PromoteMemoryToRegister.cpp revision b20724dff4485de5381b578f840df61c4cb31867
1//===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file promote memory references to be register references. It promotes 11// alloca instructions which only have loads and stores as uses. An alloca is 12// transformed by using dominator frontiers to place PHI nodes, then traversing 13// the function in depth-first order to rewrite loads and stores as appropriate. 14// This is just the standard SSA construction algorithm to construct "pruned" 15// SSA form. 16// 17//===----------------------------------------------------------------------===// 18 19#include "llvm/Transforms/Utils/PromoteMemToReg.h" 20#include "llvm/Constants.h" 21#include "llvm/DerivedTypes.h" 22#include "llvm/Function.h" 23#include "llvm/Instructions.h" 24#include "llvm/Analysis/Dominators.h" 25#include "llvm/Analysis/AliasSetTracker.h" 26#include "llvm/ADT/StringExtras.h" 27#include "llvm/Support/CFG.h" 28#include "llvm/Support/StableBasicBlockNumbering.h" 29#include <algorithm> 30using namespace llvm; 31 32/// isAllocaPromotable - Return true if this alloca is legal for promotion. 33/// This is true if there are only loads and stores to the alloca. 34/// 35bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) { 36 // FIXME: If the memory unit is of pointer or integer type, we can permit 37 // assignments to subsections of the memory unit. 38 39 // Only allow direct loads and stores... 40 for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end(); 41 UI != UE; ++UI) // Loop over all of the uses of the alloca 42 if (isa<LoadInst>(*UI)) { 43 // noop 44 } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) { 45 if (SI->getOperand(0) == AI) 46 return false; // Don't allow a store OF the AI, only INTO the AI. 47 } else { 48 return false; // Not a load or store. 49 } 50 51 return true; 52} 53 54namespace { 55 struct PromoteMem2Reg { 56 /// Allocas - The alloca instructions being promoted. 57 /// 58 std::vector<AllocaInst*> Allocas; 59 DominatorTree &DT; 60 DominanceFrontier &DF; 61 const TargetData &TD; 62 63 /// AST - An AliasSetTracker object to update. If null, don't update it. 64 /// 65 AliasSetTracker *AST; 66 67 /// AllocaLookup - Reverse mapping of Allocas. 68 /// 69 std::map<AllocaInst*, unsigned> AllocaLookup; 70 71 /// NewPhiNodes - The PhiNodes we're adding. 72 /// 73 std::map<BasicBlock*, std::vector<PHINode*> > NewPhiNodes; 74 75 /// PointerAllocaValues - If we are updating an AliasSetTracker, then for 76 /// each alloca that is of pointer type, we keep track of what to copyValue 77 /// to the inserted PHI nodes here. 78 /// 79 std::vector<Value*> PointerAllocaValues; 80 81 /// Visited - The set of basic blocks the renamer has already visited. 82 /// 83 std::set<BasicBlock*> Visited; 84 85 /// BBNumbers - Contains a stable numbering of basic blocks to avoid 86 /// non-determinstic behavior. 87 StableBasicBlockNumbering BBNumbers; 88 89 public: 90 PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt, 91 DominanceFrontier &df, const TargetData &td, 92 AliasSetTracker *ast) 93 : Allocas(A), DT(dt), DF(df), TD(td), AST(ast) {} 94 95 void run(); 96 97 private: 98 void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum, 99 std::set<PHINode*> &DeadPHINodes); 100 void PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI); 101 void PromoteLocallyUsedAllocas(BasicBlock *BB, 102 const std::vector<AllocaInst*> &AIs); 103 104 void RenamePass(BasicBlock *BB, BasicBlock *Pred, 105 std::vector<Value*> &IncVals); 106 bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version, 107 std::set<PHINode*> &InsertedPHINodes); 108 }; 109} // end of anonymous namespace 110 111void PromoteMem2Reg::run() { 112 Function &F = *DF.getRoot()->getParent(); 113 114 // LocallyUsedAllocas - Keep track of all of the alloca instructions which are 115 // only used in a single basic block. These instructions can be efficiently 116 // promoted by performing a single linear scan over that one block. Since 117 // individual basic blocks are sometimes large, we group together all allocas 118 // that are live in a single basic block by the basic block they are live in. 119 std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas; 120 121 if (AST) PointerAllocaValues.resize(Allocas.size()); 122 123 for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) { 124 AllocaInst *AI = Allocas[AllocaNum]; 125 126 assert(isAllocaPromotable(AI, TD) && 127 "Cannot promote non-promotable alloca!"); 128 assert(AI->getParent()->getParent() == &F && 129 "All allocas should be in the same function, which is same as DF!"); 130 131 if (AI->use_empty()) { 132 // If there are no uses of the alloca, just delete it now. 133 if (AST) AST->deleteValue(AI); 134 AI->getParent()->getInstList().erase(AI); 135 136 // Remove the alloca from the Allocas list, since it has been processed 137 Allocas[AllocaNum] = Allocas.back(); 138 Allocas.pop_back(); 139 --AllocaNum; 140 continue; 141 } 142 143 // Calculate the set of read and write-locations for each alloca. This is 144 // analogous to finding the 'uses' and 'definitions' of each variable. 145 std::vector<BasicBlock*> DefiningBlocks; 146 std::vector<BasicBlock*> UsingBlocks; 147 148 BasicBlock *OnlyBlock = 0; 149 bool OnlyUsedInOneBlock = true; 150 151 // As we scan the uses of the alloca instruction, keep track of stores, and 152 // decide whether all of the loads and stores to the alloca are within the 153 // same basic block. 154 Value *AllocaPointerVal = 0; 155 for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){ 156 Instruction *User = cast<Instruction>(*U); 157 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 158 // Remember the basic blocks which define new values for the alloca 159 DefiningBlocks.push_back(SI->getParent()); 160 AllocaPointerVal = SI->getOperand(0); 161 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 162 // Otherwise it must be a load instruction, keep track of variable reads 163 UsingBlocks.push_back(LI->getParent()); 164 AllocaPointerVal = LI; 165 } 166 167 if (OnlyUsedInOneBlock) { 168 if (OnlyBlock == 0) 169 OnlyBlock = User->getParent(); 170 else if (OnlyBlock != User->getParent()) 171 OnlyUsedInOneBlock = false; 172 } 173 } 174 175 // If the alloca is only read and written in one basic block, just perform a 176 // linear sweep over the block to eliminate it. 177 if (OnlyUsedInOneBlock) { 178 LocallyUsedAllocas[OnlyBlock].push_back(AI); 179 180 // Remove the alloca from the Allocas list, since it will be processed. 181 Allocas[AllocaNum] = Allocas.back(); 182 Allocas.pop_back(); 183 --AllocaNum; 184 continue; 185 } 186 187 if (AST) 188 PointerAllocaValues[AllocaNum] = AllocaPointerVal; 189 190 // If we haven't computed a numbering for the BB's in the function, do so 191 // now. 192 BBNumbers.compute(F); 193 194 // Compute the locations where PhiNodes need to be inserted. Look at the 195 // dominance frontier of EACH basic-block we have a write in. 196 // 197 unsigned CurrentVersion = 0; 198 std::set<PHINode*> InsertedPHINodes; 199 std::vector<unsigned> DFBlocks; 200 while (!DefiningBlocks.empty()) { 201 BasicBlock *BB = DefiningBlocks.back(); 202 DefiningBlocks.pop_back(); 203 204 // Look up the DF for this write, add it to PhiNodes 205 DominanceFrontier::const_iterator it = DF.find(BB); 206 if (it != DF.end()) { 207 const DominanceFrontier::DomSetType &S = it->second; 208 209 // In theory we don't need the indirection through the DFBlocks vector. 210 // In practice, the order of calling QueuePhiNode would depend on the 211 // (unspecified) ordering of basic blocks in the dominance frontier, 212 // which would give PHI nodes non-determinstic subscripts. Fix this by 213 // processing blocks in order of the occurance in the function. 214 for (DominanceFrontier::DomSetType::iterator P = S.begin(),PE = S.end(); 215 P != PE; ++P) 216 DFBlocks.push_back(BBNumbers.getNumber(*P)); 217 218 // Sort by which the block ordering in the function. 219 std::sort(DFBlocks.begin(), DFBlocks.end()); 220 221 for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) { 222 BasicBlock *BB = BBNumbers.getBlock(DFBlocks[i]); 223 if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes)) 224 DefiningBlocks.push_back(BB); 225 } 226 DFBlocks.clear(); 227 } 228 } 229 230 // Now that we have inserted PHI nodes along the Iterated Dominance Frontier 231 // of the writes to the variable, scan through the reads of the variable, 232 // marking PHI nodes which are actually necessary as alive (by removing them 233 // from the InsertedPHINodes set). This is not perfect: there may PHI 234 // marked alive because of loads which are dominated by stores, but there 235 // will be no unmarked PHI nodes which are actually used. 236 // 237 for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i) 238 MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes); 239 UsingBlocks.clear(); 240 241 // If there are any PHI nodes which are now known to be dead, remove them! 242 for (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(), 243 E = InsertedPHINodes.end(); I != E; ++I) { 244 PHINode *PN = *I; 245 std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()]; 246 BBPNs[AllocaNum] = 0; 247 248 // Check to see if we just removed the last inserted PHI node from this 249 // basic block. If so, remove the entry for the basic block. 250 bool HasOtherPHIs = false; 251 for (unsigned i = 0, e = BBPNs.size(); i != e; ++i) 252 if (BBPNs[i]) { 253 HasOtherPHIs = true; 254 break; 255 } 256 if (!HasOtherPHIs) 257 NewPhiNodes.erase(PN->getParent()); 258 259 if (AST && isa<PointerType>(PN->getType())) 260 AST->deleteValue(PN); 261 PN->getParent()->getInstList().erase(PN); 262 } 263 264 // Keep the reverse mapping of the 'Allocas' array. 265 AllocaLookup[Allocas[AllocaNum]] = AllocaNum; 266 } 267 268 // Process all allocas which are only used in a single basic block. 269 for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I = 270 LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){ 271 const std::vector<AllocaInst*> &Allocas = I->second; 272 assert(!Allocas.empty() && "empty alloca list??"); 273 274 // It's common for there to only be one alloca in the list. Handle it 275 // efficiently. 276 if (Allocas.size() == 1) 277 PromoteLocallyUsedAlloca(I->first, Allocas[0]); 278 else 279 PromoteLocallyUsedAllocas(I->first, Allocas); 280 } 281 282 if (Allocas.empty()) 283 return; // All of the allocas must have been trivial! 284 285 // Set the incoming values for the basic block to be null values for all of 286 // the alloca's. We do this in case there is a load of a value that has not 287 // been stored yet. In this case, it will get this null value. 288 // 289 std::vector<Value *> Values(Allocas.size()); 290 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) 291 Values[i] = UndefValue::get(Allocas[i]->getAllocatedType()); 292 293 // Walks all basic blocks in the function performing the SSA rename algorithm 294 // and inserting the phi nodes we marked as necessary 295 // 296 RenamePass(F.begin(), 0, Values); 297 298 // The renamer uses the Visited set to avoid infinite loops. Clear it now. 299 Visited.clear(); 300 301 // Remove the allocas themselves from the function... 302 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) { 303 Instruction *A = Allocas[i]; 304 305 // If there are any uses of the alloca instructions left, they must be in 306 // sections of dead code that were not processed on the dominance frontier. 307 // Just delete the users now. 308 // 309 if (!A->use_empty()) 310 A->replaceAllUsesWith(UndefValue::get(A->getType())); 311 if (AST) AST->deleteValue(A); 312 A->getParent()->getInstList().erase(A); 313 } 314 315 // At this point, the renamer has added entries to PHI nodes for all reachable 316 // code. Unfortunately, there may be blocks which are not reachable, which 317 // the renamer hasn't traversed. If this is the case, the PHI nodes may not 318 // have incoming values for all predecessors. Loop over all PHI nodes we have 319 // created, inserting null constants if they are missing any incoming values. 320 // 321 for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I = 322 NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) { 323 324 std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first)); 325 std::vector<PHINode*> &PNs = I->second; 326 assert(!PNs.empty() && "Empty PHI node list??"); 327 328 // Only do work here if there the PHI nodes are missing incoming values. We 329 // know that all PHI nodes that were inserted in a block will have the same 330 // number of incoming values, so we can just check any PHI node. 331 PHINode *FirstPHI; 332 for (unsigned i = 0; (FirstPHI = PNs[i]) == 0; ++i) 333 /*empty*/; 334 335 if (Preds.size() != FirstPHI->getNumIncomingValues()) { 336 // Ok, now we know that all of the PHI nodes are missing entries for some 337 // basic blocks. Start by sorting the incoming predecessors for efficient 338 // access. 339 std::sort(Preds.begin(), Preds.end()); 340 341 // Now we loop through all BB's which have entries in FirstPHI and remove 342 // them from the Preds list. 343 for (unsigned i = 0, e = FirstPHI->getNumIncomingValues(); i != e; ++i) { 344 // Do a log(n) search of the Preds list for the entry we want. 345 std::vector<BasicBlock*>::iterator EntIt = 346 std::lower_bound(Preds.begin(), Preds.end(), 347 FirstPHI->getIncomingBlock(i)); 348 assert(EntIt != Preds.end() && *EntIt == FirstPHI->getIncomingBlock(i)&& 349 "PHI node has entry for a block which is not a predecessor!"); 350 351 // Remove the entry 352 Preds.erase(EntIt); 353 } 354 355 // At this point, the blocks left in the preds list must have dummy 356 // entries inserted into every PHI nodes for the block. 357 for (unsigned i = 0, e = PNs.size(); i != e; ++i) 358 if (PHINode *PN = PNs[i]) { 359 Value *UndefVal = UndefValue::get(PN->getType()); 360 for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred) 361 PN->addIncoming(UndefVal, Preds[pred]); 362 } 363 } 364 } 365} 366 367// MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not 368// "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF 369// as usual (inserting the PHI nodes in the DeadPHINodes set), then processes 370// each read of the variable. For each block that reads the variable, this 371// function is called, which removes used PHI nodes from the DeadPHINodes set. 372// After all of the reads have been processed, any PHI nodes left in the 373// DeadPHINodes set are removed. 374// 375void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum, 376 std::set<PHINode*> &DeadPHINodes) { 377 // Scan the immediate dominators of this block looking for a block which has a 378 // PHI node for Alloca num. If we find it, mark the PHI node as being alive! 379 for (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) { 380 BasicBlock *DomBB = N->getBlock(); 381 std::map<BasicBlock*, std::vector<PHINode*> >::iterator 382 I = NewPhiNodes.find(DomBB); 383 if (I != NewPhiNodes.end() && I->second[AllocaNum]) { 384 // Ok, we found an inserted PHI node which dominates this value. 385 PHINode *DominatingPHI = I->second[AllocaNum]; 386 387 // Find out if we previously thought it was dead. 388 std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI); 389 if (DPNI != DeadPHINodes.end()) { 390 // Ok, until now, we thought this PHI node was dead. Mark it as being 391 // alive/needed. 392 DeadPHINodes.erase(DPNI); 393 394 // Now that we have marked the PHI node alive, also mark any PHI nodes 395 // which it might use as being alive as well. 396 for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB); 397 PI != PE; ++PI) 398 MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes); 399 } 400 } 401 } 402} 403 404/// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic 405/// block. If this is the case, avoid traversing the CFG and inserting a lot of 406/// potentially useless PHI nodes by just performing a single linear pass over 407/// the basic block using the Alloca. 408/// 409void PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) { 410 assert(!AI->use_empty() && "There are no uses of the alloca!"); 411 412 // Handle degenerate cases quickly. 413 if (AI->hasOneUse()) { 414 Instruction *U = cast<Instruction>(AI->use_back()); 415 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 416 // Must be a load of uninitialized value. 417 LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType())); 418 if (AST && isa<PointerType>(LI->getType())) 419 AST->deleteValue(LI); 420 } else { 421 // Otherwise it must be a store which is never read. 422 assert(isa<StoreInst>(U)); 423 } 424 BB->getInstList().erase(U); 425 } else { 426 // Uses of the uninitialized memory location shall get undef. 427 Value *CurVal = UndefValue::get(AI->getAllocatedType()); 428 429 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { 430 Instruction *Inst = I++; 431 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { 432 if (LI->getOperand(0) == AI) { 433 // Loads just returns the "current value"... 434 LI->replaceAllUsesWith(CurVal); 435 if (AST && isa<PointerType>(LI->getType())) 436 AST->deleteValue(LI); 437 BB->getInstList().erase(LI); 438 } 439 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 440 if (SI->getOperand(1) == AI) { 441 // Store updates the "current value"... 442 CurVal = SI->getOperand(0); 443 BB->getInstList().erase(SI); 444 } 445 } 446 } 447 } 448 449 // After traversing the basic block, there should be no more uses of the 450 // alloca, remove it now. 451 assert(AI->use_empty() && "Uses of alloca from more than one BB??"); 452 if (AST) AST->deleteValue(AI); 453 AI->getParent()->getInstList().erase(AI); 454} 455 456/// PromoteLocallyUsedAllocas - This method is just like 457/// PromoteLocallyUsedAlloca, except that it processes multiple alloca 458/// instructions in parallel. This is important in cases where we have large 459/// basic blocks, as we don't want to rescan the entire basic block for each 460/// alloca which is locally used in it (which might be a lot). 461void PromoteMem2Reg:: 462PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) { 463 std::map<AllocaInst*, Value*> CurValues; 464 for (unsigned i = 0, e = AIs.size(); i != e; ++i) 465 CurValues[AIs[i]] = 0; // Insert with null value 466 467 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { 468 Instruction *Inst = I++; 469 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { 470 // Is this a load of an alloca we are tracking? 471 if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) { 472 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI); 473 if (AIt != CurValues.end()) { 474 // Loads just returns the "current value"... 475 if (AIt->second == 0) // Uninitialized value?? 476 AIt->second = UndefValue::get(AIt->first->getAllocatedType()); 477 LI->replaceAllUsesWith(AIt->second); 478 if (AST && isa<PointerType>(LI->getType())) 479 AST->deleteValue(LI); 480 BB->getInstList().erase(LI); 481 } 482 } 483 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 484 if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) { 485 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI); 486 if (AIt != CurValues.end()) { 487 // Store updates the "current value"... 488 AIt->second = SI->getOperand(0); 489 BB->getInstList().erase(SI); 490 } 491 } 492 } 493 } 494} 495 496 497 498// QueuePhiNode - queues a phi-node to be added to a basic-block for a specific 499// Alloca returns true if there wasn't already a phi-node for that variable 500// 501bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo, 502 unsigned &Version, 503 std::set<PHINode*> &InsertedPHINodes) { 504 // Look up the basic-block in question. 505 std::vector<PHINode*> &BBPNs = NewPhiNodes[BB]; 506 if (BBPNs.empty()) BBPNs.resize(Allocas.size()); 507 508 // If the BB already has a phi node added for the i'th alloca then we're done! 509 if (BBPNs[AllocaNo]) return false; 510 511 // Create a PhiNode using the dereferenced type... and add the phi-node to the 512 // BasicBlock. 513 PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(), 514 Allocas[AllocaNo]->getName() + "." + 515 utostr(Version++), BB->begin()); 516 BBPNs[AllocaNo] = PN; 517 InsertedPHINodes.insert(PN); 518 519 if (AST && isa<PointerType>(PN->getType())) 520 AST->copyValue(PointerAllocaValues[AllocaNo], PN); 521 522 return true; 523} 524 525 526// RenamePass - Recursively traverse the CFG of the function, renaming loads and 527// stores to the allocas which we are promoting. IncomingVals indicates what 528// value each Alloca contains on exit from the predecessor block Pred. 529// 530void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred, 531 std::vector<Value*> &IncomingVals) { 532 533 // If this BB needs a PHI node, update the PHI node for each variable we need 534 // PHI nodes for. 535 std::map<BasicBlock*, std::vector<PHINode *> >::iterator 536 BBPNI = NewPhiNodes.find(BB); 537 if (BBPNI != NewPhiNodes.end()) { 538 std::vector<PHINode *> &BBPNs = BBPNI->second; 539 for (unsigned k = 0; k != BBPNs.size(); ++k) 540 if (PHINode *PN = BBPNs[k]) { 541 // Add this incoming value to the PHI node. 542 PN->addIncoming(IncomingVals[k], Pred); 543 544 // The currently active variable for this block is now the PHI. 545 IncomingVals[k] = PN; 546 } 547 } 548 549 // don't revisit nodes 550 if (Visited.count(BB)) return; 551 552 // mark as visited 553 Visited.insert(BB); 554 555 for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) { 556 Instruction *I = II++; // get the instruction, increment iterator 557 558 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 559 if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) { 560 std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src); 561 if (AI != AllocaLookup.end()) { 562 Value *V = IncomingVals[AI->second]; 563 564 // walk the use list of this load and replace all uses with r 565 LI->replaceAllUsesWith(V); 566 if (AST && isa<PointerType>(LI->getType())) 567 AST->deleteValue(LI); 568 BB->getInstList().erase(LI); 569 } 570 } 571 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 572 // Delete this instruction and mark the name as the current holder of the 573 // value 574 if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) { 575 std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest); 576 if (ai != AllocaLookup.end()) { 577 // what value were we writing? 578 IncomingVals[ai->second] = SI->getOperand(0); 579 BB->getInstList().erase(SI); 580 } 581 } 582 } 583 } 584 585 // Recurse to our successors. 586 TerminatorInst *TI = BB->getTerminator(); 587 for (unsigned i = 0; i != TI->getNumSuccessors(); i++) { 588 std::vector<Value*> OutgoingVals(IncomingVals); 589 RenamePass(TI->getSuccessor(i), BB, OutgoingVals); 590 } 591} 592 593/// PromoteMemToReg - Promote the specified list of alloca instructions into 594/// scalar registers, inserting PHI nodes as appropriate. This function makes 595/// use of DominanceFrontier information. This function does not modify the CFG 596/// of the function at all. All allocas must be from the same function. 597/// 598/// If AST is specified, the specified tracker is updated to reflect changes 599/// made to the IR. 600/// 601void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas, 602 DominatorTree &DT, DominanceFrontier &DF, 603 const TargetData &TD, AliasSetTracker *AST) { 604 // If there is nothing to do, bail out... 605 if (Allocas.empty()) return; 606 PromoteMem2Reg(Allocas, DT, DF, TD, AST).run(); 607} 608