Local.cpp revision 5649ba70fb39f2fda4791d255ae8bb373071874f
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/Operator.h" 24#include "llvm/ADT/DenseMap.h" 25#include "llvm/ADT/SmallPtrSet.h" 26#include "llvm/Analysis/DebugInfo.h" 27#include "llvm/Analysis/DIBuilder.h" 28#include "llvm/Analysis/Dominators.h" 29#include "llvm/Analysis/ConstantFolding.h" 30#include "llvm/Analysis/InstructionSimplify.h" 31#include "llvm/Analysis/ProfileInfo.h" 32#include "llvm/Analysis/ValueTracking.h" 33#include "llvm/Target/TargetData.h" 34#include "llvm/Support/CFG.h" 35#include "llvm/Support/Debug.h" 36#include "llvm/Support/GetElementPtrTypeIterator.h" 37#include "llvm/Support/IRBuilder.h" 38#include "llvm/Support/MathExtras.h" 39#include "llvm/Support/ValueHandle.h" 40#include "llvm/Support/raw_ostream.h" 41using namespace llvm; 42 43//===----------------------------------------------------------------------===// 44// Local constant propagation. 45// 46 47/// ConstantFoldTerminator - If a terminator instruction is predicated on a 48/// constant value, convert it into an unconditional branch to the constant 49/// destination. This is a nontrivial operation because the successors of this 50/// basic block must have their PHI nodes updated. 51/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch 52/// conditions and indirectbr addresses this might make dead if 53/// DeleteDeadConditions is true. 54bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions) { 55 TerminatorInst *T = BB->getTerminator(); 56 IRBuilder<> Builder(T); 57 58 // Branch - See if we are conditional jumping on constant 59 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 60 if (BI->isUnconditional()) return false; // Can't optimize uncond branch 61 BasicBlock *Dest1 = BI->getSuccessor(0); 62 BasicBlock *Dest2 = BI->getSuccessor(1); 63 64 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { 65 // Are we branching on constant? 66 // YES. Change to unconditional branch... 67 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; 68 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; 69 70 //cerr << "Function: " << T->getParent()->getParent() 71 // << "\nRemoving branch from " << T->getParent() 72 // << "\n\nTo: " << OldDest << endl; 73 74 // Let the basic block know that we are letting go of it. Based on this, 75 // it will adjust it's PHI nodes. 76 OldDest->removePredecessor(BB); 77 78 // Replace the conditional branch with an unconditional one. 79 Builder.CreateBr(Destination); 80 BI->eraseFromParent(); 81 return true; 82 } 83 84 if (Dest2 == Dest1) { // Conditional branch to same location? 85 // This branch matches something like this: 86 // br bool %cond, label %Dest, label %Dest 87 // and changes it into: br label %Dest 88 89 // Let the basic block know that we are letting go of one copy of it. 90 assert(BI->getParent() && "Terminator not inserted in block!"); 91 Dest1->removePredecessor(BI->getParent()); 92 93 // Replace the conditional branch with an unconditional one. 94 Builder.CreateBr(Dest1); 95 Value *Cond = BI->getCondition(); 96 BI->eraseFromParent(); 97 if (DeleteDeadConditions) 98 RecursivelyDeleteTriviallyDeadInstructions(Cond); 99 return true; 100 } 101 return false; 102 } 103 104 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { 105 // If we are switching on a constant, we can convert the switch into a 106 // single branch instruction! 107 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); 108 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest 109 BasicBlock *DefaultDest = TheOnlyDest; 110 assert(TheOnlyDest == SI->getDefaultDest() && 111 "Default destination is not successor #0?"); 112 113 // Figure out which case it goes to. 114 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) { 115 // Found case matching a constant operand? 116 if (SI->getSuccessorValue(i) == CI) { 117 TheOnlyDest = SI->getSuccessor(i); 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 (SI->getSuccessor(i) == DefaultDest) { 124 // Remove this entry. 125 DefaultDest->removePredecessor(SI->getParent()); 126 SI->removeCase(i); 127 --i; --e; // Don't skip an entry... 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 (SI->getSuccessor(i) != 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->getNumSuccessors() == 2) { 169 // Otherwise, we can fold this switch into a conditional branch 170 // instruction if it has only one non-default destination. 171 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), 172 SI->getSuccessorValue(1), "cond"); 173 174 // Insert the new branch. 175 Builder.CreateCondBr(Cond, SI->getSuccessor(1), SI->getSuccessor(0)); 176 177 // Delete the old switch. 178 SI->eraseFromParent(); 179 return true; 180 } 181 return false; 182 } 183 184 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 185 // indirectbr blockaddress(@F, @BB) -> br label @BB 186 if (BlockAddress *BA = 187 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 188 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 189 // Insert the new branch. 190 Builder.CreateBr(TheOnlyDest); 191 192 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 193 if (IBI->getDestination(i) == TheOnlyDest) 194 TheOnlyDest = 0; 195 else 196 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 197 } 198 Value *Address = IBI->getAddress(); 199 IBI->eraseFromParent(); 200 if (DeleteDeadConditions) 201 RecursivelyDeleteTriviallyDeadInstructions(Address); 202 203 // If we didn't find our destination in the IBI successor list, then we 204 // have undefined behavior. Replace the unconditional branch with an 205 // 'unreachable' instruction. 206 if (TheOnlyDest) { 207 BB->getTerminator()->eraseFromParent(); 208 new UnreachableInst(BB->getContext(), BB); 209 } 210 211 return true; 212 } 213 } 214 215 return false; 216} 217 218 219//===----------------------------------------------------------------------===// 220// Local dead code elimination. 221// 222 223/// isInstructionTriviallyDead - Return true if the result produced by the 224/// instruction is not used, and the instruction has no side effects. 225/// 226bool llvm::isInstructionTriviallyDead(Instruction *I) { 227 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 228 229 // We don't want debug info removed by anything this general, unless 230 // debug info is empty. 231 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 232 if (DDI->getAddress()) 233 return false; 234 return true; 235 } 236 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 237 if (DVI->getValue()) 238 return false; 239 return true; 240 } 241 242 if (!I->mayHaveSideEffects()) return true; 243 244 // Special case intrinsics that "may have side effects" but can be deleted 245 // when dead. 246 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) 247 // Safe to delete llvm.stacksave if dead. 248 if (II->getIntrinsicID() == Intrinsic::stacksave) 249 return true; 250 return false; 251} 252 253/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 254/// trivially dead instruction, delete it. If that makes any of its operands 255/// trivially dead, delete them too, recursively. Return true if any 256/// instructions were deleted. 257bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) { 258 Instruction *I = dyn_cast<Instruction>(V); 259 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I)) 260 return false; 261 262 SmallVector<Instruction*, 16> DeadInsts; 263 DeadInsts.push_back(I); 264 265 do { 266 I = DeadInsts.pop_back_val(); 267 268 // Null out all of the instruction's operands to see if any operand becomes 269 // dead as we go. 270 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 271 Value *OpV = I->getOperand(i); 272 I->setOperand(i, 0); 273 274 if (!OpV->use_empty()) continue; 275 276 // If the operand is an instruction that became dead as we nulled out the 277 // operand, and if it is 'trivially' dead, delete it in a future loop 278 // iteration. 279 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 280 if (isInstructionTriviallyDead(OpI)) 281 DeadInsts.push_back(OpI); 282 } 283 284 I->eraseFromParent(); 285 } while (!DeadInsts.empty()); 286 287 return true; 288} 289 290/// areAllUsesEqual - Check whether the uses of a value are all the same. 291/// This is similar to Instruction::hasOneUse() except this will also return 292/// true when there are no uses or multiple uses that all refer to the same 293/// value. 294static bool areAllUsesEqual(Instruction *I) { 295 Value::use_iterator UI = I->use_begin(); 296 Value::use_iterator UE = I->use_end(); 297 if (UI == UE) 298 return true; 299 300 User *TheUse = *UI; 301 for (++UI; UI != UE; ++UI) { 302 if (*UI != TheUse) 303 return false; 304 } 305 return true; 306} 307 308/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 309/// dead PHI node, due to being a def-use chain of single-use nodes that 310/// either forms a cycle or is terminated by a trivially dead instruction, 311/// delete it. If that makes any of its operands trivially dead, delete them 312/// too, recursively. Return true if a change was made. 313bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) { 314 SmallPtrSet<Instruction*, 4> Visited; 315 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 316 I = cast<Instruction>(*I->use_begin())) { 317 if (I->use_empty()) 318 return RecursivelyDeleteTriviallyDeadInstructions(I); 319 320 // If we find an instruction more than once, we're on a cycle that 321 // won't prove fruitful. 322 if (!Visited.insert(I)) { 323 // Break the cycle and delete the instruction and its operands. 324 I->replaceAllUsesWith(UndefValue::get(I->getType())); 325 (void)RecursivelyDeleteTriviallyDeadInstructions(I); 326 return true; 327 } 328 } 329 return false; 330} 331 332/// SimplifyInstructionsInBlock - Scan the specified basic block and try to 333/// simplify any instructions in it and recursively delete dead instructions. 334/// 335/// This returns true if it changed the code, note that it can delete 336/// instructions in other blocks as well in this block. 337bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) { 338 bool MadeChange = false; 339 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) { 340 Instruction *Inst = BI++; 341 342 if (Value *V = SimplifyInstruction(Inst, TD)) { 343 WeakVH BIHandle(BI); 344 ReplaceAndSimplifyAllUses(Inst, V, TD); 345 MadeChange = true; 346 if (BIHandle != BI) 347 BI = BB->begin(); 348 continue; 349 } 350 351 if (Inst->isTerminator()) 352 break; 353 354 WeakVH BIHandle(BI); 355 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst); 356 if (BIHandle != BI) 357 BI = BB->begin(); 358 } 359 return MadeChange; 360} 361 362//===----------------------------------------------------------------------===// 363// Control Flow Graph Restructuring. 364// 365 366 367/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 368/// method is called when we're about to delete Pred as a predecessor of BB. If 369/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 370/// 371/// Unlike the removePredecessor method, this attempts to simplify uses of PHI 372/// nodes that collapse into identity values. For example, if we have: 373/// x = phi(1, 0, 0, 0) 374/// y = and x, z 375/// 376/// .. and delete the predecessor corresponding to the '1', this will attempt to 377/// recursively fold the and to 0. 378void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 379 TargetData *TD) { 380 // This only adjusts blocks with PHI nodes. 381 if (!isa<PHINode>(BB->begin())) 382 return; 383 384 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 385 // them down. This will leave us with single entry phi nodes and other phis 386 // that can be removed. 387 BB->removePredecessor(Pred, true); 388 389 WeakVH PhiIt = &BB->front(); 390 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 391 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 392 393 Value *PNV = SimplifyInstruction(PN, TD); 394 if (PNV == 0) continue; 395 396 // If we're able to simplify the phi to a single value, substitute the new 397 // value into all of its uses. 398 assert(PNV != PN && "SimplifyInstruction broken!"); 399 400 Value *OldPhiIt = PhiIt; 401 ReplaceAndSimplifyAllUses(PN, PNV, TD); 402 403 // If recursive simplification ended up deleting the next PHI node we would 404 // iterate to, then our iterator is invalid, restart scanning from the top 405 // of the block. 406 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 407 } 408} 409 410 411/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 412/// predecessor is known to have one successor (DestBB!). Eliminate the edge 413/// between them, moving the instructions in the predecessor into DestBB and 414/// deleting the predecessor block. 415/// 416void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 417 // If BB has single-entry PHI nodes, fold them. 418 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 419 Value *NewVal = PN->getIncomingValue(0); 420 // Replace self referencing PHI with undef, it must be dead. 421 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 422 PN->replaceAllUsesWith(NewVal); 423 PN->eraseFromParent(); 424 } 425 426 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 427 assert(PredBB && "Block doesn't have a single predecessor!"); 428 429 // Splice all the instructions from PredBB to DestBB. 430 PredBB->getTerminator()->eraseFromParent(); 431 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 432 433 // Zap anything that took the address of DestBB. Not doing this will give the 434 // address an invalid value. 435 if (DestBB->hasAddressTaken()) { 436 BlockAddress *BA = BlockAddress::get(DestBB); 437 Constant *Replacement = 438 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 439 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 440 BA->getType())); 441 BA->destroyConstant(); 442 } 443 444 // Anything that branched to PredBB now branches to DestBB. 445 PredBB->replaceAllUsesWith(DestBB); 446 447 if (P) { 448 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 449 if (DT) { 450 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 451 DT->changeImmediateDominator(DestBB, PredBBIDom); 452 DT->eraseNode(PredBB); 453 } 454 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 455 if (PI) { 456 PI->replaceAllUses(PredBB, DestBB); 457 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 458 } 459 } 460 // Nuke BB. 461 PredBB->eraseFromParent(); 462} 463 464/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 465/// almost-empty BB ending in an unconditional branch to Succ, into succ. 466/// 467/// Assumption: Succ is the single successor for BB. 468/// 469static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 470 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 471 472 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 473 << Succ->getName() << "\n"); 474 // Shortcut, if there is only a single predecessor it must be BB and merging 475 // is always safe 476 if (Succ->getSinglePredecessor()) return true; 477 478 // Make a list of the predecessors of BB 479 typedef SmallPtrSet<BasicBlock*, 16> BlockSet; 480 BlockSet BBPreds(pred_begin(BB), pred_end(BB)); 481 482 // Use that list to make another list of common predecessors of BB and Succ 483 BlockSet CommonPreds; 484 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); 485 PI != PE; ++PI) { 486 BasicBlock *P = *PI; 487 if (BBPreds.count(P)) 488 CommonPreds.insert(P); 489 } 490 491 // Shortcut, if there are no common predecessors, merging is always safe 492 if (CommonPreds.empty()) 493 return true; 494 495 // Look at all the phi nodes in Succ, to see if they present a conflict when 496 // merging these blocks 497 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 498 PHINode *PN = cast<PHINode>(I); 499 500 // If the incoming value from BB is again a PHINode in 501 // BB which has the same incoming value for *PI as PN does, we can 502 // merge the phi nodes and then the blocks can still be merged 503 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 504 if (BBPN && BBPN->getParent() == BB) { 505 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 506 PI != PE; PI++) { 507 if (BBPN->getIncomingValueForBlock(*PI) 508 != PN->getIncomingValueForBlock(*PI)) { 509 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 510 << Succ->getName() << " is conflicting with " 511 << BBPN->getName() << " with regard to common predecessor " 512 << (*PI)->getName() << "\n"); 513 return false; 514 } 515 } 516 } else { 517 Value* Val = PN->getIncomingValueForBlock(BB); 518 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 519 PI != PE; PI++) { 520 // See if the incoming value for the common predecessor is equal to the 521 // one for BB, in which case this phi node will not prevent the merging 522 // of the block. 523 if (Val != PN->getIncomingValueForBlock(*PI)) { 524 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 525 << Succ->getName() << " is conflicting with regard to common " 526 << "predecessor " << (*PI)->getName() << "\n"); 527 return false; 528 } 529 } 530 } 531 } 532 533 return true; 534} 535 536/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 537/// unconditional branch, and contains no instructions other than PHI nodes, 538/// potential debug intrinsics and the branch. If possible, eliminate BB by 539/// rewriting all the predecessors to branch to the successor block and return 540/// true. If we can't transform, return false. 541bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 542 assert(BB != &BB->getParent()->getEntryBlock() && 543 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 544 545 // We can't eliminate infinite loops. 546 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 547 if (BB == Succ) return false; 548 549 // Check to see if merging these blocks would cause conflicts for any of the 550 // phi nodes in BB or Succ. If not, we can safely merge. 551 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 552 553 // Check for cases where Succ has multiple predecessors and a PHI node in BB 554 // has uses which will not disappear when the PHI nodes are merged. It is 555 // possible to handle such cases, but difficult: it requires checking whether 556 // BB dominates Succ, which is non-trivial to calculate in the case where 557 // Succ has multiple predecessors. Also, it requires checking whether 558 // constructing the necessary self-referential PHI node doesn't intoduce any 559 // conflicts; this isn't too difficult, but the previous code for doing this 560 // was incorrect. 561 // 562 // Note that if this check finds a live use, BB dominates Succ, so BB is 563 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 564 // folding the branch isn't profitable in that case anyway. 565 if (!Succ->getSinglePredecessor()) { 566 BasicBlock::iterator BBI = BB->begin(); 567 while (isa<PHINode>(*BBI)) { 568 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 569 UI != E; ++UI) { 570 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 571 if (PN->getIncomingBlock(UI) != BB) 572 return false; 573 } else { 574 return false; 575 } 576 } 577 ++BBI; 578 } 579 } 580 581 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 582 583 if (isa<PHINode>(Succ->begin())) { 584 // If there is more than one pred of succ, and there are PHI nodes in 585 // the successor, then we need to add incoming edges for the PHI nodes 586 // 587 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 588 589 // Loop over all of the PHI nodes in the successor of BB. 590 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 591 PHINode *PN = cast<PHINode>(I); 592 Value *OldVal = PN->removeIncomingValue(BB, false); 593 assert(OldVal && "No entry in PHI for Pred BB!"); 594 595 // If this incoming value is one of the PHI nodes in BB, the new entries 596 // in the PHI node are the entries from the old PHI. 597 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 598 PHINode *OldValPN = cast<PHINode>(OldVal); 599 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 600 // Note that, since we are merging phi nodes and BB and Succ might 601 // have common predecessors, we could end up with a phi node with 602 // identical incoming branches. This will be cleaned up later (and 603 // will trigger asserts if we try to clean it up now, without also 604 // simplifying the corresponding conditional branch). 605 PN->addIncoming(OldValPN->getIncomingValue(i), 606 OldValPN->getIncomingBlock(i)); 607 } else { 608 // Add an incoming value for each of the new incoming values. 609 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 610 PN->addIncoming(OldVal, BBPreds[i]); 611 } 612 } 613 } 614 615 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 616 if (Succ->getSinglePredecessor()) { 617 // BB is the only predecessor of Succ, so Succ will end up with exactly 618 // the same predecessors BB had. 619 Succ->getInstList().splice(Succ->begin(), 620 BB->getInstList(), BB->begin()); 621 } else { 622 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 623 assert(PN->use_empty() && "There shouldn't be any uses here!"); 624 PN->eraseFromParent(); 625 } 626 } 627 628 // Everything that jumped to BB now goes to Succ. 629 BB->replaceAllUsesWith(Succ); 630 if (!Succ->hasName()) Succ->takeName(BB); 631 BB->eraseFromParent(); // Delete the old basic block. 632 return true; 633} 634 635/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 636/// nodes in this block. This doesn't try to be clever about PHI nodes 637/// which differ only in the order of the incoming values, but instcombine 638/// orders them so it usually won't matter. 639/// 640bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 641 bool Changed = false; 642 643 // This implementation doesn't currently consider undef operands 644 // specially. Theroetically, two phis which are identical except for 645 // one having an undef where the other doesn't could be collapsed. 646 647 // Map from PHI hash values to PHI nodes. If multiple PHIs have 648 // the same hash value, the element is the first PHI in the 649 // linked list in CollisionMap. 650 DenseMap<uintptr_t, PHINode *> HashMap; 651 652 // Maintain linked lists of PHI nodes with common hash values. 653 DenseMap<PHINode *, PHINode *> CollisionMap; 654 655 // Examine each PHI. 656 for (BasicBlock::iterator I = BB->begin(); 657 PHINode *PN = dyn_cast<PHINode>(I++); ) { 658 // Compute a hash value on the operands. Instcombine will likely have sorted 659 // them, which helps expose duplicates, but we have to check all the 660 // operands to be safe in case instcombine hasn't run. 661 uintptr_t Hash = 0; 662 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 663 // This hash algorithm is quite weak as hash functions go, but it seems 664 // to do a good enough job for this particular purpose, and is very quick. 665 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 666 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 667 } 668 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 669 Hash >>= 1; 670 // If we've never seen this hash value before, it's a unique PHI. 671 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 672 HashMap.insert(std::make_pair(Hash, PN)); 673 if (Pair.second) continue; 674 // Otherwise it's either a duplicate or a hash collision. 675 for (PHINode *OtherPN = Pair.first->second; ; ) { 676 if (OtherPN->isIdenticalTo(PN)) { 677 // A duplicate. Replace this PHI with its duplicate. 678 PN->replaceAllUsesWith(OtherPN); 679 PN->eraseFromParent(); 680 Changed = true; 681 break; 682 } 683 // A non-duplicate hash collision. 684 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 685 if (I == CollisionMap.end()) { 686 // Set this PHI to be the head of the linked list of colliding PHIs. 687 PHINode *Old = Pair.first->second; 688 Pair.first->second = PN; 689 CollisionMap[PN] = Old; 690 break; 691 } 692 // Procede to the next PHI in the list. 693 OtherPN = I->second; 694 } 695 } 696 697 return Changed; 698} 699 700/// enforceKnownAlignment - If the specified pointer points to an object that 701/// we control, modify the object's alignment to PrefAlign. This isn't 702/// often possible though. If alignment is important, a more reliable approach 703/// is to simply align all global variables and allocation instructions to 704/// their preferred alignment from the beginning. 705/// 706static unsigned enforceKnownAlignment(Value *V, unsigned Align, 707 unsigned PrefAlign) { 708 709 User *U = dyn_cast<User>(V); 710 if (!U) return Align; 711 712 switch (Operator::getOpcode(U)) { 713 default: break; 714 case Instruction::BitCast: 715 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign); 716 case Instruction::GetElementPtr: { 717 // If all indexes are zero, it is just the alignment of the base pointer. 718 bool AllZeroOperands = true; 719 for (User::op_iterator i = U->op_begin() + 1, e = U->op_end(); i != e; ++i) 720 if (!isa<Constant>(*i) || 721 !cast<Constant>(*i)->isNullValue()) { 722 AllZeroOperands = false; 723 break; 724 } 725 726 if (AllZeroOperands) { 727 // Treat this like a bitcast. 728 return enforceKnownAlignment(U->getOperand(0), Align, PrefAlign); 729 } 730 return Align; 731 } 732 case Instruction::Alloca: { 733 AllocaInst *AI = cast<AllocaInst>(V); 734 // If there is a requested alignment and if this is an alloca, round up. 735 if (AI->getAlignment() >= PrefAlign) 736 return AI->getAlignment(); 737 AI->setAlignment(PrefAlign); 738 return PrefAlign; 739 } 740 } 741 742 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 743 // If there is a large requested alignment and we can, bump up the alignment 744 // of the global. 745 if (GV->isDeclaration()) return Align; 746 747 if (GV->getAlignment() >= PrefAlign) 748 return GV->getAlignment(); 749 // We can only increase the alignment of the global if it has no alignment 750 // specified or if it is not assigned a section. If it is assigned a 751 // section, the global could be densely packed with other objects in the 752 // section, increasing the alignment could cause padding issues. 753 if (!GV->hasSection() || GV->getAlignment() == 0) 754 GV->setAlignment(PrefAlign); 755 return GV->getAlignment(); 756 } 757 758 return Align; 759} 760 761/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 762/// we can determine, return it, otherwise return 0. If PrefAlign is specified, 763/// and it is more than the alignment of the ultimate object, see if we can 764/// increase the alignment of the ultimate object, making this check succeed. 765unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 766 const TargetData *TD) { 767 assert(V->getType()->isPointerTy() && 768 "getOrEnforceKnownAlignment expects a pointer!"); 769 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 770 APInt Mask = APInt::getAllOnesValue(BitWidth); 771 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 772 ComputeMaskedBits(V, Mask, 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); 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