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Diffstat (limited to 'lib/Transforms/Utils/PromoteMemoryToRegister.cpp')
| -rw-r--r-- | lib/Transforms/Utils/PromoteMemoryToRegister.cpp | 676 |
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diff --git a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp new file mode 100644 index 0000000000..d6e6b6cbb1 --- /dev/null +++ b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp @@ -0,0 +1,676 @@ +//===- 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/StringExtras.h" +#include "llvm/Support/CFG.h" +#include "llvm/Support/StableBasicBlockNumbering.h" +#include <algorithm> +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. +/// +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 { + return false; // Not a load or store. + } + + return true; +} + +namespace { + struct PromoteMem2Reg { + /// Allocas - The alloca instructions being promoted. + /// + std::vector<AllocaInst*> Allocas; + std::vector<AllocaInst*> &RetryList; + DominatorTree &DT; + DominanceFrontier &DF; + const TargetData &TD; + + /// 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. + /// + std::map<BasicBlock*, std::vector<PHINode*> > NewPhiNodes; + + /// 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. + /// + 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, + std::vector<AllocaInst*> &Retry, DominatorTree &dt, + DominanceFrontier &df, const TargetData &td, + AliasSetTracker *ast) + : Allocas(A), RetryList(Retry), DT(dt), DF(df), TD(td), AST(ast) {} + + void run(); + + /// dominates - Return true if I1 dominates I2 using the DominatorTree. + /// + bool dominates(Instruction *I1, Instruction *I2) const { + if (InvokeInst *II = dyn_cast<InvokeInst>(I1)) + I1 = II->getNormalDest()->begin(); + return DT[I1->getParent()]->dominates(DT[I2->getParent()]); + } + + private: + void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum, + std::set<PHINode*> &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, + 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; + + if (AST) PointerAllocaValues.resize(Allocas.size()); + + 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. + if (AST) AST->deleteValue(AI); + 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. + 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); + } 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()); + 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 (AST) + PointerAllocaValues[AllocaNum] = AllocaPointerVal; + + // 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::const_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()); + + if (AST && isa<PointerType>(PN->getType())) + AST->deleteValue(PN); + 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*> &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 + // + 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(UndefValue::get(A->getType())); + if (AST) AST->deleteValue(A); + 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 undef values 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??"); + + // 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. + PHINode *SomePHI = 0; + for (unsigned i = 0, e = PNs.size(); i != e; ++i) + if (PNs[i]) { + if (Value *V = PNs[i]->hasConstantValue(true)) { + if (!isa<Instruction>(V) || dominates(cast<Instruction>(V), PNs[i])) { + if (AST && isa<PointerType>(PNs[i]->getType())) + AST->deleteValue(PNs[i]); + PNs[i]->replaceAllUsesWith(V); + PNs[i]->eraseFromParent(); + PNs[i] = 0; + } + } + if (PNs[i]) + SomePHI = PNs[i]; + } + + // 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. + if (SomePHI && Preds.size() != SomePHI->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 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. + std::vector<BasicBlock*>::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. + for (unsigned i = 0, e = PNs.size(); i != e; ++i) + if (PHINode *PN = PNs[i]) { + Value *UndefVal = UndefValue::get(PN->getType()); + for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred) + PN->addIncoming(UndefVal, 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. +/// +/// 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, + 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. + PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(), + Allocas[AllocaNo]->getName() + "." + + utostr(Version++), BB->begin()); + BBPNs[AllocaNo] = PN; + 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 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); + 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++) { + 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. +/// +/// If AST is specified, the specified tracker is updated to reflect changes +/// made to the IR. +/// +void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas, + DominatorTree &DT, DominanceFrontier &DF, + const TargetData &TD, AliasSetTracker *AST) { + // If there is nothing to do, bail out... + if (Allocas.empty()) return; + + std::vector<AllocaInst*> RetryList; + PromoteMem2Reg(Allocas, RetryList, DT, DF, TD, AST).run(); + + // PromoteMem2Reg may not have been able to promote all of the allocas in one + // pass, run it again if needed. + 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); + } + + std::vector<AllocaInst*> NewAllocas; + std::swap(NewAllocas, RetryList); + PromoteMem2Reg(NewAllocas, RetryList, DT, DF, TD, AST).run(); + } +} |