From b5500b9ca0102f1ccaf32f0e77e96d0739aded9b Mon Sep 17 00:00:00 2001 From: pascal Date: Sat, 3 Sep 2016 22:46:54 +0000 Subject: Use the space freed up by sparc and zaurus to import LLVM. ok hackroom@ --- .../Transforms/Utils/PromoteMemoryToRegister.cpp | 993 +++++++++++++++++++++ 1 file changed, 993 insertions(+) create mode 100644 gnu/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp (limited to 'gnu/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp') diff --git a/gnu/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/gnu/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp new file mode 100644 index 00000000000..c4f9b9f6140 --- /dev/null +++ b/gnu/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp @@ -0,0 +1,993 @@ +//===- 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 iterated dominator frontiers to place PHI nodes, then +// traversing the function in depth-first order to rewrite loads and stores as +// appropriate. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/PromoteMemToReg.h" +#include "llvm/ADT/ArrayRef.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasSetTracker.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/IteratedDominanceFrontier.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/CFG.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DIBuilder.h" +#include "llvm/IR/DebugInfo.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/Transforms/Utils/Local.h" +#include +using namespace llvm; + +#define DEBUG_TYPE "mem2reg" + +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"); + +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. + unsigned AS = AI->getType()->getAddressSpace(); + + // Only allow direct and non-volatile loads and stores... + for (const User *U : AI->users()) { + if (const LoadInst *LI = dyn_cast(U)) { + // Note that atomic loads can be transformed; atomic semantics do + // not have any meaning for a local alloca. + if (LI->isVolatile()) + return false; + } else if (const StoreInst *SI = dyn_cast(U)) { + if (SI->getOperand(0) == AI) + return false; // Don't allow a store OF the AI, only INTO the AI. + // Note that atomic stores can be transformed; atomic semantics do + // not have any meaning for a local alloca. + if (SI->isVolatile()) + return false; + } else if (const IntrinsicInst *II = dyn_cast(U)) { + if (II->getIntrinsicID() != Intrinsic::lifetime_start && + II->getIntrinsicID() != Intrinsic::lifetime_end) + return false; + } else if (const BitCastInst *BCI = dyn_cast(U)) { + if (BCI->getType() != Type::getInt8PtrTy(U->getContext(), AS)) + return false; + if (!onlyUsedByLifetimeMarkers(BCI)) + return false; + } else if (const GetElementPtrInst *GEPI = dyn_cast(U)) { + if (GEPI->getType() != Type::getInt8PtrTy(U->getContext(), AS)) + return false; + if (!GEPI->hasAllZeroIndices()) + return false; + if (!onlyUsedByLifetimeMarkers(GEPI)) + return false; + } else { + return false; + } + } + + return true; +} + +namespace { + +struct AllocaInfo { + SmallVector DefiningBlocks; + SmallVector UsingBlocks; + + StoreInst *OnlyStore; + BasicBlock *OnlyBlock; + bool OnlyUsedInOneBlock; + + Value *AllocaPointerVal; + DbgDeclareInst *DbgDeclare; + + void clear() { + DefiningBlocks.clear(); + UsingBlocks.clear(); + OnlyStore = nullptr; + OnlyBlock = nullptr; + OnlyUsedInOneBlock = true; + AllocaPointerVal = nullptr; + DbgDeclare = nullptr; + } + + /// Scan the uses of the specified alloca, filling in the AllocaInfo used + /// by the rest of the pass to reason about the uses of this alloca. + 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 (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) { + Instruction *User = cast(*UI++); + + if (StoreInst *SI = dyn_cast(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(User); + // Otherwise it must be a load instruction, keep track of variable + // reads. + UsingBlocks.push_back(LI->getParent()); + AllocaPointerVal = LI; + } + + if (OnlyUsedInOneBlock) { + if (!OnlyBlock) + OnlyBlock = User->getParent(); + else if (OnlyBlock != User->getParent()) + OnlyUsedInOneBlock = false; + } + } + + DbgDeclare = FindAllocaDbgDeclare(AI); + } +}; + +// Data package used by RenamePass() +class RenamePassData { +public: + typedef std::vector ValVector; + + RenamePassData() : BB(nullptr), Pred(nullptr), Values() {} + 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); + } +}; + +/// \brief 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 LargeBlockInfo { + /// \brief 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 InstNumbers; + +public: + + /// This code only looks at accesses to allocas. + static bool isInterestingInstruction(const Instruction *I) { + return (isa(I) && isa(I->getOperand(0))) || + (isa(I) && isa(I->getOperand(1))); + } + + /// 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::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 (const Instruction &BBI : *BB) + 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 PromoteMem2Reg { + /// The alloca instructions being promoted. + std::vector Allocas; + DominatorTree &DT; + DIBuilder DIB; + + /// An AliasSetTracker object to update. If null, don't update it. + AliasSetTracker *AST; + + /// A cache of @llvm.assume intrinsics used by SimplifyInstruction. + AssumptionCache *AC; + + /// Reverse mapping of Allocas. + DenseMap AllocaLookup; + + /// \brief The PhiNodes we're adding. + /// + /// That map is used to simplify some Phi nodes as we iterate over it, so + /// it should have deterministic iterators. We could use a MapVector, but + /// since we already maintain a map from BasicBlock* to a stable numbering + /// (BBNumbers), the DenseMap is more efficient (also supports removal). + DenseMap, PHINode *> NewPhiNodes; + + /// For each PHI node, keep track of which entry in Allocas it corresponds + /// to. + DenseMap PhiToAllocaMap; + + /// 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 PointerAllocaValues; + + /// For each alloca, we keep track of the dbg.declare intrinsic that + /// describes it, if any, so that we can convert it to a dbg.value + /// intrinsic if the alloca gets promoted. + SmallVector AllocaDbgDeclares; + + /// The set of basic blocks the renamer has already visited. + /// + SmallPtrSet Visited; + + /// Contains a stable numbering of basic blocks to avoid non-determinstic + /// behavior. + DenseMap BBNumbers; + + /// Lazily compute the number of predecessors a block has. + DenseMap BBNumPreds; + +public: + PromoteMem2Reg(ArrayRef Allocas, DominatorTree &DT, + AliasSetTracker *AST, AssumptionCache *AC) + : Allocas(Allocas.begin(), Allocas.end()), DT(DT), + DIB(*DT.getRoot()->getParent()->getParent(), /*AllowUnresolved*/ false), + AST(AST), AC(AC) {} + + void run(); + +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 ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info, + const SmallPtrSetImpl &DefBlocks, + SmallPtrSetImpl &LiveInBlocks); + void RenamePass(BasicBlock *BB, BasicBlock *Pred, + RenamePassData::ValVector &IncVals, + std::vector &Worklist); + bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version); +}; + +} // end of anonymous namespace + +static void removeLifetimeIntrinsicUsers(AllocaInst *AI) { + // Knowing that this alloca is promotable, we know that it's safe to kill all + // instructions except for load and store. + + for (auto UI = AI->user_begin(), UE = AI->user_end(); UI != UE;) { + Instruction *I = cast(*UI); + ++UI; + if (isa(I) || isa(I)) + continue; + + if (!I->getType()->isVoidTy()) { + // The only users of this bitcast/GEP instruction are lifetime intrinsics. + // Follow the use/def chain to erase them now instead of leaving it for + // dead code elimination later. + for (auto UUI = I->user_begin(), UUE = I->user_end(); UUI != UUE;) { + Instruction *Inst = cast(*UUI); + ++UUI; + Inst->eraseFromParent(); + } + } + I->eraseFromParent(); + } +} + +/// \brief Rewrite as many loads as possible given a single store. +/// +/// When there is only a single store, we can use the domtree to trivially +/// replace all of the dominated loads with the stored value. Do so, and return +/// true if this has successfully promoted the alloca entirely. If this returns +/// false there were some loads which were not dominated by the single store +/// and thus must be phi-ed with undef. We fall back to the standard alloca +/// promotion algorithm in that case. +static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info, + LargeBlockInfo &LBI, + DominatorTree &DT, + AliasSetTracker *AST) { + StoreInst *OnlyStore = Info.OnlyStore; + bool StoringGlobalVal = !isa(OnlyStore->getOperand(0)); + BasicBlock *StoreBB = OnlyStore->getParent(); + int StoreIndex = -1; + + // Clear out UsingBlocks. We will reconstruct it here if needed. + Info.UsingBlocks.clear(); + + for (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) { + Instruction *UserInst = cast(*UI++); + if (!isa(UserInst)) { + assert(UserInst == OnlyStore && "Should only have load/stores"); + continue; + } + LoadInst *LI = cast(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 && + !DT.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. + Value *ReplVal = OnlyStore->getOperand(0); + // If the replacement value is the load, this must occur in unreachable + // code. + if (ReplVal == LI) + ReplVal = UndefValue::get(LI->getType()); + LI->replaceAllUsesWith(ReplVal); + if (AST && LI->getType()->isPointerTy()) + AST->deleteValue(LI); + LI->eraseFromParent(); + LBI.deleteValue(LI); + } + + // Finally, after the scan, check to see if the store is all that is left. + if (!Info.UsingBlocks.empty()) + return false; // If not, we'll have to fall back for the remainder. + + // Record debuginfo for the store and remove the declaration's + // debuginfo. + if (DbgDeclareInst *DDI = Info.DbgDeclare) { + DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false); + ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore, DIB); + DDI->eraseFromParent(); + LBI.deleteValue(DDI); + } + // Remove the (now dead) store and alloca. + Info.OnlyStore->eraseFromParent(); + LBI.deleteValue(Info.OnlyStore); + + if (AST) + AST->deleteValue(AI); + AI->eraseFromParent(); + LBI.deleteValue(AI); + return true; +} + +/// 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 false. This is necessary in cases where, due to control flow, the +/// alloca is undefined only on some control flow paths. e.g. code like +/// this is correct in LLVM IR: +/// // A is an alloca with no stores so far +/// for (...) { +/// int t = *A; +/// if (!first_iteration) +/// use(t); +/// *A = 42; +/// } +static bool promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info, + LargeBlockInfo &LBI, + AliasSetTracker *AST) { + // 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. + + // Walk the use-def list of the alloca, getting the locations of all stores. + typedef SmallVector, 64> StoresByIndexTy; + StoresByIndexTy StoresByIndex; + + for (User *U : AI->users()) + if (StoreInst *SI = dyn_cast(U)) + StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI)); + + // Sort the stores by their index, making it efficient to do a lookup with a + // binary search. + std::sort(StoresByIndex.begin(), StoresByIndex.end(), less_first()); + + // Walk all of the loads from this alloca, replacing them with the nearest + // store above them, if any. + for (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) { + LoadInst *LI = dyn_cast(*UI++); + if (!LI) + continue; + + unsigned LoadIdx = LBI.getInstructionIndex(LI); + + // Find the nearest store that has a lower index than this load. + StoresByIndexTy::iterator I = + std::lower_bound(StoresByIndex.begin(), StoresByIndex.end(), + std::make_pair(LoadIdx, + static_cast(nullptr)), + less_first()); + if (I == StoresByIndex.begin()) { + if (StoresByIndex.empty()) + // If there are no stores, the load takes the undef value. + LI->replaceAllUsesWith(UndefValue::get(LI->getType())); + else + // There is no store before this load, bail out (load may be affected + // by the following stores - see main comment). + return false; + } + else + // Otherwise, there was a store before this load, the load takes its value. + LI->replaceAllUsesWith(std::prev(I)->second->getOperand(0)); + + if (AST && LI->getType()->isPointerTy()) + AST->deleteValue(LI); + LI->eraseFromParent(); + LBI.deleteValue(LI); + } + + // Remove the (now dead) stores and alloca. + while (!AI->use_empty()) { + StoreInst *SI = cast(AI->user_back()); + // Record debuginfo for the store before removing it. + if (DbgDeclareInst *DDI = Info.DbgDeclare) { + DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false); + ConvertDebugDeclareToDebugValue(DDI, SI, DIB); + } + SI->eraseFromParent(); + LBI.deleteValue(SI); + } + + if (AST) + AST->deleteValue(AI); + AI->eraseFromParent(); + LBI.deleteValue(AI); + + // The alloca's debuginfo can be removed as well. + if (DbgDeclareInst *DDI = Info.DbgDeclare) { + DDI->eraseFromParent(); + LBI.deleteValue(DDI); + } + + ++NumLocalPromoted; + return true; +} + +void PromoteMem2Reg::run() { + Function &F = *DT.getRoot()->getParent(); + + if (AST) + PointerAllocaValues.resize(Allocas.size()); + AllocaDbgDeclares.resize(Allocas.size()); + + AllocaInfo Info; + LargeBlockInfo LBI; + IDFCalculator IDF(DT); + + 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!"); + + removeLifetimeIntrinsicUsers(AI); + + 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) { + if (rewriteSingleStoreAlloca(AI, Info, LBI, DT, AST)) { + // 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, AST)) { + // The alloca has been processed, move on. + RemoveFromAllocasList(AllocaNum); + 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 (auto &BB : F) + BBNumbers[&BB] = 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; + + // Remember the dbg.declare intrinsic describing this alloca, if any. + if (Info.DbgDeclare) + AllocaDbgDeclares[AllocaNum] = Info.DbgDeclare; + + // 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. + + + // Unique the set of defining blocks for efficient lookup. + SmallPtrSet 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 LiveInBlocks; + ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks); + + // 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. + IDF.setLiveInBlocks(LiveInBlocks); + IDF.setDefiningBlocks(DefBlocks); + SmallVector PHIBlocks; + IDF.calculate(PHIBlocks); + if (PHIBlocks.size() > 1) + std::sort(PHIBlocks.begin(), PHIBlocks.end(), + [this](BasicBlock *A, BasicBlock *B) { + return BBNumbers.lookup(A) < BBNumbers.lookup(B); + }); + + unsigned CurrentVersion = 0; + for (unsigned i = 0, e = PHIBlocks.size(); i != e; ++i) + QueuePhiNode(PHIBlocks[i], AllocaNum, CurrentVersion); + } + + 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] = 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 + // + std::vector RenamePassWorkList; + RenamePassWorkList.emplace_back(&F.front(), nullptr, std::move(Values)); + do { + RenamePassData RPD; + RPD.swap(RenamePassWorkList.back()); + RenamePassWorkList.pop_back(); + // RenamePass may add new worklist entries. + RenamePass(RPD.BB, RPD.Pred, RPD.Values, RenamePassWorkList); + } while (!RenamePassWorkList.empty()); + + // 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 + // unreachable basic blocks that were not processed by walking the dominator + // tree. Just delete the users now. + if (!A->use_empty()) + A->replaceAllUsesWith(UndefValue::get(A->getType())); + if (AST) + AST->deleteValue(A); + A->eraseFromParent(); + } + + const DataLayout &DL = F.getParent()->getDataLayout(); + + // Remove alloca's dbg.declare instrinsics from the function. + for (unsigned i = 0, e = AllocaDbgDeclares.size(); i != e; ++i) + if (DbgDeclareInst *DDI = AllocaDbgDeclares[i]) + DDI->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; + + // Iterating over NewPhiNodes is deterministic, so it is safe to try to + // simplify and RAUW them as we go. If it was not, we could add uses to + // the values we replace with in a non-deterministic order, thus creating + // non-deterministic def->use chains. + for (DenseMap, 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 = SimplifyInstruction(PN, DL, nullptr, &DT, AC)) { + if (AST && PN->getType()->isPointerTy()) + 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, 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 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. + SmallVectorImpl::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(BBI++)) && + SomePHI->getNumIncomingValues() == NumBadPreds) { + Value *UndefVal = UndefValue::get(SomePHI->getType()); + for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred) + SomePHI->addIncoming(UndefVal, Preds[pred]); + } + } + + NewPhiNodes.clear(); +} + +/// \brief 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 SmallPtrSetImpl &DefBlocks, + SmallPtrSetImpl &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 LiveInBlockWorklist(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(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; + } + + if (LoadInst *LI = dyn_cast(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).second) + 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); + } + } +} + +/// \brief Queue 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) { + // Look up the basic-block in question. + PHINode *&PN = NewPhiNodes[std::make_pair(BBNumbers[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(), getNumPreds(BB), + Allocas[AllocaNo]->getName() + "." + Twine(Version++), + &BB->front()); + ++NumPHIInsert; + PhiToAllocaMap[PN] = AllocaNo; + + if (AST && PN->getType()->isPointerTy()) + AST->copyValue(PointerAllocaValues[AllocaNo], PN); + + return true; +} + +/// \brief 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 &Worklist) { +NextIteration: + // If we are inserting any phi nodes into this BB, they will already be in the + // block. + if (PHINode *APN = dyn_cast(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 = std::count(succ_begin(Pred), succ_end(Pred), BB); + 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(PNI); + if (!APN) + 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).second) + return; + + for (BasicBlock::iterator II = BB->begin(); !isa(II);) { + Instruction *I = &*II++; // get the instruction, increment iterator + + if (LoadInst *LI = dyn_cast(I)) { + AllocaInst *Src = dyn_cast(LI->getPointerOperand()); + if (!Src) + continue; + + DenseMap::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 && LI->getType()->isPointerTy()) + AST->deleteValue(LI); + BB->getInstList().erase(LI); + } else if (StoreInst *SI = dyn_cast(I)) { + // Delete this instruction and mark the name as the current holder of the + // value + AllocaInst *Dest = dyn_cast(SI->getPointerOperand()); + if (!Dest) + continue; + + DenseMap::iterator ai = AllocaLookup.find(Dest); + if (ai == AllocaLookup.end()) + continue; + + // what value were we writing? + IncomingVals[ai->second] = SI->getOperand(0); + // Record debuginfo for the store before removing it. + if (DbgDeclareInst *DDI = AllocaDbgDeclares[ai->second]) + ConvertDebugDeclareToDebugValue(DDI, SI, DIB); + 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 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).second) + Worklist.emplace_back(*I, Pred, IncomingVals); + + goto NextIteration; +} + +void llvm::PromoteMemToReg(ArrayRef Allocas, DominatorTree &DT, + AliasSetTracker *AST, AssumptionCache *AC) { + // If there is nothing to do, bail out... + if (Allocas.empty()) + return; + + PromoteMem2Reg(Allocas, DT, AST, AC).run(); +} -- cgit v1.2.3-59-g8ed1b