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/DebugInfo.h" 18 #include "llvm/DerivedTypes.h" 19 #include "llvm/DIBuilder.h" 20 #include "llvm/GlobalAlias.h" 21 #include "llvm/GlobalVariable.h" 22 #include "llvm/Instructions.h" 23 #include "llvm/Intrinsics.h" 24 #include "llvm/IntrinsicInst.h" 25 #include "llvm/Metadata.h" 26 #include "llvm/Operator.h" 27 #include "llvm/ADT/DenseMap.h" 28 #include "llvm/ADT/SmallPtrSet.h" 29 #include "llvm/Analysis/Dominators.h" 30 #include "llvm/Analysis/InstructionSimplify.h" 31 #include "llvm/Analysis/MemoryBuiltins.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" 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 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->getDefaultDest(); 110 BasicBlock *DefaultDest = TheOnlyDest; 111 112 // Figure out which case it goes to. 113 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 114 i != e; ++i) { 115 // Found case matching a constant operand? 116 if (i.getCaseValue() == CI) { 117 TheOnlyDest = i.getCaseSuccessor(); 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 (i.getCaseSuccessor() == DefaultDest) { 124 // Remove this entry. 125 DefaultDest->removePredecessor(SI->getParent()); 126 SI->removeCase(i); 127 --i; --e; 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 (i.getCaseSuccessor() != 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->getNumCases() == 1) { 169 // Otherwise, we can fold this switch into a conditional branch 170 // instruction if it has only one non-default destination. 171 SwitchInst::CaseIt FirstCase = SI->case_begin(); 172 IntegersSubset& Case = FirstCase.getCaseValueEx(); 173 if (Case.isSingleNumber()) { 174 // FIXME: Currently work with ConstantInt based numbers. 175 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), 176 Case.getSingleNumber(0).toConstantInt(), 177 "cond"); 178 179 // Insert the new branch. 180 Builder.CreateCondBr(Cond, FirstCase.getCaseSuccessor(), 181 SI->getDefaultDest()); 182 183 // Delete the old switch. 184 SI->eraseFromParent(); 185 return true; 186 } 187 } 188 return false; 189 } 190 191 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 192 // indirectbr blockaddress(@F, @BB) -> br label @BB 193 if (BlockAddress *BA = 194 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 195 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 196 // Insert the new branch. 197 Builder.CreateBr(TheOnlyDest); 198 199 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 200 if (IBI->getDestination(i) == TheOnlyDest) 201 TheOnlyDest = 0; 202 else 203 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 204 } 205 Value *Address = IBI->getAddress(); 206 IBI->eraseFromParent(); 207 if (DeleteDeadConditions) 208 RecursivelyDeleteTriviallyDeadInstructions(Address); 209 210 // If we didn't find our destination in the IBI successor list, then we 211 // have undefined behavior. Replace the unconditional branch with an 212 // 'unreachable' instruction. 213 if (TheOnlyDest) { 214 BB->getTerminator()->eraseFromParent(); 215 new UnreachableInst(BB->getContext(), BB); 216 } 217 218 return true; 219 } 220 } 221 222 return false; 223 } 224 225 226 //===----------------------------------------------------------------------===// 227 // Local dead code elimination. 228 // 229 230 /// isInstructionTriviallyDead - Return true if the result produced by the 231 /// instruction is not used, and the instruction has no side effects. 232 /// 233 bool llvm::isInstructionTriviallyDead(Instruction *I) { 234 if (!I->use_empty() || isa<TerminatorInst>(I)) return false; 235 236 // We don't want the landingpad instruction removed by anything this general. 237 if (isa<LandingPadInst>(I)) 238 return false; 239 240 // We don't want debug info removed by anything this general, unless 241 // debug info is empty. 242 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 243 if (DDI->getAddress()) 244 return false; 245 return true; 246 } 247 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 248 if (DVI->getValue()) 249 return false; 250 return true; 251 } 252 253 if (!I->mayHaveSideEffects()) return true; 254 255 // Special case intrinsics that "may have side effects" but can be deleted 256 // when dead. 257 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 258 // Safe to delete llvm.stacksave if dead. 259 if (II->getIntrinsicID() == Intrinsic::stacksave) 260 return true; 261 262 // Lifetime intrinsics are dead when their right-hand is undef. 263 if (II->getIntrinsicID() == Intrinsic::lifetime_start || 264 II->getIntrinsicID() == Intrinsic::lifetime_end) 265 return isa<UndefValue>(II->getArgOperand(1)); 266 } 267 268 if (isAllocLikeFn(I)) return true; 269 270 if (CallInst *CI = isFreeCall(I)) 271 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0))) 272 return C->isNullValue() || isa<UndefValue>(C); 273 274 return false; 275 } 276 277 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 278 /// trivially dead instruction, delete it. If that makes any of its operands 279 /// trivially dead, delete them too, recursively. Return true if any 280 /// instructions were deleted. 281 bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) { 282 Instruction *I = dyn_cast<Instruction>(V); 283 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I)) 284 return false; 285 286 SmallVector<Instruction*, 16> DeadInsts; 287 DeadInsts.push_back(I); 288 289 do { 290 I = DeadInsts.pop_back_val(); 291 292 // Null out all of the instruction's operands to see if any operand becomes 293 // dead as we go. 294 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 295 Value *OpV = I->getOperand(i); 296 I->setOperand(i, 0); 297 298 if (!OpV->use_empty()) continue; 299 300 // If the operand is an instruction that became dead as we nulled out the 301 // operand, and if it is 'trivially' dead, delete it in a future loop 302 // iteration. 303 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 304 if (isInstructionTriviallyDead(OpI)) 305 DeadInsts.push_back(OpI); 306 } 307 308 I->eraseFromParent(); 309 } while (!DeadInsts.empty()); 310 311 return true; 312 } 313 314 /// areAllUsesEqual - Check whether the uses of a value are all the same. 315 /// This is similar to Instruction::hasOneUse() except this will also return 316 /// true when there are no uses or multiple uses that all refer to the same 317 /// value. 318 static bool areAllUsesEqual(Instruction *I) { 319 Value::use_iterator UI = I->use_begin(); 320 Value::use_iterator UE = I->use_end(); 321 if (UI == UE) 322 return true; 323 324 User *TheUse = *UI; 325 for (++UI; UI != UE; ++UI) { 326 if (*UI != TheUse) 327 return false; 328 } 329 return true; 330 } 331 332 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 333 /// dead PHI node, due to being a def-use chain of single-use nodes that 334 /// either forms a cycle or is terminated by a trivially dead instruction, 335 /// delete it. If that makes any of its operands trivially dead, delete them 336 /// too, recursively. Return true if a change was made. 337 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) { 338 SmallPtrSet<Instruction*, 4> Visited; 339 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 340 I = cast<Instruction>(*I->use_begin())) { 341 if (I->use_empty()) 342 return RecursivelyDeleteTriviallyDeadInstructions(I); 343 344 // If we find an instruction more than once, we're on a cycle that 345 // won't prove fruitful. 346 if (!Visited.insert(I)) { 347 // Break the cycle and delete the instruction and its operands. 348 I->replaceAllUsesWith(UndefValue::get(I->getType())); 349 (void)RecursivelyDeleteTriviallyDeadInstructions(I); 350 return true; 351 } 352 } 353 return false; 354 } 355 356 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to 357 /// simplify any instructions in it and recursively delete dead instructions. 358 /// 359 /// This returns true if it changed the code, note that it can delete 360 /// instructions in other blocks as well in this block. 361 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) { 362 bool MadeChange = false; 363 364 #ifndef NDEBUG 365 // In debug builds, ensure that the terminator of the block is never replaced 366 // or deleted by these simplifications. The idea of simplification is that it 367 // cannot introduce new instructions, and there is no way to replace the 368 // terminator of a block without introducing a new instruction. 369 AssertingVH<Instruction> TerminatorVH(--BB->end()); 370 #endif 371 372 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) { 373 assert(!BI->isTerminator()); 374 Instruction *Inst = BI++; 375 376 WeakVH BIHandle(BI); 377 if (recursivelySimplifyInstruction(Inst, TD)) { 378 MadeChange = true; 379 if (BIHandle != BI) 380 BI = BB->begin(); 381 continue; 382 } 383 384 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst); 385 if (BIHandle != BI) 386 BI = BB->begin(); 387 } 388 return MadeChange; 389 } 390 391 //===----------------------------------------------------------------------===// 392 // Control Flow Graph Restructuring. 393 // 394 395 396 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 397 /// method is called when we're about to delete Pred as a predecessor of BB. If 398 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 399 /// 400 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI 401 /// nodes that collapse into identity values. For example, if we have: 402 /// x = phi(1, 0, 0, 0) 403 /// y = and x, z 404 /// 405 /// .. and delete the predecessor corresponding to the '1', this will attempt to 406 /// recursively fold the and to 0. 407 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, 408 TargetData *TD) { 409 // This only adjusts blocks with PHI nodes. 410 if (!isa<PHINode>(BB->begin())) 411 return; 412 413 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 414 // them down. This will leave us with single entry phi nodes and other phis 415 // that can be removed. 416 BB->removePredecessor(Pred, true); 417 418 WeakVH PhiIt = &BB->front(); 419 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 420 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 421 Value *OldPhiIt = PhiIt; 422 423 if (!recursivelySimplifyInstruction(PN, TD)) 424 continue; 425 426 // If recursive simplification ended up deleting the next PHI node we would 427 // iterate to, then our iterator is invalid, restart scanning from the top 428 // of the block. 429 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 430 } 431 } 432 433 434 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 435 /// predecessor is known to have one successor (DestBB!). Eliminate the edge 436 /// between them, moving the instructions in the predecessor into DestBB and 437 /// deleting the predecessor block. 438 /// 439 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { 440 // If BB has single-entry PHI nodes, fold them. 441 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 442 Value *NewVal = PN->getIncomingValue(0); 443 // Replace self referencing PHI with undef, it must be dead. 444 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 445 PN->replaceAllUsesWith(NewVal); 446 PN->eraseFromParent(); 447 } 448 449 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 450 assert(PredBB && "Block doesn't have a single predecessor!"); 451 452 // Zap anything that took the address of DestBB. Not doing this will give the 453 // address an invalid value. 454 if (DestBB->hasAddressTaken()) { 455 BlockAddress *BA = BlockAddress::get(DestBB); 456 Constant *Replacement = 457 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 458 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 459 BA->getType())); 460 BA->destroyConstant(); 461 } 462 463 // Anything that branched to PredBB now branches to DestBB. 464 PredBB->replaceAllUsesWith(DestBB); 465 466 // Splice all the instructions from PredBB to DestBB. 467 PredBB->getTerminator()->eraseFromParent(); 468 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 469 470 if (P) { 471 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); 472 if (DT) { 473 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 474 DT->changeImmediateDominator(DestBB, PredBBIDom); 475 DT->eraseNode(PredBB); 476 } 477 ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); 478 if (PI) { 479 PI->replaceAllUses(PredBB, DestBB); 480 PI->removeEdge(ProfileInfo::getEdge(PredBB, DestBB)); 481 } 482 } 483 // Nuke BB. 484 PredBB->eraseFromParent(); 485 } 486 487 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 488 /// almost-empty BB ending in an unconditional branch to Succ, into succ. 489 /// 490 /// Assumption: Succ is the single successor for BB. 491 /// 492 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 493 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 494 495 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 496 << Succ->getName() << "\n"); 497 // Shortcut, if there is only a single predecessor it must be BB and merging 498 // is always safe 499 if (Succ->getSinglePredecessor()) return true; 500 501 // Make a list of the predecessors of BB 502 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 503 504 // Look at all the phi nodes in Succ, to see if they present a conflict when 505 // merging these blocks 506 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 507 PHINode *PN = cast<PHINode>(I); 508 509 // If the incoming value from BB is again a PHINode in 510 // BB which has the same incoming value for *PI as PN does, we can 511 // merge the phi nodes and then the blocks can still be merged 512 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 513 if (BBPN && BBPN->getParent() == BB) { 514 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 515 BasicBlock *IBB = PN->getIncomingBlock(PI); 516 if (BBPreds.count(IBB) && 517 BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) { 518 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 519 << Succ->getName() << " is conflicting with " 520 << BBPN->getName() << " with regard to common predecessor " 521 << IBB->getName() << "\n"); 522 return false; 523 } 524 } 525 } else { 526 Value* Val = PN->getIncomingValueForBlock(BB); 527 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 528 // See if the incoming value for the common predecessor is equal to the 529 // one for BB, in which case this phi node will not prevent the merging 530 // of the block. 531 BasicBlock *IBB = PN->getIncomingBlock(PI); 532 if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) { 533 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 534 << Succ->getName() << " is conflicting with regard to common " 535 << "predecessor " << IBB->getName() << "\n"); 536 return false; 537 } 538 } 539 } 540 } 541 542 return true; 543 } 544 545 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 546 /// unconditional branch, and contains no instructions other than PHI nodes, 547 /// potential side-effect free intrinsics and the branch. If possible, 548 /// eliminate BB by rewriting all the predecessors to branch to the successor 549 /// block and return true. If we can't transform, return false. 550 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 551 assert(BB != &BB->getParent()->getEntryBlock() && 552 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 553 554 // We can't eliminate infinite loops. 555 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 556 if (BB == Succ) return false; 557 558 // Check to see if merging these blocks would cause conflicts for any of the 559 // phi nodes in BB or Succ. If not, we can safely merge. 560 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 561 562 // Check for cases where Succ has multiple predecessors and a PHI node in BB 563 // has uses which will not disappear when the PHI nodes are merged. It is 564 // possible to handle such cases, but difficult: it requires checking whether 565 // BB dominates Succ, which is non-trivial to calculate in the case where 566 // Succ has multiple predecessors. Also, it requires checking whether 567 // constructing the necessary self-referential PHI node doesn't intoduce any 568 // conflicts; this isn't too difficult, but the previous code for doing this 569 // was incorrect. 570 // 571 // Note that if this check finds a live use, BB dominates Succ, so BB is 572 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 573 // folding the branch isn't profitable in that case anyway. 574 if (!Succ->getSinglePredecessor()) { 575 BasicBlock::iterator BBI = BB->begin(); 576 while (isa<PHINode>(*BBI)) { 577 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); 578 UI != E; ++UI) { 579 if (PHINode* PN = dyn_cast<PHINode>(*UI)) { 580 if (PN->getIncomingBlock(UI) != BB) 581 return false; 582 } else { 583 return false; 584 } 585 } 586 ++BBI; 587 } 588 } 589 590 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 591 592 if (isa<PHINode>(Succ->begin())) { 593 // If there is more than one pred of succ, and there are PHI nodes in 594 // the successor, then we need to add incoming edges for the PHI nodes 595 // 596 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 597 598 // Loop over all of the PHI nodes in the successor of BB. 599 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 600 PHINode *PN = cast<PHINode>(I); 601 Value *OldVal = PN->removeIncomingValue(BB, false); 602 assert(OldVal && "No entry in PHI for Pred BB!"); 603 604 // If this incoming value is one of the PHI nodes in BB, the new entries 605 // in the PHI node are the entries from the old PHI. 606 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 607 PHINode *OldValPN = cast<PHINode>(OldVal); 608 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) 609 // Note that, since we are merging phi nodes and BB and Succ might 610 // have common predecessors, we could end up with a phi node with 611 // identical incoming branches. This will be cleaned up later (and 612 // will trigger asserts if we try to clean it up now, without also 613 // simplifying the corresponding conditional branch). 614 PN->addIncoming(OldValPN->getIncomingValue(i), 615 OldValPN->getIncomingBlock(i)); 616 } else { 617 // Add an incoming value for each of the new incoming values. 618 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) 619 PN->addIncoming(OldVal, BBPreds[i]); 620 } 621 } 622 } 623 624 if (Succ->getSinglePredecessor()) { 625 // BB is the only predecessor of Succ, so Succ will end up with exactly 626 // the same predecessors BB had. 627 628 // Copy over any phi, debug or lifetime instruction. 629 BB->getTerminator()->eraseFromParent(); 630 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList()); 631 } else { 632 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 633 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 634 assert(PN->use_empty() && "There shouldn't be any uses here!"); 635 PN->eraseFromParent(); 636 } 637 } 638 639 // Everything that jumped to BB now goes to Succ. 640 BB->replaceAllUsesWith(Succ); 641 if (!Succ->hasName()) Succ->takeName(BB); 642 BB->eraseFromParent(); // Delete the old basic block. 643 return true; 644 } 645 646 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 647 /// nodes in this block. This doesn't try to be clever about PHI nodes 648 /// which differ only in the order of the incoming values, but instcombine 649 /// orders them so it usually won't matter. 650 /// 651 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 652 bool Changed = false; 653 654 // This implementation doesn't currently consider undef operands 655 // specially. Theoretically, two phis which are identical except for 656 // one having an undef where the other doesn't could be collapsed. 657 658 // Map from PHI hash values to PHI nodes. If multiple PHIs have 659 // the same hash value, the element is the first PHI in the 660 // linked list in CollisionMap. 661 DenseMap<uintptr_t, PHINode *> HashMap; 662 663 // Maintain linked lists of PHI nodes with common hash values. 664 DenseMap<PHINode *, PHINode *> CollisionMap; 665 666 // Examine each PHI. 667 for (BasicBlock::iterator I = BB->begin(); 668 PHINode *PN = dyn_cast<PHINode>(I++); ) { 669 // Compute a hash value on the operands. Instcombine will likely have sorted 670 // them, which helps expose duplicates, but we have to check all the 671 // operands to be safe in case instcombine hasn't run. 672 uintptr_t Hash = 0; 673 // This hash algorithm is quite weak as hash functions go, but it seems 674 // to do a good enough job for this particular purpose, and is very quick. 675 for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { 676 Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); 677 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 678 } 679 for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end(); 680 I != E; ++I) { 681 Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I)); 682 Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); 683 } 684 // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. 685 Hash >>= 1; 686 // If we've never seen this hash value before, it's a unique PHI. 687 std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = 688 HashMap.insert(std::make_pair(Hash, PN)); 689 if (Pair.second) continue; 690 // Otherwise it's either a duplicate or a hash collision. 691 for (PHINode *OtherPN = Pair.first->second; ; ) { 692 if (OtherPN->isIdenticalTo(PN)) { 693 // A duplicate. Replace this PHI with its duplicate. 694 PN->replaceAllUsesWith(OtherPN); 695 PN->eraseFromParent(); 696 Changed = true; 697 break; 698 } 699 // A non-duplicate hash collision. 700 DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); 701 if (I == CollisionMap.end()) { 702 // Set this PHI to be the head of the linked list of colliding PHIs. 703 PHINode *Old = Pair.first->second; 704 Pair.first->second = PN; 705 CollisionMap[PN] = Old; 706 break; 707 } 708 // Proceed to the next PHI in the list. 709 OtherPN = I->second; 710 } 711 } 712 713 return Changed; 714 } 715 716 /// enforceKnownAlignment - If the specified pointer points to an object that 717 /// we control, modify the object's alignment to PrefAlign. This isn't 718 /// often possible though. If alignment is important, a more reliable approach 719 /// is to simply align all global variables and allocation instructions to 720 /// their preferred alignment from the beginning. 721 /// 722 static unsigned enforceKnownAlignment(Value *V, unsigned Align, 723 unsigned PrefAlign, const TargetData *TD) { 724 V = V->stripPointerCasts(); 725 726 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 727 // If the preferred alignment is greater than the natural stack alignment 728 // then don't round up. This avoids dynamic stack realignment. 729 if (TD && TD->exceedsNaturalStackAlignment(PrefAlign)) 730 return Align; 731 // If there is a requested alignment and if this is an alloca, round up. 732 if (AI->getAlignment() >= PrefAlign) 733 return AI->getAlignment(); 734 AI->setAlignment(PrefAlign); 735 return PrefAlign; 736 } 737 738 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { 739 // If there is a large requested alignment and we can, bump up the alignment 740 // of the global. 741 if (GV->isDeclaration()) return Align; 742 // If the memory we set aside for the global may not be the memory used by 743 // the final program then it is impossible for us to reliably enforce the 744 // preferred alignment. 745 if (GV->isWeakForLinker()) return Align; 746 747 if (GV->getAlignment() >= PrefAlign) 748 return GV->getAlignment(); 749 // We can only increase the alignment of the global if it has no alignment 750 // specified or if it is not assigned a section. If it is assigned a 751 // section, the global could be densely packed with other objects in the 752 // section, increasing the alignment could cause padding issues. 753 if (!GV->hasSection() || GV->getAlignment() == 0) 754 GV->setAlignment(PrefAlign); 755 return GV->getAlignment(); 756 } 757 758 return Align; 759 } 760 761 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that 762 /// we can determine, return it, otherwise return 0. If PrefAlign is specified, 763 /// and it is more than the alignment of the ultimate object, see if we can 764 /// increase the alignment of the ultimate object, making this check succeed. 765 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 766 const TargetData *TD) { 767 assert(V->getType()->isPointerTy() && 768 "getOrEnforceKnownAlignment expects a pointer!"); 769 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64; 770 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 771 ComputeMaskedBits(V, KnownZero, KnownOne, TD); 772 unsigned TrailZ = KnownZero.countTrailingOnes(); 773 774 // Avoid trouble with rediculously large TrailZ values, such as 775 // those computed from a null pointer. 776 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 777 778 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); 779 780 // LLVM doesn't support alignments larger than this currently. 781 Align = std::min(Align, +Value::MaximumAlignment); 782 783 if (PrefAlign > Align) 784 Align = enforceKnownAlignment(V, Align, PrefAlign, TD); 785 786 // We don't need to make any adjustment. 787 return Align; 788 } 789 790 ///===---------------------------------------------------------------------===// 791 /// Dbg Intrinsic utilities 792 /// 793 794 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 795 /// that has an associated llvm.dbg.decl intrinsic. 796 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 797 StoreInst *SI, DIBuilder &Builder) { 798 DIVariable DIVar(DDI->getVariable()); 799 if (!DIVar.Verify()) 800 return false; 801 802 Instruction *DbgVal = NULL; 803 // If an argument is zero extended then use argument directly. The ZExt 804 // may be zapped by an optimization pass in future. 805 Argument *ExtendedArg = NULL; 806 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) 807 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); 808 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) 809 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); 810 if (ExtendedArg) 811 DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI); 812 else 813 DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI); 814 815 // Propagate any debug metadata from the store onto the dbg.value. 816 DebugLoc SIDL = SI->getDebugLoc(); 817 if (!SIDL.isUnknown()) 818 DbgVal->setDebugLoc(SIDL); 819 // Otherwise propagate debug metadata from dbg.declare. 820 else 821 DbgVal->setDebugLoc(DDI->getDebugLoc()); 822 return true; 823 } 824 825 /// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value 826 /// that has an associated llvm.dbg.decl intrinsic. 827 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 828 LoadInst *LI, DIBuilder &Builder) { 829 DIVariable DIVar(DDI->getVariable()); 830 if (!DIVar.Verify()) 831 return false; 832 833 Instruction *DbgVal = 834 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, 835 DIVar, LI); 836 837 // Propagate any debug metadata from the store onto the dbg.value. 838 DebugLoc LIDL = LI->getDebugLoc(); 839 if (!LIDL.isUnknown()) 840 DbgVal->setDebugLoc(LIDL); 841 // Otherwise propagate debug metadata from dbg.declare. 842 else 843 DbgVal->setDebugLoc(DDI->getDebugLoc()); 844 return true; 845 } 846 847 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 848 /// of llvm.dbg.value intrinsics. 849 bool llvm::LowerDbgDeclare(Function &F) { 850 DIBuilder DIB(*F.getParent()); 851 SmallVector<DbgDeclareInst *, 4> Dbgs; 852 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 853 for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ++BI) { 854 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(BI)) 855 Dbgs.push_back(DDI); 856 } 857 if (Dbgs.empty()) 858 return false; 859 860 for (SmallVector<DbgDeclareInst *, 4>::iterator I = Dbgs.begin(), 861 E = Dbgs.end(); I != E; ++I) { 862 DbgDeclareInst *DDI = *I; 863 if (AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) { 864 bool RemoveDDI = true; 865 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 866 UI != E; ++UI) 867 if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) 868 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 869 else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) 870 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 871 else 872 RemoveDDI = false; 873 if (RemoveDDI) 874 DDI->eraseFromParent(); 875 } 876 } 877 return true; 878 } 879 880 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the 881 /// alloca 'V', if any. 882 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { 883 if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V)) 884 for (Value::use_iterator UI = DebugNode->use_begin(), 885 E = DebugNode->use_end(); UI != E; ++UI) 886 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI)) 887 return DDI; 888 889 return 0; 890 } 891