SSAUpdater.cpp revision c827939046670a9800659b83e2048f1d3a79a531
1//===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===// 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 file implements the SSAUpdater class. 11// 12//===----------------------------------------------------------------------===// 13 14#define DEBUG_TYPE "ssaupdater" 15#include "llvm/Constants.h" 16#include "llvm/Instructions.h" 17#include "llvm/IntrinsicInst.h" 18#include "llvm/ADT/DenseMap.h" 19#include "llvm/Analysis/DIBuilder.h" 20#include "llvm/Analysis/InstructionSimplify.h" 21#include "llvm/Support/AlignOf.h" 22#include "llvm/Support/Allocator.h" 23#include "llvm/Support/CFG.h" 24#include "llvm/Support/Debug.h" 25#include "llvm/Support/raw_ostream.h" 26#include "llvm/Transforms/Utils/BasicBlockUtils.h" 27#include "llvm/Transforms/Utils/Local.h" 28#include "llvm/Transforms/Utils/SSAUpdater.h" 29#include "llvm/Transforms/Utils/SSAUpdaterImpl.h" 30 31using namespace llvm; 32 33typedef DenseMap<BasicBlock*, Value*> AvailableValsTy; 34static AvailableValsTy &getAvailableVals(void *AV) { 35 return *static_cast<AvailableValsTy*>(AV); 36} 37 38SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI) 39 : AV(0), ProtoType(0), ProtoName(), InsertedPHIs(NewPHI) {} 40 41SSAUpdater::~SSAUpdater() { 42 delete &getAvailableVals(AV); 43} 44 45/// Initialize - Reset this object to get ready for a new set of SSA 46/// updates with type 'Ty'. PHI nodes get a name based on 'Name'. 47void SSAUpdater::Initialize(const Type *Ty, StringRef Name) { 48 if (AV == 0) 49 AV = new AvailableValsTy(); 50 else 51 getAvailableVals(AV).clear(); 52 ProtoType = Ty; 53 ProtoName = Name; 54} 55 56/// HasValueForBlock - Return true if the SSAUpdater already has a value for 57/// the specified block. 58bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const { 59 return getAvailableVals(AV).count(BB); 60} 61 62/// AddAvailableValue - Indicate that a rewritten value is available in the 63/// specified block with the specified value. 64void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) { 65 assert(ProtoType != 0 && "Need to initialize SSAUpdater"); 66 assert(ProtoType == V->getType() && 67 "All rewritten values must have the same type"); 68 getAvailableVals(AV)[BB] = V; 69} 70 71/// IsEquivalentPHI - Check if PHI has the same incoming value as specified 72/// in ValueMapping for each predecessor block. 73static bool IsEquivalentPHI(PHINode *PHI, 74 DenseMap<BasicBlock*, Value*> &ValueMapping) { 75 unsigned PHINumValues = PHI->getNumIncomingValues(); 76 if (PHINumValues != ValueMapping.size()) 77 return false; 78 79 // Scan the phi to see if it matches. 80 for (unsigned i = 0, e = PHINumValues; i != e; ++i) 81 if (ValueMapping[PHI->getIncomingBlock(i)] != 82 PHI->getIncomingValue(i)) { 83 return false; 84 } 85 86 return true; 87} 88 89/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is 90/// live at the end of the specified block. 91Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) { 92 Value *Res = GetValueAtEndOfBlockInternal(BB); 93 return Res; 94} 95 96/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that 97/// is live in the middle of the specified block. 98/// 99/// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one 100/// important case: if there is a definition of the rewritten value after the 101/// 'use' in BB. Consider code like this: 102/// 103/// X1 = ... 104/// SomeBB: 105/// use(X) 106/// X2 = ... 107/// br Cond, SomeBB, OutBB 108/// 109/// In this case, there are two values (X1 and X2) added to the AvailableVals 110/// set by the client of the rewriter, and those values are both live out of 111/// their respective blocks. However, the use of X happens in the *middle* of 112/// a block. Because of this, we need to insert a new PHI node in SomeBB to 113/// merge the appropriate values, and this value isn't live out of the block. 114/// 115Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) { 116 // If there is no definition of the renamed variable in this block, just use 117 // GetValueAtEndOfBlock to do our work. 118 if (!HasValueForBlock(BB)) 119 return GetValueAtEndOfBlock(BB); 120 121 // Otherwise, we have the hard case. Get the live-in values for each 122 // predecessor. 123 SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues; 124 Value *SingularValue = 0; 125 126 // We can get our predecessor info by walking the pred_iterator list, but it 127 // is relatively slow. If we already have PHI nodes in this block, walk one 128 // of them to get the predecessor list instead. 129 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) { 130 for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) { 131 BasicBlock *PredBB = SomePhi->getIncomingBlock(i); 132 Value *PredVal = GetValueAtEndOfBlock(PredBB); 133 PredValues.push_back(std::make_pair(PredBB, PredVal)); 134 135 // Compute SingularValue. 136 if (i == 0) 137 SingularValue = PredVal; 138 else if (PredVal != SingularValue) 139 SingularValue = 0; 140 } 141 } else { 142 bool isFirstPred = true; 143 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 144 BasicBlock *PredBB = *PI; 145 Value *PredVal = GetValueAtEndOfBlock(PredBB); 146 PredValues.push_back(std::make_pair(PredBB, PredVal)); 147 148 // Compute SingularValue. 149 if (isFirstPred) { 150 SingularValue = PredVal; 151 isFirstPred = false; 152 } else if (PredVal != SingularValue) 153 SingularValue = 0; 154 } 155 } 156 157 // If there are no predecessors, just return undef. 158 if (PredValues.empty()) 159 return UndefValue::get(ProtoType); 160 161 // Otherwise, if all the merged values are the same, just use it. 162 if (SingularValue != 0) 163 return SingularValue; 164 165 // Otherwise, we do need a PHI: check to see if we already have one available 166 // in this block that produces the right value. 167 if (isa<PHINode>(BB->begin())) { 168 DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(), 169 PredValues.end()); 170 PHINode *SomePHI; 171 for (BasicBlock::iterator It = BB->begin(); 172 (SomePHI = dyn_cast<PHINode>(It)); ++It) { 173 if (IsEquivalentPHI(SomePHI, ValueMapping)) 174 return SomePHI; 175 } 176 } 177 178 // Ok, we have no way out, insert a new one now. 179 PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(), 180 ProtoName, &BB->front()); 181 182 // Fill in all the predecessors of the PHI. 183 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) 184 InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first); 185 186 // See if the PHI node can be merged to a single value. This can happen in 187 // loop cases when we get a PHI of itself and one other value. 188 if (Value *V = SimplifyInstruction(InsertedPHI)) { 189 InsertedPHI->eraseFromParent(); 190 return V; 191 } 192 193 // Set DebugLoc. 194 InsertedPHI->setDebugLoc(GetFirstDebugLocInBasicBlock(BB)); 195 196 // If the client wants to know about all new instructions, tell it. 197 if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI); 198 199 DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n"); 200 return InsertedPHI; 201} 202 203/// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes, 204/// which use their value in the corresponding predecessor. 205void SSAUpdater::RewriteUse(Use &U) { 206 Instruction *User = cast<Instruction>(U.getUser()); 207 208 Value *V; 209 if (PHINode *UserPN = dyn_cast<PHINode>(User)) 210 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U)); 211 else 212 V = GetValueInMiddleOfBlock(User->getParent()); 213 214 U.set(V); 215} 216 217/// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse. However, 218/// this version of the method can rewrite uses in the same block as a 219/// definition, because it assumes that all uses of a value are below any 220/// inserted values. 221void SSAUpdater::RewriteUseAfterInsertions(Use &U) { 222 Instruction *User = cast<Instruction>(U.getUser()); 223 224 Value *V; 225 if (PHINode *UserPN = dyn_cast<PHINode>(User)) 226 V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U)); 227 else 228 V = GetValueAtEndOfBlock(User->getParent()); 229 230 U.set(V); 231} 232 233/// PHIiter - Iterator for PHI operands. This is used for the PHI_iterator 234/// in the SSAUpdaterImpl template. 235namespace { 236 class PHIiter { 237 private: 238 PHINode *PHI; 239 unsigned idx; 240 241 public: 242 explicit PHIiter(PHINode *P) // begin iterator 243 : PHI(P), idx(0) {} 244 PHIiter(PHINode *P, bool) // end iterator 245 : PHI(P), idx(PHI->getNumIncomingValues()) {} 246 247 PHIiter &operator++() { ++idx; return *this; } 248 bool operator==(const PHIiter& x) const { return idx == x.idx; } 249 bool operator!=(const PHIiter& x) const { return !operator==(x); } 250 Value *getIncomingValue() { return PHI->getIncomingValue(idx); } 251 BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); } 252 }; 253} 254 255/// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template, 256/// specialized for SSAUpdater. 257namespace llvm { 258template<> 259class SSAUpdaterTraits<SSAUpdater> { 260public: 261 typedef BasicBlock BlkT; 262 typedef Value *ValT; 263 typedef PHINode PhiT; 264 265 typedef succ_iterator BlkSucc_iterator; 266 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); } 267 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); } 268 269 typedef PHIiter PHI_iterator; 270 static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); } 271 static inline PHI_iterator PHI_end(PhiT *PHI) { 272 return PHI_iterator(PHI, true); 273 } 274 275 /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds 276 /// vector, set Info->NumPreds, and allocate space in Info->Preds. 277 static void FindPredecessorBlocks(BasicBlock *BB, 278 SmallVectorImpl<BasicBlock*> *Preds) { 279 // We can get our predecessor info by walking the pred_iterator list, 280 // but it is relatively slow. If we already have PHI nodes in this 281 // block, walk one of them to get the predecessor list instead. 282 if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) { 283 for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI) 284 Preds->push_back(SomePhi->getIncomingBlock(PI)); 285 } else { 286 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 287 Preds->push_back(*PI); 288 } 289 } 290 291 /// GetUndefVal - Get an undefined value of the same type as the value 292 /// being handled. 293 static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) { 294 return UndefValue::get(Updater->ProtoType); 295 } 296 297 /// CreateEmptyPHI - Create a new PHI instruction in the specified block. 298 /// Reserve space for the operands but do not fill them in yet. 299 static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds, 300 SSAUpdater *Updater) { 301 PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds, 302 Updater->ProtoName, &BB->front()); 303 return PHI; 304 } 305 306 /// AddPHIOperand - Add the specified value as an operand of the PHI for 307 /// the specified predecessor block. 308 static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) { 309 PHI->addIncoming(Val, Pred); 310 } 311 312 /// InstrIsPHI - Check if an instruction is a PHI. 313 /// 314 static PHINode *InstrIsPHI(Instruction *I) { 315 return dyn_cast<PHINode>(I); 316 } 317 318 /// ValueIsPHI - Check if a value is a PHI. 319 /// 320 static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) { 321 return dyn_cast<PHINode>(Val); 322 } 323 324 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source 325 /// operands, i.e., it was just added. 326 static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) { 327 PHINode *PHI = ValueIsPHI(Val, Updater); 328 if (PHI && PHI->getNumIncomingValues() == 0) 329 return PHI; 330 return 0; 331 } 332 333 /// GetPHIValue - For the specified PHI instruction, return the value 334 /// that it defines. 335 static Value *GetPHIValue(PHINode *PHI) { 336 return PHI; 337 } 338}; 339 340} // End llvm namespace 341 342/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry 343/// for the specified BB and if so, return it. If not, construct SSA form by 344/// first calculating the required placement of PHIs and then inserting new 345/// PHIs where needed. 346Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) { 347 AvailableValsTy &AvailableVals = getAvailableVals(AV); 348 if (Value *V = AvailableVals[BB]) 349 return V; 350 351 SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs); 352 return Impl.GetValue(BB); 353} 354 355//===----------------------------------------------------------------------===// 356// LoadAndStorePromoter Implementation 357//===----------------------------------------------------------------------===// 358 359LoadAndStorePromoter:: 360LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts, 361 SSAUpdater &S, DbgDeclareInst *DD, DIBuilder *&DB, 362 StringRef BaseName) : SSA(S), DDI(DD), DIB(DB) { 363 if (Insts.empty()) return; 364 365 Value *SomeVal; 366 if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0])) 367 SomeVal = LI; 368 else 369 SomeVal = cast<StoreInst>(Insts[0])->getOperand(0); 370 371 if (BaseName.empty()) 372 BaseName = SomeVal->getName(); 373 SSA.Initialize(SomeVal->getType(), BaseName); 374} 375 376 377void LoadAndStorePromoter:: 378run(const SmallVectorImpl<Instruction*> &Insts) const { 379 380 // First step: bucket up uses of the alloca by the block they occur in. 381 // This is important because we have to handle multiple defs/uses in a block 382 // ourselves: SSAUpdater is purely for cross-block references. 383 // FIXME: Want a TinyVector<Instruction*> since there is often 0/1 element. 384 DenseMap<BasicBlock*, std::vector<Instruction*> > UsesByBlock; 385 386 for (unsigned i = 0, e = Insts.size(); i != e; ++i) { 387 Instruction *User = Insts[i]; 388 UsesByBlock[User->getParent()].push_back(User); 389 } 390 391 // Okay, now we can iterate over all the blocks in the function with uses, 392 // processing them. Keep track of which loads are loading a live-in value. 393 // Walk the uses in the use-list order to be determinstic. 394 SmallVector<LoadInst*, 32> LiveInLoads; 395 DenseMap<Value*, Value*> ReplacedLoads; 396 397 for (unsigned i = 0, e = Insts.size(); i != e; ++i) { 398 Instruction *User = Insts[i]; 399 BasicBlock *BB = User->getParent(); 400 std::vector<Instruction*> &BlockUses = UsesByBlock[BB]; 401 402 // If this block has already been processed, ignore this repeat use. 403 if (BlockUses.empty()) continue; 404 405 // Okay, this is the first use in the block. If this block just has a 406 // single user in it, we can rewrite it trivially. 407 if (BlockUses.size() == 1) { 408 // If it is a store, it is a trivial def of the value in the block. 409 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 410 if (DDI) { 411 if (!DIB) 412 DIB = new DIBuilder(*SI->getParent()->getParent()->getParent()); 413 ConvertDebugDeclareToDebugValue(DDI, SI, *DIB); 414 } 415 SSA.AddAvailableValue(BB, SI->getOperand(0)); 416 } else 417 // Otherwise it is a load, queue it to rewrite as a live-in load. 418 LiveInLoads.push_back(cast<LoadInst>(User)); 419 BlockUses.clear(); 420 continue; 421 } 422 423 // Otherwise, check to see if this block is all loads. 424 bool HasStore = false; 425 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) { 426 if (isa<StoreInst>(BlockUses[i])) { 427 HasStore = true; 428 break; 429 } 430 } 431 432 // If so, we can queue them all as live in loads. We don't have an 433 // efficient way to tell which on is first in the block and don't want to 434 // scan large blocks, so just add all loads as live ins. 435 if (!HasStore) { 436 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) 437 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i])); 438 BlockUses.clear(); 439 continue; 440 } 441 442 // Otherwise, we have mixed loads and stores (or just a bunch of stores). 443 // Since SSAUpdater is purely for cross-block values, we need to determine 444 // the order of these instructions in the block. If the first use in the 445 // block is a load, then it uses the live in value. The last store defines 446 // the live out value. We handle this by doing a linear scan of the block. 447 Value *StoredValue = 0; 448 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) { 449 if (LoadInst *L = dyn_cast<LoadInst>(II)) { 450 // If this is a load from an unrelated pointer, ignore it. 451 if (!isInstInList(L, Insts)) continue; 452 453 // If we haven't seen a store yet, this is a live in use, otherwise 454 // use the stored value. 455 if (StoredValue) { 456 replaceLoadWithValue(L, StoredValue); 457 L->replaceAllUsesWith(StoredValue); 458 ReplacedLoads[L] = StoredValue; 459 } else { 460 LiveInLoads.push_back(L); 461 } 462 continue; 463 } 464 465 if (StoreInst *SI = dyn_cast<StoreInst>(II)) { 466 // If this is a store to an unrelated pointer, ignore it. 467 if (!isInstInList(SI, Insts)) continue; 468 469 if (DDI) { 470 if (!DIB) 471 DIB = new DIBuilder(*SI->getParent()->getParent()->getParent()); 472 ConvertDebugDeclareToDebugValue(DDI, SI, *DIB); 473 } 474 475 // Remember that this is the active value in the block. 476 StoredValue = SI->getOperand(0); 477 } 478 } 479 480 // The last stored value that happened is the live-out for the block. 481 assert(StoredValue && "Already checked that there is a store in block"); 482 SSA.AddAvailableValue(BB, StoredValue); 483 BlockUses.clear(); 484 } 485 486 // Okay, now we rewrite all loads that use live-in values in the loop, 487 // inserting PHI nodes as necessary. 488 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) { 489 LoadInst *ALoad = LiveInLoads[i]; 490 Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent()); 491 replaceLoadWithValue(ALoad, NewVal); 492 493 // Avoid assertions in unreachable code. 494 if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType()); 495 ALoad->replaceAllUsesWith(NewVal); 496 ReplacedLoads[ALoad] = NewVal; 497 } 498 499 // Allow the client to do stuff before we start nuking things. 500 doExtraRewritesBeforeFinalDeletion(); 501 502 // Now that everything is rewritten, delete the old instructions from the 503 // function. They should all be dead now. 504 for (unsigned i = 0, e = Insts.size(); i != e; ++i) { 505 Instruction *User = Insts[i]; 506 507 // If this is a load that still has uses, then the load must have been added 508 // as a live value in the SSAUpdate data structure for a block (e.g. because 509 // the loaded value was stored later). In this case, we need to recursively 510 // propagate the updates until we get to the real value. 511 if (!User->use_empty()) { 512 Value *NewVal = ReplacedLoads[User]; 513 assert(NewVal && "not a replaced load?"); 514 515 // Propagate down to the ultimate replacee. The intermediately loads 516 // could theoretically already have been deleted, so we don't want to 517 // dereference the Value*'s. 518 DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal); 519 while (RLI != ReplacedLoads.end()) { 520 NewVal = RLI->second; 521 RLI = ReplacedLoads.find(NewVal); 522 } 523 524 replaceLoadWithValue(cast<LoadInst>(User), NewVal); 525 User->replaceAllUsesWith(NewVal); 526 } 527 528 instructionDeleted(User); 529 User->eraseFromParent(); 530 } 531 532 if (DDI) 533 DDI->eraseFromParent(); 534} 535