Local.cpp revision cd35e09a4a3c640b9da0b1dfe3548a605c929ae5
1//===-- Local.cpp - Functions to perform local transformations ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This family of functions perform various local transformations to the 11// program. 12// 13//===----------------------------------------------------------------------===// 14 15#include "llvm/Transforms/Utils/Local.h" 16#include "llvm/Constants.h" 17#include "llvm/GlobalAlias.h" 18#include "llvm/GlobalVariable.h" 19#include "llvm/DerivedTypes.h" 20#include "llvm/Instructions.h" 21#include "llvm/Intrinsics.h" 22#include "llvm/IntrinsicInst.h" 23#include "llvm/Metadata.h" 24#include "llvm/Operator.h" 25#include "llvm/ADT/DenseMap.h" 26#include "llvm/ADT/SmallPtrSet.h" 27#include "llvm/Analysis/DebugInfo.h" 28#include "llvm/Analysis/DIBuilder.h" 29#include "llvm/Analysis/Dominators.h" 30#include "llvm/Analysis/ConstantFolding.h" 31#include "llvm/Analysis/InstructionSimplify.h" 32#include "llvm/Analysis/ProfileInfo.h" 33#include "llvm/Analysis/ValueTracking.h" 34#include "llvm/Target/TargetData.h" 35#include "llvm/Support/CFG.h" 36#include "llvm/Support/Debug.h" 37#include "llvm/Support/GetElementPtrTypeIterator.h" 38#include "llvm/Support/IRBuilder.h" 39#include "llvm/Support/MathExtras.h" 40#include "llvm/Support/ValueHandle.h" 41#include "llvm/Support/raw_ostream.h" 42using namespace llvm; 43 44//===----------------------------------------------------------------------===// 45// Local constant propagation. 46// 47 48/// ConstantFoldTerminator - If a terminator instruction is predicated on a 49/// constant value, convert it into an unconditional branch to the constant 50/// destination. This is a nontrivial operation because the successors of this 51/// basic block must have their PHI nodes updated. 52/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch 53/// conditions and indirectbr addresses this might make dead if 54/// DeleteDeadConditions is true. 55bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions) { 56 TerminatorInst *T = BB->getTerminator(); 57 IRBuilder<> Builder(T); 58 59 // Branch - See if we are conditional jumping on constant 60 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 61 if (BI->isUnconditional()) return false; // Can't optimize uncond branch 62 BasicBlock *Dest1 = BI->getSuccessor(0); 63 BasicBlock *Dest2 = BI->getSuccessor(1); 64 65 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { 66 // Are we branching on constant? 67 // YES. Change to unconditional branch... 68 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; 69 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; 70 71 //cerr << "Function: " << T->getParent()->getParent() 72 // << "\nRemoving branch from " << T->getParent() 73 // << "\n\nTo: " << OldDest << endl; 74 75 // Let the basic block know that we are letting go of it. Based on this, 76 // it will adjust it's PHI nodes. 77 OldDest->removePredecessor(BB); 78 79 // Replace the conditional branch with an unconditional one. 80 Builder.CreateBr(Destination); 81 BI->eraseFromParent(); 82 return true; 83 } 84 85 if (Dest2 == Dest1) { // Conditional branch to same location? 86 // This branch matches something like this: 87 // br bool %cond, label %Dest, label %Dest 88 // and changes it into: br label %Dest 89 90 // Let the basic block know that we are letting go of one copy of it. 91 assert(BI->getParent() && "Terminator not inserted in block!"); 92 Dest1->removePredecessor(BI->getParent()); 93 94 // Replace the conditional branch with an unconditional one. 95 Builder.CreateBr(Dest1); 96 Value *Cond = BI->getCondition(); 97 BI->eraseFromParent(); 98 if (DeleteDeadConditions) 99 RecursivelyDeleteTriviallyDeadInstructions(Cond); 100 return true; 101 } 102 return false; 103 } 104 105 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { 106 // If we are switching on a constant, we can convert the switch into a 107 // single branch instruction! 108 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); 109 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest 110 BasicBlock *DefaultDest = TheOnlyDest; 111 assert(TheOnlyDest == SI->getDefaultDest() && 112 "Default destination is not successor #0?"); 113 114 // Figure out which case it goes to. 115 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) { 116 // Found case matching a constant operand? 117 if (SI->getSuccessorValue(i) == CI) { 118 TheOnlyDest = SI->getSuccessor(i); 119 break; 120 } 121 122 // Check to see if this branch is going to the same place as the default 123 // dest. If so, eliminate it as an explicit compare. 124 if (SI->getSuccessor(i) == DefaultDest) { 125 // Remove this entry. 126 DefaultDest->removePredecessor(SI->getParent()); 127 SI->removeCase(i); 128 --i; --e; // Don't skip an entry... 129 continue; 130 } 131 132 // Otherwise, check to see if the switch only branches to one destination. 133 // We do this by reseting "TheOnlyDest" to null when we find two non-equal 134 // destinations. 135 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0; 136 } 137 138 if (CI && !TheOnlyDest) { 139 // Branching on a constant, but not any of the cases, go to the default 140 // successor. 141 TheOnlyDest = SI->getDefaultDest(); 142 } 143 144 // If we found a single destination that we can fold the switch into, do so 145 // now. 146 if (TheOnlyDest) { 147 // Insert the new branch. 148 Builder.CreateBr(TheOnlyDest); 149 BasicBlock *BB = SI->getParent(); 150 151 // Remove entries from PHI nodes which we no longer branch to... 152 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) { 153 // Found case matching a constant operand? 154 BasicBlock *Succ = SI->getSuccessor(i); 155 if (Succ == TheOnlyDest) 156 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest 157 else 158 Succ->removePredecessor(BB); 159 } 160 161 // Delete the old switch. 162 Value *Cond = SI->getCondition(); 163 SI->eraseFromParent(); 164 if (DeleteDeadConditions) 165 RecursivelyDeleteTriviallyDeadInstructions(Cond); 166 return true; 167 } 168 169 if (SI->getNumSuccessors() == 2) { 170 // Otherwise, we can fold this switch into a conditional branch 171 // instruction if it has only one non-default destination. 172 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), 173 SI->getSuccessorValue(1), "cond"); 174 175 // Insert the new branch. 176 Builder.CreateCondBr(Cond, SI->getSuccessor(1), SI->getSuccessor(0)); 177 178 // Delete the old switch. 179 SI->eraseFromParent(); 180 return true; 181 } 182 return false; 183 } 184 185 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 186 // indirectbr blockaddress(@F, @BB) -> br label @BB 187 if (BlockAddress *BA = 188 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 189 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 190 // Insert the new branch. 191 Builder.CreateBr(TheOnlyDest); 192 193 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 194 if (IBI->getDestination(i) == TheOnlyDest) 195 TheOnlyDest = 0; 196 else 197 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 198 } 199 Value *Address = IBI->getAddress(); 200 IBI->eraseFromParent(); 201 if (DeleteDeadConditions) 202 RecursivelyDeleteTriviallyDeadInstructions(Address); 203 204 // If we didn't find our destination in the IBI successor list, then we 205 // have undefined behavior. Replace the unconditional branch with an 206 // 'unreachable' instruction. 207 if (TheOnlyDest) { 208 BB->getTerminator()->eraseFromParent(); 209 new UnreachableInst(BB->getContext(), BB); 210 } 211 212 return true; 213 } 214 } 215 216 return false; 217} 218 219 220//===----------------------------------------------------------------------===// 221// Local dead code elimination. 222// 223 224/// isInstructionTriviallyDead - Return true if the result produced by the 225/// instruction is not used, and the instruction has no side effects. 226/// 227bool llvm::isInstructionTriviallyDead(Instruction *I) { 228 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 229 230 // We don't want debug info removed by anything this general, unless 231 // debug info is empty. 232 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 233 if (DDI->getAddress()) 234 return false; 235 return true; 236 } 237 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 238 if (DVI->getValue()) 239 return false; 240 return true; 241 } 242 243 if (!I->mayHaveSideEffects()) return true; 244 245 // Special case intrinsics that "may have side effects" but can be deleted 246 // when dead. 247 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) 248 // Safe to delete llvm.stacksave if dead. 249 if (II->getIntrinsicID() == Intrinsic::stacksave) 250 return true; 251 return false; 252} 253 254/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 255/// trivially dead instruction, delete it. If that makes any of its operands 256/// trivially dead, delete them too, recursively. Return true if any 257/// instructions were deleted. 258bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) { 259 Instruction *I = dyn_cast<Instruction>(V); 260 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I)) 261 return false; 262 263 SmallVector<Instruction*, 16> DeadInsts; 264 DeadInsts.push_back(I); 265 266 do { 267 I = DeadInsts.pop_back_val(); 268 269 // Null out all of the instruction's operands to see if any operand becomes 270 // dead as we go. 271 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 272 Value *OpV = I->getOperand(i); 273 I->setOperand(i, 0); 274 275 if (!OpV->use_empty()) continue; 276 277 // If the operand is an instruction that became dead as we nulled out the 278 // operand, and if it is 'trivially' dead, delete it in a future loop 279 // iteration. 280 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 281 if (isInstructionTriviallyDead(OpI)) 282 DeadInsts.push_back(OpI); 283 } 284 285 I->eraseFromParent(); 286 } while (!DeadInsts.empty()); 287 288 return true; 289} 290 291/// areAllUsesEqual - Check whether the uses of a value are all the same. 292/// This is similar to Instruction::hasOneUse() except this will also return 293/// true when there are no uses or multiple uses that all refer to the same 294/// value. 295static bool areAllUsesEqual(Instruction *I) { 296 Value::use_iterator UI = I->use_begin(); 297 Value::use_iterator UE = I->use_end(); 298 if (UI == UE) 299 return true; 300 301 User *TheUse = *UI; 302 for (++UI; UI != UE; ++UI) { 303 if (*UI != TheUse) 304 return false; 305 } 306 return true; 307} 308 309/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 310/// dead PHI node, due to being a def-use chain of single-use nodes that 311/// either forms a cycle or is terminated by a trivially dead instruction, 312/// delete it. If that makes any of its operands trivially dead, delete them 313/// too, recursively. Return true if a change was made. 314bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) { 315 SmallPtrSet<Instruction*, 4> Visited; 316 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 317 I = cast<Instruction>(*I->use_begin())) { 318 if (I->use_empty()) 319 return RecursivelyDeleteTriviallyDeadInstructions(I); 320 321 // If we find an instruction more than once, we're on a cycle that 322 // won't prove fruitful. 323 if (!Visited.insert(I)) { 324 // Break the cycle and delete the instruction and its operands. 325 I->replaceAllUsesWith(UndefValue::get(I->getType())); 326 (void)RecursivelyDeleteTriviallyDeadInstructions(I); 327 return true; 328 } 329 } 330 return false; 331} 332 333/// SimplifyInstructionsInBlock - Scan the specified basic block and try to 334/// simplify any instructions in it and recursively delete dead instructions. 335/// 336/// This returns true if it changed the code, note that it can delete 337/// instructions in other blocks as well in this block. 338bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) { 339 bool MadeChange = false; 340 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) { 341 Instruction *Inst = BI++; 342 343 if (Value *V = SimplifyInstruction(Inst, TD)) { 344 WeakVH BIHandle(BI); 345 ReplaceAndSimplifyAllUses(Inst, V, TD); 346 MadeChange = true; 347 if (BIHandle != BI) 348 BI = BB->begin(); 349 continue; 350 } 351 352 if (Inst->isTerminator()) 353 break; 354 355 WeakVH BIHandle(BI); 356 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst); 357 if (BIHandle != BI) 358 BI = BB->begin(); 359 } 360 return MadeChange; 361} 362 363//===----------------------------------------------------------------------===// 364// Control Flow Graph Restructuring. 365// 366 367 368/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 369/// method is called when we're about to delete Pred as a predecessor of BB. If 370/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 371/// 372/// Unlike the removePredecessor method, this attempts to simplify uses of PHI 373/// nodes that collapse into identity values. For example, if we have: 374/// x = phi(1, 0, 0, 0) 375/// y = and x, z 376/// 377/// .. and delete the predecessor corresponding to the '1', this will attempt to 378/// recursively fold the and to 0. 379void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 380 TargetData *TD) { 381 // This only adjusts blocks with PHI nodes. 382 if (!isa<PHINode>(BB->begin())) 383 return; 384 385 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 386 // them down. This will leave us with single entry phi nodes and other phis 387 // that can be removed. 388 BB->removePredecessor(Pred, true); 389 390 WeakVH PhiIt = &BB->front(); 391 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 392 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 393 394 Value *PNV = SimplifyInstruction(PN, TD); 395 if (PNV == 0) continue; 396 397 // If we're able to simplify the phi to a single value, substitute the new 398 // value into all of its uses. 399 assert(PNV != PN && "SimplifyInstruction broken!"); 400 401 Value *OldPhiIt = PhiIt; 402 ReplaceAndSimplifyAllUses(PN, PNV, TD); 403 404 // If recursive simplification ended up deleting the next PHI node we would 405 // iterate to, then our iterator is invalid, restart scanning from the top 406 // of the block. 407 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 408 } 409} 410 411 412/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 413/// predecessor is known to have one successor (DestBB!). Eliminate the edge 414/// between them, moving the instructions in the predecessor into DestBB and 415/// deleting the predecessor block. 416/// 417void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 418 // If BB has single-entry PHI nodes, fold them. 419 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 420 Value *NewVal = PN->getIncomingValue(0); 421 // Replace self referencing PHI with undef, it must be dead. 422 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 423 PN->replaceAllUsesWith(NewVal); 424 PN->eraseFromParent(); 425 } 426 427 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 428 assert(PredBB && "Block doesn't have a single predecessor!"); 429 430 // Zap anything that took the address of DestBB. Not doing this will give the 431 // address an invalid value. 432 if (DestBB->hasAddressTaken()) { 433 BlockAddress *BA = BlockAddress::get(DestBB); 434 Constant *Replacement = 435 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 436 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 437 BA->getType())); 438 BA->destroyConstant(); 439 } 440 441 // Anything that branched to PredBB now branches to DestBB. 442 PredBB->replaceAllUsesWith(DestBB); 443 444 // Splice all the instructions from PredBB to DestBB. 445 PredBB->getTerminator()->eraseFromParent(); 446 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 447 448 if (P) { 449 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 450 if (DT) { 451 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 452 DT->changeImmediateDominator(DestBB, PredBBIDom); 453 DT->eraseNode(PredBB); 454 } 455 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 456 if (PI) { 457 PI->replaceAllUses(PredBB, DestBB); 458 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 459 } 460 } 461 // Nuke BB. 462 PredBB->eraseFromParent(); 463} 464 465/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 466/// almost-empty BB ending in an unconditional branch to Succ, into succ. 467/// 468/// Assumption: Succ is the single successor for BB. 469/// 470static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 471 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 472 473 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 474 << Succ->getName() << "\n"); 475 // Shortcut, if there is only a single predecessor it must be BB and merging 476 // is always safe 477 if (Succ->getSinglePredecessor()) return true; 478 479 // Make a list of the predecessors of BB 480 typedef SmallPtrSet<BasicBlock*, 16> BlockSet; 481 BlockSet BBPreds(pred_begin(BB), pred_end(BB)); 482 483 // Use that list to make another list of common predecessors of BB and Succ 484 BlockSet CommonPreds; 485 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); 486 PI != PE; ++PI) { 487 BasicBlock *P = *PI; 488 if (BBPreds.count(P)) 489 CommonPreds.insert(P); 490 } 491 492 // Shortcut, if there are no common predecessors, merging is always safe 493 if (CommonPreds.empty()) 494 return true; 495 496 // Look at all the phi nodes in Succ, to see if they present a conflict when 497 // merging these blocks 498 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 499 PHINode *PN = cast<PHINode>(I); 500 501 // If the incoming value from BB is again a PHINode in 502 // BB which has the same incoming value for *PI as PN does, we can 503 // merge the phi nodes and then the blocks can still be merged 504 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 505 if (BBPN && BBPN->getParent() == BB) { 506 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 507 PI != PE; PI++) { 508 if (BBPN->getIncomingValueForBlock(*PI) 509 != PN->getIncomingValueForBlock(*PI)) { 510 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 511 << Succ->getName() << " is conflicting with " 512 << BBPN->getName() << " with regard to common predecessor " 513 << (*PI)->getName() << "\n"); 514 return false; 515 } 516 } 517 } else { 518 Value* Val = PN->getIncomingValueForBlock(BB); 519 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 520 PI != PE; PI++) { 521 // See if the incoming value for the common predecessor is equal to the 522 // one for BB, in which case this phi node will not prevent the merging 523 // of the block. 524 if (Val != PN->getIncomingValueForBlock(*PI)) { 525 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 526 << Succ->getName() << " is conflicting with regard to common " 527 << "predecessor " << (*PI)->getName() << "\n"); 528 return false; 529 } 530 } 531 } 532 } 533 534 return true; 535} 536 537/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 538/// unconditional branch, and contains no instructions other than PHI nodes, 539/// potential debug intrinsics and the branch. If possible, eliminate BB by 540/// rewriting all the predecessors to branch to the successor block and return 541/// true. If we can't transform, return false. 542bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 543 assert(BB != &BB->getParent()->getEntryBlock() && 544 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 545 546 // We can't eliminate infinite loops. 547 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 548 if (BB == Succ) return false; 549 550 // Check to see if merging these blocks would cause conflicts for any of the 551 // phi nodes in BB or Succ. If not, we can safely merge. 552 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 553 554 // Check for cases where Succ has multiple predecessors and a PHI node in BB 555 // has uses which will not disappear when the PHI nodes are merged. It is 556 // possible to handle such cases, but difficult: it requires checking whether 557 // BB dominates Succ, which is non-trivial to calculate in the case where 558 // Succ has multiple predecessors. Also, it requires checking whether 559 // constructing the necessary self-referential PHI node doesn't intoduce any 560 // conflicts; this isn't too difficult, but the previous code for doing this 561 // was incorrect. 562 // 563 // Note that if this check finds a live use, BB dominates Succ, so BB is 564 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 565 // folding the branch isn't profitable in that case anyway. 566 if (!Succ->getSinglePredecessor()) { 567 BasicBlock::iterator BBI = BB->begin(); 568 while (isa<PHINode>(*BBI)) { 569 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 570 UI != E; ++UI) { 571 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 572 if (PN->getIncomingBlock(UI) != BB) 573 return false; 574 } else { 575 return false; 576 } 577 } 578 ++BBI; 579 } 580 } 581 582 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 583 584 if (isa<PHINode>(Succ->begin())) { 585 // If there is more than one pred of succ, and there are PHI nodes in 586 // the successor, then we need to add incoming edges for the PHI nodes 587 // 588 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 589 590 // Loop over all of the PHI nodes in the successor of BB. 591 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 592 PHINode *PN = cast<PHINode>(I); 593 Value *OldVal = PN->removeIncomingValue(BB, false); 594 assert(OldVal && "No entry in PHI for Pred BB!"); 595 596 // If this incoming value is one of the PHI nodes in BB, the new entries 597 // in the PHI node are the entries from the old PHI. 598 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 599 PHINode *OldValPN = cast<PHINode>(OldVal); 600 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 601 // Note that, since we are merging phi nodes and BB and Succ might 602 // have common predecessors, we could end up with a phi node with 603 // identical incoming branches. This will be cleaned up later (and 604 // will trigger asserts if we try to clean it up now, without also 605 // simplifying the corresponding conditional branch). 606 PN->addIncoming(OldValPN->getIncomingValue(i), 607 OldValPN->getIncomingBlock(i)); 608 } else { 609 // Add an incoming value for each of the new incoming values. 610 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 611 PN->addIncoming(OldVal, BBPreds[i]); 612 } 613 } 614 } 615 616 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 617 if (Succ->getSinglePredecessor()) { 618 // BB is the only predecessor of Succ, so Succ will end up with exactly 619 // the same predecessors BB had. 620 Succ->getInstList().splice(Succ->begin(), 621 BB->getInstList(), BB->begin()); 622 } else { 623 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 624 assert(PN->use_empty() && "There shouldn't be any uses here!"); 625 PN->eraseFromParent(); 626 } 627 } 628 629 // Everything that jumped to BB now goes to Succ. 630 BB->replaceAllUsesWith(Succ); 631 if (!Succ->hasName()) Succ->takeName(BB); 632 BB->eraseFromParent(); // Delete the old basic block. 633 return true; 634} 635 636/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 637/// nodes in this block. This doesn't try to be clever about PHI nodes 638/// which differ only in the order of the incoming values, but instcombine 639/// orders them so it usually won't matter. 640/// 641bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 642 bool Changed = false; 643 644 // This implementation doesn't currently consider undef operands 645 // specially. Theroetically, two phis which are identical except for 646 // one having an undef where the other doesn't could be collapsed. 647 648 // Map from PHI hash values to PHI nodes. If multiple PHIs have 649 // the same hash value, the element is the first PHI in the 650 // linked list in CollisionMap. 651 DenseMap<uintptr_t, PHINode *> HashMap; 652 653 // Maintain linked lists of PHI nodes with common hash values. 654 DenseMap<PHINode *, PHINode *> CollisionMap; 655 656 // Examine each PHI. 657 for (BasicBlock::iterator I = BB->begin(); 658 PHINode *PN = dyn_cast<PHINode>(I++); ) { 659 // Compute a hash value on the operands. Instcombine will likely have sorted 660 // them, which helps expose duplicates, but we have to check all the 661 // operands to be safe in case instcombine hasn't run. 662 uintptr_t Hash = 0; 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 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 666 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 667 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 668 } 669 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end(); 670 I != E; ++I) { 671 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I)); 672 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 673 } 674 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 675 Hash >>= 1; 676 // If we've never seen this hash value before, it's a unique PHI. 677 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 678 HashMap.insert(std::make_pair(Hash, PN)); 679 if (Pair.second) continue; 680 // Otherwise it's either a duplicate or a hash collision. 681 for (PHINode *OtherPN = Pair.first->second; ; ) { 682 if (OtherPN->isIdenticalTo(PN)) { 683 // A duplicate. Replace this PHI with its duplicate. 684 PN->replaceAllUsesWith(OtherPN); 685 PN->eraseFromParent(); 686 Changed = true; 687 break; 688 } 689 // A non-duplicate hash collision. 690 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 691 if (I == CollisionMap.end()) { 692 // Set this PHI to be the head of the linked list of colliding PHIs. 693 PHINode *Old = Pair.first->second; 694 Pair.first->second = PN; 695 CollisionMap[PN] = Old; 696 break; 697 } 698 // Procede to the next PHI in the list. 699 OtherPN = I->second; 700 } 701 } 702 703 return Changed; 704} 705 706/// enforceKnownAlignment - If the specified pointer points to an object that 707/// we control, modify the object's alignment to PrefAlign. This isn't 708/// often possible though. If alignment is important, a more reliable approach 709/// is to simply align all global variables and allocation instructions to 710/// their preferred alignment from the beginning. 711/// 712static unsigned enforceKnownAlignment(Value *V, unsigned Align, 713 unsigned PrefAlign) { 714 V = V->stripPointerCasts(); 715 716 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 717 // If there is a requested alignment and if this is an alloca, round up. 718 if (AI->getAlignment() >= PrefAlign) 719 return AI->getAlignment(); 720 AI->setAlignment(PrefAlign); 721 return PrefAlign; 722 } 723 724 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 725 // If there is a large requested alignment and we can, bump up the alignment 726 // of the global. 727 if (GV->isDeclaration()) return Align; 728 729 if (GV->getAlignment() >= PrefAlign) 730 return GV->getAlignment(); 731 // We can only increase the alignment of the global if it has no alignment 732 // specified or if it is not assigned a section. If it is assigned a 733 // section, the global could be densely packed with other objects in the 734 // section, increasing the alignment could cause padding issues. 735 if (!GV->hasSection() || GV->getAlignment() == 0) 736 GV->setAlignment(PrefAlign); 737 return GV->getAlignment(); 738 } 739 740 return Align; 741} 742 743/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 744/// we can determine, return it, otherwise return 0. If PrefAlign is specified, 745/// and it is more than the alignment of the ultimate object, see if we can 746/// increase the alignment of the ultimate object, making this check succeed. 747unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 748 const TargetData *TD) { 749 assert(V->getType()->isPointerTy() && 750 "getOrEnforceKnownAlignment expects a pointer!"); 751 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 752 APInt Mask = APInt::getAllOnesValue(BitWidth); 753 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 754 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD); 755 unsigned TrailZ = KnownZero.countTrailingOnes(); 756 757 // Avoid trouble with rediculously large TrailZ values, such as 758 // those computed from a null pointer. 759 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 760 761 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 762 763 // LLVM doesn't support alignments larger than this currently. 764 Align = std::min(Align, +Value::MaximumAlignment); 765 766 if (PrefAlign > Align) 767 Align = enforceKnownAlignment(V, Align, PrefAlign); 768 769 // We don't need to make any adjustment. 770 return Align; 771} 772 773///===---------------------------------------------------------------------===// 774/// Dbg Intrinsic utilities 775/// 776 777/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 778/// that has an associated llvm.dbg.decl intrinsic. 779bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 780 StoreInst *SI, DIBuilder &Builder) { 781 DIVariable DIVar(DDI->getVariable()); 782 if (!DIVar.Verify()) 783 return false; 784 785 Instruction *DbgVal = NULL; 786 // If an argument is zero extended then use argument directly. The ZExt 787 // may be zapped by an optimization pass in future. 788 Argument *ExtendedArg = NULL; 789 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) 790 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); 791 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) 792 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); 793 if (ExtendedArg) 794 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI); 795 else 796 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI); 797 798 // Propagate any debug metadata from the store onto the dbg.value. 799 DebugLoc SIDL = SI->getDebugLoc(); 800 if (!SIDL.isUnknown()) 801 DbgVal->setDebugLoc(SIDL); 802 // Otherwise propagate debug metadata from dbg.declare. 803 else 804 DbgVal->setDebugLoc(DDI->getDebugLoc()); 805 return true; 806} 807 808/// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 809/// that has an associated llvm.dbg.decl intrinsic. 810bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 811 LoadInst *LI, DIBuilder &Builder) { 812 DIVariable DIVar(DDI->getVariable()); 813 if (!DIVar.Verify()) 814 return false; 815 816 Instruction *DbgVal = 817 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 818 DIVar, LI); 819 820 // Propagate any debug metadata from the store onto the dbg.value. 821 DebugLoc LIDL = LI->getDebugLoc(); 822 if (!LIDL.isUnknown()) 823 DbgVal->setDebugLoc(LIDL); 824 // Otherwise propagate debug metadata from dbg.declare. 825 else 826 DbgVal->setDebugLoc(DDI->getDebugLoc()); 827 return true; 828} 829 830/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 831/// of llvm.dbg.value intrinsics. 832bool llvm::LowerDbgDeclare(Function &F) { 833 DIBuilder DIB(*F.getParent()); 834 SmallVector<DbgDeclareInst *, 4> Dbgs; 835 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 836 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 837 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 838 Dbgs.push_back(DDI); 839 } 840 if (Dbgs.empty()) 841 return false; 842 843 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(), 844 E = Dbgs.end(); I != E; ++I) { 845 DbgDeclareInst *DDI = *I; 846 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) { 847 bool RemoveDDI = true; 848 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 849 UI != E; ++UI) 850 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 851 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 852 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 853 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 854 else 855 RemoveDDI = false; 856 if (RemoveDDI) 857 DDI->eraseFromParent(); 858 } 859 } 860 return true; 861} 862 863/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the 864/// alloca 'V', if any. 865DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { 866 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V)) 867 for (Value::use_iterator UI = DebugNode->use_begin(), 868 E = DebugNode->use_end(); UI != E; ++UI) 869 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI)) 870 return DDI; 871 872 return 0; 873} 874