Local.cpp revision 36fae67831517f132255118b45b21a8cf199a012
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/ADT/DenseMap.h" 24#include "llvm/ADT/SmallPtrSet.h" 25#include "llvm/Analysis/DebugInfo.h" 26#include "llvm/Analysis/DIBuilder.h" 27#include "llvm/Analysis/Dominators.h" 28#include "llvm/Analysis/ConstantFolding.h" 29#include "llvm/Analysis/InstructionSimplify.h" 30#include "llvm/Analysis/ProfileInfo.h" 31#include "llvm/Analysis/ValueTracking.h" 32#include "llvm/Target/TargetData.h" 33#include "llvm/Support/CFG.h" 34#include "llvm/Support/Debug.h" 35#include "llvm/Support/GetElementPtrTypeIterator.h" 36#include "llvm/Support/MathExtras.h" 37#include "llvm/Support/ValueHandle.h" 38#include "llvm/Support/raw_ostream.h" 39using namespace llvm; 40 41//===----------------------------------------------------------------------===// 42// Local constant propagation. 43// 44 45// ConstantFoldTerminator - If a terminator instruction is predicated on a 46// constant value, convert it into an unconditional branch to the constant 47// destination. 48// 49bool llvm::ConstantFoldTerminator(BasicBlock *BB) { 50 TerminatorInst *T = BB->getTerminator(); 51 52 // Branch - See if we are conditional jumping on constant 53 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 54 if (BI->isUnconditional()) return false; // Can't optimize uncond branch 55 BasicBlock *Dest1 = BI->getSuccessor(0); 56 BasicBlock *Dest2 = BI->getSuccessor(1); 57 58 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { 59 // Are we branching on constant? 60 // YES. Change to unconditional branch... 61 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; 62 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; 63 64 //cerr << "Function: " << T->getParent()->getParent() 65 // << "\nRemoving branch from " << T->getParent() 66 // << "\n\nTo: " << OldDest << endl; 67 68 // Let the basic block know that we are letting go of it. Based on this, 69 // it will adjust it's PHI nodes. 70 assert(BI->getParent() && "Terminator not inserted in block!"); 71 OldDest->removePredecessor(BI->getParent()); 72 73 // Replace the conditional branch with an unconditional one. 74 BranchInst::Create(Destination, BI); 75 BI->eraseFromParent(); 76 return true; 77 } 78 79 if (Dest2 == Dest1) { // Conditional branch to same location? 80 // This branch matches something like this: 81 // br bool %cond, label %Dest, label %Dest 82 // and changes it into: br label %Dest 83 84 // Let the basic block know that we are letting go of one copy of it. 85 assert(BI->getParent() && "Terminator not inserted in block!"); 86 Dest1->removePredecessor(BI->getParent()); 87 88 // Replace the conditional branch with an unconditional one. 89 BranchInst::Create(Dest1, BI); 90 BI->eraseFromParent(); 91 return true; 92 } 93 return false; 94 } 95 96 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { 97 // If we are switching on a constant, we can convert the switch into a 98 // single branch instruction! 99 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); 100 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest 101 BasicBlock *DefaultDest = TheOnlyDest; 102 assert(TheOnlyDest == SI->getDefaultDest() && 103 "Default destination is not successor #0?"); 104 105 // Figure out which case it goes to. 106 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) { 107 // Found case matching a constant operand? 108 if (SI->getSuccessorValue(i) == CI) { 109 TheOnlyDest = SI->getSuccessor(i); 110 break; 111 } 112 113 // Check to see if this branch is going to the same place as the default 114 // dest. If so, eliminate it as an explicit compare. 115 if (SI->getSuccessor(i) == DefaultDest) { 116 // Remove this entry. 117 DefaultDest->removePredecessor(SI->getParent()); 118 SI->removeCase(i); 119 --i; --e; // Don't skip an entry... 120 continue; 121 } 122 123 // Otherwise, check to see if the switch only branches to one destination. 124 // We do this by reseting "TheOnlyDest" to null when we find two non-equal 125 // destinations. 126 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0; 127 } 128 129 if (CI && !TheOnlyDest) { 130 // Branching on a constant, but not any of the cases, go to the default 131 // successor. 132 TheOnlyDest = SI->getDefaultDest(); 133 } 134 135 // If we found a single destination that we can fold the switch into, do so 136 // now. 137 if (TheOnlyDest) { 138 // Insert the new branch. 139 BranchInst::Create(TheOnlyDest, SI); 140 BasicBlock *BB = SI->getParent(); 141 142 // Remove entries from PHI nodes which we no longer branch to... 143 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) { 144 // Found case matching a constant operand? 145 BasicBlock *Succ = SI->getSuccessor(i); 146 if (Succ == TheOnlyDest) 147 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest 148 else 149 Succ->removePredecessor(BB); 150 } 151 152 // Delete the old switch. 153 BB->getInstList().erase(SI); 154 return true; 155 } 156 157 if (SI->getNumSuccessors() == 2) { 158 // Otherwise, we can fold this switch into a conditional branch 159 // instruction if it has only one non-default destination. 160 Value *Cond = new ICmpInst(SI, ICmpInst::ICMP_EQ, SI->getCondition(), 161 SI->getSuccessorValue(1), "cond"); 162 // Insert the new branch. 163 BranchInst::Create(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI); 164 165 // Delete the old switch. 166 SI->eraseFromParent(); 167 return true; 168 } 169 return false; 170 } 171 172 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 173 // indirectbr blockaddress(@F, @BB) -> br label @BB 174 if (BlockAddress *BA = 175 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 176 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 177 // Insert the new branch. 178 BranchInst::Create(TheOnlyDest, IBI); 179 180 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 181 if (IBI->getDestination(i) == TheOnlyDest) 182 TheOnlyDest = 0; 183 else 184 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 185 } 186 IBI->eraseFromParent(); 187 188 // If we didn't find our destination in the IBI successor list, then we 189 // have undefined behavior. Replace the unconditional branch with an 190 // 'unreachable' instruction. 191 if (TheOnlyDest) { 192 BB->getTerminator()->eraseFromParent(); 193 new UnreachableInst(BB->getContext(), BB); 194 } 195 196 return true; 197 } 198 } 199 200 return false; 201} 202 203 204//===----------------------------------------------------------------------===// 205// Local dead code elimination. 206// 207 208/// isInstructionTriviallyDead - Return true if the result produced by the 209/// instruction is not used, and the instruction has no side effects. 210/// 211bool llvm::isInstructionTriviallyDead(Instruction *I) { 212 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 213 214 // We don't want debug info removed by anything this general, unless 215 // debug info is empty. 216 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 217 if (DDI->getAddress()) 218 return false; 219 else 220 return true; 221 } else if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 222 if (DVI->getValue()) 223 return false; 224 else 225 return true; 226 } 227 228 if (!I->mayHaveSideEffects()) return true; 229 230 // Special case intrinsics that "may have side effects" but can be deleted 231 // when dead. 232 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) 233 // Safe to delete llvm.stacksave if dead. 234 if (II->getIntrinsicID() == Intrinsic::stacksave) 235 return true; 236 return false; 237} 238 239/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 240/// trivially dead instruction, delete it. If that makes any of its operands 241/// trivially dead, delete them too, recursively. Return true if any 242/// instructions were deleted. 243bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) { 244 Instruction *I = dyn_cast<Instruction>(V); 245 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I)) 246 return false; 247 248 SmallVector<Instruction*, 16> DeadInsts; 249 DeadInsts.push_back(I); 250 251 do { 252 I = DeadInsts.pop_back_val(); 253 254 // Null out all of the instruction's operands to see if any operand becomes 255 // dead as we go. 256 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 257 Value *OpV = I->getOperand(i); 258 I->setOperand(i, 0); 259 260 if (!OpV->use_empty()) continue; 261 262 // If the operand is an instruction that became dead as we nulled out the 263 // operand, and if it is 'trivially' dead, delete it in a future loop 264 // iteration. 265 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 266 if (isInstructionTriviallyDead(OpI)) 267 DeadInsts.push_back(OpI); 268 } 269 270 I->eraseFromParent(); 271 } while (!DeadInsts.empty()); 272 273 return true; 274} 275 276/// areAllUsesEqual - Check whether the uses of a value are all the same. 277/// This is similar to Instruction::hasOneUse() except this will also return 278/// true when there are no uses or multiple uses that all refer to the same 279/// value. 280static bool areAllUsesEqual(Instruction *I) { 281 Value::use_iterator UI = I->use_begin(); 282 Value::use_iterator UE = I->use_end(); 283 if (UI == UE) 284 return true; 285 286 User *TheUse = *UI; 287 for (++UI; UI != UE; ++UI) { 288 if (*UI != TheUse) 289 return false; 290 } 291 return true; 292} 293 294/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 295/// dead PHI node, due to being a def-use chain of single-use nodes that 296/// either forms a cycle or is terminated by a trivially dead instruction, 297/// delete it. If that makes any of its operands trivially dead, delete them 298/// too, recursively. Return true if a change was made. 299bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) { 300 SmallPtrSet<Instruction*, 4> Visited; 301 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 302 I = cast<Instruction>(*I->use_begin())) { 303 if (I->use_empty()) 304 return RecursivelyDeleteTriviallyDeadInstructions(I); 305 306 // If we find an instruction more than once, we're on a cycle that 307 // won't prove fruitful. 308 if (!Visited.insert(I)) { 309 // Break the cycle and delete the instruction and its operands. 310 I->replaceAllUsesWith(UndefValue::get(I->getType())); 311 (void)RecursivelyDeleteTriviallyDeadInstructions(I); 312 return true; 313 } 314 } 315 return false; 316} 317 318/// SimplifyInstructionsInBlock - Scan the specified basic block and try to 319/// simplify any instructions in it and recursively delete dead instructions. 320/// 321/// This returns true if it changed the code, note that it can delete 322/// instructions in other blocks as well in this block. 323bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) { 324 bool MadeChange = false; 325 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) { 326 Instruction *Inst = BI++; 327 328 if (Value *V = SimplifyInstruction(Inst, TD)) { 329 WeakVH BIHandle(BI); 330 ReplaceAndSimplifyAllUses(Inst, V, TD); 331 MadeChange = true; 332 if (BIHandle != BI) 333 BI = BB->begin(); 334 continue; 335 } 336 337 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst); 338 } 339 return MadeChange; 340} 341 342//===----------------------------------------------------------------------===// 343// Control Flow Graph Restructuring. 344// 345 346 347/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 348/// method is called when we're about to delete Pred as a predecessor of BB. If 349/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 350/// 351/// Unlike the removePredecessor method, this attempts to simplify uses of PHI 352/// nodes that collapse into identity values. For example, if we have: 353/// x = phi(1, 0, 0, 0) 354/// y = and x, z 355/// 356/// .. and delete the predecessor corresponding to the '1', this will attempt to 357/// recursively fold the and to 0. 358void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 359 TargetData *TD) { 360 // This only adjusts blocks with PHI nodes. 361 if (!isa<PHINode>(BB->begin())) 362 return; 363 364 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 365 // them down. This will leave us with single entry phi nodes and other phis 366 // that can be removed. 367 BB->removePredecessor(Pred, true); 368 369 WeakVH PhiIt = &BB->front(); 370 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 371 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 372 373 Value *PNV = SimplifyInstruction(PN, TD); 374 if (PNV == 0) continue; 375 376 // If we're able to simplify the phi to a single value, substitute the new 377 // value into all of its uses. 378 assert(PNV != PN && "SimplifyInstruction broken!"); 379 380 Value *OldPhiIt = PhiIt; 381 ReplaceAndSimplifyAllUses(PN, PNV, TD); 382 383 // If recursive simplification ended up deleting the next PHI node we would 384 // iterate to, then our iterator is invalid, restart scanning from the top 385 // of the block. 386 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 387 } 388} 389 390 391/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 392/// predecessor is known to have one successor (DestBB!). Eliminate the edge 393/// between them, moving the instructions in the predecessor into DestBB and 394/// deleting the predecessor block. 395/// 396void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 397 // If BB has single-entry PHI nodes, fold them. 398 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 399 Value *NewVal = PN->getIncomingValue(0); 400 // Replace self referencing PHI with undef, it must be dead. 401 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 402 PN->replaceAllUsesWith(NewVal); 403 PN->eraseFromParent(); 404 } 405 406 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 407 assert(PredBB && "Block doesn't have a single predecessor!"); 408 409 // Splice all the instructions from PredBB to DestBB. 410 PredBB->getTerminator()->eraseFromParent(); 411 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 412 413 // Zap anything that took the address of DestBB. Not doing this will give the 414 // address an invalid value. 415 if (DestBB->hasAddressTaken()) { 416 BlockAddress *BA = BlockAddress::get(DestBB); 417 Constant *Replacement = 418 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 419 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 420 BA->getType())); 421 BA->destroyConstant(); 422 } 423 424 // Anything that branched to PredBB now branches to DestBB. 425 PredBB->replaceAllUsesWith(DestBB); 426 427 if (P) { 428 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 429 if (DT) { 430 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 431 DT->changeImmediateDominator(DestBB, PredBBIDom); 432 DT->eraseNode(PredBB); 433 } 434 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 435 if (PI) { 436 PI->replaceAllUses(PredBB, DestBB); 437 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 438 } 439 } 440 // Nuke BB. 441 PredBB->eraseFromParent(); 442} 443 444/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 445/// almost-empty BB ending in an unconditional branch to Succ, into succ. 446/// 447/// Assumption: Succ is the single successor for BB. 448/// 449static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 450 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 451 452 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 453 << Succ->getName() << "\n"); 454 // Shortcut, if there is only a single predecessor it must be BB and merging 455 // is always safe 456 if (Succ->getSinglePredecessor()) return true; 457 458 // Make a list of the predecessors of BB 459 typedef SmallPtrSet<BasicBlock*, 16> BlockSet; 460 BlockSet BBPreds(pred_begin(BB), pred_end(BB)); 461 462 // Use that list to make another list of common predecessors of BB and Succ 463 BlockSet CommonPreds; 464 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); 465 PI != PE; ++PI) { 466 BasicBlock *P = *PI; 467 if (BBPreds.count(P)) 468 CommonPreds.insert(P); 469 } 470 471 // Shortcut, if there are no common predecessors, merging is always safe 472 if (CommonPreds.empty()) 473 return true; 474 475 // Look at all the phi nodes in Succ, to see if they present a conflict when 476 // merging these blocks 477 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 478 PHINode *PN = cast<PHINode>(I); 479 480 // If the incoming value from BB is again a PHINode in 481 // BB which has the same incoming value for *PI as PN does, we can 482 // merge the phi nodes and then the blocks can still be merged 483 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 484 if (BBPN && BBPN->getParent() == BB) { 485 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 486 PI != PE; PI++) { 487 if (BBPN->getIncomingValueForBlock(*PI) 488 != PN->getIncomingValueForBlock(*PI)) { 489 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 490 << Succ->getName() << " is conflicting with " 491 << BBPN->getName() << " with regard to common predecessor " 492 << (*PI)->getName() << "\n"); 493 return false; 494 } 495 } 496 } else { 497 Value* Val = PN->getIncomingValueForBlock(BB); 498 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 499 PI != PE; PI++) { 500 // See if the incoming value for the common predecessor is equal to the 501 // one for BB, in which case this phi node will not prevent the merging 502 // of the block. 503 if (Val != PN->getIncomingValueForBlock(*PI)) { 504 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 505 << Succ->getName() << " is conflicting with regard to common " 506 << "predecessor " << (*PI)->getName() << "\n"); 507 return false; 508 } 509 } 510 } 511 } 512 513 return true; 514} 515 516/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 517/// unconditional branch, and contains no instructions other than PHI nodes, 518/// potential debug intrinsics and the branch. If possible, eliminate BB by 519/// rewriting all the predecessors to branch to the successor block and return 520/// true. If we can't transform, return false. 521bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 522 assert(BB != &BB->getParent()->getEntryBlock() && 523 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 524 525 // We can't eliminate infinite loops. 526 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 527 if (BB == Succ) return false; 528 529 // Check to see if merging these blocks would cause conflicts for any of the 530 // phi nodes in BB or Succ. If not, we can safely merge. 531 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 532 533 // Check for cases where Succ has multiple predecessors and a PHI node in BB 534 // has uses which will not disappear when the PHI nodes are merged. It is 535 // possible to handle such cases, but difficult: it requires checking whether 536 // BB dominates Succ, which is non-trivial to calculate in the case where 537 // Succ has multiple predecessors. Also, it requires checking whether 538 // constructing the necessary self-referential PHI node doesn't intoduce any 539 // conflicts; this isn't too difficult, but the previous code for doing this 540 // was incorrect. 541 // 542 // Note that if this check finds a live use, BB dominates Succ, so BB is 543 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 544 // folding the branch isn't profitable in that case anyway. 545 if (!Succ->getSinglePredecessor()) { 546 BasicBlock::iterator BBI = BB->begin(); 547 while (isa<PHINode>(*BBI)) { 548 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 549 UI != E; ++UI) { 550 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 551 if (PN->getIncomingBlock(UI) != BB) 552 return false; 553 } else { 554 return false; 555 } 556 } 557 ++BBI; 558 } 559 } 560 561 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 562 563 if (isa<PHINode>(Succ->begin())) { 564 // If there is more than one pred of succ, and there are PHI nodes in 565 // the successor, then we need to add incoming edges for the PHI nodes 566 // 567 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 568 569 // Loop over all of the PHI nodes in the successor of BB. 570 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 571 PHINode *PN = cast<PHINode>(I); 572 Value *OldVal = PN->removeIncomingValue(BB, false); 573 assert(OldVal && "No entry in PHI for Pred BB!"); 574 575 // If this incoming value is one of the PHI nodes in BB, the new entries 576 // in the PHI node are the entries from the old PHI. 577 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 578 PHINode *OldValPN = cast<PHINode>(OldVal); 579 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 580 // Note that, since we are merging phi nodes and BB and Succ might 581 // have common predecessors, we could end up with a phi node with 582 // identical incoming branches. This will be cleaned up later (and 583 // will trigger asserts if we try to clean it up now, without also 584 // simplifying the corresponding conditional branch). 585 PN->addIncoming(OldValPN->getIncomingValue(i), 586 OldValPN->getIncomingBlock(i)); 587 } else { 588 // Add an incoming value for each of the new incoming values. 589 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 590 PN->addIncoming(OldVal, BBPreds[i]); 591 } 592 } 593 } 594 595 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 596 if (Succ->getSinglePredecessor()) { 597 // BB is the only predecessor of Succ, so Succ will end up with exactly 598 // the same predecessors BB had. 599 Succ->getInstList().splice(Succ->begin(), 600 BB->getInstList(), BB->begin()); 601 } else { 602 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 603 assert(PN->use_empty() && "There shouldn't be any uses here!"); 604 PN->eraseFromParent(); 605 } 606 } 607 608 // Everything that jumped to BB now goes to Succ. 609 BB->replaceAllUsesWith(Succ); 610 if (!Succ->hasName()) Succ->takeName(BB); 611 BB->eraseFromParent(); // Delete the old basic block. 612 return true; 613} 614 615/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 616/// nodes in this block. This doesn't try to be clever about PHI nodes 617/// which differ only in the order of the incoming values, but instcombine 618/// orders them so it usually won't matter. 619/// 620bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 621 bool Changed = false; 622 623 // This implementation doesn't currently consider undef operands 624 // specially. Theroetically, two phis which are identical except for 625 // one having an undef where the other doesn't could be collapsed. 626 627 // Map from PHI hash values to PHI nodes. If multiple PHIs have 628 // the same hash value, the element is the first PHI in the 629 // linked list in CollisionMap. 630 DenseMap<uintptr_t, PHINode *> HashMap; 631 632 // Maintain linked lists of PHI nodes with common hash values. 633 DenseMap<PHINode *, PHINode *> CollisionMap; 634 635 // Examine each PHI. 636 for (BasicBlock::iterator I = BB->begin(); 637 PHINode *PN = dyn_cast<PHINode>(I++); ) { 638 // Compute a hash value on the operands. Instcombine will likely have sorted 639 // them, which helps expose duplicates, but we have to check all the 640 // operands to be safe in case instcombine hasn't run. 641 uintptr_t Hash = 0; 642 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 643 // This hash algorithm is quite weak as hash functions go, but it seems 644 // to do a good enough job for this particular purpose, and is very quick. 645 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 646 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 647 } 648 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 649 Hash >>= 1; 650 // If we've never seen this hash value before, it's a unique PHI. 651 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 652 HashMap.insert(std::make_pair(Hash, PN)); 653 if (Pair.second) continue; 654 // Otherwise it's either a duplicate or a hash collision. 655 for (PHINode *OtherPN = Pair.first->second; ; ) { 656 if (OtherPN->isIdenticalTo(PN)) { 657 // A duplicate. Replace this PHI with its duplicate. 658 PN->replaceAllUsesWith(OtherPN); 659 PN->eraseFromParent(); 660 Changed = true; 661 break; 662 } 663 // A non-duplicate hash collision. 664 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 665 if (I == CollisionMap.end()) { 666 // Set this PHI to be the head of the linked list of colliding PHIs. 667 PHINode *Old = Pair.first->second; 668 Pair.first->second = PN; 669 CollisionMap[PN] = Old; 670 break; 671 } 672 // Procede to the next PHI in the list. 673 OtherPN = I->second; 674 } 675 } 676 677 return Changed; 678} 679 680/// enforceKnownAlignment - If the specified pointer points to an object that 681/// we control, modify the object's alignment to PrefAlign. This isn't 682/// often possible though. If alignment is important, a more reliable approach 683/// is to simply align all global variables and allocation instructions to 684/// their preferred alignment from the beginning. 685/// 686static unsigned enforceKnownAlignment(Value *V, unsigned Align, 687 unsigned PrefAlign) { 688 689 User *U = dyn_cast<User>(V); 690 if (!U) return Align; 691 692 switch (Operator::getOpcode(U)) { 693 default: break; 694 case Instruction::BitCast: 695 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign); 696 case Instruction::GetElementPtr: { 697 // If all indexes are zero, it is just the alignment of the base pointer. 698 bool AllZeroOperands = true; 699 for (User::op_iterator i = U->op_begin() + 1, e = U->op_end(); i != e; ++i) 700 if (!isa<Constant>(*i) || 701 !cast<Constant>(*i)->isNullValue()) { 702 AllZeroOperands = false; 703 break; 704 } 705 706 if (AllZeroOperands) { 707 // Treat this like a bitcast. 708 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign); 709 } 710 return Align; 711 } 712 case Instruction::Alloca: { 713 AllocaInst *AI = cast<AllocaInst>(V); 714 // If there is a requested alignment and if this is an alloca, round up. 715 if (AI->getAlignment() >= PrefAlign) 716 return AI->getAlignment(); 717 AI->setAlignment(PrefAlign); 718 return PrefAlign; 719 } 720 } 721 722 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 723 // If there is a large requested alignment and we can, bump up the alignment 724 // of the global. 725 if (GV->isDeclaration()) return Align; 726 727 if (GV->getAlignment() >= PrefAlign) 728 return GV->getAlignment(); 729 // We can only increase the alignment of the global if it has no alignment 730 // specified or if it is not assigned a section. If it is assigned a 731 // section, the global could be densely packed with other objects in the 732 // section, increasing the alignment could cause padding issues. 733 if (!GV->hasSection() || GV->getAlignment() == 0) 734 GV->setAlignment(PrefAlign); 735 return GV->getAlignment(); 736 } 737 738 return Align; 739} 740 741/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 742/// we can determine, return it, otherwise return 0. If PrefAlign is specified, 743/// and it is more than the alignment of the ultimate object, see if we can 744/// increase the alignment of the ultimate object, making this check succeed. 745unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 746 const TargetData *TD) { 747 assert(V->getType()->isPointerTy() && 748 "getOrEnforceKnownAlignment expects a pointer!"); 749 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 750 APInt Mask = APInt::getAllOnesValue(BitWidth); 751 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 752 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD); 753 unsigned TrailZ = KnownZero.countTrailingOnes(); 754 755 // Avoid trouble with rediculously large TrailZ values, such as 756 // those computed from a null pointer. 757 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 758 759 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 760 761 // LLVM doesn't support alignments larger than this currently. 762 Align = std::min(Align, +Value::MaximumAlignment); 763 764 if (PrefAlign > Align) 765 Align = enforceKnownAlignment(V, Align, PrefAlign); 766 767 // We don't need to make any adjustment. 768 return Align; 769} 770 771///===---------------------------------------------------------------------===// 772/// Dbg Intrinsic utilities 773/// 774 775/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 776/// that has an associated llvm.dbg.decl intrinsic. 777bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 778 StoreInst *SI, DIBuilder &Builder) { 779 DIVariable DIVar(DDI->getVariable()); 780 if (!DIVar.Verify()) 781 return false; 782 783 Instruction *DbgVal = 784 Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, 785 DIVar, SI); 786 787 // Propagate any debug metadata from the store onto the dbg.value. 788 DebugLoc SIDL = SI->getDebugLoc(); 789 if (!SIDL.isUnknown()) 790 DbgVal->setDebugLoc(SIDL); 791 // Otherwise propagate debug metadata from dbg.declare. 792 else 793 DbgVal->setDebugLoc(DDI->getDebugLoc()); 794 return true; 795} 796 797/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 798/// that has an associated llvm.dbg.decl intrinsic. 799bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 800 LoadInst *LI, DIBuilder &Builder) { 801 DIVariable DIVar(DDI->getVariable()); 802 if (!DIVar.Verify()) 803 return false; 804 805 Instruction *DbgVal = 806 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 807 DIVar, LI); 808 809 // Propagate any debug metadata from the store onto the dbg.value. 810 DebugLoc LIDL = LI->getDebugLoc(); 811 if (!LIDL.isUnknown()) 812 DbgVal->setDebugLoc(LIDL); 813 // Otherwise propagate debug metadata from dbg.declare. 814 else 815 DbgVal->setDebugLoc(DDI->getDebugLoc()); 816 return true; 817} 818 819/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 820/// of llvm.dbg.value intrinsics. 821bool llvm::LowerDbgDeclare(Function &F) { 822 DIBuilder DIB(*F.getParent()); 823 SmallVector<DbgDeclareInst *, 4> Dbgs; 824 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 825 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 826 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 827 Dbgs.push_back(DDI); 828 } 829 if (Dbgs.empty()) 830 return false; 831 832 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(), 833 E = Dbgs.end(); I != E; ++I) { 834 DbgDeclareInst *DDI = *I; 835 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) { 836 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 837 UI != E; ++UI) 838 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 839 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 840 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 841 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 842 } 843 DDI->eraseFromParent(); 844 } 845 return true; 846} 847