| //===- GVN.cpp - Eliminate redundant values and loads ---------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass performs global value numbering to eliminate fully redundant |
| // instructions. It also performs simple dead load elimination. |
| // |
| // Note that this pass does the value numbering itself; it does not use the |
| // ValueNumbering analysis passes. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "gvn" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/GlobalVariable.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/LLVMContext.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Analysis/Loads.h" |
| #include "llvm/Analysis/MemoryBuiltins.h" |
| #include "llvm/Analysis/MemoryDependenceAnalysis.h" |
| #include "llvm/Analysis/PHITransAddr.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/Assembly/Writer.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Target/TargetLibraryInfo.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/SSAUpdater.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/DepthFirstIterator.h" |
| #include "llvm/ADT/Hashing.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Support/Allocator.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/IRBuilder.h" |
| #include "llvm/Support/PatternMatch.h" |
| using namespace llvm; |
| using namespace PatternMatch; |
| |
| STATISTIC(NumGVNInstr, "Number of instructions deleted"); |
| STATISTIC(NumGVNLoad, "Number of loads deleted"); |
| STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); |
| STATISTIC(NumGVNBlocks, "Number of blocks merged"); |
| STATISTIC(NumGVNSimpl, "Number of instructions simplified"); |
| STATISTIC(NumGVNEqProp, "Number of equalities propagated"); |
| STATISTIC(NumPRELoad, "Number of loads PRE'd"); |
| |
| static cl::opt<bool> EnablePRE("enable-pre", |
| cl::init(true), cl::Hidden); |
| static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); |
| |
| //===----------------------------------------------------------------------===// |
| // ValueTable Class |
| //===----------------------------------------------------------------------===// |
| |
| /// This class holds the mapping between values and value numbers. It is used |
| /// as an efficient mechanism to determine the expression-wise equivalence of |
| /// two values. |
| namespace { |
| struct Expression { |
| uint32_t opcode; |
| Type *type; |
| SmallVector<uint32_t, 4> varargs; |
| |
| Expression(uint32_t o = ~2U) : opcode(o) { } |
| |
| bool operator==(const Expression &other) const { |
| if (opcode != other.opcode) |
| return false; |
| if (opcode == ~0U || opcode == ~1U) |
| return true; |
| if (type != other.type) |
| return false; |
| if (varargs != other.varargs) |
| return false; |
| return true; |
| } |
| |
| friend hash_code hash_value(const Expression &Value) { |
| return hash_combine(Value.opcode, Value.type, |
| hash_combine_range(Value.varargs.begin(), |
| Value.varargs.end())); |
| } |
| }; |
| |
| class ValueTable { |
| DenseMap<Value*, uint32_t> valueNumbering; |
| DenseMap<Expression, uint32_t> expressionNumbering; |
| AliasAnalysis *AA; |
| MemoryDependenceAnalysis *MD; |
| DominatorTree *DT; |
| |
| uint32_t nextValueNumber; |
| |
| Expression create_expression(Instruction* I); |
| Expression create_cmp_expression(unsigned Opcode, |
| CmpInst::Predicate Predicate, |
| Value *LHS, Value *RHS); |
| Expression create_extractvalue_expression(ExtractValueInst* EI); |
| uint32_t lookup_or_add_call(CallInst* C); |
| public: |
| ValueTable() : nextValueNumber(1) { } |
| uint32_t lookup_or_add(Value *V); |
| uint32_t lookup(Value *V) const; |
| uint32_t lookup_or_add_cmp(unsigned Opcode, CmpInst::Predicate Pred, |
| Value *LHS, Value *RHS); |
| void add(Value *V, uint32_t num); |
| void clear(); |
| void erase(Value *v); |
| void setAliasAnalysis(AliasAnalysis* A) { AA = A; } |
| AliasAnalysis *getAliasAnalysis() const { return AA; } |
| void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } |
| void setDomTree(DominatorTree* D) { DT = D; } |
| uint32_t getNextUnusedValueNumber() { return nextValueNumber; } |
| void verifyRemoved(const Value *) const; |
| }; |
| } |
| |
| namespace llvm { |
| template <> struct DenseMapInfo<Expression> { |
| static inline Expression getEmptyKey() { |
| return ~0U; |
| } |
| |
| static inline Expression getTombstoneKey() { |
| return ~1U; |
| } |
| |
| static unsigned getHashValue(const Expression e) { |
| using llvm::hash_value; |
| return static_cast<unsigned>(hash_value(e)); |
| } |
| static bool isEqual(const Expression &LHS, const Expression &RHS) { |
| return LHS == RHS; |
| } |
| }; |
| |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // ValueTable Internal Functions |
| //===----------------------------------------------------------------------===// |
| |
| Expression ValueTable::create_expression(Instruction *I) { |
| Expression e; |
| e.type = I->getType(); |
| e.opcode = I->getOpcode(); |
| for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); |
| OI != OE; ++OI) |
| e.varargs.push_back(lookup_or_add(*OI)); |
| if (I->isCommutative()) { |
| // Ensure that commutative instructions that only differ by a permutation |
| // of their operands get the same value number by sorting the operand value |
| // numbers. Since all commutative instructions have two operands it is more |
| // efficient to sort by hand rather than using, say, std::sort. |
| assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!"); |
| if (e.varargs[0] > e.varargs[1]) |
| std::swap(e.varargs[0], e.varargs[1]); |
| } |
| |
| if (CmpInst *C = dyn_cast<CmpInst>(I)) { |
| // Sort the operand value numbers so x<y and y>x get the same value number. |
| CmpInst::Predicate Predicate = C->getPredicate(); |
| if (e.varargs[0] > e.varargs[1]) { |
| std::swap(e.varargs[0], e.varargs[1]); |
| Predicate = CmpInst::getSwappedPredicate(Predicate); |
| } |
| e.opcode = (C->getOpcode() << 8) | Predicate; |
| } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) { |
| for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); |
| II != IE; ++II) |
| e.varargs.push_back(*II); |
| } |
| |
| return e; |
| } |
| |
| Expression ValueTable::create_cmp_expression(unsigned Opcode, |
| CmpInst::Predicate Predicate, |
| Value *LHS, Value *RHS) { |
| assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) && |
| "Not a comparison!"); |
| Expression e; |
| e.type = CmpInst::makeCmpResultType(LHS->getType()); |
| e.varargs.push_back(lookup_or_add(LHS)); |
| e.varargs.push_back(lookup_or_add(RHS)); |
| |
| // Sort the operand value numbers so x<y and y>x get the same value number. |
| if (e.varargs[0] > e.varargs[1]) { |
| std::swap(e.varargs[0], e.varargs[1]); |
| Predicate = CmpInst::getSwappedPredicate(Predicate); |
| } |
| e.opcode = (Opcode << 8) | Predicate; |
| return e; |
| } |
| |
| Expression ValueTable::create_extractvalue_expression(ExtractValueInst *EI) { |
| assert(EI != 0 && "Not an ExtractValueInst?"); |
| Expression e; |
| e.type = EI->getType(); |
| e.opcode = 0; |
| |
| IntrinsicInst *I = dyn_cast<IntrinsicInst>(EI->getAggregateOperand()); |
| if (I != 0 && EI->getNumIndices() == 1 && *EI->idx_begin() == 0 ) { |
| // EI might be an extract from one of our recognised intrinsics. If it |
| // is we'll synthesize a semantically equivalent expression instead on |
| // an extract value expression. |
| switch (I->getIntrinsicID()) { |
| case Intrinsic::sadd_with_overflow: |
| case Intrinsic::uadd_with_overflow: |
| e.opcode = Instruction::Add; |
| break; |
| case Intrinsic::ssub_with_overflow: |
| case Intrinsic::usub_with_overflow: |
| e.opcode = Instruction::Sub; |
| break; |
| case Intrinsic::smul_with_overflow: |
| case Intrinsic::umul_with_overflow: |
| e.opcode = Instruction::Mul; |
| break; |
| default: |
| break; |
| } |
| |
| if (e.opcode != 0) { |
| // Intrinsic recognized. Grab its args to finish building the expression. |
| assert(I->getNumArgOperands() == 2 && |
| "Expect two args for recognised intrinsics."); |
| e.varargs.push_back(lookup_or_add(I->getArgOperand(0))); |
| e.varargs.push_back(lookup_or_add(I->getArgOperand(1))); |
| return e; |
| } |
| } |
| |
| // Not a recognised intrinsic. Fall back to producing an extract value |
| // expression. |
| e.opcode = EI->getOpcode(); |
| for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end(); |
| OI != OE; ++OI) |
| e.varargs.push_back(lookup_or_add(*OI)); |
| |
| for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end(); |
| II != IE; ++II) |
| e.varargs.push_back(*II); |
| |
| return e; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // ValueTable External Functions |
| //===----------------------------------------------------------------------===// |
| |
| /// add - Insert a value into the table with a specified value number. |
| void ValueTable::add(Value *V, uint32_t num) { |
| valueNumbering.insert(std::make_pair(V, num)); |
| } |
| |
| uint32_t ValueTable::lookup_or_add_call(CallInst* C) { |
| if (AA->doesNotAccessMemory(C)) { |
| Expression exp = create_expression(C); |
| uint32_t& e = expressionNumbering[exp]; |
| if (!e) e = nextValueNumber++; |
| valueNumbering[C] = e; |
| return e; |
| } else if (AA->onlyReadsMemory(C)) { |
| Expression exp = create_expression(C); |
| uint32_t& e = expressionNumbering[exp]; |
| if (!e) { |
| e = nextValueNumber++; |
| valueNumbering[C] = e; |
| return e; |
| } |
| if (!MD) { |
| e = nextValueNumber++; |
| valueNumbering[C] = e; |
| return e; |
| } |
| |
| MemDepResult local_dep = MD->getDependency(C); |
| |
| if (!local_dep.isDef() && !local_dep.isNonLocal()) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| if (local_dep.isDef()) { |
| CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); |
| |
| if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { |
| uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); |
| uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i)); |
| if (c_vn != cd_vn) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| } |
| |
| uint32_t v = lookup_or_add(local_cdep); |
| valueNumbering[C] = v; |
| return v; |
| } |
| |
| // Non-local case. |
| const MemoryDependenceAnalysis::NonLocalDepInfo &deps = |
| MD->getNonLocalCallDependency(CallSite(C)); |
| // FIXME: Move the checking logic to MemDep! |
| CallInst* cdep = 0; |
| |
| // Check to see if we have a single dominating call instruction that is |
| // identical to C. |
| for (unsigned i = 0, e = deps.size(); i != e; ++i) { |
| const NonLocalDepEntry *I = &deps[i]; |
| if (I->getResult().isNonLocal()) |
| continue; |
| |
| // We don't handle non-definitions. If we already have a call, reject |
| // instruction dependencies. |
| if (!I->getResult().isDef() || cdep != 0) { |
| cdep = 0; |
| break; |
| } |
| |
| CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); |
| // FIXME: All duplicated with non-local case. |
| if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ |
| cdep = NonLocalDepCall; |
| continue; |
| } |
| |
| cdep = 0; |
| break; |
| } |
| |
| if (!cdep) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| if (cdep->getNumArgOperands() != C->getNumArgOperands()) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { |
| uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); |
| uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i)); |
| if (c_vn != cd_vn) { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| } |
| |
| uint32_t v = lookup_or_add(cdep); |
| valueNumbering[C] = v; |
| return v; |
| |
| } else { |
| valueNumbering[C] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| } |
| |
| /// lookup_or_add - Returns the value number for the specified value, assigning |
| /// it a new number if it did not have one before. |
| uint32_t ValueTable::lookup_or_add(Value *V) { |
| DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); |
| if (VI != valueNumbering.end()) |
| return VI->second; |
| |
| if (!isa<Instruction>(V)) { |
| valueNumbering[V] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| Instruction* I = cast<Instruction>(V); |
| Expression exp; |
| switch (I->getOpcode()) { |
| case Instruction::Call: |
| return lookup_or_add_call(cast<CallInst>(I)); |
| case Instruction::Add: |
| case Instruction::FAdd: |
| case Instruction::Sub: |
| case Instruction::FSub: |
| case Instruction::Mul: |
| case Instruction::FMul: |
| case Instruction::UDiv: |
| case Instruction::SDiv: |
| case Instruction::FDiv: |
| case Instruction::URem: |
| case Instruction::SRem: |
| case Instruction::FRem: |
| case Instruction::Shl: |
| case Instruction::LShr: |
| case Instruction::AShr: |
| case Instruction::And: |
| case Instruction::Or : |
| case Instruction::Xor: |
| case Instruction::ICmp: |
| case Instruction::FCmp: |
| case Instruction::Trunc: |
| case Instruction::ZExt: |
| case Instruction::SExt: |
| case Instruction::FPToUI: |
| case Instruction::FPToSI: |
| case Instruction::UIToFP: |
| case Instruction::SIToFP: |
| case Instruction::FPTrunc: |
| case Instruction::FPExt: |
| case Instruction::PtrToInt: |
| case Instruction::IntToPtr: |
| case Instruction::BitCast: |
| case Instruction::Select: |
| case Instruction::ExtractElement: |
| case Instruction::InsertElement: |
| case Instruction::ShuffleVector: |
| case Instruction::InsertValue: |
| case Instruction::GetElementPtr: |
| exp = create_expression(I); |
| break; |
| case Instruction::ExtractValue: |
| exp = create_extractvalue_expression(cast<ExtractValueInst>(I)); |
| break; |
| default: |
| valueNumbering[V] = nextValueNumber; |
| return nextValueNumber++; |
| } |
| |
| uint32_t& e = expressionNumbering[exp]; |
| if (!e) e = nextValueNumber++; |
| valueNumbering[V] = e; |
| return e; |
| } |
| |
| /// lookup - Returns the value number of the specified value. Fails if |
| /// the value has not yet been numbered. |
| uint32_t ValueTable::lookup(Value *V) const { |
| DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); |
| assert(VI != valueNumbering.end() && "Value not numbered?"); |
| return VI->second; |
| } |
| |
| /// lookup_or_add_cmp - Returns the value number of the given comparison, |
| /// assigning it a new number if it did not have one before. Useful when |
| /// we deduced the result of a comparison, but don't immediately have an |
| /// instruction realizing that comparison to hand. |
| uint32_t ValueTable::lookup_or_add_cmp(unsigned Opcode, |
| CmpInst::Predicate Predicate, |
| Value *LHS, Value *RHS) { |
| Expression exp = create_cmp_expression(Opcode, Predicate, LHS, RHS); |
| uint32_t& e = expressionNumbering[exp]; |
| if (!e) e = nextValueNumber++; |
| return e; |
| } |
| |
| /// clear - Remove all entries from the ValueTable. |
| void ValueTable::clear() { |
| valueNumbering.clear(); |
| expressionNumbering.clear(); |
| nextValueNumber = 1; |
| } |
| |
| /// erase - Remove a value from the value numbering. |
| void ValueTable::erase(Value *V) { |
| valueNumbering.erase(V); |
| } |
| |
| /// verifyRemoved - Verify that the value is removed from all internal data |
| /// structures. |
| void ValueTable::verifyRemoved(const Value *V) const { |
| for (DenseMap<Value*, uint32_t>::const_iterator |
| I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { |
| assert(I->first != V && "Inst still occurs in value numbering map!"); |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // GVN Pass |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| |
| class GVN : public FunctionPass { |
| bool NoLoads; |
| MemoryDependenceAnalysis *MD; |
| DominatorTree *DT; |
| const TargetData *TD; |
| const TargetLibraryInfo *TLI; |
| |
| ValueTable VN; |
| |
| /// LeaderTable - A mapping from value numbers to lists of Value*'s that |
| /// have that value number. Use findLeader to query it. |
| struct LeaderTableEntry { |
| Value *Val; |
| BasicBlock *BB; |
| LeaderTableEntry *Next; |
| }; |
| DenseMap<uint32_t, LeaderTableEntry> LeaderTable; |
| BumpPtrAllocator TableAllocator; |
| |
| SmallVector<Instruction*, 8> InstrsToErase; |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| explicit GVN(bool noloads = false) |
| : FunctionPass(ID), NoLoads(noloads), MD(0) { |
| initializeGVNPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnFunction(Function &F); |
| |
| /// markInstructionForDeletion - This removes the specified instruction from |
| /// our various maps and marks it for deletion. |
| void markInstructionForDeletion(Instruction *I) { |
| VN.erase(I); |
| InstrsToErase.push_back(I); |
| } |
| |
| const TargetData *getTargetData() const { return TD; } |
| DominatorTree &getDominatorTree() const { return *DT; } |
| AliasAnalysis *getAliasAnalysis() const { return VN.getAliasAnalysis(); } |
| MemoryDependenceAnalysis &getMemDep() const { return *MD; } |
| private: |
| /// addToLeaderTable - Push a new Value to the LeaderTable onto the list for |
| /// its value number. |
| void addToLeaderTable(uint32_t N, Value *V, BasicBlock *BB) { |
| LeaderTableEntry &Curr = LeaderTable[N]; |
| if (!Curr.Val) { |
| Curr.Val = V; |
| Curr.BB = BB; |
| return; |
| } |
| |
| LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>(); |
| Node->Val = V; |
| Node->BB = BB; |
| Node->Next = Curr.Next; |
| Curr.Next = Node; |
| } |
| |
| /// removeFromLeaderTable - Scan the list of values corresponding to a given |
| /// value number, and remove the given value if encountered. |
| void removeFromLeaderTable(uint32_t N, Value *V, BasicBlock *BB) { |
| LeaderTableEntry* Prev = 0; |
| LeaderTableEntry* Curr = &LeaderTable[N]; |
| |
| while (Curr->Val != V || Curr->BB != BB) { |
| Prev = Curr; |
| Curr = Curr->Next; |
| } |
| |
| if (Prev) { |
| Prev->Next = Curr->Next; |
| } else { |
| if (!Curr->Next) { |
| Curr->Val = 0; |
| Curr->BB = 0; |
| } else { |
| LeaderTableEntry* Next = Curr->Next; |
| Curr->Val = Next->Val; |
| Curr->BB = Next->BB; |
| Curr->Next = Next->Next; |
| } |
| } |
| } |
| |
| // List of critical edges to be split between iterations. |
| SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; |
| |
| // This transformation requires dominator postdominator info |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<DominatorTree>(); |
| AU.addRequired<TargetLibraryInfo>(); |
| if (!NoLoads) |
| AU.addRequired<MemoryDependenceAnalysis>(); |
| AU.addRequired<AliasAnalysis>(); |
| |
| AU.addPreserved<DominatorTree>(); |
| AU.addPreserved<AliasAnalysis>(); |
| } |
| |
| |
| // Helper fuctions |
| // FIXME: eliminate or document these better |
| bool processLoad(LoadInst *L); |
| bool processInstruction(Instruction *I); |
| bool processNonLocalLoad(LoadInst *L); |
| bool processBlock(BasicBlock *BB); |
| void dump(DenseMap<uint32_t, Value*> &d); |
| bool iterateOnFunction(Function &F); |
| bool performPRE(Function &F); |
| Value *findLeader(BasicBlock *BB, uint32_t num); |
| void cleanupGlobalSets(); |
| void verifyRemoved(const Instruction *I) const; |
| bool splitCriticalEdges(); |
| unsigned replaceAllDominatedUsesWith(Value *From, Value *To, |
| BasicBlock *Root); |
| bool propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root); |
| }; |
| |
| char GVN::ID = 0; |
| } |
| |
| // createGVNPass - The public interface to this file... |
| FunctionPass *llvm::createGVNPass(bool NoLoads) { |
| return new GVN(NoLoads); |
| } |
| |
| INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false) |
| INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTree) |
| INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) |
| INITIALIZE_AG_DEPENDENCY(AliasAnalysis) |
| INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false) |
| |
| void GVN::dump(DenseMap<uint32_t, Value*>& d) { |
| errs() << "{\n"; |
| for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), |
| E = d.end(); I != E; ++I) { |
| errs() << I->first << "\n"; |
| I->second->dump(); |
| } |
| errs() << "}\n"; |
| } |
| |
| /// IsValueFullyAvailableInBlock - Return true if we can prove that the value |
| /// we're analyzing is fully available in the specified block. As we go, keep |
| /// track of which blocks we know are fully alive in FullyAvailableBlocks. This |
| /// map is actually a tri-state map with the following values: |
| /// 0) we know the block *is not* fully available. |
| /// 1) we know the block *is* fully available. |
| /// 2) we do not know whether the block is fully available or not, but we are |
| /// currently speculating that it will be. |
| /// 3) we are speculating for this block and have used that to speculate for |
| /// other blocks. |
| static bool IsValueFullyAvailableInBlock(BasicBlock *BB, |
| DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { |
| // Optimistically assume that the block is fully available and check to see |
| // if we already know about this block in one lookup. |
| std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = |
| FullyAvailableBlocks.insert(std::make_pair(BB, 2)); |
| |
| // If the entry already existed for this block, return the precomputed value. |
| if (!IV.second) { |
| // If this is a speculative "available" value, mark it as being used for |
| // speculation of other blocks. |
| if (IV.first->second == 2) |
| IV.first->second = 3; |
| return IV.first->second != 0; |
| } |
| |
| // Otherwise, see if it is fully available in all predecessors. |
| pred_iterator PI = pred_begin(BB), PE = pred_end(BB); |
| |
| // If this block has no predecessors, it isn't live-in here. |
| if (PI == PE) |
| goto SpeculationFailure; |
| |
| for (; PI != PE; ++PI) |
| // If the value isn't fully available in one of our predecessors, then it |
| // isn't fully available in this block either. Undo our previous |
| // optimistic assumption and bail out. |
| if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) |
| goto SpeculationFailure; |
| |
| return true; |
| |
| // SpeculationFailure - If we get here, we found out that this is not, after |
| // all, a fully-available block. We have a problem if we speculated on this and |
| // used the speculation to mark other blocks as available. |
| SpeculationFailure: |
| char &BBVal = FullyAvailableBlocks[BB]; |
| |
| // If we didn't speculate on this, just return with it set to false. |
| if (BBVal == 2) { |
| BBVal = 0; |
| return false; |
| } |
| |
| // If we did speculate on this value, we could have blocks set to 1 that are |
| // incorrect. Walk the (transitive) successors of this block and mark them as |
| // 0 if set to one. |
| SmallVector<BasicBlock*, 32> BBWorklist; |
| BBWorklist.push_back(BB); |
| |
| do { |
| BasicBlock *Entry = BBWorklist.pop_back_val(); |
| // Note that this sets blocks to 0 (unavailable) if they happen to not |
| // already be in FullyAvailableBlocks. This is safe. |
| char &EntryVal = FullyAvailableBlocks[Entry]; |
| if (EntryVal == 0) continue; // Already unavailable. |
| |
| // Mark as unavailable. |
| EntryVal = 0; |
| |
| for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) |
| BBWorklist.push_back(*I); |
| } while (!BBWorklist.empty()); |
| |
| return false; |
| } |
| |
| |
| /// CanCoerceMustAliasedValueToLoad - Return true if |
| /// CoerceAvailableValueToLoadType will succeed. |
| static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, |
| Type *LoadTy, |
| const TargetData &TD) { |
| // If the loaded or stored value is an first class array or struct, don't try |
| // to transform them. We need to be able to bitcast to integer. |
| if (LoadTy->isStructTy() || LoadTy->isArrayTy() || |
| StoredVal->getType()->isStructTy() || |
| StoredVal->getType()->isArrayTy()) |
| return false; |
| |
| // The store has to be at least as big as the load. |
| if (TD.getTypeSizeInBits(StoredVal->getType()) < |
| TD.getTypeSizeInBits(LoadTy)) |
| return false; |
| |
| return true; |
| } |
| |
| |
| /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and |
| /// then a load from a must-aliased pointer of a different type, try to coerce |
| /// the stored value. LoadedTy is the type of the load we want to replace and |
| /// InsertPt is the place to insert new instructions. |
| /// |
| /// If we can't do it, return null. |
| static Value *CoerceAvailableValueToLoadType(Value *StoredVal, |
| Type *LoadedTy, |
| Instruction *InsertPt, |
| const TargetData &TD) { |
| if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) |
| return 0; |
| |
| // If this is already the right type, just return it. |
| Type *StoredValTy = StoredVal->getType(); |
| |
| uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); |
| uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); |
| |
| // If the store and reload are the same size, we can always reuse it. |
| if (StoreSize == LoadSize) { |
| // Pointer to Pointer -> use bitcast. |
| if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) |
| return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); |
| |
| // Convert source pointers to integers, which can be bitcast. |
| if (StoredValTy->isPointerTy()) { |
| StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); |
| StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); |
| } |
| |
| Type *TypeToCastTo = LoadedTy; |
| if (TypeToCastTo->isPointerTy()) |
| TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); |
| |
| if (StoredValTy != TypeToCastTo) |
| StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); |
| |
| // Cast to pointer if the load needs a pointer type. |
| if (LoadedTy->isPointerTy()) |
| StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); |
| |
| return StoredVal; |
| } |
| |
| // If the loaded value is smaller than the available value, then we can |
| // extract out a piece from it. If the available value is too small, then we |
| // can't do anything. |
| assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); |
| |
| // Convert source pointers to integers, which can be manipulated. |
| if (StoredValTy->isPointerTy()) { |
| StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); |
| StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); |
| } |
| |
| // Convert vectors and fp to integer, which can be manipulated. |
| if (!StoredValTy->isIntegerTy()) { |
| StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); |
| StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); |
| } |
| |
| // If this is a big-endian system, we need to shift the value down to the low |
| // bits so that a truncate will work. |
| if (TD.isBigEndian()) { |
| Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); |
| StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); |
| } |
| |
| // Truncate the integer to the right size now. |
| Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); |
| StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); |
| |
| if (LoadedTy == NewIntTy) |
| return StoredVal; |
| |
| // If the result is a pointer, inttoptr. |
| if (LoadedTy->isPointerTy()) |
| return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); |
| |
| // Otherwise, bitcast. |
| return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); |
| } |
| |
| /// AnalyzeLoadFromClobberingWrite - This function is called when we have a |
| /// memdep query of a load that ends up being a clobbering memory write (store, |
| /// memset, memcpy, memmove). This means that the write *may* provide bits used |
| /// by the load but we can't be sure because the pointers don't mustalias. |
| /// |
| /// Check this case to see if there is anything more we can do before we give |
| /// up. This returns -1 if we have to give up, or a byte number in the stored |
| /// value of the piece that feeds the load. |
| static int AnalyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr, |
| Value *WritePtr, |
| uint64_t WriteSizeInBits, |
| const TargetData &TD) { |
| // If the loaded or stored value is a first class array or struct, don't try |
| // to transform them. We need to be able to bitcast to integer. |
| if (LoadTy->isStructTy() || LoadTy->isArrayTy()) |
| return -1; |
| |
| int64_t StoreOffset = 0, LoadOffset = 0; |
| Value *StoreBase = GetPointerBaseWithConstantOffset(WritePtr, StoreOffset,TD); |
| Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, TD); |
| if (StoreBase != LoadBase) |
| return -1; |
| |
| // If the load and store are to the exact same address, they should have been |
| // a must alias. AA must have gotten confused. |
| // FIXME: Study to see if/when this happens. One case is forwarding a memset |
| // to a load from the base of the memset. |
| #if 0 |
| if (LoadOffset == StoreOffset) { |
| dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" |
| << "Base = " << *StoreBase << "\n" |
| << "Store Ptr = " << *WritePtr << "\n" |
| << "Store Offs = " << StoreOffset << "\n" |
| << "Load Ptr = " << *LoadPtr << "\n"; |
| abort(); |
| } |
| #endif |
| |
| // If the load and store don't overlap at all, the store doesn't provide |
| // anything to the load. In this case, they really don't alias at all, AA |
| // must have gotten confused. |
| uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy); |
| |
| if ((WriteSizeInBits & 7) | (LoadSize & 7)) |
| return -1; |
| uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. |
| LoadSize >>= 3; |
| |
| |
| bool isAAFailure = false; |
| if (StoreOffset < LoadOffset) |
| isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; |
| else |
| isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; |
| |
| if (isAAFailure) { |
| #if 0 |
| dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" |
| << "Base = " << *StoreBase << "\n" |
| << "Store Ptr = " << *WritePtr << "\n" |
| << "Store Offs = " << StoreOffset << "\n" |
| << "Load Ptr = " << *LoadPtr << "\n"; |
| abort(); |
| #endif |
| return -1; |
| } |
| |
| // If the Load isn't completely contained within the stored bits, we don't |
| // have all the bits to feed it. We could do something crazy in the future |
| // (issue a smaller load then merge the bits in) but this seems unlikely to be |
| // valuable. |
| if (StoreOffset > LoadOffset || |
| StoreOffset+StoreSize < LoadOffset+LoadSize) |
| return -1; |
| |
| // Okay, we can do this transformation. Return the number of bytes into the |
| // store that the load is. |
| return LoadOffset-StoreOffset; |
| } |
| |
| /// AnalyzeLoadFromClobberingStore - This function is called when we have a |
| /// memdep query of a load that ends up being a clobbering store. |
| static int AnalyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr, |
| StoreInst *DepSI, |
| const TargetData &TD) { |
| // Cannot handle reading from store of first-class aggregate yet. |
| if (DepSI->getValueOperand()->getType()->isStructTy() || |
| DepSI->getValueOperand()->getType()->isArrayTy()) |
| return -1; |
| |
| Value *StorePtr = DepSI->getPointerOperand(); |
| uint64_t StoreSize =TD.getTypeSizeInBits(DepSI->getValueOperand()->getType()); |
| return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, |
| StorePtr, StoreSize, TD); |
| } |
| |
| /// AnalyzeLoadFromClobberingLoad - This function is called when we have a |
| /// memdep query of a load that ends up being clobbered by another load. See if |
| /// the other load can feed into the second load. |
| static int AnalyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr, |
| LoadInst *DepLI, const TargetData &TD){ |
| // Cannot handle reading from store of first-class aggregate yet. |
| if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy()) |
| return -1; |
| |
| Value *DepPtr = DepLI->getPointerOperand(); |
| uint64_t DepSize = TD.getTypeSizeInBits(DepLI->getType()); |
| int R = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, TD); |
| if (R != -1) return R; |
| |
| // If we have a load/load clobber an DepLI can be widened to cover this load, |
| // then we should widen it! |
| int64_t LoadOffs = 0; |
| const Value *LoadBase = |
| GetPointerBaseWithConstantOffset(LoadPtr, LoadOffs, TD); |
| unsigned LoadSize = TD.getTypeStoreSize(LoadTy); |
| |
| unsigned Size = MemoryDependenceAnalysis:: |
| getLoadLoadClobberFullWidthSize(LoadBase, LoadOffs, LoadSize, DepLI, TD); |
| if (Size == 0) return -1; |
| |
| return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, Size*8, TD); |
| } |
| |
| |
| |
| static int AnalyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr, |
| MemIntrinsic *MI, |
| const TargetData &TD) { |
| // If the mem operation is a non-constant size, we can't handle it. |
| ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); |
| if (SizeCst == 0) return -1; |
| uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; |
| |
| // If this is memset, we just need to see if the offset is valid in the size |
| // of the memset.. |
| if (MI->getIntrinsicID() == Intrinsic::memset) |
| return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), |
| MemSizeInBits, TD); |
| |
| // If we have a memcpy/memmove, the only case we can handle is if this is a |
| // copy from constant memory. In that case, we can read directly from the |
| // constant memory. |
| MemTransferInst *MTI = cast<MemTransferInst>(MI); |
| |
| Constant *Src = dyn_cast<Constant>(MTI->getSource()); |
| if (Src == 0) return -1; |
| |
| GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src, &TD)); |
| if (GV == 0 || !GV->isConstant()) return -1; |
| |
| // See if the access is within the bounds of the transfer. |
| int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, |
| MI->getDest(), MemSizeInBits, TD); |
| if (Offset == -1) |
| return Offset; |
| |
| // Otherwise, see if we can constant fold a load from the constant with the |
| // offset applied as appropriate. |
| Src = ConstantExpr::getBitCast(Src, |
| llvm::Type::getInt8PtrTy(Src->getContext())); |
| Constant *OffsetCst = |
| ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); |
| Src = ConstantExpr::getGetElementPtr(Src, OffsetCst); |
| Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); |
| if (ConstantFoldLoadFromConstPtr(Src, &TD)) |
| return Offset; |
| return -1; |
| } |
| |
| |
| /// GetStoreValueForLoad - This function is called when we have a |
| /// memdep query of a load that ends up being a clobbering store. This means |
| /// that the store provides bits used by the load but we the pointers don't |
| /// mustalias. Check this case to see if there is anything more we can do |
| /// before we give up. |
| static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, |
| Type *LoadTy, |
| Instruction *InsertPt, const TargetData &TD){ |
| LLVMContext &Ctx = SrcVal->getType()->getContext(); |
| |
| uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8; |
| uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8; |
| |
| IRBuilder<> Builder(InsertPt->getParent(), InsertPt); |
| |
| // Compute which bits of the stored value are being used by the load. Convert |
| // to an integer type to start with. |
| if (SrcVal->getType()->isPointerTy()) |
| SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx)); |
| if (!SrcVal->getType()->isIntegerTy()) |
| SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8)); |
| |
| // Shift the bits to the least significant depending on endianness. |
| unsigned ShiftAmt; |
| if (TD.isLittleEndian()) |
| ShiftAmt = Offset*8; |
| else |
| ShiftAmt = (StoreSize-LoadSize-Offset)*8; |
| |
| if (ShiftAmt) |
| SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt); |
| |
| if (LoadSize != StoreSize) |
| SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8)); |
| |
| return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); |
| } |
| |
| /// GetLoadValueForLoad - This function is called when we have a |
| /// memdep query of a load that ends up being a clobbering load. This means |
| /// that the load *may* provide bits used by the load but we can't be sure |
| /// because the pointers don't mustalias. Check this case to see if there is |
| /// anything more we can do before we give up. |
| static Value *GetLoadValueForLoad(LoadInst *SrcVal, unsigned Offset, |
| Type *LoadTy, Instruction *InsertPt, |
| GVN &gvn) { |
| const TargetData &TD = *gvn.getTargetData(); |
| // If Offset+LoadTy exceeds the size of SrcVal, then we must be wanting to |
| // widen SrcVal out to a larger load. |
| unsigned SrcValSize = TD.getTypeStoreSize(SrcVal->getType()); |
| unsigned LoadSize = TD.getTypeStoreSize(LoadTy); |
| if (Offset+LoadSize > SrcValSize) { |
| assert(SrcVal->isSimple() && "Cannot widen volatile/atomic load!"); |
| assert(SrcVal->getType()->isIntegerTy() && "Can't widen non-integer load"); |
| // If we have a load/load clobber an DepLI can be widened to cover this |
| // load, then we should widen it to the next power of 2 size big enough! |
| unsigned NewLoadSize = Offset+LoadSize; |
| if (!isPowerOf2_32(NewLoadSize)) |
| NewLoadSize = NextPowerOf2(NewLoadSize); |
| |
| Value *PtrVal = SrcVal->getPointerOperand(); |
| |
| // Insert the new load after the old load. This ensures that subsequent |
| // memdep queries will find the new load. We can't easily remove the old |
| // load completely because it is already in the value numbering table. |
| IRBuilder<> Builder(SrcVal->getParent(), ++BasicBlock::iterator(SrcVal)); |
| Type *DestPTy = |
| IntegerType::get(LoadTy->getContext(), NewLoadSize*8); |
| DestPTy = PointerType::get(DestPTy, |
| cast<PointerType>(PtrVal->getType())->getAddressSpace()); |
| Builder.SetCurrentDebugLocation(SrcVal->getDebugLoc()); |
| PtrVal = Builder.CreateBitCast(PtrVal, DestPTy); |
| LoadInst *NewLoad = Builder.CreateLoad(PtrVal); |
| NewLoad->takeName(SrcVal); |
| NewLoad->setAlignment(SrcVal->getAlignment()); |
| |
| DEBUG(dbgs() << "GVN WIDENED LOAD: " << *SrcVal << "\n"); |
| DEBUG(dbgs() << "TO: " << *NewLoad << "\n"); |
| |
| // Replace uses of the original load with the wider load. On a big endian |
| // system, we need to shift down to get the relevant bits. |
| Value *RV = NewLoad; |
| if (TD.isBigEndian()) |
| RV = Builder.CreateLShr(RV, |
| NewLoadSize*8-SrcVal->getType()->getPrimitiveSizeInBits()); |
| RV = Builder.CreateTrunc(RV, SrcVal->getType()); |
| SrcVal->replaceAllUsesWith(RV); |
| |
| // We would like to use gvn.markInstructionForDeletion here, but we can't |
| // because the load is already memoized into the leader map table that GVN |
| // tracks. It is potentially possible to remove the load from the table, |
| // but then there all of the operations based on it would need to be |
| // rehashed. Just leave the dead load around. |
| gvn.getMemDep().removeInstruction(SrcVal); |
| SrcVal = NewLoad; |
| } |
| |
| return GetStoreValueForLoad(SrcVal, Offset, LoadTy, InsertPt, TD); |
| } |
| |
| |
| /// GetMemInstValueForLoad - This function is called when we have a |
| /// memdep query of a load that ends up being a clobbering mem intrinsic. |
| static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, |
| Type *LoadTy, Instruction *InsertPt, |
| const TargetData &TD){ |
| LLVMContext &Ctx = LoadTy->getContext(); |
| uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; |
| |
| IRBuilder<> Builder(InsertPt->getParent(), InsertPt); |
| |
| // We know that this method is only called when the mem transfer fully |
| // provides the bits for the load. |
| if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { |
| // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and |
| // independently of what the offset is. |
| Value *Val = MSI->getValue(); |
| if (LoadSize != 1) |
| Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); |
| |
| Value *OneElt = Val; |
| |
| // Splat the value out to the right number of bits. |
| for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { |
| // If we can double the number of bytes set, do it. |
| if (NumBytesSet*2 <= LoadSize) { |
| Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); |
| Val = Builder.CreateOr(Val, ShVal); |
| NumBytesSet <<= 1; |
| continue; |
| } |
| |
| // Otherwise insert one byte at a time. |
| Value *ShVal = Builder.CreateShl(Val, 1*8); |
| Val = Builder.CreateOr(OneElt, ShVal); |
| ++NumBytesSet; |
| } |
| |
| return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); |
| } |
| |
| // Otherwise, this is a memcpy/memmove from a constant global. |
| MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); |
| Constant *Src = cast<Constant>(MTI->getSource()); |
| |
| // Otherwise, see if we can constant fold a load from the constant with the |
| // offset applied as appropriate. |
| Src = ConstantExpr::getBitCast(Src, |
| llvm::Type::getInt8PtrTy(Src->getContext())); |
| Constant *OffsetCst = |
| ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); |
| Src = ConstantExpr::getGetElementPtr(Src, OffsetCst); |
| Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); |
| return ConstantFoldLoadFromConstPtr(Src, &TD); |
| } |
| |
| namespace { |
| |
| struct AvailableValueInBlock { |
| /// BB - The basic block in question. |
| BasicBlock *BB; |
| enum ValType { |
| SimpleVal, // A simple offsetted value that is accessed. |
| LoadVal, // A value produced by a load. |
| MemIntrin // A memory intrinsic which is loaded from. |
| }; |
| |
| /// V - The value that is live out of the block. |
| PointerIntPair<Value *, 2, ValType> Val; |
| |
| /// Offset - The byte offset in Val that is interesting for the load query. |
| unsigned Offset; |
| |
| static AvailableValueInBlock get(BasicBlock *BB, Value *V, |
| unsigned Offset = 0) { |
| AvailableValueInBlock Res; |
| Res.BB = BB; |
| Res.Val.setPointer(V); |
| Res.Val.setInt(SimpleVal); |
| Res.Offset = Offset; |
| return Res; |
| } |
| |
| static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, |
| unsigned Offset = 0) { |
| AvailableValueInBlock Res; |
| Res.BB = BB; |
| Res.Val.setPointer(MI); |
| Res.Val.setInt(MemIntrin); |
| Res.Offset = Offset; |
| return Res; |
| } |
| |
| static AvailableValueInBlock getLoad(BasicBlock *BB, LoadInst *LI, |
| unsigned Offset = 0) { |
| AvailableValueInBlock Res; |
| Res.BB = BB; |
| Res.Val.setPointer(LI); |
| Res.Val.setInt(LoadVal); |
| Res.Offset = Offset; |
| return Res; |
| } |
| |
| bool isSimpleValue() const { return Val.getInt() == SimpleVal; } |
| bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; } |
| bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; } |
| |
| Value *getSimpleValue() const { |
| assert(isSimpleValue() && "Wrong accessor"); |
| return Val.getPointer(); |
| } |
| |
| LoadInst *getCoercedLoadValue() const { |
| assert(isCoercedLoadValue() && "Wrong accessor"); |
| return cast<LoadInst>(Val.getPointer()); |
| } |
| |
| MemIntrinsic *getMemIntrinValue() const { |
| assert(isMemIntrinValue() && "Wrong accessor"); |
| return cast<MemIntrinsic>(Val.getPointer()); |
| } |
| |
| /// MaterializeAdjustedValue - Emit code into this block to adjust the value |
| /// defined here to the specified type. This handles various coercion cases. |
| Value *MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const { |
| Value *Res; |
| if (isSimpleValue()) { |
| Res = getSimpleValue(); |
| if (Res->getType() != LoadTy) { |
| const TargetData *TD = gvn.getTargetData(); |
| assert(TD && "Need target data to handle type mismatch case"); |
| Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), |
| *TD); |
| |
| DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " |
| << *getSimpleValue() << '\n' |
| << *Res << '\n' << "\n\n\n"); |
| } |
| } else if (isCoercedLoadValue()) { |
| LoadInst *Load = getCoercedLoadValue(); |
| if (Load->getType() == LoadTy && Offset == 0) { |
| Res = Load; |
| } else { |
| Res = GetLoadValueForLoad(Load, Offset, LoadTy, BB->getTerminator(), |
| gvn); |
| |
| DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset << " " |
| << *getCoercedLoadValue() << '\n' |
| << *Res << '\n' << "\n\n\n"); |
| } |
| } else { |
| const TargetData *TD = gvn.getTargetData(); |
| assert(TD && "Need target data to handle type mismatch case"); |
| Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, |
| LoadTy, BB->getTerminator(), *TD); |
| DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset |
| << " " << *getMemIntrinValue() << '\n' |
| << *Res << '\n' << "\n\n\n"); |
| } |
| return Res; |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, |
| /// construct SSA form, allowing us to eliminate LI. This returns the value |
| /// that should be used at LI's definition site. |
| static Value *ConstructSSAForLoadSet(LoadInst *LI, |
| SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, |
| GVN &gvn) { |
| // Check for the fully redundant, dominating load case. In this case, we can |
| // just use the dominating value directly. |
| if (ValuesPerBlock.size() == 1 && |
| gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB, |
| LI->getParent())) |
| return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), gvn); |
| |
| // Otherwise, we have to construct SSA form. |
| SmallVector<PHINode*, 8> NewPHIs; |
| SSAUpdater SSAUpdate(&NewPHIs); |
| SSAUpdate.Initialize(LI->getType(), LI->getName()); |
| |
| Type *LoadTy = LI->getType(); |
| |
| for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { |
| const AvailableValueInBlock &AV = ValuesPerBlock[i]; |
| BasicBlock *BB = AV.BB; |
| |
| if (SSAUpdate.HasValueForBlock(BB)) |
| continue; |
| |
| SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, gvn)); |
| } |
| |
| // Perform PHI construction. |
| Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); |
| |
| // If new PHI nodes were created, notify alias analysis. |
| if (V->getType()->isPointerTy()) { |
| AliasAnalysis *AA = gvn.getAliasAnalysis(); |
| |
| for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) |
| AA->copyValue(LI, NewPHIs[i]); |
| |
| // Now that we've copied information to the new PHIs, scan through |
| // them again and inform alias analysis that we've added potentially |
| // escaping uses to any values that are operands to these PHIs. |
| for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) { |
| PHINode *P = NewPHIs[i]; |
| for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii) { |
| unsigned jj = PHINode::getOperandNumForIncomingValue(ii); |
| AA->addEscapingUse(P->getOperandUse(jj)); |
| } |
| } |
| } |
| |
| return V; |
| } |
| |
| static bool isLifetimeStart(const Instruction *Inst) { |
| if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) |
| return II->getIntrinsicID() == Intrinsic::lifetime_start; |
| return false; |
| } |
| |
| /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are |
| /// non-local by performing PHI construction. |
| bool GVN::processNonLocalLoad(LoadInst *LI) { |
| // Find the non-local dependencies of the load. |
| SmallVector<NonLocalDepResult, 64> Deps; |
| AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI); |
| MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps); |
| //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: " |
| // << Deps.size() << *LI << '\n'); |
| |
| // If we had to process more than one hundred blocks to find the |
| // dependencies, this load isn't worth worrying about. Optimizing |
| // it will be too expensive. |
| unsigned NumDeps = Deps.size(); |
| if (NumDeps > 100) |
| return false; |
| |
| // If we had a phi translation failure, we'll have a single entry which is a |
| // clobber in the current block. Reject this early. |
| if (NumDeps == 1 && |
| !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) { |
| DEBUG( |
| dbgs() << "GVN: non-local load "; |
| WriteAsOperand(dbgs(), LI); |
| dbgs() << " has unknown dependencies\n"; |
| ); |
| return false; |
| } |
| |
| // Filter out useless results (non-locals, etc). Keep track of the blocks |
| // where we have a value available in repl, also keep track of whether we see |
| // dependencies that produce an unknown value for the load (such as a call |
| // that could potentially clobber the load). |
| SmallVector<AvailableValueInBlock, 64> ValuesPerBlock; |
| SmallVector<BasicBlock*, 64> UnavailableBlocks; |
| |
| for (unsigned i = 0, e = NumDeps; i != e; ++i) { |
| BasicBlock *DepBB = Deps[i].getBB(); |
| MemDepResult DepInfo = Deps[i].getResult(); |
| |
| if (!DepInfo.isDef() && !DepInfo.isClobber()) { |
| UnavailableBlocks.push_back(DepBB); |
| continue; |
| } |
| |
| if (DepInfo.isClobber()) { |
| // The address being loaded in this non-local block may not be the same as |
| // the pointer operand of the load if PHI translation occurs. Make sure |
| // to consider the right address. |
| Value *Address = Deps[i].getAddress(); |
| |
| // If the dependence is to a store that writes to a superset of the bits |
| // read by the load, we can extract the bits we need for the load from the |
| // stored value. |
| if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { |
| if (TD && Address) { |
| int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, |
| DepSI, *TD); |
| if (Offset != -1) { |
| ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, |
| DepSI->getValueOperand(), |
| Offset)); |
| continue; |
| } |
| } |
| } |
| |
| // Check to see if we have something like this: |
| // load i32* P |
| // load i8* (P+1) |
| // if we have this, replace the later with an extraction from the former. |
| if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) { |
| // If this is a clobber and L is the first instruction in its block, then |
| // we have the first instruction in the entry block. |
| if (DepLI != LI && Address && TD) { |
| int Offset = AnalyzeLoadFromClobberingLoad(LI->getType(), |
| LI->getPointerOperand(), |
| DepLI, *TD); |
| |
| if (Offset != -1) { |
| ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB,DepLI, |
| Offset)); |
| continue; |
| } |
| } |
| } |
| |
| // If the clobbering value is a memset/memcpy/memmove, see if we can |
| // forward a value on from it. |
| if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { |
| if (TD && Address) { |
| int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, |
| DepMI, *TD); |
| if (Offset != -1) { |
| ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, |
| Offset)); |
| continue; |
| } |
| } |
| } |
| |
| UnavailableBlocks.push_back(DepBB); |
| continue; |
| } |
| |
| // DepInfo.isDef() here |
| |
| Instruction *DepInst = DepInfo.getInst(); |
| |
| // Loading the allocation -> undef. |
| if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) || |
| // Loading immediately after lifetime begin -> undef. |
| isLifetimeStart(DepInst)) { |
| ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, |
| UndefValue::get(LI->getType()))); |
| continue; |
| } |
| |
| if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { |
| // Reject loads and stores that are to the same address but are of |
| // different types if we have to. |
| if (S->getValueOperand()->getType() != LI->getType()) { |
| // If the stored value is larger or equal to the loaded value, we can |
| // reuse it. |
| if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(), |
| LI->getType(), *TD)) { |
| UnavailableBlocks.push_back(DepBB); |
| continue; |
| } |
| } |
| |
| ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, |
| S->getValueOperand())); |
| continue; |
| } |
| |
| if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { |
| // If the types mismatch and we can't handle it, reject reuse of the load. |
| if (LD->getType() != LI->getType()) { |
| // If the stored value is larger or equal to the loaded value, we can |
| // reuse it. |
| if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ |
| UnavailableBlocks.push_back(DepBB); |
| continue; |
| } |
| } |
| ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB, LD)); |
| continue; |
| } |
| |
| UnavailableBlocks.push_back(DepBB); |
| continue; |
| } |
| |
| // If we have no predecessors that produce a known value for this load, exit |
| // early. |
| if (ValuesPerBlock.empty()) return false; |
| |
| // If all of the instructions we depend on produce a known value for this |
| // load, then it is fully redundant and we can use PHI insertion to compute |
| // its value. Insert PHIs and remove the fully redundant value now. |
| if (UnavailableBlocks.empty()) { |
| DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); |
| |
| // Perform PHI construction. |
| Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); |
| LI->replaceAllUsesWith(V); |
| |
| if (isa<PHINode>(V)) |
| V->takeName(LI); |
| if (V->getType()->isPointerTy()) |
| MD->invalidateCachedPointerInfo(V); |
| markInstructionForDeletion(LI); |
| ++NumGVNLoad; |
| return true; |
| } |
| |
| if (!EnablePRE || !EnableLoadPRE) |
| return false; |
| |
| // Okay, we have *some* definitions of the value. This means that the value |
| // is available in some of our (transitive) predecessors. Lets think about |
| // doing PRE of this load. This will involve inserting a new load into the |
| // predecessor when it's not available. We could do this in general, but |
| // prefer to not increase code size. As such, we only do this when we know |
| // that we only have to insert *one* load (which means we're basically moving |
| // the load, not inserting a new one). |
| |
| SmallPtrSet<BasicBlock *, 4> Blockers; |
| for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) |
| Blockers.insert(UnavailableBlocks[i]); |
| |
| // Let's find the first basic block with more than one predecessor. Walk |
| // backwards through predecessors if needed. |
| BasicBlock *LoadBB = LI->getParent(); |
| BasicBlock *TmpBB = LoadBB; |
| |
| bool isSinglePred = false; |
| bool allSingleSucc = true; |
| while (TmpBB->getSinglePredecessor()) { |
| isSinglePred = true; |
| TmpBB = TmpBB->getSinglePredecessor(); |
| if (TmpBB == LoadBB) // Infinite (unreachable) loop. |
| return false; |
| if (Blockers.count(TmpBB)) |
| return false; |
| |
| // If any of these blocks has more than one successor (i.e. if the edge we |
| // just traversed was critical), then there are other paths through this |
| // block along which the load may not be anticipated. Hoisting the load |
| // above this block would be adding the load to execution paths along |
| // which it was not previously executed. |
| if (TmpBB->getTerminator()->getNumSuccessors() != 1) |
| return false; |
| } |
| |
| assert(TmpBB); |
| LoadBB = TmpBB; |
| |
| // FIXME: It is extremely unclear what this loop is doing, other than |
| // artificially restricting loadpre. |
| if (isSinglePred) { |
| bool isHot = false; |
| for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { |
| const AvailableValueInBlock &AV = ValuesPerBlock[i]; |
| if (AV.isSimpleValue()) |
| // "Hot" Instruction is in some loop (because it dominates its dep. |
| // instruction). |
| if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue())) |
| if (DT->dominates(LI, I)) { |
| isHot = true; |
| break; |
| } |
| } |
| |
| // We are interested only in "hot" instructions. We don't want to do any |
| // mis-optimizations here. |
| if (!isHot) |
| return false; |
| } |
| |
| // Check to see how many predecessors have the loaded value fully |
| // available. |
| DenseMap<BasicBlock*, Value*> PredLoads; |
| DenseMap<BasicBlock*, char> FullyAvailableBlocks; |
| for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) |
| FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; |
| for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) |
| FullyAvailableBlocks[UnavailableBlocks[i]] = false; |
| |
| SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit; |
| for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); |
| PI != E; ++PI) { |
| BasicBlock *Pred = *PI; |
| if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) { |
| continue; |
| } |
| PredLoads[Pred] = 0; |
| |
| if (Pred->getTerminator()->getNumSuccessors() != 1) { |
| if (isa<IndirectBrInst>(Pred->getTerminator())) { |
| DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" |
| << Pred->getName() << "': " << *LI << '\n'); |
| return false; |
| } |
| |
| if (LoadBB->isLandingPad()) { |
| DEBUG(dbgs() |
| << "COULD NOT PRE LOAD BECAUSE OF LANDING PAD CRITICAL EDGE '" |
| << Pred->getName() << "': " << *LI << '\n'); |
| return false; |
| } |
| |
| unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB); |
| NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum)); |
| } |
| } |
| |
| if (!NeedToSplit.empty()) { |
| toSplit.append(NeedToSplit.begin(), NeedToSplit.end()); |
| return false; |
| } |
| |
| // Decide whether PRE is profitable for this load. |
| unsigned NumUnavailablePreds = PredLoads.size(); |
| assert(NumUnavailablePreds != 0 && |
| "Fully available value should be eliminated above!"); |
| |
| // If this load is unavailable in multiple predecessors, reject it. |
| // FIXME: If we could restructure the CFG, we could make a common pred with |
| // all the preds that don't have an available LI and insert a new load into |
| // that one block. |
| if (NumUnavailablePreds != 1) |
| return false; |
| |
| // Check if the load can safely be moved to all the unavailable predecessors. |
| bool CanDoPRE = true; |
| SmallVector<Instruction*, 8> NewInsts; |
| for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), |
| E = PredLoads.end(); I != E; ++I) { |
| BasicBlock *UnavailablePred = I->first; |
| |
| // Do PHI translation to get its value in the predecessor if necessary. The |
| // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. |
| |
| // If all preds have a single successor, then we know it is safe to insert |
| // the load on the pred (?!?), so we can insert code to materialize the |
| // pointer if it is not available. |
| PHITransAddr Address(LI->getPointerOperand(), TD); |
| Value *LoadPtr = 0; |
| if (allSingleSucc) { |
| LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, |
| *DT, NewInsts); |
| } else { |
| Address.PHITranslateValue(LoadBB, UnavailablePred, DT); |
| LoadPtr = Address.getAddr(); |
| } |
| |
| // If we couldn't find or insert a computation of this phi translated value, |
| // we fail PRE. |
| if (LoadPtr == 0) { |
| DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " |
| << *LI->getPointerOperand() << "\n"); |
| CanDoPRE = false; |
| break; |
| } |
| |
| // Make sure it is valid to move this load here. We have to watch out for: |
| // @1 = getelementptr (i8* p, ... |
| // test p and branch if == 0 |
| // load @1 |
| // It is valid to have the getelementptr before the test, even if p can |
| // be 0, as getelementptr only does address arithmetic. |
| // If we are not pushing the value through any multiple-successor blocks |
| // we do not have this case. Otherwise, check that the load is safe to |
| // put anywhere; this can be improved, but should be conservatively safe. |
| if (!allSingleSucc && |
| // FIXME: REEVALUTE THIS. |
| !isSafeToLoadUnconditionally(LoadPtr, |
| UnavailablePred->getTerminator(), |
| LI->getAlignment(), TD)) { |
| CanDoPRE = false; |
| break; |
| } |
| |
| I->second = LoadPtr; |
| } |
| |
| if (!CanDoPRE) { |
| while (!NewInsts.empty()) { |
| Instruction *I = NewInsts.pop_back_val(); |
| if (MD) MD->removeInstruction(I); |
| I->eraseFromParent(); |
| } |
| return false; |
| } |
| |
| // Okay, we can eliminate this load by inserting a reload in the predecessor |
| // and using PHI construction to get the value in the other predecessors, do |
| // it. |
| DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); |
| DEBUG(if (!NewInsts.empty()) |
| dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " |
| << *NewInsts.back() << '\n'); |
| |
| // Assign value numbers to the new instructions. |
| for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { |
| // FIXME: We really _ought_ to insert these value numbers into their |
| // parent's availability map. However, in doing so, we risk getting into |
| // ordering issues. If a block hasn't been processed yet, we would be |
| // marking a value as AVAIL-IN, which isn't what we intend. |
| VN.lookup_or_add(NewInsts[i]); |
| } |
| |
| for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), |
| E = PredLoads.end(); I != E; ++I) { |
| BasicBlock *UnavailablePred = I->first; |
| Value *LoadPtr = I->second; |
| |
| Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, |
| LI->getAlignment(), |
| UnavailablePred->getTerminator()); |
| |
| // Transfer the old load's TBAA tag to the new load. |
| if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) |
| NewLoad->setMetadata(LLVMContext::MD_tbaa, Tag); |
| |
| // Transfer DebugLoc. |
| NewLoad->setDebugLoc(LI->getDebugLoc()); |
| |
| // Add the newly created load. |
| ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, |
| NewLoad)); |
| MD->invalidateCachedPointerInfo(LoadPtr); |
| DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); |
| } |
| |
| // Perform PHI construction. |
| Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); |
| LI->replaceAllUsesWith(V); |
| if (isa<PHINode>(V)) |
| V->takeName(LI); |
| if (V->getType()->isPointerTy()) |
| MD->invalidateCachedPointerInfo(V); |
| markInstructionForDeletion(LI); |
| ++NumPRELoad; |
| return true; |
| } |
| |
| /// processLoad - Attempt to eliminate a load, first by eliminating it |
| /// locally, and then attempting non-local elimination if that fails. |
| bool GVN::processLoad(LoadInst *L) { |
| if (!MD) |
| return false; |
| |
| if (!L->isSimple()) |
| return false; |
| |
| if (L->use_empty()) { |
| markInstructionForDeletion(L); |
| return true; |
| } |
| |
| // ... to a pointer that has been loaded from before... |
| MemDepResult Dep = MD->getDependency(L); |
| |
| // If we have a clobber and target data is around, see if this is a clobber |
| // that we can fix up through code synthesis. |
| if (Dep.isClobber() && TD) { |
| // Check to see if we have something like this: |
| // store i32 123, i32* %P |
| // %A = bitcast i32* %P to i8* |
| // %B = gep i8* %A, i32 1 |
| // %C = load i8* %B |
| // |
| // We could do that by recognizing if the clobber instructions are obviously |
| // a common base + constant offset, and if the previous store (or memset) |
| // completely covers this load. This sort of thing can happen in bitfield |
| // access code. |
| Value *AvailVal = 0; |
| if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) { |
| int Offset = AnalyzeLoadFromClobberingStore(L->getType(), |
| L->getPointerOperand(), |
| DepSI, *TD); |
| if (Offset != -1) |
| AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset, |
| L->getType(), L, *TD); |
| } |
| |
| // Check to see if we have something like this: |
| // load i32* P |
| // load i8* (P+1) |
| // if we have this, replace the later with an extraction from the former. |
| if (LoadInst *DepLI = dyn_cast<LoadInst>(Dep.getInst())) { |
| // If this is a clobber and L is the first instruction in its block, then |
| // we have the first instruction in the entry block. |
| if (DepLI == L) |
| return false; |
| |
| int Offset = AnalyzeLoadFromClobberingLoad(L->getType(), |
| L->getPointerOperand(), |
| DepLI, *TD); |
| if (Offset != -1) |
| AvailVal = GetLoadValueForLoad(DepLI, Offset, L->getType(), L, *this); |
| } |
| |
| // If the clobbering value is a memset/memcpy/memmove, see if we can forward |
| // a value on from it. |
| if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { |
| int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), |
| L->getPointerOperand(), |
| DepMI, *TD); |
| if (Offset != -1) |
| AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L, *TD); |
| } |
| |
| if (AvailVal) { |
| DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' |
| << *AvailVal << '\n' << *L << "\n\n\n"); |
| |
| // Replace the load! |
| L->replaceAllUsesWith(AvailVal); |
| if (AvailVal->getType()->isPointerTy()) |
| MD->invalidateCachedPointerInfo(AvailVal); |
| markInstructionForDeletion(L); |
| ++NumGVNLoad; |
| return true; |
| } |
| } |
| |
| // If the value isn't available, don't do anything! |
| if (Dep.isClobber()) { |
| DEBUG( |
| // fast print dep, using operator<< on instruction is too slow. |
| dbgs() << "GVN: load "; |
| WriteAsOperand(dbgs(), L); |
| Instruction *I = Dep.getInst(); |
| dbgs() << " is clobbered by " << *I << '\n'; |
| ); |
| return false; |
| } |
| |
| // If it is defined in another block, try harder. |
| if (Dep.isNonLocal()) |
| return processNonLocalLoad(L); |
| |
| if (!Dep.isDef()) { |
| DEBUG( |
| // fast print dep, using operator<< on instruction is too slow. |
| dbgs() << "GVN: load "; |
| WriteAsOperand(dbgs(), L); |
| dbgs() << " has unknown dependence\n"; |
| ); |
| return false; |
| } |
| |
| Instruction *DepInst = Dep.getInst(); |
| if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { |
| Value *StoredVal = DepSI->getValueOperand(); |
| |
| // The store and load are to a must-aliased pointer, but they may not |
| // actually have the same type. See if we know how to reuse the stored |
| // value (depending on its type). |
| if (StoredVal->getType() != L->getType()) { |
| if (TD) { |
| StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), |
| L, *TD); |
| if (StoredVal == 0) |
| return false; |
| |
| DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal |
| << '\n' << *L << "\n\n\n"); |
| } |
| else |
| return false; |
| } |
| |
| // Remove it! |
| L->replaceAllUsesWith(StoredVal); |
| if (StoredVal->getType()->isPointerTy()) |
| MD->invalidateCachedPointerInfo(StoredVal); |
| markInstructionForDeletion(L); |
| ++NumGVNLoad; |
| return true; |
| } |
| |
| if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { |
| Value *AvailableVal = DepLI; |
| |
| // The loads are of a must-aliased pointer, but they may not actually have |
| // the same type. See if we know how to reuse the previously loaded value |
| // (depending on its type). |
| if (DepLI->getType() != L->getType()) { |
| if (TD) { |
| AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), |
| L, *TD); |
| if (AvailableVal == 0) |
| return false; |
| |
| DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal |
| << "\n" << *L << "\n\n\n"); |
| } |
| else |
| return false; |
| } |
| |
| // Remove it! |
| L->replaceAllUsesWith(AvailableVal); |
| if (DepLI->getType()->isPointerTy()) |
| MD->invalidateCachedPointerInfo(DepLI); |
| markInstructionForDeletion(L); |
| ++NumGVNLoad; |
| return true; |
| } |
| |
| // If this load really doesn't depend on anything, then we must be loading an |
| // undef value. This can happen when loading for a fresh allocation with no |
| // intervening stores, for example. |
| if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) { |
| L->replaceAllUsesWith(UndefValue::get(L->getType())); |
| markInstructionForDeletion(L); |
| ++NumGVNLoad; |
| return true; |
| } |
| |
| // If this load occurs either right after a lifetime begin, |
| // then the loaded value is undefined. |
| if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(DepInst)) { |
| if (II->getIntrinsicID() == Intrinsic::lifetime_start) { |
| L->replaceAllUsesWith(UndefValue::get(L->getType())); |
| markInstructionForDeletion(L); |
| ++NumGVNLoad; |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| // findLeader - In order to find a leader for a given value number at a |
| // specific basic block, we first obtain the list of all Values for that number, |
| // and then scan the list to find one whose block dominates the block in |
| // question. This is fast because dominator tree queries consist of only |
| // a few comparisons of DFS numbers. |
| Value *GVN::findLeader(BasicBlock *BB, uint32_t num) { |
| LeaderTableEntry Vals = LeaderTable[num]; |
| if (!Vals.Val) return 0; |
| |
| Value *Val = 0; |
| if (DT->dominates(Vals.BB, BB)) { |
| Val = Vals.Val; |
| if (isa<Constant>(Val)) return Val; |
| } |
| |
| LeaderTableEntry* Next = Vals.Next; |
| while (Next) { |
| if (DT->dominates(Next->BB, BB)) { |
| if (isa<Constant>(Next->Val)) return Next->Val; |
| if (!Val) Val = Next->Val; |
| } |
| |
| Next = Next->Next; |
| } |
| |
| return Val; |
| } |
| |
| /// replaceAllDominatedUsesWith - Replace all uses of 'From' with 'To' if the |
| /// use is dominated by the given basic block. Returns the number of uses that |
| /// were replaced. |
| unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To, |
| BasicBlock *Root) { |
| unsigned Count = 0; |
| for (Value::use_iterator UI = From->use_begin(), UE = From->use_end(); |
| UI != UE; ) { |
| Use &U = (UI++).getUse(); |
| |
| // If From occurs as a phi node operand then the use implicitly lives in the |
| // corresponding incoming block. Otherwise it is the block containing the |
| // user that must be dominated by Root. |
| BasicBlock *UsingBlock; |
| if (PHINode *PN = dyn_cast<PHINode>(U.getUser())) |
| UsingBlock = PN->getIncomingBlock(U); |
| else |
| UsingBlock = cast<Instruction>(U.getUser())->getParent(); |
| |
| if (DT->dominates(Root, UsingBlock)) { |
| U.set(To); |
| ++Count; |
| } |
| } |
| return Count; |
| } |
| |
| /// propagateEquality - The given values are known to be equal in every block |
| /// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with |
| /// 'RHS' everywhere in the scope. Returns whether a change was made. |
| bool GVN::propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root) { |
| if (LHS == RHS) return false; |
| assert(LHS->getType() == RHS->getType() && "Equal but types differ!"); |
| |
| // Don't try to propagate equalities between constants. |
| if (isa<Constant>(LHS) && isa<Constant>(RHS)) |
| return false; |
| |
| // Prefer a constant on the right-hand side, or an Argument if no constants. |
| if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS))) |
| std::swap(LHS, RHS); |
| assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!"); |
| |
| // If there is no obvious reason to prefer the left-hand side over the right- |
| // hand side, ensure the longest lived term is on the right-hand side, so the |
| // shortest lived term will be replaced by the longest lived. This tends to |
| // expose more simplifications. |
| uint32_t LVN = VN.lookup_or_add(LHS); |
| if ((isa<Argument>(LHS) && isa<Argument>(RHS)) || |
| (isa<Instruction>(LHS) && isa<Instruction>(RHS))) { |
| // Move the 'oldest' value to the right-hand side, using the value number as |
| // a proxy for age. |
| uint32_t RVN = VN.lookup_or_add(RHS); |
| if (LVN < RVN) { |
| std::swap(LHS, RHS); |
| LVN = RVN; |
| } |
| } |
| |
| // If value numbering later deduces that an instruction in the scope is equal |
| // to 'LHS' then ensure it will be turned into 'RHS'. |
| addToLeaderTable(LVN, RHS, Root); |
| |
| // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As |
| // LHS always has at least one use that is not dominated by Root, this will |
| // never do anything if LHS has only one use. |
| bool Changed = false; |
| if (!LHS->hasOneUse()) { |
| unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root); |
| Changed |= NumReplacements > 0; |
| NumGVNEqProp += NumReplacements; |
| } |
| |
| // Now try to deduce additional equalities from this one. For example, if the |
| // known equality was "(A != B)" == "false" then it follows that A and B are |
| // equal in the scope. Only boolean equalities with an explicit true or false |
| // RHS are currently supported. |
| if (!RHS->getType()->isIntegerTy(1)) |
| // Not a boolean equality - bail out. |
| return Changed; |
| ConstantInt *CI = dyn_cast<ConstantInt>(RHS); |
| if (!CI) |
| // RHS neither 'true' nor 'false' - bail out. |
| return Changed; |
| // Whether RHS equals 'true'. Otherwise it equals 'false'. |
| bool isKnownTrue = CI->isAllOnesValue(); |
| bool isKnownFalse = !isKnownTrue; |
| |
| // If "A && B" is known true then both A and B are known true. If "A || B" |
| // is known false then both A and B are known false. |
| Value *A, *B; |
| if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) || |
| (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) { |
| Changed |= propagateEquality(A, RHS, Root); |
| Changed |= propagateEquality(B, RHS, Root); |
| return Changed; |
| } |
| |
| // If we are propagating an equality like "(A == B)" == "true" then also |
| // propagate the equality A == B. When propagating a comparison such as |
| // "(A >= B)" == "true", replace all instances of "A < B" with "false". |
| if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) { |
| Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1); |
| |
| // If "A == B" is known true, or "A != B" is known false, then replace |
| // A with B everywhere in the scope. |
| if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) || |
| (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE)) |
| Changed |= propagateEquality(Op0, Op1, Root); |
| |
| // If "A >= B" is known true, replace "A < B" with false everywhere. |
| CmpInst::Predicate NotPred = Cmp->getInversePredicate(); |
| Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse); |
| // Since we don't have the instruction "A < B" immediately to hand, work out |
| // the value number that it would have and use that to find an appropriate |
| // instruction (if any). |
| uint32_t NextNum = VN.getNextUnusedValueNumber(); |
| uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1); |
| // If the number we were assigned was brand new then there is no point in |
| // looking for an instruction realizing it: there cannot be one! |
| if (Num < NextNum) { |
| Value *NotCmp = findLeader(Root, Num); |
| if (NotCmp && isa<Instruction>(NotCmp)) { |
| unsigned NumReplacements = |
| replaceAllDominatedUsesWith(NotCmp, NotVal, Root); |
| Changed |= NumReplacements > 0; |
| NumGVNEqProp += NumReplacements; |
| } |
| } |
| // Ensure that any instruction in scope that gets the "A < B" value number |
| // is replaced with false. |
| addToLeaderTable(Num, NotVal, Root); |
| |
| return Changed; |
| } |
| |
| return Changed; |
| } |
| |
| /// isOnlyReachableViaThisEdge - There is an edge from 'Src' to 'Dst'. Return |
| /// true if every path from the entry block to 'Dst' passes via this edge. In |
| /// particular 'Dst' must not be reachable via another edge from 'Src'. |
| static bool isOnlyReachableViaThisEdge(BasicBlock *Src, BasicBlock *Dst, |
| DominatorTree *DT) { |
| // While in theory it is interesting to consider the case in which Dst has |
| // more than one predecessor, because Dst might be part of a loop which is |
| // only reachable from Src, in practice it is pointless since at the time |
| // GVN runs all such loops have preheaders, which means that Dst will have |
| // been changed to have only one predecessor, namely Src. |
| BasicBlock *Pred = Dst->getSinglePredecessor(); |
| assert((!Pred || Pred == Src) && "No edge between these basic blocks!"); |
| (void)Src; |
| return Pred != 0; |
| } |
| |
| /// processInstruction - When calculating availability, handle an instruction |
| /// by inserting it into the appropriate sets |
| bool GVN::processInstruction(Instruction *I) { |
| // Ignore dbg info intrinsics. |
| if (isa<DbgInfoIntrinsic>(I)) |
| return false; |
| |
| // If the instruction can be easily simplified then do so now in preference |
| // to value numbering it. Value numbering often exposes redundancies, for |
| // example if it determines that %y is equal to %x then the instruction |
| // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. |
| if (Value *V = SimplifyInstruction(I, TD, TLI, DT)) { |
| I->replaceAllUsesWith(V); |
| if (MD && V->getType()->isPointerTy()) |
| MD->invalidateCachedPointerInfo(V); |
| markInstructionForDeletion(I); |
| ++NumGVNSimpl; |
| return true; |
| } |
| |
| if (LoadInst *LI = dyn_cast<LoadInst>(I)) { |
| if (processLoad(LI)) |
| return true; |
| |
| unsigned Num = VN.lookup_or_add(LI); |
| addToLeaderTable(Num, LI, LI->getParent()); |
| return false; |
| } |
| |
| // For conditional branches, we can perform simple conditional propagation on |
| // the condition value itself. |
| if (BranchInst *BI = dyn_cast<BranchInst>(I)) { |
| if (!BI->isConditional() || isa<Constant>(BI->getCondition())) |
| return false; |
| |
| Value *BranchCond = BI->getCondition(); |
| |
| BasicBlock *TrueSucc = BI->getSuccessor(0); |
| BasicBlock *FalseSucc = BI->getSuccessor(1); |
| BasicBlock *Parent = BI->getParent(); |
| bool Changed = false; |
| |
| if (isOnlyReachableViaThisEdge(Parent, TrueSucc, DT)) |
| Changed |= propagateEquality(BranchCond, |
| ConstantInt::getTrue(TrueSucc->getContext()), |
| TrueSucc); |
| |
| if (isOnlyReachableViaThisEdge(Parent, FalseSucc, DT)) |
| Changed |= propagateEquality(BranchCond, |
| ConstantInt::getFalse(FalseSucc->getContext()), |
| FalseSucc); |
| |
| return Changed; |
| } |
| |
| // For switches, propagate the case values into the case destinations. |
| if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { |
| Value *SwitchCond = SI->getCondition(); |
| BasicBlock *Parent = SI->getParent(); |
| bool Changed = false; |
| for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); |
| i != e; ++i) { |
| BasicBlock *Dst = i.getCaseSuccessor(); |
| if (isOnlyReachableViaThisEdge(Parent, Dst, DT)) |
| Changed |= propagateEquality(SwitchCond, i.getCaseValue(), Dst); |
| } |
| return Changed; |
| } |
| |
| // Instructions with void type don't return a value, so there's |
| // no point in trying to find redundancies in them. |
| if (I->getType()->isVoidTy()) return false; |
| |
| uint32_t NextNum = VN.getNextUnusedValueNumber(); |
| unsigned Num = VN.lookup_or_add(I); |
| |
| // Allocations are always uniquely numbered, so we can save time and memory |
| // by fast failing them. |
| if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) { |
| addToLeaderTable(Num, I, I->getParent()); |
| return false; |
| } |
| |
| // If the number we were assigned was a brand new VN, then we don't |
| // need to do a lookup to see if the number already exists |
| // somewhere in the domtree: it can't! |
| if (Num >= NextNum) { |
| addToLeaderTable(Num, I, I->getParent()); |
| return false; |
| } |
| |
| // Perform fast-path value-number based elimination of values inherited from |
| // dominators. |
| Value *repl = findLeader(I->getParent(), Num); |
| if (repl == 0) { |
| // Failure, just remember this instance for future use. |
| addToLeaderTable(Num, I, I->getParent()); |
| return false; |
| } |
| |
| // Remove it! |
| I->replaceAllUsesWith(repl); |
| if (MD && repl->getType()->isPointerTy()) |
| MD->invalidateCachedPointerInfo(repl); |
| markInstructionForDeletion(I); |
| return true; |
| } |
| |
| /// runOnFunction - This is the main transformation entry point for a function. |
| bool GVN::runOnFunction(Function& F) { |
| if (!NoLoads) |
| MD = &getAnalysis<MemoryDependenceAnalysis>(); |
| DT = &getAnalysis<DominatorTree>(); |
| TD = getAnalysisIfAvailable<TargetData>(); |
| TLI = &getAnalysis<TargetLibraryInfo>(); |
| VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); |
| VN.setMemDep(MD); |
| VN.setDomTree(DT); |
| |
| bool Changed = false; |
| bool ShouldContinue = true; |
| |
| // Merge unconditional branches, allowing PRE to catch more |
| // optimization opportunities. |
| for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { |
| BasicBlock *BB = FI++; |
| |
| bool removedBlock = MergeBlockIntoPredecessor(BB, this); |
| if (removedBlock) ++NumGVNBlocks; |
| |
| Changed |= removedBlock; |
| } |
| |
| unsigned Iteration = 0; |
| while (ShouldContinue) { |
| DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); |
| ShouldContinue = iterateOnFunction(F); |
| if (splitCriticalEdges()) |
| ShouldContinue = true; |
| Changed |= ShouldContinue; |
| ++Iteration; |
| } |
| |
| if (EnablePRE) { |
| bool PREChanged = true; |
| while (PREChanged) { |
| PREChanged = performPRE(F); |
| Changed |= PREChanged; |
| } |
| } |
| // FIXME: Should perform GVN again after PRE does something. PRE can move |
| // computations into blocks where they become fully redundant. Note that |
| // we can't do this until PRE's critical edge splitting updates memdep. |
| // Actually, when this happens, we should just fully integrate PRE into GVN. |
| |
| cleanupGlobalSets(); |
| |
| return Changed; |
| } |
| |
| |
| bool GVN::processBlock(BasicBlock *BB) { |
| // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function |
| // (and incrementing BI before processing an instruction). |
| assert(InstrsToErase.empty() && |
| "We expect InstrsToErase to be empty across iterations"); |
| bool ChangedFunction = false; |
| |
| for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); |
| BI != BE;) { |
| ChangedFunction |= processInstruction(BI); |
| if (InstrsToErase.empty()) { |
| ++BI; |
| continue; |
| } |
| |
| // If we need some instructions deleted, do it now. |
| NumGVNInstr += InstrsToErase.size(); |
| |
| // Avoid iterator invalidation. |
| bool AtStart = BI == BB->begin(); |
| if (!AtStart) |
| --BI; |
| |
| for (SmallVector<Instruction*, 4>::iterator I = InstrsToErase.begin(), |
| E = InstrsToErase.end(); I != E; ++I) { |
| DEBUG(dbgs() << "GVN removed: " << **I << '\n'); |
| if (MD) MD->removeInstruction(*I); |
| (*I)->eraseFromParent(); |
| DEBUG(verifyRemoved(*I)); |
| } |
| InstrsToErase.clear(); |
| |
| if (AtStart) |
| BI = BB->begin(); |
| else |
| ++BI; |
| } |
| |
| return ChangedFunction; |
| } |
| |
| /// performPRE - Perform a purely local form of PRE that looks for diamond |
| /// control flow patterns and attempts to perform simple PRE at the join point. |
| bool GVN::performPRE(Function &F) { |
| bool Changed = false; |
| DenseMap<BasicBlock*, Value*> predMap; |
| for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), |
| DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { |
| BasicBlock *CurrentBlock = *DI; |
| |
| // Nothing to PRE in the entry block. |
| if (CurrentBlock == &F.getEntryBlock()) continue; |
| |
| // Don't perform PRE on a landing pad. |
| if (CurrentBlock->isLandingPad()) continue; |
| |
| for (BasicBlock::iterator BI = CurrentBlock->begin(), |
| BE = CurrentBlock->end(); BI != BE; ) { |
| Instruction *CurInst = BI++; |
| |
| if (isa<AllocaInst>(CurInst) || |
| isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || |
| CurInst->getType()->isVoidTy() || |
| CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || |
| isa<DbgInfoIntrinsic>(CurInst)) |
| continue; |
| |
| // We don't currently value number ANY inline asm calls. |
| if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) |
| if (CallI->isInlineAsm()) |
| continue; |
| |
| uint32_t ValNo = VN.lookup(CurInst); |
| |
| // Look for the predecessors for PRE opportunities. We're |
| // only trying to solve the basic diamond case, where |
| // a value is computed in the successor and one predecessor, |
| // but not the other. We also explicitly disallow cases |
| // where the successor is its own predecessor, because they're |
| // more complicated to get right. |
| unsigned NumWith = 0; |
| unsigned NumWithout = 0; |
| BasicBlock *PREPred = 0; |
| predMap.clear(); |
| |
| for (pred_iterator PI = pred_begin(CurrentBlock), |
| PE = pred_end(CurrentBlock); PI != PE; ++PI) { |
| BasicBlock *P = *PI; |
| // We're not interested in PRE where the block is its |
| // own predecessor, or in blocks with predecessors |
| // that are not reachable. |
| if (P == CurrentBlock) { |
| NumWithout = 2; |
| break; |
| } else if (!DT->dominates(&F.getEntryBlock(), P)) { |
| NumWithout = 2; |
| break; |
| } |
| |
| Value* predV = findLeader(P, ValNo); |
| if (predV == 0) { |
| PREPred = P; |
| ++NumWithout; |
| } else if (predV == CurInst) { |
| NumWithout = 2; |
| } else { |
| predMap[P] = predV; |
| ++NumWith; |
| } |
| } |
| |
| // Don't do PRE when it might increase code size, i.e. when |
| // we would need to insert instructions in more than one pred. |
| if (NumWithout != 1 || NumWith == 0) |
| continue; |
| |
| // Don't do PRE across indirect branch. |
| if (isa<IndirectBrInst>(PREPred->getTerminator())) |
| continue; |
| |
| // We can't do PRE safely on a critical edge, so instead we schedule |
| // the edge to be split and perform the PRE the next time we iterate |
| // on the function. |
| unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); |
| if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { |
| toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); |
| continue; |
| } |
| |
| // Instantiate the expression in the predecessor that lacked it. |
| // Because we are going top-down through the block, all value numbers |
| // will be available in the predecessor by the time we need them. Any |
| // that weren't originally present will have been instantiated earlier |
| // in this loop. |
| Instruction *PREInstr = CurInst->clone(); |
| bool success = true; |
| for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { |
| Value *Op = PREInstr->getOperand(i); |
| if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) |
| continue; |
| |
| if (Value *V = findLeader(PREPred, VN.lookup(Op))) { |
| PREInstr->setOperand(i, V); |
| } else { |
| success = false; |
| break; |
| } |
| } |
| |
| // Fail out if we encounter an operand that is not available in |
| // the PRE predecessor. This is typically because of loads which |
| // are not value numbered precisely. |
| if (!success) { |
| delete PREInstr; |
| DEBUG(verifyRemoved(PREInstr)); |
| continue; |
| } |
| |
| PREInstr->insertBefore(PREPred->getTerminator()); |
| PREInstr->setName(CurInst->getName() + ".pre"); |
| PREInstr->setDebugLoc(CurInst->getDebugLoc()); |
| predMap[PREPred] = PREInstr; |
| VN.add(PREInstr, ValNo); |
| ++NumGVNPRE; |
| |
| // Update the availability map to include the new instruction. |
| addToLeaderTable(ValNo, PREInstr, PREPred); |
| |
| // Create a PHI to make the value available in this block. |
| pred_iterator PB = pred_begin(CurrentBlock), PE = pred_end(CurrentBlock); |
| PHINode* Phi = PHINode::Create(CurInst->getType(), std::distance(PB, PE), |
| CurInst->getName() + ".pre-phi", |
| CurrentBlock->begin()); |
| for (pred_iterator PI = PB; PI != PE; ++PI) { |
| BasicBlock *P = *PI; |
| Phi->addIncoming(predMap[P], P); |
| } |
| |
| VN.add(Phi, ValNo); |
| addToLeaderTable(ValNo, Phi, CurrentBlock); |
| Phi->setDebugLoc(CurInst->getDebugLoc()); |
| CurInst->replaceAllUsesWith(Phi); |
| if (Phi->getType()->isPointerTy()) { |
| // Because we have added a PHI-use of the pointer value, it has now |
| // "escaped" from alias analysis' perspective. We need to inform |
| // AA of this. |
| for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee; |
| ++ii) { |
| unsigned jj = PHINode::getOperandNumForIncomingValue(ii); |
| VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj)); |
| } |
| |
| if (MD) |
| MD->invalidateCachedPointerInfo(Phi); |
| } |
| VN.erase(CurInst); |
| removeFromLeaderTable(ValNo, CurInst, CurrentBlock); |
| |
| DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); |
| if (MD) MD->removeInstruction(CurInst); |
| CurInst->eraseFromParent(); |
| DEBUG(verifyRemoved(CurInst)); |
| Changed = true; |
| } |
| } |
| |
| if (splitCriticalEdges()) |
| Changed = true; |
| |
| return Changed; |
| } |
| |
| /// splitCriticalEdges - Split critical edges found during the previous |
| /// iteration that may enable further optimization. |
| bool GVN::splitCriticalEdges() { |
| if (toSplit.empty()) |
| return false; |
| do { |
| std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); |
| SplitCriticalEdge(Edge.first, Edge.second, this); |
| } while (!toSplit.empty()); |
| if (MD) MD->invalidateCachedPredecessors(); |
| return true; |
| } |
| |
| /// iterateOnFunction - Executes one iteration of GVN |
| bool GVN::iterateOnFunction(Function &F) { |
| cleanupGlobalSets(); |
| |
| // Top-down walk of the dominator tree |
| bool Changed = false; |
| #if 0 |
| // Needed for value numbering with phi construction to work. |
| ReversePostOrderTraversal<Function*> RPOT(&F); |
| for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), |
| RE = RPOT.end(); RI != RE; ++RI) |
| Changed |= processBlock(*RI); |
| #else |
| for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), |
| DE = df_end(DT->getRootNode()); DI != DE; ++DI) |
| Changed |= processBlock(DI->getBlock()); |
| #endif |
| |
| return Changed; |
| } |
| |
| void GVN::cleanupGlobalSets() { |
| VN.clear(); |
| LeaderTable.clear(); |
| TableAllocator.Reset(); |
| } |
| |
| /// verifyRemoved - Verify that the specified instruction does not occur in our |
| /// internal data structures. |
| void GVN::verifyRemoved(const Instruction *Inst) const { |
| VN.verifyRemoved(Inst); |
| |
| // Walk through the value number scope to make sure the instruction isn't |
| // ferreted away in it. |
| for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator |
| I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) { |
| const LeaderTableEntry *Node = &I->second; |
| assert(Node->Val != Inst && "Inst still in value numbering scope!"); |
| |
| while (Node->Next) { |
| Node = Node->Next; |
| assert(Node->Val != Inst && "Inst still in value numbering scope!"); |
| } |
| } |
| } |