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