| //===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file promote memory references to be register references. It promotes |
| // alloca instructions which only have loads and stores as uses. An alloca is |
| // transformed by using dominator frontiers to place PHI nodes, then traversing |
| // the function in depth-first order to rewrite loads and stores as appropriate. |
| // This is just the standard SSA construction algorithm to construct "pruned" |
| // SSA form. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Utils/PromoteMemToReg.h" |
| #include "llvm/Constants.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Function.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/AliasSetTracker.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/StringExtras.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Support/Compiler.h" |
| #include <algorithm> |
| using namespace llvm; |
| |
| // Provide DenseMapKeyInfo for all pointers. |
| namespace llvm { |
| template<> |
| struct DenseMapKeyInfo<std::pair<BasicBlock*, unsigned> > { |
| static inline std::pair<BasicBlock*, unsigned> getEmptyKey() { |
| return std::make_pair((BasicBlock*)-1, ~0U); |
| } |
| static inline std::pair<BasicBlock*, unsigned> getTombstoneKey() { |
| return std::make_pair((BasicBlock*)-2, 0U); |
| } |
| static unsigned getHashValue(const std::pair<BasicBlock*, unsigned> &Val) { |
| return DenseMapKeyInfo<void*>::getHashValue(Val.first) + Val.second*2; |
| } |
| static bool isPod() { return true; } |
| }; |
| } |
| |
| /// isAllocaPromotable - Return true if this alloca is legal for promotion. |
| /// This is true if there are only loads and stores to the alloca. |
| /// |
| bool llvm::isAllocaPromotable(const AllocaInst *AI) { |
| // FIXME: If the memory unit is of pointer or integer type, we can permit |
| // assignments to subsections of the memory unit. |
| |
| // Only allow direct loads and stores... |
| for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end(); |
| UI != UE; ++UI) // Loop over all of the uses of the alloca |
| if (isa<LoadInst>(*UI)) { |
| // noop |
| } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) { |
| if (SI->getOperand(0) == AI) |
| return false; // Don't allow a store OF the AI, only INTO the AI. |
| } else { |
| return false; // Not a load or store. |
| } |
| |
| return true; |
| } |
| |
| namespace { |
| |
| // Data package used by RenamePass() |
| class VISIBILITY_HIDDEN RenamePassData { |
| public: |
| RenamePassData(BasicBlock *B, BasicBlock *P, |
| const std::vector<Value *> &V) : BB(B), Pred(P), Values(V) {} |
| BasicBlock *BB; |
| BasicBlock *Pred; |
| std::vector<Value *> Values; |
| }; |
| |
| struct VISIBILITY_HIDDEN PromoteMem2Reg { |
| /// Allocas - The alloca instructions being promoted. |
| /// |
| std::vector<AllocaInst*> Allocas; |
| SmallVector<AllocaInst*, 16> &RetryList; |
| ETForest &ET; |
| DominanceFrontier &DF; |
| |
| /// AST - An AliasSetTracker object to update. If null, don't update it. |
| /// |
| AliasSetTracker *AST; |
| |
| /// AllocaLookup - Reverse mapping of Allocas. |
| /// |
| std::map<AllocaInst*, unsigned> AllocaLookup; |
| |
| /// NewPhiNodes - The PhiNodes we're adding. |
| /// |
| DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*> NewPhiNodes; |
| |
| /// PhiToAllocaMap - For each PHI node, keep track of which entry in Allocas |
| /// it corresponds to. |
| DenseMap<PHINode*, unsigned> PhiToAllocaMap; |
| |
| /// PointerAllocaValues - If we are updating an AliasSetTracker, then for |
| /// each alloca that is of pointer type, we keep track of what to copyValue |
| /// to the inserted PHI nodes here. |
| /// |
| std::vector<Value*> PointerAllocaValues; |
| |
| /// Visited - The set of basic blocks the renamer has already visited. |
| /// |
| SmallPtrSet<BasicBlock*, 16> Visited; |
| |
| /// BBNumbers - Contains a stable numbering of basic blocks to avoid |
| /// non-determinstic behavior. |
| DenseMap<BasicBlock*, unsigned> BBNumbers; |
| |
| /// RenamePassWorkList - Worklist used by RenamePass() |
| std::vector<RenamePassData> RenamePassWorkList; |
| |
| public: |
| PromoteMem2Reg(const std::vector<AllocaInst*> &A, |
| SmallVector<AllocaInst*, 16> &Retry, ETForest &et, |
| DominanceFrontier &df, AliasSetTracker *ast) |
| : Allocas(A), RetryList(Retry), ET(et), DF(df), AST(ast) {} |
| |
| void run(); |
| |
| /// properlyDominates - Return true if I1 properly dominates I2. |
| /// |
| bool properlyDominates(Instruction *I1, Instruction *I2) const { |
| if (InvokeInst *II = dyn_cast<InvokeInst>(I1)) |
| I1 = II->getNormalDest()->begin(); |
| return ET.properlyDominates(I1->getParent(), I2->getParent()); |
| } |
| |
| /// dominates - Return true if BB1 dominates BB2 using the ETForest. |
| /// |
| bool dominates(BasicBlock *BB1, BasicBlock *BB2) const { |
| return ET.dominates(BB1, BB2); |
| } |
| |
| private: |
| void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum, |
| SmallPtrSet<PHINode*, 16> &DeadPHINodes); |
| bool PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI); |
| void PromoteLocallyUsedAllocas(BasicBlock *BB, |
| const std::vector<AllocaInst*> &AIs); |
| |
| void RenamePass(BasicBlock *BB, BasicBlock *Pred, |
| std::vector<Value*> &IncVals); |
| bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version, |
| SmallPtrSet<PHINode*, 16> &InsertedPHINodes); |
| }; |
| |
| } // end of anonymous namespace |
| |
| void PromoteMem2Reg::run() { |
| Function &F = *DF.getRoot()->getParent(); |
| |
| // LocallyUsedAllocas - Keep track of all of the alloca instructions which are |
| // only used in a single basic block. These instructions can be efficiently |
| // promoted by performing a single linear scan over that one block. Since |
| // individual basic blocks are sometimes large, we group together all allocas |
| // that are live in a single basic block by the basic block they are live in. |
| std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas; |
| |
| if (AST) PointerAllocaValues.resize(Allocas.size()); |
| |
| for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) { |
| AllocaInst *AI = Allocas[AllocaNum]; |
| |
| assert(isAllocaPromotable(AI) && |
| "Cannot promote non-promotable alloca!"); |
| assert(AI->getParent()->getParent() == &F && |
| "All allocas should be in the same function, which is same as DF!"); |
| |
| if (AI->use_empty()) { |
| // If there are no uses of the alloca, just delete it now. |
| if (AST) AST->deleteValue(AI); |
| AI->eraseFromParent(); |
| |
| // Remove the alloca from the Allocas list, since it has been processed |
| Allocas[AllocaNum] = Allocas.back(); |
| Allocas.pop_back(); |
| --AllocaNum; |
| continue; |
| } |
| |
| // Calculate the set of read and write-locations for each alloca. This is |
| // analogous to finding the 'uses' and 'definitions' of each variable. |
| std::vector<BasicBlock*> DefiningBlocks; |
| std::vector<BasicBlock*> UsingBlocks; |
| |
| StoreInst *OnlyStore = 0; |
| BasicBlock *OnlyBlock = 0; |
| bool OnlyUsedInOneBlock = true; |
| |
| // As we scan the uses of the alloca instruction, keep track of stores, and |
| // decide whether all of the loads and stores to the alloca are within the |
| // same basic block. |
| Value *AllocaPointerVal = 0; |
| for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){ |
| Instruction *User = cast<Instruction>(*U); |
| if (StoreInst *SI = dyn_cast<StoreInst>(User)) { |
| // Remember the basic blocks which define new values for the alloca |
| DefiningBlocks.push_back(SI->getParent()); |
| AllocaPointerVal = SI->getOperand(0); |
| OnlyStore = SI; |
| } else { |
| LoadInst *LI = cast<LoadInst>(User); |
| // Otherwise it must be a load instruction, keep track of variable reads |
| UsingBlocks.push_back(LI->getParent()); |
| AllocaPointerVal = LI; |
| } |
| |
| if (OnlyUsedInOneBlock) { |
| if (OnlyBlock == 0) |
| OnlyBlock = User->getParent(); |
| else if (OnlyBlock != User->getParent()) |
| OnlyUsedInOneBlock = false; |
| } |
| } |
| |
| // If the alloca is only read and written in one basic block, just perform a |
| // linear sweep over the block to eliminate it. |
| if (OnlyUsedInOneBlock) { |
| LocallyUsedAllocas[OnlyBlock].push_back(AI); |
| |
| // Remove the alloca from the Allocas list, since it will be processed. |
| Allocas[AllocaNum] = Allocas.back(); |
| Allocas.pop_back(); |
| --AllocaNum; |
| continue; |
| } |
| |
| // If there is only a single store to this value, replace any loads of |
| // it that are directly dominated by the definition with the value stored. |
| if (DefiningBlocks.size() == 1) { |
| // Be aware of loads before the store. |
| std::set<BasicBlock*> ProcessedBlocks; |
| for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i) |
| // If the store dominates the block and if we haven't processed it yet, |
| // do so now. |
| if (dominates(OnlyStore->getParent(), UsingBlocks[i])) |
| if (ProcessedBlocks.insert(UsingBlocks[i]).second) { |
| BasicBlock *UseBlock = UsingBlocks[i]; |
| |
| // If the use and store are in the same block, do a quick scan to |
| // verify that there are no uses before the store. |
| if (UseBlock == OnlyStore->getParent()) { |
| BasicBlock::iterator I = UseBlock->begin(); |
| for (; &*I != OnlyStore; ++I) { // scan block for store. |
| if (isa<LoadInst>(I) && I->getOperand(0) == AI) |
| break; |
| } |
| if (&*I != OnlyStore) break; // Do not handle this case. |
| } |
| |
| // Otherwise, if this is a different block or if all uses happen |
| // after the store, do a simple linear scan to replace loads with |
| // the stored value. |
| for (BasicBlock::iterator I = UseBlock->begin(),E = UseBlock->end(); |
| I != E; ) { |
| if (LoadInst *LI = dyn_cast<LoadInst>(I++)) { |
| if (LI->getOperand(0) == AI) { |
| LI->replaceAllUsesWith(OnlyStore->getOperand(0)); |
| if (AST && isa<PointerType>(LI->getType())) |
| AST->deleteValue(LI); |
| LI->eraseFromParent(); |
| } |
| } |
| } |
| |
| // Finally, remove this block from the UsingBlock set. |
| UsingBlocks[i] = UsingBlocks.back(); |
| --i; --e; |
| } |
| |
| // Finally, after the scan, check to see if the store is all that is left. |
| if (UsingBlocks.empty()) { |
| // The alloca has been processed, move on. |
| Allocas[AllocaNum] = Allocas.back(); |
| Allocas.pop_back(); |
| --AllocaNum; |
| continue; |
| } |
| } |
| |
| |
| if (AST) |
| PointerAllocaValues[AllocaNum] = AllocaPointerVal; |
| |
| // If we haven't computed a numbering for the BB's in the function, do so |
| // now. |
| if (BBNumbers.empty()) { |
| unsigned ID = 0; |
| for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) |
| BBNumbers[I] = ID++; |
| } |
| |
| // Compute the locations where PhiNodes need to be inserted. Look at the |
| // dominance frontier of EACH basic-block we have a write in. |
| // |
| unsigned CurrentVersion = 0; |
| SmallPtrSet<PHINode*, 16> InsertedPHINodes; |
| std::vector<std::pair<unsigned, BasicBlock*> > DFBlocks; |
| while (!DefiningBlocks.empty()) { |
| BasicBlock *BB = DefiningBlocks.back(); |
| DefiningBlocks.pop_back(); |
| |
| // Look up the DF for this write, add it to PhiNodes |
| DominanceFrontier::const_iterator it = DF.find(BB); |
| if (it != DF.end()) { |
| const DominanceFrontier::DomSetType &S = it->second; |
| |
| // In theory we don't need the indirection through the DFBlocks vector. |
| // In practice, the order of calling QueuePhiNode would depend on the |
| // (unspecified) ordering of basic blocks in the dominance frontier, |
| // which would give PHI nodes non-determinstic subscripts. Fix this by |
| // processing blocks in order of the occurance in the function. |
| for (DominanceFrontier::DomSetType::const_iterator P = S.begin(), |
| PE = S.end(); P != PE; ++P) |
| DFBlocks.push_back(std::make_pair(BBNumbers[*P], *P)); |
| |
| // Sort by which the block ordering in the function. |
| std::sort(DFBlocks.begin(), DFBlocks.end()); |
| |
| for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) { |
| BasicBlock *BB = DFBlocks[i].second; |
| if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes)) |
| DefiningBlocks.push_back(BB); |
| } |
| DFBlocks.clear(); |
| } |
| } |
| |
| // Now that we have inserted PHI nodes along the Iterated Dominance Frontier |
| // of the writes to the variable, scan through the reads of the variable, |
| // marking PHI nodes which are actually necessary as alive (by removing them |
| // from the InsertedPHINodes set). This is not perfect: there may PHI |
| // marked alive because of loads which are dominated by stores, but there |
| // will be no unmarked PHI nodes which are actually used. |
| // |
| for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i) |
| MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes); |
| UsingBlocks.clear(); |
| |
| // If there are any PHI nodes which are now known to be dead, remove them! |
| for (SmallPtrSet<PHINode*, 16>::iterator I = InsertedPHINodes.begin(), |
| E = InsertedPHINodes.end(); I != E; ++I) { |
| PHINode *PN = *I; |
| bool Erased=NewPhiNodes.erase(std::make_pair(PN->getParent(), AllocaNum)); |
| Erased=Erased; |
| assert(Erased && "PHI already removed?"); |
| |
| if (AST && isa<PointerType>(PN->getType())) |
| AST->deleteValue(PN); |
| PN->eraseFromParent(); |
| PhiToAllocaMap.erase(PN); |
| } |
| |
| // Keep the reverse mapping of the 'Allocas' array. |
| AllocaLookup[Allocas[AllocaNum]] = AllocaNum; |
| } |
| |
| // Process all allocas which are only used in a single basic block. |
| for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I = |
| LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){ |
| const std::vector<AllocaInst*> &LocAllocas = I->second; |
| assert(!LocAllocas.empty() && "empty alloca list??"); |
| |
| // It's common for there to only be one alloca in the list. Handle it |
| // efficiently. |
| if (LocAllocas.size() == 1) { |
| // If we can do the quick promotion pass, do so now. |
| if (PromoteLocallyUsedAlloca(I->first, LocAllocas[0])) |
| RetryList.push_back(LocAllocas[0]); // Failed, retry later. |
| } else { |
| // Locally promote anything possible. Note that if this is unable to |
| // promote a particular alloca, it puts the alloca onto the Allocas vector |
| // for global processing. |
| PromoteLocallyUsedAllocas(I->first, LocAllocas); |
| } |
| } |
| |
| if (Allocas.empty()) |
| return; // All of the allocas must have been trivial! |
| |
| // Set the incoming values for the basic block to be null values for all of |
| // the alloca's. We do this in case there is a load of a value that has not |
| // been stored yet. In this case, it will get this null value. |
| // |
| std::vector<Value *> Values(Allocas.size()); |
| for (unsigned i = 0, e = Allocas.size(); i != e; ++i) |
| Values[i] = UndefValue::get(Allocas[i]->getAllocatedType()); |
| |
| // Walks all basic blocks in the function performing the SSA rename algorithm |
| // and inserting the phi nodes we marked as necessary |
| // |
| RenamePassWorkList.clear(); |
| RenamePassWorkList.push_back(RenamePassData(F.begin(), 0, Values)); |
| while(!RenamePassWorkList.empty()) { |
| RenamePassData RPD = RenamePassWorkList.back(); |
| RenamePassWorkList.pop_back(); |
| // RenamePass may add new worklist entries. |
| RenamePass(RPD.BB, RPD.Pred, RPD.Values); |
| } |
| |
| // The renamer uses the Visited set to avoid infinite loops. Clear it now. |
| Visited.clear(); |
| |
| // Remove the allocas themselves from the function. |
| for (unsigned i = 0, e = Allocas.size(); i != e; ++i) { |
| Instruction *A = Allocas[i]; |
| |
| // If there are any uses of the alloca instructions left, they must be in |
| // sections of dead code that were not processed on the dominance frontier. |
| // Just delete the users now. |
| // |
| if (!A->use_empty()) |
| A->replaceAllUsesWith(UndefValue::get(A->getType())); |
| if (AST) AST->deleteValue(A); |
| A->eraseFromParent(); |
| } |
| |
| |
| // Loop over all of the PHI nodes and see if there are any that we can get |
| // rid of because they merge all of the same incoming values. This can |
| // happen due to undef values coming into the PHI nodes. This process is |
| // iterative, because eliminating one PHI node can cause others to be removed. |
| bool EliminatedAPHI = true; |
| while (EliminatedAPHI) { |
| EliminatedAPHI = false; |
| |
| for (DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator I = |
| NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E;) { |
| PHINode *PN = I->second; |
| |
| // If this PHI node merges one value and/or undefs, get the value. |
| if (Value *V = PN->hasConstantValue(true)) { |
| if (!isa<Instruction>(V) || |
| properlyDominates(cast<Instruction>(V), PN)) { |
| if (AST && isa<PointerType>(PN->getType())) |
| AST->deleteValue(PN); |
| PN->replaceAllUsesWith(V); |
| PN->eraseFromParent(); |
| NewPhiNodes.erase(I++); |
| EliminatedAPHI = true; |
| continue; |
| } |
| } |
| ++I; |
| } |
| } |
| |
| // At this point, the renamer has added entries to PHI nodes for all reachable |
| // code. Unfortunately, there may be unreachable blocks which the renamer |
| // hasn't traversed. If this is the case, the PHI nodes may not |
| // have incoming values for all predecessors. Loop over all PHI nodes we have |
| // created, inserting undef values if they are missing any incoming values. |
| // |
| for (DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator I = |
| NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) { |
| // We want to do this once per basic block. As such, only process a block |
| // when we find the PHI that is the first entry in the block. |
| PHINode *SomePHI = I->second; |
| BasicBlock *BB = SomePHI->getParent(); |
| if (&BB->front() != SomePHI) |
| continue; |
| |
| // Count the number of preds for BB. |
| SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); |
| |
| // Only do work here if there the PHI nodes are missing incoming values. We |
| // know that all PHI nodes that were inserted in a block will have the same |
| // number of incoming values, so we can just check any of them. |
| if (SomePHI->getNumIncomingValues() == Preds.size()) |
| continue; |
| |
| // Ok, now we know that all of the PHI nodes are missing entries for some |
| // basic blocks. Start by sorting the incoming predecessors for efficient |
| // access. |
| std::sort(Preds.begin(), Preds.end()); |
| |
| // Now we loop through all BB's which have entries in SomePHI and remove |
| // them from the Preds list. |
| for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) { |
| // Do a log(n) search of the Preds list for the entry we want. |
| SmallVector<BasicBlock*, 16>::iterator EntIt = |
| std::lower_bound(Preds.begin(), Preds.end(), |
| SomePHI->getIncomingBlock(i)); |
| assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&& |
| "PHI node has entry for a block which is not a predecessor!"); |
| |
| // Remove the entry |
| Preds.erase(EntIt); |
| } |
| |
| // At this point, the blocks left in the preds list must have dummy |
| // entries inserted into every PHI nodes for the block. Update all the phi |
| // nodes in this block that we are inserting (there could be phis before |
| // mem2reg runs). |
| unsigned NumBadPreds = SomePHI->getNumIncomingValues(); |
| BasicBlock::iterator BBI = BB->begin(); |
| while ((SomePHI = dyn_cast<PHINode>(BBI++)) && |
| SomePHI->getNumIncomingValues() == NumBadPreds) { |
| Value *UndefVal = UndefValue::get(SomePHI->getType()); |
| for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred) |
| SomePHI->addIncoming(UndefVal, Preds[pred]); |
| } |
| } |
| |
| NewPhiNodes.clear(); |
| } |
| |
| // MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not |
| // "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF |
| // as usual (inserting the PHI nodes in the DeadPHINodes set), then processes |
| // each read of the variable. For each block that reads the variable, this |
| // function is called, which removes used PHI nodes from the DeadPHINodes set. |
| // After all of the reads have been processed, any PHI nodes left in the |
| // DeadPHINodes set are removed. |
| // |
| void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum, |
| SmallPtrSet<PHINode*, 16> &DeadPHINodes) { |
| // Scan the immediate dominators of this block looking for a block which has a |
| // PHI node for Alloca num. If we find it, mark the PHI node as being alive! |
| for (BasicBlock* DomBB = BB; DomBB; DomBB = ET.getIDom(DomBB)) { |
| DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator |
| I = NewPhiNodes.find(std::make_pair(DomBB, AllocaNum)); |
| if (I != NewPhiNodes.end()) { |
| // Ok, we found an inserted PHI node which dominates this value. |
| PHINode *DominatingPHI = I->second; |
| |
| // Find out if we previously thought it was dead. If so, mark it as being |
| // live by removing it from the DeadPHINodes set. |
| if (DeadPHINodes.erase(DominatingPHI)) { |
| // Now that we have marked the PHI node alive, also mark any PHI nodes |
| // which it might use as being alive as well. |
| for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB); |
| PI != PE; ++PI) |
| MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes); |
| } |
| } |
| } |
| } |
| |
| /// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic |
| /// block. If this is the case, avoid traversing the CFG and inserting a lot of |
| /// potentially useless PHI nodes by just performing a single linear pass over |
| /// the basic block using the Alloca. |
| /// |
| /// If we cannot promote this alloca (because it is read before it is written), |
| /// return true. This is necessary in cases where, due to control flow, the |
| /// alloca is potentially undefined on some control flow paths. e.g. code like |
| /// this is potentially correct: |
| /// |
| /// for (...) { if (c) { A = undef; undef = B; } } |
| /// |
| /// ... so long as A is not used before undef is set. |
| /// |
| bool PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) { |
| assert(!AI->use_empty() && "There are no uses of the alloca!"); |
| |
| // Handle degenerate cases quickly. |
| if (AI->hasOneUse()) { |
| Instruction *U = cast<Instruction>(AI->use_back()); |
| if (LoadInst *LI = dyn_cast<LoadInst>(U)) { |
| // Must be a load of uninitialized value. |
| LI->replaceAllUsesWith(UndefValue::get(AI->getAllocatedType())); |
| if (AST && isa<PointerType>(LI->getType())) |
| AST->deleteValue(LI); |
| } else { |
| // Otherwise it must be a store which is never read. |
| assert(isa<StoreInst>(U)); |
| } |
| BB->getInstList().erase(U); |
| } else { |
| // Uses of the uninitialized memory location shall get undef. |
| Value *CurVal = 0; |
| |
| for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { |
| Instruction *Inst = I++; |
| if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { |
| if (LI->getOperand(0) == AI) { |
| if (!CurVal) return true; // Could not locally promote! |
| |
| // Loads just returns the "current value"... |
| LI->replaceAllUsesWith(CurVal); |
| if (AST && isa<PointerType>(LI->getType())) |
| AST->deleteValue(LI); |
| BB->getInstList().erase(LI); |
| } |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { |
| if (SI->getOperand(1) == AI) { |
| // Store updates the "current value"... |
| CurVal = SI->getOperand(0); |
| BB->getInstList().erase(SI); |
| } |
| } |
| } |
| } |
| |
| // After traversing the basic block, there should be no more uses of the |
| // alloca, remove it now. |
| assert(AI->use_empty() && "Uses of alloca from more than one BB??"); |
| if (AST) AST->deleteValue(AI); |
| AI->getParent()->getInstList().erase(AI); |
| return false; |
| } |
| |
| /// PromoteLocallyUsedAllocas - This method is just like |
| /// PromoteLocallyUsedAlloca, except that it processes multiple alloca |
| /// instructions in parallel. This is important in cases where we have large |
| /// basic blocks, as we don't want to rescan the entire basic block for each |
| /// alloca which is locally used in it (which might be a lot). |
| void PromoteMem2Reg:: |
| PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) { |
| std::map<AllocaInst*, Value*> CurValues; |
| for (unsigned i = 0, e = AIs.size(); i != e; ++i) |
| CurValues[AIs[i]] = 0; // Insert with null value |
| |
| for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { |
| Instruction *Inst = I++; |
| if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { |
| // Is this a load of an alloca we are tracking? |
| if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) { |
| std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI); |
| if (AIt != CurValues.end()) { |
| // If loading an uninitialized value, allow the inter-block case to |
| // handle it. Due to control flow, this might actually be ok. |
| if (AIt->second == 0) { // Use of locally uninitialized value?? |
| RetryList.push_back(AI); // Retry elsewhere. |
| CurValues.erase(AIt); // Stop tracking this here. |
| if (CurValues.empty()) return; |
| } else { |
| // Loads just returns the "current value"... |
| LI->replaceAllUsesWith(AIt->second); |
| if (AST && isa<PointerType>(LI->getType())) |
| AST->deleteValue(LI); |
| BB->getInstList().erase(LI); |
| } |
| } |
| } |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { |
| if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) { |
| std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI); |
| if (AIt != CurValues.end()) { |
| // Store updates the "current value"... |
| AIt->second = SI->getOperand(0); |
| BB->getInstList().erase(SI); |
| } |
| } |
| } |
| } |
| } |
| |
| |
| |
| // QueuePhiNode - queues a phi-node to be added to a basic-block for a specific |
| // Alloca returns true if there wasn't already a phi-node for that variable |
| // |
| bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo, |
| unsigned &Version, |
| SmallPtrSet<PHINode*, 16> &InsertedPHINodes) { |
| // Look up the basic-block in question. |
| PHINode *&PN = NewPhiNodes[std::make_pair(BB, AllocaNo)]; |
| |
| // If the BB already has a phi node added for the i'th alloca then we're done! |
| if (PN) return false; |
| |
| // Create a PhiNode using the dereferenced type... and add the phi-node to the |
| // BasicBlock. |
| PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(), |
| Allocas[AllocaNo]->getName() + "." + |
| utostr(Version++), BB->begin()); |
| PhiToAllocaMap[PN] = AllocaNo; |
| |
| InsertedPHINodes.insert(PN); |
| |
| if (AST && isa<PointerType>(PN->getType())) |
| AST->copyValue(PointerAllocaValues[AllocaNo], PN); |
| |
| return true; |
| } |
| |
| |
| // RenamePass - Recursively traverse the CFG of the function, renaming loads and |
| // stores to the allocas which we are promoting. IncomingVals indicates what |
| // value each Alloca contains on exit from the predecessor block Pred. |
| // |
| void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred, |
| std::vector<Value*> &IncomingVals) { |
| // If we are inserting any phi nodes into this BB, they will already be in the |
| // block. |
| if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) { |
| // Pred may have multiple edges to BB. If so, we want to add N incoming |
| // values to each PHI we are inserting on the first time we see the edge. |
| // Check to see if APN already has incoming values from Pred. This also |
| // prevents us from modifying PHI nodes that are not currently being |
| // inserted. |
| bool HasPredEntries = false; |
| for (unsigned i = 0, e = APN->getNumIncomingValues(); i != e; ++i) { |
| if (APN->getIncomingBlock(i) == Pred) { |
| HasPredEntries = true; |
| break; |
| } |
| } |
| |
| // If we have PHI nodes to update, compute the number of edges from Pred to |
| // BB. |
| if (!HasPredEntries) { |
| TerminatorInst *PredTerm = Pred->getTerminator(); |
| unsigned NumEdges = 0; |
| for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) { |
| if (PredTerm->getSuccessor(i) == BB) |
| ++NumEdges; |
| } |
| assert(NumEdges && "Must be at least one edge from Pred to BB!"); |
| |
| // Add entries for all the phis. |
| BasicBlock::iterator PNI = BB->begin(); |
| do { |
| unsigned AllocaNo = PhiToAllocaMap[APN]; |
| |
| // Add N incoming values to the PHI node. |
| for (unsigned i = 0; i != NumEdges; ++i) |
| APN->addIncoming(IncomingVals[AllocaNo], Pred); |
| |
| // The currently active variable for this block is now the PHI. |
| IncomingVals[AllocaNo] = APN; |
| |
| // Get the next phi node. |
| ++PNI; |
| APN = dyn_cast<PHINode>(PNI); |
| if (APN == 0) break; |
| |
| // Verify it doesn't already have entries for Pred. If it does, it is |
| // not being inserted by this mem2reg invocation. |
| HasPredEntries = false; |
| for (unsigned i = 0, e = APN->getNumIncomingValues(); i != e; ++i) { |
| if (APN->getIncomingBlock(i) == Pred) { |
| HasPredEntries = true; |
| break; |
| } |
| } |
| } while (!HasPredEntries); |
| } |
| } |
| |
| // Don't revisit blocks. |
| if (!Visited.insert(BB)) return; |
| |
| for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) { |
| Instruction *I = II++; // get the instruction, increment iterator |
| |
| if (LoadInst *LI = dyn_cast<LoadInst>(I)) { |
| if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) { |
| std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src); |
| if (AI != AllocaLookup.end()) { |
| Value *V = IncomingVals[AI->second]; |
| |
| // walk the use list of this load and replace all uses with r |
| LI->replaceAllUsesWith(V); |
| if (AST && isa<PointerType>(LI->getType())) |
| AST->deleteValue(LI); |
| BB->getInstList().erase(LI); |
| } |
| } |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { |
| // Delete this instruction and mark the name as the current holder of the |
| // value |
| if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) { |
| std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest); |
| if (ai != AllocaLookup.end()) { |
| // what value were we writing? |
| IncomingVals[ai->second] = SI->getOperand(0); |
| BB->getInstList().erase(SI); |
| } |
| } |
| } |
| } |
| |
| // Recurse to our successors. |
| TerminatorInst *TI = BB->getTerminator(); |
| for (unsigned i = 0; i != TI->getNumSuccessors(); i++) |
| RenamePassWorkList.push_back(RenamePassData(TI->getSuccessor(i), BB, IncomingVals)); |
| } |
| |
| /// PromoteMemToReg - Promote the specified list of alloca instructions into |
| /// scalar registers, inserting PHI nodes as appropriate. This function makes |
| /// use of DominanceFrontier information. This function does not modify the CFG |
| /// of the function at all. All allocas must be from the same function. |
| /// |
| /// If AST is specified, the specified tracker is updated to reflect changes |
| /// made to the IR. |
| /// |
| void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas, |
| ETForest &ET, DominanceFrontier &DF, |
| AliasSetTracker *AST) { |
| // If there is nothing to do, bail out... |
| if (Allocas.empty()) return; |
| |
| SmallVector<AllocaInst*, 16> RetryList; |
| PromoteMem2Reg(Allocas, RetryList, ET, DF, AST).run(); |
| |
| // PromoteMem2Reg may not have been able to promote all of the allocas in one |
| // pass, run it again if needed. |
| std::vector<AllocaInst*> NewAllocas; |
| while (!RetryList.empty()) { |
| // If we need to retry some allocas, this is due to there being no store |
| // before a read in a local block. To counteract this, insert a store of |
| // undef into the alloca right after the alloca itself. |
| for (unsigned i = 0, e = RetryList.size(); i != e; ++i) { |
| BasicBlock::iterator BBI = RetryList[i]; |
| |
| new StoreInst(UndefValue::get(RetryList[i]->getAllocatedType()), |
| RetryList[i], ++BBI); |
| } |
| |
| NewAllocas.assign(RetryList.begin(), RetryList.end()); |
| RetryList.clear(); |
| PromoteMem2Reg(NewAllocas, RetryList, ET, DF, AST).run(); |
| NewAllocas.clear(); |
| } |
| } |