1 //===-- Local.cpp - Functions to perform local transformations ------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This family of functions perform various local transformations to the 11 // program. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Transforms/Utils/Local.h" 16 #include "llvm/Constants.h" 17 #include "llvm/GlobalAlias.h" 18 #include "llvm/GlobalVariable.h" 19 #include "llvm/DerivedTypes.h" 20 #include "llvm/Instructions.h" 21 #include "llvm/Intrinsics.h" 22 #include "llvm/IntrinsicInst.h" 23 #include "llvm/Metadata.h" 24 #include "llvm/Operator.h" 25 #include "llvm/ADT/DenseMap.h" 26 #include "llvm/ADT/SmallPtrSet.h" 27 #include "llvm/Analysis/DebugInfo.h" 28 #include "llvm/Analysis/DIBuilder.h" 29 #include "llvm/Analysis/Dominators.h" 30 #include "llvm/Analysis/InstructionSimplify.h" 31 #include "llvm/Analysis/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" 41 using 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. 54 bool 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 /// 226 bool llvm::isInstructionTriviallyDead(Instruction *I) { 227 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 228 229 // We don't want the landingpad instruction removed by anything this general. 230 if (isa<LandingPadInst>(I)) 231 return false; 232 233 // We don't want debug info removed by anything this general, unless 234 // debug info is empty. 235 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 236 if (DDI->getAddress()) 237 return false; 238 return true; 239 } 240 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 241 if (DVI->getValue()) 242 return false; 243 return true; 244 } 245 246 if (!I->mayHaveSideEffects()) return true; 247 248 // Special case intrinsics that "may have side effects" but can be deleted 249 // when dead. 250 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 251 // Safe to delete llvm.stacksave if dead. 252 if (II->getIntrinsicID() == Intrinsic::stacksave) 253 return true; 254 255 // Lifetime intrinsics are dead when their right-hand is undef. 256 if (II->getIntrinsicID() == Intrinsic::lifetime_start || 257 II->getIntrinsicID() == Intrinsic::lifetime_end) 258 return isa<UndefValue>(II->getArgOperand(1)); 259 } 260 return false; 261 } 262 263 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 264 /// trivially dead instruction, delete it. If that makes any of its operands 265 /// trivially dead, delete them too, recursively. Return true if any 266 /// instructions were deleted. 267 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) { 268 Instruction *I = dyn_cast<Instruction>(V); 269 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I)) 270 return false; 271 272 SmallVector<Instruction*, 16> DeadInsts; 273 DeadInsts.push_back(I); 274 275 do { 276 I = DeadInsts.pop_back_val(); 277 278 // Null out all of the instruction's operands to see if any operand becomes 279 // dead as we go. 280 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 281 Value *OpV = I->getOperand(i); 282 I->setOperand(i, 0); 283 284 if (!OpV->use_empty()) continue; 285 286 // If the operand is an instruction that became dead as we nulled out the 287 // operand, and if it is 'trivially' dead, delete it in a future loop 288 // iteration. 289 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 290 if (isInstructionTriviallyDead(OpI)) 291 DeadInsts.push_back(OpI); 292 } 293 294 I->eraseFromParent(); 295 } while (!DeadInsts.empty()); 296 297 return true; 298 } 299 300 /// areAllUsesEqual - Check whether the uses of a value are all the same. 301 /// This is similar to Instruction::hasOneUse() except this will also return 302 /// true when there are no uses or multiple uses that all refer to the same 303 /// value. 304 static bool areAllUsesEqual(Instruction *I) { 305 Value::use_iterator UI = I->use_begin(); 306 Value::use_iterator UE = I->use_end(); 307 if (UI == UE) 308 return true; 309 310 User *TheUse = *UI; 311 for (++UI; UI != UE; ++UI) { 312 if (*UI != TheUse) 313 return false; 314 } 315 return true; 316 } 317 318 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 319 /// dead PHI node, due to being a def-use chain of single-use nodes that 320 /// either forms a cycle or is terminated by a trivially dead instruction, 321 /// delete it. If that makes any of its operands trivially dead, delete them 322 /// too, recursively. Return true if a change was made. 323 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) { 324 SmallPtrSet<Instruction*, 4> Visited; 325 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 326 I = cast<Instruction>(*I->use_begin())) { 327 if (I->use_empty()) 328 return RecursivelyDeleteTriviallyDeadInstructions(I); 329 330 // If we find an instruction more than once, we're on a cycle that 331 // won't prove fruitful. 332 if (!Visited.insert(I)) { 333 // Break the cycle and delete the instruction and its operands. 334 I->replaceAllUsesWith(UndefValue::get(I->getType())); 335 (void)RecursivelyDeleteTriviallyDeadInstructions(I); 336 return true; 337 } 338 } 339 return false; 340 } 341 342 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to 343 /// simplify any instructions in it and recursively delete dead instructions. 344 /// 345 /// This returns true if it changed the code, note that it can delete 346 /// instructions in other blocks as well in this block. 347 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) { 348 bool MadeChange = false; 349 for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) { 350 Instruction *Inst = BI++; 351 352 if (Value *V = SimplifyInstruction(Inst, TD)) { 353 WeakVH BIHandle(BI); 354 ReplaceAndSimplifyAllUses(Inst, V, TD); 355 MadeChange = true; 356 if (BIHandle != BI) 357 BI = BB->begin(); 358 continue; 359 } 360 361 if (Inst->isTerminator()) 362 break; 363 364 WeakVH BIHandle(BI); 365 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst); 366 if (BIHandle != BI) 367 BI = BB->begin(); 368 } 369 return MadeChange; 370 } 371 372 //===----------------------------------------------------------------------===// 373 // Control Flow Graph Restructuring. 374 // 375 376 377 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 378 /// method is called when we're about to delete Pred as a predecessor of BB. If 379 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 380 /// 381 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI 382 /// nodes that collapse into identity values. For example, if we have: 383 /// x = phi(1, 0, 0, 0) 384 /// y = and x, z 385 /// 386 /// .. and delete the predecessor corresponding to the '1', this will attempt to 387 /// recursively fold the and to 0. 388 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 389 TargetData *TD) { 390 // This only adjusts blocks with PHI nodes. 391 if (!isa<PHINode>(BB->begin())) 392 return; 393 394 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 395 // them down. This will leave us with single entry phi nodes and other phis 396 // that can be removed. 397 BB->removePredecessor(Pred, true); 398 399 WeakVH PhiIt = &BB->front(); 400 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 401 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 402 403 Value *PNV = SimplifyInstruction(PN, TD); 404 if (PNV == 0) continue; 405 406 // If we're able to simplify the phi to a single value, substitute the new 407 // value into all of its uses. 408 assert(PNV != PN && "SimplifyInstruction broken!"); 409 410 Value *OldPhiIt = PhiIt; 411 ReplaceAndSimplifyAllUses(PN, PNV, TD); 412 413 // If recursive simplification ended up deleting the next PHI node we would 414 // iterate to, then our iterator is invalid, restart scanning from the top 415 // of the block. 416 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 417 } 418 } 419 420 421 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 422 /// predecessor is known to have one successor (DestBB!). Eliminate the edge 423 /// between them, moving the instructions in the predecessor into DestBB and 424 /// deleting the predecessor block. 425 /// 426 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 427 // If BB has single-entry PHI nodes, fold them. 428 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 429 Value *NewVal = PN->getIncomingValue(0); 430 // Replace self referencing PHI with undef, it must be dead. 431 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 432 PN->replaceAllUsesWith(NewVal); 433 PN->eraseFromParent(); 434 } 435 436 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 437 assert(PredBB && "Block doesn't have a single predecessor!"); 438 439 // Zap anything that took the address of DestBB. Not doing this will give the 440 // address an invalid value. 441 if (DestBB->hasAddressTaken()) { 442 BlockAddress *BA = BlockAddress::get(DestBB); 443 Constant *Replacement = 444 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 445 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 446 BA->getType())); 447 BA->destroyConstant(); 448 } 449 450 // Anything that branched to PredBB now branches to DestBB. 451 PredBB->replaceAllUsesWith(DestBB); 452 453 // Splice all the instructions from PredBB to DestBB. 454 PredBB->getTerminator()->eraseFromParent(); 455 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 456 457 if (P) { 458 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 459 if (DT) { 460 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 461 DT->changeImmediateDominator(DestBB, PredBBIDom); 462 DT->eraseNode(PredBB); 463 } 464 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 465 if (PI) { 466 PI->replaceAllUses(PredBB, DestBB); 467 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 468 } 469 } 470 // Nuke BB. 471 PredBB->eraseFromParent(); 472 } 473 474 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 475 /// almost-empty BB ending in an unconditional branch to Succ, into succ. 476 /// 477 /// Assumption: Succ is the single successor for BB. 478 /// 479 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 480 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 481 482 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 483 << Succ->getName() << "\n"); 484 // Shortcut, if there is only a single predecessor it must be BB and merging 485 // is always safe 486 if (Succ->getSinglePredecessor()) return true; 487 488 // Make a list of the predecessors of BB 489 typedef SmallPtrSet<BasicBlock*, 16> BlockSet; 490 BlockSet BBPreds(pred_begin(BB), pred_end(BB)); 491 492 // Use that list to make another list of common predecessors of BB and Succ 493 BlockSet CommonPreds; 494 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); 495 PI != PE; ++PI) { 496 BasicBlock *P = *PI; 497 if (BBPreds.count(P)) 498 CommonPreds.insert(P); 499 } 500 501 // Shortcut, if there are no common predecessors, merging is always safe 502 if (CommonPreds.empty()) 503 return true; 504 505 // Look at all the phi nodes in Succ, to see if they present a conflict when 506 // merging these blocks 507 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 508 PHINode *PN = cast<PHINode>(I); 509 510 // If the incoming value from BB is again a PHINode in 511 // BB which has the same incoming value for *PI as PN does, we can 512 // merge the phi nodes and then the blocks can still be merged 513 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 514 if (BBPN && BBPN->getParent() == BB) { 515 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 516 PI != PE; PI++) { 517 if (BBPN->getIncomingValueForBlock(*PI) 518 != PN->getIncomingValueForBlock(*PI)) { 519 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 520 << Succ->getName() << " is conflicting with " 521 << BBPN->getName() << " with regard to common predecessor " 522 << (*PI)->getName() << "\n"); 523 return false; 524 } 525 } 526 } else { 527 Value* Val = PN->getIncomingValueForBlock(BB); 528 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end(); 529 PI != PE; PI++) { 530 // See if the incoming value for the common predecessor is equal to the 531 // one for BB, in which case this phi node will not prevent the merging 532 // of the block. 533 if (Val != PN->getIncomingValueForBlock(*PI)) { 534 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 535 << Succ->getName() << " is conflicting with regard to common " 536 << "predecessor " << (*PI)->getName() << "\n"); 537 return false; 538 } 539 } 540 } 541 } 542 543 return true; 544 } 545 546 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 547 /// unconditional branch, and contains no instructions other than PHI nodes, 548 /// potential side-effect free intrinsics and the branch. If possible, 549 /// eliminate BB by rewriting all the predecessors to branch to the successor 550 /// block and return true. If we can't transform, return false. 551 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 552 assert(BB != &BB->getParent()->getEntryBlock() && 553 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 554 555 // We can't eliminate infinite loops. 556 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 557 if (BB == Succ) return false; 558 559 // Check to see if merging these blocks would cause conflicts for any of the 560 // phi nodes in BB or Succ. If not, we can safely merge. 561 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 562 563 // Check for cases where Succ has multiple predecessors and a PHI node in BB 564 // has uses which will not disappear when the PHI nodes are merged. It is 565 // possible to handle such cases, but difficult: it requires checking whether 566 // BB dominates Succ, which is non-trivial to calculate in the case where 567 // Succ has multiple predecessors. Also, it requires checking whether 568 // constructing the necessary self-referential PHI node doesn't intoduce any 569 // conflicts; this isn't too difficult, but the previous code for doing this 570 // was incorrect. 571 // 572 // Note that if this check finds a live use, BB dominates Succ, so BB is 573 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 574 // folding the branch isn't profitable in that case anyway. 575 if (!Succ->getSinglePredecessor()) { 576 BasicBlock::iterator BBI = BB->begin(); 577 while (isa<PHINode>(*BBI)) { 578 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 579 UI != E; ++UI) { 580 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 581 if (PN->getIncomingBlock(UI) != BB) 582 return false; 583 } else { 584 return false; 585 } 586 } 587 ++BBI; 588 } 589 } 590 591 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 592 593 if (isa<PHINode>(Succ->begin())) { 594 // If there is more than one pred of succ, and there are PHI nodes in 595 // the successor, then we need to add incoming edges for the PHI nodes 596 // 597 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 598 599 // Loop over all of the PHI nodes in the successor of BB. 600 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 601 PHINode *PN = cast<PHINode>(I); 602 Value *OldVal = PN->removeIncomingValue(BB, false); 603 assert(OldVal && "No entry in PHI for Pred BB!"); 604 605 // If this incoming value is one of the PHI nodes in BB, the new entries 606 // in the PHI node are the entries from the old PHI. 607 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 608 PHINode *OldValPN = cast<PHINode>(OldVal); 609 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 610 // Note that, since we are merging phi nodes and BB and Succ might 611 // have common predecessors, we could end up with a phi node with 612 // identical incoming branches. This will be cleaned up later (and 613 // will trigger asserts if we try to clean it up now, without also 614 // simplifying the corresponding conditional branch). 615 PN->addIncoming(OldValPN->getIncomingValue(i), 616 OldValPN->getIncomingBlock(i)); 617 } else { 618 // Add an incoming value for each of the new incoming values. 619 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 620 PN->addIncoming(OldVal, BBPreds[i]); 621 } 622 } 623 } 624 625 if (Succ->getSinglePredecessor()) { 626 // BB is the only predecessor of Succ, so Succ will end up with exactly 627 // the same predecessors BB had. 628 629 // Copy over any phi, debug or lifetime instruction. 630 BB->getTerminator()->eraseFromParent(); 631 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList()); 632 } else { 633 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 634 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 635 assert(PN->use_empty() && "There shouldn't be any uses here!"); 636 PN->eraseFromParent(); 637 } 638 } 639 640 // Everything that jumped to BB now goes to Succ. 641 BB->replaceAllUsesWith(Succ); 642 if (!Succ->hasName()) Succ->takeName(BB); 643 BB->eraseFromParent(); // Delete the old basic block. 644 return true; 645 } 646 647 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 648 /// nodes in this block. This doesn't try to be clever about PHI nodes 649 /// which differ only in the order of the incoming values, but instcombine 650 /// orders them so it usually won't matter. 651 /// 652 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 653 bool Changed = false; 654 655 // This implementation doesn't currently consider undef operands 656 // specially. Theoretically, two phis which are identical except for 657 // one having an undef where the other doesn't could be collapsed. 658 659 // Map from PHI hash values to PHI nodes. If multiple PHIs have 660 // the same hash value, the element is the first PHI in the 661 // linked list in CollisionMap. 662 DenseMap<uintptr_t, PHINode *> HashMap; 663 664 // Maintain linked lists of PHI nodes with common hash values. 665 DenseMap<PHINode *, PHINode *> CollisionMap; 666 667 // Examine each PHI. 668 for (BasicBlock::iterator I = BB->begin(); 669 PHINode *PN = dyn_cast<PHINode>(I++); ) { 670 // Compute a hash value on the operands. Instcombine will likely have sorted 671 // them, which helps expose duplicates, but we have to check all the 672 // operands to be safe in case instcombine hasn't run. 673 uintptr_t Hash = 0; 674 // This hash algorithm is quite weak as hash functions go, but it seems 675 // to do a good enough job for this particular purpose, and is very quick. 676 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 677 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 678 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 679 } 680 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end(); 681 I != E; ++I) { 682 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I)); 683 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 684 } 685 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 686 Hash >>= 1; 687 // If we've never seen this hash value before, it's a unique PHI. 688 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 689 HashMap.insert(std::make_pair(Hash, PN)); 690 if (Pair.second) continue; 691 // Otherwise it's either a duplicate or a hash collision. 692 for (PHINode *OtherPN = Pair.first->second; ; ) { 693 if (OtherPN->isIdenticalTo(PN)) { 694 // A duplicate. Replace this PHI with its duplicate. 695 PN->replaceAllUsesWith(OtherPN); 696 PN->eraseFromParent(); 697 Changed = true; 698 break; 699 } 700 // A non-duplicate hash collision. 701 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 702 if (I == CollisionMap.end()) { 703 // Set this PHI to be the head of the linked list of colliding PHIs. 704 PHINode *Old = Pair.first->second; 705 Pair.first->second = PN; 706 CollisionMap[PN] = Old; 707 break; 708 } 709 // Procede to the next PHI in the list. 710 OtherPN = I->second; 711 } 712 } 713 714 return Changed; 715 } 716 717 /// enforceKnownAlignment - If the specified pointer points to an object that 718 /// we control, modify the object's alignment to PrefAlign. This isn't 719 /// often possible though. If alignment is important, a more reliable approach 720 /// is to simply align all global variables and allocation instructions to 721 /// their preferred alignment from the beginning. 722 /// 723 static unsigned enforceKnownAlignment(Value *V, unsigned Align, 724 unsigned PrefAlign, const TargetData *TD) { 725 V = V->stripPointerCasts(); 726 727 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 728 // If the preferred alignment is greater than the natural stack alignment 729 // then don't round up. This avoids dynamic stack realignment. 730 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign)) 731 return Align; 732 // If there is a requested alignment and if this is an alloca, round up. 733 if (AI->getAlignment() >= PrefAlign) 734 return AI->getAlignment(); 735 AI->setAlignment(PrefAlign); 736 return PrefAlign; 737 } 738 739 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 740 // If there is a large requested alignment and we can, bump up the alignment 741 // of the global. 742 if (GV->isDeclaration()) return Align; 743 744 if (GV->getAlignment() >= PrefAlign) 745 return GV->getAlignment(); 746 // We can only increase the alignment of the global if it has no alignment 747 // specified or if it is not assigned a section. If it is assigned a 748 // section, the global could be densely packed with other objects in the 749 // section, increasing the alignment could cause padding issues. 750 if (!GV->hasSection() || GV->getAlignment() == 0) 751 GV->setAlignment(PrefAlign); 752 return GV->getAlignment(); 753 } 754 755 return Align; 756 } 757 758 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 759 /// we can determine, return it, otherwise return 0. If PrefAlign is specified, 760 /// and it is more than the alignment of the ultimate object, see if we can 761 /// increase the alignment of the ultimate object, making this check succeed. 762 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 763 const TargetData *TD) { 764 assert(V->getType()->isPointerTy() && 765 "getOrEnforceKnownAlignment expects a pointer!"); 766 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 767 APInt Mask = APInt::getAllOnesValue(BitWidth); 768 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 769 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD); 770 unsigned TrailZ = KnownZero.countTrailingOnes(); 771 772 // Avoid trouble with rediculously large TrailZ values, such as 773 // those computed from a null pointer. 774 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 775 776 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 777 778 // LLVM doesn't support alignments larger than this currently. 779 Align = std::min(Align, +Value::MaximumAlignment); 780 781 if (PrefAlign > Align) 782 Align = enforceKnownAlignment(V, Align, PrefAlign, TD); 783 784 // We don't need to make any adjustment. 785 return Align; 786 } 787 788 ///===---------------------------------------------------------------------===// 789 /// Dbg Intrinsic utilities 790 /// 791 792 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 793 /// that has an associated llvm.dbg.decl intrinsic. 794 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 795 StoreInst *SI, DIBuilder &Builder) { 796 DIVariable DIVar(DDI->getVariable()); 797 if (!DIVar.Verify()) 798 return false; 799 800 Instruction *DbgVal = NULL; 801 // If an argument is zero extended then use argument directly. The ZExt 802 // may be zapped by an optimization pass in future. 803 Argument *ExtendedArg = NULL; 804 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) 805 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); 806 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) 807 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); 808 if (ExtendedArg) 809 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI); 810 else 811 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI); 812 813 // Propagate any debug metadata from the store onto the dbg.value. 814 DebugLoc SIDL = SI->getDebugLoc(); 815 if (!SIDL.isUnknown()) 816 DbgVal->setDebugLoc(SIDL); 817 // Otherwise propagate debug metadata from dbg.declare. 818 else 819 DbgVal->setDebugLoc(DDI->getDebugLoc()); 820 return true; 821 } 822 823 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 824 /// that has an associated llvm.dbg.decl intrinsic. 825 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 826 LoadInst *LI, DIBuilder &Builder) { 827 DIVariable DIVar(DDI->getVariable()); 828 if (!DIVar.Verify()) 829 return false; 830 831 Instruction *DbgVal = 832 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 833 DIVar, LI); 834 835 // Propagate any debug metadata from the store onto the dbg.value. 836 DebugLoc LIDL = LI->getDebugLoc(); 837 if (!LIDL.isUnknown()) 838 DbgVal->setDebugLoc(LIDL); 839 // Otherwise propagate debug metadata from dbg.declare. 840 else 841 DbgVal->setDebugLoc(DDI->getDebugLoc()); 842 return true; 843 } 844 845 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 846 /// of llvm.dbg.value intrinsics. 847 bool llvm::LowerDbgDeclare(Function &F) { 848 DIBuilder DIB(*F.getParent()); 849 SmallVector<DbgDeclareInst *, 4> Dbgs; 850 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 851 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 852 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 853 Dbgs.push_back(DDI); 854 } 855 if (Dbgs.empty()) 856 return false; 857 858 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(), 859 E = Dbgs.end(); I != E; ++I) { 860 DbgDeclareInst *DDI = *I; 861 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) { 862 bool RemoveDDI = true; 863 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 864 UI != E; ++UI) 865 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 866 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 867 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 868 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 869 else 870 RemoveDDI = false; 871 if (RemoveDDI) 872 DDI->eraseFromParent(); 873 } 874 } 875 return true; 876 } 877 878 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the 879 /// alloca 'V', if any. 880 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { 881 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V)) 882 for (Value::use_iterator UI = DebugNode->use_begin(), 883 E = DebugNode->use_end(); UI != E; ++UI) 884 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI)) 885 return DDI; 886 887 return 0; 888 } 889