LLVM API Documentation
00001 //===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This file promote memory references to be register references. It promotes 00011 // alloca instructions which only have loads and stores as uses. An alloca is 00012 // transformed by using dominator frontiers to place PHI nodes, then traversing 00013 // the function in depth-first order to rewrite loads and stores as appropriate. 00014 // This is just the standard SSA construction algorithm to construct "pruned" 00015 // SSA form. 00016 // 00017 //===----------------------------------------------------------------------===// 00018 00019 #include "llvm/Transforms/Utils/PromoteMemToReg.h" 00020 #include "llvm/Constants.h" 00021 #include "llvm/DerivedTypes.h" 00022 #include "llvm/Function.h" 00023 #include "llvm/Instructions.h" 00024 #include "llvm/Analysis/Dominators.h" 00025 #include "llvm/Analysis/AliasSetTracker.h" 00026 #include "llvm/ADT/StringExtras.h" 00027 #include "llvm/Support/CFG.h" 00028 #include "llvm/Support/StableBasicBlockNumbering.h" 00029 #include <algorithm> 00030 using namespace llvm; 00031 00032 /// isAllocaPromotable - Return true if this alloca is legal for promotion. 00033 /// This is true if there are only loads and stores to the alloca. 00034 /// 00035 bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) { 00036 // FIXME: If the memory unit is of pointer or integer type, we can permit 00037 // assignments to subsections of the memory unit. 00038 00039 // Only allow direct loads and stores... 00040 for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end(); 00041 UI != UE; ++UI) // Loop over all of the uses of the alloca 00042 if (isa<LoadInst>(*UI)) { 00043 // noop 00044 } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) { 00045 if (SI->getOperand(0) == AI) 00046 return false; // Don't allow a store OF the AI, only INTO the AI. 00047 } else { 00048 return false; // Not a load or store. 00049 } 00050 00051 return true; 00052 } 00053 00054 namespace { 00055 struct PromoteMem2Reg { 00056 /// Allocas - The alloca instructions being promoted. 00057 /// 00058 std::vector<AllocaInst*> Allocas; 00059 std::vector<AllocaInst*> &RetryList; 00060 DominatorTree &DT; 00061 DominanceFrontier &DF; 00062 const TargetData &TD; 00063 00064 /// AST - An AliasSetTracker object to update. If null, don't update it. 00065 /// 00066 AliasSetTracker *AST; 00067 00068 /// AllocaLookup - Reverse mapping of Allocas. 00069 /// 00070 std::map<AllocaInst*, unsigned> AllocaLookup; 00071 00072 /// NewPhiNodes - The PhiNodes we're adding. 00073 /// 00074 std::map<BasicBlock*, std::vector<PHINode*> > NewPhiNodes; 00075 00076 /// PointerAllocaValues - If we are updating an AliasSetTracker, then for 00077 /// each alloca that is of pointer type, we keep track of what to copyValue 00078 /// to the inserted PHI nodes here. 00079 /// 00080 std::vector<Value*> PointerAllocaValues; 00081 00082 /// Visited - The set of basic blocks the renamer has already visited. 00083 /// 00084 std::set<BasicBlock*> Visited; 00085 00086 /// BBNumbers - Contains a stable numbering of basic blocks to avoid 00087 /// non-determinstic behavior. 00088 StableBasicBlockNumbering BBNumbers; 00089 00090 public: 00091 PromoteMem2Reg(const std::vector<AllocaInst*> &A, 00092 std::vector<AllocaInst*> &Retry, DominatorTree &dt, 00093 DominanceFrontier &df, const TargetData &td, 00094 AliasSetTracker *ast) 00095 : Allocas(A), RetryList(Retry), DT(dt), DF(df), TD(td), AST(ast) {} 00096 00097 void run(); 00098 00099 /// properlyDominates - Return true if I1 properly dominates I2. 00100 /// 00101 bool properlyDominates(Instruction *I1, Instruction *I2) const { 00102 if (InvokeInst *II = dyn_cast<InvokeInst>(I1)) 00103 I1 = II->getNormalDest()->begin(); 00104 return DT[I1->getParent()]->properlyDominates(DT[I2->getParent()]); 00105 } 00106 00107 /// dominates - Return true if BB1 dominates BB2 using the DominatorTree. 00108 /// 00109 bool dominates(BasicBlock *BB1, BasicBlock *BB2) const { 00110 return DT[BB1]->dominates(DT[BB2]); 00111 } 00112 00113 private: 00114 void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum, 00115 std::set<PHINode*> &DeadPHINodes); 00116 bool PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI); 00117 void PromoteLocallyUsedAllocas(BasicBlock *BB, 00118 const std::vector<AllocaInst*> &AIs); 00119 00120 void RenamePass(BasicBlock *BB, BasicBlock *Pred, 00121 std::vector<Value*> &IncVals); 00122 bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version, 00123 std::set<PHINode*> &InsertedPHINodes); 00124 }; 00125 } // end of anonymous namespace 00126 00127 void PromoteMem2Reg::run() { 00128 Function &F = *DF.getRoot()->getParent(); 00129 00130 // LocallyUsedAllocas - Keep track of all of the alloca instructions which are 00131 // only used in a single basic block. These instructions can be efficiently 00132 // promoted by performing a single linear scan over that one block. Since 00133 // individual basic blocks are sometimes large, we group together all allocas 00134 // that are live in a single basic block by the basic block they are live in. 00135 std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas; 00136 00137 if (AST) PointerAllocaValues.resize(Allocas.size()); 00138 00139 for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) { 00140 AllocaInst *AI = Allocas[AllocaNum]; 00141 00142 assert(isAllocaPromotable(AI, TD) && 00143 "Cannot promote non-promotable alloca!"); 00144 assert(AI->getParent()->getParent() == &F && 00145 "All allocas should be in the same function, which is same as DF!"); 00146 00147 if (AI->use_empty()) { 00148 // If there are no uses of the alloca, just delete it now. 00149 if (AST) AST->deleteValue(AI); 00150 AI->getParent()->getInstList().erase(AI); 00151 00152 // Remove the alloca from the Allocas list, since it has been processed 00153 Allocas[AllocaNum] = Allocas.back(); 00154 Allocas.pop_back(); 00155 --AllocaNum; 00156 continue; 00157 } 00158 00159 // Calculate the set of read and write-locations for each alloca. This is 00160 // analogous to finding the 'uses' and 'definitions' of each variable. 00161 std::vector<BasicBlock*> DefiningBlocks; 00162 std::vector<BasicBlock*> UsingBlocks; 00163 00164 StoreInst *OnlyStore = 0; 00165 BasicBlock *OnlyBlock = 0; 00166 bool OnlyUsedInOneBlock = true; 00167 00168 // As we scan the uses of the alloca instruction, keep track of stores, and 00169 // decide whether all of the loads and stores to the alloca are within the 00170 // same basic block. 00171 Value *AllocaPointerVal = 0; 00172 for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){ 00173 Instruction *User = cast<Instruction>(*U); 00174 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 00175 // Remember the basic blocks which define new values for the alloca 00176 DefiningBlocks.push_back(SI->getParent()); 00177 AllocaPointerVal = SI->getOperand(0); 00178 OnlyStore = SI; 00179 } else { 00180 LoadInst *LI = cast<LoadInst>(User); 00181 // Otherwise it must be a load instruction, keep track of variable reads 00182 UsingBlocks.push_back(LI->getParent()); 00183 AllocaPointerVal = LI; 00184 } 00185 00186 if (OnlyUsedInOneBlock) { 00187 if (OnlyBlock == 0) 00188 OnlyBlock = User->getParent(); 00189 else if (OnlyBlock != User->getParent()) 00190 OnlyUsedInOneBlock = false; 00191 } 00192 } 00193 00194 // If the alloca is only read and written in one basic block, just perform a 00195 // linear sweep over the block to eliminate it. 00196 if (OnlyUsedInOneBlock) { 00197 LocallyUsedAllocas[OnlyBlock].push_back(AI); 00198 00199 // Remove the alloca from the Allocas list, since it will be processed. 00200 Allocas[AllocaNum] = Allocas.back(); 00201 Allocas.pop_back(); 00202 --AllocaNum; 00203 continue; 00204 } 00205 00206 // If there is only a single store to this value, replace any loads of 00207 // it that are directly dominated by the definition with the value stored. 00208 if (DefiningBlocks.size() == 1) { 00209 // Be aware of loads before the store. 00210 std::set<BasicBlock*> ProcessedBlocks; 00211 for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i) 00212 // If the store dominates the block and if we haven't processed it yet, 00213 // do so now. 00214 if (dominates(OnlyStore->getParent(), UsingBlocks[i])) 00215 if (ProcessedBlocks.insert(UsingBlocks[i]).second) { 00216 BasicBlock *UseBlock = UsingBlocks[i]; 00217 00218 // If the use and store are in the same block, do a quick scan to 00219 // verify that there are no uses before the store. 00220 if (UseBlock == OnlyStore->getParent()) { 00221 BasicBlock::iterator I = UseBlock->begin(); 00222 for (; &*I != OnlyStore; ++I) { // scan block for store. 00223 if (isa<LoadInst>(I) && I->getOperand(0) == AI) 00224 break; 00225 } 00226 if (&*I != OnlyStore) break; // Do not handle this case. 00227 } 00228 00229 // Otherwise, if this is a different block or if all uses happen 00230 // after the store, do a simple linear scan to replace loads with 00231 // the stored value. 00232 for (BasicBlock::iterator I = UseBlock->begin(),E = UseBlock->end(); 00233 I != E; ) { 00234 if (LoadInst *LI = dyn_cast<LoadInst>(I++)) { 00235 if (LI->getOperand(0) == AI) { 00236 LI->replaceAllUsesWith(OnlyStore->getOperand(0)); 00237 if (AST && isa<PointerType>(LI->getType())) 00238 AST->deleteValue(LI); 00239 LI->eraseFromParent(); 00240 } 00241 } 00242 } 00243 00244 // Finally, remove this block from the UsingBlock set. 00245 UsingBlocks[i] = UsingBlocks.back(); 00246 --i; --e; 00247 } 00248 00249 // Finally, after the scan, check to see if the store is all that is left. 00250 if (UsingBlocks.empty()) { 00251 // The alloca has been processed, move on. 00252 Allocas[AllocaNum] = Allocas.back(); 00253 Allocas.pop_back(); 00254 --AllocaNum; 00255 continue; 00256 } 00257 } 00258 00259 00260 if (AST) 00261 PointerAllocaValues[AllocaNum] = AllocaPointerVal; 00262 00263 // If we haven't computed a numbering for the BB's in the function, do so 00264 // now. 00265 BBNumbers.compute(F); 00266 00267 // Compute the locations where PhiNodes need to be inserted. Look at the 00268 // dominance frontier of EACH basic-block we have a write in. 00269 // 00270 unsigned CurrentVersion = 0; 00271 std::set<PHINode*> InsertedPHINodes; 00272 std::vector<unsigned> DFBlocks; 00273 while (!DefiningBlocks.empty()) { 00274 BasicBlock *BB = DefiningBlocks.back(); 00275 DefiningBlocks.pop_back(); 00276 00277 // Look up the DF for this write, add it to PhiNodes 00278 DominanceFrontier::const_iterator it = DF.find(BB); 00279 if (it != DF.end()) { 00280 const DominanceFrontier::DomSetType &S = it->second; 00281 00282 // In theory we don't need the indirection through the DFBlocks vector. 00283 // In practice, the order of calling QueuePhiNode would depend on the 00284 // (unspecified) ordering of basic blocks in the dominance frontier, 00285 // which would give PHI nodes non-determinstic subscripts. Fix this by 00286 // processing blocks in order of the occurance in the function. 00287 for (DominanceFrontier::DomSetType::const_iterator P = S.begin(), 00288 PE = S.end(); P != PE; ++P) 00289 DFBlocks.push_back(BBNumbers.getNumber(*P)); 00290 00291 // Sort by which the block ordering in the function. 00292 std::sort(DFBlocks.begin(), DFBlocks.end()); 00293 00294 for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) { 00295 BasicBlock *BB = BBNumbers.getBlock(DFBlocks[i]); 00296 if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes)) 00297 DefiningBlocks.push_back(BB); 00298 } 00299 DFBlocks.clear(); 00300 } 00301 } 00302 00303 // Now that we have inserted PHI nodes along the Iterated Dominance Frontier 00304 // of the writes to the variable, scan through the reads of the variable, 00305 // marking PHI nodes which are actually necessary as alive (by removing them 00306 // from the InsertedPHINodes set). This is not perfect: there may PHI 00307 // marked alive because of loads which are dominated by stores, but there 00308 // will be no unmarked PHI nodes which are actually used. 00309 // 00310 for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i) 00311 MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes); 00312 UsingBlocks.clear(); 00313 00314 // If there are any PHI nodes which are now known to be dead, remove them! 00315 for (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(), 00316 E = InsertedPHINodes.end(); I != E; ++I) { 00317 PHINode *PN = *I; 00318 std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()]; 00319 BBPNs[AllocaNum] = 0; 00320 00321 // Check to see if we just removed the last inserted PHI node from this 00322 // basic block. If so, remove the entry for the basic block. 00323 bool HasOtherPHIs = false; 00324 for (unsigned i = 0, e = BBPNs.size(); i != e; ++i) 00325 if (BBPNs[i]) { 00326 HasOtherPHIs = true; 00327 break; 00328 } 00329 if (!HasOtherPHIs) 00330 NewPhiNodes.erase(PN->getParent()); 00331 00332 if (AST && isa<PointerType>(PN->getType())) 00333 AST->deleteValue(PN); 00334 PN->getParent()->getInstList().erase(PN); 00335 } 00336 00337 // Keep the reverse mapping of the 'Allocas' array. 00338 AllocaLookup[Allocas[AllocaNum]] = AllocaNum; 00339 } 00340 00341 // Process all allocas which are only used in a single basic block. 00342 for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I = 00343 LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){ 00344 const std::vector<AllocaInst*> &LocAllocas = I->second; 00345 assert(!LocAllocas.empty() && "empty alloca list??"); 00346 00347 // It's common for there to only be one alloca in the list. Handle it 00348 // efficiently. 00349 if (LocAllocas.size() == 1) { 00350 // If we can do the quick promotion pass, do so now. 00351 if (PromoteLocallyUsedAlloca(I->first, LocAllocas[0])) 00352 RetryList.push_back(LocAllocas[0]); // Failed, retry later. 00353 } else { 00354 // Locally promote anything possible. Note that if this is unable to 00355 // promote a particular alloca, it puts the alloca onto the Allocas vector 00356 // for global processing. 00357 PromoteLocallyUsedAllocas(I->first, LocAllocas); 00358 } 00359 } 00360 00361 if (Allocas.empty()) 00362 return; // All of the allocas must have been trivial! 00363 00364 // Set the incoming values for the basic block to be null values for all of 00365 // the alloca's. We do this in case there is a load of a value that has not 00366 // been stored yet. In this case, it will get this null value. 00367 // 00368 std::vector<Value *> Values(Allocas.size()); 00369 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) 00370 Values[i] = UndefValue::get(Allocas[i]->getAllocatedType()); 00371 00372 // Walks all basic blocks in the function performing the SSA rename algorithm 00373 // and inserting the phi nodes we marked as necessary 00374 // 00375 RenamePass(F.begin(), 0, Values); 00376 00377 // The renamer uses the Visited set to avoid infinite loops. Clear it now. 00378 Visited.clear(); 00379 00380 // Remove the allocas themselves from the function... 00381 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) { 00382 Instruction *A = Allocas[i]; 00383 00384 // If there are any uses of the alloca instructions left, they must be in 00385 // sections of dead code that were not processed on the dominance frontier. 00386 // Just delete the users now. 00387 // 00388 if (!A->use_empty()) 00389 A->replaceAllUsesWith(UndefValue::get(A->getType())); 00390 if (AST) AST->deleteValue(A); 00391 A->getParent()->getInstList().erase(A); 00392 } 00393 00394 // At this point, the renamer has added entries to PHI nodes for all reachable 00395 // code. Unfortunately, there may be blocks which are not reachable, which 00396 // the renamer hasn't traversed. If this is the case, the PHI nodes may not 00397 // have incoming values for all predecessors. Loop over all PHI nodes we have 00398 // created, inserting undef values if they are missing any incoming values. 00399 // 00400 for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I = 00401 NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) { 00402 00403 std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first)); 00404 std::vector<PHINode*> &PNs = I->second; 00405 assert(!PNs.empty() && "Empty PHI node list??"); 00406 00407 // Loop over all of the PHI nodes and see if there are any that we can get 00408 // rid of because they merge all of the same incoming values. This can 00409 // happen due to undef values coming into the PHI nodes. 00410 PHINode *SomePHI = 0; 00411 for (unsigned i = 0, e = PNs.size(); i != e; ++i) 00412 if (PNs[i]) { 00413 if (Value *V = PNs[i]->hasConstantValue(true)) { 00414 if (!isa<Instruction>(V) || 00415 properlyDominates(cast<Instruction>(V), PNs[i])) { 00416 if (AST && isa<PointerType>(PNs[i]->getType())) 00417 AST->deleteValue(PNs[i]); 00418 PNs[i]->replaceAllUsesWith(V); 00419 PNs[i]->eraseFromParent(); 00420 PNs[i] = 0; 00421 } 00422 } 00423 if (PNs[i]) 00424 SomePHI = PNs[i]; 00425 } 00426 00427 // Only do work here if there the PHI nodes are missing incoming values. We 00428 // know that all PHI nodes that were inserted in a block will have the same 00429 // number of incoming values, so we can just check any PHI node. 00430 if (SomePHI && Preds.size() != SomePHI->getNumIncomingValues()) { 00431 // Ok, now we know that all of the PHI nodes are missing entries for some 00432 // basic blocks. Start by sorting the incoming predecessors for efficient 00433 // access. 00434 std::sort(Preds.begin(), Preds.end()); 00435 00436 // Now we loop through all BB's which have entries in SomePHI and remove 00437 // them from the Preds list. 00438 for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) { 00439 // Do a log(n) search of the Preds list for the entry we want. 00440 std::vector<BasicBlock*>::iterator EntIt = 00441 std::lower_bound(Preds.begin(), Preds.end(), 00442 SomePHI->getIncomingBlock(i)); 00443 assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&& 00444 "PHI node has entry for a block which is not a predecessor!"); 00445 00446 // Remove the entry 00447 Preds.erase(EntIt); 00448 } 00449 00450 // At this point, the blocks left in the preds list must have dummy 00451 // entries inserted into every PHI nodes for the block. 00452 for (unsigned i = 0, e = PNs.size(); i != e; ++i) 00453 if (PHINode *PN = PNs[i]) { 00454 Value *UndefVal = UndefValue::get(PN->getType()); 00455 for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred) 00456 PN->addIncoming(UndefVal, Preds[pred]); 00457 } 00458 } 00459 } 00460 } 00461 00462 // MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not 00463 // "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF 00464 // as usual (inserting the PHI nodes in the DeadPHINodes set), then processes 00465 // each read of the variable. For each block that reads the variable, this 00466 // function is called, which removes used PHI nodes from the DeadPHINodes set. 00467 // After all of the reads have been processed, any PHI nodes left in the 00468 // DeadPHINodes set are removed. 00469 // 00470 void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum, 00471 std::set<PHINode*> &DeadPHINodes) { 00472 // Scan the immediate dominators of this block looking for a block which has a 00473 // PHI node for Alloca num. If we find it, mark the PHI node as being alive! 00474 for (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) { 00475 BasicBlock *DomBB = N->getBlock(); 00476 std::map<BasicBlock*, std::vector<PHINode*> >::iterator 00477 I = NewPhiNodes.find(DomBB); 00478 if (I != NewPhiNodes.end() && I->second[AllocaNum]) { 00479 // Ok, we found an inserted PHI node which dominates this value. 00480 PHINode *DominatingPHI = I->second[AllocaNum]; 00481 00482 // Find out if we previously thought it was dead. 00483 std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI); 00484 if (DPNI != DeadPHINodes.end()) { 00485 // Ok, until now, we thought this PHI node was dead. Mark it as being 00486 // alive/needed. 00487 DeadPHINodes.erase(DPNI); 00488 00489 // Now that we have marked the PHI node alive, also mark any PHI nodes 00490 // which it might use as being alive as well. 00491 for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB); 00492 PI != PE; ++PI) 00493 MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes); 00494 } 00495 } 00496 } 00497 } 00498 00499 /// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic 00500 /// block. If this is the case, avoid traversing the CFG and inserting a lot of 00501 /// potentially useless PHI nodes by just performing a single linear pass over 00502 /// the basic block using the Alloca. 00503 /// 00504 /// If we cannot promote this alloca (because it is read before it is written), 00505 /// return true. This is necessary in cases where, due to control flow, the 00506 /// alloca is potentially undefined on some control flow paths. e.g. code like 00507 /// this is potentially correct: 00508 /// 00509 /// for (...) { if (c) { A = undef; undef = B; } } 00510 /// 00511 /// ... so long as A is not used before undef is set. 00512 /// 00513 bool PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) { 00514 assert(!AI->use_empty() && "There are no uses of the alloca!"); 00515 00516 // Handle degenerate cases quickly. 00517 if (AI->hasOneUse()) { 00518 Instruction *U = cast<Instruction>(AI->use_back()); 00519 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 00520 // Must be a load of uninitialized value. 00521 LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType())); 00522 if (AST && isa<PointerType>(LI->getType())) 00523 AST->deleteValue(LI); 00524 } else { 00525 // Otherwise it must be a store which is never read. 00526 assert(isa<StoreInst>(U)); 00527 } 00528 BB->getInstList().erase(U); 00529 } else { 00530 // Uses of the uninitialized memory location shall get undef. 00531 Value *CurVal = 0; 00532 00533 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { 00534 Instruction *Inst = I++; 00535 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { 00536 if (LI->getOperand(0) == AI) { 00537 if (!CurVal) return true; // Could not locally promote! 00538 00539 // Loads just returns the "current value"... 00540 LI->replaceAllUsesWith(CurVal); 00541 if (AST && isa<PointerType>(LI->getType())) 00542 AST->deleteValue(LI); 00543 BB->getInstList().erase(LI); 00544 } 00545 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 00546 if (SI->getOperand(1) == AI) { 00547 // Store updates the "current value"... 00548 CurVal = SI->getOperand(0); 00549 BB->getInstList().erase(SI); 00550 } 00551 } 00552 } 00553 } 00554 00555 // After traversing the basic block, there should be no more uses of the 00556 // alloca, remove it now. 00557 assert(AI->use_empty() && "Uses of alloca from more than one BB??"); 00558 if (AST) AST->deleteValue(AI); 00559 AI->getParent()->getInstList().erase(AI); 00560 return false; 00561 } 00562 00563 /// PromoteLocallyUsedAllocas - This method is just like 00564 /// PromoteLocallyUsedAlloca, except that it processes multiple alloca 00565 /// instructions in parallel. This is important in cases where we have large 00566 /// basic blocks, as we don't want to rescan the entire basic block for each 00567 /// alloca which is locally used in it (which might be a lot). 00568 void PromoteMem2Reg:: 00569 PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) { 00570 std::map<AllocaInst*, Value*> CurValues; 00571 for (unsigned i = 0, e = AIs.size(); i != e; ++i) 00572 CurValues[AIs[i]] = 0; // Insert with null value 00573 00574 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { 00575 Instruction *Inst = I++; 00576 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { 00577 // Is this a load of an alloca we are tracking? 00578 if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) { 00579 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI); 00580 if (AIt != CurValues.end()) { 00581 // If loading an uninitialized value, allow the inter-block case to 00582 // handle it. Due to control flow, this might actually be ok. 00583 if (AIt->second == 0) { // Use of locally uninitialized value?? 00584 RetryList.push_back(AI); // Retry elsewhere. 00585 CurValues.erase(AIt); // Stop tracking this here. 00586 if (CurValues.empty()) return; 00587 } else { 00588 // Loads just returns the "current value"... 00589 LI->replaceAllUsesWith(AIt->second); 00590 if (AST && isa<PointerType>(LI->getType())) 00591 AST->deleteValue(LI); 00592 BB->getInstList().erase(LI); 00593 } 00594 } 00595 } 00596 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 00597 if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) { 00598 std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI); 00599 if (AIt != CurValues.end()) { 00600 // Store updates the "current value"... 00601 AIt->second = SI->getOperand(0); 00602 BB->getInstList().erase(SI); 00603 } 00604 } 00605 } 00606 } 00607 } 00608 00609 00610 00611 // QueuePhiNode - queues a phi-node to be added to a basic-block for a specific 00612 // Alloca returns true if there wasn't already a phi-node for that variable 00613 // 00614 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo, 00615 unsigned &Version, 00616 std::set<PHINode*> &InsertedPHINodes) { 00617 // Look up the basic-block in question. 00618 std::vector<PHINode*> &BBPNs = NewPhiNodes[BB]; 00619 if (BBPNs.empty()) BBPNs.resize(Allocas.size()); 00620 00621 // If the BB already has a phi node added for the i'th alloca then we're done! 00622 if (BBPNs[AllocaNo]) return false; 00623 00624 // Create a PhiNode using the dereferenced type... and add the phi-node to the 00625 // BasicBlock. 00626 PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(), 00627 Allocas[AllocaNo]->getName() + "." + 00628 utostr(Version++), BB->begin()); 00629 BBPNs[AllocaNo] = PN; 00630 InsertedPHINodes.insert(PN); 00631 00632 if (AST && isa<PointerType>(PN->getType())) 00633 AST->copyValue(PointerAllocaValues[AllocaNo], PN); 00634 00635 return true; 00636 } 00637 00638 00639 // RenamePass - Recursively traverse the CFG of the function, renaming loads and 00640 // stores to the allocas which we are promoting. IncomingVals indicates what 00641 // value each Alloca contains on exit from the predecessor block Pred. 00642 // 00643 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred, 00644 std::vector<Value*> &IncomingVals) { 00645 00646 // If this BB needs a PHI node, update the PHI node for each variable we need 00647 // PHI nodes for. 00648 std::map<BasicBlock*, std::vector<PHINode *> >::iterator 00649 BBPNI = NewPhiNodes.find(BB); 00650 if (BBPNI != NewPhiNodes.end()) { 00651 std::vector<PHINode *> &BBPNs = BBPNI->second; 00652 for (unsigned k = 0; k != BBPNs.size(); ++k) 00653 if (PHINode *PN = BBPNs[k]) { 00654 // Add this incoming value to the PHI node. 00655 PN->addIncoming(IncomingVals[k], Pred); 00656 00657 // The currently active variable for this block is now the PHI. 00658 IncomingVals[k] = PN; 00659 } 00660 } 00661 00662 // don't revisit nodes 00663 if (Visited.count(BB)) return; 00664 00665 // mark as visited 00666 Visited.insert(BB); 00667 00668 for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) { 00669 Instruction *I = II++; // get the instruction, increment iterator 00670 00671 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 00672 if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) { 00673 std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src); 00674 if (AI != AllocaLookup.end()) { 00675 Value *V = IncomingVals[AI->second]; 00676 00677 // walk the use list of this load and replace all uses with r 00678 LI->replaceAllUsesWith(V); 00679 if (AST && isa<PointerType>(LI->getType())) 00680 AST->deleteValue(LI); 00681 BB->getInstList().erase(LI); 00682 } 00683 } 00684 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 00685 // Delete this instruction and mark the name as the current holder of the 00686 // value 00687 if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) { 00688 std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest); 00689 if (ai != AllocaLookup.end()) { 00690 // what value were we writing? 00691 IncomingVals[ai->second] = SI->getOperand(0); 00692 BB->getInstList().erase(SI); 00693 } 00694 } 00695 } 00696 } 00697 00698 // Recurse to our successors. 00699 TerminatorInst *TI = BB->getTerminator(); 00700 for (unsigned i = 0; i != TI->getNumSuccessors(); i++) { 00701 std::vector<Value*> OutgoingVals(IncomingVals); 00702 RenamePass(TI->getSuccessor(i), BB, OutgoingVals); 00703 } 00704 } 00705 00706 /// PromoteMemToReg - Promote the specified list of alloca instructions into 00707 /// scalar registers, inserting PHI nodes as appropriate. This function makes 00708 /// use of DominanceFrontier information. This function does not modify the CFG 00709 /// of the function at all. All allocas must be from the same function. 00710 /// 00711 /// If AST is specified, the specified tracker is updated to reflect changes 00712 /// made to the IR. 00713 /// 00714 void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas, 00715 DominatorTree &DT, DominanceFrontier &DF, 00716 const TargetData &TD, AliasSetTracker *AST) { 00717 // If there is nothing to do, bail out... 00718 if (Allocas.empty()) return; 00719 00720 std::vector<AllocaInst*> RetryList; 00721 PromoteMem2Reg(Allocas, RetryList, DT, DF, TD, AST).run(); 00722 00723 // PromoteMem2Reg may not have been able to promote all of the allocas in one 00724 // pass, run it again if needed. 00725 while (!RetryList.empty()) { 00726 // If we need to retry some allocas, this is due to there being no store 00727 // before a read in a local block. To counteract this, insert a store of 00728 // undef into the alloca right after the alloca itself. 00729 for (unsigned i = 0, e = RetryList.size(); i != e; ++i) { 00730 BasicBlock::iterator BBI = RetryList[i]; 00731 00732 new StoreInst(UndefValue::get(RetryList[i]->getAllocatedType()), 00733 RetryList[i], ++BBI); 00734 } 00735 00736 std::vector<AllocaInst*> NewAllocas; 00737 std::swap(NewAllocas, RetryList); 00738 PromoteMem2Reg(NewAllocas, RetryList, DT, DF, TD, AST).run(); 00739 } 00740 }