| //===- 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. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "early-cse" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/RecyclingAllocator.h" |
| #include "llvm/ADT/ScopedHashTable.h" |
| #include "llvm/ADT/Statistic.h" |
| using namespace llvm; |
| |
| 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"); |
| |
| static unsigned getHash(const void *V) { |
| return DenseMapInfo<const void*>::getHashValue(V); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // SimpleValue |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| /// SimpleValue - Instances of this struct represent 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 { |
| // SimpleValue is POD. |
| template<> struct isPodLike<SimpleValue> { |
| static const bool value = true; |
| }; |
| |
| 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. |
| unsigned Res = 0; |
| for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i) |
| Res ^= getHash(Inst->getOperand(i)) << (i & 0xF); |
| |
| if (CastInst *CI = dyn_cast<CastInst>(Inst)) |
| Res ^= getHash(CI->getType()); |
| else if (CmpInst *CI = dyn_cast<CmpInst>(Inst)) |
| Res ^= CI->getPredicate(); |
| else if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst)) { |
| for (ExtractValueInst::idx_iterator I = EVI->idx_begin(), |
| E = EVI->idx_end(); I != E; ++I) |
| Res ^= *I; |
| } else if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst)) { |
| for (InsertValueInst::idx_iterator I = IVI->idx_begin(), |
| E = IVI->idx_end(); I != E; ++I) |
| Res ^= *I; |
| } else { |
| // nothing extra to hash in. |
| 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 (Res << 1) ^ Inst->getOpcode(); |
| } |
| |
| 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; |
| return LHSI->isIdenticalTo(RHSI); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // CallValue |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| /// CallValue - Instances of this struct represent 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 == 0 || !CI->onlyReadsMemory()) |
| return false; |
| return true; |
| } |
| }; |
| } |
| |
| namespace llvm { |
| // CallValue is POD. |
| template<> struct isPodLike<CallValue> { |
| static const bool value = true; |
| }; |
| |
| 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 in all of the operands as pointers. |
| unsigned Res = 0; |
| for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i) { |
| assert(!Inst->getOperand(i)->getType()->isMetadataTy() && |
| "Cannot value number calls with metadata operands"); |
| Res ^= getHash(Inst->getOperand(i)) << (i & 0xF); |
| } |
| |
| // Mix in the opcode. |
| return (Res << 1) ^ Inst->getOpcode(); |
| } |
| |
| 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 pass. |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| |
| /// EarlyCSE - 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 FunctionPass { |
| public: |
| const TargetData *TD; |
| DominatorTree *DT; |
| typedef RecyclingAllocator<BumpPtrAllocator, |
| ScopedHashTableVal<SimpleValue, Value*> > AllocatorTy; |
| typedef ScopedHashTable<SimpleValue, Value*, DenseMapInfo<SimpleValue>, |
| AllocatorTy> ScopedHTType; |
| |
| /// AvailableValues - This scoped hash table contains 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; |
| |
| /// AvailableLoads - This scoped hash table contains 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; |
| |
| /// AvailableCalls - This scoped hash table contains 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; |
| |
| /// CurrentGeneration - This is the current generation of the memory value. |
| unsigned CurrentGeneration; |
| |
| static char ID; |
| explicit EarlyCSE() : FunctionPass(ID) { |
| initializeEarlyCSEPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnFunction(Function &F); |
| |
| private: |
| |
| bool processNode(DomTreeNode *Node); |
| |
| // This transformation requires dominator postdominator info |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<DominatorTree>(); |
| AU.setPreservesCFG(); |
| } |
| }; |
| } |
| |
| char EarlyCSE::ID = 0; |
| |
| // createEarlyCSEPass - The public interface to this file. |
| FunctionPass *llvm::createEarlyCSEPass() { |
| return new EarlyCSE(); |
| } |
| |
| INITIALIZE_PASS_BEGIN(EarlyCSE, "early-cse", "Early CSE", false, false) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTree) |
| INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false) |
| |
| bool EarlyCSE::processNode(DomTreeNode *Node) { |
| // Define a scope in the scoped hash table. When we are done processing this |
| // domtree node and recurse back up to our parent domtree node, this will pop |
| // off all the values we install. |
| ScopedHTType::ScopeTy Scope(*AvailableValues); |
| |
| // Define a scope for the load values so that anything we add will get |
| // popped when we recurse back up to our parent domtree node. |
| LoadHTType::ScopeTy LoadScope(*AvailableLoads); |
| |
| // Define a scope for the call values so that anything we add will get |
| // popped when we recurse back up to our parent domtree node. |
| CallHTType::ScopeTy CallScope(*AvailableCalls); |
| |
| 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() == 0) |
| ++CurrentGeneration; |
| |
| /// 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. |
| StoreInst *LastStore = 0; |
| |
| bool Changed = false; |
| |
| // 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)) { |
| DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n'); |
| Inst->eraseFromParent(); |
| Changed = true; |
| ++NumSimplify; |
| continue; |
| } |
| |
| // If the instruction can be simplified (e.g. X+0 = X) then replace it with |
| // its simpler value. |
| if (Value *V = SimplifyInstruction(Inst, TD, DT)) { |
| 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; |
| } |
| |
| // If this is a non-volatile load, process it. |
| if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { |
| // Ignore volatile loads. |
| if (!LI->isSimple()) { |
| LastStore = 0; |
| 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(Inst->getOperand(0)); |
| if (InVal.first != 0 && InVal.second == CurrentGeneration) { |
| DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << *Inst << " to: " |
| << *InVal.first << '\n'); |
| if (!Inst->use_empty()) Inst->replaceAllUsesWith(InVal.first); |
| Inst->eraseFromParent(); |
| Changed = true; |
| ++NumCSELoad; |
| continue; |
| } |
| |
| // Otherwise, remember that we have this instruction. |
| AvailableLoads->insert(Inst->getOperand(0), |
| std::pair<Value*, unsigned>(Inst, CurrentGeneration)); |
| LastStore = 0; |
| continue; |
| } |
| |
| // If this instruction may read from memory, forget LastStore. |
| if (Inst->mayReadFromMemory()) |
| LastStore = 0; |
| |
| // 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 != 0 && 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 (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { |
| // 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 && |
| LastStore->getPointerOperand() == SI->getPointerOperand()) { |
| DEBUG(dbgs() << "EarlyCSE DEAD STORE: " << *LastStore << " due to: " |
| << *Inst << '\n'); |
| LastStore->eraseFromParent(); |
| Changed = true; |
| ++NumDSE; |
| LastStore = 0; |
| continue; |
| } |
| |
| // 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(SI->getPointerOperand(), |
| std::pair<Value*, unsigned>(SI->getValueOperand(), CurrentGeneration)); |
| |
| // Remember that this was the last store we saw for DSE. |
| if (SI->isSimple()) |
| LastStore = SI; |
| } |
| } |
| } |
| |
| unsigned LiveOutGeneration = CurrentGeneration; |
| for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I) { |
| Changed |= processNode(*I); |
| // Pop any generation changes off the stack from the recursive walk. |
| CurrentGeneration = LiveOutGeneration; |
| } |
| return Changed; |
| } |
| |
| |
| bool EarlyCSE::runOnFunction(Function &F) { |
| TD = getAnalysisIfAvailable<TargetData>(); |
| DT = &getAnalysis<DominatorTree>(); |
| |
| // Tables that the pass uses when walking the domtree. |
| ScopedHTType AVTable; |
| AvailableValues = &AVTable; |
| LoadHTType LoadTable; |
| AvailableLoads = &LoadTable; |
| CallHTType CallTable; |
| AvailableCalls = &CallTable; |
| |
| CurrentGeneration = 0; |
| return processNode(DT->getRootNode()); |
| } |