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/DIBuilder.h" 18 #include "llvm/DebugInfo.h" 19 #include "llvm/DerivedTypes.h" 20 #include "llvm/GlobalAlias.h" 21 #include "llvm/GlobalVariable.h" 22 #include "llvm/IRBuilder.h" 23 #include "llvm/Instructions.h" 24 #include "llvm/IntrinsicInst.h" 25 #include "llvm/Intrinsics.h" 26 #include "llvm/Metadata.h" 27 #include "llvm/Operator.h" 28 #include "llvm/ADT/DenseMap.h" 29 #include "llvm/ADT/SmallPtrSet.h" 30 #include "llvm/Analysis/Dominators.h" 31 #include "llvm/Analysis/InstructionSimplify.h" 32 #include "llvm/Analysis/MemoryBuiltins.h" 33 #include "llvm/Analysis/ProfileInfo.h" 34 #include "llvm/Analysis/ValueTracking.h" 35 #include "llvm/Support/CFG.h" 36 #include "llvm/Support/Debug.h" 37 #include "llvm/Support/GetElementPtrTypeIterator.h" 38 #include "llvm/Support/MathExtras.h" 39 #include "llvm/Support/ValueHandle.h" 40 #include "llvm/Support/raw_ostream.h" 41 #include "llvm/Target/TargetData.h" 42 using 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. 55 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions, 56 const TargetLibraryInfo *TLI) { 57 TerminatorInst *T = BB->getTerminator(); 58 IRBuilder<> Builder(T); 59 60 // Branch - See if we are conditional jumping on constant 61 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 62 if (BI->isUnconditional()) return false; // Can't optimize uncond branch 63 BasicBlock *Dest1 = BI->getSuccessor(0); 64 BasicBlock *Dest2 = BI->getSuccessor(1); 65 66 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { 67 // Are we branching on constant? 68 // YES. Change to unconditional branch... 69 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; 70 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; 71 72 //cerr << "Function: " << T->getParent()->getParent() 73 // << "\nRemoving branch from " << T->getParent() 74 // << "\n\nTo: " << OldDest << endl; 75 76 // Let the basic block know that we are letting go of it. Based on this, 77 // it will adjust it's PHI nodes. 78 OldDest->removePredecessor(BB); 79 80 // Replace the conditional branch with an unconditional one. 81 Builder.CreateBr(Destination); 82 BI->eraseFromParent(); 83 return true; 84 } 85 86 if (Dest2 == Dest1) { // Conditional branch to same location? 87 // This branch matches something like this: 88 // br bool %cond, label %Dest, label %Dest 89 // and changes it into: br label %Dest 90 91 // Let the basic block know that we are letting go of one copy of it. 92 assert(BI->getParent() && "Terminator not inserted in block!"); 93 Dest1->removePredecessor(BI->getParent()); 94 95 // Replace the conditional branch with an unconditional one. 96 Builder.CreateBr(Dest1); 97 Value *Cond = BI->getCondition(); 98 BI->eraseFromParent(); 99 if (DeleteDeadConditions) 100 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); 101 return true; 102 } 103 return false; 104 } 105 106 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { 107 // If we are switching on a constant, we can convert the switch into a 108 // single branch instruction! 109 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); 110 BasicBlock *TheOnlyDest = SI->getDefaultDest(); 111 BasicBlock *DefaultDest = TheOnlyDest; 112 113 // Figure out which case it goes to. 114 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 115 i != e; ++i) { 116 // Found case matching a constant operand? 117 if (i.getCaseValue() == CI) { 118 TheOnlyDest = i.getCaseSuccessor(); 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 (i.getCaseSuccessor() == DefaultDest) { 125 // Remove this entry. 126 DefaultDest->removePredecessor(SI->getParent()); 127 SI->removeCase(i); 128 --i; --e; 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 (i.getCaseSuccessor() != 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, TLI); 166 return true; 167 } 168 169 if (SI->getNumCases() == 1) { 170 // Otherwise, we can fold this switch into a conditional branch 171 // instruction if it has only one non-default destination. 172 SwitchInst::CaseIt FirstCase = SI->case_begin(); 173 IntegersSubset& Case = FirstCase.getCaseValueEx(); 174 if (Case.isSingleNumber()) { 175 // FIXME: Currently work with ConstantInt based numbers. 176 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), 177 Case.getSingleNumber(0).toConstantInt(), 178 "cond"); 179 180 // Insert the new branch. 181 Builder.CreateCondBr(Cond, FirstCase.getCaseSuccessor(), 182 SI->getDefaultDest()); 183 184 // Delete the old switch. 185 SI->eraseFromParent(); 186 return true; 187 } 188 } 189 return false; 190 } 191 192 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 193 // indirectbr blockaddress(@F, @BB) -> br label @BB 194 if (BlockAddress *BA = 195 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 196 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 197 // Insert the new branch. 198 Builder.CreateBr(TheOnlyDest); 199 200 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 201 if (IBI->getDestination(i) == TheOnlyDest) 202 TheOnlyDest = 0; 203 else 204 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 205 } 206 Value *Address = IBI->getAddress(); 207 IBI->eraseFromParent(); 208 if (DeleteDeadConditions) 209 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI); 210 211 // If we didn't find our destination in the IBI successor list, then we 212 // have undefined behavior. Replace the unconditional branch with an 213 // 'unreachable' instruction. 214 if (TheOnlyDest) { 215 BB->getTerminator()->eraseFromParent(); 216 new UnreachableInst(BB->getContext(), BB); 217 } 218 219 return true; 220 } 221 } 222 223 return false; 224 } 225 226 227 //===----------------------------------------------------------------------===// 228 // Local dead code elimination. 229 // 230 231 /// isInstructionTriviallyDead - Return true if the result produced by the 232 /// instruction is not used, and the instruction has no side effects. 233 /// 234 bool llvm::isInstructionTriviallyDead(Instruction *I, 235 const TargetLibraryInfo *TLI) { 236 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 237 238 // We don't want the landingpad instruction removed by anything this general. 239 if (isa<LandingPadInst>(I)) 240 return false; 241 242 // We don't want debug info removed by anything this general, unless 243 // debug info is empty. 244 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 245 if (DDI->getAddress()) 246 return false; 247 return true; 248 } 249 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 250 if (DVI->getValue()) 251 return false; 252 return true; 253 } 254 255 if (!I->mayHaveSideEffects()) return true; 256 257 // Special case intrinsics that "may have side effects" but can be deleted 258 // when dead. 259 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 260 // Safe to delete llvm.stacksave if dead. 261 if (II->getIntrinsicID() == Intrinsic::stacksave) 262 return true; 263 264 // Lifetime intrinsics are dead when their right-hand is undef. 265 if (II->getIntrinsicID() == Intrinsic::lifetime_start || 266 II->getIntrinsicID() == Intrinsic::lifetime_end) 267 return isa<UndefValue>(II->getArgOperand(1)); 268 } 269 270 if (isAllocLikeFn(I, TLI)) return true; 271 272 if (CallInst *CI = isFreeCall(I, TLI)) 273 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0))) 274 return C->isNullValue() || isa<UndefValue>(C); 275 276 return false; 277 } 278 279 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 280 /// trivially dead instruction, delete it. If that makes any of its operands 281 /// trivially dead, delete them too, recursively. Return true if any 282 /// instructions were deleted. 283 bool 284 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V, 285 const TargetLibraryInfo *TLI) { 286 Instruction *I = dyn_cast<Instruction>(V); 287 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI)) 288 return false; 289 290 SmallVector<Instruction*, 16> DeadInsts; 291 DeadInsts.push_back(I); 292 293 do { 294 I = DeadInsts.pop_back_val(); 295 296 // Null out all of the instruction's operands to see if any operand becomes 297 // dead as we go. 298 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 299 Value *OpV = I->getOperand(i); 300 I->setOperand(i, 0); 301 302 if (!OpV->use_empty()) continue; 303 304 // If the operand is an instruction that became dead as we nulled out the 305 // operand, and if it is 'trivially' dead, delete it in a future loop 306 // iteration. 307 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 308 if (isInstructionTriviallyDead(OpI, TLI)) 309 DeadInsts.push_back(OpI); 310 } 311 312 I->eraseFromParent(); 313 } while (!DeadInsts.empty()); 314 315 return true; 316 } 317 318 /// areAllUsesEqual - Check whether the uses of a value are all the same. 319 /// This is similar to Instruction::hasOneUse() except this will also return 320 /// true when there are no uses or multiple uses that all refer to the same 321 /// value. 322 static bool areAllUsesEqual(Instruction *I) { 323 Value::use_iterator UI = I->use_begin(); 324 Value::use_iterator UE = I->use_end(); 325 if (UI == UE) 326 return true; 327 328 User *TheUse = *UI; 329 for (++UI; UI != UE; ++UI) { 330 if (*UI != TheUse) 331 return false; 332 } 333 return true; 334 } 335 336 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 337 /// dead PHI node, due to being a def-use chain of single-use nodes that 338 /// either forms a cycle or is terminated by a trivially dead instruction, 339 /// delete it. If that makes any of its operands trivially dead, delete them 340 /// too, recursively. Return true if a change was made. 341 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN, 342 const TargetLibraryInfo *TLI) { 343 SmallPtrSet<Instruction*, 4> Visited; 344 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 345 I = cast<Instruction>(*I->use_begin())) { 346 if (I->use_empty()) 347 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 348 349 // If we find an instruction more than once, we're on a cycle that 350 // won't prove fruitful. 351 if (!Visited.insert(I)) { 352 // Break the cycle and delete the instruction and its operands. 353 I->replaceAllUsesWith(UndefValue::get(I->getType())); 354 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 355 return true; 356 } 357 } 358 return false; 359 } 360 361 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to 362 /// simplify any instructions in it and recursively delete dead instructions. 363 /// 364 /// This returns true if it changed the code, note that it can delete 365 /// instructions in other blocks as well in this block. 366 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD, 367 const TargetLibraryInfo *TLI) { 368 bool MadeChange = false; 369 370 #ifndef NDEBUG 371 // In debug builds, ensure that the terminator of the block is never replaced 372 // or deleted by these simplifications. The idea of simplification is that it 373 // cannot introduce new instructions, and there is no way to replace the 374 // terminator of a block without introducing a new instruction. 375 AssertingVH<Instruction> TerminatorVH(--BB->end()); 376 #endif 377 378 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) { 379 assert(!BI->isTerminator()); 380 Instruction *Inst = BI++; 381 382 WeakVH BIHandle(BI); 383 if (recursivelySimplifyInstruction(Inst, TD)) { 384 MadeChange = true; 385 if (BIHandle != BI) 386 BI = BB->begin(); 387 continue; 388 } 389 390 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI); 391 if (BIHandle != BI) 392 BI = BB->begin(); 393 } 394 return MadeChange; 395 } 396 397 //===----------------------------------------------------------------------===// 398 // Control Flow Graph Restructuring. 399 // 400 401 402 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 403 /// method is called when we're about to delete Pred as a predecessor of BB. If 404 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 405 /// 406 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI 407 /// nodes that collapse into identity values. For example, if we have: 408 /// x = phi(1, 0, 0, 0) 409 /// y = and x, z 410 /// 411 /// .. and delete the predecessor corresponding to the '1', this will attempt to 412 /// recursively fold the and to 0. 413 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 414 TargetData *TD) { 415 // This only adjusts blocks with PHI nodes. 416 if (!isa<PHINode>(BB->begin())) 417 return; 418 419 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 420 // them down. This will leave us with single entry phi nodes and other phis 421 // that can be removed. 422 BB->removePredecessor(Pred, true); 423 424 WeakVH PhiIt = &BB->front(); 425 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 426 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 427 Value *OldPhiIt = PhiIt; 428 429 if (!recursivelySimplifyInstruction(PN, TD)) 430 continue; 431 432 // If recursive simplification ended up deleting the next PHI node we would 433 // iterate to, then our iterator is invalid, restart scanning from the top 434 // of the block. 435 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 436 } 437 } 438 439 440 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 441 /// predecessor is known to have one successor (DestBB!). Eliminate the edge 442 /// between them, moving the instructions in the predecessor into DestBB and 443 /// deleting the predecessor block. 444 /// 445 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 446 // If BB has single-entry PHI nodes, fold them. 447 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 448 Value *NewVal = PN->getIncomingValue(0); 449 // Replace self referencing PHI with undef, it must be dead. 450 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 451 PN->replaceAllUsesWith(NewVal); 452 PN->eraseFromParent(); 453 } 454 455 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 456 assert(PredBB && "Block doesn't have a single predecessor!"); 457 458 // Zap anything that took the address of DestBB. Not doing this will give the 459 // address an invalid value. 460 if (DestBB->hasAddressTaken()) { 461 BlockAddress *BA = BlockAddress::get(DestBB); 462 Constant *Replacement = 463 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 464 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 465 BA->getType())); 466 BA->destroyConstant(); 467 } 468 469 // Anything that branched to PredBB now branches to DestBB. 470 PredBB->replaceAllUsesWith(DestBB); 471 472 // Splice all the instructions from PredBB to DestBB. 473 PredBB->getTerminator()->eraseFromParent(); 474 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 475 476 if (P) { 477 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 478 if (DT) { 479 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 480 DT->changeImmediateDominator(DestBB, PredBBIDom); 481 DT->eraseNode(PredBB); 482 } 483 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 484 if (PI) { 485 PI->replaceAllUses(PredBB, DestBB); 486 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 487 } 488 } 489 // Nuke BB. 490 PredBB->eraseFromParent(); 491 } 492 493 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 494 /// almost-empty BB ending in an unconditional branch to Succ, into succ. 495 /// 496 /// Assumption: Succ is the single successor for BB. 497 /// 498 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 499 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 500 501 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 502 << Succ->getName() << "\n"); 503 // Shortcut, if there is only a single predecessor it must be BB and merging 504 // is always safe 505 if (Succ->getSinglePredecessor()) return true; 506 507 // Make a list of the predecessors of BB 508 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 509 510 // Look at all the phi nodes in Succ, to see if they present a conflict when 511 // merging these blocks 512 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 513 PHINode *PN = cast<PHINode>(I); 514 515 // If the incoming value from BB is again a PHINode in 516 // BB which has the same incoming value for *PI as PN does, we can 517 // merge the phi nodes and then the blocks can still be merged 518 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 519 if (BBPN && BBPN->getParent() == BB) { 520 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 521 BasicBlock *IBB = PN->getIncomingBlock(PI); 522 if (BBPreds.count(IBB) && 523 BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) { 524 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 525 << Succ->getName() << " is conflicting with " 526 << BBPN->getName() << " with regard to common predecessor " 527 << IBB->getName() << "\n"); 528 return false; 529 } 530 } 531 } else { 532 Value* Val = PN->getIncomingValueForBlock(BB); 533 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 534 // See if the incoming value for the common predecessor is equal to the 535 // one for BB, in which case this phi node will not prevent the merging 536 // of the block. 537 BasicBlock *IBB = PN->getIncomingBlock(PI); 538 if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) { 539 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 540 << Succ->getName() << " is conflicting with regard to common " 541 << "predecessor " << IBB->getName() << "\n"); 542 return false; 543 } 544 } 545 } 546 } 547 548 return true; 549 } 550 551 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 552 /// unconditional branch, and contains no instructions other than PHI nodes, 553 /// potential side-effect free intrinsics and the branch. If possible, 554 /// eliminate BB by rewriting all the predecessors to branch to the successor 555 /// block and return true. If we can't transform, return false. 556 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 557 assert(BB != &BB->getParent()->getEntryBlock() && 558 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 559 560 // We can't eliminate infinite loops. 561 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 562 if (BB == Succ) return false; 563 564 // Check to see if merging these blocks would cause conflicts for any of the 565 // phi nodes in BB or Succ. If not, we can safely merge. 566 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 567 568 // Check for cases where Succ has multiple predecessors and a PHI node in BB 569 // has uses which will not disappear when the PHI nodes are merged. It is 570 // possible to handle such cases, but difficult: it requires checking whether 571 // BB dominates Succ, which is non-trivial to calculate in the case where 572 // Succ has multiple predecessors. Also, it requires checking whether 573 // constructing the necessary self-referential PHI node doesn't intoduce any 574 // conflicts; this isn't too difficult, but the previous code for doing this 575 // was incorrect. 576 // 577 // Note that if this check finds a live use, BB dominates Succ, so BB is 578 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 579 // folding the branch isn't profitable in that case anyway. 580 if (!Succ->getSinglePredecessor()) { 581 BasicBlock::iterator BBI = BB->begin(); 582 while (isa<PHINode>(*BBI)) { 583 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 584 UI != E; ++UI) { 585 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 586 if (PN->getIncomingBlock(UI) != BB) 587 return false; 588 } else { 589 return false; 590 } 591 } 592 ++BBI; 593 } 594 } 595 596 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 597 598 if (isa<PHINode>(Succ->begin())) { 599 // If there is more than one pred of succ, and there are PHI nodes in 600 // the successor, then we need to add incoming edges for the PHI nodes 601 // 602 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 603 604 // Loop over all of the PHI nodes in the successor of BB. 605 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 606 PHINode *PN = cast<PHINode>(I); 607 Value *OldVal = PN->removeIncomingValue(BB, false); 608 assert(OldVal && "No entry in PHI for Pred BB!"); 609 610 // If this incoming value is one of the PHI nodes in BB, the new entries 611 // in the PHI node are the entries from the old PHI. 612 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 613 PHINode *OldValPN = cast<PHINode>(OldVal); 614 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 615 // Note that, since we are merging phi nodes and BB and Succ might 616 // have common predecessors, we could end up with a phi node with 617 // identical incoming branches. This will be cleaned up later (and 618 // will trigger asserts if we try to clean it up now, without also 619 // simplifying the corresponding conditional branch). 620 PN->addIncoming(OldValPN->getIncomingValue(i), 621 OldValPN->getIncomingBlock(i)); 622 } else { 623 // Add an incoming value for each of the new incoming values. 624 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 625 PN->addIncoming(OldVal, BBPreds[i]); 626 } 627 } 628 } 629 630 if (Succ->getSinglePredecessor()) { 631 // BB is the only predecessor of Succ, so Succ will end up with exactly 632 // the same predecessors BB had. 633 634 // Copy over any phi, debug or lifetime instruction. 635 BB->getTerminator()->eraseFromParent(); 636 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList()); 637 } else { 638 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 639 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 640 assert(PN->use_empty() && "There shouldn't be any uses here!"); 641 PN->eraseFromParent(); 642 } 643 } 644 645 // Everything that jumped to BB now goes to Succ. 646 BB->replaceAllUsesWith(Succ); 647 if (!Succ->hasName()) Succ->takeName(BB); 648 BB->eraseFromParent(); // Delete the old basic block. 649 return true; 650 } 651 652 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 653 /// nodes in this block. This doesn't try to be clever about PHI nodes 654 /// which differ only in the order of the incoming values, but instcombine 655 /// orders them so it usually won't matter. 656 /// 657 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 658 bool Changed = false; 659 660 // This implementation doesn't currently consider undef operands 661 // specially. Theoretically, two phis which are identical except for 662 // one having an undef where the other doesn't could be collapsed. 663 664 // Map from PHI hash values to PHI nodes. If multiple PHIs have 665 // the same hash value, the element is the first PHI in the 666 // linked list in CollisionMap. 667 DenseMap<uintptr_t, PHINode *> HashMap; 668 669 // Maintain linked lists of PHI nodes with common hash values. 670 DenseMap<PHINode *, PHINode *> CollisionMap; 671 672 // Examine each PHI. 673 for (BasicBlock::iterator I = BB->begin(); 674 PHINode *PN = dyn_cast<PHINode>(I++); ) { 675 // Compute a hash value on the operands. Instcombine will likely have sorted 676 // them, which helps expose duplicates, but we have to check all the 677 // operands to be safe in case instcombine hasn't run. 678 uintptr_t Hash = 0; 679 // This hash algorithm is quite weak as hash functions go, but it seems 680 // to do a good enough job for this particular purpose, and is very quick. 681 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 682 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 683 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 684 } 685 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end(); 686 I != E; ++I) { 687 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I)); 688 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 689 } 690 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 691 Hash >>= 1; 692 // If we've never seen this hash value before, it's a unique PHI. 693 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 694 HashMap.insert(std::make_pair(Hash, PN)); 695 if (Pair.second) continue; 696 // Otherwise it's either a duplicate or a hash collision. 697 for (PHINode *OtherPN = Pair.first->second; ; ) { 698 if (OtherPN->isIdenticalTo(PN)) { 699 // A duplicate. Replace this PHI with its duplicate. 700 PN->replaceAllUsesWith(OtherPN); 701 PN->eraseFromParent(); 702 Changed = true; 703 break; 704 } 705 // A non-duplicate hash collision. 706 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 707 if (I == CollisionMap.end()) { 708 // Set this PHI to be the head of the linked list of colliding PHIs. 709 PHINode *Old = Pair.first->second; 710 Pair.first->second = PN; 711 CollisionMap[PN] = Old; 712 break; 713 } 714 // Proceed to the next PHI in the list. 715 OtherPN = I->second; 716 } 717 } 718 719 return Changed; 720 } 721 722 /// enforceKnownAlignment - If the specified pointer points to an object that 723 /// we control, modify the object's alignment to PrefAlign. This isn't 724 /// often possible though. If alignment is important, a more reliable approach 725 /// is to simply align all global variables and allocation instructions to 726 /// their preferred alignment from the beginning. 727 /// 728 static unsigned enforceKnownAlignment(Value *V, unsigned Align, 729 unsigned PrefAlign, const TargetData *TD) { 730 V = V->stripPointerCasts(); 731 732 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 733 // If the preferred alignment is greater than the natural stack alignment 734 // then don't round up. This avoids dynamic stack realignment. 735 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign)) 736 return Align; 737 // If there is a requested alignment and if this is an alloca, round up. 738 if (AI->getAlignment() >= PrefAlign) 739 return AI->getAlignment(); 740 AI->setAlignment(PrefAlign); 741 return PrefAlign; 742 } 743 744 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 745 // If there is a large requested alignment and we can, bump up the alignment 746 // of the global. 747 if (GV->isDeclaration()) return Align; 748 // If the memory we set aside for the global may not be the memory used by 749 // the final program then it is impossible for us to reliably enforce the 750 // preferred alignment. 751 if (GV->isWeakForLinker()) return Align; 752 753 if (GV->getAlignment() >= PrefAlign) 754 return GV->getAlignment(); 755 // We can only increase the alignment of the global if it has no alignment 756 // specified or if it is not assigned a section. If it is assigned a 757 // section, the global could be densely packed with other objects in the 758 // section, increasing the alignment could cause padding issues. 759 if (!GV->hasSection() || GV->getAlignment() == 0) 760 GV->setAlignment(PrefAlign); 761 return GV->getAlignment(); 762 } 763 764 return Align; 765 } 766 767 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 768 /// we can determine, return it, otherwise return 0. If PrefAlign is specified, 769 /// and it is more than the alignment of the ultimate object, see if we can 770 /// increase the alignment of the ultimate object, making this check succeed. 771 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 772 const TargetData *TD) { 773 assert(V->getType()->isPointerTy() && 774 "getOrEnforceKnownAlignment expects a pointer!"); 775 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 776 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 777 ComputeMaskedBits(V, KnownZero, KnownOne, TD); 778 unsigned TrailZ = KnownZero.countTrailingOnes(); 779 780 // Avoid trouble with rediculously large TrailZ values, such as 781 // those computed from a null pointer. 782 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 783 784 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 785 786 // LLVM doesn't support alignments larger than this currently. 787 Align = std::min(Align, +Value::MaximumAlignment); 788 789 if (PrefAlign > Align) 790 Align = enforceKnownAlignment(V, Align, PrefAlign, TD); 791 792 // We don't need to make any adjustment. 793 return Align; 794 } 795 796 ///===---------------------------------------------------------------------===// 797 /// Dbg Intrinsic utilities 798 /// 799 800 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 801 /// that has an associated llvm.dbg.decl intrinsic. 802 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 803 StoreInst *SI, DIBuilder &Builder) { 804 DIVariable DIVar(DDI->getVariable()); 805 if (!DIVar.Verify()) 806 return false; 807 808 Instruction *DbgVal = NULL; 809 // If an argument is zero extended then use argument directly. The ZExt 810 // may be zapped by an optimization pass in future. 811 Argument *ExtendedArg = NULL; 812 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) 813 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); 814 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) 815 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); 816 if (ExtendedArg) 817 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI); 818 else 819 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI); 820 821 // Propagate any debug metadata from the store onto the dbg.value. 822 DebugLoc SIDL = SI->getDebugLoc(); 823 if (!SIDL.isUnknown()) 824 DbgVal->setDebugLoc(SIDL); 825 // Otherwise propagate debug metadata from dbg.declare. 826 else 827 DbgVal->setDebugLoc(DDI->getDebugLoc()); 828 return true; 829 } 830 831 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 832 /// that has an associated llvm.dbg.decl intrinsic. 833 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 834 LoadInst *LI, DIBuilder &Builder) { 835 DIVariable DIVar(DDI->getVariable()); 836 if (!DIVar.Verify()) 837 return false; 838 839 Instruction *DbgVal = 840 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 841 DIVar, LI); 842 843 // Propagate any debug metadata from the store onto the dbg.value. 844 DebugLoc LIDL = LI->getDebugLoc(); 845 if (!LIDL.isUnknown()) 846 DbgVal->setDebugLoc(LIDL); 847 // Otherwise propagate debug metadata from dbg.declare. 848 else 849 DbgVal->setDebugLoc(DDI->getDebugLoc()); 850 return true; 851 } 852 853 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 854 /// of llvm.dbg.value intrinsics. 855 bool llvm::LowerDbgDeclare(Function &F) { 856 DIBuilder DIB(*F.getParent()); 857 SmallVector<DbgDeclareInst *, 4> Dbgs; 858 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 859 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 860 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 861 Dbgs.push_back(DDI); 862 } 863 if (Dbgs.empty()) 864 return false; 865 866 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(), 867 E = Dbgs.end(); I != E; ++I) { 868 DbgDeclareInst *DDI = *I; 869 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) { 870 bool RemoveDDI = true; 871 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 872 UI != E; ++UI) 873 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 874 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 875 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 876 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 877 else 878 RemoveDDI = false; 879 if (RemoveDDI) 880 DDI->eraseFromParent(); 881 } 882 } 883 return true; 884 } 885 886 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the 887 /// alloca 'V', if any. 888 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { 889 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V)) 890 for (Value::use_iterator UI = DebugNode->use_begin(), 891 E = DebugNode->use_end(); UI != E; ++UI) 892 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI)) 893 return DDI; 894 895 return 0; 896 } 897