Local.cpp revision eeb7f4ce2dca47453d5e39448a4aa61c1c7d72d1
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 return true; 220 } 221 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 222 if (DVI->getValue()) 223 return false; 224 return true; 225 } 226 227 if (!I->mayHaveSideEffects()) return true; 228 229 // Special case intrinsics that "may have side effects" but can be deleted 230 // when dead. 231 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) 232 // Safe to delete llvm.stacksave if dead. 233 if (II->getIntrinsicID() == Intrinsic::stacksave) 234 return true; 235 return false; 236} 237 238/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 239/// trivially dead instruction, delete it. If that makes any of its operands 240/// trivially dead, delete them too, recursively. Return true if any 241/// instructions were deleted. 242bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) { 243 Instruction *I = dyn_cast<Instruction>(V); 244 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I)) 245 return false; 246 247 SmallVector<Instruction*, 16> DeadInsts; 248 DeadInsts.push_back(I); 249 250 do { 251 I = DeadInsts.pop_back_val(); 252 253 // Null out all of the instruction's operands to see if any operand becomes 254 // dead as we go. 255 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 256 Value *OpV = I->getOperand(i); 257 I->setOperand(i, 0); 258 259 if (!OpV->use_empty()) continue; 260 261 // If the operand is an instruction that became dead as we nulled out the 262 // operand, and if it is 'trivially' dead, delete it in a future loop 263 // iteration. 264 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 265 if (isInstructionTriviallyDead(OpI)) 266 DeadInsts.push_back(OpI); 267 } 268 269 I->eraseFromParent(); 270 } while (!DeadInsts.empty()); 271 272 return true; 273} 274 275/// areAllUsesEqual - Check whether the uses of a value are all the same. 276/// This is similar to Instruction::hasOneUse() except this will also return 277/// true when there are no uses or multiple uses that all refer to the same 278/// value. 279static bool areAllUsesEqual(Instruction *I) { 280 Value::use_iterator UI = I->use_begin(); 281 Value::use_iterator UE = I->use_end(); 282 if (UI == UE) 283 return true; 284 285 User *TheUse = *UI; 286 for (++UI; UI != UE; ++UI) { 287 if (*UI != TheUse) 288 return false; 289 } 290 return true; 291} 292 293/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 294/// dead PHI node, due to being a def-use chain of single-use nodes that 295/// either forms a cycle or is terminated by a trivially dead instruction, 296/// delete it. If that makes any of its operands trivially dead, delete them 297/// too, recursively. Return true if a change was made. 298bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) { 299 SmallPtrSet<Instruction*, 4> Visited; 300 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 301 I = cast<Instruction>(*I->use_begin())) { 302 if (I->use_empty()) 303 return RecursivelyDeleteTriviallyDeadInstructions(I); 304 305 // If we find an instruction more than once, we're on a cycle that 306 // won't prove fruitful. 307 if (!Visited.insert(I)) { 308 // Break the cycle and delete the instruction and its operands. 309 I->replaceAllUsesWith(UndefValue::get(I->getType())); 310 (void)RecursivelyDeleteTriviallyDeadInstructions(I); 311 return true; 312 } 313 } 314 return false; 315} 316 317/// SimplifyInstructionsInBlock - Scan the specified basic block and try to 318/// simplify any instructions in it and recursively delete dead instructions. 319/// 320/// This returns true if it changed the code, note that it can delete 321/// instructions in other blocks as well in this block. 322bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) { 323 bool MadeChange = false; 324 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) { 325 Instruction *Inst = BI++; 326 327 if (Value *V = SimplifyInstruction(Inst, TD)) { 328 WeakVH BIHandle(BI); 329 ReplaceAndSimplifyAllUses(Inst, V, TD); 330 MadeChange = true; 331 if (BIHandle != BI) 332 BI = BB->begin(); 333 continue; 334 } 335 336 if (Inst->isTerminator()) 337 break; 338 339 WeakVH BIHandle(BI); 340 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst); 341 if (BIHandle != BI) 342 BI = BB->begin(); 343 } 344 return MadeChange; 345} 346 347//===----------------------------------------------------------------------===// 348// Control Flow Graph Restructuring. 349// 350 351 352/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 353/// method is called when we're about to delete Pred as a predecessor of BB. If 354/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 355/// 356/// Unlike the removePredecessor method, this attempts to simplify uses of PHI 357/// nodes that collapse into identity values. For example, if we have: 358/// x = phi(1, 0, 0, 0) 359/// y = and x, z 360/// 361/// .. and delete the predecessor corresponding to the '1', this will attempt to 362/// recursively fold the and to 0. 363void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 364 TargetData *TD) { 365 // This only adjusts blocks with PHI nodes. 366 if (!isa<PHINode>(BB->begin())) 367 return; 368 369 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 370 // them down. This will leave us with single entry phi nodes and other phis 371 // that can be removed. 372 BB->removePredecessor(Pred, true); 373 374 WeakVH PhiIt = &BB->front(); 375 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 376 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 377 378 Value *PNV = SimplifyInstruction(PN, TD); 379 if (PNV == 0) continue; 380 381 // If we're able to simplify the phi to a single value, substitute the new 382 // value into all of its uses. 383 assert(PNV != PN && "SimplifyInstruction broken!"); 384 385 Value *OldPhiIt = PhiIt; 386 ReplaceAndSimplifyAllUses(PN, PNV, TD); 387 388 // If recursive simplification ended up deleting the next PHI node we would 389 // iterate to, then our iterator is invalid, restart scanning from the top 390 // of the block. 391 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 392 } 393} 394 395 396/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 397/// predecessor is known to have one successor (DestBB!). Eliminate the edge 398/// between them, moving the instructions in the predecessor into DestBB and 399/// deleting the predecessor block. 400/// 401void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 402 // If BB has single-entry PHI nodes, fold them. 403 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 404 Value *NewVal = PN->getIncomingValue(0); 405 // Replace self referencing PHI with undef, it must be dead. 406 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 407 PN->replaceAllUsesWith(NewVal); 408 PN->eraseFromParent(); 409 } 410 411 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 412 assert(PredBB && "Block doesn't have a single predecessor!"); 413 414 // Splice all the instructions from PredBB to DestBB. 415 PredBB->getTerminator()->eraseFromParent(); 416 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 417 418 // Zap anything that took the address of DestBB. Not doing this will give the 419 // address an invalid value. 420 if (DestBB->hasAddressTaken()) { 421 BlockAddress *BA = BlockAddress::get(DestBB); 422 Constant *Replacement = 423 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 424 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 425 BA->getType())); 426 BA->destroyConstant(); 427 } 428 429 // Anything that branched to PredBB now branches to DestBB. 430 PredBB->replaceAllUsesWith(DestBB); 431 432 if (P) { 433 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 434 if (DT) { 435 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 436 DT->changeImmediateDominator(DestBB, PredBBIDom); 437 DT->eraseNode(PredBB); 438 } 439 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 440 if (PI) { 441 PI->replaceAllUses(PredBB, DestBB); 442 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 443 } 444 } 445 // Nuke BB. 446 PredBB->eraseFromParent(); 447} 448 449/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 450/// almost-empty BB ending in an unconditional branch to Succ, into succ. 451/// 452/// Assumption: Succ is the single successor for BB. 453/// 454static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 455 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 456 457 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 458 << Succ->getName() << "\n"); 459 // Shortcut, if there is only a single predecessor it must be BB and merging 460 // is always safe 461 if (Succ->getSinglePredecessor()) return true; 462 463 // Make a list of the predecessors of BB 464 typedef SmallPtrSet<BasicBlock*, 16> BlockSet; 465 BlockSet BBPreds(pred_begin(BB), pred_end(BB)); 466 467 // Use that list to make another list of common predecessors of BB and Succ 468 BlockSet CommonPreds; 469 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); 470 PI != PE; ++PI) { 471 BasicBlock *P = *PI; 472 if (BBPreds.count(P)) 473 CommonPreds.insert(P); 474 } 475 476 // Shortcut, if there are no common predecessors, merging is always safe 477 if (CommonPreds.empty()) 478 return true; 479 480 // Look at all the phi nodes in Succ, to see if they present a conflict when 481 // merging these blocks 482 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 483 PHINode *PN = cast<PHINode>(I); 484 485 // If the incoming value from BB is again a PHINode in 486 // BB which has the same incoming value for *PI as PN does, we can 487 // merge the phi nodes and then the blocks can still be merged 488 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 489 if (BBPN && BBPN->getParent() == BB) { 490 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 491 PI != PE; PI++) { 492 if (BBPN->getIncomingValueForBlock(*PI) 493 != PN->getIncomingValueForBlock(*PI)) { 494 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 495 << Succ->getName() << " is conflicting with " 496 << BBPN->getName() << " with regard to common predecessor " 497 << (*PI)->getName() << "\n"); 498 return false; 499 } 500 } 501 } else { 502 Value* Val = PN->getIncomingValueForBlock(BB); 503 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 504 PI != PE; PI++) { 505 // See if the incoming value for the common predecessor is equal to the 506 // one for BB, in which case this phi node will not prevent the merging 507 // of the block. 508 if (Val != PN->getIncomingValueForBlock(*PI)) { 509 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 510 << Succ->getName() << " is conflicting with regard to common " 511 << "predecessor " << (*PI)->getName() << "\n"); 512 return false; 513 } 514 } 515 } 516 } 517 518 return true; 519} 520 521/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 522/// unconditional branch, and contains no instructions other than PHI nodes, 523/// potential debug intrinsics and the branch. If possible, eliminate BB by 524/// rewriting all the predecessors to branch to the successor block and return 525/// true. If we can't transform, return false. 526bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 527 assert(BB != &BB->getParent()->getEntryBlock() && 528 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 529 530 // We can't eliminate infinite loops. 531 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 532 if (BB == Succ) return false; 533 534 // Check to see if merging these blocks would cause conflicts for any of the 535 // phi nodes in BB or Succ. If not, we can safely merge. 536 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 537 538 // Check for cases where Succ has multiple predecessors and a PHI node in BB 539 // has uses which will not disappear when the PHI nodes are merged. It is 540 // possible to handle such cases, but difficult: it requires checking whether 541 // BB dominates Succ, which is non-trivial to calculate in the case where 542 // Succ has multiple predecessors. Also, it requires checking whether 543 // constructing the necessary self-referential PHI node doesn't intoduce any 544 // conflicts; this isn't too difficult, but the previous code for doing this 545 // was incorrect. 546 // 547 // Note that if this check finds a live use, BB dominates Succ, so BB is 548 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 549 // folding the branch isn't profitable in that case anyway. 550 if (!Succ->getSinglePredecessor()) { 551 BasicBlock::iterator BBI = BB->begin(); 552 while (isa<PHINode>(*BBI)) { 553 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 554 UI != E; ++UI) { 555 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 556 if (PN->getIncomingBlock(UI) != BB) 557 return false; 558 } else { 559 return false; 560 } 561 } 562 ++BBI; 563 } 564 } 565 566 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 567 568 if (isa<PHINode>(Succ->begin())) { 569 // If there is more than one pred of succ, and there are PHI nodes in 570 // the successor, then we need to add incoming edges for the PHI nodes 571 // 572 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 573 574 // Loop over all of the PHI nodes in the successor of BB. 575 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 576 PHINode *PN = cast<PHINode>(I); 577 Value *OldVal = PN->removeIncomingValue(BB, false); 578 assert(OldVal && "No entry in PHI for Pred BB!"); 579 580 // If this incoming value is one of the PHI nodes in BB, the new entries 581 // in the PHI node are the entries from the old PHI. 582 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 583 PHINode *OldValPN = cast<PHINode>(OldVal); 584 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 585 // Note that, since we are merging phi nodes and BB and Succ might 586 // have common predecessors, we could end up with a phi node with 587 // identical incoming branches. This will be cleaned up later (and 588 // will trigger asserts if we try to clean it up now, without also 589 // simplifying the corresponding conditional branch). 590 PN->addIncoming(OldValPN->getIncomingValue(i), 591 OldValPN->getIncomingBlock(i)); 592 } else { 593 // Add an incoming value for each of the new incoming values. 594 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 595 PN->addIncoming(OldVal, BBPreds[i]); 596 } 597 } 598 } 599 600 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 601 if (Succ->getSinglePredecessor()) { 602 // BB is the only predecessor of Succ, so Succ will end up with exactly 603 // the same predecessors BB had. 604 Succ->getInstList().splice(Succ->begin(), 605 BB->getInstList(), BB->begin()); 606 } else { 607 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 608 assert(PN->use_empty() && "There shouldn't be any uses here!"); 609 PN->eraseFromParent(); 610 } 611 } 612 613 // Everything that jumped to BB now goes to Succ. 614 BB->replaceAllUsesWith(Succ); 615 if (!Succ->hasName()) Succ->takeName(BB); 616 BB->eraseFromParent(); // Delete the old basic block. 617 return true; 618} 619 620/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 621/// nodes in this block. This doesn't try to be clever about PHI nodes 622/// which differ only in the order of the incoming values, but instcombine 623/// orders them so it usually won't matter. 624/// 625bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 626 bool Changed = false; 627 628 // This implementation doesn't currently consider undef operands 629 // specially. Theroetically, two phis which are identical except for 630 // one having an undef where the other doesn't could be collapsed. 631 632 // Map from PHI hash values to PHI nodes. If multiple PHIs have 633 // the same hash value, the element is the first PHI in the 634 // linked list in CollisionMap. 635 DenseMap<uintptr_t, PHINode *> HashMap; 636 637 // Maintain linked lists of PHI nodes with common hash values. 638 DenseMap<PHINode *, PHINode *> CollisionMap; 639 640 // Examine each PHI. 641 for (BasicBlock::iterator I = BB->begin(); 642 PHINode *PN = dyn_cast<PHINode>(I++); ) { 643 // Compute a hash value on the operands. Instcombine will likely have sorted 644 // them, which helps expose duplicates, but we have to check all the 645 // operands to be safe in case instcombine hasn't run. 646 uintptr_t Hash = 0; 647 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 648 // This hash algorithm is quite weak as hash functions go, but it seems 649 // to do a good enough job for this particular purpose, and is very quick. 650 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 651 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 652 } 653 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 654 Hash >>= 1; 655 // If we've never seen this hash value before, it's a unique PHI. 656 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 657 HashMap.insert(std::make_pair(Hash, PN)); 658 if (Pair.second) continue; 659 // Otherwise it's either a duplicate or a hash collision. 660 for (PHINode *OtherPN = Pair.first->second; ; ) { 661 if (OtherPN->isIdenticalTo(PN)) { 662 // A duplicate. Replace this PHI with its duplicate. 663 PN->replaceAllUsesWith(OtherPN); 664 PN->eraseFromParent(); 665 Changed = true; 666 break; 667 } 668 // A non-duplicate hash collision. 669 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 670 if (I == CollisionMap.end()) { 671 // Set this PHI to be the head of the linked list of colliding PHIs. 672 PHINode *Old = Pair.first->second; 673 Pair.first->second = PN; 674 CollisionMap[PN] = Old; 675 break; 676 } 677 // Procede to the next PHI in the list. 678 OtherPN = I->second; 679 } 680 } 681 682 return Changed; 683} 684 685/// enforceKnownAlignment - If the specified pointer points to an object that 686/// we control, modify the object's alignment to PrefAlign. This isn't 687/// often possible though. If alignment is important, a more reliable approach 688/// is to simply align all global variables and allocation instructions to 689/// their preferred alignment from the beginning. 690/// 691static unsigned enforceKnownAlignment(Value *V, unsigned Align, 692 unsigned PrefAlign) { 693 694 User *U = dyn_cast<User>(V); 695 if (!U) return Align; 696 697 switch (Operator::getOpcode(U)) { 698 default: break; 699 case Instruction::BitCast: 700 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign); 701 case Instruction::GetElementPtr: { 702 // If all indexes are zero, it is just the alignment of the base pointer. 703 bool AllZeroOperands = true; 704 for (User::op_iterator i = U->op_begin() + 1, e = U->op_end(); i != e; ++i) 705 if (!isa<Constant>(*i) || 706 !cast<Constant>(*i)->isNullValue()) { 707 AllZeroOperands = false; 708 break; 709 } 710 711 if (AllZeroOperands) { 712 // Treat this like a bitcast. 713 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign); 714 } 715 return Align; 716 } 717 case Instruction::Alloca: { 718 AllocaInst *AI = cast<AllocaInst>(V); 719 // If there is a requested alignment and if this is an alloca, round up. 720 if (AI->getAlignment() >= PrefAlign) 721 return AI->getAlignment(); 722 AI->setAlignment(PrefAlign); 723 return PrefAlign; 724 } 725 } 726 727 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 728 // If there is a large requested alignment and we can, bump up the alignment 729 // of the global. 730 if (GV->isDeclaration()) return Align; 731 732 if (GV->getAlignment() >= PrefAlign) 733 return GV->getAlignment(); 734 // We can only increase the alignment of the global if it has no alignment 735 // specified or if it is not assigned a section. If it is assigned a 736 // section, the global could be densely packed with other objects in the 737 // section, increasing the alignment could cause padding issues. 738 if (!GV->hasSection() || GV->getAlignment() == 0) 739 GV->setAlignment(PrefAlign); 740 return GV->getAlignment(); 741 } 742 743 return Align; 744} 745 746/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 747/// we can determine, return it, otherwise return 0. If PrefAlign is specified, 748/// and it is more than the alignment of the ultimate object, see if we can 749/// increase the alignment of the ultimate object, making this check succeed. 750unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 751 const TargetData *TD) { 752 assert(V->getType()->isPointerTy() && 753 "getOrEnforceKnownAlignment expects a pointer!"); 754 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 755 APInt Mask = APInt::getAllOnesValue(BitWidth); 756 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 757 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD); 758 unsigned TrailZ = KnownZero.countTrailingOnes(); 759 760 // Avoid trouble with rediculously large TrailZ values, such as 761 // those computed from a null pointer. 762 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 763 764 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 765 766 // LLVM doesn't support alignments larger than this currently. 767 Align = std::min(Align, +Value::MaximumAlignment); 768 769 if (PrefAlign > Align) 770 Align = enforceKnownAlignment(V, Align, PrefAlign); 771 772 // We don't need to make any adjustment. 773 return Align; 774} 775 776///===---------------------------------------------------------------------===// 777/// Dbg Intrinsic utilities 778/// 779 780/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 781/// that has an associated llvm.dbg.decl intrinsic. 782bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 783 StoreInst *SI, DIBuilder &Builder) { 784 DIVariable DIVar(DDI->getVariable()); 785 if (!DIVar.Verify()) 786 return false; 787 788 Instruction *DbgVal = 789 Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, 790 DIVar, SI); 791 792 // Propagate any debug metadata from the store onto the dbg.value. 793 DebugLoc SIDL = SI->getDebugLoc(); 794 if (!SIDL.isUnknown()) 795 DbgVal->setDebugLoc(SIDL); 796 // Otherwise propagate debug metadata from dbg.declare. 797 else 798 DbgVal->setDebugLoc(DDI->getDebugLoc()); 799 return true; 800} 801 802/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 803/// that has an associated llvm.dbg.decl intrinsic. 804bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 805 LoadInst *LI, DIBuilder &Builder) { 806 DIVariable DIVar(DDI->getVariable()); 807 if (!DIVar.Verify()) 808 return false; 809 810 Instruction *DbgVal = 811 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 812 DIVar, LI); 813 814 // Propagate any debug metadata from the store onto the dbg.value. 815 DebugLoc LIDL = LI->getDebugLoc(); 816 if (!LIDL.isUnknown()) 817 DbgVal->setDebugLoc(LIDL); 818 // Otherwise propagate debug metadata from dbg.declare. 819 else 820 DbgVal->setDebugLoc(DDI->getDebugLoc()); 821 return true; 822} 823 824/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 825/// of llvm.dbg.value intrinsics. 826bool llvm::LowerDbgDeclare(Function &F) { 827 DIBuilder DIB(*F.getParent()); 828 SmallVector<DbgDeclareInst *, 4> Dbgs; 829 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 830 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 831 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 832 Dbgs.push_back(DDI); 833 } 834 if (Dbgs.empty()) 835 return false; 836 837 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(), 838 E = Dbgs.end(); I != E; ++I) { 839 DbgDeclareInst *DDI = *I; 840 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) { 841 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 842 UI != E; ++UI) 843 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 844 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 845 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 846 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 847 } 848 DDI->eraseFromParent(); 849 } 850 return true; 851} 852