoc LIDL = LI->getDebugLoc(); 840 if (!LIDL.isUnknown()) 841 DbgVal->setDebugLoc(LIDL); 842 // Otherwise propagate debug metadata from dbg.declare. 843 else 844 DbgVal->setDebugLoc(DDI->getDebugLoc()); 845 return true; 846} 847 848/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 849/// of llvm.dbg.value intrinsics. 850bool llvm::LowerDbgDeclare(Function &F) { 851 DIBuilder DIB(*F.getParent()); 852 SmallVector<DbgDeclareInst *, 4> Dbgs; 853 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 854 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 855 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 856 Dbgs.push_back(DDI); 857 } 858 if (Dbgs.empty()) 859 return false; 860 861 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(), 862 E = Dbgs.end(); I != E; ++I) { 863 DbgDeclareInst *DDI = *I; 864 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) { 865 bool RemoveDDI = true; 866 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 867 UI != E; ++UI) 868 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 869 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 870 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 871 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 872 else 873 RemoveDDI = false; 874 if (RemoveDDI) 875 DDI->eraseFromParent(); 876 } 877 } 878 return true; 879} 880 881/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the 882/// alloca 'V', if any. 883DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { 884 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V)) 885 for (Value::use_iterator UI = DebugNode->use_begin(), 886 E = DebugNode->use_end(); UI != E; ++UI) 887 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI)) 888 return DDI; 889 890 return 0; 891} 892