| //===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file promotes 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. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "mem2reg" |
| #include "llvm/Transforms/Utils/PromoteMemToReg.h" |
| #include "llvm/Constants.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Function.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/LLVMContext.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/Statistic.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Support/Compiler.h" |
| #include <algorithm> |
| using namespace llvm; |
| |
| STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block"); |
| STATISTIC(NumSingleStore, "Number of alloca's promoted with a single store"); |
| STATISTIC(NumDeadAlloca, "Number of dead alloca's removed"); |
| STATISTIC(NumPHIInsert, "Number of PHI nodes inserted"); |
| |
| // Provide DenseMapInfo for all pointers. |
| namespace llvm { |
| template<> |
| struct DenseMapInfo<std::pair<BasicBlock*, unsigned> > { |
| typedef std::pair<BasicBlock*, unsigned> EltTy; |
| static inline EltTy getEmptyKey() { |
| return EltTy(reinterpret_cast<BasicBlock*>(-1), ~0U); |
| } |
| static inline EltTy getTombstoneKey() { |
| return EltTy(reinterpret_cast<BasicBlock*>(-2), 0U); |
| } |
| static unsigned getHashValue(const std::pair<BasicBlock*, unsigned> &Val) { |
| return DenseMapInfo<void*>::getHashValue(Val.first) + Val.second*2; |
| } |
| static bool isEqual(const EltTy &LHS, const EltTy &RHS) { |
| return LHS == RHS; |
| } |
| 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 and non-volatile 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 (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) { |
| if (LI->isVolatile()) |
| return false; |
| } 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. |
| if (SI->isVolatile()) |
| return false; |
| } else if (const BitCastInst *BC = dyn_cast<BitCastInst>(*UI)) { |
| // A bitcast that does not feed into debug info inhibits promotion. |
| if (!BC->hasOneUse() || !isa<DbgInfoIntrinsic>(*BC->use_begin())) |
| return false; |
| // If the only use is by debug info, this alloca will not exist in |
| // non-debug code, so don't try to promote; this ensures the same |
| // codegen with debug info. Otherwise, debug info should not |
| // inhibit promotion (but we must examine other uses). |
| if (AI->hasOneUse()) |
| return false; |
| } else { |
| return false; |
| } |
| |
| return true; |
| } |
| |
| namespace { |
| struct AllocaInfo; |
| |
| // Data package used by RenamePass() |
| class VISIBILITY_HIDDEN RenamePassData { |
| public: |
| typedef std::vector<Value *> ValVector; |
| |
| RenamePassData() {} |
| RenamePassData(BasicBlock *B, BasicBlock *P, |
| const ValVector &V) : BB(B), Pred(P), Values(V) {} |
| BasicBlock *BB; |
| BasicBlock *Pred; |
| ValVector Values; |
| |
| void swap(RenamePassData &RHS) { |
| std::swap(BB, RHS.BB); |
| std::swap(Pred, RHS.Pred); |
| Values.swap(RHS.Values); |
| } |
| }; |
| |
| /// LargeBlockInfo - This assigns and keeps a per-bb relative ordering of |
| /// load/store instructions in the block that directly load or store an alloca. |
| /// |
| /// This functionality is important because it avoids scanning large basic |
| /// blocks multiple times when promoting many allocas in the same block. |
| class VISIBILITY_HIDDEN LargeBlockInfo { |
| /// InstNumbers - For each instruction that we track, keep the index of the |
| /// instruction. The index starts out as the number of the instruction from |
| /// the start of the block. |
| DenseMap<const Instruction *, unsigned> InstNumbers; |
| public: |
| |
| /// isInterestingInstruction - This code only looks at accesses to allocas. |
| static bool isInterestingInstruction(const Instruction *I) { |
| return (isa<LoadInst>(I) && isa<AllocaInst>(I->getOperand(0))) || |
| (isa<StoreInst>(I) && isa<AllocaInst>(I->getOperand(1))); |
| } |
| |
| /// getInstructionIndex - Get or calculate the index of the specified |
| /// instruction. |
| unsigned getInstructionIndex(const Instruction *I) { |
| assert(isInterestingInstruction(I) && |
| "Not a load/store to/from an alloca?"); |
| |
| // If we already have this instruction number, return it. |
| DenseMap<const Instruction *, unsigned>::iterator It = InstNumbers.find(I); |
| if (It != InstNumbers.end()) return It->second; |
| |
| // Scan the whole block to get the instruction. This accumulates |
| // information for every interesting instruction in the block, in order to |
| // avoid gratuitus rescans. |
| const BasicBlock *BB = I->getParent(); |
| unsigned InstNo = 0; |
| for (BasicBlock::const_iterator BBI = BB->begin(), E = BB->end(); |
| BBI != E; ++BBI) |
| if (isInterestingInstruction(BBI)) |
| InstNumbers[BBI] = InstNo++; |
| It = InstNumbers.find(I); |
| |
| assert(It != InstNumbers.end() && "Didn't insert instruction?"); |
| return It->second; |
| } |
| |
| void deleteValue(const Instruction *I) { |
| InstNumbers.erase(I); |
| } |
| |
| void clear() { |
| InstNumbers.clear(); |
| } |
| }; |
| |
| struct VISIBILITY_HIDDEN PromoteMem2Reg { |
| /// Allocas - The alloca instructions being promoted. |
| /// |
| std::vector<AllocaInst*> Allocas; |
| DominatorTree &DT; |
| DominanceFrontier &DF; |
| |
| /// AST - An AliasSetTracker object to update. If null, don't update it. |
| /// |
| AliasSetTracker *AST; |
| |
| LLVMContext &Context; |
| |
| /// 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; |
| |
| /// BBNumPreds - Lazily compute the number of predecessors a block has. |
| DenseMap<const BasicBlock*, unsigned> BBNumPreds; |
| public: |
| PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt, |
| DominanceFrontier &df, AliasSetTracker *ast, |
| LLVMContext &C) |
| : Allocas(A), DT(dt), DF(df), AST(ast), Context(C) {} |
| |
| 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 DT.properlyDominates(I1->getParent(), I2->getParent()); |
| } |
| |
| /// dominates - Return true if BB1 dominates BB2 using the DominatorTree. |
| /// |
| bool dominates(BasicBlock *BB1, BasicBlock *BB2) const { |
| return DT.dominates(BB1, BB2); |
| } |
| |
| private: |
| void RemoveFromAllocasList(unsigned &AllocaIdx) { |
| Allocas[AllocaIdx] = Allocas.back(); |
| Allocas.pop_back(); |
| --AllocaIdx; |
| } |
| |
| unsigned getNumPreds(const BasicBlock *BB) { |
| unsigned &NP = BBNumPreds[BB]; |
| if (NP == 0) |
| NP = std::distance(pred_begin(BB), pred_end(BB))+1; |
| return NP-1; |
| } |
| |
| void DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum, |
| AllocaInfo &Info); |
| void ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info, |
| const SmallPtrSet<BasicBlock*, 32> &DefBlocks, |
| SmallPtrSet<BasicBlock*, 32> &LiveInBlocks); |
| |
| void RewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info, |
| LargeBlockInfo &LBI); |
| void PromoteSingleBlockAlloca(AllocaInst *AI, AllocaInfo &Info, |
| LargeBlockInfo &LBI); |
| |
| |
| void RenamePass(BasicBlock *BB, BasicBlock *Pred, |
| RenamePassData::ValVector &IncVals, |
| std::vector<RenamePassData> &Worklist); |
| bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version, |
| SmallPtrSet<PHINode*, 16> &InsertedPHINodes); |
| }; |
| |
| struct AllocaInfo { |
| std::vector<BasicBlock*> DefiningBlocks; |
| std::vector<BasicBlock*> UsingBlocks; |
| |
| StoreInst *OnlyStore; |
| BasicBlock *OnlyBlock; |
| bool OnlyUsedInOneBlock; |
| |
| Value *AllocaPointerVal; |
| |
| void clear() { |
| DefiningBlocks.clear(); |
| UsingBlocks.clear(); |
| OnlyStore = 0; |
| OnlyBlock = 0; |
| OnlyUsedInOneBlock = true; |
| AllocaPointerVal = 0; |
| } |
| |
| /// AnalyzeAlloca - Scan the uses of the specified alloca, filling in our |
| /// ivars. |
| void AnalyzeAlloca(AllocaInst *AI) { |
| clear(); |
| |
| // 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. |
| for (Value::use_iterator U = AI->use_begin(), E = AI->use_end(); |
| U != E;) { |
| Instruction *User = cast<Instruction>(*U); |
| ++U; |
| if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { |
| // Remove any uses of this alloca in DbgInfoInstrinsics. |
| assert(BC->hasOneUse() && "Unexpected alloca uses!"); |
| DbgInfoIntrinsic *DI = cast<DbgInfoIntrinsic>(*BC->use_begin()); |
| DI->eraseFromParent(); |
| BC->eraseFromParent(); |
| continue; |
| } |
| else 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; |
| } |
| } |
| } |
| }; |
| } // end of anonymous namespace |
| |
| |
| void PromoteMem2Reg::run() { |
| Function &F = *DF.getRoot()->getParent(); |
| |
| if (AST) PointerAllocaValues.resize(Allocas.size()); |
| |
| AllocaInfo Info; |
| LargeBlockInfo LBI; |
| |
| 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 |
| RemoveFromAllocasList(AllocaNum); |
| ++NumDeadAlloca; |
| continue; |
| } |
| |
| // Calculate the set of read and write-locations for each alloca. This is |
| // analogous to finding the 'uses' and 'definitions' of each variable. |
| Info.AnalyzeAlloca(AI); |
| |
| // 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 (Info.DefiningBlocks.size() == 1) { |
| RewriteSingleStoreAlloca(AI, Info, LBI); |
| |
| // Finally, after the scan, check to see if the store is all that is left. |
| if (Info.UsingBlocks.empty()) { |
| // Remove the (now dead) store and alloca. |
| Info.OnlyStore->eraseFromParent(); |
| LBI.deleteValue(Info.OnlyStore); |
| |
| if (AST) AST->deleteValue(AI); |
| AI->eraseFromParent(); |
| LBI.deleteValue(AI); |
| |
| // The alloca has been processed, move on. |
| RemoveFromAllocasList(AllocaNum); |
| |
| ++NumSingleStore; |
| continue; |
| } |
| } |
| |
| // If the alloca is only read and written in one basic block, just perform a |
| // linear sweep over the block to eliminate it. |
| if (Info.OnlyUsedInOneBlock) { |
| PromoteSingleBlockAlloca(AI, Info, LBI); |
| |
| // Finally, after the scan, check to see if the stores are all that is |
| // left. |
| if (Info.UsingBlocks.empty()) { |
| |
| // Remove the (now dead) stores and alloca. |
| while (!AI->use_empty()) { |
| StoreInst *SI = cast<StoreInst>(AI->use_back()); |
| SI->eraseFromParent(); |
| LBI.deleteValue(SI); |
| } |
| |
| if (AST) AST->deleteValue(AI); |
| AI->eraseFromParent(); |
| LBI.deleteValue(AI); |
| |
| // The alloca has been processed, move on. |
| RemoveFromAllocasList(AllocaNum); |
| |
| ++NumLocalPromoted; |
| continue; |
| } |
| } |
| |
| // 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++; |
| } |
| |
| // If we have an AST to keep updated, remember some pointer value that is |
| // stored into the alloca. |
| if (AST) |
| PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal; |
| |
| // Keep the reverse mapping of the 'Allocas' array for the rename pass. |
| AllocaLookup[Allocas[AllocaNum]] = AllocaNum; |
| |
| // At this point, we're committed to promoting the alloca using IDF's, and |
| // the standard SSA construction algorithm. Determine which blocks need PHI |
| // nodes and see if we can optimize out some work by avoiding insertion of |
| // dead phi nodes. |
| DetermineInsertionPoint(AI, AllocaNum, Info); |
| } |
| |
| if (Allocas.empty()) |
| return; // All of the allocas must have been trivial! |
| |
| LBI.clear(); |
| |
| |
| // 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. |
| // |
| RenamePassData::ValVector Values(Allocas.size()); |
| for (unsigned i = 0, e = Allocas.size(); i != e; ++i) |
| Values[i] = Context.getUndef(Allocas[i]->getAllocatedType()); |
| |
| // Walks all basic blocks in the function performing the SSA rename algorithm |
| // and inserting the phi nodes we marked as necessary |
| // |
| std::vector<RenamePassData> RenamePassWorkList; |
| RenamePassWorkList.push_back(RenamePassData(F.begin(), 0, Values)); |
| while (!RenamePassWorkList.empty()) { |
| RenamePassData RPD; |
| RPD.swap(RenamePassWorkList.back()); |
| RenamePassWorkList.pop_back(); |
| // RenamePass may add new worklist entries. |
| RenamePass(RPD.BB, RPD.Pred, RPD.Values, RenamePassWorkList); |
| } |
| |
| // 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(Context.getUndef(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; |
| |
| // 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() == getNumPreds(BB)) |
| continue; |
| |
| // Get the preds for BB. |
| SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); |
| |
| // 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 = Context.getUndef(SomePHI->getType()); |
| for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred) |
| SomePHI->addIncoming(UndefVal, Preds[pred]); |
| } |
| } |
| |
| NewPhiNodes.clear(); |
| } |
| |
| |
| /// ComputeLiveInBlocks - Determine which blocks the value is live in. These |
| /// are blocks which lead to uses. Knowing this allows us to avoid inserting |
| /// PHI nodes into blocks which don't lead to uses (thus, the inserted phi nodes |
| /// would be dead). |
| void PromoteMem2Reg:: |
| ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info, |
| const SmallPtrSet<BasicBlock*, 32> &DefBlocks, |
| SmallPtrSet<BasicBlock*, 32> &LiveInBlocks) { |
| |
| // To determine liveness, we must iterate through the predecessors of blocks |
| // where the def is live. Blocks are added to the worklist if we need to |
| // check their predecessors. Start with all the using blocks. |
| SmallVector<BasicBlock*, 64> LiveInBlockWorklist; |
| LiveInBlockWorklist.insert(LiveInBlockWorklist.end(), |
| Info.UsingBlocks.begin(), Info.UsingBlocks.end()); |
| |
| // If any of the using blocks is also a definition block, check to see if the |
| // definition occurs before or after the use. If it happens before the use, |
| // the value isn't really live-in. |
| for (unsigned i = 0, e = LiveInBlockWorklist.size(); i != e; ++i) { |
| BasicBlock *BB = LiveInBlockWorklist[i]; |
| if (!DefBlocks.count(BB)) continue; |
| |
| // Okay, this is a block that both uses and defines the value. If the first |
| // reference to the alloca is a def (store), then we know it isn't live-in. |
| for (BasicBlock::iterator I = BB->begin(); ; ++I) { |
| if (StoreInst *SI = dyn_cast<StoreInst>(I)) { |
| if (SI->getOperand(1) != AI) continue; |
| |
| // We found a store to the alloca before a load. The alloca is not |
| // actually live-in here. |
| LiveInBlockWorklist[i] = LiveInBlockWorklist.back(); |
| LiveInBlockWorklist.pop_back(); |
| --i, --e; |
| break; |
| } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) { |
| if (LI->getOperand(0) != AI) continue; |
| |
| // Okay, we found a load before a store to the alloca. It is actually |
| // live into this block. |
| break; |
| } |
| } |
| } |
| |
| // Now that we have a set of blocks where the phi is live-in, recursively add |
| // their predecessors until we find the full region the value is live. |
| while (!LiveInBlockWorklist.empty()) { |
| BasicBlock *BB = LiveInBlockWorklist.pop_back_val(); |
| |
| // The block really is live in here, insert it into the set. If already in |
| // the set, then it has already been processed. |
| if (!LiveInBlocks.insert(BB)) |
| continue; |
| |
| // Since the value is live into BB, it is either defined in a predecessor or |
| // live into it to. Add the preds to the worklist unless they are a |
| // defining block. |
| for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { |
| BasicBlock *P = *PI; |
| |
| // The value is not live into a predecessor if it defines the value. |
| if (DefBlocks.count(P)) |
| continue; |
| |
| // Otherwise it is, add to the worklist. |
| LiveInBlockWorklist.push_back(P); |
| } |
| } |
| } |
| |
| /// DetermineInsertionPoint - At this point, we're committed to promoting the |
| /// alloca using IDF's, and the standard SSA construction algorithm. Determine |
| /// which blocks need phi nodes and see if we can optimize out some work by |
| /// avoiding insertion of dead phi nodes. |
| void PromoteMem2Reg::DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum, |
| AllocaInfo &Info) { |
| |
| // Unique the set of defining blocks for efficient lookup. |
| SmallPtrSet<BasicBlock*, 32> DefBlocks; |
| DefBlocks.insert(Info.DefiningBlocks.begin(), Info.DefiningBlocks.end()); |
| |
| // Determine which blocks the value is live in. These are blocks which lead |
| // to uses. |
| SmallPtrSet<BasicBlock*, 32> LiveInBlocks; |
| ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks); |
| |
| // 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 (!Info.DefiningBlocks.empty()) { |
| BasicBlock *BB = Info.DefiningBlocks.back(); |
| Info.DefiningBlocks.pop_back(); |
| |
| // Look up the DF for this write, add it to defining blocks. |
| DominanceFrontier::const_iterator it = DF.find(BB); |
| if (it == DF.end()) continue; |
| |
| 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) { |
| // If the frontier block is not in the live-in set for the alloca, don't |
| // bother processing it. |
| if (!LiveInBlocks.count(*P)) |
| continue; |
| |
| DFBlocks.push_back(std::make_pair(BBNumbers[*P], *P)); |
| } |
| |
| // Sort by which the block ordering in the function. |
| if (DFBlocks.size() > 1) |
| 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)) |
| Info.DefiningBlocks.push_back(BB); |
| } |
| DFBlocks.clear(); |
| } |
| } |
| |
| /// RewriteSingleStoreAlloca - 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. |
| void PromoteMem2Reg::RewriteSingleStoreAlloca(AllocaInst *AI, |
| AllocaInfo &Info, |
| LargeBlockInfo &LBI) { |
| StoreInst *OnlyStore = Info.OnlyStore; |
| bool StoringGlobalVal = !isa<Instruction>(OnlyStore->getOperand(0)); |
| BasicBlock *StoreBB = OnlyStore->getParent(); |
| int StoreIndex = -1; |
| |
| // Clear out UsingBlocks. We will reconstruct it here if needed. |
| Info.UsingBlocks.clear(); |
| |
| for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E; ) { |
| Instruction *UserInst = cast<Instruction>(*UI++); |
| if (!isa<LoadInst>(UserInst)) { |
| assert(UserInst == OnlyStore && "Should only have load/stores"); |
| continue; |
| } |
| LoadInst *LI = cast<LoadInst>(UserInst); |
| |
| // Okay, if we have a load from the alloca, we want to replace it with the |
| // only value stored to the alloca. We can do this if the value is |
| // dominated by the store. If not, we use the rest of the mem2reg machinery |
| // to insert the phi nodes as needed. |
| if (!StoringGlobalVal) { // Non-instructions are always dominated. |
| if (LI->getParent() == StoreBB) { |
| // If we have a use that is in the same block as the store, compare the |
| // indices of the two instructions to see which one came first. If the |
| // load came before the store, we can't handle it. |
| if (StoreIndex == -1) |
| StoreIndex = LBI.getInstructionIndex(OnlyStore); |
| |
| if (unsigned(StoreIndex) > LBI.getInstructionIndex(LI)) { |
| // Can't handle this load, bail out. |
| Info.UsingBlocks.push_back(StoreBB); |
| continue; |
| } |
| |
| } else if (LI->getParent() != StoreBB && |
| !dominates(StoreBB, LI->getParent())) { |
| // If the load and store are in different blocks, use BB dominance to |
| // check their relationships. If the store doesn't dom the use, bail |
| // out. |
| Info.UsingBlocks.push_back(LI->getParent()); |
| continue; |
| } |
| } |
| |
| // Otherwise, we *can* safely rewrite this load. |
| LI->replaceAllUsesWith(OnlyStore->getOperand(0)); |
| if (AST && isa<PointerType>(LI->getType())) |
| AST->deleteValue(LI); |
| LI->eraseFromParent(); |
| LBI.deleteValue(LI); |
| } |
| } |
| |
| |
| /// StoreIndexSearchPredicate - This is a helper predicate used to search by the |
| /// first element of a pair. |
| struct StoreIndexSearchPredicate { |
| bool operator()(const std::pair<unsigned, StoreInst*> &LHS, |
| const std::pair<unsigned, StoreInst*> &RHS) { |
| return LHS.first < RHS.first; |
| } |
| }; |
| |
| /// PromoteSingleBlockAlloca - 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. |
| /// |
| void PromoteMem2Reg::PromoteSingleBlockAlloca(AllocaInst *AI, AllocaInfo &Info, |
| LargeBlockInfo &LBI) { |
| // The trickiest case to handle is when we have large blocks. Because of this, |
| // this code is optimized assuming that large blocks happen. This does not |
| // significantly pessimize the small block case. This uses LargeBlockInfo to |
| // make it efficient to get the index of various operations in the block. |
| |
| // Clear out UsingBlocks. We will reconstruct it here if needed. |
| Info.UsingBlocks.clear(); |
| |
| // Walk the use-def list of the alloca, getting the locations of all stores. |
| typedef SmallVector<std::pair<unsigned, StoreInst*>, 64> StoresByIndexTy; |
| StoresByIndexTy StoresByIndex; |
| |
| for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); |
| UI != E; ++UI) |
| if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) |
| StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI)); |
| |
| // If there are no stores to the alloca, just replace any loads with undef. |
| if (StoresByIndex.empty()) { |
| for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;) |
| if (LoadInst *LI = dyn_cast<LoadInst>(*UI++)) { |
| LI->replaceAllUsesWith(Context.getUndef(LI->getType())); |
| if (AST && isa<PointerType>(LI->getType())) |
| AST->deleteValue(LI); |
| LBI.deleteValue(LI); |
| LI->eraseFromParent(); |
| } |
| return; |
| } |
| |
| // Sort the stores by their index, making it efficient to do a lookup with a |
| // binary search. |
| std::sort(StoresByIndex.begin(), StoresByIndex.end()); |
| |
| // Walk all of the loads from this alloca, replacing them with the nearest |
| // store above them, if any. |
| for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;) { |
| LoadInst *LI = dyn_cast<LoadInst>(*UI++); |
| if (!LI) continue; |
| |
| unsigned LoadIdx = LBI.getInstructionIndex(LI); |
| |
| // Find the nearest store that has a lower than this load. |
| StoresByIndexTy::iterator I = |
| std::lower_bound(StoresByIndex.begin(), StoresByIndex.end(), |
| std::pair<unsigned, StoreInst*>(LoadIdx, 0), |
| StoreIndexSearchPredicate()); |
| |
| // If there is no store before this load, then we can't promote this load. |
| if (I == StoresByIndex.begin()) { |
| // Can't handle this load, bail out. |
| Info.UsingBlocks.push_back(LI->getParent()); |
| continue; |
| } |
| |
| // Otherwise, there was a store before this load, the load takes its value. |
| --I; |
| LI->replaceAllUsesWith(I->second->getOperand(0)); |
| if (AST && isa<PointerType>(LI->getType())) |
| AST->deleteValue(LI); |
| LI->eraseFromParent(); |
| LBI.deleteValue(LI); |
| } |
| } |
| |
| |
| // 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 = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(), |
| Allocas[AllocaNo]->getName() + "." + Version++, |
| BB->begin()); |
| ++NumPHIInsert; |
| PhiToAllocaMap[PN] = AllocaNo; |
| PN->reserveOperandSpace(getNumPreds(BB)); |
| |
| 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, |
| RenamePassData::ValVector &IncomingVals, |
| std::vector<RenamePassData> &Worklist) { |
| NextIteration: |
| // 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())) { |
| // If we have PHI nodes to update, compute the number of edges from Pred to |
| // BB. |
| if (PhiToAllocaMap.count(APN)) { |
| // We want to be able to distinguish between PHI nodes being inserted by |
| // this invocation of mem2reg from those phi nodes that already existed in |
| // the IR before mem2reg was run. We determine that APN is being inserted |
| // because it is missing incoming edges. All other PHI nodes being |
| // inserted by this pass of mem2reg will have the same number of incoming |
| // operands so far. Remember this count. |
| unsigned NewPHINumOperands = APN->getNumOperands(); |
| |
| unsigned NumEdges = 0; |
| for (succ_iterator I = succ_begin(Pred), E = succ_end(Pred); I != E; ++I) |
| if (*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 that it is missing entries. If not, it is not being inserted |
| // by this mem2reg invocation so we want to ignore it. |
| } while (APN->getNumOperands() == NewPHINumOperands); |
| } |
| } |
| |
| // 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)) { |
| AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand()); |
| if (!Src) continue; |
| |
| std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src); |
| if (AI == AllocaLookup.end()) continue; |
| |
| Value *V = IncomingVals[AI->second]; |
| |
| // Anything using the load now uses the current value. |
| 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 |
| AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand()); |
| if (!Dest) continue; |
| |
| std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest); |
| if (ai == AllocaLookup.end()) |
| continue; |
| |
| // what value were we writing? |
| IncomingVals[ai->second] = SI->getOperand(0); |
| BB->getInstList().erase(SI); |
| } |
| } |
| |
| // 'Recurse' to our successors. |
| succ_iterator I = succ_begin(BB), E = succ_end(BB); |
| if (I == E) return; |
| |
| // Keep track of the successors so we don't visit the same successor twice |
| SmallPtrSet<BasicBlock*, 8> VisitedSuccs; |
| |
| // Handle the first successor without using the worklist. |
| VisitedSuccs.insert(*I); |
| Pred = BB; |
| BB = *I; |
| ++I; |
| |
| for (; I != E; ++I) |
| if (VisitedSuccs.insert(*I)) |
| Worklist.push_back(RenamePassData(*I, Pred, IncomingVals)); |
| |
| goto NextIteration; |
| } |
| |
| /// 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, |
| LLVMContext &Context, AliasSetTracker *AST) { |
| // If there is nothing to do, bail out... |
| if (Allocas.empty()) return; |
| |
| PromoteMem2Reg(Allocas, DT, DF, AST, Context).run(); |
| } |