| //===- 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 (or that have |
| // PHI nodes which are only loaded from). 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/Analysis/Dominators.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Function.h" |
| #include "llvm/Constant.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Support/StableBasicBlockNumbering.h" |
| #include "Support/StringExtras.h" |
| using namespace llvm; |
| |
| /// isAllocaPromotable - Return true if this alloca is legal for promotion. |
| /// This is true if there are only loads and stores to the alloca... of if there |
| /// is a PHI node using the address which can be trivially transformed. |
| /// |
| bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) { |
| // 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 if (const PHINode *PN = dyn_cast<PHINode>(*UI)) { |
| // We only support PHI nodes in a few simple cases. The PHI node is only |
| // allowed to have one use, which must be a load instruction, and can only |
| // use alloca instructions (no random pointers). Also, there cannot be |
| // any accesses to AI between the PHI node and the use of the PHI. |
| if (!PN->hasOneUse()) return false; |
| |
| // Our transformation causes the unconditional loading of all pointer |
| // operands to the PHI node. Because this could cause a fault if there is |
| // a critical edge in the CFG and if one of the pointers is illegal, we |
| // refuse to promote PHI nodes unless they are obviously safe. For now, |
| // obviously safe means that all of the operands are allocas. |
| // |
| // If we wanted to extend this code to break critical edges, this |
| // restriction could be relaxed, and we could even handle uses of the PHI |
| // node that are volatile loads or stores. |
| // |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| if (!isa<AllocaInst>(PN->getIncomingValue(i))) |
| return false; |
| |
| // Now make sure the one user instruction is in the same basic block as |
| // the PHI, and that there are no loads or stores between the PHI node and |
| // the access. |
| BasicBlock::const_iterator UI = cast<Instruction>(PN->use_back()); |
| if (!isa<LoadInst>(UI) || cast<LoadInst>(UI)->isVolatile()) return false; |
| |
| // Scan looking for memory accesses. |
| // FIXME: this should REALLY use alias analysis. |
| for (--UI; !isa<PHINode>(UI); --UI) |
| if (isa<LoadInst>(UI) || isa<StoreInst>(UI) || isa<CallInst>(UI)) |
| return false; |
| |
| // If we got this far, we can promote the PHI use. |
| } else if (const SelectInst *SI = dyn_cast<SelectInst>(*UI)) { |
| // We only support selects in a few simple cases. The select is only |
| // allowed to have one use, which must be a load instruction, and can only |
| // use alloca instructions (no random pointers). Also, there cannot be |
| // any accesses to AI between the PHI node and the use of the PHI. |
| if (!SI->hasOneUse()) return false; |
| |
| // Our transformation causes the unconditional loading of all pointer |
| // operands of the select. Because this could cause a fault if there is a |
| // critical edge in the CFG and if one of the pointers is illegal, we |
| // refuse to promote the select unless it is obviously safe. For now, |
| // obviously safe means that all of the operands are allocas. |
| // |
| if (!isa<AllocaInst>(SI->getOperand(1)) || |
| !isa<AllocaInst>(SI->getOperand(2))) |
| return false; |
| |
| // Now make sure the one user instruction is in the same basic block as |
| // the PHI, and that there are no loads or stores between the PHI node and |
| // the access. |
| BasicBlock::const_iterator UI = cast<Instruction>(SI->use_back()); |
| if (!isa<LoadInst>(UI) || cast<LoadInst>(UI)->isVolatile()) return false; |
| |
| // Scan looking for memory accesses. |
| // FIXME: this should REALLY use alias analysis. |
| for (--UI; &*UI != SI; --UI) |
| if (isa<LoadInst>(UI) || isa<StoreInst>(UI) || isa<CallInst>(UI)) |
| return false; |
| |
| // If we got this far, we can promote the select use. |
| } else { |
| return false; // Not a load, store, or promotable PHI? |
| } |
| |
| return true; |
| } |
| |
| namespace { |
| struct PromoteMem2Reg { |
| // Allocas - The alloca instructions being promoted |
| std::vector<AllocaInst*> Allocas; |
| DominatorTree &DT; |
| DominanceFrontier &DF; |
| const TargetData &TD; |
| |
| // AllocaLookup - Reverse mapping of Allocas |
| std::map<AllocaInst*, unsigned> AllocaLookup; |
| |
| // NewPhiNodes - The PhiNodes we're adding. |
| std::map<BasicBlock*, std::vector<PHINode*> > NewPhiNodes; |
| |
| // Visited - The set of basic blocks the renamer has already visited. |
| std::set<BasicBlock*> Visited; |
| |
| // BBNumbers - Contains a stable numbering of basic blocks to avoid |
| // non-determinstic behavior. |
| StableBasicBlockNumbering BBNumbers; |
| |
| public: |
| PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt, |
| DominanceFrontier &df, const TargetData &td) |
| : Allocas(A), DT(dt), DF(df), TD(td) {} |
| |
| void run(); |
| |
| private: |
| void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum, |
| std::set<PHINode*> &DeadPHINodes); |
| void 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, |
| std::set<PHINode*> &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; |
| |
| |
| for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) { |
| AllocaInst *AI = Allocas[AllocaNum]; |
| |
| assert(isAllocaPromotable(AI, TD) && |
| "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. |
| AI->getParent()->getInstList().erase(AI); |
| |
| // 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; |
| |
| 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. |
| RestartUseScan: |
| 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()); |
| } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { |
| // Otherwise it must be a load instruction, keep track of variable reads |
| UsingBlocks.push_back(LI->getParent()); |
| } else if (SelectInst *SI = dyn_cast<SelectInst>(User)) { |
| // Because of the restrictions we placed on Select instruction uses |
| // above things are very simple. Transform the PHI of addresses into a |
| // select of loaded values. |
| LoadInst *Load = cast<LoadInst>(SI->use_back()); |
| std::string LoadName = Load->getName(); Load->setName(""); |
| |
| Value *TrueVal = new LoadInst(SI->getOperand(1), |
| SI->getOperand(1)->getName()+".val", SI); |
| Value *FalseVal = new LoadInst(SI->getOperand(2), |
| SI->getOperand(2)->getName()+".val", SI); |
| |
| Value *NewSI = new SelectInst(SI->getOperand(0), TrueVal, |
| FalseVal, Load->getName(), SI); |
| Load->replaceAllUsesWith(NewSI); |
| Load->getParent()->getInstList().erase(Load); |
| SI->getParent()->getInstList().erase(SI); |
| |
| // Restart our scan of uses... |
| DefiningBlocks.clear(); |
| UsingBlocks.clear(); |
| goto RestartUseScan; |
| } else { |
| // Because of the restrictions we placed on PHI node uses above, the PHI |
| // node reads the block in any using predecessors. Transform the PHI of |
| // addresses into a PHI of loaded values. |
| PHINode *PN = cast<PHINode>(User); |
| assert(PN->hasOneUse() && "Cannot handle PHI Node with != 1 use!"); |
| LoadInst *PNUser = cast<LoadInst>(PN->use_back()); |
| std::string PNUserName = PNUser->getName(); PNUser->setName(""); |
| |
| // Create the new PHI node and insert load instructions as appropriate. |
| PHINode *NewPN = new PHINode(AI->getAllocatedType(), PNUserName, PN); |
| std::map<BasicBlock*, LoadInst*> NewLoads; |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { |
| BasicBlock *Pred = PN->getIncomingBlock(i); |
| LoadInst *&NewLoad = NewLoads[Pred]; |
| if (NewLoad == 0) // Insert the new load in the predecessor |
| NewLoad = new LoadInst(PN->getIncomingValue(i), |
| PN->getIncomingValue(i)->getName()+".val", |
| Pred->getTerminator()); |
| NewPN->addIncoming(NewLoad, Pred); |
| } |
| |
| // Remove the old load. |
| PNUser->replaceAllUsesWith(NewPN); |
| PNUser->getParent()->getInstList().erase(PNUser); |
| |
| // Remove the old PHI node. |
| PN->getParent()->getInstList().erase(PN); |
| |
| // Restart our scan of uses... |
| DefiningBlocks.clear(); |
| UsingBlocks.clear(); |
| goto RestartUseScan; |
| } |
| |
| 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 we haven't computed a numbering for the BB's in the function, do so |
| // now. |
| BBNumbers.compute(F); |
| |
| // 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; |
| std::set<PHINode*> InsertedPHINodes; |
| std::vector<unsigned> 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::iterator P = S.begin(),PE = S.end(); |
| P != PE; ++P) |
| DFBlocks.push_back(BBNumbers.getNumber(*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 = BBNumbers.getBlock(DFBlocks[i]); |
| 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 (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(), |
| E = InsertedPHINodes.end(); I != E; ++I) { |
| PHINode *PN = *I; |
| std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()]; |
| BBPNs[AllocaNum] = 0; |
| |
| // Check to see if we just removed the last inserted PHI node from this |
| // basic block. If so, remove the entry for the basic block. |
| bool HasOtherPHIs = false; |
| for (unsigned i = 0, e = BBPNs.size(); i != e; ++i) |
| if (BBPNs[i]) { |
| HasOtherPHIs = true; |
| break; |
| } |
| if (!HasOtherPHIs) |
| NewPhiNodes.erase(PN->getParent()); |
| |
| PN->getParent()->getInstList().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*> &Allocas = I->second; |
| assert(!Allocas.empty() && "empty alloca list??"); |
| |
| // It's common for there to only be one alloca in the list. Handle it |
| // efficiently. |
| if (Allocas.size() == 1) |
| PromoteLocallyUsedAlloca(I->first, Allocas[0]); |
| else |
| PromoteLocallyUsedAllocas(I->first, Allocas); |
| } |
| |
| 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] = Constant::getNullValue(Allocas[i]->getAllocatedType()); |
| |
| // Walks all basic blocks in the function performing the SSA rename algorithm |
| // and inserting the phi nodes we marked as necessary |
| // |
| RenamePass(F.begin(), 0, 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(Constant::getNullValue(A->getType())); |
| A->getParent()->getInstList().erase(A); |
| } |
| |
| // At this point, the renamer has added entries to PHI nodes for all reachable |
| // code. Unfortunately, there may be blocks which are not reachable, 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 null constants if they are missing any incoming values. |
| // |
| for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I = |
| NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) { |
| |
| std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first)); |
| std::vector<PHINode*> &PNs = I->second; |
| assert(!PNs.empty() && "Empty PHI node list??"); |
| |
| // 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 PHI node. |
| PHINode *FirstPHI; |
| for (unsigned i = 0; (FirstPHI = PNs[i]) == 0; ++i) |
| /*empty*/; |
| |
| if (Preds.size() != FirstPHI->getNumIncomingValues()) { |
| // 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 FirstPHI and remove |
| // them from the Preds list. |
| for (unsigned i = 0, e = FirstPHI->getNumIncomingValues(); i != e; ++i) { |
| // Do a log(n) search of the Preds list for the entry we want. |
| std::vector<BasicBlock*>::iterator EntIt = |
| std::lower_bound(Preds.begin(), Preds.end(), |
| FirstPHI->getIncomingBlock(i)); |
| assert(EntIt != Preds.end() && *EntIt == FirstPHI->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. |
| for (unsigned i = 0, e = PNs.size(); i != e; ++i) |
| if (PHINode *PN = PNs[i]) { |
| Value *NullVal = Constant::getNullValue(PN->getType()); |
| for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred) |
| PN->addIncoming(NullVal, Preds[pred]); |
| } |
| } |
| } |
| } |
| |
| // 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, |
| std::set<PHINode*> &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 (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) { |
| BasicBlock *DomBB = N->getBlock(); |
| std::map<BasicBlock*, std::vector<PHINode*> >::iterator |
| I = NewPhiNodes.find(DomBB); |
| if (I != NewPhiNodes.end() && I->second[AllocaNum]) { |
| // Ok, we found an inserted PHI node which dominates this value. |
| PHINode *DominatingPHI = I->second[AllocaNum]; |
| |
| // Find out if we previously thought it was dead. |
| std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI); |
| if (DPNI != DeadPHINodes.end()) { |
| // Ok, until now, we thought this PHI node was dead. Mark it as being |
| // alive/needed. |
| DeadPHINodes.erase(DPNI); |
| |
| // 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. |
| /// |
| void 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(Constant::getNullValue(AI->getAllocatedType())); |
| } 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 zero... |
| Value *CurVal = Constant::getNullValue(AI->getAllocatedType()); |
| |
| 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) { |
| // Loads just returns the "current value"... |
| LI->replaceAllUsesWith(CurVal); |
| 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??"); |
| AI->getParent()->getInstList().erase(AI); |
| } |
| |
| /// 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()) { |
| // Loads just returns the "current value"... |
| if (AIt->second == 0) // Uninitialized value?? |
| AIt->second =Constant::getNullValue(AIt->first->getAllocatedType()); |
| LI->replaceAllUsesWith(AIt->second); |
| 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, |
| std::set<PHINode*> &InsertedPHINodes) { |
| // Look up the basic-block in question |
| std::vector<PHINode*> &BBPNs = NewPhiNodes[BB]; |
| if (BBPNs.empty()) BBPNs.resize(Allocas.size()); |
| |
| // If the BB already has a phi node added for the i'th alloca then we're done! |
| if (BBPNs[AllocaNo]) return false; |
| |
| // Create a PhiNode using the dereferenced type... and add the phi-node to the |
| // BasicBlock. |
| BBPNs[AllocaNo] = new PHINode(Allocas[AllocaNo]->getAllocatedType(), |
| Allocas[AllocaNo]->getName() + "." + |
| utostr(Version++), BB->begin()); |
| InsertedPHINodes.insert(BBPNs[AllocaNo]); |
| 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 this BB needs a PHI node, update the PHI node for each variable we need |
| // PHI nodes for. |
| std::map<BasicBlock*, std::vector<PHINode *> >::iterator |
| BBPNI = NewPhiNodes.find(BB); |
| if (BBPNI != NewPhiNodes.end()) { |
| std::vector<PHINode *> &BBPNs = BBPNI->second; |
| for (unsigned k = 0; k != BBPNs.size(); ++k) |
| if (PHINode *PN = BBPNs[k]) { |
| // Add this incoming value to the PHI node. |
| PN->addIncoming(IncomingVals[k], Pred); |
| |
| // The currently active variable for this block is now the PHI. |
| IncomingVals[k] = PN; |
| } |
| } |
| |
| // don't revisit nodes |
| if (Visited.count(BB)) return; |
| |
| // mark as visited |
| Visited.insert(BB); |
| |
| 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); |
| 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++) { |
| std::vector<Value*> OutgoingVals(IncomingVals); |
| RenamePass(TI->getSuccessor(i), BB, OutgoingVals); |
| } |
| } |
| |
| /// 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. |
| /// |
| void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas, |
| DominatorTree &DT, DominanceFrontier &DF, |
| const TargetData &TD) { |
| // If there is nothing to do, bail out... |
| if (Allocas.empty()) return; |
| PromoteMem2Reg(Allocas, DT, DF, TD).run(); |
| } |
