diff options
Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/EarlyCSE.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/EarlyCSE.cpp | 890 |
1 files changed, 890 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/contrib/llvm/lib/Transforms/Scalar/EarlyCSE.cpp new file mode 100644 index 0000000..7ef062e --- /dev/null +++ b/contrib/llvm/lib/Transforms/Scalar/EarlyCSE.cpp @@ -0,0 +1,890 @@ +//===- EarlyCSE.cpp - Simple and fast CSE pass ----------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This pass performs a simple dominator tree walk that eliminates trivially +// redundant instructions. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Scalar/EarlyCSE.h" +#include "llvm/ADT/Hashing.h" +#include "llvm/ADT/ScopedHashTable.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/GlobalsModRef.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/PatternMatch.h" +#include "llvm/Pass.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/RecyclingAllocator.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Transforms/Utils/Local.h" +#include <deque> +using namespace llvm; +using namespace llvm::PatternMatch; + +#define DEBUG_TYPE "early-cse" + +STATISTIC(NumSimplify, "Number of instructions simplified or DCE'd"); +STATISTIC(NumCSE, "Number of instructions CSE'd"); +STATISTIC(NumCSELoad, "Number of load instructions CSE'd"); +STATISTIC(NumCSECall, "Number of call instructions CSE'd"); +STATISTIC(NumDSE, "Number of trivial dead stores removed"); + +//===----------------------------------------------------------------------===// +// SimpleValue +//===----------------------------------------------------------------------===// + +namespace { +/// \brief Struct representing the available values in the scoped hash table. +struct SimpleValue { + Instruction *Inst; + + SimpleValue(Instruction *I) : Inst(I) { + assert((isSentinel() || canHandle(I)) && "Inst can't be handled!"); + } + + bool isSentinel() const { + return Inst == DenseMapInfo<Instruction *>::getEmptyKey() || + Inst == DenseMapInfo<Instruction *>::getTombstoneKey(); + } + + static bool canHandle(Instruction *Inst) { + // This can only handle non-void readnone functions. + if (CallInst *CI = dyn_cast<CallInst>(Inst)) + return CI->doesNotAccessMemory() && !CI->getType()->isVoidTy(); + return isa<CastInst>(Inst) || isa<BinaryOperator>(Inst) || + isa<GetElementPtrInst>(Inst) || isa<CmpInst>(Inst) || + isa<SelectInst>(Inst) || isa<ExtractElementInst>(Inst) || + isa<InsertElementInst>(Inst) || isa<ShuffleVectorInst>(Inst) || + isa<ExtractValueInst>(Inst) || isa<InsertValueInst>(Inst); + } +}; +} + +namespace llvm { +template <> struct DenseMapInfo<SimpleValue> { + static inline SimpleValue getEmptyKey() { + return DenseMapInfo<Instruction *>::getEmptyKey(); + } + static inline SimpleValue getTombstoneKey() { + return DenseMapInfo<Instruction *>::getTombstoneKey(); + } + static unsigned getHashValue(SimpleValue Val); + static bool isEqual(SimpleValue LHS, SimpleValue RHS); +}; +} + +unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) { + Instruction *Inst = Val.Inst; + // Hash in all of the operands as pointers. + if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(Inst)) { + Value *LHS = BinOp->getOperand(0); + Value *RHS = BinOp->getOperand(1); + if (BinOp->isCommutative() && BinOp->getOperand(0) > BinOp->getOperand(1)) + std::swap(LHS, RHS); + + if (isa<OverflowingBinaryOperator>(BinOp)) { + // Hash the overflow behavior + unsigned Overflow = + BinOp->hasNoSignedWrap() * OverflowingBinaryOperator::NoSignedWrap | + BinOp->hasNoUnsignedWrap() * + OverflowingBinaryOperator::NoUnsignedWrap; + return hash_combine(BinOp->getOpcode(), Overflow, LHS, RHS); + } + + return hash_combine(BinOp->getOpcode(), LHS, RHS); + } + + if (CmpInst *CI = dyn_cast<CmpInst>(Inst)) { + Value *LHS = CI->getOperand(0); + Value *RHS = CI->getOperand(1); + CmpInst::Predicate Pred = CI->getPredicate(); + if (Inst->getOperand(0) > Inst->getOperand(1)) { + std::swap(LHS, RHS); + Pred = CI->getSwappedPredicate(); + } + return hash_combine(Inst->getOpcode(), Pred, LHS, RHS); + } + + if (CastInst *CI = dyn_cast<CastInst>(Inst)) + return hash_combine(CI->getOpcode(), CI->getType(), CI->getOperand(0)); + + if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst)) + return hash_combine(EVI->getOpcode(), EVI->getOperand(0), + hash_combine_range(EVI->idx_begin(), EVI->idx_end())); + + if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst)) + return hash_combine(IVI->getOpcode(), IVI->getOperand(0), + IVI->getOperand(1), + hash_combine_range(IVI->idx_begin(), IVI->idx_end())); + + assert((isa<CallInst>(Inst) || isa<BinaryOperator>(Inst) || + isa<GetElementPtrInst>(Inst) || isa<SelectInst>(Inst) || + isa<ExtractElementInst>(Inst) || isa<InsertElementInst>(Inst) || + isa<ShuffleVectorInst>(Inst)) && + "Invalid/unknown instruction"); + + // Mix in the opcode. + return hash_combine( + Inst->getOpcode(), + hash_combine_range(Inst->value_op_begin(), Inst->value_op_end())); +} + +bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) { + Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst; + + if (LHS.isSentinel() || RHS.isSentinel()) + return LHSI == RHSI; + + if (LHSI->getOpcode() != RHSI->getOpcode()) + return false; + if (LHSI->isIdenticalTo(RHSI)) + return true; + + // If we're not strictly identical, we still might be a commutable instruction + if (BinaryOperator *LHSBinOp = dyn_cast<BinaryOperator>(LHSI)) { + if (!LHSBinOp->isCommutative()) + return false; + + assert(isa<BinaryOperator>(RHSI) && + "same opcode, but different instruction type?"); + BinaryOperator *RHSBinOp = cast<BinaryOperator>(RHSI); + + // Check overflow attributes + if (isa<OverflowingBinaryOperator>(LHSBinOp)) { + assert(isa<OverflowingBinaryOperator>(RHSBinOp) && + "same opcode, but different operator type?"); + if (LHSBinOp->hasNoUnsignedWrap() != RHSBinOp->hasNoUnsignedWrap() || + LHSBinOp->hasNoSignedWrap() != RHSBinOp->hasNoSignedWrap()) + return false; + } + + // Commuted equality + return LHSBinOp->getOperand(0) == RHSBinOp->getOperand(1) && + LHSBinOp->getOperand(1) == RHSBinOp->getOperand(0); + } + if (CmpInst *LHSCmp = dyn_cast<CmpInst>(LHSI)) { + assert(isa<CmpInst>(RHSI) && + "same opcode, but different instruction type?"); + CmpInst *RHSCmp = cast<CmpInst>(RHSI); + // Commuted equality + return LHSCmp->getOperand(0) == RHSCmp->getOperand(1) && + LHSCmp->getOperand(1) == RHSCmp->getOperand(0) && + LHSCmp->getSwappedPredicate() == RHSCmp->getPredicate(); + } + + return false; +} + +//===----------------------------------------------------------------------===// +// CallValue +//===----------------------------------------------------------------------===// + +namespace { +/// \brief Struct representing the available call values in the scoped hash +/// table. +struct CallValue { + Instruction *Inst; + + CallValue(Instruction *I) : Inst(I) { + assert((isSentinel() || canHandle(I)) && "Inst can't be handled!"); + } + + bool isSentinel() const { + return Inst == DenseMapInfo<Instruction *>::getEmptyKey() || + Inst == DenseMapInfo<Instruction *>::getTombstoneKey(); + } + + static bool canHandle(Instruction *Inst) { + // Don't value number anything that returns void. + if (Inst->getType()->isVoidTy()) + return false; + + CallInst *CI = dyn_cast<CallInst>(Inst); + if (!CI || !CI->onlyReadsMemory()) + return false; + return true; + } +}; +} + +namespace llvm { +template <> struct DenseMapInfo<CallValue> { + static inline CallValue getEmptyKey() { + return DenseMapInfo<Instruction *>::getEmptyKey(); + } + static inline CallValue getTombstoneKey() { + return DenseMapInfo<Instruction *>::getTombstoneKey(); + } + static unsigned getHashValue(CallValue Val); + static bool isEqual(CallValue LHS, CallValue RHS); +}; +} + +unsigned DenseMapInfo<CallValue>::getHashValue(CallValue Val) { + Instruction *Inst = Val.Inst; + // Hash all of the operands as pointers and mix in the opcode. + return hash_combine( + Inst->getOpcode(), + hash_combine_range(Inst->value_op_begin(), Inst->value_op_end())); +} + +bool DenseMapInfo<CallValue>::isEqual(CallValue LHS, CallValue RHS) { + Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst; + if (LHS.isSentinel() || RHS.isSentinel()) + return LHSI == RHSI; + return LHSI->isIdenticalTo(RHSI); +} + +//===----------------------------------------------------------------------===// +// EarlyCSE implementation +//===----------------------------------------------------------------------===// + +namespace { +/// \brief A simple and fast domtree-based CSE pass. +/// +/// This pass does a simple depth-first walk over the dominator tree, +/// eliminating trivially redundant instructions and using instsimplify to +/// canonicalize things as it goes. It is intended to be fast and catch obvious +/// cases so that instcombine and other passes are more effective. It is +/// expected that a later pass of GVN will catch the interesting/hard cases. +class EarlyCSE { +public: + const TargetLibraryInfo &TLI; + const TargetTransformInfo &TTI; + DominatorTree &DT; + AssumptionCache &AC; + typedef RecyclingAllocator< + BumpPtrAllocator, ScopedHashTableVal<SimpleValue, Value *>> AllocatorTy; + typedef ScopedHashTable<SimpleValue, Value *, DenseMapInfo<SimpleValue>, + AllocatorTy> ScopedHTType; + + /// \brief A scoped hash table of the current values of all of our simple + /// scalar expressions. + /// + /// As we walk down the domtree, we look to see if instructions are in this: + /// if so, we replace them with what we find, otherwise we insert them so + /// that dominated values can succeed in their lookup. + ScopedHTType AvailableValues; + + /// A scoped hash table of the current values of previously encounted memory + /// locations. + /// + /// This allows us to get efficient access to dominating loads or stores when + /// we have a fully redundant load. In addition to the most recent load, we + /// keep track of a generation count of the read, which is compared against + /// the current generation count. The current generation count is incremented + /// after every possibly writing memory operation, which ensures that we only + /// CSE loads with other loads that have no intervening store. Ordering + /// events (such as fences or atomic instructions) increment the generation + /// count as well; essentially, we model these as writes to all possible + /// locations. Note that atomic and/or volatile loads and stores can be + /// present the table; it is the responsibility of the consumer to inspect + /// the atomicity/volatility if needed. + struct LoadValue { + Value *Data; + unsigned Generation; + int MatchingId; + bool IsAtomic; + LoadValue() + : Data(nullptr), Generation(0), MatchingId(-1), IsAtomic(false) {} + LoadValue(Value *Data, unsigned Generation, unsigned MatchingId, + bool IsAtomic) + : Data(Data), Generation(Generation), MatchingId(MatchingId), + IsAtomic(IsAtomic) {} + }; + typedef RecyclingAllocator<BumpPtrAllocator, + ScopedHashTableVal<Value *, LoadValue>> + LoadMapAllocator; + typedef ScopedHashTable<Value *, LoadValue, DenseMapInfo<Value *>, + LoadMapAllocator> LoadHTType; + LoadHTType AvailableLoads; + + /// \brief A scoped hash table of the current values of read-only call + /// values. + /// + /// It uses the same generation count as loads. + typedef ScopedHashTable<CallValue, std::pair<Value *, unsigned>> CallHTType; + CallHTType AvailableCalls; + + /// \brief This is the current generation of the memory value. + unsigned CurrentGeneration; + + /// \brief Set up the EarlyCSE runner for a particular function. + EarlyCSE(const TargetLibraryInfo &TLI, const TargetTransformInfo &TTI, + DominatorTree &DT, AssumptionCache &AC) + : TLI(TLI), TTI(TTI), DT(DT), AC(AC), CurrentGeneration(0) {} + + bool run(); + +private: + // Almost a POD, but needs to call the constructors for the scoped hash + // tables so that a new scope gets pushed on. These are RAII so that the + // scope gets popped when the NodeScope is destroyed. + class NodeScope { + public: + NodeScope(ScopedHTType &AvailableValues, LoadHTType &AvailableLoads, + CallHTType &AvailableCalls) + : Scope(AvailableValues), LoadScope(AvailableLoads), + CallScope(AvailableCalls) {} + + private: + NodeScope(const NodeScope &) = delete; + void operator=(const NodeScope &) = delete; + + ScopedHTType::ScopeTy Scope; + LoadHTType::ScopeTy LoadScope; + CallHTType::ScopeTy CallScope; + }; + + // Contains all the needed information to create a stack for doing a depth + // first tranversal of the tree. This includes scopes for values, loads, and + // calls as well as the generation. There is a child iterator so that the + // children do not need to be store spearately. + class StackNode { + public: + StackNode(ScopedHTType &AvailableValues, LoadHTType &AvailableLoads, + CallHTType &AvailableCalls, unsigned cg, DomTreeNode *n, + DomTreeNode::iterator child, DomTreeNode::iterator end) + : CurrentGeneration(cg), ChildGeneration(cg), Node(n), ChildIter(child), + EndIter(end), Scopes(AvailableValues, AvailableLoads, AvailableCalls), + Processed(false) {} + + // Accessors. + unsigned currentGeneration() { return CurrentGeneration; } + unsigned childGeneration() { return ChildGeneration; } + void childGeneration(unsigned generation) { ChildGeneration = generation; } + DomTreeNode *node() { return Node; } + DomTreeNode::iterator childIter() { return ChildIter; } + DomTreeNode *nextChild() { + DomTreeNode *child = *ChildIter; + ++ChildIter; + return child; + } + DomTreeNode::iterator end() { return EndIter; } + bool isProcessed() { return Processed; } + void process() { Processed = true; } + + private: + StackNode(const StackNode &) = delete; + void operator=(const StackNode &) = delete; + + // Members. + unsigned CurrentGeneration; + unsigned ChildGeneration; + DomTreeNode *Node; + DomTreeNode::iterator ChildIter; + DomTreeNode::iterator EndIter; + NodeScope Scopes; + bool Processed; + }; + + /// \brief Wrapper class to handle memory instructions, including loads, + /// stores and intrinsic loads and stores defined by the target. + class ParseMemoryInst { + public: + ParseMemoryInst(Instruction *Inst, const TargetTransformInfo &TTI) + : IsTargetMemInst(false), Inst(Inst) { + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) + if (TTI.getTgtMemIntrinsic(II, Info) && Info.NumMemRefs == 1) + IsTargetMemInst = true; + } + bool isLoad() const { + if (IsTargetMemInst) return Info.ReadMem; + return isa<LoadInst>(Inst); + } + bool isStore() const { + if (IsTargetMemInst) return Info.WriteMem; + return isa<StoreInst>(Inst); + } + bool isAtomic() const { + if (IsTargetMemInst) { + assert(Info.IsSimple && "need to refine IsSimple in TTI"); + return false; + } + return Inst->isAtomic(); + } + bool isUnordered() const { + if (IsTargetMemInst) { + assert(Info.IsSimple && "need to refine IsSimple in TTI"); + return true; + } + if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { + return LI->isUnordered(); + } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + return SI->isUnordered(); + } + // Conservative answer + return !Inst->isAtomic(); + } + + bool isVolatile() const { + if (IsTargetMemInst) { + assert(Info.IsSimple && "need to refine IsSimple in TTI"); + return false; + } + if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { + return LI->isVolatile(); + } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + return SI->isVolatile(); + } + // Conservative answer + return true; + } + + + bool isMatchingMemLoc(const ParseMemoryInst &Inst) const { + return (getPointerOperand() == Inst.getPointerOperand() && + getMatchingId() == Inst.getMatchingId()); + } + bool isValid() const { return getPointerOperand() != nullptr; } + + // For regular (non-intrinsic) loads/stores, this is set to -1. For + // intrinsic loads/stores, the id is retrieved from the corresponding + // field in the MemIntrinsicInfo structure. That field contains + // non-negative values only. + int getMatchingId() const { + if (IsTargetMemInst) return Info.MatchingId; + return -1; + } + Value *getPointerOperand() const { + if (IsTargetMemInst) return Info.PtrVal; + if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { + return LI->getPointerOperand(); + } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + return SI->getPointerOperand(); + } + return nullptr; + } + bool mayReadFromMemory() const { + if (IsTargetMemInst) return Info.ReadMem; + return Inst->mayReadFromMemory(); + } + bool mayWriteToMemory() const { + if (IsTargetMemInst) return Info.WriteMem; + return Inst->mayWriteToMemory(); + } + + private: + bool IsTargetMemInst; + MemIntrinsicInfo Info; + Instruction *Inst; + }; + + bool processNode(DomTreeNode *Node); + + Value *getOrCreateResult(Value *Inst, Type *ExpectedType) const { + if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) + return LI; + else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) + return SI->getValueOperand(); + assert(isa<IntrinsicInst>(Inst) && "Instruction not supported"); + return TTI.getOrCreateResultFromMemIntrinsic(cast<IntrinsicInst>(Inst), + ExpectedType); + } +}; +} + +bool EarlyCSE::processNode(DomTreeNode *Node) { + BasicBlock *BB = Node->getBlock(); + + // If this block has a single predecessor, then the predecessor is the parent + // of the domtree node and all of the live out memory values are still current + // in this block. If this block has multiple predecessors, then they could + // have invalidated the live-out memory values of our parent value. For now, + // just be conservative and invalidate memory if this block has multiple + // predecessors. + if (!BB->getSinglePredecessor()) + ++CurrentGeneration; + + // If this node has a single predecessor which ends in a conditional branch, + // we can infer the value of the branch condition given that we took this + // path. We need the single predeccesor to ensure there's not another path + // which reaches this block where the condition might hold a different + // value. Since we're adding this to the scoped hash table (like any other + // def), it will have been popped if we encounter a future merge block. + if (BasicBlock *Pred = BB->getSinglePredecessor()) + if (auto *BI = dyn_cast<BranchInst>(Pred->getTerminator())) + if (BI->isConditional()) + if (auto *CondInst = dyn_cast<Instruction>(BI->getCondition())) + if (SimpleValue::canHandle(CondInst)) { + assert(BI->getSuccessor(0) == BB || BI->getSuccessor(1) == BB); + auto *ConditionalConstant = (BI->getSuccessor(0) == BB) ? + ConstantInt::getTrue(BB->getContext()) : + ConstantInt::getFalse(BB->getContext()); + AvailableValues.insert(CondInst, ConditionalConstant); + DEBUG(dbgs() << "EarlyCSE CVP: Add conditional value for '" + << CondInst->getName() << "' as " << *ConditionalConstant + << " in " << BB->getName() << "\n"); + // Replace all dominated uses with the known value + replaceDominatedUsesWith(CondInst, ConditionalConstant, DT, + BasicBlockEdge(Pred, BB)); + } + + /// LastStore - Keep track of the last non-volatile store that we saw... for + /// as long as there in no instruction that reads memory. If we see a store + /// to the same location, we delete the dead store. This zaps trivial dead + /// stores which can occur in bitfield code among other things. + Instruction *LastStore = nullptr; + + bool Changed = false; + const DataLayout &DL = BB->getModule()->getDataLayout(); + + // See if any instructions in the block can be eliminated. If so, do it. If + // not, add them to AvailableValues. + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) { + Instruction *Inst = &*I++; + + // Dead instructions should just be removed. + if (isInstructionTriviallyDead(Inst, &TLI)) { + DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n'); + Inst->eraseFromParent(); + Changed = true; + ++NumSimplify; + continue; + } + + // Skip assume intrinsics, they don't really have side effects (although + // they're marked as such to ensure preservation of control dependencies), + // and this pass will not disturb any of the assumption's control + // dependencies. + if (match(Inst, m_Intrinsic<Intrinsic::assume>())) { + DEBUG(dbgs() << "EarlyCSE skipping assumption: " << *Inst << '\n'); + continue; + } + + // If the instruction can be simplified (e.g. X+0 = X) then replace it with + // its simpler value. + if (Value *V = SimplifyInstruction(Inst, DL, &TLI, &DT, &AC)) { + DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << " to: " << *V << '\n'); + Inst->replaceAllUsesWith(V); + Inst->eraseFromParent(); + Changed = true; + ++NumSimplify; + continue; + } + + // If this is a simple instruction that we can value number, process it. + if (SimpleValue::canHandle(Inst)) { + // See if the instruction has an available value. If so, use it. + if (Value *V = AvailableValues.lookup(Inst)) { + DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << " to: " << *V << '\n'); + Inst->replaceAllUsesWith(V); + Inst->eraseFromParent(); + Changed = true; + ++NumCSE; + continue; + } + + // Otherwise, just remember that this value is available. + AvailableValues.insert(Inst, Inst); + continue; + } + + ParseMemoryInst MemInst(Inst, TTI); + // If this is a non-volatile load, process it. + if (MemInst.isValid() && MemInst.isLoad()) { + // (conservatively) we can't peak past the ordering implied by this + // operation, but we can add this load to our set of available values + if (MemInst.isVolatile() || !MemInst.isUnordered()) { + LastStore = nullptr; + ++CurrentGeneration; + } + + // If we have an available version of this load, and if it is the right + // generation, replace this instruction. + LoadValue InVal = AvailableLoads.lookup(MemInst.getPointerOperand()); + if (InVal.Data != nullptr && InVal.Generation == CurrentGeneration && + InVal.MatchingId == MemInst.getMatchingId() && + // We don't yet handle removing loads with ordering of any kind. + !MemInst.isVolatile() && MemInst.isUnordered() && + // We can't replace an atomic load with one which isn't also atomic. + InVal.IsAtomic >= MemInst.isAtomic()) { + Value *Op = getOrCreateResult(InVal.Data, Inst->getType()); + if (Op != nullptr) { + DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << *Inst + << " to: " << *InVal.Data << '\n'); + if (!Inst->use_empty()) + Inst->replaceAllUsesWith(Op); + Inst->eraseFromParent(); + Changed = true; + ++NumCSELoad; + continue; + } + } + + // Otherwise, remember that we have this instruction. + AvailableLoads.insert( + MemInst.getPointerOperand(), + LoadValue(Inst, CurrentGeneration, MemInst.getMatchingId(), + MemInst.isAtomic())); + LastStore = nullptr; + continue; + } + + // If this instruction may read from memory, forget LastStore. + // Load/store intrinsics will indicate both a read and a write to + // memory. The target may override this (e.g. so that a store intrinsic + // does not read from memory, and thus will be treated the same as a + // regular store for commoning purposes). + if (Inst->mayReadFromMemory() && + !(MemInst.isValid() && !MemInst.mayReadFromMemory())) + LastStore = nullptr; + + // If this is a read-only call, process it. + if (CallValue::canHandle(Inst)) { + // If we have an available version of this call, and if it is the right + // generation, replace this instruction. + std::pair<Value *, unsigned> InVal = AvailableCalls.lookup(Inst); + if (InVal.first != nullptr && InVal.second == CurrentGeneration) { + DEBUG(dbgs() << "EarlyCSE CSE CALL: " << *Inst + << " to: " << *InVal.first << '\n'); + if (!Inst->use_empty()) + Inst->replaceAllUsesWith(InVal.first); + Inst->eraseFromParent(); + Changed = true; + ++NumCSECall; + continue; + } + + // Otherwise, remember that we have this instruction. + AvailableCalls.insert( + Inst, std::pair<Value *, unsigned>(Inst, CurrentGeneration)); + continue; + } + + // A release fence requires that all stores complete before it, but does + // not prevent the reordering of following loads 'before' the fence. As a + // result, we don't need to consider it as writing to memory and don't need + // to advance the generation. We do need to prevent DSE across the fence, + // but that's handled above. + if (FenceInst *FI = dyn_cast<FenceInst>(Inst)) + if (FI->getOrdering() == Release) { + assert(Inst->mayReadFromMemory() && "relied on to prevent DSE above"); + continue; + } + + // write back DSE - If we write back the same value we just loaded from + // the same location and haven't passed any intervening writes or ordering + // operations, we can remove the write. The primary benefit is in allowing + // the available load table to remain valid and value forward past where + // the store originally was. + if (MemInst.isValid() && MemInst.isStore()) { + LoadValue InVal = AvailableLoads.lookup(MemInst.getPointerOperand()); + if (InVal.Data && + InVal.Data == getOrCreateResult(Inst, InVal.Data->getType()) && + InVal.Generation == CurrentGeneration && + InVal.MatchingId == MemInst.getMatchingId() && + // We don't yet handle removing stores with ordering of any kind. + !MemInst.isVolatile() && MemInst.isUnordered()) { + assert((!LastStore || + ParseMemoryInst(LastStore, TTI).getPointerOperand() == + MemInst.getPointerOperand()) && + "can't have an intervening store!"); + DEBUG(dbgs() << "EarlyCSE DSE (writeback): " << *Inst << '\n'); + Inst->eraseFromParent(); + Changed = true; + ++NumDSE; + // We can avoid incrementing the generation count since we were able + // to eliminate this store. + continue; + } + } + + // Okay, this isn't something we can CSE at all. Check to see if it is + // something that could modify memory. If so, our available memory values + // cannot be used so bump the generation count. + if (Inst->mayWriteToMemory()) { + ++CurrentGeneration; + + if (MemInst.isValid() && MemInst.isStore()) { + // We do a trivial form of DSE if there are two stores to the same + // location with no intervening loads. Delete the earlier store. + // At the moment, we don't remove ordered stores, but do remove + // unordered atomic stores. There's no special requirement (for + // unordered atomics) about removing atomic stores only in favor of + // other atomic stores since we we're going to execute the non-atomic + // one anyway and the atomic one might never have become visible. + if (LastStore) { + ParseMemoryInst LastStoreMemInst(LastStore, TTI); + assert(LastStoreMemInst.isUnordered() && + !LastStoreMemInst.isVolatile() && + "Violated invariant"); + if (LastStoreMemInst.isMatchingMemLoc(MemInst)) { + DEBUG(dbgs() << "EarlyCSE DEAD STORE: " << *LastStore + << " due to: " << *Inst << '\n'); + LastStore->eraseFromParent(); + Changed = true; + ++NumDSE; + LastStore = nullptr; + } + // fallthrough - we can exploit information about this store + } + + // Okay, we just invalidated anything we knew about loaded values. Try + // to salvage *something* by remembering that the stored value is a live + // version of the pointer. It is safe to forward from volatile stores + // to non-volatile loads, so we don't have to check for volatility of + // the store. + AvailableLoads.insert( + MemInst.getPointerOperand(), + LoadValue(Inst, CurrentGeneration, MemInst.getMatchingId(), + MemInst.isAtomic())); + + // Remember that this was the last unordered store we saw for DSE. We + // don't yet handle DSE on ordered or volatile stores since we don't + // have a good way to model the ordering requirement for following + // passes once the store is removed. We could insert a fence, but + // since fences are slightly stronger than stores in their ordering, + // it's not clear this is a profitable transform. Another option would + // be to merge the ordering with that of the post dominating store. + if (MemInst.isUnordered() && !MemInst.isVolatile()) + LastStore = Inst; + else + LastStore = nullptr; + } + } + } + + return Changed; +} + +bool EarlyCSE::run() { + // Note, deque is being used here because there is significant performance + // gains over vector when the container becomes very large due to the + // specific access patterns. For more information see the mailing list + // discussion on this: + // http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20120116/135228.html + std::deque<StackNode *> nodesToProcess; + + bool Changed = false; + + // Process the root node. + nodesToProcess.push_back(new StackNode( + AvailableValues, AvailableLoads, AvailableCalls, CurrentGeneration, + DT.getRootNode(), DT.getRootNode()->begin(), DT.getRootNode()->end())); + + // Save the current generation. + unsigned LiveOutGeneration = CurrentGeneration; + + // Process the stack. + while (!nodesToProcess.empty()) { + // Grab the first item off the stack. Set the current generation, remove + // the node from the stack, and process it. + StackNode *NodeToProcess = nodesToProcess.back(); + + // Initialize class members. + CurrentGeneration = NodeToProcess->currentGeneration(); + + // Check if the node needs to be processed. + if (!NodeToProcess->isProcessed()) { + // Process the node. + Changed |= processNode(NodeToProcess->node()); + NodeToProcess->childGeneration(CurrentGeneration); + NodeToProcess->process(); + } else if (NodeToProcess->childIter() != NodeToProcess->end()) { + // Push the next child onto the stack. + DomTreeNode *child = NodeToProcess->nextChild(); + nodesToProcess.push_back( + new StackNode(AvailableValues, AvailableLoads, AvailableCalls, + NodeToProcess->childGeneration(), child, child->begin(), + child->end())); + } else { + // It has been processed, and there are no more children to process, + // so delete it and pop it off the stack. + delete NodeToProcess; + nodesToProcess.pop_back(); + } + } // while (!nodes...) + + // Reset the current generation. + CurrentGeneration = LiveOutGeneration; + + return Changed; +} + +PreservedAnalyses EarlyCSEPass::run(Function &F, + AnalysisManager<Function> *AM) { + auto &TLI = AM->getResult<TargetLibraryAnalysis>(F); + auto &TTI = AM->getResult<TargetIRAnalysis>(F); + auto &DT = AM->getResult<DominatorTreeAnalysis>(F); + auto &AC = AM->getResult<AssumptionAnalysis>(F); + + EarlyCSE CSE(TLI, TTI, DT, AC); + + if (!CSE.run()) + return PreservedAnalyses::all(); + + // CSE preserves the dominator tree because it doesn't mutate the CFG. + // FIXME: Bundle this with other CFG-preservation. + PreservedAnalyses PA; + PA.preserve<DominatorTreeAnalysis>(); + return PA; +} + +namespace { +/// \brief A simple and fast domtree-based CSE pass. +/// +/// This pass does a simple depth-first walk over the dominator tree, +/// eliminating trivially redundant instructions and using instsimplify to +/// canonicalize things as it goes. It is intended to be fast and catch obvious +/// cases so that instcombine and other passes are more effective. It is +/// expected that a later pass of GVN will catch the interesting/hard cases. +class EarlyCSELegacyPass : public FunctionPass { +public: + static char ID; + + EarlyCSELegacyPass() : FunctionPass(ID) { + initializeEarlyCSELegacyPassPass(*PassRegistry::getPassRegistry()); + } + + bool runOnFunction(Function &F) override { + if (skipOptnoneFunction(F)) + return false; + + auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); + auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); + auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); + + EarlyCSE CSE(TLI, TTI, DT, AC); + + return CSE.run(); + } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired<AssumptionCacheTracker>(); + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); + AU.addRequired<TargetTransformInfoWrapperPass>(); + AU.addPreserved<GlobalsAAWrapperPass>(); + AU.setPreservesCFG(); + } +}; +} + +char EarlyCSELegacyPass::ID = 0; + +FunctionPass *llvm::createEarlyCSEPass() { return new EarlyCSELegacyPass(); } + +INITIALIZE_PASS_BEGIN(EarlyCSELegacyPass, "early-cse", "Early CSE", false, + false) +INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_END(EarlyCSELegacyPass, "early-cse", "Early CSE", false, false) |
