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/ADT/DenseMap.h" 17 #include "llvm/ADT/DenseSet.h" 18 #include "llvm/ADT/Hashing.h" 19 #include "llvm/ADT/STLExtras.h" 20 #include "llvm/ADT/SetVector.h" 21 #include "llvm/ADT/SmallPtrSet.h" 22 #include "llvm/ADT/Statistic.h" 23 #include "llvm/Analysis/EHPersonalities.h" 24 #include "llvm/Analysis/InstructionSimplify.h" 25 #include "llvm/Analysis/LazyValueInfo.h" 26 #include "llvm/Analysis/MemoryBuiltins.h" 27 #include "llvm/Analysis/ValueTracking.h" 28 #include "llvm/IR/CFG.h" 29 #include "llvm/IR/ConstantRange.h" 30 #include "llvm/IR/Constants.h" 31 #include "llvm/IR/DIBuilder.h" 32 #include "llvm/IR/DataLayout.h" 33 #include "llvm/IR/DebugInfo.h" 34 #include "llvm/IR/DerivedTypes.h" 35 #include "llvm/IR/Dominators.h" 36 #include "llvm/IR/GetElementPtrTypeIterator.h" 37 #include "llvm/IR/GlobalAlias.h" 38 #include "llvm/IR/GlobalVariable.h" 39 #include "llvm/IR/IRBuilder.h" 40 #include "llvm/IR/Instructions.h" 41 #include "llvm/IR/IntrinsicInst.h" 42 #include "llvm/IR/Intrinsics.h" 43 #include "llvm/IR/MDBuilder.h" 44 #include "llvm/IR/Metadata.h" 45 #include "llvm/IR/Operator.h" 46 #include "llvm/IR/PatternMatch.h" 47 #include "llvm/IR/ValueHandle.h" 48 #include "llvm/Support/Debug.h" 49 #include "llvm/Support/KnownBits.h" 50 #include "llvm/Support/MathExtras.h" 51 #include "llvm/Support/raw_ostream.h" 52 using namespace llvm; 53 using namespace llvm::PatternMatch; 54 55 #define DEBUG_TYPE "local" 56 57 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed"); 58 59 //===----------------------------------------------------------------------===// 60 // Local constant propagation. 61 // 62 63 /// ConstantFoldTerminator - If a terminator instruction is predicated on a 64 /// constant value, convert it into an unconditional branch to the constant 65 /// destination. This is a nontrivial operation because the successors of this 66 /// basic block must have their PHI nodes updated. 67 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch 68 /// conditions and indirectbr addresses this might make dead if 69 /// DeleteDeadConditions is true. 70 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions, 71 const TargetLibraryInfo *TLI) { 72 TerminatorInst *T = BB->getTerminator(); 73 IRBuilder<> Builder(T); 74 75 // Branch - See if we are conditional jumping on constant 76 if (BranchInst *BI = dyn_cast<BranchInst>(T)) { 77 if (BI->isUnconditional()) return false; // Can't optimize uncond branch 78 BasicBlock *Dest1 = BI->getSuccessor(0); 79 BasicBlock *Dest2 = BI->getSuccessor(1); 80 81 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { 82 // Are we branching on constant? 83 // YES. Change to unconditional branch... 84 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; 85 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; 86 87 //cerr << "Function: " << T->getParent()->getParent() 88 // << "\nRemoving branch from " << T->getParent() 89 // << "\n\nTo: " << OldDest << endl; 90 91 // Let the basic block know that we are letting go of it. Based on this, 92 // it will adjust it's PHI nodes. 93 OldDest->removePredecessor(BB); 94 95 // Replace the conditional branch with an unconditional one. 96 Builder.CreateBr(Destination); 97 BI->eraseFromParent(); 98 return true; 99 } 100 101 if (Dest2 == Dest1) { // Conditional branch to same location? 102 // This branch matches something like this: 103 // br bool %cond, label %Dest, label %Dest 104 // and changes it into: br label %Dest 105 106 // Let the basic block know that we are letting go of one copy of it. 107 assert(BI->getParent() && "Terminator not inserted in block!"); 108 Dest1->removePredecessor(BI->getParent()); 109 110 // Replace the conditional branch with an unconditional one. 111 Builder.CreateBr(Dest1); 112 Value *Cond = BI->getCondition(); 113 BI->eraseFromParent(); 114 if (DeleteDeadConditions) 115 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); 116 return true; 117 } 118 return false; 119 } 120 121 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { 122 // If we are switching on a constant, we can convert the switch to an 123 // unconditional branch. 124 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); 125 BasicBlock *DefaultDest = SI->getDefaultDest(); 126 BasicBlock *TheOnlyDest = DefaultDest; 127 128 // If the default is unreachable, ignore it when searching for TheOnlyDest. 129 if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) && 130 SI->getNumCases() > 0) { 131 TheOnlyDest = SI->case_begin()->getCaseSuccessor(); 132 } 133 134 // Figure out which case it goes to. 135 for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) { 136 // Found case matching a constant operand? 137 if (i->getCaseValue() == CI) { 138 TheOnlyDest = i->getCaseSuccessor(); 139 break; 140 } 141 142 // Check to see if this branch is going to the same place as the default 143 // dest. If so, eliminate it as an explicit compare. 144 if (i->getCaseSuccessor() == DefaultDest) { 145 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof); 146 unsigned NCases = SI->getNumCases(); 147 // Fold the case metadata into the default if there will be any branches 148 // left, unless the metadata doesn't match the switch. 149 if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) { 150 // Collect branch weights into a vector. 151 SmallVector<uint32_t, 8> Weights; 152 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e; 153 ++MD_i) { 154 auto *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i)); 155 Weights.push_back(CI->getValue().getZExtValue()); 156 } 157 // Merge weight of this case to the default weight. 158 unsigned idx = i->getCaseIndex(); 159 Weights[0] += Weights[idx+1]; 160 // Remove weight for this case. 161 std::swap(Weights[idx+1], Weights.back()); 162 Weights.pop_back(); 163 SI->setMetadata(LLVMContext::MD_prof, 164 MDBuilder(BB->getContext()). 165 createBranchWeights(Weights)); 166 } 167 // Remove this entry. 168 DefaultDest->removePredecessor(SI->getParent()); 169 i = SI->removeCase(i); 170 e = SI->case_end(); 171 continue; 172 } 173 174 // Otherwise, check to see if the switch only branches to one destination. 175 // We do this by reseting "TheOnlyDest" to null when we find two non-equal 176 // destinations. 177 if (i->getCaseSuccessor() != TheOnlyDest) 178 TheOnlyDest = nullptr; 179 180 // Increment this iterator as we haven't removed the case. 181 ++i; 182 } 183 184 if (CI && !TheOnlyDest) { 185 // Branching on a constant, but not any of the cases, go to the default 186 // successor. 187 TheOnlyDest = SI->getDefaultDest(); 188 } 189 190 // If we found a single destination that we can fold the switch into, do so 191 // now. 192 if (TheOnlyDest) { 193 // Insert the new branch. 194 Builder.CreateBr(TheOnlyDest); 195 BasicBlock *BB = SI->getParent(); 196 197 // Remove entries from PHI nodes which we no longer branch to... 198 for (BasicBlock *Succ : SI->successors()) { 199 // Found case matching a constant operand? 200 if (Succ == TheOnlyDest) 201 TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest 202 else 203 Succ->removePredecessor(BB); 204 } 205 206 // Delete the old switch. 207 Value *Cond = SI->getCondition(); 208 SI->eraseFromParent(); 209 if (DeleteDeadConditions) 210 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); 211 return true; 212 } 213 214 if (SI->getNumCases() == 1) { 215 // Otherwise, we can fold this switch into a conditional branch 216 // instruction if it has only one non-default destination. 217 auto FirstCase = *SI->case_begin(); 218 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), 219 FirstCase.getCaseValue(), "cond"); 220 221 // Insert the new branch. 222 BranchInst *NewBr = Builder.CreateCondBr(Cond, 223 FirstCase.getCaseSuccessor(), 224 SI->getDefaultDest()); 225 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof); 226 if (MD && MD->getNumOperands() == 3) { 227 ConstantInt *SICase = 228 mdconst::dyn_extract<ConstantInt>(MD->getOperand(2)); 229 ConstantInt *SIDef = 230 mdconst::dyn_extract<ConstantInt>(MD->getOperand(1)); 231 assert(SICase && SIDef); 232 // The TrueWeight should be the weight for the single case of SI. 233 NewBr->setMetadata(LLVMContext::MD_prof, 234 MDBuilder(BB->getContext()). 235 createBranchWeights(SICase->getValue().getZExtValue(), 236 SIDef->getValue().getZExtValue())); 237 } 238 239 // Update make.implicit metadata to the newly-created conditional branch. 240 MDNode *MakeImplicitMD = SI->getMetadata(LLVMContext::MD_make_implicit); 241 if (MakeImplicitMD) 242 NewBr->setMetadata(LLVMContext::MD_make_implicit, MakeImplicitMD); 243 244 // Delete the old switch. 245 SI->eraseFromParent(); 246 return true; 247 } 248 return false; 249 } 250 251 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { 252 // indirectbr blockaddress(@F, @BB) -> br label @BB 253 if (BlockAddress *BA = 254 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { 255 BasicBlock *TheOnlyDest = BA->getBasicBlock(); 256 // Insert the new branch. 257 Builder.CreateBr(TheOnlyDest); 258 259 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { 260 if (IBI->getDestination(i) == TheOnlyDest) 261 TheOnlyDest = nullptr; 262 else 263 IBI->getDestination(i)->removePredecessor(IBI->getParent()); 264 } 265 Value *Address = IBI->getAddress(); 266 IBI->eraseFromParent(); 267 if (DeleteDeadConditions) 268 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI); 269 270 // If we didn't find our destination in the IBI successor list, then we 271 // have undefined behavior. Replace the unconditional branch with an 272 // 'unreachable' instruction. 273 if (TheOnlyDest) { 274 BB->getTerminator()->eraseFromParent(); 275 new UnreachableInst(BB->getContext(), BB); 276 } 277 278 return true; 279 } 280 } 281 282 return false; 283 } 284 285 286 //===----------------------------------------------------------------------===// 287 // Local dead code elimination. 288 // 289 290 /// isInstructionTriviallyDead - Return true if the result produced by the 291 /// instruction is not used, and the instruction has no side effects. 292 /// 293 bool llvm::isInstructionTriviallyDead(Instruction *I, 294 const TargetLibraryInfo *TLI) { 295 if (!I->use_empty()) 296 return false; 297 return wouldInstructionBeTriviallyDead(I, TLI); 298 } 299 300 bool llvm::wouldInstructionBeTriviallyDead(Instruction *I, 301 const TargetLibraryInfo *TLI) { 302 if (isa<TerminatorInst>(I)) 303 return false; 304 305 // We don't want the landingpad-like instructions removed by anything this 306 // general. 307 if (I->isEHPad()) 308 return false; 309 310 // We don't want debug info removed by anything this general, unless 311 // debug info is empty. 312 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { 313 if (DDI->getAddress()) 314 return false; 315 return true; 316 } 317 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { 318 if (DVI->getValue()) 319 return false; 320 return true; 321 } 322 323 if (!I->mayHaveSideEffects()) 324 return true; 325 326 // Special case intrinsics that "may have side effects" but can be deleted 327 // when dead. 328 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 329 // Safe to delete llvm.stacksave if dead. 330 if (II->getIntrinsicID() == Intrinsic::stacksave) 331 return true; 332 333 // Lifetime intrinsics are dead when their right-hand is undef. 334 if (II->getIntrinsicID() == Intrinsic::lifetime_start || 335 II->getIntrinsicID() == Intrinsic::lifetime_end) 336 return isa<UndefValue>(II->getArgOperand(1)); 337 338 // Assumptions are dead if their condition is trivially true. Guards on 339 // true are operationally no-ops. In the future we can consider more 340 // sophisticated tradeoffs for guards considering potential for check 341 // widening, but for now we keep things simple. 342 if (II->getIntrinsicID() == Intrinsic::assume || 343 II->getIntrinsicID() == Intrinsic::experimental_guard) { 344 if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0))) 345 return !Cond->isZero(); 346 347 return false; 348 } 349 } 350 351 if (isAllocLikeFn(I, TLI)) 352 return true; 353 354 if (CallInst *CI = isFreeCall(I, TLI)) 355 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0))) 356 return C->isNullValue() || isa<UndefValue>(C); 357 358 if (CallSite CS = CallSite(I)) 359 if (isMathLibCallNoop(CS, TLI)) 360 return true; 361 362 return false; 363 } 364 365 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a 366 /// trivially dead instruction, delete it. If that makes any of its operands 367 /// trivially dead, delete them too, recursively. Return true if any 368 /// instructions were deleted. 369 bool 370 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V, 371 const TargetLibraryInfo *TLI) { 372 Instruction *I = dyn_cast<Instruction>(V); 373 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI)) 374 return false; 375 376 SmallVector<Instruction*, 16> DeadInsts; 377 DeadInsts.push_back(I); 378 379 do { 380 I = DeadInsts.pop_back_val(); 381 382 // Null out all of the instruction's operands to see if any operand becomes 383 // dead as we go. 384 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 385 Value *OpV = I->getOperand(i); 386 I->setOperand(i, nullptr); 387 388 if (!OpV->use_empty()) continue; 389 390 // If the operand is an instruction that became dead as we nulled out the 391 // operand, and if it is 'trivially' dead, delete it in a future loop 392 // iteration. 393 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 394 if (isInstructionTriviallyDead(OpI, TLI)) 395 DeadInsts.push_back(OpI); 396 } 397 398 I->eraseFromParent(); 399 } while (!DeadInsts.empty()); 400 401 return true; 402 } 403 404 /// areAllUsesEqual - Check whether the uses of a value are all the same. 405 /// This is similar to Instruction::hasOneUse() except this will also return 406 /// true when there are no uses or multiple uses that all refer to the same 407 /// value. 408 static bool areAllUsesEqual(Instruction *I) { 409 Value::user_iterator UI = I->user_begin(); 410 Value::user_iterator UE = I->user_end(); 411 if (UI == UE) 412 return true; 413 414 User *TheUse = *UI; 415 for (++UI; UI != UE; ++UI) { 416 if (*UI != TheUse) 417 return false; 418 } 419 return true; 420 } 421 422 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively 423 /// dead PHI node, due to being a def-use chain of single-use nodes that 424 /// either forms a cycle or is terminated by a trivially dead instruction, 425 /// delete it. If that makes any of its operands trivially dead, delete them 426 /// too, recursively. Return true if a change was made. 427 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN, 428 const TargetLibraryInfo *TLI) { 429 SmallPtrSet<Instruction*, 4> Visited; 430 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); 431 I = cast<Instruction>(*I->user_begin())) { 432 if (I->use_empty()) 433 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 434 435 // If we find an instruction more than once, we're on a cycle that 436 // won't prove fruitful. 437 if (!Visited.insert(I).second) { 438 // Break the cycle and delete the instruction and its operands. 439 I->replaceAllUsesWith(UndefValue::get(I->getType())); 440 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 441 return true; 442 } 443 } 444 return false; 445 } 446 447 static bool 448 simplifyAndDCEInstruction(Instruction *I, 449 SmallSetVector<Instruction *, 16> &WorkList, 450 const DataLayout &DL, 451 const TargetLibraryInfo *TLI) { 452 if (isInstructionTriviallyDead(I, TLI)) { 453 // Null out all of the instruction's operands to see if any operand becomes 454 // dead as we go. 455 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 456 Value *OpV = I->getOperand(i); 457 I->setOperand(i, nullptr); 458 459 if (!OpV->use_empty() || I == OpV) 460 continue; 461 462 // If the operand is an instruction that became dead as we nulled out the 463 // operand, and if it is 'trivially' dead, delete it in a future loop 464 // iteration. 465 if (Instruction *OpI = dyn_cast<Instruction>(OpV)) 466 if (isInstructionTriviallyDead(OpI, TLI)) 467 WorkList.insert(OpI); 468 } 469 470 I->eraseFromParent(); 471 472 return true; 473 } 474 475 if (Value *SimpleV = SimplifyInstruction(I, DL)) { 476 // Add the users to the worklist. CAREFUL: an instruction can use itself, 477 // in the case of a phi node. 478 for (User *U : I->users()) { 479 if (U != I) { 480 WorkList.insert(cast<Instruction>(U)); 481 } 482 } 483 484 // Replace the instruction with its simplified value. 485 bool Changed = false; 486 if (!I->use_empty()) { 487 I->replaceAllUsesWith(SimpleV); 488 Changed = true; 489 } 490 if (isInstructionTriviallyDead(I, TLI)) { 491 I->eraseFromParent(); 492 Changed = true; 493 } 494 return Changed; 495 } 496 return false; 497 } 498 499 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to 500 /// simplify any instructions in it and recursively delete dead instructions. 501 /// 502 /// This returns true if it changed the code, note that it can delete 503 /// instructions in other blocks as well in this block. 504 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, 505 const TargetLibraryInfo *TLI) { 506 bool MadeChange = false; 507 const DataLayout &DL = BB->getModule()->getDataLayout(); 508 509 #ifndef NDEBUG 510 // In debug builds, ensure that the terminator of the block is never replaced 511 // or deleted by these simplifications. The idea of simplification is that it 512 // cannot introduce new instructions, and there is no way to replace the 513 // terminator of a block without introducing a new instruction. 514 AssertingVH<Instruction> TerminatorVH(&BB->back()); 515 #endif 516 517 SmallSetVector<Instruction *, 16> WorkList; 518 // Iterate over the original function, only adding insts to the worklist 519 // if they actually need to be revisited. This avoids having to pre-init 520 // the worklist with the entire function's worth of instructions. 521 for (BasicBlock::iterator BI = BB->begin(), E = std::prev(BB->end()); 522 BI != E;) { 523 assert(!BI->isTerminator()); 524 Instruction *I = &*BI; 525 ++BI; 526 527 // We're visiting this instruction now, so make sure it's not in the 528 // worklist from an earlier visit. 529 if (!WorkList.count(I)) 530 MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI); 531 } 532 533 while (!WorkList.empty()) { 534 Instruction *I = WorkList.pop_back_val(); 535 MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI); 536 } 537 return MadeChange; 538 } 539 540 //===----------------------------------------------------------------------===// 541 // Control Flow Graph Restructuring. 542 // 543 544 545 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this 546 /// method is called when we're about to delete Pred as a predecessor of BB. If 547 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. 548 /// 549 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI 550 /// nodes that collapse into identity values. For example, if we have: 551 /// x = phi(1, 0, 0, 0) 552 /// y = and x, z 553 /// 554 /// .. and delete the predecessor corresponding to the '1', this will attempt to 555 /// recursively fold the and to 0. 556 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred) { 557 // This only adjusts blocks with PHI nodes. 558 if (!isa<PHINode>(BB->begin())) 559 return; 560 561 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify 562 // them down. This will leave us with single entry phi nodes and other phis 563 // that can be removed. 564 BB->removePredecessor(Pred, true); 565 566 WeakTrackingVH PhiIt = &BB->front(); 567 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { 568 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); 569 Value *OldPhiIt = PhiIt; 570 571 if (!recursivelySimplifyInstruction(PN)) 572 continue; 573 574 // If recursive simplification ended up deleting the next PHI node we would 575 // iterate to, then our iterator is invalid, restart scanning from the top 576 // of the block. 577 if (PhiIt != OldPhiIt) PhiIt = &BB->front(); 578 } 579 } 580 581 582 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its 583 /// predecessor is known to have one successor (DestBB!). Eliminate the edge 584 /// between them, moving the instructions in the predecessor into DestBB and 585 /// deleting the predecessor block. 586 /// 587 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, DominatorTree *DT) { 588 // If BB has single-entry PHI nodes, fold them. 589 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { 590 Value *NewVal = PN->getIncomingValue(0); 591 // Replace self referencing PHI with undef, it must be dead. 592 if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); 593 PN->replaceAllUsesWith(NewVal); 594 PN->eraseFromParent(); 595 } 596 597 BasicBlock *PredBB = DestBB->getSinglePredecessor(); 598 assert(PredBB && "Block doesn't have a single predecessor!"); 599 600 // Zap anything that took the address of DestBB. Not doing this will give the 601 // address an invalid value. 602 if (DestBB->hasAddressTaken()) { 603 BlockAddress *BA = BlockAddress::get(DestBB); 604 Constant *Replacement = 605 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); 606 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 607 BA->getType())); 608 BA->destroyConstant(); 609 } 610 611 // Anything that branched to PredBB now branches to DestBB. 612 PredBB->replaceAllUsesWith(DestBB); 613 614 // Splice all the instructions from PredBB to DestBB. 615 PredBB->getTerminator()->eraseFromParent(); 616 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); 617 618 // If the PredBB is the entry block of the function, move DestBB up to 619 // become the entry block after we erase PredBB. 620 if (PredBB == &DestBB->getParent()->getEntryBlock()) 621 DestBB->moveAfter(PredBB); 622 623 if (DT) { 624 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock(); 625 DT->changeImmediateDominator(DestBB, PredBBIDom); 626 DT->eraseNode(PredBB); 627 } 628 // Nuke BB. 629 PredBB->eraseFromParent(); 630 } 631 632 /// CanMergeValues - Return true if we can choose one of these values to use 633 /// in place of the other. Note that we will always choose the non-undef 634 /// value to keep. 635 static bool CanMergeValues(Value *First, Value *Second) { 636 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second); 637 } 638 639 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an 640 /// almost-empty BB ending in an unconditional branch to Succ, into Succ. 641 /// 642 /// Assumption: Succ is the single successor for BB. 643 /// 644 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { 645 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); 646 647 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " 648 << Succ->getName() << "\n"); 649 // Shortcut, if there is only a single predecessor it must be BB and merging 650 // is always safe 651 if (Succ->getSinglePredecessor()) return true; 652 653 // Make a list of the predecessors of BB 654 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); 655 656 // Look at all the phi nodes in Succ, to see if they present a conflict when 657 // merging these blocks 658 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 659 PHINode *PN = cast<PHINode>(I); 660 661 // If the incoming value from BB is again a PHINode in 662 // BB which has the same incoming value for *PI as PN does, we can 663 // merge the phi nodes and then the blocks can still be merged 664 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); 665 if (BBPN && BBPN->getParent() == BB) { 666 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 667 BasicBlock *IBB = PN->getIncomingBlock(PI); 668 if (BBPreds.count(IBB) && 669 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB), 670 PN->getIncomingValue(PI))) { 671 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 672 << Succ->getName() << " is conflicting with " 673 << BBPN->getName() << " with regard to common predecessor " 674 << IBB->getName() << "\n"); 675 return false; 676 } 677 } 678 } else { 679 Value* Val = PN->getIncomingValueForBlock(BB); 680 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { 681 // See if the incoming value for the common predecessor is equal to the 682 // one for BB, in which case this phi node will not prevent the merging 683 // of the block. 684 BasicBlock *IBB = PN->getIncomingBlock(PI); 685 if (BBPreds.count(IBB) && 686 !CanMergeValues(Val, PN->getIncomingValue(PI))) { 687 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " 688 << Succ->getName() << " is conflicting with regard to common " 689 << "predecessor " << IBB->getName() << "\n"); 690 return false; 691 } 692 } 693 } 694 } 695 696 return true; 697 } 698 699 typedef SmallVector<BasicBlock *, 16> PredBlockVector; 700 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap; 701 702 /// \brief Determines the value to use as the phi node input for a block. 703 /// 704 /// Select between \p OldVal any value that we know flows from \p BB 705 /// to a particular phi on the basis of which one (if either) is not 706 /// undef. Update IncomingValues based on the selected value. 707 /// 708 /// \param OldVal The value we are considering selecting. 709 /// \param BB The block that the value flows in from. 710 /// \param IncomingValues A map from block-to-value for other phi inputs 711 /// that we have examined. 712 /// 713 /// \returns the selected value. 714 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB, 715 IncomingValueMap &IncomingValues) { 716 if (!isa<UndefValue>(OldVal)) { 717 assert((!IncomingValues.count(BB) || 718 IncomingValues.find(BB)->second == OldVal) && 719 "Expected OldVal to match incoming value from BB!"); 720 721 IncomingValues.insert(std::make_pair(BB, OldVal)); 722 return OldVal; 723 } 724 725 IncomingValueMap::const_iterator It = IncomingValues.find(BB); 726 if (It != IncomingValues.end()) return It->second; 727 728 return OldVal; 729 } 730 731 /// \brief Create a map from block to value for the operands of a 732 /// given phi. 733 /// 734 /// Create a map from block to value for each non-undef value flowing 735 /// into \p PN. 736 /// 737 /// \param PN The phi we are collecting the map for. 738 /// \param IncomingValues [out] The map from block to value for this phi. 739 static void gatherIncomingValuesToPhi(PHINode *PN, 740 IncomingValueMap &IncomingValues) { 741 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 742 BasicBlock *BB = PN->getIncomingBlock(i); 743 Value *V = PN->getIncomingValue(i); 744 745 if (!isa<UndefValue>(V)) 746 IncomingValues.insert(std::make_pair(BB, V)); 747 } 748 } 749 750 /// \brief Replace the incoming undef values to a phi with the values 751 /// from a block-to-value map. 752 /// 753 /// \param PN The phi we are replacing the undefs in. 754 /// \param IncomingValues A map from block to value. 755 static void replaceUndefValuesInPhi(PHINode *PN, 756 const IncomingValueMap &IncomingValues) { 757 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 758 Value *V = PN->getIncomingValue(i); 759 760 if (!isa<UndefValue>(V)) continue; 761 762 BasicBlock *BB = PN->getIncomingBlock(i); 763 IncomingValueMap::const_iterator It = IncomingValues.find(BB); 764 if (It == IncomingValues.end()) continue; 765 766 PN->setIncomingValue(i, It->second); 767 } 768 } 769 770 /// \brief Replace a value flowing from a block to a phi with 771 /// potentially multiple instances of that value flowing from the 772 /// block's predecessors to the phi. 773 /// 774 /// \param BB The block with the value flowing into the phi. 775 /// \param BBPreds The predecessors of BB. 776 /// \param PN The phi that we are updating. 777 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB, 778 const PredBlockVector &BBPreds, 779 PHINode *PN) { 780 Value *OldVal = PN->removeIncomingValue(BB, false); 781 assert(OldVal && "No entry in PHI for Pred BB!"); 782 783 IncomingValueMap IncomingValues; 784 785 // We are merging two blocks - BB, and the block containing PN - and 786 // as a result we need to redirect edges from the predecessors of BB 787 // to go to the block containing PN, and update PN 788 // accordingly. Since we allow merging blocks in the case where the 789 // predecessor and successor blocks both share some predecessors, 790 // and where some of those common predecessors might have undef 791 // values flowing into PN, we want to rewrite those values to be 792 // consistent with the non-undef values. 793 794 gatherIncomingValuesToPhi(PN, IncomingValues); 795 796 // If this incoming value is one of the PHI nodes in BB, the new entries 797 // in the PHI node are the entries from the old PHI. 798 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { 799 PHINode *OldValPN = cast<PHINode>(OldVal); 800 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) { 801 // Note that, since we are merging phi nodes and BB and Succ might 802 // have common predecessors, we could end up with a phi node with 803 // identical incoming branches. This will be cleaned up later (and 804 // will trigger asserts if we try to clean it up now, without also 805 // simplifying the corresponding conditional branch). 806 BasicBlock *PredBB = OldValPN->getIncomingBlock(i); 807 Value *PredVal = OldValPN->getIncomingValue(i); 808 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB, 809 IncomingValues); 810 811 // And add a new incoming value for this predecessor for the 812 // newly retargeted branch. 813 PN->addIncoming(Selected, PredBB); 814 } 815 } else { 816 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) { 817 // Update existing incoming values in PN for this 818 // predecessor of BB. 819 BasicBlock *PredBB = BBPreds[i]; 820 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB, 821 IncomingValues); 822 823 // And add a new incoming value for this predecessor for the 824 // newly retargeted branch. 825 PN->addIncoming(Selected, PredBB); 826 } 827 } 828 829 replaceUndefValuesInPhi(PN, IncomingValues); 830 } 831 832 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an 833 /// unconditional branch, and contains no instructions other than PHI nodes, 834 /// potential side-effect free intrinsics and the branch. If possible, 835 /// eliminate BB by rewriting all the predecessors to branch to the successor 836 /// block and return true. If we can't transform, return false. 837 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { 838 assert(BB != &BB->getParent()->getEntryBlock() && 839 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); 840 841 // We can't eliminate infinite loops. 842 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); 843 if (BB == Succ) return false; 844 845 // Check to see if merging these blocks would cause conflicts for any of the 846 // phi nodes in BB or Succ. If not, we can safely merge. 847 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; 848 849 // Check for cases where Succ has multiple predecessors and a PHI node in BB 850 // has uses which will not disappear when the PHI nodes are merged. It is 851 // possible to handle such cases, but difficult: it requires checking whether 852 // BB dominates Succ, which is non-trivial to calculate in the case where 853 // Succ has multiple predecessors. Also, it requires checking whether 854 // constructing the necessary self-referential PHI node doesn't introduce any 855 // conflicts; this isn't too difficult, but the previous code for doing this 856 // was incorrect. 857 // 858 // Note that if this check finds a live use, BB dominates Succ, so BB is 859 // something like a loop pre-header (or rarely, a part of an irreducible CFG); 860 // folding the branch isn't profitable in that case anyway. 861 if (!Succ->getSinglePredecessor()) { 862 BasicBlock::iterator BBI = BB->begin(); 863 while (isa<PHINode>(*BBI)) { 864 for (Use &U : BBI->uses()) { 865 if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) { 866 if (PN->getIncomingBlock(U) != BB) 867 return false; 868 } else { 869 return false; 870 } 871 } 872 ++BBI; 873 } 874 } 875 876 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); 877 878 if (isa<PHINode>(Succ->begin())) { 879 // If there is more than one pred of succ, and there are PHI nodes in 880 // the successor, then we need to add incoming edges for the PHI nodes 881 // 882 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB)); 883 884 // Loop over all of the PHI nodes in the successor of BB. 885 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { 886 PHINode *PN = cast<PHINode>(I); 887 888 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN); 889 } 890 } 891 892 if (Succ->getSinglePredecessor()) { 893 // BB is the only predecessor of Succ, so Succ will end up with exactly 894 // the same predecessors BB had. 895 896 // Copy over any phi, debug or lifetime instruction. 897 BB->getTerminator()->eraseFromParent(); 898 Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(), 899 BB->getInstList()); 900 } else { 901 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 902 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. 903 assert(PN->use_empty() && "There shouldn't be any uses here!"); 904 PN->eraseFromParent(); 905 } 906 } 907 908 // If the unconditional branch we replaced contains llvm.loop metadata, we 909 // add the metadata to the branch instructions in the predecessors. 910 unsigned LoopMDKind = BB->getContext().getMDKindID("llvm.loop"); 911 Instruction *TI = BB->getTerminator(); 912 if (TI) 913 if (MDNode *LoopMD = TI->getMetadata(LoopMDKind)) 914 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 915 BasicBlock *Pred = *PI; 916 Pred->getTerminator()->setMetadata(LoopMDKind, LoopMD); 917 } 918 919 // Everything that jumped to BB now goes to Succ. 920 BB->replaceAllUsesWith(Succ); 921 if (!Succ->hasName()) Succ->takeName(BB); 922 BB->eraseFromParent(); // Delete the old basic block. 923 return true; 924 } 925 926 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI 927 /// nodes in this block. This doesn't try to be clever about PHI nodes 928 /// which differ only in the order of the incoming values, but instcombine 929 /// orders them so it usually won't matter. 930 /// 931 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { 932 // This implementation doesn't currently consider undef operands 933 // specially. Theoretically, two phis which are identical except for 934 // one having an undef where the other doesn't could be collapsed. 935 936 struct PHIDenseMapInfo { 937 static PHINode *getEmptyKey() { 938 return DenseMapInfo<PHINode *>::getEmptyKey(); 939 } 940 static PHINode *getTombstoneKey() { 941 return DenseMapInfo<PHINode *>::getTombstoneKey(); 942 } 943 static unsigned getHashValue(PHINode *PN) { 944 // Compute a hash value on the operands. Instcombine will likely have 945 // sorted them, which helps expose duplicates, but we have to check all 946 // the operands to be safe in case instcombine hasn't run. 947 return static_cast<unsigned>(hash_combine( 948 hash_combine_range(PN->value_op_begin(), PN->value_op_end()), 949 hash_combine_range(PN->block_begin(), PN->block_end()))); 950 } 951 static bool isEqual(PHINode *LHS, PHINode *RHS) { 952 if (LHS == getEmptyKey() || LHS == getTombstoneKey() || 953 RHS == getEmptyKey() || RHS == getTombstoneKey()) 954 return LHS == RHS; 955 return LHS->isIdenticalTo(RHS); 956 } 957 }; 958 959 // Set of unique PHINodes. 960 DenseSet<PHINode *, PHIDenseMapInfo> PHISet; 961 962 // Examine each PHI. 963 bool Changed = false; 964 for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) { 965 auto Inserted = PHISet.insert(PN); 966 if (!Inserted.second) { 967 // A duplicate. Replace this PHI with its duplicate. 968 PN->replaceAllUsesWith(*Inserted.first); 969 PN->eraseFromParent(); 970 Changed = true; 971 972 // The RAUW can change PHIs that we already visited. Start over from the 973 // beginning. 974 PHISet.clear(); 975 I = BB->begin(); 976 } 977 } 978 979 return Changed; 980 } 981 982 /// enforceKnownAlignment - If the specified pointer points to an object that 983 /// we control, modify the object's alignment to PrefAlign. This isn't 984 /// often possible though. If alignment is important, a more reliable approach 985 /// is to simply align all global variables and allocation instructions to 986 /// their preferred alignment from the beginning. 987 /// 988 static unsigned enforceKnownAlignment(Value *V, unsigned Align, 989 unsigned PrefAlign, 990 const DataLayout &DL) { 991 assert(PrefAlign > Align); 992 993 V = V->stripPointerCasts(); 994 995 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { 996 // TODO: ideally, computeKnownBits ought to have used 997 // AllocaInst::getAlignment() in its computation already, making 998 // the below max redundant. But, as it turns out, 999 // stripPointerCasts recurses through infinite layers of bitcasts, 1000 // while computeKnownBits is not allowed to traverse more than 6 1001 // levels. 1002 Align = std::max(AI->getAlignment(), Align); 1003 if (PrefAlign <= Align) 1004 return Align; 1005 1006 // If the preferred alignment is greater than the natural stack alignment 1007 // then don't round up. This avoids dynamic stack realignment. 1008 if (DL.exceedsNaturalStackAlignment(PrefAlign)) 1009 return Align; 1010 AI->setAlignment(PrefAlign); 1011 return PrefAlign; 1012 } 1013 1014 if (auto *GO = dyn_cast<GlobalObject>(V)) { 1015 // TODO: as above, this shouldn't be necessary. 1016 Align = std::max(GO->getAlignment(), Align); 1017 if (PrefAlign <= Align) 1018 return Align; 1019 1020 // If there is a large requested alignment and we can, bump up the alignment 1021 // of the global. If the memory we set aside for the global may not be the 1022 // memory used by the final program then it is impossible for us to reliably 1023 // enforce the preferred alignment. 1024 if (!GO->canIncreaseAlignment()) 1025 return Align; 1026 1027 GO->setAlignment(PrefAlign); 1028 return PrefAlign; 1029 } 1030 1031 return Align; 1032 } 1033 1034 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, 1035 const DataLayout &DL, 1036 const Instruction *CxtI, 1037 AssumptionCache *AC, 1038 const DominatorTree *DT) { 1039 assert(V->getType()->isPointerTy() && 1040 "getOrEnforceKnownAlignment expects a pointer!"); 1041 1042 KnownBits Known = computeKnownBits(V, DL, 0, AC, CxtI, DT); 1043 unsigned TrailZ = Known.countMinTrailingZeros(); 1044 1045 // Avoid trouble with ridiculously large TrailZ values, such as 1046 // those computed from a null pointer. 1047 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); 1048 1049 unsigned Align = 1u << std::min(Known.getBitWidth() - 1, TrailZ); 1050 1051 // LLVM doesn't support alignments larger than this currently. 1052 Align = std::min(Align, +Value::MaximumAlignment); 1053 1054 if (PrefAlign > Align) 1055 Align = enforceKnownAlignment(V, Align, PrefAlign, DL); 1056 1057 // We don't need to make any adjustment. 1058 return Align; 1059 } 1060 1061 ///===---------------------------------------------------------------------===// 1062 /// Dbg Intrinsic utilities 1063 /// 1064 1065 /// See if there is a dbg.value intrinsic for DIVar before I. 1066 static bool LdStHasDebugValue(DILocalVariable *DIVar, DIExpression *DIExpr, 1067 Instruction *I) { 1068 // Since we can't guarantee that the original dbg.declare instrinsic 1069 // is removed by LowerDbgDeclare(), we need to make sure that we are 1070 // not inserting the same dbg.value intrinsic over and over. 1071 llvm::BasicBlock::InstListType::iterator PrevI(I); 1072 if (PrevI != I->getParent()->getInstList().begin()) { 1073 --PrevI; 1074 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI)) 1075 if (DVI->getValue() == I->getOperand(0) && 1076 DVI->getOffset() == 0 && 1077 DVI->getVariable() == DIVar && 1078 DVI->getExpression() == DIExpr) 1079 return true; 1080 } 1081 return false; 1082 } 1083 1084 /// See if there is a dbg.value intrinsic for DIVar for the PHI node. 1085 static bool PhiHasDebugValue(DILocalVariable *DIVar, 1086 DIExpression *DIExpr, 1087 PHINode *APN) { 1088 // Since we can't guarantee that the original dbg.declare instrinsic 1089 // is removed by LowerDbgDeclare(), we need to make sure that we are 1090 // not inserting the same dbg.value intrinsic over and over. 1091 SmallVector<DbgValueInst *, 1> DbgValues; 1092 findDbgValues(DbgValues, APN); 1093 for (auto *DVI : DbgValues) { 1094 assert(DVI->getValue() == APN); 1095 assert(DVI->getOffset() == 0); 1096 if ((DVI->getVariable() == DIVar) && (DVI->getExpression() == DIExpr)) 1097 return true; 1098 } 1099 return false; 1100 } 1101 1102 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value 1103 /// that has an associated llvm.dbg.decl intrinsic. 1104 void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 1105 StoreInst *SI, DIBuilder &Builder) { 1106 auto *DIVar = DDI->getVariable(); 1107 assert(DIVar && "Missing variable"); 1108 auto *DIExpr = DDI->getExpression(); 1109 Value *DV = SI->getOperand(0); 1110 1111 // If an argument is zero extended then use argument directly. The ZExt 1112 // may be zapped by an optimization pass in future. 1113 Argument *ExtendedArg = nullptr; 1114 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) 1115 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); 1116 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) 1117 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); 1118 if (ExtendedArg) { 1119 // If this DDI was already describing only a fragment of a variable, ensure 1120 // that fragment is appropriately narrowed here. 1121 // But if a fragment wasn't used, describe the value as the original 1122 // argument (rather than the zext or sext) so that it remains described even 1123 // if the sext/zext is optimized away. This widens the variable description, 1124 // leaving it up to the consumer to know how the smaller value may be 1125 // represented in a larger register. 1126 if (auto Fragment = DIExpr->getFragmentInfo()) { 1127 unsigned FragmentOffset = Fragment->OffsetInBits; 1128 SmallVector<uint64_t, 3> Ops(DIExpr->elements_begin(), 1129 DIExpr->elements_end() - 3); 1130 Ops.push_back(dwarf::DW_OP_LLVM_fragment); 1131 Ops.push_back(FragmentOffset); 1132 const DataLayout &DL = DDI->getModule()->getDataLayout(); 1133 Ops.push_back(DL.getTypeSizeInBits(ExtendedArg->getType())); 1134 DIExpr = Builder.createExpression(Ops); 1135 } 1136 DV = ExtendedArg; 1137 } 1138 if (!LdStHasDebugValue(DIVar, DIExpr, SI)) 1139 Builder.insertDbgValueIntrinsic(DV, 0, DIVar, DIExpr, DDI->getDebugLoc(), 1140 SI); 1141 } 1142 1143 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value 1144 /// that has an associated llvm.dbg.decl intrinsic. 1145 void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 1146 LoadInst *LI, DIBuilder &Builder) { 1147 auto *DIVar = DDI->getVariable(); 1148 auto *DIExpr = DDI->getExpression(); 1149 assert(DIVar && "Missing variable"); 1150 1151 if (LdStHasDebugValue(DIVar, DIExpr, LI)) 1152 return; 1153 1154 // We are now tracking the loaded value instead of the address. In the 1155 // future if multi-location support is added to the IR, it might be 1156 // preferable to keep tracking both the loaded value and the original 1157 // address in case the alloca can not be elided. 1158 Instruction *DbgValue = Builder.insertDbgValueIntrinsic( 1159 LI, 0, DIVar, DIExpr, DDI->getDebugLoc(), (Instruction *)nullptr); 1160 DbgValue->insertAfter(LI); 1161 } 1162 1163 /// Inserts a llvm.dbg.value intrinsic after a phi 1164 /// that has an associated llvm.dbg.decl intrinsic. 1165 void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, 1166 PHINode *APN, DIBuilder &Builder) { 1167 auto *DIVar = DDI->getVariable(); 1168 auto *DIExpr = DDI->getExpression(); 1169 assert(DIVar && "Missing variable"); 1170 1171 if (PhiHasDebugValue(DIVar, DIExpr, APN)) 1172 return; 1173 1174 BasicBlock *BB = APN->getParent(); 1175 auto InsertionPt = BB->getFirstInsertionPt(); 1176 1177 // The block may be a catchswitch block, which does not have a valid 1178 // insertion point. 1179 // FIXME: Insert dbg.value markers in the successors when appropriate. 1180 if (InsertionPt != BB->end()) 1181 Builder.insertDbgValueIntrinsic(APN, 0, DIVar, DIExpr, DDI->getDebugLoc(), 1182 &*InsertionPt); 1183 } 1184 1185 /// Determine whether this alloca is either a VLA or an array. 1186 static bool isArray(AllocaInst *AI) { 1187 return AI->isArrayAllocation() || 1188 AI->getType()->getElementType()->isArrayTy(); 1189 } 1190 1191 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set 1192 /// of llvm.dbg.value intrinsics. 1193 bool llvm::LowerDbgDeclare(Function &F) { 1194 DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false); 1195 SmallVector<DbgDeclareInst *, 4> Dbgs; 1196 for (auto &FI : F) 1197 for (Instruction &BI : FI) 1198 if (auto DDI = dyn_cast<DbgDeclareInst>(&BI)) 1199 Dbgs.push_back(DDI); 1200 1201 if (Dbgs.empty()) 1202 return false; 1203 1204 for (auto &I : Dbgs) { 1205 DbgDeclareInst *DDI = I; 1206 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress()); 1207 // If this is an alloca for a scalar variable, insert a dbg.value 1208 // at each load and store to the alloca and erase the dbg.declare. 1209 // The dbg.values allow tracking a variable even if it is not 1210 // stored on the stack, while the dbg.declare can only describe 1211 // the stack slot (and at a lexical-scope granularity). Later 1212 // passes will attempt to elide the stack slot. 1213 if (AI && !isArray(AI)) { 1214 for (auto &AIUse : AI->uses()) { 1215 User *U = AIUse.getUser(); 1216 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 1217 if (AIUse.getOperandNo() == 1) 1218 ConvertDebugDeclareToDebugValue(DDI, SI, DIB); 1219 } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 1220 ConvertDebugDeclareToDebugValue(DDI, LI, DIB); 1221 } else if (CallInst *CI = dyn_cast<CallInst>(U)) { 1222 // This is a call by-value or some other instruction that 1223 // takes a pointer to the variable. Insert a *value* 1224 // intrinsic that describes the alloca. 1225 DIB.insertDbgValueIntrinsic(AI, 0, DDI->getVariable(), 1226 DDI->getExpression(), DDI->getDebugLoc(), 1227 CI); 1228 } 1229 } 1230 DDI->eraseFromParent(); 1231 } 1232 } 1233 return true; 1234 } 1235 1236 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the 1237 /// alloca 'V', if any. 1238 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { 1239 if (auto *L = LocalAsMetadata::getIfExists(V)) 1240 if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L)) 1241 for (User *U : MDV->users()) 1242 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U)) 1243 return DDI; 1244 1245 return nullptr; 1246 } 1247 1248 void llvm::findDbgValues(SmallVectorImpl<DbgValueInst *> &DbgValues, Value *V) { 1249 if (auto *L = LocalAsMetadata::getIfExists(V)) 1250 if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L)) 1251 for (User *U : MDV->users()) 1252 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U)) 1253 DbgValues.push_back(DVI); 1254 } 1255 1256 1257 bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress, 1258 Instruction *InsertBefore, DIBuilder &Builder, 1259 bool Deref, int Offset) { 1260 DbgDeclareInst *DDI = FindAllocaDbgDeclare(Address); 1261 if (!DDI) 1262 return false; 1263 DebugLoc Loc = DDI->getDebugLoc(); 1264 auto *DIVar = DDI->getVariable(); 1265 auto *DIExpr = DDI->getExpression(); 1266 assert(DIVar && "Missing variable"); 1267 DIExpr = DIExpression::prepend(DIExpr, Deref, Offset); 1268 // Insert llvm.dbg.declare immediately after the original alloca, and remove 1269 // old llvm.dbg.declare. 1270 Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, InsertBefore); 1271 DDI->eraseFromParent(); 1272 return true; 1273 } 1274 1275 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress, 1276 DIBuilder &Builder, bool Deref, int Offset) { 1277 return replaceDbgDeclare(AI, NewAllocaAddress, AI->getNextNode(), Builder, 1278 Deref, Offset); 1279 } 1280 1281 static void replaceOneDbgValueForAlloca(DbgValueInst *DVI, Value *NewAddress, 1282 DIBuilder &Builder, int Offset) { 1283 DebugLoc Loc = DVI->getDebugLoc(); 1284 auto *DIVar = DVI->getVariable(); 1285 auto *DIExpr = DVI->getExpression(); 1286 assert(DIVar && "Missing variable"); 1287 1288 // This is an alloca-based llvm.dbg.value. The first thing it should do with 1289 // the alloca pointer is dereference it. Otherwise we don't know how to handle 1290 // it and give up. 1291 if (!DIExpr || DIExpr->getNumElements() < 1 || 1292 DIExpr->getElement(0) != dwarf::DW_OP_deref) 1293 return; 1294 1295 // Insert the offset immediately after the first deref. 1296 // We could just change the offset argument of dbg.value, but it's unsigned... 1297 if (Offset) { 1298 SmallVector<uint64_t, 4> Ops; 1299 Ops.push_back(dwarf::DW_OP_deref); 1300 DIExpression::appendOffset(Ops, Offset); 1301 Ops.append(DIExpr->elements_begin() + 1, DIExpr->elements_end()); 1302 DIExpr = Builder.createExpression(Ops); 1303 } 1304 1305 Builder.insertDbgValueIntrinsic(NewAddress, DVI->getOffset(), DIVar, DIExpr, 1306 Loc, DVI); 1307 DVI->eraseFromParent(); 1308 } 1309 1310 void llvm::replaceDbgValueForAlloca(AllocaInst *AI, Value *NewAllocaAddress, 1311 DIBuilder &Builder, int Offset) { 1312 if (auto *L = LocalAsMetadata::getIfExists(AI)) 1313 if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L)) 1314 for (auto UI = MDV->use_begin(), UE = MDV->use_end(); UI != UE;) { 1315 Use &U = *UI++; 1316 if (auto *DVI = dyn_cast<DbgValueInst>(U.getUser())) 1317 replaceOneDbgValueForAlloca(DVI, NewAllocaAddress, Builder, Offset); 1318 } 1319 } 1320 1321 void llvm::salvageDebugInfo(Instruction &I) { 1322 SmallVector<DbgValueInst *, 1> DbgValues; 1323 auto &M = *I.getModule(); 1324 1325 auto MDWrap = [&](Value *V) { 1326 return MetadataAsValue::get(I.getContext(), ValueAsMetadata::get(V)); 1327 }; 1328 1329 if (isa<BitCastInst>(&I)) { 1330 findDbgValues(DbgValues, &I); 1331 for (auto *DVI : DbgValues) { 1332 // Bitcasts are entirely irrelevant for debug info. Rewrite the dbg.value 1333 // to use the cast's source. 1334 DVI->setOperand(0, MDWrap(I.getOperand(0))); 1335 DEBUG(dbgs() << "SALVAGE: " << *DVI << '\n'); 1336 } 1337 } else if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) { 1338 findDbgValues(DbgValues, &I); 1339 for (auto *DVI : DbgValues) { 1340 unsigned BitWidth = 1341 M.getDataLayout().getPointerSizeInBits(GEP->getPointerAddressSpace()); 1342 APInt Offset(BitWidth, 0); 1343 // Rewrite a constant GEP into a DIExpression. Since we are performing 1344 // arithmetic to compute the variable's *value* in the DIExpression, we 1345 // need to mark the expression with a DW_OP_stack_value. 1346 if (GEP->accumulateConstantOffset(M.getDataLayout(), Offset)) { 1347 auto *DIExpr = DVI->getExpression(); 1348 DIBuilder DIB(M, /*AllowUnresolved*/ false); 1349 // GEP offsets are i32 and thus always fit into an int64_t. 1350 DIExpr = DIExpression::prepend(DIExpr, DIExpression::NoDeref, 1351 Offset.getSExtValue(), 1352 DIExpression::WithStackValue); 1353 DVI->setOperand(0, MDWrap(I.getOperand(0))); 1354 DVI->setOperand(3, MetadataAsValue::get(I.getContext(), DIExpr)); 1355 DEBUG(dbgs() << "SALVAGE: " << *DVI << '\n'); 1356 } 1357 } 1358 } else if (isa<LoadInst>(&I)) { 1359 findDbgValues(DbgValues, &I); 1360 for (auto *DVI : DbgValues) { 1361 // Rewrite the load into DW_OP_deref. 1362 auto *DIExpr = DVI->getExpression(); 1363 DIBuilder DIB(M, /*AllowUnresolved*/ false); 1364 DIExpr = DIExpression::prepend(DIExpr, DIExpression::WithDeref); 1365 DVI->setOperand(0, MDWrap(I.getOperand(0))); 1366 DVI->setOperand(3, MetadataAsValue::get(I.getContext(), DIExpr)); 1367 DEBUG(dbgs() << "SALVAGE: " << *DVI << '\n'); 1368 } 1369 } 1370 } 1371 1372 unsigned llvm::removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB) { 1373 unsigned NumDeadInst = 0; 1374 // Delete the instructions backwards, as it has a reduced likelihood of 1375 // having to update as many def-use and use-def chains. 1376 Instruction *EndInst = BB->getTerminator(); // Last not to be deleted. 1377 while (EndInst != &BB->front()) { 1378 // Delete the next to last instruction. 1379 Instruction *Inst = &*--EndInst->getIterator(); 1380 if (!Inst->use_empty() && !Inst->getType()->isTokenTy()) 1381 Inst->replaceAllUsesWith(UndefValue::get(Inst->getType())); 1382 if (Inst->isEHPad() || Inst->getType()->isTokenTy()) { 1383 EndInst = Inst; 1384 continue; 1385 } 1386 if (!isa<DbgInfoIntrinsic>(Inst)) 1387 ++NumDeadInst; 1388 Inst->eraseFromParent(); 1389 } 1390 return NumDeadInst; 1391 } 1392 1393 unsigned llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap, 1394 bool PreserveLCSSA) { 1395 BasicBlock *BB = I->getParent(); 1396 // Loop over all of the successors, removing BB's entry from any PHI 1397 // nodes. 1398 for (BasicBlock *Successor : successors(BB)) 1399 Successor->removePredecessor(BB, PreserveLCSSA); 1400 1401 // Insert a call to llvm.trap right before this. This turns the undefined 1402 // behavior into a hard fail instead of falling through into random code. 1403 if (UseLLVMTrap) { 1404 Function *TrapFn = 1405 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap); 1406 CallInst *CallTrap = CallInst::Create(TrapFn, "", I); 1407 CallTrap->setDebugLoc(I->getDebugLoc()); 1408 } 1409 new UnreachableInst(I->getContext(), I); 1410 1411 // All instructions after this are dead. 1412 unsigned NumInstrsRemoved = 0; 1413 BasicBlock::iterator BBI = I->getIterator(), BBE = BB->end(); 1414 while (BBI != BBE) { 1415 if (!BBI->use_empty()) 1416 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType())); 1417 BB->getInstList().erase(BBI++); 1418 ++NumInstrsRemoved; 1419 } 1420 return NumInstrsRemoved; 1421 } 1422 1423 /// changeToCall - Convert the specified invoke into a normal call. 1424 static void changeToCall(InvokeInst *II) { 1425 SmallVector<Value*, 8> Args(II->arg_begin(), II->arg_end()); 1426 SmallVector<OperandBundleDef, 1> OpBundles; 1427 II->getOperandBundlesAsDefs(OpBundles); 1428 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, OpBundles, 1429 "", II); 1430 NewCall->takeName(II); 1431 NewCall->setCallingConv(II->getCallingConv()); 1432 NewCall->setAttributes(II->getAttributes()); 1433 NewCall->setDebugLoc(II->getDebugLoc()); 1434 II->replaceAllUsesWith(NewCall); 1435 1436 // Follow the call by a branch to the normal destination. 1437 BranchInst::Create(II->getNormalDest(), II); 1438 1439 // Update PHI nodes in the unwind destination 1440 II->getUnwindDest()->removePredecessor(II->getParent()); 1441 II->eraseFromParent(); 1442 } 1443 1444 BasicBlock *llvm::changeToInvokeAndSplitBasicBlock(CallInst *CI, 1445 BasicBlock *UnwindEdge) { 1446 BasicBlock *BB = CI->getParent(); 1447 1448 // Convert this function call into an invoke instruction. First, split the 1449 // basic block. 1450 BasicBlock *Split = 1451 BB->splitBasicBlock(CI->getIterator(), CI->getName() + ".noexc"); 1452 1453 // Delete the unconditional branch inserted by splitBasicBlock 1454 BB->getInstList().pop_back(); 1455 1456 // Create the new invoke instruction. 1457 SmallVector<Value *, 8> InvokeArgs(CI->arg_begin(), CI->arg_end()); 1458 SmallVector<OperandBundleDef, 1> OpBundles; 1459 1460 CI->getOperandBundlesAsDefs(OpBundles); 1461 1462 // Note: we're round tripping operand bundles through memory here, and that 1463 // can potentially be avoided with a cleverer API design that we do not have 1464 // as of this time. 1465 1466 InvokeInst *II = InvokeInst::Create(CI->getCalledValue(), Split, UnwindEdge, 1467 InvokeArgs, OpBundles, CI->getName(), BB); 1468 II->setDebugLoc(CI->getDebugLoc()); 1469 II->setCallingConv(CI->getCallingConv()); 1470 II->setAttributes(CI->getAttributes()); 1471 1472 // Make sure that anything using the call now uses the invoke! This also 1473 // updates the CallGraph if present, because it uses a WeakTrackingVH. 1474 CI->replaceAllUsesWith(II); 1475 1476 // Delete the original call 1477 Split->getInstList().pop_front(); 1478 return Split; 1479 } 1480 1481 static bool markAliveBlocks(Function &F, 1482 SmallPtrSetImpl<BasicBlock*> &Reachable) { 1483 1484 SmallVector<BasicBlock*, 128> Worklist; 1485 BasicBlock *BB = &F.front(); 1486 Worklist.push_back(BB); 1487 Reachable.insert(BB); 1488 bool Changed = false; 1489 do { 1490 BB = Worklist.pop_back_val(); 1491 1492 // Do a quick scan of the basic block, turning any obviously unreachable 1493 // instructions into LLVM unreachable insts. The instruction combining pass 1494 // canonicalizes unreachable insts into stores to null or undef. 1495 for (Instruction &I : *BB) { 1496 // Assumptions that are known to be false are equivalent to unreachable. 1497 // Also, if the condition is undefined, then we make the choice most 1498 // beneficial to the optimizer, and choose that to also be unreachable. 1499 if (auto *II = dyn_cast<IntrinsicInst>(&I)) { 1500 if (II->getIntrinsicID() == Intrinsic::assume) { 1501 if (match(II->getArgOperand(0), m_CombineOr(m_Zero(), m_Undef()))) { 1502 // Don't insert a call to llvm.trap right before the unreachable. 1503 changeToUnreachable(II, false); 1504 Changed = true; 1505 break; 1506 } 1507 } 1508 1509 if (II->getIntrinsicID() == Intrinsic::experimental_guard) { 1510 // A call to the guard intrinsic bails out of the current compilation 1511 // unit if the predicate passed to it is false. If the predicate is a 1512 // constant false, then we know the guard will bail out of the current 1513 // compile unconditionally, so all code following it is dead. 1514 // 1515 // Note: unlike in llvm.assume, it is not "obviously profitable" for 1516 // guards to treat `undef` as `false` since a guard on `undef` can 1517 // still be useful for widening. 1518 if (match(II->getArgOperand(0), m_Zero())) 1519 if (!isa<UnreachableInst>(II->getNextNode())) { 1520 changeToUnreachable(II->getNextNode(), /*UseLLVMTrap=*/ false); 1521 Changed = true; 1522 break; 1523 } 1524 } 1525 } 1526 1527 if (auto *CI = dyn_cast<CallInst>(&I)) { 1528 Value *Callee = CI->getCalledValue(); 1529 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) { 1530 changeToUnreachable(CI, /*UseLLVMTrap=*/false); 1531 Changed = true; 1532 break; 1533 } 1534 if (CI->doesNotReturn()) { 1535 // If we found a call to a no-return function, insert an unreachable 1536 // instruction after it. Make sure there isn't *already* one there 1537 // though. 1538 if (!isa<UnreachableInst>(CI->getNextNode())) { 1539 // Don't insert a call to llvm.trap right before the unreachable. 1540 changeToUnreachable(CI->getNextNode(), false); 1541 Changed = true; 1542 } 1543 break; 1544 } 1545 } 1546 1547 // Store to undef and store to null are undefined and used to signal that 1548 // they should be changed to unreachable by passes that can't modify the 1549 // CFG. 1550 if (auto *SI = dyn_cast<StoreInst>(&I)) { 1551 // Don't touch volatile stores. 1552 if (SI->isVolatile()) continue; 1553 1554 Value *Ptr = SI->getOperand(1); 1555 1556 if (isa<UndefValue>(Ptr) || 1557 (isa<ConstantPointerNull>(Ptr) && 1558 SI->getPointerAddressSpace() == 0)) { 1559 changeToUnreachable(SI, true); 1560 Changed = true; 1561 break; 1562 } 1563 } 1564 } 1565 1566 TerminatorInst *Terminator = BB->getTerminator(); 1567 if (auto *II = dyn_cast<InvokeInst>(Terminator)) { 1568 // Turn invokes that call 'nounwind' functions into ordinary calls. 1569 Value *Callee = II->getCalledValue(); 1570 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) { 1571 changeToUnreachable(II, true); 1572 Changed = true; 1573 } else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) { 1574 if (II->use_empty() && II->onlyReadsMemory()) { 1575 // jump to the normal destination branch. 1576 BranchInst::Create(II->getNormalDest(), II); 1577 II->getUnwindDest()->removePredecessor(II->getParent()); 1578 II->eraseFromParent(); 1579 } else 1580 changeToCall(II); 1581 Changed = true; 1582 } 1583 } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(Terminator)) { 1584 // Remove catchpads which cannot be reached. 1585 struct CatchPadDenseMapInfo { 1586 static CatchPadInst *getEmptyKey() { 1587 return DenseMapInfo<CatchPadInst *>::getEmptyKey(); 1588 } 1589 static CatchPadInst *getTombstoneKey() { 1590 return DenseMapInfo<CatchPadInst *>::getTombstoneKey(); 1591 } 1592 static unsigned getHashValue(CatchPadInst *CatchPad) { 1593 return static_cast<unsigned>(hash_combine_range( 1594 CatchPad->value_op_begin(), CatchPad->value_op_end())); 1595 } 1596 static bool isEqual(CatchPadInst *LHS, CatchPadInst *RHS) { 1597 if (LHS == getEmptyKey() || LHS == getTombstoneKey() || 1598 RHS == getEmptyKey() || RHS == getTombstoneKey()) 1599 return LHS == RHS; 1600 return LHS->isIdenticalTo(RHS); 1601 } 1602 }; 1603 1604 // Set of unique CatchPads. 1605 SmallDenseMap<CatchPadInst *, detail::DenseSetEmpty, 4, 1606 CatchPadDenseMapInfo, detail::DenseSetPair<CatchPadInst *>> 1607 HandlerSet; 1608 detail::DenseSetEmpty Empty; 1609 for (CatchSwitchInst::handler_iterator I = CatchSwitch->handler_begin(), 1610 E = CatchSwitch->handler_end(); 1611 I != E; ++I) { 1612 BasicBlock *HandlerBB = *I; 1613 auto *CatchPad = cast<CatchPadInst>(HandlerBB->getFirstNonPHI()); 1614 if (!HandlerSet.insert({CatchPad, Empty}).second) { 1615 CatchSwitch->removeHandler(I); 1616 --I; 1617 --E; 1618 Changed = true; 1619 } 1620 } 1621 } 1622 1623 Changed |= ConstantFoldTerminator(BB, true); 1624 for (BasicBlock *Successor : successors(BB)) 1625 if (Reachable.insert(Successor).second) 1626 Worklist.push_back(Successor); 1627 } while (!Worklist.empty()); 1628 return Changed; 1629 } 1630 1631 void llvm::removeUnwindEdge(BasicBlock *BB) { 1632 TerminatorInst *TI = BB->getTerminator(); 1633 1634 if (auto *II = dyn_cast<InvokeInst>(TI)) { 1635 changeToCall(II); 1636 return; 1637 } 1638 1639 TerminatorInst *NewTI; 1640 BasicBlock *UnwindDest; 1641 1642 if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) { 1643 NewTI = CleanupReturnInst::Create(CRI->getCleanupPad(), nullptr, CRI); 1644 UnwindDest = CRI->getUnwindDest(); 1645 } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(TI)) { 1646 auto *NewCatchSwitch = CatchSwitchInst::Create( 1647 CatchSwitch->getParentPad(), nullptr, CatchSwitch->getNumHandlers(), 1648 CatchSwitch->getName(), CatchSwitch); 1649 for (BasicBlock *PadBB : CatchSwitch->handlers()) 1650 NewCatchSwitch->addHandler(PadBB); 1651 1652 NewTI = NewCatchSwitch; 1653 UnwindDest = CatchSwitch->getUnwindDest(); 1654 } else { 1655 llvm_unreachable("Could not find unwind successor"); 1656 } 1657 1658 NewTI->takeName(TI); 1659 NewTI->setDebugLoc(TI->getDebugLoc()); 1660 UnwindDest->removePredecessor(BB); 1661 TI->replaceAllUsesWith(NewTI); 1662 TI->eraseFromParent(); 1663 } 1664 1665 /// removeUnreachableBlocks - Remove blocks that are not reachable, even 1666 /// if they are in a dead cycle. Return true if a change was made, false 1667 /// otherwise. If `LVI` is passed, this function preserves LazyValueInfo 1668 /// after modifying the CFG. 1669 bool llvm::removeUnreachableBlocks(Function &F, LazyValueInfo *LVI) { 1670 SmallPtrSet<BasicBlock*, 16> Reachable; 1671 bool Changed = markAliveBlocks(F, Reachable); 1672 1673 // If there are unreachable blocks in the CFG... 1674 if (Reachable.size() == F.size()) 1675 return Changed; 1676 1677 assert(Reachable.size() < F.size()); 1678 NumRemoved += F.size()-Reachable.size(); 1679 1680 // Loop over all of the basic blocks that are not reachable, dropping all of 1681 // their internal references... 1682 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) { 1683 if (Reachable.count(&*BB)) 1684 continue; 1685 1686 for (BasicBlock *Successor : successors(&*BB)) 1687 if (Reachable.count(Successor)) 1688 Successor->removePredecessor(&*BB); 1689 if (LVI) 1690 LVI->eraseBlock(&*BB); 1691 BB->dropAllReferences(); 1692 } 1693 1694 for (Function::iterator I = ++F.begin(); I != F.end();) 1695 if (!Reachable.count(&*I)) 1696 I = F.getBasicBlockList().erase(I); 1697 else 1698 ++I; 1699 1700 return true; 1701 } 1702 1703 void llvm::combineMetadata(Instruction *K, const Instruction *J, 1704 ArrayRef<unsigned> KnownIDs) { 1705 SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata; 1706 K->dropUnknownNonDebugMetadata(KnownIDs); 1707 K->getAllMetadataOtherThanDebugLoc(Metadata); 1708 for (const auto &MD : Metadata) { 1709 unsigned Kind = MD.first; 1710 MDNode *JMD = J->getMetadata(Kind); 1711 MDNode *KMD = MD.second; 1712 1713 switch (Kind) { 1714 default: 1715 K->setMetadata(Kind, nullptr); // Remove unknown metadata 1716 break; 1717 case LLVMContext::MD_dbg: 1718 llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg"); 1719 case LLVMContext::MD_tbaa: 1720 K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD)); 1721 break; 1722 case LLVMContext::MD_alias_scope: 1723 K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD)); 1724 break; 1725 case LLVMContext::MD_noalias: 1726 case LLVMContext::MD_mem_parallel_loop_access: 1727 K->setMetadata(Kind, MDNode::intersect(JMD, KMD)); 1728 break; 1729 case LLVMContext::MD_range: 1730 K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD)); 1731 break; 1732 case LLVMContext::MD_fpmath: 1733 K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD)); 1734 break; 1735 case LLVMContext::MD_invariant_load: 1736 // Only set the !invariant.load if it is present in both instructions. 1737 K->setMetadata(Kind, JMD); 1738 break; 1739 case LLVMContext::MD_nonnull: 1740 // Only set the !nonnull if it is present in both instructions. 1741 K->setMetadata(Kind, JMD); 1742 break; 1743 case LLVMContext::MD_invariant_group: 1744 // Preserve !invariant.group in K. 1745 break; 1746 case LLVMContext::MD_align: 1747 K->setMetadata(Kind, 1748 MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD)); 1749 break; 1750 case LLVMContext::MD_dereferenceable: 1751 case LLVMContext::MD_dereferenceable_or_null: 1752 K->setMetadata(Kind, 1753 MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD)); 1754 break; 1755 } 1756 } 1757 // Set !invariant.group from J if J has it. If both instructions have it 1758 // then we will just pick it from J - even when they are different. 1759 // Also make sure that K is load or store - f.e. combining bitcast with load 1760 // could produce bitcast with invariant.group metadata, which is invalid. 1761 // FIXME: we should try to preserve both invariant.group md if they are 1762 // different, but right now instruction can only have one invariant.group. 1763 if (auto *JMD = J->getMetadata(LLVMContext::MD_invariant_group)) 1764 if (isa<LoadInst>(K) || isa<StoreInst>(K)) 1765 K->setMetadata(LLVMContext::MD_invariant_group, JMD); 1766 } 1767 1768 void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J) { 1769 unsigned KnownIDs[] = { 1770 LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope, 1771 LLVMContext::MD_noalias, LLVMContext::MD_range, 1772 LLVMContext::MD_invariant_load, LLVMContext::MD_nonnull, 1773 LLVMContext::MD_invariant_group, LLVMContext::MD_align, 1774 LLVMContext::MD_dereferenceable, 1775 LLVMContext::MD_dereferenceable_or_null}; 1776 combineMetadata(K, J, KnownIDs); 1777 } 1778 1779 template <typename RootType, typename DominatesFn> 1780 static unsigned replaceDominatedUsesWith(Value *From, Value *To, 1781 const RootType &Root, 1782 const DominatesFn &Dominates) { 1783 assert(From->getType() == To->getType()); 1784 1785 unsigned Count = 0; 1786 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end(); 1787 UI != UE;) { 1788 Use &U = *UI++; 1789 if (!Dominates(Root, U)) 1790 continue; 1791 U.set(To); 1792 DEBUG(dbgs() << "Replace dominated use of '" << From->getName() << "' as " 1793 << *To << " in " << *U << "\n"); 1794 ++Count; 1795 } 1796 return Count; 1797 } 1798 1799 unsigned llvm::replaceNonLocalUsesWith(Instruction *From, Value *To) { 1800 assert(From->getType() == To->getType()); 1801 auto *BB = From->getParent(); 1802 unsigned Count = 0; 1803 1804 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end(); 1805 UI != UE;) { 1806 Use &U = *UI++; 1807 auto *I = cast<Instruction>(U.getUser()); 1808 if (I->getParent() == BB) 1809 continue; 1810 U.set(To); 1811 ++Count; 1812 } 1813 return Count; 1814 } 1815 1816 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To, 1817 DominatorTree &DT, 1818 const BasicBlockEdge &Root) { 1819 auto Dominates = [&DT](const BasicBlockEdge &Root, const Use &U) { 1820 return DT.dominates(Root, U); 1821 }; 1822 return ::replaceDominatedUsesWith(From, To, Root, Dominates); 1823 } 1824 1825 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To, 1826 DominatorTree &DT, 1827 const BasicBlock *BB) { 1828 auto ProperlyDominates = [&DT](const BasicBlock *BB, const Use &U) { 1829 auto *I = cast<Instruction>(U.getUser())->getParent(); 1830 return DT.properlyDominates(BB, I); 1831 }; 1832 return ::replaceDominatedUsesWith(From, To, BB, ProperlyDominates); 1833 } 1834 1835 bool llvm::callsGCLeafFunction(ImmutableCallSite CS) { 1836 // Check if the function is specifically marked as a gc leaf function. 1837 if (CS.hasFnAttr("gc-leaf-function")) 1838 return true; 1839 if (const Function *F = CS.getCalledFunction()) { 1840 if (F->hasFnAttribute("gc-leaf-function")) 1841 return true; 1842 1843 if (auto IID = F->getIntrinsicID()) 1844 // Most LLVM intrinsics do not take safepoints. 1845 return IID != Intrinsic::experimental_gc_statepoint && 1846 IID != Intrinsic::experimental_deoptimize; 1847 } 1848 1849 return false; 1850 } 1851 1852 void llvm::copyNonnullMetadata(const LoadInst &OldLI, MDNode *N, 1853 LoadInst &NewLI) { 1854 auto *NewTy = NewLI.getType(); 1855 1856 // This only directly applies if the new type is also a pointer. 1857 if (NewTy->isPointerTy()) { 1858 NewLI.setMetadata(LLVMContext::MD_nonnull, N); 1859 return; 1860 } 1861 1862 // The only other translation we can do is to integral loads with !range 1863 // metadata. 1864 if (!NewTy->isIntegerTy()) 1865 return; 1866 1867 MDBuilder MDB(NewLI.getContext()); 1868 const Value *Ptr = OldLI.getPointerOperand(); 1869 auto *ITy = cast<IntegerType>(NewTy); 1870 auto *NullInt = ConstantExpr::getPtrToInt( 1871 ConstantPointerNull::get(cast<PointerType>(Ptr->getType())), ITy); 1872 auto *NonNullInt = ConstantExpr::getAdd(NullInt, ConstantInt::get(ITy, 1)); 1873 NewLI.setMetadata(LLVMContext::MD_range, 1874 MDB.createRange(NonNullInt, NullInt)); 1875 } 1876 1877 void llvm::copyRangeMetadata(const DataLayout &DL, const LoadInst &OldLI, 1878 MDNode *N, LoadInst &NewLI) { 1879 auto *NewTy = NewLI.getType(); 1880 1881 // Give up unless it is converted to a pointer where there is a single very 1882 // valuable mapping we can do reliably. 1883 // FIXME: It would be nice to propagate this in more ways, but the type 1884 // conversions make it hard. 1885 if (!NewTy->isPointerTy()) 1886 return; 1887 1888 unsigned BitWidth = DL.getTypeSizeInBits(NewTy); 1889 if (!getConstantRangeFromMetadata(*N).contains(APInt(BitWidth, 0))) { 1890 MDNode *NN = MDNode::get(OldLI.getContext(), None); 1891 NewLI.setMetadata(LLVMContext::MD_nonnull, NN); 1892 } 1893 } 1894 1895 namespace { 1896 /// A potential constituent of a bitreverse or bswap expression. See 1897 /// collectBitParts for a fuller explanation. 1898 struct BitPart { 1899 BitPart(Value *P, unsigned BW) : Provider(P) { 1900 Provenance.resize(BW); 1901 } 1902 1903 /// The Value that this is a bitreverse/bswap of. 1904 Value *Provider; 1905 /// The "provenance" of each bit. Provenance[A] = B means that bit A 1906 /// in Provider becomes bit B in the result of this expression. 1907 SmallVector<int8_t, 32> Provenance; // int8_t means max size is i128. 1908 1909 enum { Unset = -1 }; 1910 }; 1911 } // end anonymous namespace 1912 1913 /// Analyze the specified subexpression and see if it is capable of providing 1914 /// pieces of a bswap or bitreverse. The subexpression provides a potential 1915 /// piece of a bswap or bitreverse if it can be proven that each non-zero bit in 1916 /// the output of the expression came from a corresponding bit in some other 1917 /// value. This function is recursive, and the end result is a mapping of 1918 /// bitnumber to bitnumber. It is the caller's responsibility to validate that 1919 /// the bitnumber to bitnumber mapping is correct for a bswap or bitreverse. 1920 /// 1921 /// For example, if the current subexpression if "(shl i32 %X, 24)" then we know 1922 /// that the expression deposits the low byte of %X into the high byte of the 1923 /// result and that all other bits are zero. This expression is accepted and a 1924 /// BitPart is returned with Provider set to %X and Provenance[24-31] set to 1925 /// [0-7]. 1926 /// 1927 /// To avoid revisiting values, the BitPart results are memoized into the 1928 /// provided map. To avoid unnecessary copying of BitParts, BitParts are 1929 /// constructed in-place in the \c BPS map. Because of this \c BPS needs to 1930 /// store BitParts objects, not pointers. As we need the concept of a nullptr 1931 /// BitParts (Value has been analyzed and the analysis failed), we an Optional 1932 /// type instead to provide the same functionality. 1933 /// 1934 /// Because we pass around references into \c BPS, we must use a container that 1935 /// does not invalidate internal references (std::map instead of DenseMap). 1936 /// 1937 static const Optional<BitPart> & 1938 collectBitParts(Value *V, bool MatchBSwaps, bool MatchBitReversals, 1939 std::map<Value *, Optional<BitPart>> &BPS) { 1940 auto I = BPS.find(V); 1941 if (I != BPS.end()) 1942 return I->second; 1943 1944 auto &Result = BPS[V] = None; 1945 auto BitWidth = cast<IntegerType>(V->getType())->getBitWidth(); 1946 1947 if (Instruction *I = dyn_cast<Instruction>(V)) { 1948 // If this is an or instruction, it may be an inner node of the bswap. 1949 if (I->getOpcode() == Instruction::Or) { 1950 auto &A = collectBitParts(I->getOperand(0), MatchBSwaps, 1951 MatchBitReversals, BPS); 1952 auto &B = collectBitParts(I->getOperand(1), MatchBSwaps, 1953 MatchBitReversals, BPS); 1954 if (!A || !B) 1955 return Result; 1956 1957 // Try and merge the two together. 1958 if (!A->Provider || A->Provider != B->Provider) 1959 return Result; 1960 1961 Result = BitPart(A->Provider, BitWidth); 1962 for (unsigned i = 0; i < A->Provenance.size(); ++i) { 1963 if (A->Provenance[i] != BitPart::Unset && 1964 B->Provenance[i] != BitPart::Unset && 1965 A->Provenance[i] != B->Provenance[i]) 1966 return Result = None; 1967 1968 if (A->Provenance[i] == BitPart::Unset) 1969 Result->Provenance[i] = B->Provenance[i]; 1970 else 1971 Result->Provenance[i] = A->Provenance[i]; 1972 } 1973 1974 return Result; 1975 } 1976 1977 // If this is a logical shift by a constant, recurse then shift the result. 1978 if (I->isLogicalShift() && isa<ConstantInt>(I->getOperand(1))) { 1979 unsigned BitShift = 1980 cast<ConstantInt>(I->getOperand(1))->getLimitedValue(~0U); 1981 // Ensure the shift amount is defined. 1982 if (BitShift > BitWidth) 1983 return Result; 1984 1985 auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps, 1986 MatchBitReversals, BPS); 1987 if (!Res) 1988 return Result; 1989 Result = Res; 1990 1991 // Perform the "shift" on BitProvenance. 1992 auto &P = Result->Provenance; 1993 if (I->getOpcode() == Instruction::Shl) { 1994 P.erase(std::prev(P.end(), BitShift), P.end()); 1995 P.insert(P.begin(), BitShift, BitPart::Unset); 1996 } else { 1997 P.erase(P.begin(), std::next(P.begin(), BitShift)); 1998 P.insert(P.end(), BitShift, BitPart::Unset); 1999 } 2000 2001 return Result; 2002 } 2003 2004 // If this is a logical 'and' with a mask that clears bits, recurse then 2005 // unset the appropriate bits. 2006 if (I->getOpcode() == Instruction::And && 2007 isa<ConstantInt>(I->getOperand(1))) { 2008 APInt Bit(I->getType()->getPrimitiveSizeInBits(), 1); 2009 const APInt &AndMask = cast<ConstantInt>(I->getOperand(1))->getValue(); 2010 2011 // Check that the mask allows a multiple of 8 bits for a bswap, for an 2012 // early exit. 2013 unsigned NumMaskedBits = AndMask.countPopulation(); 2014 if (!MatchBitReversals && NumMaskedBits % 8 != 0) 2015 return Result; 2016 2017 auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps, 2018 MatchBitReversals, BPS); 2019 if (!Res) 2020 return Result; 2021 Result = Res; 2022 2023 for (unsigned i = 0; i < BitWidth; ++i, Bit <<= 1) 2024 // If the AndMask is zero for this bit, clear the bit. 2025 if ((AndMask & Bit) == 0) 2026 Result->Provenance[i] = BitPart::Unset; 2027 return Result; 2028 } 2029 2030 // If this is a zext instruction zero extend the result. 2031 if (I->getOpcode() == Instruction::ZExt) { 2032 auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps, 2033 MatchBitReversals, BPS); 2034 if (!Res) 2035 return Result; 2036 2037 Result = BitPart(Res->Provider, BitWidth); 2038 auto NarrowBitWidth = 2039 cast<IntegerType>(cast<ZExtInst>(I)->getSrcTy())->getBitWidth(); 2040 for (unsigned i = 0; i < NarrowBitWidth; ++i) 2041 Result->Provenance[i] = Res->Provenance[i]; 2042 for (unsigned i = NarrowBitWidth; i < BitWidth; ++i) 2043 Result->Provenance[i] = BitPart::Unset; 2044 return Result; 2045 } 2046 } 2047 2048 // Okay, we got to something that isn't a shift, 'or' or 'and'. This must be 2049 // the input value to the bswap/bitreverse. 2050 Result = BitPart(V, BitWidth); 2051 for (unsigned i = 0; i < BitWidth; ++i) 2052 Result->Provenance[i] = i; 2053 return Result; 2054 } 2055 2056 static bool bitTransformIsCorrectForBSwap(unsigned From, unsigned To, 2057 unsigned BitWidth) { 2058 if (From % 8 != To % 8) 2059 return false; 2060 // Convert from bit indices to byte indices and check for a byte reversal. 2061 From >>= 3; 2062 To >>= 3; 2063 BitWidth >>= 3; 2064 return From == BitWidth - To - 1; 2065 } 2066 2067 static bool bitTransformIsCorrectForBitReverse(unsigned From, unsigned To, 2068 unsigned BitWidth) { 2069 return From == BitWidth - To - 1; 2070 } 2071 2072 /// Given an OR instruction, check to see if this is a bitreverse 2073 /// idiom. If so, insert the new intrinsic and return true. 2074 bool llvm::recognizeBSwapOrBitReverseIdiom( 2075 Instruction *I, bool MatchBSwaps, bool MatchBitReversals, 2076 SmallVectorImpl<Instruction *> &InsertedInsts) { 2077 if (Operator::getOpcode(I) != Instruction::Or) 2078 return false; 2079 if (!MatchBSwaps && !MatchBitReversals) 2080 return false; 2081 IntegerType *ITy = dyn_cast<IntegerType>(I->getType()); 2082 if (!ITy || ITy->getBitWidth() > 128) 2083 return false; // Can't do vectors or integers > 128 bits. 2084 unsigned BW = ITy->getBitWidth(); 2085 2086 unsigned DemandedBW = BW; 2087 IntegerType *DemandedTy = ITy; 2088 if (I->hasOneUse()) { 2089 if (TruncInst *Trunc = dyn_cast<TruncInst>(I->user_back())) { 2090 DemandedTy = cast<IntegerType>(Trunc->getType()); 2091 DemandedBW = DemandedTy->getBitWidth(); 2092 } 2093 } 2094 2095 // Try to find all the pieces corresponding to the bswap. 2096 std::map<Value *, Optional<BitPart>> BPS; 2097 auto Res = collectBitParts(I, MatchBSwaps, MatchBitReversals, BPS); 2098 if (!Res) 2099 return false; 2100 auto &BitProvenance = Res->Provenance; 2101 2102 // Now, is the bit permutation correct for a bswap or a bitreverse? We can 2103 // only byteswap values with an even number of bytes. 2104 bool OKForBSwap = DemandedBW % 16 == 0, OKForBitReverse = true; 2105 for (unsigned i = 0; i < DemandedBW; ++i) { 2106 OKForBSwap &= 2107 bitTransformIsCorrectForBSwap(BitProvenance[i], i, DemandedBW); 2108 OKForBitReverse &= 2109 bitTransformIsCorrectForBitReverse(BitProvenance[i], i, DemandedBW); 2110 } 2111 2112 Intrinsic::ID Intrin; 2113 if (OKForBSwap && MatchBSwaps) 2114 Intrin = Intrinsic::bswap; 2115 else if (OKForBitReverse && MatchBitReversals) 2116 Intrin = Intrinsic::bitreverse; 2117 else 2118 return false; 2119 2120 if (ITy != DemandedTy) { 2121 Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, DemandedTy); 2122 Value *Provider = Res->Provider; 2123 IntegerType *ProviderTy = cast<IntegerType>(Provider->getType()); 2124 // We may need to truncate the provider. 2125 if (DemandedTy != ProviderTy) { 2126 auto *Trunc = CastInst::Create(Instruction::Trunc, Provider, DemandedTy, 2127 "trunc", I); 2128 InsertedInsts.push_back(Trunc); 2129 Provider = Trunc; 2130 } 2131 auto *CI = CallInst::Create(F, Provider, "rev", I); 2132 InsertedInsts.push_back(CI); 2133 auto *ExtInst = CastInst::Create(Instruction::ZExt, CI, ITy, "zext", I); 2134 InsertedInsts.push_back(ExtInst); 2135 return true; 2136 } 2137 2138 Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, ITy); 2139 InsertedInsts.push_back(CallInst::Create(F, Res->Provider, "rev", I)); 2140 return true; 2141 } 2142 2143 // CodeGen has special handling for some string functions that may replace 2144 // them with target-specific intrinsics. Since that'd skip our interceptors 2145 // in ASan/MSan/TSan/DFSan, and thus make us miss some memory accesses, 2146 // we mark affected calls as NoBuiltin, which will disable optimization 2147 // in CodeGen. 2148 void llvm::maybeMarkSanitizerLibraryCallNoBuiltin( 2149 CallInst *CI, const TargetLibraryInfo *TLI) { 2150 Function *F = CI->getCalledFunction(); 2151 LibFunc Func; 2152 if (F && !F->hasLocalLinkage() && F->hasName() && 2153 TLI->getLibFunc(F->getName(), Func) && TLI->hasOptimizedCodeGen(Func) && 2154 !F->doesNotAccessMemory()) 2155 CI->addAttribute(AttributeList::FunctionIndex, Attribute::NoBuiltin); 2156 } 2157 2158 bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) { 2159 // We can't have a PHI with a metadata type. 2160 if (I->getOperand(OpIdx)->getType()->isMetadataTy()) 2161 return false; 2162 2163 // Early exit. 2164 if (!isa<Constant>(I->getOperand(OpIdx))) 2165 return true; 2166 2167 switch (I->getOpcode()) { 2168 default: 2169 return true; 2170 case Instruction::Call: 2171 case Instruction::Invoke: 2172 // Can't handle inline asm. Skip it. 2173 if (isa<InlineAsm>(ImmutableCallSite(I).getCalledValue())) 2174 return false; 2175 // Many arithmetic intrinsics have no issue taking a 2176 // variable, however it's hard to distingish these from 2177 // specials such as @llvm.frameaddress that require a constant. 2178 if (isa<IntrinsicInst>(I)) 2179 return false; 2180 2181 // Constant bundle operands may need to retain their constant-ness for 2182 // correctness. 2183 if (ImmutableCallSite(I).isBundleOperand(OpIdx)) 2184 return false; 2185 return true; 2186 case Instruction::ShuffleVector: 2187 // Shufflevector masks are constant. 2188 return OpIdx != 2; 2189 case Instruction::Switch: 2190 case Instruction::ExtractValue: 2191 // All operands apart from the first are constant. 2192 return OpIdx == 0; 2193 case Instruction::InsertValue: 2194 // All operands apart from the first and the second are constant. 2195 return OpIdx < 2; 2196 case Instruction::Alloca: 2197 // Static allocas (constant size in the entry block) are handled by 2198 // prologue/epilogue insertion so they're free anyway. We definitely don't 2199 // want to make them non-constant. 2200 return !dyn_cast<AllocaInst>(I)->isStaticAlloca(); 2201 case Instruction::GetElementPtr: 2202 if (OpIdx == 0) 2203 return true; 2204 gep_type_iterator It = gep_type_begin(I); 2205 for (auto E = std::next(It, OpIdx); It != E; ++It) 2206 if (It.isStruct()) 2207 return false; 2208 return true; 2209 } 2210 } 2211