1 //===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file promotes memory references to be register references. It promotes 10 // alloca instructions which only have loads and stores as uses. An alloca is 11 // transformed by using iterated dominator frontiers to place PHI nodes, then 12 // traversing the function in depth-first order to rewrite loads and stores as 13 // appropriate. 14 // 15 //===----------------------------------------------------------------------===// 16 17 #include "llvm/ADT/ArrayRef.h" 18 #include "llvm/ADT/DenseMap.h" 19 #include "llvm/ADT/STLExtras.h" 20 #include "llvm/ADT/SmallPtrSet.h" 21 #include "llvm/ADT/SmallVector.h" 22 #include "llvm/ADT/Statistic.h" 23 #include "llvm/ADT/Twine.h" 24 #include "llvm/Analysis/AssumptionCache.h" 25 #include "llvm/Analysis/InstructionSimplify.h" 26 #include "llvm/Analysis/IteratedDominanceFrontier.h" 27 #include "llvm/Analysis/ValueTracking.h" 28 #include "llvm/IR/BasicBlock.h" 29 #include "llvm/IR/CFG.h" 30 #include "llvm/IR/Constant.h" 31 #include "llvm/IR/Constants.h" 32 #include "llvm/IR/DIBuilder.h" 33 #include "llvm/IR/DebugInfo.h" 34 #include "llvm/IR/DebugProgramInstruction.h" 35 #include "llvm/IR/Dominators.h" 36 #include "llvm/IR/Function.h" 37 #include "llvm/IR/InstrTypes.h" 38 #include "llvm/IR/Instruction.h" 39 #include "llvm/IR/Instructions.h" 40 #include "llvm/IR/IntrinsicInst.h" 41 #include "llvm/IR/Intrinsics.h" 42 #include "llvm/IR/LLVMContext.h" 43 #include "llvm/IR/Module.h" 44 #include "llvm/IR/Type.h" 45 #include "llvm/IR/User.h" 46 #include "llvm/Support/Casting.h" 47 #include "llvm/Transforms/Utils/Local.h" 48 #include "llvm/Transforms/Utils/PromoteMemToReg.h" 49 #include <algorithm> 50 #include <cassert> 51 #include <iterator> 52 #include <utility> 53 #include <vector> 54 55 using namespace llvm; 56 57 #define DEBUG_TYPE "mem2reg" 58 59 STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block"); 60 STATISTIC(NumSingleStore, "Number of alloca's promoted with a single store"); 61 STATISTIC(NumDeadAlloca, "Number of dead alloca's removed"); 62 STATISTIC(NumPHIInsert, "Number of PHI nodes inserted"); 63 64 bool llvm::isAllocaPromotable(const AllocaInst *AI) { 65 // Only allow direct and non-volatile loads and stores... 66 for (const User *U : AI->users()) { 67 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { 68 // Note that atomic loads can be transformed; atomic semantics do 69 // not have any meaning for a local alloca. 70 if (LI->isVolatile() || LI->getType() != AI->getAllocatedType()) 71 return false; 72 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) { 73 if (SI->getValueOperand() == AI || 74 SI->getValueOperand()->getType() != AI->getAllocatedType()) 75 return false; // Don't allow a store OF the AI, only INTO the AI. 76 // Note that atomic stores can be transformed; atomic semantics do 77 // not have any meaning for a local alloca. 78 if (SI->isVolatile()) 79 return false; 80 } else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) { 81 if (!II->isLifetimeStartOrEnd() && !II->isDroppable()) 82 return false; 83 } else if (const BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { 84 if (!onlyUsedByLifetimeMarkersOrDroppableInsts(BCI)) 85 return false; 86 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 87 if (!GEPI->hasAllZeroIndices()) 88 return false; 89 if (!onlyUsedByLifetimeMarkersOrDroppableInsts(GEPI)) 90 return false; 91 } else if (const AddrSpaceCastInst *ASCI = dyn_cast<AddrSpaceCastInst>(U)) { 92 if (!onlyUsedByLifetimeMarkers(ASCI)) 93 return false; 94 } else { 95 return false; 96 } 97 } 98 99 return true; 100 } 101 102 namespace { 103 104 static DPValue *createDebugValue(DIBuilder &DIB, Value *NewValue, 105 DILocalVariable *Variable, 106 DIExpression *Expression, const DILocation *DI, 107 DPValue *InsertBefore) { 108 (void)DIB; 109 return DPValue::createDPValue(NewValue, Variable, Expression, DI, 110 *InsertBefore); 111 } 112 static DbgValueInst *createDebugValue(DIBuilder &DIB, Value *NewValue, 113 DILocalVariable *Variable, 114 DIExpression *Expression, 115 const DILocation *DI, 116 Instruction *InsertBefore) { 117 return static_cast<DbgValueInst *>(DIB.insertDbgValueIntrinsic( 118 NewValue, Variable, Expression, DI, InsertBefore)); 119 } 120 121 /// Helper for updating assignment tracking debug info when promoting allocas. 122 class AssignmentTrackingInfo { 123 /// DbgAssignIntrinsics linked to the alloca with at most one per variable 124 /// fragment. (i.e. not be a comprehensive set if there are multiple 125 /// dbg.assigns for one variable fragment). 126 SmallVector<DbgVariableIntrinsic *> DbgAssigns; 127 SmallVector<DPValue *> DPVAssigns; 128 129 public: 130 void init(AllocaInst *AI) { 131 SmallSet<DebugVariable, 2> Vars; 132 for (DbgAssignIntrinsic *DAI : at::getAssignmentMarkers(AI)) { 133 if (Vars.insert(DebugVariable(DAI)).second) 134 DbgAssigns.push_back(DAI); 135 } 136 for (DPValue *DPV : at::getDPVAssignmentMarkers(AI)) { 137 if (Vars.insert(DebugVariable(DPV)).second) 138 DPVAssigns.push_back(DPV); 139 } 140 } 141 142 /// Update assignment tracking debug info given for the to-be-deleted store 143 /// \p ToDelete that stores to this alloca. 144 void 145 updateForDeletedStore(StoreInst *ToDelete, DIBuilder &DIB, 146 SmallSet<DbgAssignIntrinsic *, 8> *DbgAssignsToDelete, 147 SmallSet<DPValue *, 8> *DPVAssignsToDelete) const { 148 // There's nothing to do if the alloca doesn't have any variables using 149 // assignment tracking. 150 if (DbgAssigns.empty() && DPVAssigns.empty()) 151 return; 152 153 // Insert a dbg.value where the linked dbg.assign is and remember to delete 154 // the dbg.assign later. Demoting to dbg.value isn't necessary for 155 // correctness but does reduce compile time and memory usage by reducing 156 // unnecessary function-local metadata. Remember that we've seen a 157 // dbg.assign for each variable fragment for the untracked store handling 158 // (after this loop). 159 SmallSet<DebugVariableAggregate, 2> VarHasDbgAssignForStore; 160 auto InsertValueForAssign = [&](auto *DbgAssign, auto *&AssignList) { 161 VarHasDbgAssignForStore.insert(DebugVariableAggregate(DbgAssign)); 162 AssignList->insert(DbgAssign); 163 createDebugValue(DIB, DbgAssign->getValue(), DbgAssign->getVariable(), 164 DbgAssign->getExpression(), DbgAssign->getDebugLoc(), 165 DbgAssign); 166 }; 167 for (auto *Assign : at::getAssignmentMarkers(ToDelete)) 168 InsertValueForAssign(Assign, DbgAssignsToDelete); 169 for (auto *Assign : at::getDPVAssignmentMarkers(ToDelete)) 170 InsertValueForAssign(Assign, DPVAssignsToDelete); 171 172 // It's possible for variables using assignment tracking to have no 173 // dbg.assign linked to this store. These are variables in DbgAssigns that 174 // are missing from VarHasDbgAssignForStore. Since there isn't a dbg.assign 175 // to mark the assignment - and the store is going to be deleted - insert a 176 // dbg.value to do that now. An untracked store may be either one that 177 // cannot be represented using assignment tracking (non-const offset or 178 // size) or one that is trackable but has had its DIAssignID attachment 179 // dropped accidentally. 180 auto ConvertUnlinkedAssignToValue = [&](auto *Assign) { 181 if (VarHasDbgAssignForStore.contains(DebugVariableAggregate(Assign))) 182 return; 183 ConvertDebugDeclareToDebugValue(Assign, ToDelete, DIB); 184 }; 185 for_each(DbgAssigns, ConvertUnlinkedAssignToValue); 186 for_each(DPVAssigns, ConvertUnlinkedAssignToValue); 187 } 188 189 /// Update assignment tracking debug info given for the newly inserted PHI \p 190 /// NewPhi. 191 void updateForNewPhi(PHINode *NewPhi, DIBuilder &DIB) const { 192 // Regardless of the position of dbg.assigns relative to stores, the 193 // incoming values into a new PHI should be the same for the (imaginary) 194 // debug-phi. 195 for (auto *DAI : DbgAssigns) 196 ConvertDebugDeclareToDebugValue(DAI, NewPhi, DIB); 197 for (auto *DPV : DPVAssigns) 198 ConvertDebugDeclareToDebugValue(DPV, NewPhi, DIB); 199 } 200 201 void clear() { 202 DbgAssigns.clear(); 203 DPVAssigns.clear(); 204 } 205 bool empty() { return DbgAssigns.empty() && DPVAssigns.empty(); } 206 }; 207 208 struct AllocaInfo { 209 using DbgUserVec = SmallVector<DbgVariableIntrinsic *, 1>; 210 using DPUserVec = SmallVector<DPValue *, 1>; 211 212 SmallVector<BasicBlock *, 32> DefiningBlocks; 213 SmallVector<BasicBlock *, 32> UsingBlocks; 214 215 StoreInst *OnlyStore; 216 BasicBlock *OnlyBlock; 217 bool OnlyUsedInOneBlock; 218 219 /// Debug users of the alloca - does not include dbg.assign intrinsics. 220 DbgUserVec DbgUsers; 221 DPUserVec DPUsers; 222 /// Helper to update assignment tracking debug info. 223 AssignmentTrackingInfo AssignmentTracking; 224 225 void clear() { 226 DefiningBlocks.clear(); 227 UsingBlocks.clear(); 228 OnlyStore = nullptr; 229 OnlyBlock = nullptr; 230 OnlyUsedInOneBlock = true; 231 DbgUsers.clear(); 232 DPUsers.clear(); 233 AssignmentTracking.clear(); 234 } 235 236 /// Scan the uses of the specified alloca, filling in the AllocaInfo used 237 /// by the rest of the pass to reason about the uses of this alloca. 238 void AnalyzeAlloca(AllocaInst *AI) { 239 clear(); 240 241 // As we scan the uses of the alloca instruction, keep track of stores, 242 // and decide whether all of the loads and stores to the alloca are within 243 // the same basic block. 244 for (User *U : AI->users()) { 245 Instruction *User = cast<Instruction>(U); 246 247 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 248 // Remember the basic blocks which define new values for the alloca 249 DefiningBlocks.push_back(SI->getParent()); 250 OnlyStore = SI; 251 } else { 252 LoadInst *LI = cast<LoadInst>(User); 253 // Otherwise it must be a load instruction, keep track of variable 254 // reads. 255 UsingBlocks.push_back(LI->getParent()); 256 } 257 258 if (OnlyUsedInOneBlock) { 259 if (!OnlyBlock) 260 OnlyBlock = User->getParent(); 261 else if (OnlyBlock != User->getParent()) 262 OnlyUsedInOneBlock = false; 263 } 264 } 265 DbgUserVec AllDbgUsers; 266 SmallVector<DPValue *> AllDPUsers; 267 findDbgUsers(AllDbgUsers, AI, &AllDPUsers); 268 std::copy_if(AllDbgUsers.begin(), AllDbgUsers.end(), 269 std::back_inserter(DbgUsers), [](DbgVariableIntrinsic *DII) { 270 return !isa<DbgAssignIntrinsic>(DII); 271 }); 272 std::copy_if(AllDPUsers.begin(), AllDPUsers.end(), 273 std::back_inserter(DPUsers), 274 [](DPValue *DPV) { return !DPV->isDbgAssign(); }); 275 AssignmentTracking.init(AI); 276 } 277 }; 278 279 /// Data package used by RenamePass(). 280 struct RenamePassData { 281 using ValVector = std::vector<Value *>; 282 using LocationVector = std::vector<DebugLoc>; 283 284 RenamePassData(BasicBlock *B, BasicBlock *P, ValVector V, LocationVector L) 285 : BB(B), Pred(P), Values(std::move(V)), Locations(std::move(L)) {} 286 287 BasicBlock *BB; 288 BasicBlock *Pred; 289 ValVector Values; 290 LocationVector Locations; 291 }; 292 293 /// This assigns and keeps a per-bb relative ordering of load/store 294 /// instructions in the block that directly load or store an alloca. 295 /// 296 /// This functionality is important because it avoids scanning large basic 297 /// blocks multiple times when promoting many allocas in the same block. 298 class LargeBlockInfo { 299 /// For each instruction that we track, keep the index of the 300 /// instruction. 301 /// 302 /// The index starts out as the number of the instruction from the start of 303 /// the block. 304 DenseMap<const Instruction *, unsigned> InstNumbers; 305 306 public: 307 308 /// This code only looks at accesses to allocas. 309 static bool isInterestingInstruction(const Instruction *I) { 310 return (isa<LoadInst>(I) && isa<AllocaInst>(I->getOperand(0))) || 311 (isa<StoreInst>(I) && isa<AllocaInst>(I->getOperand(1))); 312 } 313 314 /// Get or calculate the index of the specified instruction. 315 unsigned getInstructionIndex(const Instruction *I) { 316 assert(isInterestingInstruction(I) && 317 "Not a load/store to/from an alloca?"); 318 319 // If we already have this instruction number, return it. 320 DenseMap<const Instruction *, unsigned>::iterator It = InstNumbers.find(I); 321 if (It != InstNumbers.end()) 322 return It->second; 323 324 // Scan the whole block to get the instruction. This accumulates 325 // information for every interesting instruction in the block, in order to 326 // avoid gratuitus rescans. 327 const BasicBlock *BB = I->getParent(); 328 unsigned InstNo = 0; 329 for (const Instruction &BBI : *BB) 330 if (isInterestingInstruction(&BBI)) 331 InstNumbers[&BBI] = InstNo++; 332 It = InstNumbers.find(I); 333 334 assert(It != InstNumbers.end() && "Didn't insert instruction?"); 335 return It->second; 336 } 337 338 void deleteValue(const Instruction *I) { InstNumbers.erase(I); } 339 340 void clear() { InstNumbers.clear(); } 341 }; 342 343 struct PromoteMem2Reg { 344 /// The alloca instructions being promoted. 345 std::vector<AllocaInst *> Allocas; 346 347 DominatorTree &DT; 348 DIBuilder DIB; 349 350 /// A cache of @llvm.assume intrinsics used by SimplifyInstruction. 351 AssumptionCache *AC; 352 353 const SimplifyQuery SQ; 354 355 /// Reverse mapping of Allocas. 356 DenseMap<AllocaInst *, unsigned> AllocaLookup; 357 358 /// The PhiNodes we're adding. 359 /// 360 /// That map is used to simplify some Phi nodes as we iterate over it, so 361 /// it should have deterministic iterators. We could use a MapVector, but 362 /// since we already maintain a map from BasicBlock* to a stable numbering 363 /// (BBNumbers), the DenseMap is more efficient (also supports removal). 364 DenseMap<std::pair<unsigned, unsigned>, PHINode *> NewPhiNodes; 365 366 /// For each PHI node, keep track of which entry in Allocas it corresponds 367 /// to. 368 DenseMap<PHINode *, unsigned> PhiToAllocaMap; 369 370 /// For each alloca, we keep track of the dbg.declare intrinsic that 371 /// describes it, if any, so that we can convert it to a dbg.value 372 /// intrinsic if the alloca gets promoted. 373 SmallVector<AllocaInfo::DbgUserVec, 8> AllocaDbgUsers; 374 SmallVector<AllocaInfo::DPUserVec, 8> AllocaDPUsers; 375 376 /// For each alloca, keep an instance of a helper class that gives us an easy 377 /// way to update assignment tracking debug info if the alloca is promoted. 378 SmallVector<AssignmentTrackingInfo, 8> AllocaATInfo; 379 /// A set of dbg.assigns to delete because they've been demoted to 380 /// dbg.values. Call cleanUpDbgAssigns to delete them. 381 SmallSet<DbgAssignIntrinsic *, 8> DbgAssignsToDelete; 382 SmallSet<DPValue *, 8> DPVAssignsToDelete; 383 384 /// The set of basic blocks the renamer has already visited. 385 SmallPtrSet<BasicBlock *, 16> Visited; 386 387 /// Contains a stable numbering of basic blocks to avoid non-determinstic 388 /// behavior. 389 DenseMap<BasicBlock *, unsigned> BBNumbers; 390 391 /// Lazily compute the number of predecessors a block has. 392 DenseMap<const BasicBlock *, unsigned> BBNumPreds; 393 394 public: 395 PromoteMem2Reg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT, 396 AssumptionCache *AC) 397 : Allocas(Allocas.begin(), Allocas.end()), DT(DT), 398 DIB(*DT.getRoot()->getParent()->getParent(), /*AllowUnresolved*/ false), 399 AC(AC), SQ(DT.getRoot()->getParent()->getParent()->getDataLayout(), 400 nullptr, &DT, AC) {} 401 402 void run(); 403 404 private: 405 void RemoveFromAllocasList(unsigned &AllocaIdx) { 406 Allocas[AllocaIdx] = Allocas.back(); 407 Allocas.pop_back(); 408 --AllocaIdx; 409 } 410 411 unsigned getNumPreds(const BasicBlock *BB) { 412 unsigned &NP = BBNumPreds[BB]; 413 if (NP == 0) 414 NP = pred_size(BB) + 1; 415 return NP - 1; 416 } 417 418 void ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info, 419 const SmallPtrSetImpl<BasicBlock *> &DefBlocks, 420 SmallPtrSetImpl<BasicBlock *> &LiveInBlocks); 421 void RenamePass(BasicBlock *BB, BasicBlock *Pred, 422 RenamePassData::ValVector &IncVals, 423 RenamePassData::LocationVector &IncLocs, 424 std::vector<RenamePassData> &Worklist); 425 bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version); 426 427 /// Delete dbg.assigns that have been demoted to dbg.values. 428 void cleanUpDbgAssigns() { 429 for (auto *DAI : DbgAssignsToDelete) 430 DAI->eraseFromParent(); 431 DbgAssignsToDelete.clear(); 432 for (auto *DPV : DPVAssignsToDelete) 433 DPV->eraseFromParent(); 434 DPVAssignsToDelete.clear(); 435 } 436 }; 437 438 } // end anonymous namespace 439 440 /// Given a LoadInst LI this adds assume(LI != null) after it. 441 static void addAssumeNonNull(AssumptionCache *AC, LoadInst *LI) { 442 Function *AssumeIntrinsic = 443 Intrinsic::getDeclaration(LI->getModule(), Intrinsic::assume); 444 ICmpInst *LoadNotNull = new ICmpInst(ICmpInst::ICMP_NE, LI, 445 Constant::getNullValue(LI->getType())); 446 LoadNotNull->insertAfter(LI); 447 CallInst *CI = CallInst::Create(AssumeIntrinsic, {LoadNotNull}); 448 CI->insertAfter(LoadNotNull); 449 AC->registerAssumption(cast<AssumeInst>(CI)); 450 } 451 452 static void convertMetadataToAssumes(LoadInst *LI, Value *Val, 453 const DataLayout &DL, AssumptionCache *AC, 454 const DominatorTree *DT) { 455 // If the load was marked as nonnull we don't want to lose that information 456 // when we erase this Load. So we preserve it with an assume. As !nonnull 457 // returns poison while assume violations are immediate undefined behavior, 458 // we can only do this if the value is known non-poison. 459 if (AC && LI->getMetadata(LLVMContext::MD_nonnull) && 460 LI->getMetadata(LLVMContext::MD_noundef) && 461 !isKnownNonZero(Val, DL, 0, AC, LI, DT)) 462 addAssumeNonNull(AC, LI); 463 } 464 465 static void removeIntrinsicUsers(AllocaInst *AI) { 466 // Knowing that this alloca is promotable, we know that it's safe to kill all 467 // instructions except for load and store. 468 469 for (Use &U : llvm::make_early_inc_range(AI->uses())) { 470 Instruction *I = cast<Instruction>(U.getUser()); 471 if (isa<LoadInst>(I) || isa<StoreInst>(I)) 472 continue; 473 474 // Drop the use of AI in droppable instructions. 475 if (I->isDroppable()) { 476 I->dropDroppableUse(U); 477 continue; 478 } 479 480 if (!I->getType()->isVoidTy()) { 481 // The only users of this bitcast/GEP instruction are lifetime intrinsics. 482 // Follow the use/def chain to erase them now instead of leaving it for 483 // dead code elimination later. 484 for (Use &UU : llvm::make_early_inc_range(I->uses())) { 485 Instruction *Inst = cast<Instruction>(UU.getUser()); 486 487 // Drop the use of I in droppable instructions. 488 if (Inst->isDroppable()) { 489 Inst->dropDroppableUse(UU); 490 continue; 491 } 492 Inst->eraseFromParent(); 493 } 494 } 495 I->eraseFromParent(); 496 } 497 } 498 499 /// Rewrite as many loads as possible given a single store. 500 /// 501 /// When there is only a single store, we can use the domtree to trivially 502 /// replace all of the dominated loads with the stored value. Do so, and return 503 /// true if this has successfully promoted the alloca entirely. If this returns 504 /// false there were some loads which were not dominated by the single store 505 /// and thus must be phi-ed with undef. We fall back to the standard alloca 506 /// promotion algorithm in that case. 507 static bool 508 rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info, LargeBlockInfo &LBI, 509 const DataLayout &DL, DominatorTree &DT, 510 AssumptionCache *AC, 511 SmallSet<DbgAssignIntrinsic *, 8> *DbgAssignsToDelete, 512 SmallSet<DPValue *, 8> *DPVAssignsToDelete) { 513 StoreInst *OnlyStore = Info.OnlyStore; 514 bool StoringGlobalVal = !isa<Instruction>(OnlyStore->getOperand(0)); 515 BasicBlock *StoreBB = OnlyStore->getParent(); 516 int StoreIndex = -1; 517 518 // Clear out UsingBlocks. We will reconstruct it here if needed. 519 Info.UsingBlocks.clear(); 520 521 for (User *U : make_early_inc_range(AI->users())) { 522 Instruction *UserInst = cast<Instruction>(U); 523 if (UserInst == OnlyStore) 524 continue; 525 LoadInst *LI = cast<LoadInst>(UserInst); 526 527 // Okay, if we have a load from the alloca, we want to replace it with the 528 // only value stored to the alloca. We can do this if the value is 529 // dominated by the store. If not, we use the rest of the mem2reg machinery 530 // to insert the phi nodes as needed. 531 if (!StoringGlobalVal) { // Non-instructions are always dominated. 532 if (LI->getParent() == StoreBB) { 533 // If we have a use that is in the same block as the store, compare the 534 // indices of the two instructions to see which one came first. If the 535 // load came before the store, we can't handle it. 536 if (StoreIndex == -1) 537 StoreIndex = LBI.getInstructionIndex(OnlyStore); 538 539 if (unsigned(StoreIndex) > LBI.getInstructionIndex(LI)) { 540 // Can't handle this load, bail out. 541 Info.UsingBlocks.push_back(StoreBB); 542 continue; 543 } 544 } else if (!DT.dominates(StoreBB, LI->getParent())) { 545 // If the load and store are in different blocks, use BB dominance to 546 // check their relationships. If the store doesn't dom the use, bail 547 // out. 548 Info.UsingBlocks.push_back(LI->getParent()); 549 continue; 550 } 551 } 552 553 // Otherwise, we *can* safely rewrite this load. 554 Value *ReplVal = OnlyStore->getOperand(0); 555 // If the replacement value is the load, this must occur in unreachable 556 // code. 557 if (ReplVal == LI) 558 ReplVal = PoisonValue::get(LI->getType()); 559 560 convertMetadataToAssumes(LI, ReplVal, DL, AC, &DT); 561 LI->replaceAllUsesWith(ReplVal); 562 LI->eraseFromParent(); 563 LBI.deleteValue(LI); 564 } 565 566 // Finally, after the scan, check to see if the store is all that is left. 567 if (!Info.UsingBlocks.empty()) 568 return false; // If not, we'll have to fall back for the remainder. 569 570 DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false); 571 // Update assignment tracking info for the store we're going to delete. 572 Info.AssignmentTracking.updateForDeletedStore( 573 Info.OnlyStore, DIB, DbgAssignsToDelete, DPVAssignsToDelete); 574 575 // Record debuginfo for the store and remove the declaration's 576 // debuginfo. 577 auto ConvertDebugInfoForStore = [&](auto &Container) { 578 for (auto *DbgItem : Container) { 579 if (DbgItem->isAddressOfVariable()) { 580 ConvertDebugDeclareToDebugValue(DbgItem, Info.OnlyStore, DIB); 581 DbgItem->eraseFromParent(); 582 } else if (DbgItem->getExpression()->startsWithDeref()) { 583 DbgItem->eraseFromParent(); 584 } 585 } 586 }; 587 ConvertDebugInfoForStore(Info.DbgUsers); 588 ConvertDebugInfoForStore(Info.DPUsers); 589 590 // Remove dbg.assigns linked to the alloca as these are now redundant. 591 at::deleteAssignmentMarkers(AI); 592 593 // Remove the (now dead) store and alloca. 594 Info.OnlyStore->eraseFromParent(); 595 LBI.deleteValue(Info.OnlyStore); 596 597 AI->eraseFromParent(); 598 return true; 599 } 600 601 /// Many allocas are only used within a single basic block. If this is the 602 /// case, avoid traversing the CFG and inserting a lot of potentially useless 603 /// PHI nodes by just performing a single linear pass over the basic block 604 /// using the Alloca. 605 /// 606 /// If we cannot promote this alloca (because it is read before it is written), 607 /// return false. This is necessary in cases where, due to control flow, the 608 /// alloca is undefined only on some control flow paths. e.g. code like 609 /// this is correct in LLVM IR: 610 /// // A is an alloca with no stores so far 611 /// for (...) { 612 /// int t = *A; 613 /// if (!first_iteration) 614 /// use(t); 615 /// *A = 42; 616 /// } 617 static bool 618 promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info, 619 LargeBlockInfo &LBI, const DataLayout &DL, 620 DominatorTree &DT, AssumptionCache *AC, 621 SmallSet<DbgAssignIntrinsic *, 8> *DbgAssignsToDelete, 622 SmallSet<DPValue *, 8> *DPVAssignsToDelete) { 623 // The trickiest case to handle is when we have large blocks. Because of this, 624 // this code is optimized assuming that large blocks happen. This does not 625 // significantly pessimize the small block case. This uses LargeBlockInfo to 626 // make it efficient to get the index of various operations in the block. 627 628 // Walk the use-def list of the alloca, getting the locations of all stores. 629 using StoresByIndexTy = SmallVector<std::pair<unsigned, StoreInst *>, 64>; 630 StoresByIndexTy StoresByIndex; 631 632 for (User *U : AI->users()) 633 if (StoreInst *SI = dyn_cast<StoreInst>(U)) 634 StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI)); 635 636 // Sort the stores by their index, making it efficient to do a lookup with a 637 // binary search. 638 llvm::sort(StoresByIndex, less_first()); 639 640 // Walk all of the loads from this alloca, replacing them with the nearest 641 // store above them, if any. 642 for (User *U : make_early_inc_range(AI->users())) { 643 LoadInst *LI = dyn_cast<LoadInst>(U); 644 if (!LI) 645 continue; 646 647 unsigned LoadIdx = LBI.getInstructionIndex(LI); 648 649 // Find the nearest store that has a lower index than this load. 650 StoresByIndexTy::iterator I = llvm::lower_bound( 651 StoresByIndex, 652 std::make_pair(LoadIdx, static_cast<StoreInst *>(nullptr)), 653 less_first()); 654 Value *ReplVal; 655 if (I == StoresByIndex.begin()) { 656 if (StoresByIndex.empty()) 657 // If there are no stores, the load takes the undef value. 658 ReplVal = UndefValue::get(LI->getType()); 659 else 660 // There is no store before this load, bail out (load may be affected 661 // by the following stores - see main comment). 662 return false; 663 } else { 664 // Otherwise, there was a store before this load, the load takes its 665 // value. 666 ReplVal = std::prev(I)->second->getOperand(0); 667 } 668 669 convertMetadataToAssumes(LI, ReplVal, DL, AC, &DT); 670 671 // If the replacement value is the load, this must occur in unreachable 672 // code. 673 if (ReplVal == LI) 674 ReplVal = PoisonValue::get(LI->getType()); 675 676 LI->replaceAllUsesWith(ReplVal); 677 LI->eraseFromParent(); 678 LBI.deleteValue(LI); 679 } 680 681 // Remove the (now dead) stores and alloca. 682 DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false); 683 while (!AI->use_empty()) { 684 StoreInst *SI = cast<StoreInst>(AI->user_back()); 685 // Update assignment tracking info for the store we're going to delete. 686 Info.AssignmentTracking.updateForDeletedStore(SI, DIB, DbgAssignsToDelete, 687 DPVAssignsToDelete); 688 // Record debuginfo for the store before removing it. 689 auto DbgUpdateForStore = [&](auto &Container) { 690 for (auto *DbgItem : Container) { 691 if (DbgItem->isAddressOfVariable()) { 692 ConvertDebugDeclareToDebugValue(DbgItem, SI, DIB); 693 } 694 } 695 }; 696 DbgUpdateForStore(Info.DbgUsers); 697 DbgUpdateForStore(Info.DPUsers); 698 699 SI->eraseFromParent(); 700 LBI.deleteValue(SI); 701 } 702 703 // Remove dbg.assigns linked to the alloca as these are now redundant. 704 at::deleteAssignmentMarkers(AI); 705 AI->eraseFromParent(); 706 707 // The alloca's debuginfo can be removed as well. 708 auto DbgUpdateForAlloca = [&](auto &Container) { 709 for (auto *DbgItem : Container) 710 if (DbgItem->isAddressOfVariable() || 711 DbgItem->getExpression()->startsWithDeref()) 712 DbgItem->eraseFromParent(); 713 }; 714 DbgUpdateForAlloca(Info.DbgUsers); 715 DbgUpdateForAlloca(Info.DPUsers); 716 717 ++NumLocalPromoted; 718 return true; 719 } 720 721 void PromoteMem2Reg::run() { 722 Function &F = *DT.getRoot()->getParent(); 723 724 AllocaDbgUsers.resize(Allocas.size()); 725 AllocaATInfo.resize(Allocas.size()); 726 AllocaDPUsers.resize(Allocas.size()); 727 728 AllocaInfo Info; 729 LargeBlockInfo LBI; 730 ForwardIDFCalculator IDF(DT); 731 732 for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) { 733 AllocaInst *AI = Allocas[AllocaNum]; 734 735 assert(isAllocaPromotable(AI) && "Cannot promote non-promotable alloca!"); 736 assert(AI->getParent()->getParent() == &F && 737 "All allocas should be in the same function, which is same as DF!"); 738 739 removeIntrinsicUsers(AI); 740 741 if (AI->use_empty()) { 742 // If there are no uses of the alloca, just delete it now. 743 AI->eraseFromParent(); 744 745 // Remove the alloca from the Allocas list, since it has been processed 746 RemoveFromAllocasList(AllocaNum); 747 ++NumDeadAlloca; 748 continue; 749 } 750 751 // Calculate the set of read and write-locations for each alloca. This is 752 // analogous to finding the 'uses' and 'definitions' of each variable. 753 Info.AnalyzeAlloca(AI); 754 755 // If there is only a single store to this value, replace any loads of 756 // it that are directly dominated by the definition with the value stored. 757 if (Info.DefiningBlocks.size() == 1) { 758 if (rewriteSingleStoreAlloca(AI, Info, LBI, SQ.DL, DT, AC, 759 &DbgAssignsToDelete, &DPVAssignsToDelete)) { 760 // The alloca has been processed, move on. 761 RemoveFromAllocasList(AllocaNum); 762 ++NumSingleStore; 763 continue; 764 } 765 } 766 767 // If the alloca is only read and written in one basic block, just perform a 768 // linear sweep over the block to eliminate it. 769 if (Info.OnlyUsedInOneBlock && 770 promoteSingleBlockAlloca(AI, Info, LBI, SQ.DL, DT, AC, 771 &DbgAssignsToDelete, &DPVAssignsToDelete)) { 772 // The alloca has been processed, move on. 773 RemoveFromAllocasList(AllocaNum); 774 continue; 775 } 776 777 // If we haven't computed a numbering for the BB's in the function, do so 778 // now. 779 if (BBNumbers.empty()) { 780 unsigned ID = 0; 781 for (auto &BB : F) 782 BBNumbers[&BB] = ID++; 783 } 784 785 // Remember the dbg.declare intrinsic describing this alloca, if any. 786 if (!Info.DbgUsers.empty()) 787 AllocaDbgUsers[AllocaNum] = Info.DbgUsers; 788 if (!Info.AssignmentTracking.empty()) 789 AllocaATInfo[AllocaNum] = Info.AssignmentTracking; 790 if (!Info.DPUsers.empty()) 791 AllocaDPUsers[AllocaNum] = Info.DPUsers; 792 793 // Keep the reverse mapping of the 'Allocas' array for the rename pass. 794 AllocaLookup[Allocas[AllocaNum]] = AllocaNum; 795 796 // Unique the set of defining blocks for efficient lookup. 797 SmallPtrSet<BasicBlock *, 32> DefBlocks(Info.DefiningBlocks.begin(), 798 Info.DefiningBlocks.end()); 799 800 // Determine which blocks the value is live in. These are blocks which lead 801 // to uses. 802 SmallPtrSet<BasicBlock *, 32> LiveInBlocks; 803 ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks); 804 805 // At this point, we're committed to promoting the alloca using IDF's, and 806 // the standard SSA construction algorithm. Determine which blocks need phi 807 // nodes and see if we can optimize out some work by avoiding insertion of 808 // dead phi nodes. 809 IDF.setLiveInBlocks(LiveInBlocks); 810 IDF.setDefiningBlocks(DefBlocks); 811 SmallVector<BasicBlock *, 32> PHIBlocks; 812 IDF.calculate(PHIBlocks); 813 llvm::sort(PHIBlocks, [this](BasicBlock *A, BasicBlock *B) { 814 return BBNumbers.find(A)->second < BBNumbers.find(B)->second; 815 }); 816 817 unsigned CurrentVersion = 0; 818 for (BasicBlock *BB : PHIBlocks) 819 QueuePhiNode(BB, AllocaNum, CurrentVersion); 820 } 821 822 if (Allocas.empty()) { 823 cleanUpDbgAssigns(); 824 return; // All of the allocas must have been trivial! 825 } 826 LBI.clear(); 827 828 // Set the incoming values for the basic block to be null values for all of 829 // the alloca's. We do this in case there is a load of a value that has not 830 // been stored yet. In this case, it will get this null value. 831 RenamePassData::ValVector Values(Allocas.size()); 832 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) 833 Values[i] = UndefValue::get(Allocas[i]->getAllocatedType()); 834 835 // When handling debug info, treat all incoming values as if they have unknown 836 // locations until proven otherwise. 837 RenamePassData::LocationVector Locations(Allocas.size()); 838 839 // Walks all basic blocks in the function performing the SSA rename algorithm 840 // and inserting the phi nodes we marked as necessary 841 std::vector<RenamePassData> RenamePassWorkList; 842 RenamePassWorkList.emplace_back(&F.front(), nullptr, std::move(Values), 843 std::move(Locations)); 844 do { 845 RenamePassData RPD = std::move(RenamePassWorkList.back()); 846 RenamePassWorkList.pop_back(); 847 // RenamePass may add new worklist entries. 848 RenamePass(RPD.BB, RPD.Pred, RPD.Values, RPD.Locations, RenamePassWorkList); 849 } while (!RenamePassWorkList.empty()); 850 851 // The renamer uses the Visited set to avoid infinite loops. Clear it now. 852 Visited.clear(); 853 854 // Remove the allocas themselves from the function. 855 for (Instruction *A : Allocas) { 856 // Remove dbg.assigns linked to the alloca as these are now redundant. 857 at::deleteAssignmentMarkers(A); 858 // If there are any uses of the alloca instructions left, they must be in 859 // unreachable basic blocks that were not processed by walking the dominator 860 // tree. Just delete the users now. 861 if (!A->use_empty()) 862 A->replaceAllUsesWith(PoisonValue::get(A->getType())); 863 A->eraseFromParent(); 864 } 865 866 // Remove alloca's dbg.declare intrinsics from the function. 867 auto RemoveDbgDeclares = [&](auto &Container) { 868 for (auto &DbgUsers : Container) { 869 for (auto *DbgItem : DbgUsers) 870 if (DbgItem->isAddressOfVariable() || 871 DbgItem->getExpression()->startsWithDeref()) 872 DbgItem->eraseFromParent(); 873 } 874 }; 875 RemoveDbgDeclares(AllocaDbgUsers); 876 RemoveDbgDeclares(AllocaDPUsers); 877 878 // Loop over all of the PHI nodes and see if there are any that we can get 879 // rid of because they merge all of the same incoming values. This can 880 // happen due to undef values coming into the PHI nodes. This process is 881 // iterative, because eliminating one PHI node can cause others to be removed. 882 bool EliminatedAPHI = true; 883 while (EliminatedAPHI) { 884 EliminatedAPHI = false; 885 886 // Iterating over NewPhiNodes is deterministic, so it is safe to try to 887 // simplify and RAUW them as we go. If it was not, we could add uses to 888 // the values we replace with in a non-deterministic order, thus creating 889 // non-deterministic def->use chains. 890 for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator 891 I = NewPhiNodes.begin(), 892 E = NewPhiNodes.end(); 893 I != E;) { 894 PHINode *PN = I->second; 895 896 // If this PHI node merges one value and/or undefs, get the value. 897 if (Value *V = simplifyInstruction(PN, SQ)) { 898 PN->replaceAllUsesWith(V); 899 PN->eraseFromParent(); 900 NewPhiNodes.erase(I++); 901 EliminatedAPHI = true; 902 continue; 903 } 904 ++I; 905 } 906 } 907 908 // At this point, the renamer has added entries to PHI nodes for all reachable 909 // code. Unfortunately, there may be unreachable blocks which the renamer 910 // hasn't traversed. If this is the case, the PHI nodes may not 911 // have incoming values for all predecessors. Loop over all PHI nodes we have 912 // created, inserting poison values if they are missing any incoming values. 913 for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator 914 I = NewPhiNodes.begin(), 915 E = NewPhiNodes.end(); 916 I != E; ++I) { 917 // We want to do this once per basic block. As such, only process a block 918 // when we find the PHI that is the first entry in the block. 919 PHINode *SomePHI = I->second; 920 BasicBlock *BB = SomePHI->getParent(); 921 if (&BB->front() != SomePHI) 922 continue; 923 924 // Only do work here if there the PHI nodes are missing incoming values. We 925 // know that all PHI nodes that were inserted in a block will have the same 926 // number of incoming values, so we can just check any of them. 927 if (SomePHI->getNumIncomingValues() == getNumPreds(BB)) 928 continue; 929 930 // Get the preds for BB. 931 SmallVector<BasicBlock *, 16> Preds(predecessors(BB)); 932 933 // Ok, now we know that all of the PHI nodes are missing entries for some 934 // basic blocks. Start by sorting the incoming predecessors for efficient 935 // access. 936 auto CompareBBNumbers = [this](BasicBlock *A, BasicBlock *B) { 937 return BBNumbers.find(A)->second < BBNumbers.find(B)->second; 938 }; 939 llvm::sort(Preds, CompareBBNumbers); 940 941 // Now we loop through all BB's which have entries in SomePHI and remove 942 // them from the Preds list. 943 for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) { 944 // Do a log(n) search of the Preds list for the entry we want. 945 SmallVectorImpl<BasicBlock *>::iterator EntIt = llvm::lower_bound( 946 Preds, SomePHI->getIncomingBlock(i), CompareBBNumbers); 947 assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i) && 948 "PHI node has entry for a block which is not a predecessor!"); 949 950 // Remove the entry 951 Preds.erase(EntIt); 952 } 953 954 // At this point, the blocks left in the preds list must have dummy 955 // entries inserted into every PHI nodes for the block. Update all the phi 956 // nodes in this block that we are inserting (there could be phis before 957 // mem2reg runs). 958 unsigned NumBadPreds = SomePHI->getNumIncomingValues(); 959 BasicBlock::iterator BBI = BB->begin(); 960 while ((SomePHI = dyn_cast<PHINode>(BBI++)) && 961 SomePHI->getNumIncomingValues() == NumBadPreds) { 962 Value *PoisonVal = PoisonValue::get(SomePHI->getType()); 963 for (BasicBlock *Pred : Preds) 964 SomePHI->addIncoming(PoisonVal, Pred); 965 } 966 } 967 968 NewPhiNodes.clear(); 969 cleanUpDbgAssigns(); 970 } 971 972 /// Determine which blocks the value is live in. 973 /// 974 /// These are blocks which lead to uses. Knowing this allows us to avoid 975 /// inserting PHI nodes into blocks which don't lead to uses (thus, the 976 /// inserted phi nodes would be dead). 977 void PromoteMem2Reg::ComputeLiveInBlocks( 978 AllocaInst *AI, AllocaInfo &Info, 979 const SmallPtrSetImpl<BasicBlock *> &DefBlocks, 980 SmallPtrSetImpl<BasicBlock *> &LiveInBlocks) { 981 // To determine liveness, we must iterate through the predecessors of blocks 982 // where the def is live. Blocks are added to the worklist if we need to 983 // check their predecessors. Start with all the using blocks. 984 SmallVector<BasicBlock *, 64> LiveInBlockWorklist(Info.UsingBlocks.begin(), 985 Info.UsingBlocks.end()); 986 987 // If any of the using blocks is also a definition block, check to see if the 988 // definition occurs before or after the use. If it happens before the use, 989 // the value isn't really live-in. 990 for (unsigned i = 0, e = LiveInBlockWorklist.size(); i != e; ++i) { 991 BasicBlock *BB = LiveInBlockWorklist[i]; 992 if (!DefBlocks.count(BB)) 993 continue; 994 995 // Okay, this is a block that both uses and defines the value. If the first 996 // reference to the alloca is a def (store), then we know it isn't live-in. 997 for (BasicBlock::iterator I = BB->begin();; ++I) { 998 if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 999 if (SI->getOperand(1) != AI) 1000 continue; 1001 1002 // We found a store to the alloca before a load. The alloca is not 1003 // actually live-in here. 1004 LiveInBlockWorklist[i] = LiveInBlockWorklist.back(); 1005 LiveInBlockWorklist.pop_back(); 1006 --i; 1007 --e; 1008 break; 1009 } 1010 1011 if (LoadInst *LI = dyn_cast<LoadInst>(I)) 1012 // Okay, we found a load before a store to the alloca. It is actually 1013 // live into this block. 1014 if (LI->getOperand(0) == AI) 1015 break; 1016 } 1017 } 1018 1019 // Now that we have a set of blocks where the phi is live-in, recursively add 1020 // their predecessors until we find the full region the value is live. 1021 while (!LiveInBlockWorklist.empty()) { 1022 BasicBlock *BB = LiveInBlockWorklist.pop_back_val(); 1023 1024 // The block really is live in here, insert it into the set. If already in 1025 // the set, then it has already been processed. 1026 if (!LiveInBlocks.insert(BB).second) 1027 continue; 1028 1029 // Since the value is live into BB, it is either defined in a predecessor or 1030 // live into it to. Add the preds to the worklist unless they are a 1031 // defining block. 1032 for (BasicBlock *P : predecessors(BB)) { 1033 // The value is not live into a predecessor if it defines the value. 1034 if (DefBlocks.count(P)) 1035 continue; 1036 1037 // Otherwise it is, add to the worklist. 1038 LiveInBlockWorklist.push_back(P); 1039 } 1040 } 1041 } 1042 1043 /// Queue a phi-node to be added to a basic-block for a specific Alloca. 1044 /// 1045 /// Returns true if there wasn't already a phi-node for that variable 1046 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo, 1047 unsigned &Version) { 1048 // Look up the basic-block in question. 1049 PHINode *&PN = NewPhiNodes[std::make_pair(BBNumbers[BB], AllocaNo)]; 1050 1051 // If the BB already has a phi node added for the i'th alloca then we're done! 1052 if (PN) 1053 return false; 1054 1055 // Create a PhiNode using the dereferenced type... and add the phi-node to the 1056 // BasicBlock. 1057 PN = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(), getNumPreds(BB), 1058 Allocas[AllocaNo]->getName() + "." + Twine(Version++)); 1059 PN->insertBefore(BB->begin()); 1060 ++NumPHIInsert; 1061 PhiToAllocaMap[PN] = AllocaNo; 1062 return true; 1063 } 1064 1065 /// Update the debug location of a phi. \p ApplyMergedLoc indicates whether to 1066 /// create a merged location incorporating \p DL, or to set \p DL directly. 1067 static void updateForIncomingValueLocation(PHINode *PN, DebugLoc DL, 1068 bool ApplyMergedLoc) { 1069 if (ApplyMergedLoc) 1070 PN->applyMergedLocation(PN->getDebugLoc(), DL); 1071 else 1072 PN->setDebugLoc(DL); 1073 } 1074 1075 /// Recursively traverse the CFG of the function, renaming loads and 1076 /// stores to the allocas which we are promoting. 1077 /// 1078 /// IncomingVals indicates what value each Alloca contains on exit from the 1079 /// predecessor block Pred. 1080 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred, 1081 RenamePassData::ValVector &IncomingVals, 1082 RenamePassData::LocationVector &IncomingLocs, 1083 std::vector<RenamePassData> &Worklist) { 1084 NextIteration: 1085 // If we are inserting any phi nodes into this BB, they will already be in the 1086 // block. 1087 if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) { 1088 // If we have PHI nodes to update, compute the number of edges from Pred to 1089 // BB. 1090 if (PhiToAllocaMap.count(APN)) { 1091 // We want to be able to distinguish between PHI nodes being inserted by 1092 // this invocation of mem2reg from those phi nodes that already existed in 1093 // the IR before mem2reg was run. We determine that APN is being inserted 1094 // because it is missing incoming edges. All other PHI nodes being 1095 // inserted by this pass of mem2reg will have the same number of incoming 1096 // operands so far. Remember this count. 1097 unsigned NewPHINumOperands = APN->getNumOperands(); 1098 1099 unsigned NumEdges = llvm::count(successors(Pred), BB); 1100 assert(NumEdges && "Must be at least one edge from Pred to BB!"); 1101 1102 // Add entries for all the phis. 1103 BasicBlock::iterator PNI = BB->begin(); 1104 do { 1105 unsigned AllocaNo = PhiToAllocaMap[APN]; 1106 1107 // Update the location of the phi node. 1108 updateForIncomingValueLocation(APN, IncomingLocs[AllocaNo], 1109 APN->getNumIncomingValues() > 0); 1110 1111 // Add N incoming values to the PHI node. 1112 for (unsigned i = 0; i != NumEdges; ++i) 1113 APN->addIncoming(IncomingVals[AllocaNo], Pred); 1114 1115 // The currently active variable for this block is now the PHI. 1116 IncomingVals[AllocaNo] = APN; 1117 AllocaATInfo[AllocaNo].updateForNewPhi(APN, DIB); 1118 auto ConvertDbgDeclares = [&](auto &Container) { 1119 for (auto *DbgItem : Container) 1120 if (DbgItem->isAddressOfVariable()) 1121 ConvertDebugDeclareToDebugValue(DbgItem, APN, DIB); 1122 }; 1123 ConvertDbgDeclares(AllocaDbgUsers[AllocaNo]); 1124 ConvertDbgDeclares(AllocaDPUsers[AllocaNo]); 1125 1126 // Get the next phi node. 1127 ++PNI; 1128 APN = dyn_cast<PHINode>(PNI); 1129 if (!APN) 1130 break; 1131 1132 // Verify that it is missing entries. If not, it is not being inserted 1133 // by this mem2reg invocation so we want to ignore it. 1134 } while (APN->getNumOperands() == NewPHINumOperands); 1135 } 1136 } 1137 1138 // Don't revisit blocks. 1139 if (!Visited.insert(BB).second) 1140 return; 1141 1142 for (BasicBlock::iterator II = BB->begin(); !II->isTerminator();) { 1143 Instruction *I = &*II++; // get the instruction, increment iterator 1144 1145 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1146 AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand()); 1147 if (!Src) 1148 continue; 1149 1150 DenseMap<AllocaInst *, unsigned>::iterator AI = AllocaLookup.find(Src); 1151 if (AI == AllocaLookup.end()) 1152 continue; 1153 1154 Value *V = IncomingVals[AI->second]; 1155 convertMetadataToAssumes(LI, V, SQ.DL, AC, &DT); 1156 1157 // Anything using the load now uses the current value. 1158 LI->replaceAllUsesWith(V); 1159 LI->eraseFromParent(); 1160 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 1161 // Delete this instruction and mark the name as the current holder of the 1162 // value 1163 AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand()); 1164 if (!Dest) 1165 continue; 1166 1167 DenseMap<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest); 1168 if (ai == AllocaLookup.end()) 1169 continue; 1170 1171 // what value were we writing? 1172 unsigned AllocaNo = ai->second; 1173 IncomingVals[AllocaNo] = SI->getOperand(0); 1174 1175 // Record debuginfo for the store before removing it. 1176 IncomingLocs[AllocaNo] = SI->getDebugLoc(); 1177 AllocaATInfo[AllocaNo].updateForDeletedStore(SI, DIB, &DbgAssignsToDelete, 1178 &DPVAssignsToDelete); 1179 auto ConvertDbgDeclares = [&](auto &Container) { 1180 for (auto *DbgItem : Container) 1181 if (DbgItem->isAddressOfVariable()) 1182 ConvertDebugDeclareToDebugValue(DbgItem, SI, DIB); 1183 }; 1184 ConvertDbgDeclares(AllocaDbgUsers[ai->second]); 1185 ConvertDbgDeclares(AllocaDPUsers[ai->second]); 1186 SI->eraseFromParent(); 1187 } 1188 } 1189 1190 // 'Recurse' to our successors. 1191 succ_iterator I = succ_begin(BB), E = succ_end(BB); 1192 if (I == E) 1193 return; 1194 1195 // Keep track of the successors so we don't visit the same successor twice 1196 SmallPtrSet<BasicBlock *, 8> VisitedSuccs; 1197 1198 // Handle the first successor without using the worklist. 1199 VisitedSuccs.insert(*I); 1200 Pred = BB; 1201 BB = *I; 1202 ++I; 1203 1204 for (; I != E; ++I) 1205 if (VisitedSuccs.insert(*I).second) 1206 Worklist.emplace_back(*I, Pred, IncomingVals, IncomingLocs); 1207 1208 goto NextIteration; 1209 } 1210 1211 void llvm::PromoteMemToReg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT, 1212 AssumptionCache *AC) { 1213 // If there is nothing to do, bail out... 1214 if (Allocas.empty()) 1215 return; 1216 1217 PromoteMem2Reg(Allocas, DT, AC).run(); 1218 } 1219