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Diffstat (limited to 'contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp | 872 |
1 files changed, 872 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp new file mode 100644 index 0000000..0b01c38 --- /dev/null +++ b/contrib/llvm/lib/Transforms/IPO/MergeFunctions.cpp @@ -0,0 +1,872 @@ +//===- MergeFunctions.cpp - Merge identical functions ---------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This pass looks for equivalent functions that are mergable and folds them. +// +// A hash is computed from the function, based on its type and number of +// basic blocks. +// +// Once all hashes are computed, we perform an expensive equality comparison +// on each function pair. This takes n^2/2 comparisons per bucket, so it's +// important that the hash function be high quality. The equality comparison +// iterates through each instruction in each basic block. +// +// When a match is found the functions are folded. If both functions are +// overridable, we move the functionality into a new internal function and +// leave two overridable thunks to it. +// +//===----------------------------------------------------------------------===// +// +// Future work: +// +// * virtual functions. +// +// Many functions have their address taken by the virtual function table for +// the object they belong to. However, as long as it's only used for a lookup +// and call, this is irrelevant, and we'd like to fold such functions. +// +// * switch from n^2 pair-wise comparisons to an n-way comparison for each +// bucket. +// +// * be smarter about bitcasts. +// +// In order to fold functions, we will sometimes add either bitcast instructions +// or bitcast constant expressions. Unfortunately, this can confound further +// analysis since the two functions differ where one has a bitcast and the +// other doesn't. We should learn to look through bitcasts. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "mergefunc" +#include "llvm/Transforms/IPO.h" +#include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/FoldingSet.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/Constants.h" +#include "llvm/InlineAsm.h" +#include "llvm/Instructions.h" +#include "llvm/LLVMContext.h" +#include "llvm/Module.h" +#include "llvm/Operator.h" +#include "llvm/Pass.h" +#include "llvm/Support/CallSite.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/IRBuilder.h" +#include "llvm/Support/ValueHandle.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Target/TargetData.h" +#include <vector> +using namespace llvm; + +STATISTIC(NumFunctionsMerged, "Number of functions merged"); +STATISTIC(NumThunksWritten, "Number of thunks generated"); +STATISTIC(NumAliasesWritten, "Number of aliases generated"); +STATISTIC(NumDoubleWeak, "Number of new functions created"); + +/// Creates a hash-code for the function which is the same for any two +/// functions that will compare equal, without looking at the instructions +/// inside the function. +static unsigned profileFunction(const Function *F) { + FunctionType *FTy = F->getFunctionType(); + + FoldingSetNodeID ID; + ID.AddInteger(F->size()); + ID.AddInteger(F->getCallingConv()); + ID.AddBoolean(F->hasGC()); + ID.AddBoolean(FTy->isVarArg()); + ID.AddInteger(FTy->getReturnType()->getTypeID()); + for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) + ID.AddInteger(FTy->getParamType(i)->getTypeID()); + return ID.ComputeHash(); +} + +namespace { + +/// ComparableFunction - A struct that pairs together functions with a +/// TargetData so that we can keep them together as elements in the DenseSet. +class ComparableFunction { +public: + static const ComparableFunction EmptyKey; + static const ComparableFunction TombstoneKey; + static TargetData * const LookupOnly; + + ComparableFunction(Function *Func, TargetData *TD) + : Func(Func), Hash(profileFunction(Func)), TD(TD) {} + + Function *getFunc() const { return Func; } + unsigned getHash() const { return Hash; } + TargetData *getTD() const { return TD; } + + // Drops AssertingVH reference to the function. Outside of debug mode, this + // does nothing. + void release() { + assert(Func && + "Attempted to release function twice, or release empty/tombstone!"); + Func = NULL; + } + +private: + explicit ComparableFunction(unsigned Hash) + : Func(NULL), Hash(Hash), TD(NULL) {} + + AssertingVH<Function> Func; + unsigned Hash; + TargetData *TD; +}; + +const ComparableFunction ComparableFunction::EmptyKey = ComparableFunction(0); +const ComparableFunction ComparableFunction::TombstoneKey = + ComparableFunction(1); +TargetData *const ComparableFunction::LookupOnly = (TargetData*)(-1); + +} + +namespace llvm { + template <> + struct DenseMapInfo<ComparableFunction> { + static ComparableFunction getEmptyKey() { + return ComparableFunction::EmptyKey; + } + static ComparableFunction getTombstoneKey() { + return ComparableFunction::TombstoneKey; + } + static unsigned getHashValue(const ComparableFunction &CF) { + return CF.getHash(); + } + static bool isEqual(const ComparableFunction &LHS, + const ComparableFunction &RHS); + }; +} + +namespace { + +/// FunctionComparator - Compares two functions to determine whether or not +/// they will generate machine code with the same behaviour. TargetData is +/// used if available. The comparator always fails conservatively (erring on the +/// side of claiming that two functions are different). +class FunctionComparator { +public: + FunctionComparator(const TargetData *TD, const Function *F1, + const Function *F2) + : F1(F1), F2(F2), TD(TD) {} + + /// Test whether the two functions have equivalent behaviour. + bool compare(); + +private: + /// Test whether two basic blocks have equivalent behaviour. + bool compare(const BasicBlock *BB1, const BasicBlock *BB2); + + /// Assign or look up previously assigned numbers for the two values, and + /// return whether the numbers are equal. Numbers are assigned in the order + /// visited. + bool enumerate(const Value *V1, const Value *V2); + + /// Compare two Instructions for equivalence, similar to + /// Instruction::isSameOperationAs but with modifications to the type + /// comparison. + bool isEquivalentOperation(const Instruction *I1, + const Instruction *I2) const; + + /// Compare two GEPs for equivalent pointer arithmetic. + bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2); + bool isEquivalentGEP(const GetElementPtrInst *GEP1, + const GetElementPtrInst *GEP2) { + return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2)); + } + + /// Compare two Types, treating all pointer types as equal. + bool isEquivalentType(Type *Ty1, Type *Ty2) const; + + // The two functions undergoing comparison. + const Function *F1, *F2; + + const TargetData *TD; + + DenseMap<const Value *, const Value *> id_map; + DenseSet<const Value *> seen_values; +}; + +} + +// Any two pointers in the same address space are equivalent, intptr_t and +// pointers are equivalent. Otherwise, standard type equivalence rules apply. +bool FunctionComparator::isEquivalentType(Type *Ty1, + Type *Ty2) const { + if (Ty1 == Ty2) + return true; + if (Ty1->getTypeID() != Ty2->getTypeID()) { + if (TD) { + LLVMContext &Ctx = Ty1->getContext(); + if (isa<PointerType>(Ty1) && Ty2 == TD->getIntPtrType(Ctx)) return true; + if (isa<PointerType>(Ty2) && Ty1 == TD->getIntPtrType(Ctx)) return true; + } + return false; + } + + switch (Ty1->getTypeID()) { + default: + llvm_unreachable("Unknown type!"); + // Fall through in Release mode. + case Type::IntegerTyID: + case Type::VectorTyID: + // Ty1 == Ty2 would have returned true earlier. + return false; + + case Type::VoidTyID: + case Type::FloatTyID: + case Type::DoubleTyID: + case Type::X86_FP80TyID: + case Type::FP128TyID: + case Type::PPC_FP128TyID: + case Type::LabelTyID: + case Type::MetadataTyID: + return true; + + case Type::PointerTyID: { + PointerType *PTy1 = cast<PointerType>(Ty1); + PointerType *PTy2 = cast<PointerType>(Ty2); + return PTy1->getAddressSpace() == PTy2->getAddressSpace(); + } + + case Type::StructTyID: { + StructType *STy1 = cast<StructType>(Ty1); + StructType *STy2 = cast<StructType>(Ty2); + if (STy1->getNumElements() != STy2->getNumElements()) + return false; + + if (STy1->isPacked() != STy2->isPacked()) + return false; + + for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) { + if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i))) + return false; + } + return true; + } + + case Type::FunctionTyID: { + FunctionType *FTy1 = cast<FunctionType>(Ty1); + FunctionType *FTy2 = cast<FunctionType>(Ty2); + if (FTy1->getNumParams() != FTy2->getNumParams() || + FTy1->isVarArg() != FTy2->isVarArg()) + return false; + + if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType())) + return false; + + for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) { + if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i))) + return false; + } + return true; + } + + case Type::ArrayTyID: { + ArrayType *ATy1 = cast<ArrayType>(Ty1); + ArrayType *ATy2 = cast<ArrayType>(Ty2); + return ATy1->getNumElements() == ATy2->getNumElements() && + isEquivalentType(ATy1->getElementType(), ATy2->getElementType()); + } + } +} + +// Determine whether the two operations are the same except that pointer-to-A +// and pointer-to-B are equivalent. This should be kept in sync with +// Instruction::isSameOperationAs. +bool FunctionComparator::isEquivalentOperation(const Instruction *I1, + const Instruction *I2) const { + // Differences from Instruction::isSameOperationAs: + // * replace type comparison with calls to isEquivalentType. + // * we test for I->hasSameSubclassOptionalData (nuw/nsw/tail) at the top + // * because of the above, we don't test for the tail bit on calls later on + if (I1->getOpcode() != I2->getOpcode() || + I1->getNumOperands() != I2->getNumOperands() || + !isEquivalentType(I1->getType(), I2->getType()) || + !I1->hasSameSubclassOptionalData(I2)) + return false; + + // We have two instructions of identical opcode and #operands. Check to see + // if all operands are the same type + for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i) + if (!isEquivalentType(I1->getOperand(i)->getType(), + I2->getOperand(i)->getType())) + return false; + + // Check special state that is a part of some instructions. + if (const LoadInst *LI = dyn_cast<LoadInst>(I1)) + return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() && + LI->getAlignment() == cast<LoadInst>(I2)->getAlignment() && + LI->getOrdering() == cast<LoadInst>(I2)->getOrdering() && + LI->getSynchScope() == cast<LoadInst>(I2)->getSynchScope(); + if (const StoreInst *SI = dyn_cast<StoreInst>(I1)) + return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() && + SI->getAlignment() == cast<StoreInst>(I2)->getAlignment() && + SI->getOrdering() == cast<StoreInst>(I2)->getOrdering() && + SI->getSynchScope() == cast<StoreInst>(I2)->getSynchScope(); + if (const CmpInst *CI = dyn_cast<CmpInst>(I1)) + return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate(); + if (const CallInst *CI = dyn_cast<CallInst>(I1)) + return CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() && + CI->getAttributes() == cast<CallInst>(I2)->getAttributes(); + if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1)) + return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() && + CI->getAttributes() == cast<InvokeInst>(I2)->getAttributes(); + if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) + return IVI->getIndices() == cast<InsertValueInst>(I2)->getIndices(); + if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) + return EVI->getIndices() == cast<ExtractValueInst>(I2)->getIndices(); + if (const FenceInst *FI = dyn_cast<FenceInst>(I1)) + return FI->getOrdering() == cast<FenceInst>(I2)->getOrdering() && + FI->getSynchScope() == cast<FenceInst>(I2)->getSynchScope(); + if (const AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(I1)) + return CXI->isVolatile() == cast<AtomicCmpXchgInst>(I2)->isVolatile() && + CXI->getOrdering() == cast<AtomicCmpXchgInst>(I2)->getOrdering() && + CXI->getSynchScope() == cast<AtomicCmpXchgInst>(I2)->getSynchScope(); + if (const AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(I1)) + return RMWI->getOperation() == cast<AtomicRMWInst>(I2)->getOperation() && + RMWI->isVolatile() == cast<AtomicRMWInst>(I2)->isVolatile() && + RMWI->getOrdering() == cast<AtomicRMWInst>(I2)->getOrdering() && + RMWI->getSynchScope() == cast<AtomicRMWInst>(I2)->getSynchScope(); + + return true; +} + +// Determine whether two GEP operations perform the same underlying arithmetic. +bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1, + const GEPOperator *GEP2) { + // When we have target data, we can reduce the GEP down to the value in bytes + // added to the address. + if (TD && GEP1->hasAllConstantIndices() && GEP2->hasAllConstantIndices()) { + SmallVector<Value *, 8> Indices1(GEP1->idx_begin(), GEP1->idx_end()); + SmallVector<Value *, 8> Indices2(GEP2->idx_begin(), GEP2->idx_end()); + uint64_t Offset1 = TD->getIndexedOffset(GEP1->getPointerOperandType(), + Indices1); + uint64_t Offset2 = TD->getIndexedOffset(GEP2->getPointerOperandType(), + Indices2); + return Offset1 == Offset2; + } + + if (GEP1->getPointerOperand()->getType() != + GEP2->getPointerOperand()->getType()) + return false; + + if (GEP1->getNumOperands() != GEP2->getNumOperands()) + return false; + + for (unsigned i = 0, e = GEP1->getNumOperands(); i != e; ++i) { + if (!enumerate(GEP1->getOperand(i), GEP2->getOperand(i))) + return false; + } + + return true; +} + +// Compare two values used by the two functions under pair-wise comparison. If +// this is the first time the values are seen, they're added to the mapping so +// that we will detect mismatches on next use. +bool FunctionComparator::enumerate(const Value *V1, const Value *V2) { + // Check for function @f1 referring to itself and function @f2 referring to + // itself, or referring to each other, or both referring to either of them. + // They're all equivalent if the two functions are otherwise equivalent. + if (V1 == F1 && V2 == F2) + return true; + if (V1 == F2 && V2 == F1) + return true; + + if (const Constant *C1 = dyn_cast<Constant>(V1)) { + if (V1 == V2) return true; + const Constant *C2 = dyn_cast<Constant>(V2); + if (!C2) return false; + // TODO: constant expressions with GEP or references to F1 or F2. + if (C1->isNullValue() && C2->isNullValue() && + isEquivalentType(C1->getType(), C2->getType())) + return true; + // Try bitcasting C2 to C1's type. If the bitcast is legal and returns C1 + // then they must have equal bit patterns. + return C1->getType()->canLosslesslyBitCastTo(C2->getType()) && + C1 == ConstantExpr::getBitCast(const_cast<Constant*>(C2), C1->getType()); + } + + if (isa<InlineAsm>(V1) || isa<InlineAsm>(V2)) + return V1 == V2; + + // Check that V1 maps to V2. If we find a value that V1 maps to then we simply + // check whether it's equal to V2. When there is no mapping then we need to + // ensure that V2 isn't already equivalent to something else. For this + // purpose, we track the V2 values in a set. + + const Value *&map_elem = id_map[V1]; + if (map_elem) + return map_elem == V2; + if (!seen_values.insert(V2).second) + return false; + map_elem = V2; + return true; +} + +// Test whether two basic blocks have equivalent behaviour. +bool FunctionComparator::compare(const BasicBlock *BB1, const BasicBlock *BB2) { + BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end(); + BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end(); + + do { + if (!enumerate(F1I, F2I)) + return false; + + if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) { + const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(F2I); + if (!GEP2) + return false; + + if (!enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand())) + return false; + + if (!isEquivalentGEP(GEP1, GEP2)) + return false; + } else { + if (!isEquivalentOperation(F1I, F2I)) + return false; + + assert(F1I->getNumOperands() == F2I->getNumOperands()); + for (unsigned i = 0, e = F1I->getNumOperands(); i != e; ++i) { + Value *OpF1 = F1I->getOperand(i); + Value *OpF2 = F2I->getOperand(i); + + if (!enumerate(OpF1, OpF2)) + return false; + + if (OpF1->getValueID() != OpF2->getValueID() || + !isEquivalentType(OpF1->getType(), OpF2->getType())) + return false; + } + } + + ++F1I, ++F2I; + } while (F1I != F1E && F2I != F2E); + + return F1I == F1E && F2I == F2E; +} + +// Test whether the two functions have equivalent behaviour. +bool FunctionComparator::compare() { + // We need to recheck everything, but check the things that weren't included + // in the hash first. + + if (F1->getAttributes() != F2->getAttributes()) + return false; + + if (F1->hasGC() != F2->hasGC()) + return false; + + if (F1->hasGC() && F1->getGC() != F2->getGC()) + return false; + + if (F1->hasSection() != F2->hasSection()) + return false; + + if (F1->hasSection() && F1->getSection() != F2->getSection()) + return false; + + if (F1->isVarArg() != F2->isVarArg()) + return false; + + // TODO: if it's internal and only used in direct calls, we could handle this + // case too. + if (F1->getCallingConv() != F2->getCallingConv()) + return false; + + if (!isEquivalentType(F1->getFunctionType(), F2->getFunctionType())) + return false; + + assert(F1->arg_size() == F2->arg_size() && + "Identically typed functions have different numbers of args!"); + + // Visit the arguments so that they get enumerated in the order they're + // passed in. + for (Function::const_arg_iterator f1i = F1->arg_begin(), + f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) { + if (!enumerate(f1i, f2i)) + llvm_unreachable("Arguments repeat!"); + } + + // We do a CFG-ordered walk since the actual ordering of the blocks in the + // linked list is immaterial. Our walk starts at the entry block for both + // functions, then takes each block from each terminator in order. As an + // artifact, this also means that unreachable blocks are ignored. + SmallVector<const BasicBlock *, 8> F1BBs, F2BBs; + SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1. + + F1BBs.push_back(&F1->getEntryBlock()); + F2BBs.push_back(&F2->getEntryBlock()); + + VisitedBBs.insert(F1BBs[0]); + while (!F1BBs.empty()) { + const BasicBlock *F1BB = F1BBs.pop_back_val(); + const BasicBlock *F2BB = F2BBs.pop_back_val(); + + if (!enumerate(F1BB, F2BB) || !compare(F1BB, F2BB)) + return false; + + const TerminatorInst *F1TI = F1BB->getTerminator(); + const TerminatorInst *F2TI = F2BB->getTerminator(); + + assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors()); + for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) { + if (!VisitedBBs.insert(F1TI->getSuccessor(i))) + continue; + + F1BBs.push_back(F1TI->getSuccessor(i)); + F2BBs.push_back(F2TI->getSuccessor(i)); + } + } + return true; +} + +namespace { + +/// MergeFunctions finds functions which will generate identical machine code, +/// by considering all pointer types to be equivalent. Once identified, +/// MergeFunctions will fold them by replacing a call to one to a call to a +/// bitcast of the other. +/// +class MergeFunctions : public ModulePass { +public: + static char ID; + MergeFunctions() + : ModulePass(ID), HasGlobalAliases(false) { + initializeMergeFunctionsPass(*PassRegistry::getPassRegistry()); + } + + bool runOnModule(Module &M); + +private: + typedef DenseSet<ComparableFunction> FnSetType; + + /// A work queue of functions that may have been modified and should be + /// analyzed again. + std::vector<WeakVH> Deferred; + + /// Insert a ComparableFunction into the FnSet, or merge it away if it's + /// equal to one that's already present. + bool insert(ComparableFunction &NewF); + + /// Remove a Function from the FnSet and queue it up for a second sweep of + /// analysis. + void remove(Function *F); + + /// Find the functions that use this Value and remove them from FnSet and + /// queue the functions. + void removeUsers(Value *V); + + /// Replace all direct calls of Old with calls of New. Will bitcast New if + /// necessary to make types match. + void replaceDirectCallers(Function *Old, Function *New); + + /// Merge two equivalent functions. Upon completion, G may be deleted, or may + /// be converted into a thunk. In either case, it should never be visited + /// again. + void mergeTwoFunctions(Function *F, Function *G); + + /// Replace G with a thunk or an alias to F. Deletes G. + void writeThunkOrAlias(Function *F, Function *G); + + /// Replace G with a simple tail call to bitcast(F). Also replace direct uses + /// of G with bitcast(F). Deletes G. + void writeThunk(Function *F, Function *G); + + /// Replace G with an alias to F. Deletes G. + void writeAlias(Function *F, Function *G); + + /// The set of all distinct functions. Use the insert() and remove() methods + /// to modify it. + FnSetType FnSet; + + /// TargetData for more accurate GEP comparisons. May be NULL. + TargetData *TD; + + /// Whether or not the target supports global aliases. + bool HasGlobalAliases; +}; + +} // end anonymous namespace + +char MergeFunctions::ID = 0; +INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false) + +ModulePass *llvm::createMergeFunctionsPass() { + return new MergeFunctions(); +} + +bool MergeFunctions::runOnModule(Module &M) { + bool Changed = false; + TD = getAnalysisIfAvailable<TargetData>(); + + for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { + if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) + Deferred.push_back(WeakVH(I)); + } + FnSet.resize(Deferred.size()); + + do { + std::vector<WeakVH> Worklist; + Deferred.swap(Worklist); + + DEBUG(dbgs() << "size of module: " << M.size() << '\n'); + DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n'); + + // Insert only strong functions and merge them. Strong function merging + // always deletes one of them. + for (std::vector<WeakVH>::iterator I = Worklist.begin(), + E = Worklist.end(); I != E; ++I) { + if (!*I) continue; + Function *F = cast<Function>(*I); + if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && + !F->mayBeOverridden()) { + ComparableFunction CF = ComparableFunction(F, TD); + Changed |= insert(CF); + } + } + + // Insert only weak functions and merge them. By doing these second we + // create thunks to the strong function when possible. When two weak + // functions are identical, we create a new strong function with two weak + // weak thunks to it which are identical but not mergable. + for (std::vector<WeakVH>::iterator I = Worklist.begin(), + E = Worklist.end(); I != E; ++I) { + if (!*I) continue; + Function *F = cast<Function>(*I); + if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && + F->mayBeOverridden()) { + ComparableFunction CF = ComparableFunction(F, TD); + Changed |= insert(CF); + } + } + DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n'); + } while (!Deferred.empty()); + + FnSet.clear(); + + return Changed; +} + +bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS, + const ComparableFunction &RHS) { + if (LHS.getFunc() == RHS.getFunc() && + LHS.getHash() == RHS.getHash()) + return true; + if (!LHS.getFunc() || !RHS.getFunc()) + return false; + + // One of these is a special "underlying pointer comparison only" object. + if (LHS.getTD() == ComparableFunction::LookupOnly || + RHS.getTD() == ComparableFunction::LookupOnly) + return false; + + assert(LHS.getTD() == RHS.getTD() && + "Comparing functions for different targets"); + + return FunctionComparator(LHS.getTD(), LHS.getFunc(), + RHS.getFunc()).compare(); +} + +// Replace direct callers of Old with New. +void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) { + Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType()); + for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end(); + UI != UE;) { + Value::use_iterator TheIter = UI; + ++UI; + CallSite CS(*TheIter); + if (CS && CS.isCallee(TheIter)) { + remove(CS.getInstruction()->getParent()->getParent()); + TheIter.getUse().set(BitcastNew); + } + } +} + +// Replace G with an alias to F if possible, or else a thunk to F. Deletes G. +void MergeFunctions::writeThunkOrAlias(Function *F, Function *G) { + if (HasGlobalAliases && G->hasUnnamedAddr()) { + if (G->hasExternalLinkage() || G->hasLocalLinkage() || + G->hasWeakLinkage()) { + writeAlias(F, G); + return; + } + } + + writeThunk(F, G); +} + +// Replace G with a simple tail call to bitcast(F). Also replace direct uses +// of G with bitcast(F). Deletes G. +void MergeFunctions::writeThunk(Function *F, Function *G) { + if (!G->mayBeOverridden()) { + // Redirect direct callers of G to F. + replaceDirectCallers(G, F); + } + + // If G was internal then we may have replaced all uses of G with F. If so, + // stop here and delete G. There's no need for a thunk. + if (G->hasLocalLinkage() && G->use_empty()) { + G->eraseFromParent(); + return; + } + + Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "", + G->getParent()); + BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG); + IRBuilder<false> Builder(BB); + + SmallVector<Value *, 16> Args; + unsigned i = 0; + FunctionType *FFTy = F->getFunctionType(); + for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end(); + AI != AE; ++AI) { + Args.push_back(Builder.CreateBitCast(AI, FFTy->getParamType(i))); + ++i; + } + + CallInst *CI = Builder.CreateCall(F, Args); + CI->setTailCall(); + CI->setCallingConv(F->getCallingConv()); + if (NewG->getReturnType()->isVoidTy()) { + Builder.CreateRetVoid(); + } else { + Builder.CreateRet(Builder.CreateBitCast(CI, NewG->getReturnType())); + } + + NewG->copyAttributesFrom(G); + NewG->takeName(G); + removeUsers(G); + G->replaceAllUsesWith(NewG); + G->eraseFromParent(); + + DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n'); + ++NumThunksWritten; +} + +// Replace G with an alias to F and delete G. +void MergeFunctions::writeAlias(Function *F, Function *G) { + Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType()); + GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "", + BitcastF, G->getParent()); + F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); + GA->takeName(G); + GA->setVisibility(G->getVisibility()); + removeUsers(G); + G->replaceAllUsesWith(GA); + G->eraseFromParent(); + + DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n'); + ++NumAliasesWritten; +} + +// Merge two equivalent functions. Upon completion, Function G is deleted. +void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) { + if (F->mayBeOverridden()) { + assert(G->mayBeOverridden()); + + if (HasGlobalAliases) { + // Make them both thunks to the same internal function. + Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "", + F->getParent()); + H->copyAttributesFrom(F); + H->takeName(F); + removeUsers(F); + F->replaceAllUsesWith(H); + + unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment()); + + writeAlias(F, G); + writeAlias(F, H); + + F->setAlignment(MaxAlignment); + F->setLinkage(GlobalValue::PrivateLinkage); + } else { + // We can't merge them. Instead, pick one and update all direct callers + // to call it and hope that we improve the instruction cache hit rate. + replaceDirectCallers(G, F); + } + + ++NumDoubleWeak; + } else { + writeThunkOrAlias(F, G); + } + + ++NumFunctionsMerged; +} + +// Insert a ComparableFunction into the FnSet, or merge it away if equal to one +// that was already inserted. +bool MergeFunctions::insert(ComparableFunction &NewF) { + std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF); + if (Result.second) { + DEBUG(dbgs() << "Inserting as unique: " << NewF.getFunc()->getName() << '\n'); + return false; + } + + const ComparableFunction &OldF = *Result.first; + + // Never thunk a strong function to a weak function. + assert(!OldF.getFunc()->mayBeOverridden() || + NewF.getFunc()->mayBeOverridden()); + + DEBUG(dbgs() << " " << OldF.getFunc()->getName() << " == " + << NewF.getFunc()->getName() << '\n'); + + Function *DeleteF = NewF.getFunc(); + NewF.release(); + mergeTwoFunctions(OldF.getFunc(), DeleteF); + return true; +} + +// Remove a function from FnSet. If it was already in FnSet, add it to Deferred +// so that we'll look at it in the next round. +void MergeFunctions::remove(Function *F) { + // We need to make sure we remove F, not a function "equal" to F per the + // function equality comparator. + // + // The special "lookup only" ComparableFunction bypasses the expensive + // function comparison in favour of a pointer comparison on the underlying + // Function*'s. + ComparableFunction CF = ComparableFunction(F, ComparableFunction::LookupOnly); + if (FnSet.erase(CF)) { + DEBUG(dbgs() << "Removed " << F->getName() << " from set and deferred it.\n"); + Deferred.push_back(F); + } +} + +// For each instruction used by the value, remove() the function that contains +// the instruction. This should happen right before a call to RAUW. +void MergeFunctions::removeUsers(Value *V) { + std::vector<Value *> Worklist; + Worklist.push_back(V); + while (!Worklist.empty()) { + Value *V = Worklist.back(); + Worklist.pop_back(); + + for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); + UI != UE; ++UI) { + Use &U = UI.getUse(); + if (Instruction *I = dyn_cast<Instruction>(U.getUser())) { + remove(I->getParent()->getParent()); + } else if (isa<GlobalValue>(U.getUser())) { + // do nothing + } else if (Constant *C = dyn_cast<Constant>(U.getUser())) { + for (Value::use_iterator CUI = C->use_begin(), CUE = C->use_end(); + CUI != CUE; ++CUI) + Worklist.push_back(*CUI); + } + } + } +} |
