| //===- 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/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: |
| Function &F; |
| 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; |
| |
| /// \brief A scoped hash table of the current values of loads. |
| /// |
| /// This allows us to get efficient access to dominating loads 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. |
| typedef RecyclingAllocator< |
| BumpPtrAllocator, |
| ScopedHashTableVal<Value *, std::pair<Value *, unsigned>>> |
| LoadMapAllocator; |
| typedef ScopedHashTable<Value *, std::pair<Value *, unsigned>, |
| 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(Function &F, const TargetLibraryInfo &TLI, |
| const TargetTransformInfo &TTI, DominatorTree &DT, |
| AssumptionCache &AC) |
| : F(F), 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) |
| : Load(false), Store(false), Vol(false), MayReadFromMemory(false), |
| MayWriteToMemory(false), MatchingId(-1), Ptr(nullptr) { |
| MayReadFromMemory = Inst->mayReadFromMemory(); |
| MayWriteToMemory = Inst->mayWriteToMemory(); |
| if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { |
| MemIntrinsicInfo Info; |
| if (!TTI.getTgtMemIntrinsic(II, Info)) |
| return; |
| if (Info.NumMemRefs == 1) { |
| Store = Info.WriteMem; |
| Load = Info.ReadMem; |
| MatchingId = Info.MatchingId; |
| MayReadFromMemory = Info.ReadMem; |
| MayWriteToMemory = Info.WriteMem; |
| Vol = Info.Vol; |
| Ptr = Info.PtrVal; |
| } |
| } else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { |
| Load = true; |
| Vol = !LI->isSimple(); |
| Ptr = LI->getPointerOperand(); |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { |
| Store = true; |
| Vol = !SI->isSimple(); |
| Ptr = SI->getPointerOperand(); |
| } |
| } |
| bool isLoad() { return Load; } |
| bool isStore() { return Store; } |
| bool isVolatile() { return Vol; } |
| bool isMatchingMemLoc(const ParseMemoryInst &Inst) { |
| return Ptr == Inst.Ptr && MatchingId == Inst.MatchingId; |
| } |
| bool isValid() { return Ptr != nullptr; } |
| int getMatchingId() { return MatchingId; } |
| Value *getPtr() { return Ptr; } |
| bool mayReadFromMemory() { return MayReadFromMemory; } |
| bool mayWriteToMemory() { return MayWriteToMemory; } |
| |
| private: |
| bool Load; |
| bool Store; |
| bool Vol; |
| bool MayReadFromMemory; |
| bool MayWriteToMemory; |
| // 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 MatchingId; |
| Value *Ptr; |
| }; |
| |
| 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()) { |
| // Ignore volatile loads. |
| if (MemInst.isVolatile()) { |
| LastStore = nullptr; |
| // Don't CSE across synchronization boundaries. |
| if (Inst->mayWriteToMemory()) |
| ++CurrentGeneration; |
| continue; |
| } |
| |
| // If we have an available version of this load, and if it is the right |
| // generation, replace this instruction. |
| std::pair<Value *, unsigned> InVal = |
| AvailableLoads.lookup(MemInst.getPtr()); |
| if (InVal.first != nullptr && InVal.second == CurrentGeneration) { |
| Value *Op = getOrCreateResult(InVal.first, Inst->getType()); |
| if (Op != nullptr) { |
| DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << *Inst |
| << " to: " << *InVal.first << '\n'); |
| if (!Inst->use_empty()) |
| Inst->replaceAllUsesWith(Op); |
| Inst->eraseFromParent(); |
| Changed = true; |
| ++NumCSELoad; |
| continue; |
| } |
| } |
| |
| // Otherwise, remember that we have this instruction. |
| AvailableLoads.insert(MemInst.getPtr(), std::pair<Value *, unsigned>( |
| Inst, CurrentGeneration)); |
| 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; |
| } |
| |
| // 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. |
| if (LastStore) { |
| ParseMemoryInst LastStoreMemInst(LastStore, TTI); |
| 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.getPtr(), std::pair<Value *, unsigned>( |
| Inst, CurrentGeneration)); |
| |
| // Remember that this was the last store we saw for DSE. |
| if (!MemInst.isVolatile()) |
| LastStore = Inst; |
| } |
| } |
| } |
| |
| 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.cs.uiuc.edu/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(F, 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(F, 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.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) |