//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This pass transforms simple global variables that never have their address // taken. If obviously true, it marks read/write globals as constant, deletes // variables only stored to, etc. // //===----------------------------------------------------------------------===// #include "llvm/Transforms/IPO.h" #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallSet.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/ConstantFolding.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/IR/CallSite.h" #include "llvm/IR/CallingConv.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/GetElementPtrTypeIterator.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/Module.h" #include "llvm/IR/Operator.h" #include "llvm/IR/ValueHandle.h" #include "llvm/Pass.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Target/TargetLibraryInfo.h" #include "llvm/Transforms/Utils/CtorUtils.h" #include "llvm/Transforms/Utils/GlobalStatus.h" #include "llvm/Transforms/Utils/ModuleUtils.h" #include <algorithm> #include <deque> using namespace llvm; #define DEBUG_TYPE "globalopt" STATISTIC(NumMarked , "Number of globals marked constant"); STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr"); STATISTIC(NumSRA , "Number of aggregate globals broken into scalars"); STATISTIC(NumHeapSRA , "Number of heap objects SRA'd"); STATISTIC(NumSubstitute,"Number of globals with initializers stored into them"); STATISTIC(NumDeleted , "Number of globals deleted"); STATISTIC(NumFnDeleted , "Number of functions deleted"); STATISTIC(NumGlobUses , "Number of global uses devirtualized"); STATISTIC(NumLocalized , "Number of globals localized"); STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans"); STATISTIC(NumFastCallFns , "Number of functions converted to fastcc"); STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated"); STATISTIC(NumNestRemoved , "Number of nest attributes removed"); STATISTIC(NumAliasesResolved, "Number of global aliases resolved"); STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated"); STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed"); namespace { struct GlobalOpt : public ModulePass { void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired<TargetLibraryInfo>(); } static char ID; // Pass identification, replacement for typeid GlobalOpt() : ModulePass(ID) { initializeGlobalOptPass(*PassRegistry::getPassRegistry()); } bool runOnModule(Module &M) override; private: bool OptimizeFunctions(Module &M); bool OptimizeGlobalVars(Module &M); bool OptimizeGlobalAliases(Module &M); bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI); bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI, const GlobalStatus &GS); bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn); const DataLayout *DL; TargetLibraryInfo *TLI; }; } char GlobalOpt::ID = 0; INITIALIZE_PASS_BEGIN(GlobalOpt, "globalopt", "Global Variable Optimizer", false, false) INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) INITIALIZE_PASS_END(GlobalOpt, "globalopt", "Global Variable Optimizer", false, false) ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); } /// isLeakCheckerRoot - Is this global variable possibly used by a leak checker /// as a root? If so, we might not really want to eliminate the stores to it. static bool isLeakCheckerRoot(GlobalVariable *GV) { // A global variable is a root if it is a pointer, or could plausibly contain // a pointer. There are two challenges; one is that we could have a struct // the has an inner member which is a pointer. We recurse through the type to // detect these (up to a point). The other is that we may actually be a union // of a pointer and another type, and so our LLVM type is an integer which // gets converted into a pointer, or our type is an [i8 x #] with a pointer // potentially contained here. if (GV->hasPrivateLinkage()) return false; SmallVector<Type *, 4> Types; Types.push_back(cast<PointerType>(GV->getType())->getElementType()); unsigned Limit = 20; do { Type *Ty = Types.pop_back_val(); switch (Ty->getTypeID()) { default: break; case Type::PointerTyID: return true; case Type::ArrayTyID: case Type::VectorTyID: { SequentialType *STy = cast<SequentialType>(Ty); Types.push_back(STy->getElementType()); break; } case Type::StructTyID: { StructType *STy = cast<StructType>(Ty); if (STy->isOpaque()) return true; for (StructType::element_iterator I = STy->element_begin(), E = STy->element_end(); I != E; ++I) { Type *InnerTy = *I; if (isa<PointerType>(InnerTy)) return true; if (isa<CompositeType>(InnerTy)) Types.push_back(InnerTy); } break; } } if (--Limit == 0) return true; } while (!Types.empty()); return false; } /// Given a value that is stored to a global but never read, determine whether /// it's safe to remove the store and the chain of computation that feeds the /// store. static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) { do { if (isa<Constant>(V)) return true; if (!V->hasOneUse()) return false; if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) || isa<GlobalValue>(V)) return false; if (isAllocationFn(V, TLI)) return true; Instruction *I = cast<Instruction>(V); if (I->mayHaveSideEffects()) return false; if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) { if (!GEP->hasAllConstantIndices()) return false; } else if (I->getNumOperands() != 1) { return false; } V = I->getOperand(0); } while (1); } /// CleanupPointerRootUsers - This GV is a pointer root. Loop over all users /// of the global and clean up any that obviously don't assign the global a /// value that isn't dynamically allocated. /// static bool CleanupPointerRootUsers(GlobalVariable *GV, const TargetLibraryInfo *TLI) { // A brief explanation of leak checkers. The goal is to find bugs where // pointers are forgotten, causing an accumulating growth in memory // usage over time. The common strategy for leak checkers is to whitelist the // memory pointed to by globals at exit. This is popular because it also // solves another problem where the main thread of a C++ program may shut down // before other threads that are still expecting to use those globals. To // handle that case, we expect the program may create a singleton and never // destroy it. bool Changed = false; // If Dead[n].first is the only use of a malloc result, we can delete its // chain of computation and the store to the global in Dead[n].second. SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead; // Constants can't be pointers to dynamically allocated memory. for (Value::user_iterator UI = GV->user_begin(), E = GV->user_end(); UI != E;) { User *U = *UI++; if (StoreInst *SI = dyn_cast<StoreInst>(U)) { Value *V = SI->getValueOperand(); if (isa<Constant>(V)) { Changed = true; SI->eraseFromParent(); } else if (Instruction *I = dyn_cast<Instruction>(V)) { if (I->hasOneUse()) Dead.push_back(std::make_pair(I, SI)); } } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) { if (isa<Constant>(MSI->getValue())) { Changed = true; MSI->eraseFromParent(); } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) { if (I->hasOneUse()) Dead.push_back(std::make_pair(I, MSI)); } } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) { GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource()); if (MemSrc && MemSrc->isConstant()) { Changed = true; MTI->eraseFromParent(); } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) { if (I->hasOneUse()) Dead.push_back(std::make_pair(I, MTI)); } } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { if (CE->use_empty()) { CE->destroyConstant(); Changed = true; } } else if (Constant *C = dyn_cast<Constant>(U)) { if (isSafeToDestroyConstant(C)) { C->destroyConstant(); // This could have invalidated UI, start over from scratch. Dead.clear(); CleanupPointerRootUsers(GV, TLI); return true; } } } for (int i = 0, e = Dead.size(); i != e; ++i) { if (IsSafeComputationToRemove(Dead[i].first, TLI)) { Dead[i].second->eraseFromParent(); Instruction *I = Dead[i].first; do { if (isAllocationFn(I, TLI)) break; Instruction *J = dyn_cast<Instruction>(I->getOperand(0)); if (!J) break; I->eraseFromParent(); I = J; } while (1); I->eraseFromParent(); } } return Changed; } /// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all /// users of the global, cleaning up the obvious ones. This is largely just a /// quick scan over the use list to clean up the easy and obvious cruft. This /// returns true if it made a change. static bool CleanupConstantGlobalUsers(Value *V, Constant *Init, const DataLayout *DL, TargetLibraryInfo *TLI) { bool Changed = false; // Note that we need to use a weak value handle for the worklist items. When // we delete a constant array, we may also be holding pointer to one of its // elements (or an element of one of its elements if we're dealing with an // array of arrays) in the worklist. SmallVector<WeakVH, 8> WorkList(V->user_begin(), V->user_end()); while (!WorkList.empty()) { Value *UV = WorkList.pop_back_val(); if (!UV) continue; User *U = cast<User>(UV); if (LoadInst *LI = dyn_cast<LoadInst>(U)) { if (Init) { // Replace the load with the initializer. LI->replaceAllUsesWith(Init); LI->eraseFromParent(); Changed = true; } } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { // Store must be unreachable or storing Init into the global. SI->eraseFromParent(); Changed = true; } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { if (CE->getOpcode() == Instruction::GetElementPtr) { Constant *SubInit = nullptr; if (Init) SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); Changed |= CleanupConstantGlobalUsers(CE, SubInit, DL, TLI); } else if ((CE->getOpcode() == Instruction::BitCast && CE->getType()->isPointerTy()) || CE->getOpcode() == Instruction::AddrSpaceCast) { // Pointer cast, delete any stores and memsets to the global. Changed |= CleanupConstantGlobalUsers(CE, nullptr, DL, TLI); } if (CE->use_empty()) { CE->destroyConstant(); Changed = true; } } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { // Do not transform "gepinst (gep constexpr (GV))" here, because forming // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold // and will invalidate our notion of what Init is. Constant *SubInit = nullptr; if (!isa<ConstantExpr>(GEP->getOperand(0))) { ConstantExpr *CE = dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, DL, TLI)); if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr) SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); // If the initializer is an all-null value and we have an inbounds GEP, // we already know what the result of any load from that GEP is. // TODO: Handle splats. if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds()) SubInit = Constant::getNullValue(GEP->getType()->getElementType()); } Changed |= CleanupConstantGlobalUsers(GEP, SubInit, DL, TLI); if (GEP->use_empty()) { GEP->eraseFromParent(); Changed = true; } } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv if (MI->getRawDest() == V) { MI->eraseFromParent(); Changed = true; } } else if (Constant *C = dyn_cast<Constant>(U)) { // If we have a chain of dead constantexprs or other things dangling from // us, and if they are all dead, nuke them without remorse. if (isSafeToDestroyConstant(C)) { C->destroyConstant(); CleanupConstantGlobalUsers(V, Init, DL, TLI); return true; } } } return Changed; } /// isSafeSROAElementUse - Return true if the specified instruction is a safe /// user of a derived expression from a global that we want to SROA. static bool isSafeSROAElementUse(Value *V) { // We might have a dead and dangling constant hanging off of here. if (Constant *C = dyn_cast<Constant>(V)) return isSafeToDestroyConstant(C); Instruction *I = dyn_cast<Instruction>(V); if (!I) return false; // Loads are ok. if (isa<LoadInst>(I)) return true; // Stores *to* the pointer are ok. if (StoreInst *SI = dyn_cast<StoreInst>(I)) return SI->getOperand(0) != V; // Otherwise, it must be a GEP. GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I); if (!GEPI) return false; if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) || !cast<Constant>(GEPI->getOperand(1))->isNullValue()) return false; for (User *U : GEPI->users()) if (!isSafeSROAElementUse(U)) return false; return true; } /// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value. /// Look at it and its uses and decide whether it is safe to SROA this global. /// static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) { // The user of the global must be a GEP Inst or a ConstantExpr GEP. if (!isa<GetElementPtrInst>(U) && (!isa<ConstantExpr>(U) || cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr)) return false; // Check to see if this ConstantExpr GEP is SRA'able. In particular, we // don't like < 3 operand CE's, and we don't like non-constant integer // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some // value of C. if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) || !cast<Constant>(U->getOperand(1))->isNullValue() || !isa<ConstantInt>(U->getOperand(2))) return false; gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U); ++GEPI; // Skip over the pointer index. // If this is a use of an array allocation, do a bit more checking for sanity. if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) { uint64_t NumElements = AT->getNumElements(); ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2)); // Check to make sure that index falls within the array. If not, // something funny is going on, so we won't do the optimization. // if (Idx->getZExtValue() >= NumElements) return false; // We cannot scalar repl this level of the array unless any array // sub-indices are in-range constants. In particular, consider: // A[0][i]. We cannot know that the user isn't doing invalid things like // allowing i to index an out-of-range subscript that accesses A[1]. // // Scalar replacing *just* the outer index of the array is probably not // going to be a win anyway, so just give up. for (++GEPI; // Skip array index. GEPI != E; ++GEPI) { uint64_t NumElements; if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI)) NumElements = SubArrayTy->getNumElements(); else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI)) NumElements = SubVectorTy->getNumElements(); else { assert((*GEPI)->isStructTy() && "Indexed GEP type is not array, vector, or struct!"); continue; } ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand()); if (!IdxVal || IdxVal->getZExtValue() >= NumElements) return false; } } for (User *UU : U->users()) if (!isSafeSROAElementUse(UU)) return false; return true; } /// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it /// is safe for us to perform this transformation. /// static bool GlobalUsersSafeToSRA(GlobalValue *GV) { for (User *U : GV->users()) if (!IsUserOfGlobalSafeForSRA(U, GV)) return false; return true; } /// SRAGlobal - Perform scalar replacement of aggregates on the specified global /// variable. This opens the door for other optimizations by exposing the /// behavior of the program in a more fine-grained way. We have determined that /// this transformation is safe already. We return the first global variable we /// insert so that the caller can reprocess it. static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) { // Make sure this global only has simple uses that we can SRA. if (!GlobalUsersSafeToSRA(GV)) return nullptr; assert(GV->hasLocalLinkage() && !GV->isConstant()); Constant *Init = GV->getInitializer(); Type *Ty = Init->getType(); std::vector<GlobalVariable*> NewGlobals; Module::GlobalListType &Globals = GV->getParent()->getGlobalList(); // Get the alignment of the global, either explicit or target-specific. unsigned StartAlignment = GV->getAlignment(); if (StartAlignment == 0) StartAlignment = DL.getABITypeAlignment(GV->getType()); if (StructType *STy = dyn_cast<StructType>(Ty)) { NewGlobals.reserve(STy->getNumElements()); const StructLayout &Layout = *DL.getStructLayout(STy); for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { Constant *In = Init->getAggregateElement(i); assert(In && "Couldn't get element of initializer?"); GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false, GlobalVariable::InternalLinkage, In, GV->getName()+"."+Twine(i), GV->getThreadLocalMode(), GV->getType()->getAddressSpace()); Globals.insert(GV, NGV); NewGlobals.push_back(NGV); // Calculate the known alignment of the field. If the original aggregate // had 256 byte alignment for example, something might depend on that: // propagate info to each field. uint64_t FieldOffset = Layout.getElementOffset(i); unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset); if (NewAlign > DL.getABITypeAlignment(STy->getElementType(i))) NGV->setAlignment(NewAlign); } } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) { unsigned NumElements = 0; if (ArrayType *ATy = dyn_cast<ArrayType>(STy)) NumElements = ATy->getNumElements(); else NumElements = cast<VectorType>(STy)->getNumElements(); if (NumElements > 16 && GV->hasNUsesOrMore(16)) return nullptr; // It's not worth it. NewGlobals.reserve(NumElements); uint64_t EltSize = DL.getTypeAllocSize(STy->getElementType()); unsigned EltAlign = DL.getABITypeAlignment(STy->getElementType()); for (unsigned i = 0, e = NumElements; i != e; ++i) { Constant *In = Init->getAggregateElement(i); assert(In && "Couldn't get element of initializer?"); GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false, GlobalVariable::InternalLinkage, In, GV->getName()+"."+Twine(i), GV->getThreadLocalMode(), GV->getType()->getAddressSpace()); Globals.insert(GV, NGV); NewGlobals.push_back(NGV); // Calculate the known alignment of the field. If the original aggregate // had 256 byte alignment for example, something might depend on that: // propagate info to each field. unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i); if (NewAlign > EltAlign) NGV->setAlignment(NewAlign); } } if (NewGlobals.empty()) return nullptr; DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV); Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext())); // Loop over all of the uses of the global, replacing the constantexpr geps, // with smaller constantexpr geps or direct references. while (!GV->use_empty()) { User *GEP = GV->user_back(); assert(((isa<ConstantExpr>(GEP) && cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); // Ignore the 1th operand, which has to be zero or else the program is quite // broken (undefined). Get the 2nd operand, which is the structure or array // index. unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. Value *NewPtr = NewGlobals[Val]; // Form a shorter GEP if needed. if (GEP->getNumOperands() > 3) { if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { SmallVector<Constant*, 8> Idxs; Idxs.push_back(NullInt); for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) Idxs.push_back(CE->getOperand(i)); NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs); } else { GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); SmallVector<Value*, 8> Idxs; Idxs.push_back(NullInt); for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) Idxs.push_back(GEPI->getOperand(i)); NewPtr = GetElementPtrInst::Create(NewPtr, Idxs, GEPI->getName()+"."+Twine(Val),GEPI); } } GEP->replaceAllUsesWith(NewPtr); if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) GEPI->eraseFromParent(); else cast<ConstantExpr>(GEP)->destroyConstant(); } // Delete the old global, now that it is dead. Globals.erase(GV); ++NumSRA; // Loop over the new globals array deleting any globals that are obviously // dead. This can arise due to scalarization of a structure or an array that // has elements that are dead. unsigned FirstGlobal = 0; for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) if (NewGlobals[i]->use_empty()) { Globals.erase(NewGlobals[i]); if (FirstGlobal == i) ++FirstGlobal; } return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : nullptr; } /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified /// value will trap if the value is dynamically null. PHIs keeps track of any /// phi nodes we've seen to avoid reprocessing them. static bool AllUsesOfValueWillTrapIfNull(const Value *V, SmallPtrSet<const PHINode*, 8> &PHIs) { for (const User *U : V->users()) if (isa<LoadInst>(U)) { // Will trap. } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) { if (SI->getOperand(0) == V) { //cerr << "NONTRAPPING USE: " << *U; return false; // Storing the value. } } else if (const CallInst *CI = dyn_cast<CallInst>(U)) { if (CI->getCalledValue() != V) { //cerr << "NONTRAPPING USE: " << *U; return false; // Not calling the ptr } } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) { if (II->getCalledValue() != V) { //cerr << "NONTRAPPING USE: " << *U; return false; // Not calling the ptr } } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) { if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; } else if (const PHINode *PN = dyn_cast<PHINode>(U)) { // If we've already seen this phi node, ignore it, it has already been // checked. if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs)) return false; } else if (isa<ICmpInst>(U) && isa<ConstantPointerNull>(U->getOperand(1))) { // Ignore icmp X, null } else { //cerr << "NONTRAPPING USE: " << *U; return false; } return true; } /// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads /// from GV will trap if the loaded value is null. Note that this also permits /// comparisons of the loaded value against null, as a special case. static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) { for (const User *U : GV->users()) if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { SmallPtrSet<const PHINode*, 8> PHIs; if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) return false; } else if (isa<StoreInst>(U)) { // Ignore stores to the global. } else { // We don't know or understand this user, bail out. //cerr << "UNKNOWN USER OF GLOBAL!: " << *U; return false; } return true; } static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) { bool Changed = false; for (auto UI = V->user_begin(), E = V->user_end(); UI != E; ) { Instruction *I = cast<Instruction>(*UI++); if (LoadInst *LI = dyn_cast<LoadInst>(I)) { LI->setOperand(0, NewV); Changed = true; } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { if (SI->getOperand(1) == V) { SI->setOperand(1, NewV); Changed = true; } } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { CallSite CS(I); if (CS.getCalledValue() == V) { // Calling through the pointer! Turn into a direct call, but be careful // that the pointer is not also being passed as an argument. CS.setCalledFunction(NewV); Changed = true; bool PassedAsArg = false; for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) if (CS.getArgument(i) == V) { PassedAsArg = true; CS.setArgument(i, NewV); } if (PassedAsArg) { // Being passed as an argument also. Be careful to not invalidate UI! UI = V->user_begin(); } } } else if (CastInst *CI = dyn_cast<CastInst>(I)) { Changed |= OptimizeAwayTrappingUsesOfValue(CI, ConstantExpr::getCast(CI->getOpcode(), NewV, CI->getType())); if (CI->use_empty()) { Changed = true; CI->eraseFromParent(); } } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { // Should handle GEP here. SmallVector<Constant*, 8> Idxs; Idxs.reserve(GEPI->getNumOperands()-1); for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end(); i != e; ++i) if (Constant *C = dyn_cast<Constant>(*i)) Idxs.push_back(C); else break; if (Idxs.size() == GEPI->getNumOperands()-1) Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, ConstantExpr::getGetElementPtr(NewV, Idxs)); if (GEPI->use_empty()) { Changed = true; GEPI->eraseFromParent(); } } } return Changed; } /// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null /// value stored into it. If there are uses of the loaded value that would trap /// if the loaded value is dynamically null, then we know that they cannot be /// reachable with a null optimize away the load. static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV, const DataLayout *DL, TargetLibraryInfo *TLI) { bool Changed = false; // Keep track of whether we are able to remove all the uses of the global // other than the store that defines it. bool AllNonStoreUsesGone = true; // Replace all uses of loads with uses of uses of the stored value. for (Value::user_iterator GUI = GV->user_begin(), E = GV->user_end(); GUI != E;){ User *GlobalUser = *GUI++; if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) { Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV); // If we were able to delete all uses of the loads if (LI->use_empty()) { LI->eraseFromParent(); Changed = true; } else { AllNonStoreUsesGone = false; } } else if (isa<StoreInst>(GlobalUser)) { // Ignore the store that stores "LV" to the global. assert(GlobalUser->getOperand(1) == GV && "Must be storing *to* the global"); } else { AllNonStoreUsesGone = false; // If we get here we could have other crazy uses that are transitively // loaded. assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) || isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) || isa<BitCastInst>(GlobalUser) || isa<GetElementPtrInst>(GlobalUser)) && "Only expect load and stores!"); } } if (Changed) { DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV); ++NumGlobUses; } // If we nuked all of the loads, then none of the stores are needed either, // nor is the global. if (AllNonStoreUsesGone) { if (isLeakCheckerRoot(GV)) { Changed |= CleanupPointerRootUsers(GV, TLI); } else { Changed = true; CleanupConstantGlobalUsers(GV, nullptr, DL, TLI); } if (GV->use_empty()) { DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n"); Changed = true; GV->eraseFromParent(); ++NumDeleted; } } return Changed; } /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the /// instructions that are foldable. static void ConstantPropUsersOf(Value *V, const DataLayout *DL, TargetLibraryInfo *TLI) { for (Value::user_iterator UI = V->user_begin(), E = V->user_end(); UI != E; ) if (Instruction *I = dyn_cast<Instruction>(*UI++)) if (Constant *NewC = ConstantFoldInstruction(I, DL, TLI)) { I->replaceAllUsesWith(NewC); // Advance UI to the next non-I use to avoid invalidating it! // Instructions could multiply use V. while (UI != E && *UI == I) ++UI; I->eraseFromParent(); } } /// OptimizeGlobalAddressOfMalloc - This function takes the specified global /// variable, and transforms the program as if it always contained the result of /// the specified malloc. Because it is always the result of the specified /// malloc, there is no reason to actually DO the malloc. Instead, turn the /// malloc into a global, and any loads of GV as uses of the new global. static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, CallInst *CI, Type *AllocTy, ConstantInt *NElements, const DataLayout *DL, TargetLibraryInfo *TLI) { DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n'); Type *GlobalType; if (NElements->getZExtValue() == 1) GlobalType = AllocTy; else // If we have an array allocation, the global variable is of an array. GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue()); // Create the new global variable. The contents of the malloc'd memory is // undefined, so initialize with an undef value. GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(), GlobalType, false, GlobalValue::InternalLinkage, UndefValue::get(GlobalType), GV->getName()+".body", GV, GV->getThreadLocalMode()); // If there are bitcast users of the malloc (which is typical, usually we have // a malloc + bitcast) then replace them with uses of the new global. Update // other users to use the global as well. BitCastInst *TheBC = nullptr; while (!CI->use_empty()) { Instruction *User = cast<Instruction>(CI->user_back()); if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { if (BCI->getType() == NewGV->getType()) { BCI->replaceAllUsesWith(NewGV); BCI->eraseFromParent(); } else { BCI->setOperand(0, NewGV); } } else { if (!TheBC) TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI); User->replaceUsesOfWith(CI, TheBC); } } Constant *RepValue = NewGV; if (NewGV->getType() != GV->getType()->getElementType()) RepValue = ConstantExpr::getBitCast(RepValue, GV->getType()->getElementType()); // If there is a comparison against null, we will insert a global bool to // keep track of whether the global was initialized yet or not. GlobalVariable *InitBool = new GlobalVariable(Type::getInt1Ty(GV->getContext()), false, GlobalValue::InternalLinkage, ConstantInt::getFalse(GV->getContext()), GV->getName()+".init", GV->getThreadLocalMode()); bool InitBoolUsed = false; // Loop over all uses of GV, processing them in turn. while (!GV->use_empty()) { if (StoreInst *SI = dyn_cast<StoreInst>(GV->user_back())) { // The global is initialized when the store to it occurs. new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0, SI->getOrdering(), SI->getSynchScope(), SI); SI->eraseFromParent(); continue; } LoadInst *LI = cast<LoadInst>(GV->user_back()); while (!LI->use_empty()) { Use &LoadUse = *LI->use_begin(); ICmpInst *ICI = dyn_cast<ICmpInst>(LoadUse.getUser()); if (!ICI) { LoadUse = RepValue; continue; } // Replace the cmp X, 0 with a use of the bool value. // Sink the load to where the compare was, if atomic rules allow us to. Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0, LI->getOrdering(), LI->getSynchScope(), LI->isUnordered() ? (Instruction*)ICI : LI); InitBoolUsed = true; switch (ICI->getPredicate()) { default: llvm_unreachable("Unknown ICmp Predicate!"); case ICmpInst::ICMP_ULT: case ICmpInst::ICMP_SLT: // X < null -> always false LV = ConstantInt::getFalse(GV->getContext()); break; case ICmpInst::ICMP_ULE: case ICmpInst::ICMP_SLE: case ICmpInst::ICMP_EQ: LV = BinaryOperator::CreateNot(LV, "notinit", ICI); break; case ICmpInst::ICMP_NE: case ICmpInst::ICMP_UGE: case ICmpInst::ICMP_SGE: case ICmpInst::ICMP_UGT: case ICmpInst::ICMP_SGT: break; // no change. } ICI->replaceAllUsesWith(LV); ICI->eraseFromParent(); } LI->eraseFromParent(); } // If the initialization boolean was used, insert it, otherwise delete it. if (!InitBoolUsed) { while (!InitBool->use_empty()) // Delete initializations cast<StoreInst>(InitBool->user_back())->eraseFromParent(); delete InitBool; } else GV->getParent()->getGlobalList().insert(GV, InitBool); // Now the GV is dead, nuke it and the malloc.. GV->eraseFromParent(); CI->eraseFromParent(); // To further other optimizations, loop over all users of NewGV and try to // constant prop them. This will promote GEP instructions with constant // indices into GEP constant-exprs, which will allow global-opt to hack on it. ConstantPropUsersOf(NewGV, DL, TLI); if (RepValue != NewGV) ConstantPropUsersOf(RepValue, DL, TLI); return NewGV; } /// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking /// to make sure that there are no complex uses of V. We permit simple things /// like dereferencing the pointer, but not storing through the address, unless /// it is to the specified global. static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V, const GlobalVariable *GV, SmallPtrSet<const PHINode*, 8> &PHIs) { for (const User *U : V->users()) { const Instruction *Inst = cast<Instruction>(U); if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { continue; // Fine, ignore. } if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) { if (SI->getOperand(0) == V && SI->getOperand(1) != GV) return false; // Storing the pointer itself... bad. continue; // Otherwise, storing through it, or storing into GV... fine. } // Must index into the array and into the struct. if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) { if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) return false; continue; } if (const PHINode *PN = dyn_cast<PHINode>(Inst)) { // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI // cycles. if (PHIs.insert(PN)) if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) return false; continue; } if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) return false; continue; } return false; } return true; } /// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV /// somewhere. Transform all uses of the allocation into loads from the /// global and uses of the resultant pointer. Further, delete the store into /// GV. This assumes that these value pass the /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, GlobalVariable *GV) { while (!Alloc->use_empty()) { Instruction *U = cast<Instruction>(*Alloc->user_begin()); Instruction *InsertPt = U; if (StoreInst *SI = dyn_cast<StoreInst>(U)) { // If this is the store of the allocation into the global, remove it. if (SI->getOperand(1) == GV) { SI->eraseFromParent(); continue; } } else if (PHINode *PN = dyn_cast<PHINode>(U)) { // Insert the load in the corresponding predecessor, not right before the // PHI. InsertPt = PN->getIncomingBlock(*Alloc->use_begin())->getTerminator(); } else if (isa<BitCastInst>(U)) { // Must be bitcast between the malloc and store to initialize the global. ReplaceUsesOfMallocWithGlobal(U, GV); U->eraseFromParent(); continue; } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { // If this is a "GEP bitcast" and the user is a store to the global, then // just process it as a bitcast. if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->user_back())) if (SI->getOperand(1) == GV) { // Must be bitcast GEP between the malloc and store to initialize // the global. ReplaceUsesOfMallocWithGlobal(GEPI, GV); GEPI->eraseFromParent(); continue; } } // Insert a load from the global, and use it instead of the malloc. Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); U->replaceUsesOfWith(Alloc, NL); } } /// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi /// of a load) are simple enough to perform heap SRA on. This permits GEP's /// that index through the array and struct field, icmps of null, and PHIs. static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V, SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs, SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) { // We permit two users of the load: setcc comparing against the null // pointer, and a getelementptr of a specific form. for (const User *U : V->users()) { const Instruction *UI = cast<Instruction>(U); // Comparison against null is ok. if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UI)) { if (!isa<ConstantPointerNull>(ICI->getOperand(1))) return false; continue; } // getelementptr is also ok, but only a simple form. if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) { // Must index into the array and into the struct. if (GEPI->getNumOperands() < 3) return false; // Otherwise the GEP is ok. continue; } if (const PHINode *PN = dyn_cast<PHINode>(UI)) { if (!LoadUsingPHIsPerLoad.insert(PN)) // This means some phi nodes are dependent on each other. // Avoid infinite looping! return false; if (!LoadUsingPHIs.insert(PN)) // If we have already analyzed this PHI, then it is safe. continue; // Make sure all uses of the PHI are simple enough to transform. if (!LoadUsesSimpleEnoughForHeapSRA(PN, LoadUsingPHIs, LoadUsingPHIsPerLoad)) return false; continue; } // Otherwise we don't know what this is, not ok. return false; } return true; } /// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from /// GV are simple enough to perform HeapSRA, return true. static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV, Instruction *StoredVal) { SmallPtrSet<const PHINode*, 32> LoadUsingPHIs; SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad; for (const User *U : GV->users()) if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, LoadUsingPHIsPerLoad)) return false; LoadUsingPHIsPerLoad.clear(); } // If we reach here, we know that all uses of the loads and transitive uses // (through PHI nodes) are simple enough to transform. However, we don't know // that all inputs the to the PHI nodes are in the same equivalence sets. // Check to verify that all operands of the PHIs are either PHIS that can be // transformed, loads from GV, or MI itself. for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin() , E = LoadUsingPHIs.end(); I != E; ++I) { const PHINode *PN = *I; for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { Value *InVal = PN->getIncomingValue(op); // PHI of the stored value itself is ok. if (InVal == StoredVal) continue; if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) { // One of the PHIs in our set is (optimistically) ok. if (LoadUsingPHIs.count(InPN)) continue; return false; } // Load from GV is ok. if (const LoadInst *LI = dyn_cast<LoadInst>(InVal)) if (LI->getOperand(0) == GV) continue; // UNDEF? NULL? // Anything else is rejected. return false; } } return true; } static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { std::vector<Value*> &FieldVals = InsertedScalarizedValues[V]; if (FieldNo >= FieldVals.size()) FieldVals.resize(FieldNo+1); // If we already have this value, just reuse the previously scalarized // version. if (Value *FieldVal = FieldVals[FieldNo]) return FieldVal; // Depending on what instruction this is, we have several cases. Value *Result; if (LoadInst *LI = dyn_cast<LoadInst>(V)) { // This is a scalarized version of the load from the global. Just create // a new Load of the scalarized global. Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo, InsertedScalarizedValues, PHIsToRewrite), LI->getName()+".f"+Twine(FieldNo), LI); } else if (PHINode *PN = dyn_cast<PHINode>(V)) { // PN's type is pointer to struct. Make a new PHI of pointer to struct // field. PointerType *PTy = cast<PointerType>(PN->getType()); StructType *ST = cast<StructType>(PTy->getElementType()); unsigned AS = PTy->getAddressSpace(); PHINode *NewPN = PHINode::Create(PointerType::get(ST->getElementType(FieldNo), AS), PN->getNumIncomingValues(), PN->getName()+".f"+Twine(FieldNo), PN); Result = NewPN; PHIsToRewrite.push_back(std::make_pair(PN, FieldNo)); } else { llvm_unreachable("Unknown usable value"); } return FieldVals[FieldNo] = Result; } /// RewriteHeapSROALoadUser - Given a load instruction and a value derived from /// the load, rewrite the derived value to use the HeapSRoA'd load. static void RewriteHeapSROALoadUser(Instruction *LoadUser, DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { // If this is a comparison against null, handle it. if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { assert(isa<ConstantPointerNull>(SCI->getOperand(1))); // If we have a setcc of the loaded pointer, we can use a setcc of any // field. Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, InsertedScalarizedValues, PHIsToRewrite); Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, Constant::getNullValue(NPtr->getType()), SCI->getName()); SCI->replaceAllUsesWith(New); SCI->eraseFromParent(); return; } // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) && "Unexpected GEPI!"); // Load the pointer for this field. unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, InsertedScalarizedValues, PHIsToRewrite); // Create the new GEP idx vector. SmallVector<Value*, 8> GEPIdx; GEPIdx.push_back(GEPI->getOperand(1)); GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx, GEPI->getName(), GEPI); GEPI->replaceAllUsesWith(NGEPI); GEPI->eraseFromParent(); return; } // Recursively transform the users of PHI nodes. This will lazily create the // PHIs that are needed for individual elements. Keep track of what PHIs we // see in InsertedScalarizedValues so that we don't get infinite loops (very // antisocial). If the PHI is already in InsertedScalarizedValues, it has // already been seen first by another load, so its uses have already been // processed. PHINode *PN = cast<PHINode>(LoadUser); if (!InsertedScalarizedValues.insert(std::make_pair(PN, std::vector<Value*>())).second) return; // If this is the first time we've seen this PHI, recursively process all // users. for (auto UI = PN->user_begin(), E = PN->user_end(); UI != E;) { Instruction *User = cast<Instruction>(*UI++); RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); } } /// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr /// is a value loaded from the global. Eliminate all uses of Ptr, making them /// use FieldGlobals instead. All uses of loaded values satisfy /// AllGlobalLoadUsesSimpleEnoughForHeapSRA. static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { for (auto UI = Load->user_begin(), E = Load->user_end(); UI != E;) { Instruction *User = cast<Instruction>(*UI++); RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); } if (Load->use_empty()) { Load->eraseFromParent(); InsertedScalarizedValues.erase(Load); } } /// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break /// it up into multiple allocations of arrays of the fields. static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI, Value *NElems, const DataLayout *DL, const TargetLibraryInfo *TLI) { DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n'); Type *MAT = getMallocAllocatedType(CI, TLI); StructType *STy = cast<StructType>(MAT); // There is guaranteed to be at least one use of the malloc (storing // it into GV). If there are other uses, change them to be uses of // the global to simplify later code. This also deletes the store // into GV. ReplaceUsesOfMallocWithGlobal(CI, GV); // Okay, at this point, there are no users of the malloc. Insert N // new mallocs at the same place as CI, and N globals. std::vector<Value*> FieldGlobals; std::vector<Value*> FieldMallocs; unsigned AS = GV->getType()->getPointerAddressSpace(); for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ Type *FieldTy = STy->getElementType(FieldNo); PointerType *PFieldTy = PointerType::get(FieldTy, AS); GlobalVariable *NGV = new GlobalVariable(*GV->getParent(), PFieldTy, false, GlobalValue::InternalLinkage, Constant::getNullValue(PFieldTy), GV->getName() + ".f" + Twine(FieldNo), GV, GV->getThreadLocalMode()); FieldGlobals.push_back(NGV); unsigned TypeSize = DL->getTypeAllocSize(FieldTy); if (StructType *ST = dyn_cast<StructType>(FieldTy)) TypeSize = DL->getStructLayout(ST)->getSizeInBytes(); Type *IntPtrTy = DL->getIntPtrType(CI->getType()); Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy, ConstantInt::get(IntPtrTy, TypeSize), NElems, nullptr, CI->getName() + ".f" + Twine(FieldNo)); FieldMallocs.push_back(NMI); new StoreInst(NMI, NGV, CI); } // The tricky aspect of this transformation is handling the case when malloc // fails. In the original code, malloc failing would set the result pointer // of malloc to null. In this case, some mallocs could succeed and others // could fail. As such, we emit code that looks like this: // F0 = malloc(field0) // F1 = malloc(field1) // F2 = malloc(field2) // if (F0 == 0 || F1 == 0 || F2 == 0) { // if (F0) { free(F0); F0 = 0; } // if (F1) { free(F1); F1 = 0; } // if (F2) { free(F2); F2 = 0; } // } // The malloc can also fail if its argument is too large. Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0); Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0), ConstantZero, "isneg"); for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i], Constant::getNullValue(FieldMallocs[i]->getType()), "isnull"); RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI); } // Split the basic block at the old malloc. BasicBlock *OrigBB = CI->getParent(); BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont"); // Create the block to check the first condition. Put all these blocks at the // end of the function as they are unlikely to be executed. BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(), "malloc_ret_null", OrigBB->getParent()); // Remove the uncond branch from OrigBB to ContBB, turning it into a cond // branch on RunningOr. OrigBB->getTerminator()->eraseFromParent(); BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); // Within the NullPtrBlock, we need to emit a comparison and branch for each // pointer, because some may be null while others are not. for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, Constant::getNullValue(GVVal->getType())); BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it", OrigBB->getParent()); BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next", OrigBB->getParent()); Instruction *BI = BranchInst::Create(FreeBlock, NextBlock, Cmp, NullPtrBlock); // Fill in FreeBlock. CallInst::CreateFree(GVVal, BI); new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], FreeBlock); BranchInst::Create(NextBlock, FreeBlock); NullPtrBlock = NextBlock; } BranchInst::Create(ContBB, NullPtrBlock); // CI is no longer needed, remove it. CI->eraseFromParent(); /// InsertedScalarizedLoads - As we process loads, if we can't immediately /// update all uses of the load, keep track of what scalarized loads are /// inserted for a given load. DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues; InsertedScalarizedValues[GV] = FieldGlobals; std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite; // Okay, the malloc site is completely handled. All of the uses of GV are now // loads, and all uses of those loads are simple. Rewrite them to use loads // of the per-field globals instead. for (auto UI = GV->user_begin(), E = GV->user_end(); UI != E;) { Instruction *User = cast<Instruction>(*UI++); if (LoadInst *LI = dyn_cast<LoadInst>(User)) { RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite); continue; } // Must be a store of null. StoreInst *SI = cast<StoreInst>(User); assert(isa<ConstantPointerNull>(SI->getOperand(0)) && "Unexpected heap-sra user!"); // Insert a store of null into each global. for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType()); Constant *Null = Constant::getNullValue(PT->getElementType()); new StoreInst(Null, FieldGlobals[i], SI); } // Erase the original store. SI->eraseFromParent(); } // While we have PHIs that are interesting to rewrite, do it. while (!PHIsToRewrite.empty()) { PHINode *PN = PHIsToRewrite.back().first; unsigned FieldNo = PHIsToRewrite.back().second; PHIsToRewrite.pop_back(); PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); // Add all the incoming values. This can materialize more phis. for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { Value *InVal = PN->getIncomingValue(i); InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, PHIsToRewrite); FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); } } // Drop all inter-phi links and any loads that made it this far. for (DenseMap<Value*, std::vector<Value*> >::iterator I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); I != E; ++I) { if (PHINode *PN = dyn_cast<PHINode>(I->first)) PN->dropAllReferences(); else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) LI->dropAllReferences(); } // Delete all the phis and loads now that inter-references are dead. for (DenseMap<Value*, std::vector<Value*> >::iterator I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); I != E; ++I) { if (PHINode *PN = dyn_cast<PHINode>(I->first)) PN->eraseFromParent(); else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) LI->eraseFromParent(); } // The old global is now dead, remove it. GV->eraseFromParent(); ++NumHeapSRA; return cast<GlobalVariable>(FieldGlobals[0]); } /// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a /// pointer global variable with a single value stored it that is a malloc or /// cast of malloc. static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, CallInst *CI, Type *AllocTy, AtomicOrdering Ordering, Module::global_iterator &GVI, const DataLayout *DL, TargetLibraryInfo *TLI) { if (!DL) return false; // If this is a malloc of an abstract type, don't touch it. if (!AllocTy->isSized()) return false; // We can't optimize this global unless all uses of it are *known* to be // of the malloc value, not of the null initializer value (consider a use // that compares the global's value against zero to see if the malloc has // been reached). To do this, we check to see if all uses of the global // would trap if the global were null: this proves that they must all // happen after the malloc. if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) return false; // We can't optimize this if the malloc itself is used in a complex way, // for example, being stored into multiple globals. This allows the // malloc to be stored into the specified global, loaded icmp'd, and // GEP'd. These are all things we could transform to using the global // for. SmallPtrSet<const PHINode*, 8> PHIs; if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs)) return false; // If we have a global that is only initialized with a fixed size malloc, // transform the program to use global memory instead of malloc'd memory. // This eliminates dynamic allocation, avoids an indirection accessing the // data, and exposes the resultant global to further GlobalOpt. // We cannot optimize the malloc if we cannot determine malloc array size. Value *NElems = getMallocArraySize(CI, DL, TLI, true); if (!NElems) return false; if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems)) // Restrict this transformation to only working on small allocations // (2048 bytes currently), as we don't want to introduce a 16M global or // something. if (NElements->getZExtValue() * DL->getTypeAllocSize(AllocTy) < 2048) { GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, DL, TLI); return true; } // If the allocation is an array of structures, consider transforming this // into multiple malloc'd arrays, one for each field. This is basically // SRoA for malloc'd memory. if (Ordering != NotAtomic) return false; // If this is an allocation of a fixed size array of structs, analyze as a // variable size array. malloc [100 x struct],1 -> malloc struct, 100 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1)) if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy)) AllocTy = AT->getElementType(); StructType *AllocSTy = dyn_cast<StructType>(AllocTy); if (!AllocSTy) return false; // This the structure has an unreasonable number of fields, leave it // alone. if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 && AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) { // If this is a fixed size array, transform the Malloc to be an alloc of // structs. malloc [100 x struct],1 -> malloc struct, 100 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) { Type *IntPtrTy = DL->getIntPtrType(CI->getType()); unsigned TypeSize = DL->getStructLayout(AllocSTy)->getSizeInBytes(); Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize); Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements()); Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy, AllocSize, NumElements, nullptr, CI->getName()); Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI); CI->replaceAllUsesWith(Cast); CI->eraseFromParent(); if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc)) CI = cast<CallInst>(BCI->getOperand(0)); else CI = cast<CallInst>(Malloc); } GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, DL, TLI, true), DL, TLI); return true; } return false; } // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge // that only one value (besides its initializer) is ever stored to the global. static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, AtomicOrdering Ordering, Module::global_iterator &GVI, const DataLayout *DL, TargetLibraryInfo *TLI) { // Ignore no-op GEPs and bitcasts. StoredOnceVal = StoredOnceVal->stripPointerCasts(); // If we are dealing with a pointer global that is initialized to null and // only has one (non-null) value stored into it, then we can optimize any // users of the loaded value (often calls and loads) that would trap if the // value was null. if (GV->getInitializer()->getType()->isPointerTy() && GV->getInitializer()->isNullValue()) { if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { if (GV->getInitializer()->getType() != SOVC->getType()) SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); // Optimize away any trapping uses of the loaded value. if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, DL, TLI)) return true; } else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) { Type *MallocType = getMallocAllocatedType(CI, TLI); if (MallocType && TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI, DL, TLI)) return true; } } return false; } /// TryToShrinkGlobalToBoolean - At this point, we have learned that the only /// two values ever stored into GV are its initializer and OtherVal. See if we /// can shrink the global into a boolean and select between the two values /// whenever it is used. This exposes the values to other scalar optimizations. static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { Type *GVElType = GV->getType()->getElementType(); // If GVElType is already i1, it is already shrunk. If the type of the GV is // an FP value, pointer or vector, don't do this optimization because a select // between them is very expensive and unlikely to lead to later // simplification. In these cases, we typically end up with "cond ? v1 : v2" // where v1 and v2 both require constant pool loads, a big loss. if (GVElType == Type::getInt1Ty(GV->getContext()) || GVElType->isFloatingPointTy() || GVElType->isPointerTy() || GVElType->isVectorTy()) return false; // Walk the use list of the global seeing if all the uses are load or store. // If there is anything else, bail out. for (User *U : GV->users()) if (!isa<LoadInst>(U) && !isa<StoreInst>(U)) return false; DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV); // Create the new global, initializing it to false. GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()), false, GlobalValue::InternalLinkage, ConstantInt::getFalse(GV->getContext()), GV->getName()+".b", GV->getThreadLocalMode(), GV->getType()->getAddressSpace()); GV->getParent()->getGlobalList().insert(GV, NewGV); Constant *InitVal = GV->getInitializer(); assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) && "No reason to shrink to bool!"); // If initialized to zero and storing one into the global, we can use a cast // instead of a select to synthesize the desired value. bool IsOneZero = false; if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) IsOneZero = InitVal->isNullValue() && CI->isOne(); while (!GV->use_empty()) { Instruction *UI = cast<Instruction>(GV->user_back()); if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { // Change the store into a boolean store. bool StoringOther = SI->getOperand(0) == OtherVal; // Only do this if we weren't storing a loaded value. Value *StoreVal; if (StoringOther || SI->getOperand(0) == InitVal) { StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()), StoringOther); } else { // Otherwise, we are storing a previously loaded copy. To do this, // change the copy from copying the original value to just copying the // bool. Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); // If we've already replaced the input, StoredVal will be a cast or // select instruction. If not, it will be a load of the original // global. if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { assert(LI->getOperand(0) == GV && "Not a copy!"); // Insert a new load, to preserve the saved value. StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0, LI->getOrdering(), LI->getSynchScope(), LI); } else { assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && "This is not a form that we understand!"); StoreVal = StoredVal->getOperand(0); assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); } } new StoreInst(StoreVal, NewGV, false, 0, SI->getOrdering(), SI->getSynchScope(), SI); } else { // Change the load into a load of bool then a select. LoadInst *LI = cast<LoadInst>(UI); LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0, LI->getOrdering(), LI->getSynchScope(), LI); Value *NSI; if (IsOneZero) NSI = new ZExtInst(NLI, LI->getType(), "", LI); else NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); NSI->takeName(LI); LI->replaceAllUsesWith(NSI); } UI->eraseFromParent(); } // Retain the name of the old global variable. People who are debugging their // programs may expect these variables to be named the same. NewGV->takeName(GV); GV->eraseFromParent(); return true; } /// ProcessGlobal - Analyze the specified global variable and optimize it if /// possible. If we make a change, return true. bool GlobalOpt::ProcessGlobal(GlobalVariable *GV, Module::global_iterator &GVI) { // Do more involved optimizations if the global is internal. GV->removeDeadConstantUsers(); if (GV->use_empty()) { DEBUG(dbgs() << "GLOBAL DEAD: " << *GV); GV->eraseFromParent(); ++NumDeleted; return true; } if (!GV->hasLocalLinkage()) return false; GlobalStatus GS; if (GlobalStatus::analyzeGlobal(GV, GS)) return false; if (!GS.IsCompared && !GV->hasUnnamedAddr()) { GV->setUnnamedAddr(true); NumUnnamed++; } if (GV->isConstant() || !GV->hasInitializer()) return false; return ProcessInternalGlobal(GV, GVI, GS); } /// ProcessInternalGlobal - Analyze the specified global variable and optimize /// it if possible. If we make a change, return true. bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, Module::global_iterator &GVI, const GlobalStatus &GS) { // If this is a first class global and has only one accessing function // and this function is main (which we know is not recursive), we replace // the global with a local alloca in this function. // // NOTE: It doesn't make sense to promote non-single-value types since we // are just replacing static memory to stack memory. // // If the global is in different address space, don't bring it to stack. if (!GS.HasMultipleAccessingFunctions && GS.AccessingFunction && !GS.HasNonInstructionUser && GV->getType()->getElementType()->isSingleValueType() && GS.AccessingFunction->getName() == "main" && GS.AccessingFunction->hasExternalLinkage() && GV->getType()->getAddressSpace() == 0) { DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV); Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction ->getEntryBlock().begin()); Type *ElemTy = GV->getType()->getElementType(); // FIXME: Pass Global's alignment when globals have alignment AllocaInst *Alloca = new AllocaInst(ElemTy, nullptr, GV->getName(), &FirstI); if (!isa<UndefValue>(GV->getInitializer())) new StoreInst(GV->getInitializer(), Alloca, &FirstI); GV->replaceAllUsesWith(Alloca); GV->eraseFromParent(); ++NumLocalized; return true; } // If the global is never loaded (but may be stored to), it is dead. // Delete it now. if (!GS.IsLoaded) { DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV); bool Changed; if (isLeakCheckerRoot(GV)) { // Delete any constant stores to the global. Changed = CleanupPointerRootUsers(GV, TLI); } else { // Delete any stores we can find to the global. We may not be able to // make it completely dead though. Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI); } // If the global is dead now, delete it. if (GV->use_empty()) { GV->eraseFromParent(); ++NumDeleted; Changed = true; } return Changed; } else if (GS.StoredType <= GlobalStatus::InitializerStored) { DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n"); GV->setConstant(true); // Clean up any obviously simplifiable users now. CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI); // If the global is dead now, just nuke it. if (GV->use_empty()) { DEBUG(dbgs() << " *** Marking constant allowed us to simplify " << "all users and delete global!\n"); GV->eraseFromParent(); ++NumDeleted; } ++NumMarked; return true; } else if (!GV->getInitializer()->getType()->isSingleValueType()) { if (DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>()) { const DataLayout &DL = DLP->getDataLayout(); if (GlobalVariable *FirstNewGV = SRAGlobal(GV, DL)) { GVI = FirstNewGV; // Don't skip the newly produced globals! return true; } } } else if (GS.StoredType == GlobalStatus::StoredOnce) { // If the initial value for the global was an undef value, and if only // one other value was stored into it, we can just change the // initializer to be the stored value, then delete all stores to the // global. This allows us to mark it constant. if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) if (isa<UndefValue>(GV->getInitializer())) { // Change the initial value here. GV->setInitializer(SOVConstant); // Clean up any obviously simplifiable users now. CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI); if (GV->use_empty()) { DEBUG(dbgs() << " *** Substituting initializer allowed us to " << "simplify all users and delete global!\n"); GV->eraseFromParent(); ++NumDeleted; } else { GVI = GV; } ++NumSubstitute; return true; } // Try to optimize globals based on the knowledge that only one value // (besides its initializer) is ever stored to the global. if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, GVI, DL, TLI)) return true; // Otherwise, if the global was not a boolean, we can shrink it to be a // boolean. if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) { if (GS.Ordering == NotAtomic) { if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) { ++NumShrunkToBool; return true; } } } } return false; } /// ChangeCalleesToFastCall - Walk all of the direct calls of the specified /// function, changing them to FastCC. static void ChangeCalleesToFastCall(Function *F) { for (User *U : F->users()) { if (isa<BlockAddress>(U)) continue; CallSite CS(cast<Instruction>(U)); CS.setCallingConv(CallingConv::Fast); } } static AttributeSet StripNest(LLVMContext &C, const AttributeSet &Attrs) { for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { unsigned Index = Attrs.getSlotIndex(i); if (!Attrs.getSlotAttributes(i).hasAttribute(Index, Attribute::Nest)) continue; // There can be only one. return Attrs.removeAttribute(C, Index, Attribute::Nest); } return Attrs; } static void RemoveNestAttribute(Function *F) { F->setAttributes(StripNest(F->getContext(), F->getAttributes())); for (User *U : F->users()) { if (isa<BlockAddress>(U)) continue; CallSite CS(cast<Instruction>(U)); CS.setAttributes(StripNest(F->getContext(), CS.getAttributes())); } } /// Return true if this is a calling convention that we'd like to change. The /// idea here is that we don't want to mess with the convention if the user /// explicitly requested something with performance implications like coldcc, /// GHC, or anyregcc. static bool isProfitableToMakeFastCC(Function *F) { CallingConv::ID CC = F->getCallingConv(); // FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc? return CC == CallingConv::C || CC == CallingConv::X86_ThisCall; } bool GlobalOpt::OptimizeFunctions(Module &M) { bool Changed = false; // Optimize functions. for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { Function *F = FI++; // Functions without names cannot be referenced outside this module. if (!F->hasName() && !F->isDeclaration() && !F->hasLocalLinkage()) F->setLinkage(GlobalValue::InternalLinkage); F->removeDeadConstantUsers(); if (F->isDefTriviallyDead()) { F->eraseFromParent(); Changed = true; ++NumFnDeleted; } else if (F->hasLocalLinkage()) { if (isProfitableToMakeFastCC(F) && !F->isVarArg() && !F->hasAddressTaken()) { // If this function has a calling convention worth changing, is not a // varargs function, and is only called directly, promote it to use the // Fast calling convention. F->setCallingConv(CallingConv::Fast); ChangeCalleesToFastCall(F); ++NumFastCallFns; Changed = true; } if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && !F->hasAddressTaken()) { // The function is not used by a trampoline intrinsic, so it is safe // to remove the 'nest' attribute. RemoveNestAttribute(F); ++NumNestRemoved; Changed = true; } } } return Changed; } bool GlobalOpt::OptimizeGlobalVars(Module &M) { bool Changed = false; SmallSet<const Comdat *, 8> NotDiscardableComdats; for (const GlobalVariable &GV : M.globals()) if (const Comdat *C = GV.getComdat()) if (!GV.isDiscardableIfUnused()) NotDiscardableComdats.insert(C); for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); GVI != E; ) { GlobalVariable *GV = GVI++; // Global variables without names cannot be referenced outside this module. if (!GV->hasName() && !GV->isDeclaration() && !GV->hasLocalLinkage()) GV->setLinkage(GlobalValue::InternalLinkage); // Simplify the initializer. if (GV->hasInitializer()) if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) { Constant *New = ConstantFoldConstantExpression(CE, DL, TLI); if (New && New != CE) GV->setInitializer(New); } if (GV->isDiscardableIfUnused()) { if (const Comdat *C = GV->getComdat()) if (NotDiscardableComdats.count(C)) continue; Changed |= ProcessGlobal(GV, GVI); } } return Changed; } static inline bool isSimpleEnoughValueToCommit(Constant *C, SmallPtrSet<Constant*, 8> &SimpleConstants, const DataLayout *DL); /// isSimpleEnoughValueToCommit - Return true if the specified constant can be /// handled by the code generator. We don't want to generate something like: /// void *X = &X/42; /// because the code generator doesn't have a relocation that can handle that. /// /// This function should be called if C was not found (but just got inserted) /// in SimpleConstants to avoid having to rescan the same constants all the /// time. static bool isSimpleEnoughValueToCommitHelper(Constant *C, SmallPtrSet<Constant*, 8> &SimpleConstants, const DataLayout *DL) { // Simple global addresses are supported, do not allow dllimport or // thread-local globals. if (auto *GV = dyn_cast<GlobalValue>(C)) return !GV->hasDLLImportStorageClass() && !GV->isThreadLocal(); // Simple integer, undef, constant aggregate zero, etc are all supported. if (C->getNumOperands() == 0 || isa<BlockAddress>(C)) return true; // Aggregate values are safe if all their elements are. if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) || isa<ConstantVector>(C)) { for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) { Constant *Op = cast<Constant>(C->getOperand(i)); if (!isSimpleEnoughValueToCommit(Op, SimpleConstants, DL)) return false; } return true; } // We don't know exactly what relocations are allowed in constant expressions, // so we allow &global+constantoffset, which is safe and uniformly supported // across targets. ConstantExpr *CE = cast<ConstantExpr>(C); switch (CE->getOpcode()) { case Instruction::BitCast: // Bitcast is fine if the casted value is fine. return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); case Instruction::IntToPtr: case Instruction::PtrToInt: // int <=> ptr is fine if the int type is the same size as the // pointer type. if (!DL || DL->getTypeSizeInBits(CE->getType()) != DL->getTypeSizeInBits(CE->getOperand(0)->getType())) return false; return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); // GEP is fine if it is simple + constant offset. case Instruction::GetElementPtr: for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) if (!isa<ConstantInt>(CE->getOperand(i))) return false; return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); case Instruction::Add: // We allow simple+cst. if (!isa<ConstantInt>(CE->getOperand(1))) return false; return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); } return false; } static inline bool isSimpleEnoughValueToCommit(Constant *C, SmallPtrSet<Constant*, 8> &SimpleConstants, const DataLayout *DL) { // If we already checked this constant, we win. if (!SimpleConstants.insert(C)) return true; // Check the constant. return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, DL); } /// isSimpleEnoughPointerToCommit - Return true if this constant is simple /// enough for us to understand. In particular, if it is a cast to anything /// other than from one pointer type to another pointer type, we punt. /// We basically just support direct accesses to globals and GEP's of /// globals. This should be kept up to date with CommitValueTo. static bool isSimpleEnoughPointerToCommit(Constant *C) { // Conservatively, avoid aggregate types. This is because we don't // want to worry about them partially overlapping other stores. if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType()) return false; if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) // Do not allow weak/*_odr/linkonce linkage or external globals. return GV->hasUniqueInitializer(); if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) { // Handle a constantexpr gep. if (CE->getOpcode() == Instruction::GetElementPtr && isa<GlobalVariable>(CE->getOperand(0)) && cast<GEPOperator>(CE)->isInBounds()) { GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or // external globals. if (!GV->hasUniqueInitializer()) return false; // The first index must be zero. ConstantInt *CI = dyn_cast<ConstantInt>(*std::next(CE->op_begin())); if (!CI || !CI->isZero()) return false; // The remaining indices must be compile-time known integers within the // notional bounds of the corresponding static array types. if (!CE->isGEPWithNoNotionalOverIndexing()) return false; return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); // A constantexpr bitcast from a pointer to another pointer is a no-op, // and we know how to evaluate it by moving the bitcast from the pointer // operand to the value operand. } else if (CE->getOpcode() == Instruction::BitCast && isa<GlobalVariable>(CE->getOperand(0))) { // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or // external globals. return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer(); } } return false; } /// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global /// initializer. This returns 'Init' modified to reflect 'Val' stored into it. /// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, ConstantExpr *Addr, unsigned OpNo) { // Base case of the recursion. if (OpNo == Addr->getNumOperands()) { assert(Val->getType() == Init->getType() && "Type mismatch!"); return Val; } SmallVector<Constant*, 32> Elts; if (StructType *STy = dyn_cast<StructType>(Init->getType())) { // Break up the constant into its elements. for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) Elts.push_back(Init->getAggregateElement(i)); // Replace the element that we are supposed to. ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); unsigned Idx = CU->getZExtValue(); assert(Idx < STy->getNumElements() && "Struct index out of range!"); Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1); // Return the modified struct. return ConstantStruct::get(STy, Elts); } ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); SequentialType *InitTy = cast<SequentialType>(Init->getType()); uint64_t NumElts; if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy)) NumElts = ATy->getNumElements(); else NumElts = InitTy->getVectorNumElements(); // Break up the array into elements. for (uint64_t i = 0, e = NumElts; i != e; ++i) Elts.push_back(Init->getAggregateElement(i)); assert(CI->getZExtValue() < NumElts); Elts[CI->getZExtValue()] = EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1); if (Init->getType()->isArrayTy()) return ConstantArray::get(cast<ArrayType>(InitTy), Elts); return ConstantVector::get(Elts); } /// CommitValueTo - We have decided that Addr (which satisfies the predicate /// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. static void CommitValueTo(Constant *Val, Constant *Addr) { if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { assert(GV->hasInitializer()); GV->setInitializer(Val); return; } ConstantExpr *CE = cast<ConstantExpr>(Addr); GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2)); } namespace { /// Evaluator - This class evaluates LLVM IR, producing the Constant /// representing each SSA instruction. Changes to global variables are stored /// in a mapping that can be iterated over after the evaluation is complete. /// Once an evaluation call fails, the evaluation object should not be reused. class Evaluator { public: Evaluator(const DataLayout *DL, const TargetLibraryInfo *TLI) : DL(DL), TLI(TLI) { ValueStack.emplace_back(); } ~Evaluator() { for (auto &Tmp : AllocaTmps) // If there are still users of the alloca, the program is doing something // silly, e.g. storing the address of the alloca somewhere and using it // later. Since this is undefined, we'll just make it be null. if (!Tmp->use_empty()) Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); } /// EvaluateFunction - Evaluate a call to function F, returning true if /// successful, false if we can't evaluate it. ActualArgs contains the formal /// arguments for the function. bool EvaluateFunction(Function *F, Constant *&RetVal, const SmallVectorImpl<Constant*> &ActualArgs); /// EvaluateBlock - Evaluate all instructions in block BB, returning true if /// successful, false if we can't evaluate it. NewBB returns the next BB that /// control flows into, or null upon return. bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB); Constant *getVal(Value *V) { if (Constant *CV = dyn_cast<Constant>(V)) return CV; Constant *R = ValueStack.back().lookup(V); assert(R && "Reference to an uncomputed value!"); return R; } void setVal(Value *V, Constant *C) { ValueStack.back()[V] = C; } const DenseMap<Constant*, Constant*> &getMutatedMemory() const { return MutatedMemory; } const SmallPtrSet<GlobalVariable*, 8> &getInvariants() const { return Invariants; } private: Constant *ComputeLoadResult(Constant *P); /// ValueStack - As we compute SSA register values, we store their contents /// here. The back of the deque contains the current function and the stack /// contains the values in the calling frames. std::deque<DenseMap<Value*, Constant*>> ValueStack; /// CallStack - This is used to detect recursion. In pathological situations /// we could hit exponential behavior, but at least there is nothing /// unbounded. SmallVector<Function*, 4> CallStack; /// MutatedMemory - For each store we execute, we update this map. Loads /// check this to get the most up-to-date value. If evaluation is successful, /// this state is committed to the process. DenseMap<Constant*, Constant*> MutatedMemory; /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable /// to represent its body. This vector is needed so we can delete the /// temporary globals when we are done. SmallVector<std::unique_ptr<GlobalVariable>, 32> AllocaTmps; /// Invariants - These global variables have been marked invariant by the /// static constructor. SmallPtrSet<GlobalVariable*, 8> Invariants; /// SimpleConstants - These are constants we have checked and know to be /// simple enough to live in a static initializer of a global. SmallPtrSet<Constant*, 8> SimpleConstants; const DataLayout *DL; const TargetLibraryInfo *TLI; }; } // anonymous namespace /// ComputeLoadResult - Return the value that would be computed by a load from /// P after the stores reflected by 'memory' have been performed. If we can't /// decide, return null. Constant *Evaluator::ComputeLoadResult(Constant *P) { // If this memory location has been recently stored, use the stored value: it // is the most up-to-date. DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P); if (I != MutatedMemory.end()) return I->second; // Access it. if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { if (GV->hasDefinitiveInitializer()) return GV->getInitializer(); return nullptr; } // Handle a constantexpr getelementptr. if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) if (CE->getOpcode() == Instruction::GetElementPtr && isa<GlobalVariable>(CE->getOperand(0))) { GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); if (GV->hasDefinitiveInitializer()) return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); } return nullptr; // don't know how to evaluate. } /// EvaluateBlock - Evaluate all instructions in block BB, returning true if /// successful, false if we can't evaluate it. NewBB returns the next BB that /// control flows into, or null upon return. bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB) { // This is the main evaluation loop. while (1) { Constant *InstResult = nullptr; DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n"); if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { if (!SI->isSimple()) { DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n"); return false; // no volatile/atomic accesses. } Constant *Ptr = getVal(SI->getOperand(1)); if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) { DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr); Ptr = ConstantFoldConstantExpression(CE, DL, TLI); DEBUG(dbgs() << "; To: " << *Ptr << "\n"); } if (!isSimpleEnoughPointerToCommit(Ptr)) { // If this is too complex for us to commit, reject it. DEBUG(dbgs() << "Pointer is too complex for us to evaluate store."); return false; } Constant *Val = getVal(SI->getOperand(0)); // If this might be too difficult for the backend to handle (e.g. the addr // of one global variable divided by another) then we can't commit it. if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) { DEBUG(dbgs() << "Store value is too complex to evaluate store. " << *Val << "\n"); return false; } if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) { if (CE->getOpcode() == Instruction::BitCast) { DEBUG(dbgs() << "Attempting to resolve bitcast on constant ptr.\n"); // If we're evaluating a store through a bitcast, then we need // to pull the bitcast off the pointer type and push it onto the // stored value. Ptr = CE->getOperand(0); Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType(); // In order to push the bitcast onto the stored value, a bitcast // from NewTy to Val's type must be legal. If it's not, we can try // introspecting NewTy to find a legal conversion. while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) { // If NewTy is a struct, we can convert the pointer to the struct // into a pointer to its first member. // FIXME: This could be extended to support arrays as well. if (StructType *STy = dyn_cast<StructType>(NewTy)) { NewTy = STy->getTypeAtIndex(0U); IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32); Constant *IdxZero = ConstantInt::get(IdxTy, 0, false); Constant * const IdxList[] = {IdxZero, IdxZero}; Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList); if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) Ptr = ConstantFoldConstantExpression(CE, DL, TLI); // If we can't improve the situation by introspecting NewTy, // we have to give up. } else { DEBUG(dbgs() << "Failed to bitcast constant ptr, can not " "evaluate.\n"); return false; } } // If we found compatible types, go ahead and push the bitcast // onto the stored value. Val = ConstantExpr::getBitCast(Val, NewTy); DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n"); } } MutatedMemory[Ptr] = Val; } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { InstResult = ConstantExpr::get(BO->getOpcode(), getVal(BO->getOperand(0)), getVal(BO->getOperand(1))); DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: " << *InstResult << "\n"); } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { InstResult = ConstantExpr::getCompare(CI->getPredicate(), getVal(CI->getOperand(0)), getVal(CI->getOperand(1))); DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult << "\n"); } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { InstResult = ConstantExpr::getCast(CI->getOpcode(), getVal(CI->getOperand(0)), CI->getType()); DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult << "\n"); } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)), getVal(SI->getOperand(1)), getVal(SI->getOperand(2))); DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult << "\n"); } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { Constant *P = getVal(GEP->getOperand(0)); SmallVector<Constant*, 8> GEPOps; for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e; ++i) GEPOps.push_back(getVal(*i)); InstResult = ConstantExpr::getGetElementPtr(P, GEPOps, cast<GEPOperator>(GEP)->isInBounds()); DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult << "\n"); } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { if (!LI->isSimple()) { DEBUG(dbgs() << "Found a Load! Not a simple load, can not evaluate.\n"); return false; // no volatile/atomic accesses. } Constant *Ptr = getVal(LI->getOperand(0)); if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) { Ptr = ConstantFoldConstantExpression(CE, DL, TLI); DEBUG(dbgs() << "Found a constant pointer expression, constant " "folding: " << *Ptr << "\n"); } InstResult = ComputeLoadResult(Ptr); if (!InstResult) { DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load." "\n"); return false; // Could not evaluate load. } DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n"); } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { if (AI->isArrayAllocation()) { DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n"); return false; // Cannot handle array allocs. } Type *Ty = AI->getType()->getElementType(); AllocaTmps.push_back( make_unique<GlobalVariable>(Ty, false, GlobalValue::InternalLinkage, UndefValue::get(Ty), AI->getName())); InstResult = AllocaTmps.back().get(); DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n"); } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) { CallSite CS(CurInst); // Debug info can safely be ignored here. if (isa<DbgInfoIntrinsic>(CS.getInstruction())) { DEBUG(dbgs() << "Ignoring debug info.\n"); ++CurInst; continue; } // Cannot handle inline asm. if (isa<InlineAsm>(CS.getCalledValue())) { DEBUG(dbgs() << "Found inline asm, can not evaluate.\n"); return false; } if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) { if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) { if (MSI->isVolatile()) { DEBUG(dbgs() << "Can not optimize a volatile memset " << "intrinsic.\n"); return false; } Constant *Ptr = getVal(MSI->getDest()); Constant *Val = getVal(MSI->getValue()); Constant *DestVal = ComputeLoadResult(getVal(Ptr)); if (Val->isNullValue() && DestVal && DestVal->isNullValue()) { // This memset is a no-op. DEBUG(dbgs() << "Ignoring no-op memset.\n"); ++CurInst; continue; } } if (II->getIntrinsicID() == Intrinsic::lifetime_start || II->getIntrinsicID() == Intrinsic::lifetime_end) { DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n"); ++CurInst; continue; } if (II->getIntrinsicID() == Intrinsic::invariant_start) { // We don't insert an entry into Values, as it doesn't have a // meaningful return value. if (!II->use_empty()) { DEBUG(dbgs() << "Found unused invariant_start. Can't evaluate.\n"); return false; } ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0)); Value *PtrArg = getVal(II->getArgOperand(1)); Value *Ptr = PtrArg->stripPointerCasts(); if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) { Type *ElemTy = cast<PointerType>(GV->getType())->getElementType(); if (DL && !Size->isAllOnesValue() && Size->getValue().getLimitedValue() >= DL->getTypeStoreSize(ElemTy)) { Invariants.insert(GV); DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV << "\n"); } else { DEBUG(dbgs() << "Found a global var, but can not treat it as an " "invariant.\n"); } } // Continue even if we do nothing. ++CurInst; continue; } DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n"); return false; } // Resolve function pointers. Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue())); if (!Callee || Callee->mayBeOverridden()) { DEBUG(dbgs() << "Can not resolve function pointer.\n"); return false; // Cannot resolve. } SmallVector<Constant*, 8> Formals; for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i) Formals.push_back(getVal(*i)); if (Callee->isDeclaration()) { // If this is a function we can constant fold, do it. if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) { InstResult = C; DEBUG(dbgs() << "Constant folded function call. Result: " << *InstResult << "\n"); } else { DEBUG(dbgs() << "Can not constant fold function call.\n"); return false; } } else { if (Callee->getFunctionType()->isVarArg()) { DEBUG(dbgs() << "Can not constant fold vararg function call.\n"); return false; } Constant *RetVal = nullptr; // Execute the call, if successful, use the return value. ValueStack.emplace_back(); if (!EvaluateFunction(Callee, RetVal, Formals)) { DEBUG(dbgs() << "Failed to evaluate function.\n"); return false; } ValueStack.pop_back(); InstResult = RetVal; if (InstResult) { DEBUG(dbgs() << "Successfully evaluated function. Result: " << InstResult << "\n\n"); } else { DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n"); } } } else if (isa<TerminatorInst>(CurInst)) { DEBUG(dbgs() << "Found a terminator instruction.\n"); if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { if (BI->isUnconditional()) { NextBB = BI->getSuccessor(0); } else { ConstantInt *Cond = dyn_cast<ConstantInt>(getVal(BI->getCondition())); if (!Cond) return false; // Cannot determine. NextBB = BI->getSuccessor(!Cond->getZExtValue()); } } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { ConstantInt *Val = dyn_cast<ConstantInt>(getVal(SI->getCondition())); if (!Val) return false; // Cannot determine. NextBB = SI->findCaseValue(Val).getCaseSuccessor(); } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) { Value *Val = getVal(IBI->getAddress())->stripPointerCasts(); if (BlockAddress *BA = dyn_cast<BlockAddress>(Val)) NextBB = BA->getBasicBlock(); else return false; // Cannot determine. } else if (isa<ReturnInst>(CurInst)) { NextBB = nullptr; } else { // invoke, unwind, resume, unreachable. DEBUG(dbgs() << "Can not handle terminator."); return false; // Cannot handle this terminator. } // We succeeded at evaluating this block! DEBUG(dbgs() << "Successfully evaluated block.\n"); return true; } else { // Did not know how to evaluate this! DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction." "\n"); return false; } if (!CurInst->use_empty()) { if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult)) InstResult = ConstantFoldConstantExpression(CE, DL, TLI); setVal(CurInst, InstResult); } // If we just processed an invoke, we finished evaluating the block. if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) { NextBB = II->getNormalDest(); DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n"); return true; } // Advance program counter. ++CurInst; } } /// EvaluateFunction - Evaluate a call to function F, returning true if /// successful, false if we can't evaluate it. ActualArgs contains the formal /// arguments for the function. bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal, const SmallVectorImpl<Constant*> &ActualArgs) { // Check to see if this function is already executing (recursion). If so, // bail out. TODO: we might want to accept limited recursion. if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) return false; CallStack.push_back(F); // Initialize arguments to the incoming values specified. unsigned ArgNo = 0; for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; ++AI, ++ArgNo) setVal(AI, ActualArgs[ArgNo]); // ExecutedBlocks - We only handle non-looping, non-recursive code. As such, // we can only evaluate any one basic block at most once. This set keeps // track of what we have executed so we can detect recursive cases etc. SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; // CurBB - The current basic block we're evaluating. BasicBlock *CurBB = F->begin(); BasicBlock::iterator CurInst = CurBB->begin(); while (1) { BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings. DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n"); if (!EvaluateBlock(CurInst, NextBB)) return false; if (!NextBB) { // Successfully running until there's no next block means that we found // the return. Fill it the return value and pop the call stack. ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator()); if (RI->getNumOperands()) RetVal = getVal(RI->getOperand(0)); CallStack.pop_back(); return true; } // Okay, we succeeded in evaluating this control flow. See if we have // executed the new block before. If so, we have a looping function, // which we cannot evaluate in reasonable time. if (!ExecutedBlocks.insert(NextBB)) return false; // looped! // Okay, we have never been in this block before. Check to see if there // are any PHI nodes. If so, evaluate them with information about where // we came from. PHINode *PN = nullptr; for (CurInst = NextBB->begin(); (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB))); // Advance to the next block. CurBB = NextBB; } } /// EvaluateStaticConstructor - Evaluate static constructors in the function, if /// we can. Return true if we can, false otherwise. static bool EvaluateStaticConstructor(Function *F, const DataLayout *DL, const TargetLibraryInfo *TLI) { // Call the function. Evaluator Eval(DL, TLI); Constant *RetValDummy; bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy, SmallVector<Constant*, 0>()); if (EvalSuccess) { ++NumCtorsEvaluated; // We succeeded at evaluation: commit the result. DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" << F->getName() << "' to " << Eval.getMutatedMemory().size() << " stores.\n"); for (DenseMap<Constant*, Constant*>::const_iterator I = Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end(); I != E; ++I) CommitValueTo(I->second, I->first); for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I = Eval.getInvariants().begin(), E = Eval.getInvariants().end(); I != E; ++I) (*I)->setConstant(true); } return EvalSuccess; } static int compareNames(Constant *const *A, Constant *const *B) { return (*A)->getName().compare((*B)->getName()); } static void setUsedInitializer(GlobalVariable &V, SmallPtrSet<GlobalValue *, 8> Init) { if (Init.empty()) { V.eraseFromParent(); return; } // Type of pointer to the array of pointers. PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext(), 0); SmallVector<llvm::Constant *, 8> UsedArray; for (SmallPtrSet<GlobalValue *, 8>::iterator I = Init.begin(), E = Init.end(); I != E; ++I) { Constant *Cast = ConstantExpr::getPointerBitCastOrAddrSpaceCast(*I, Int8PtrTy); UsedArray.push_back(Cast); } // Sort to get deterministic order. array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames); ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size()); Module *M = V.getParent(); V.removeFromParent(); GlobalVariable *NV = new GlobalVariable(*M, ATy, false, llvm::GlobalValue::AppendingLinkage, llvm::ConstantArray::get(ATy, UsedArray), ""); NV->takeName(&V); NV->setSection("llvm.metadata"); delete &V; } namespace { /// \brief An easy to access representation of llvm.used and llvm.compiler.used. class LLVMUsed { SmallPtrSet<GlobalValue *, 8> Used; SmallPtrSet<GlobalValue *, 8> CompilerUsed; GlobalVariable *UsedV; GlobalVariable *CompilerUsedV; public: LLVMUsed(Module &M) { UsedV = collectUsedGlobalVariables(M, Used, false); CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true); } typedef SmallPtrSet<GlobalValue *, 8>::iterator iterator; iterator usedBegin() { return Used.begin(); } iterator usedEnd() { return Used.end(); } iterator compilerUsedBegin() { return CompilerUsed.begin(); } iterator compilerUsedEnd() { return CompilerUsed.end(); } bool usedCount(GlobalValue *GV) const { return Used.count(GV); } bool compilerUsedCount(GlobalValue *GV) const { return CompilerUsed.count(GV); } bool usedErase(GlobalValue *GV) { return Used.erase(GV); } bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); } bool usedInsert(GlobalValue *GV) { return Used.insert(GV); } bool compilerUsedInsert(GlobalValue *GV) { return CompilerUsed.insert(GV); } void syncVariablesAndSets() { if (UsedV) setUsedInitializer(*UsedV, Used); if (CompilerUsedV) setUsedInitializer(*CompilerUsedV, CompilerUsed); } }; } static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) { if (GA.use_empty()) // No use at all. return false; assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) && "We should have removed the duplicated " "element from llvm.compiler.used"); if (!GA.hasOneUse()) // Strictly more than one use. So at least one is not in llvm.used and // llvm.compiler.used. return true; // Exactly one use. Check if it is in llvm.used or llvm.compiler.used. return !U.usedCount(&GA) && !U.compilerUsedCount(&GA); } static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V, const LLVMUsed &U) { unsigned N = 2; assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) && "We should have removed the duplicated " "element from llvm.compiler.used"); if (U.usedCount(&V) || U.compilerUsedCount(&V)) ++N; return V.hasNUsesOrMore(N); } static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) { if (!GA.hasLocalLinkage()) return true; return U.usedCount(&GA) || U.compilerUsedCount(&GA); } static bool hasUsesToReplace(GlobalAlias &GA, LLVMUsed &U, bool &RenameTarget) { RenameTarget = false; bool Ret = false; if (hasUseOtherThanLLVMUsed(GA, U)) Ret = true; // If the alias is externally visible, we may still be able to simplify it. if (!mayHaveOtherReferences(GA, U)) return Ret; // If the aliasee has internal linkage, give it the name and linkage // of the alias, and delete the alias. This turns: // define internal ... @f(...) // @a = alias ... @f // into: // define ... @a(...) Constant *Aliasee = GA.getAliasee(); GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); if (!Target->hasLocalLinkage()) return Ret; // Do not perform the transform if multiple aliases potentially target the // aliasee. This check also ensures that it is safe to replace the section // and other attributes of the aliasee with those of the alias. if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U)) return Ret; RenameTarget = true; return true; } bool GlobalOpt::OptimizeGlobalAliases(Module &M) { bool Changed = false; LLVMUsed Used(M); for (SmallPtrSet<GlobalValue *, 8>::iterator I = Used.usedBegin(), E = Used.usedEnd(); I != E; ++I) Used.compilerUsedErase(*I); for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;) { Module::alias_iterator J = I++; // Aliases without names cannot be referenced outside this module. if (!J->hasName() && !J->isDeclaration() && !J->hasLocalLinkage()) J->setLinkage(GlobalValue::InternalLinkage); // If the aliasee may change at link time, nothing can be done - bail out. if (J->mayBeOverridden()) continue; Constant *Aliasee = J->getAliasee(); GlobalValue *Target = dyn_cast<GlobalValue>(Aliasee->stripPointerCasts()); // We can't trivially replace the alias with the aliasee if the aliasee is // non-trivial in some way. // TODO: Try to handle non-zero GEPs of local aliasees. if (!Target) continue; Target->removeDeadConstantUsers(); // Make all users of the alias use the aliasee instead. bool RenameTarget; if (!hasUsesToReplace(*J, Used, RenameTarget)) continue; J->replaceAllUsesWith(ConstantExpr::getBitCast(Aliasee, J->getType())); ++NumAliasesResolved; Changed = true; if (RenameTarget) { // Give the aliasee the name, linkage and other attributes of the alias. Target->takeName(J); Target->setLinkage(J->getLinkage()); Target->setVisibility(J->getVisibility()); Target->setDLLStorageClass(J->getDLLStorageClass()); if (Used.usedErase(J)) Used.usedInsert(Target); if (Used.compilerUsedErase(J)) Used.compilerUsedInsert(Target); } else if (mayHaveOtherReferences(*J, Used)) continue; // Delete the alias. M.getAliasList().erase(J); ++NumAliasesRemoved; Changed = true; } Used.syncVariablesAndSets(); return Changed; } static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) { if (!TLI->has(LibFunc::cxa_atexit)) return nullptr; Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit)); if (!Fn) return nullptr; FunctionType *FTy = Fn->getFunctionType(); // Checking that the function has the right return type, the right number of // parameters and that they all have pointer types should be enough. if (!FTy->getReturnType()->isIntegerTy() || FTy->getNumParams() != 3 || !FTy->getParamType(0)->isPointerTy() || !FTy->getParamType(1)->isPointerTy() || !FTy->getParamType(2)->isPointerTy()) return nullptr; return Fn; } /// cxxDtorIsEmpty - Returns whether the given function is an empty C++ /// destructor and can therefore be eliminated. /// Note that we assume that other optimization passes have already simplified /// the code so we only look for a function with a single basic block, where /// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and /// other side-effect free instructions. static bool cxxDtorIsEmpty(const Function &Fn, SmallPtrSet<const Function *, 8> &CalledFunctions) { // FIXME: We could eliminate C++ destructors if they're readonly/readnone and // nounwind, but that doesn't seem worth doing. if (Fn.isDeclaration()) return false; if (++Fn.begin() != Fn.end()) return false; const BasicBlock &EntryBlock = Fn.getEntryBlock(); for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end(); I != E; ++I) { if (const CallInst *CI = dyn_cast<CallInst>(I)) { // Ignore debug intrinsics. if (isa<DbgInfoIntrinsic>(CI)) continue; const Function *CalledFn = CI->getCalledFunction(); if (!CalledFn) return false; SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions); // Don't treat recursive functions as empty. if (!NewCalledFunctions.insert(CalledFn)) return false; if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions)) return false; } else if (isa<ReturnInst>(*I)) return true; // We're done. else if (I->mayHaveSideEffects()) return false; // Destructor with side effects, bail. } return false; } bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) { /// Itanium C++ ABI p3.3.5: /// /// After constructing a global (or local static) object, that will require /// destruction on exit, a termination function is registered as follows: /// /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d ); /// /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the /// call f(p) when DSO d is unloaded, before all such termination calls /// registered before this one. It returns zero if registration is /// successful, nonzero on failure. // This pass will look for calls to __cxa_atexit where the function is trivial // and remove them. bool Changed = false; for (auto I = CXAAtExitFn->user_begin(), E = CXAAtExitFn->user_end(); I != E;) { // We're only interested in calls. Theoretically, we could handle invoke // instructions as well, but neither llvm-gcc nor clang generate invokes // to __cxa_atexit. CallInst *CI = dyn_cast<CallInst>(*I++); if (!CI) continue; Function *DtorFn = dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts()); if (!DtorFn) continue; SmallPtrSet<const Function *, 8> CalledFunctions; if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions)) continue; // Just remove the call. CI->replaceAllUsesWith(Constant::getNullValue(CI->getType())); CI->eraseFromParent(); ++NumCXXDtorsRemoved; Changed |= true; } return Changed; } bool GlobalOpt::runOnModule(Module &M) { bool Changed = false; DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); DL = DLP ? &DLP->getDataLayout() : nullptr; TLI = &getAnalysis<TargetLibraryInfo>(); bool LocalChange = true; while (LocalChange) { LocalChange = false; // Delete functions that are trivially dead, ccc -> fastcc LocalChange |= OptimizeFunctions(M); // Optimize global_ctors list. LocalChange |= optimizeGlobalCtorsList(M, [&](Function *F) { return EvaluateStaticConstructor(F, DL, TLI); }); // Optimize non-address-taken globals. LocalChange |= OptimizeGlobalVars(M); // Resolve aliases, when possible. LocalChange |= OptimizeGlobalAliases(M); // Try to remove trivial global destructors if they are not removed // already. Function *CXAAtExitFn = FindCXAAtExit(M, TLI); if (CXAAtExitFn) LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn); Changed |= LocalChange; } // TODO: Move all global ctors functions to the end of the module for code // layout. return Changed; }