//===- 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. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "globalopt" #include "llvm/Transforms/IPO.h" #include "llvm/CallingConv.h" #include "llvm/Constants.h" #include "llvm/DerivedTypes.h" #include "llvm/Instructions.h" #include "llvm/IntrinsicInst.h" #include "llvm/Module.h" #include "llvm/Operator.h" #include "llvm/Pass.h" #include "llvm/Analysis/ConstantFolding.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Target/TargetData.h" #include "llvm/Target/TargetLibraryInfo.h" #include "llvm/Support/CallSite.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/raw_ostream.h" #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/ADT/STLExtras.h" #include using namespace llvm; 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 GlobalStatus; struct GlobalOpt : public ModulePass { virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.addRequired(); } static char ID; // Pass identification, replacement for typeid GlobalOpt() : ModulePass(ID) { initializeGlobalOptPass(*PassRegistry::getPassRegistry()); } bool runOnModule(Module &M); private: GlobalVariable *FindGlobalCtors(Module &M); bool OptimizeFunctions(Module &M); bool OptimizeGlobalVars(Module &M); bool OptimizeGlobalAliases(Module &M); bool OptimizeGlobalCtorsList(GlobalVariable *&GCL); bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI); bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI, const SmallPtrSet &PHIUsers, const GlobalStatus &GS); bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn); }; } 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(); } namespace { /// GlobalStatus - As we analyze each global, keep track of some information /// about it. If we find out that the address of the global is taken, none of /// this info will be accurate. struct GlobalStatus { /// isCompared - True if the global's address is used in a comparison. bool isCompared; /// isLoaded - True if the global is ever loaded. If the global isn't ever /// loaded it can be deleted. bool isLoaded; /// StoredType - Keep track of what stores to the global look like. /// enum StoredType { /// NotStored - There is no store to this global. It can thus be marked /// constant. NotStored, /// isInitializerStored - This global is stored to, but the only thing /// stored is the constant it was initialized with. This is only tracked /// for scalar globals. isInitializerStored, /// isStoredOnce - This global is stored to, but only its initializer and /// one other value is ever stored to it. If this global isStoredOnce, we /// track the value stored to it in StoredOnceValue below. This is only /// tracked for scalar globals. isStoredOnce, /// isStored - This global is stored to by multiple values or something else /// that we cannot track. isStored } StoredType; /// StoredOnceValue - If only one value (besides the initializer constant) is /// ever stored to this global, keep track of what value it is. Value *StoredOnceValue; /// AccessingFunction/HasMultipleAccessingFunctions - These start out /// null/false. When the first accessing function is noticed, it is recorded. /// When a second different accessing function is noticed, /// HasMultipleAccessingFunctions is set to true. const Function *AccessingFunction; bool HasMultipleAccessingFunctions; /// HasNonInstructionUser - Set to true if this global has a user that is not /// an instruction (e.g. a constant expr or GV initializer). bool HasNonInstructionUser; /// HasPHIUser - Set to true if this global has a user that is a PHI node. bool HasPHIUser; /// AtomicOrdering - Set to the strongest atomic ordering requirement. AtomicOrdering Ordering; GlobalStatus() : isCompared(false), isLoaded(false), StoredType(NotStored), StoredOnceValue(0), AccessingFunction(0), HasMultipleAccessingFunctions(false), HasNonInstructionUser(false), HasPHIUser(false), Ordering(NotAtomic) {} }; } /// StrongerOrdering - Return the stronger of the two ordering. If the two /// orderings are acquire and release, then return AcquireRelease. /// static AtomicOrdering StrongerOrdering(AtomicOrdering X, AtomicOrdering Y) { if (X == Acquire && Y == Release) return AcquireRelease; if (Y == Acquire && X == Release) return AcquireRelease; return (AtomicOrdering)std::max(X, Y); } /// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used /// by constants itself. Note that constants cannot be cyclic, so this test is /// pretty easy to implement recursively. /// static bool SafeToDestroyConstant(const Constant *C) { if (isa(C)) return false; for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI) if (const Constant *CU = dyn_cast(*UI)) { if (!SafeToDestroyConstant(CU)) return false; } else return false; return true; } /// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus /// structure. If the global has its address taken, return true to indicate we /// can't do anything with it. /// static bool AnalyzeGlobal(const Value *V, GlobalStatus &GS, SmallPtrSet &PHIUsers) { for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) { const User *U = *UI; if (const ConstantExpr *CE = dyn_cast(U)) { GS.HasNonInstructionUser = true; // If the result of the constantexpr isn't pointer type, then we won't // know to expect it in various places. Just reject early. if (!isa(CE->getType())) return true; if (AnalyzeGlobal(CE, GS, PHIUsers)) return true; } else if (const Instruction *I = dyn_cast(U)) { if (!GS.HasMultipleAccessingFunctions) { const Function *F = I->getParent()->getParent(); if (GS.AccessingFunction == 0) GS.AccessingFunction = F; else if (GS.AccessingFunction != F) GS.HasMultipleAccessingFunctions = true; } if (const LoadInst *LI = dyn_cast(I)) { GS.isLoaded = true; // Don't hack on volatile loads. if (LI->isVolatile()) return true; GS.Ordering = StrongerOrdering(GS.Ordering, LI->getOrdering()); } else if (const StoreInst *SI = dyn_cast(I)) { // Don't allow a store OF the address, only stores TO the address. if (SI->getOperand(0) == V) return true; // Don't hack on volatile stores. if (SI->isVolatile()) return true; GS.Ordering = StrongerOrdering(GS.Ordering, SI->getOrdering()); // If this is a direct store to the global (i.e., the global is a scalar // value, not an aggregate), keep more specific information about // stores. if (GS.StoredType != GlobalStatus::isStored) { if (const GlobalVariable *GV = dyn_cast( SI->getOperand(1))) { Value *StoredVal = SI->getOperand(0); if (StoredVal == GV->getInitializer()) { if (GS.StoredType < GlobalStatus::isInitializerStored) GS.StoredType = GlobalStatus::isInitializerStored; } else if (isa(StoredVal) && cast(StoredVal)->getOperand(0) == GV) { if (GS.StoredType < GlobalStatus::isInitializerStored) GS.StoredType = GlobalStatus::isInitializerStored; } else if (GS.StoredType < GlobalStatus::isStoredOnce) { GS.StoredType = GlobalStatus::isStoredOnce; GS.StoredOnceValue = StoredVal; } else if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue == StoredVal) { // noop. } else { GS.StoredType = GlobalStatus::isStored; } } else { GS.StoredType = GlobalStatus::isStored; } } } else if (isa(I)) { if (AnalyzeGlobal(I, GS, PHIUsers)) return true; } else if (isa(I)) { if (AnalyzeGlobal(I, GS, PHIUsers)) return true; } else if (const PHINode *PN = dyn_cast(I)) { // PHI nodes we can check just like select or GEP instructions, but we // have to be careful about infinite recursion. if (PHIUsers.insert(PN)) // Not already visited. if (AnalyzeGlobal(I, GS, PHIUsers)) return true; GS.HasPHIUser = true; } else if (isa(I)) { GS.isCompared = true; } else if (const MemTransferInst *MTI = dyn_cast(I)) { if (MTI->isVolatile()) return true; if (MTI->getArgOperand(0) == V) GS.StoredType = GlobalStatus::isStored; if (MTI->getArgOperand(1) == V) GS.isLoaded = true; } else if (const MemSetInst *MSI = dyn_cast(I)) { assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!"); if (MSI->isVolatile()) return true; GS.StoredType = GlobalStatus::isStored; } else { return true; // Any other non-load instruction might take address! } } else if (const Constant *C = dyn_cast(U)) { GS.HasNonInstructionUser = true; // We might have a dead and dangling constant hanging off of here. if (!SafeToDestroyConstant(C)) return true; } else { GS.HasNonInstructionUser = true; // Otherwise must be some other user. return true; } } return false; } /// 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) { bool Changed = false; for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) { User *U = *UI++; if (LoadInst *LI = dyn_cast(U)) { if (Init) { // Replace the load with the initializer. LI->replaceAllUsesWith(Init); LI->eraseFromParent(); Changed = true; } } else if (StoreInst *SI = dyn_cast(U)) { // Store must be unreachable or storing Init into the global. SI->eraseFromParent(); Changed = true; } else if (ConstantExpr *CE = dyn_cast(U)) { if (CE->getOpcode() == Instruction::GetElementPtr) { Constant *SubInit = 0; if (Init) SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); Changed |= CleanupConstantGlobalUsers(CE, SubInit); } else if (CE->getOpcode() == Instruction::BitCast && CE->getType()->isPointerTy()) { // Pointer cast, delete any stores and memsets to the global. Changed |= CleanupConstantGlobalUsers(CE, 0); } if (CE->use_empty()) { CE->destroyConstant(); Changed = true; } } else if (GetElementPtrInst *GEP = dyn_cast(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 = 0; if (!isa(GEP->getOperand(0))) { // FIXME: use TargetData/TargetLibraryInfo for smarter constant folding. ConstantExpr *CE = dyn_cast_or_null(ConstantFoldInstruction(GEP)); if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr) SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); } Changed |= CleanupConstantGlobalUsers(GEP, SubInit); if (GEP->use_empty()) { GEP->eraseFromParent(); Changed = true; } } else if (MemIntrinsic *MI = dyn_cast(U)) { // memset/cpy/mv if (MI->getRawDest() == V) { MI->eraseFromParent(); Changed = true; } } else if (Constant *C = dyn_cast(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 (SafeToDestroyConstant(C)) { C->destroyConstant(); // This could have invalidated UI, start over from scratch. CleanupConstantGlobalUsers(V, Init); 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(V)) return SafeToDestroyConstant(C); Instruction *I = dyn_cast(V); if (!I) return false; // Loads are ok. if (isa(I)) return true; // Stores *to* the pointer are ok. if (StoreInst *SI = dyn_cast(I)) return SI->getOperand(0) != V; // Otherwise, it must be a GEP. GetElementPtrInst *GEPI = dyn_cast(I); if (GEPI == 0) return false; if (GEPI->getNumOperands() < 3 || !isa(GEPI->getOperand(1)) || !cast(GEPI->getOperand(1))->isNullValue()) return false; for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end(); I != E; ++I) if (!isSafeSROAElementUse(*I)) 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(U) && (!isa(U) || cast(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(U->getOperand(1)) || !cast(U->getOperand(1))->isNullValue() || !isa(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(*GEPI)) { uint64_t NumElements = AT->getNumElements(); ConstantInt *Idx = cast(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(*GEPI)) NumElements = SubArrayTy->getNumElements(); else if (VectorType *SubVectorTy = dyn_cast(*GEPI)) NumElements = SubVectorTy->getNumElements(); else { assert((*GEPI)->isStructTy() && "Indexed GEP type is not array, vector, or struct!"); continue; } ConstantInt *IdxVal = dyn_cast(GEPI.getOperand()); if (!IdxVal || IdxVal->getZExtValue() >= NumElements) return false; } } for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I) if (!isSafeSROAElementUse(*I)) 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 (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; ++UI) { if (!IsUserOfGlobalSafeForSRA(*UI, 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 TargetData &TD) { // Make sure this global only has simple uses that we can SRA. if (!GlobalUsersSafeToSRA(GV)) return 0; assert(GV->hasLocalLinkage() && !GV->isConstant()); Constant *Init = GV->getInitializer(); Type *Ty = Init->getType(); std::vector 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 = TD.getABITypeAlignment(GV->getType()); if (StructType *STy = dyn_cast(Ty)) { NewGlobals.reserve(STy->getNumElements()); const StructLayout &Layout = *TD.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->isThreadLocal(), 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 > TD.getABITypeAlignment(STy->getElementType(i))) NGV->setAlignment(NewAlign); } } else if (SequentialType *STy = dyn_cast(Ty)) { unsigned NumElements = 0; if (ArrayType *ATy = dyn_cast(STy)) NumElements = ATy->getNumElements(); else NumElements = cast(STy)->getNumElements(); if (NumElements > 16 && GV->hasNUsesOrMore(16)) return 0; // It's not worth it. NewGlobals.reserve(NumElements); uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType()); unsigned EltAlign = TD.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->isThreadLocal(), 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 0; 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->use_back(); assert(((isa(GEP) && cast(GEP)->getOpcode()==Instruction::GetElementPtr)|| isa(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(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(GEP)) { SmallVector 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(NewPtr), Idxs); } else { GetElementPtrInst *GEPI = cast(GEP); SmallVector 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(GEP)) GEPI->eraseFromParent(); else cast(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] : 0; } /// 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 &PHIs) { for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) { const User *U = *UI; if (isa(U)) { // Will trap. } else if (const StoreInst *SI = dyn_cast(U)) { if (SI->getOperand(0) == V) { //cerr << "NONTRAPPING USE: " << *U; return false; // Storing the value. } } else if (const CallInst *CI = dyn_cast(U)) { if (CI->getCalledValue() != V) { //cerr << "NONTRAPPING USE: " << *U; return false; // Not calling the ptr } } else if (const InvokeInst *II = dyn_cast(U)) { if (II->getCalledValue() != V) { //cerr << "NONTRAPPING USE: " << *U; return false; // Not calling the ptr } } else if (const BitCastInst *CI = dyn_cast(U)) { if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; } else if (const GetElementPtrInst *GEPI = dyn_cast(U)) { if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; } else if (const PHINode *PN = dyn_cast(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(U) && isa(UI->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 (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; ++UI) { const User *U = *UI; if (const LoadInst *LI = dyn_cast(U)) { SmallPtrSet PHIs; if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) return false; } else if (isa(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 (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) { Instruction *I = cast(*UI++); if (LoadInst *LI = dyn_cast(I)) { LI->setOperand(0, NewV); Changed = true; } else if (StoreInst *SI = dyn_cast(I)) { if (SI->getOperand(1) == V) { SI->setOperand(1, NewV); Changed = true; } } else if (isa(I) || isa(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->use_begin(); } } } else if (CastInst *CI = dyn_cast(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(I)) { // Should handle GEP here. SmallVector 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(*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) { 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::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){ User *GlobalUser = *GUI++; if (LoadInst *LI = dyn_cast(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(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(GlobalUser) || isa(GlobalUser) || isa(GlobalUser) || isa(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) { DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n"); CleanupConstantGlobalUsers(GV, 0); if (GV->use_empty()) { GV->eraseFromParent(); ++NumDeleted; } Changed = true; } return Changed; } /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the /// instructions that are foldable. static void ConstantPropUsersOf(Value *V) { for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) if (Instruction *I = dyn_cast(*UI++)) // FIXME: use TargetData/TargetLibraryInfo for smarter constant folding. if (Constant *NewC = ConstantFoldInstruction(I)) { 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, TargetData *TD) { 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->isThreadLocal()); // 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 = 0; while (!CI->use_empty()) { Instruction *User = cast(CI->use_back()); if (BitCastInst *BCI = dyn_cast(User)) { if (BCI->getType() == NewGV->getType()) { BCI->replaceAllUsesWith(NewGV); BCI->eraseFromParent(); } else { BCI->setOperand(0, NewGV); } } else { if (TheBC == 0) 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->isThreadLocal()); bool InitBoolUsed = false; // Loop over all uses of GV, processing them in turn. while (!GV->use_empty()) { if (StoreInst *SI = dyn_cast(GV->use_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(GV->use_back()); while (!LI->use_empty()) { Use &LoadUse = LI->use_begin().getUse(); if (!isa(LoadUse.getUser())) { LoadUse = RepValue; continue; } ICmpInst *ICI = cast(LoadUse.getUser()); // 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(InitBool->use_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); if (RepValue != NewGV) ConstantPropUsersOf(RepValue); 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 &PHIs) { for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) { const Instruction *Inst = cast(*UI); if (isa(Inst) || isa(Inst)) { continue; // Fine, ignore. } if (const StoreInst *SI = dyn_cast(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(Inst) && Inst->getNumOperands() >= 3) { if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) return false; continue; } if (const PHINode *PN = dyn_cast(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(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(*Alloc->use_begin()); Instruction *InsertPt = U; if (StoreInst *SI = dyn_cast(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(U)) { // Insert the load in the corresponding predecessor, not right before the // PHI. InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator(); } else if (isa(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(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(GEPI->use_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 &LoadUsingPHIs, SmallPtrSet &LoadUsingPHIsPerLoad) { // We permit two users of the load: setcc comparing against the null // pointer, and a getelementptr of a specific form. for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) { const Instruction *User = cast(*UI); // Comparison against null is ok. if (const ICmpInst *ICI = dyn_cast(User)) { if (!isa(ICI->getOperand(1))) return false; continue; } // getelementptr is also ok, but only a simple form. if (const GetElementPtrInst *GEPI = dyn_cast(User)) { // 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(User)) { 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 LoadUsingPHIs; SmallPtrSet LoadUsingPHIsPerLoad; for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; ++UI) if (const LoadInst *LI = dyn_cast(*UI)) { 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_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(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(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 > &InsertedScalarizedValues, std::vector > &PHIsToRewrite) { std::vector &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(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(V)) { // PN's type is pointer to struct. Make a new PHI of pointer to struct // field. StructType *ST = cast(cast(PN->getType())->getElementType()); PHINode *NewPN = PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)), 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 > &InsertedScalarizedValues, std::vector > &PHIsToRewrite) { // If this is a comparison against null, handle it. if (ICmpInst *SCI = dyn_cast(LoadUser)) { assert(isa(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(LoadUser)) { assert(GEPI->getNumOperands() >= 3 && isa(GEPI->getOperand(2)) && "Unexpected GEPI!"); // Load the pointer for this field. unsigned FieldNo = cast(GEPI->getOperand(2))->getZExtValue(); Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, InsertedScalarizedValues, PHIsToRewrite); // Create the new GEP idx vector. SmallVector 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(LoadUser); if (!InsertedScalarizedValues.insert(std::make_pair(PN, std::vector())).second) return; // If this is the first time we've seen this PHI, recursively process all // users. for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) { Instruction *User = cast(*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 > &InsertedScalarizedValues, std::vector > &PHIsToRewrite) { for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end(); UI != E; ) { Instruction *User = cast(*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, TargetData *TD) { DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n'); Type *MAT = getMallocAllocatedType(CI); StructType *STy = cast(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 FieldGlobals; std::vector FieldMallocs; for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ Type *FieldTy = STy->getElementType(FieldNo); PointerType *PFieldTy = PointerType::getUnqual(FieldTy); GlobalVariable *NGV = new GlobalVariable(*GV->getParent(), PFieldTy, false, GlobalValue::InternalLinkage, Constant::getNullValue(PFieldTy), GV->getName() + ".f" + Twine(FieldNo), GV, GV->isThreadLocal()); FieldGlobals.push_back(NGV); unsigned TypeSize = TD->getTypeAllocSize(FieldTy); if (StructType *ST = dyn_cast(FieldTy)) TypeSize = TD->getStructLayout(ST)->getSizeInBytes(); Type *IntPtrTy = TD->getIntPtrType(CI->getContext()); Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy, ConstantInt::get(IntPtrTy, TypeSize), NElems, 0, 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 > InsertedScalarizedValues; InsertedScalarizedValues[GV] = FieldGlobals; std::vector > 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 (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) { Instruction *User = cast(*UI++); if (LoadInst *LI = dyn_cast(User)) { RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite); continue; } // Must be a store of null. StoreInst *SI = cast(User); assert(isa(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(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(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 >::iterator I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); I != E; ++I) { if (PHINode *PN = dyn_cast(I->first)) PN->dropAllReferences(); else if (LoadInst *LI = dyn_cast(I->first)) LI->dropAllReferences(); } // Delete all the phis and loads now that inter-references are dead. for (DenseMap >::iterator I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); I != E; ++I) { if (PHINode *PN = dyn_cast(I->first)) PN->eraseFromParent(); else if (LoadInst *LI = dyn_cast(I->first)) LI->eraseFromParent(); } // The old global is now dead, remove it. GV->eraseFromParent(); ++NumHeapSRA; return cast(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, TargetData *TD) { if (!TD) 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 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, TD, true); if (!NElems) return false; if (ConstantInt *NElements = dyn_cast(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() * TD->getTypeAllocSize(AllocTy) < 2048) { GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD); 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(AllocTy)) AllocTy = AT->getElementType(); StructType *AllocSTy = dyn_cast(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(getMallocAllocatedType(CI))) { Type *IntPtrTy = TD->getIntPtrType(CI->getContext()); unsigned TypeSize = TD->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, 0, CI->getName()); Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI); CI->replaceAllUsesWith(Cast); CI->eraseFromParent(); CI = dyn_cast(Malloc) ? extractMallocCallFromBitCast(Malloc) : cast(Malloc); } GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, true), TD); 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, TargetData *TD) { // 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(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)) return true; } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) { Type *MallocType = getMallocAllocatedType(CI); if (MallocType && TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI, TD)) 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 (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){ User *U = *I; if (!isa(U) && !isa(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->isThreadLocal()); 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(OtherVal)) IsOneZero = InitVal->isNullValue() && CI->isOne(); while (!GV->use_empty()) { Instruction *UI = cast(GV->use_back()); if (StoreInst *SI = dyn_cast(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(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(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(StoredVal) || isa(StoredVal)) && "This is not a form that we understand!"); StoreVal = StoredVal->getOperand(0); assert(isa(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(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(); } GV->eraseFromParent(); return true; } /// ProcessInternalGlobal - 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) { if (!GV->hasLocalLinkage()) return false; // 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; } SmallPtrSet PHIUsers; GlobalStatus GS; if (AnalyzeGlobal(GV, GS, PHIUsers)) return false; if (!GS.isCompared && !GV->hasUnnamedAddr()) { GV->setUnnamedAddr(true); NumUnnamed++; } if (GV->isConstant() || !GV->hasInitializer()) return false; return ProcessInternalGlobal(GV, GVI, PHIUsers, 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 SmallPtrSet &PHIUsers, 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 can make // this global a local variable) 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(*GS.AccessingFunction ->getEntryBlock().begin()); Type *ElemTy = GV->getType()->getElementType(); // FIXME: Pass Global's alignment when globals have alignment AllocaInst *Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI); if (!isa(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); // Delete any stores we can find to the global. We may not be able to // make it completely dead though. bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer()); // If the global is dead now, delete it. if (GV->use_empty()) { GV->eraseFromParent(); ++NumDeleted; Changed = true; } return Changed; } else if (GS.StoredType <= GlobalStatus::isInitializerStored) { DEBUG(dbgs() << "MARKING CONSTANT: " << *GV); GV->setConstant(true); // Clean up any obviously simplifiable users now. CleanupConstantGlobalUsers(GV, GV->getInitializer()); // 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 (TargetData *TD = getAnalysisIfAvailable()) if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) { GVI = FirstNewGV; // Don't skip the newly produced globals! return true; } } else if (GS.StoredType == GlobalStatus::isStoredOnce) { // 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(GS.StoredOnceValue)) if (isa(GV->getInitializer())) { // Change the initial value here. GV->setInitializer(SOVConstant); // Clean up any obviously simplifiable users now. CleanupConstantGlobalUsers(GV, GV->getInitializer()); 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, getAnalysisIfAvailable())) return true; // Otherwise, if the global was not a boolean, we can shrink it to be a // boolean. if (Constant *SOVConstant = dyn_cast(GS.StoredOnceValue)) 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 (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ CallSite User(cast(*UI)); User.setCallingConv(CallingConv::Fast); } } static AttrListPtr StripNest(const AttrListPtr &Attrs) { for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0) continue; // There can be only one. return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest); } return Attrs; } static void RemoveNestAttribute(Function *F) { F->setAttributes(StripNest(F->getAttributes())); for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ CallSite User(cast(*UI)); User.setAttributes(StripNest(User.getAttributes())); } } 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->setLinkage(GlobalValue::InternalLinkage); F->removeDeadConstantUsers(); if (F->isDefTriviallyDead()) { F->eraseFromParent(); Changed = true; ++NumFnDeleted; } else if (F->hasLocalLinkage()) { if (F->getCallingConv() == CallingConv::C && !F->isVarArg() && !F->hasAddressTaken()) { // If this function has C calling conventions, 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; 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->setLinkage(GlobalValue::InternalLinkage); // Simplify the initializer. if (GV->hasInitializer()) if (ConstantExpr *CE = dyn_cast(GV->getInitializer())) { TargetData *TD = getAnalysisIfAvailable(); TargetLibraryInfo *TLI = &getAnalysis(); Constant *New = ConstantFoldConstantExpression(CE, TD, TLI); if (New && New != CE) GV->setInitializer(New); } Changed |= ProcessGlobal(GV, GVI); } return Changed; } /// FindGlobalCtors - Find the llvm.global_ctors list, verifying that all /// initializers have an init priority of 65535. GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) { GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors"); if (GV == 0) return 0; // Verify that the initializer is simple enough for us to handle. We are // only allowed to optimize the initializer if it is unique. if (!GV->hasUniqueInitializer()) return 0; if (isa(GV->getInitializer())) return GV; ConstantArray *CA = cast(GV->getInitializer()); for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { if (isa(*i)) continue; ConstantStruct *CS = cast(*i); if (isa(CS->getOperand(1))) continue; // Must have a function or null ptr. if (!isa(CS->getOperand(1))) return 0; // Init priority must be standard. ConstantInt *CI = cast(CS->getOperand(0)); if (CI->getZExtValue() != 65535) return 0; } return GV; } /// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand, /// return a list of the functions and null terminator as a vector. static std::vector ParseGlobalCtors(GlobalVariable *GV) { if (GV->getInitializer()->isNullValue()) return std::vector(); ConstantArray *CA = cast(GV->getInitializer()); std::vector Result; Result.reserve(CA->getNumOperands()); for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { ConstantStruct *CS = cast(*i); Result.push_back(dyn_cast(CS->getOperand(1))); } return Result; } /// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the /// specified array, returning the new global to use. static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, const std::vector &Ctors) { // If we made a change, reassemble the initializer list. Constant *CSVals[2]; CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 65535); CSVals[1] = 0; StructType *StructTy = cast ( cast(GCL->getType()->getElementType())->getElementType()); // Create the new init list. std::vector CAList; for (unsigned i = 0, e = Ctors.size(); i != e; ++i) { if (Ctors[i]) { CSVals[1] = Ctors[i]; } else { Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()), false); PointerType *PFTy = PointerType::getUnqual(FTy); CSVals[1] = Constant::getNullValue(PFTy); CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 0x7fffffff); } CAList.push_back(ConstantStruct::get(StructTy, CSVals)); } // Create the array initializer. Constant *CA = ConstantArray::get(ArrayType::get(StructTy, CAList.size()), CAList); // If we didn't change the number of elements, don't create a new GV. if (CA->getType() == GCL->getInitializer()->getType()) { GCL->setInitializer(CA); return GCL; } // Create the new global and insert it next to the existing list. GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(), GCL->getLinkage(), CA, "", GCL->isThreadLocal()); GCL->getParent()->getGlobalList().insert(GCL, NGV); NGV->takeName(GCL); // Nuke the old list, replacing any uses with the new one. if (!GCL->use_empty()) { Constant *V = NGV; if (V->getType() != GCL->getType()) V = ConstantExpr::getBitCast(V, GCL->getType()); GCL->replaceAllUsesWith(V); } GCL->eraseFromParent(); if (Ctors.size()) return NGV; else return 0; } static Constant *getVal(DenseMap &ComputedValues, Value *V) { if (Constant *CV = dyn_cast(V)) return CV; Constant *R = ComputedValues[V]; assert(R && "Reference to an uncomputed value!"); return R; } static inline bool isSimpleEnoughValueToCommit(Constant *C, SmallPtrSet &SimpleConstants, const TargetData *TD); /// 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 &SimpleConstants, const TargetData *TD) { // Simple integer, undef, constant aggregate zero, global addresses, etc are // all supported. if (C->getNumOperands() == 0 || isa(C) || isa(C)) return true; // Aggregate values are safe if all their elements are. if (isa(C) || isa(C) || isa(C)) { for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) { Constant *Op = cast(C->getOperand(i)); if (!isSimpleEnoughValueToCommit(Op, SimpleConstants, TD)) 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(C); switch (CE->getOpcode()) { case Instruction::BitCast: // Bitcast is fine if the casted value is fine. return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD); case Instruction::IntToPtr: case Instruction::PtrToInt: // int <=> ptr is fine if the int type is the same size as the // pointer type. if (!TD || TD->getTypeSizeInBits(CE->getType()) != TD->getTypeSizeInBits(CE->getOperand(0)->getType())) return false; return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD); // GEP is fine if it is simple + constant offset. case Instruction::GetElementPtr: for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) if (!isa(CE->getOperand(i))) return false; return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD); case Instruction::Add: // We allow simple+cst. if (!isa(CE->getOperand(1))) return false; return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD); } return false; } static inline bool isSimpleEnoughValueToCommit(Constant *C, SmallPtrSet &SimpleConstants, const TargetData *TD) { // If we already checked this constant, we win. if (!SimpleConstants.insert(C)) return true; // Check the constant. return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, TD); } /// 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(C->getType())->getElementType()->isSingleValueType()) return false; if (GlobalVariable *GV = dyn_cast(C)) // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or // external globals. return GV->hasUniqueInitializer(); if (ConstantExpr *CE = dyn_cast(C)) { // Handle a constantexpr gep. if (CE->getOpcode() == Instruction::GetElementPtr && isa(CE->getOperand(0)) && cast(CE)->isInBounds()) { GlobalVariable *GV = cast(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(*llvm::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(CE->getOperand(0))) { // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or // external globals. return cast(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 Elts; if (StructType *STy = dyn_cast(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(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(Addr->getOperand(OpNo)); SequentialType *InitTy = cast(Init->getType()); uint64_t NumElts; if (ArrayType *ATy = dyn_cast(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(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(Addr)) { assert(GV->hasInitializer()); GV->setInitializer(Val); return; } ConstantExpr *CE = cast(Addr); GlobalVariable *GV = cast(CE->getOperand(0)); GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2)); } /// 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. static Constant *ComputeLoadResult(Constant *P, const DenseMap &Memory) { // If this memory location has been recently stored, use the stored value: it // is the most up-to-date. DenseMap::const_iterator I = Memory.find(P); if (I != Memory.end()) return I->second; // Access it. if (GlobalVariable *GV = dyn_cast(P)) { if (GV->hasDefinitiveInitializer()) return GV->getInitializer(); return 0; } // Handle a constantexpr getelementptr. if (ConstantExpr *CE = dyn_cast(P)) if (CE->getOpcode() == Instruction::GetElementPtr && isa(CE->getOperand(0))) { GlobalVariable *GV = cast(CE->getOperand(0)); if (GV->hasDefinitiveInitializer()) return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); } return 0; // don't know how to evaluate. } static bool EvaluateFunction(Function *F, Constant *&RetVal, const SmallVectorImpl &ActualArgs, std::vector &CallStack, DenseMap &MutatedMemory, std::vector &AllocaTmps, SmallPtrSet &SimpleConstants, const TargetData *TD, const TargetLibraryInfo *TLI); /// 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. static bool EvaluateBlock(BasicBlock *BB, BasicBlock *&NextBB, std::vector &CallStack, DenseMap &Values, DenseMap &MutatedMemory, std::vector &AllocaTmps, SmallPtrSet &SimpleConstants, const TargetData *TD, const TargetLibraryInfo *TLI) { // CurInst - The current instruction we're evaluating. BasicBlock::iterator CurInst = BB->getFirstNonPHI(); // This is the main evaluation loop. while (1) { Constant *InstResult = 0; if (StoreInst *SI = dyn_cast(CurInst)) { if (!SI->isSimple()) return false; // no volatile/atomic accesses. Constant *Ptr = getVal(Values, SI->getOperand(1)); if (!isSimpleEnoughPointerToCommit(Ptr)) // If this is too complex for us to commit, reject it. return false; Constant *Val = getVal(Values, 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, TD)) return false; if (ConstantExpr *CE = dyn_cast(Ptr)) if (CE->getOpcode() == Instruction::BitCast) { // 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(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(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 we can't improve the situation by introspecting NewTy, // we have to give up. } else { return false; } } // If we found compatible types, go ahead and push the bitcast // onto the stored value. Val = ConstantExpr::getBitCast(Val, NewTy); } MutatedMemory[Ptr] = Val; } else if (BinaryOperator *BO = dyn_cast(CurInst)) { InstResult = ConstantExpr::get(BO->getOpcode(), getVal(Values, BO->getOperand(0)), getVal(Values, BO->getOperand(1))); } else if (CmpInst *CI = dyn_cast(CurInst)) { InstResult = ConstantExpr::getCompare(CI->getPredicate(), getVal(Values, CI->getOperand(0)), getVal(Values, CI->getOperand(1))); } else if (CastInst *CI = dyn_cast(CurInst)) { InstResult = ConstantExpr::getCast(CI->getOpcode(), getVal(Values, CI->getOperand(0)), CI->getType()); } else if (SelectInst *SI = dyn_cast(CurInst)) { InstResult = ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)), getVal(Values, SI->getOperand(1)), getVal(Values, SI->getOperand(2))); } else if (GetElementPtrInst *GEP = dyn_cast(CurInst)) { Constant *P = getVal(Values, GEP->getOperand(0)); SmallVector GEPOps; for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e; ++i) GEPOps.push_back(getVal(Values, *i)); InstResult = ConstantExpr::getGetElementPtr(P, GEPOps, cast(GEP)->isInBounds()); } else if (LoadInst *LI = dyn_cast(CurInst)) { if (!LI->isSimple()) return false; // no volatile/atomic accesses. InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)), MutatedMemory); if (InstResult == 0) return false; // Could not evaluate load. } else if (AllocaInst *AI = dyn_cast(CurInst)) { if (AI->isArrayAllocation()) return false; // Cannot handle array allocs. Type *Ty = AI->getType()->getElementType(); AllocaTmps.push_back(new GlobalVariable(Ty, false, GlobalValue::InternalLinkage, UndefValue::get(Ty), AI->getName())); InstResult = AllocaTmps.back(); } else if (CallInst *CI = dyn_cast(CurInst)) { // Debug info can safely be ignored here. if (isa(CI)) { ++CurInst; continue; } // Cannot handle inline asm. if (isa(CI->getCalledValue())) return false; if (MemSetInst *MSI = dyn_cast(CI)) { if (MSI->isVolatile()) return false; Constant *Ptr = getVal(Values, MSI->getDest()); Constant *Val = getVal(Values, MSI->getValue()); Constant *DestVal = ComputeLoadResult(getVal(Values, Ptr), MutatedMemory); if (Val->isNullValue() && DestVal && DestVal->isNullValue()) { // This memset is a no-op. ++CurInst; continue; } return false; } // Resolve function pointers. Function *Callee = dyn_cast(getVal(Values, CI->getCalledValue())); if (!Callee) return false; // Cannot resolve. SmallVector Formals; CallSite CS(CI); for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i) Formals.push_back(getVal(Values, *i)); if (Callee->isDeclaration()) { // If this is a function we can constant fold, do it. if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) { InstResult = C; } else { return false; } } else { if (Callee->getFunctionType()->isVarArg()) return false; Constant *RetVal; // Execute the call, if successful, use the return value. if (!EvaluateFunction(Callee, RetVal, Formals, CallStack, MutatedMemory, AllocaTmps, SimpleConstants, TD, TLI)) return false; InstResult = RetVal; } } else if (isa(CurInst)) { if (BranchInst *BI = dyn_cast(CurInst)) { if (BI->isUnconditional()) { NextBB = BI->getSuccessor(0); } else { ConstantInt *Cond = dyn_cast(getVal(Values, BI->getCondition())); if (!Cond) return false; // Cannot determine. NextBB = BI->getSuccessor(!Cond->getZExtValue()); } } else if (SwitchInst *SI = dyn_cast(CurInst)) { ConstantInt *Val = dyn_cast(getVal(Values, SI->getCondition())); if (!Val) return false; // Cannot determine. unsigned ValTISucc = SI->resolveSuccessorIndex(SI->findCaseValue(Val)); NextBB = SI->getSuccessor(ValTISucc); } else if (IndirectBrInst *IBI = dyn_cast(CurInst)) { Value *Val = getVal(Values, IBI->getAddress())->stripPointerCasts(); if (BlockAddress *BA = dyn_cast(Val)) NextBB = BA->getBasicBlock(); else return false; // Cannot determine. } else if (isa(CurInst)) { NextBB = 0; } else { // invoke, unwind, resume, unreachable. return false; // Cannot handle this terminator. } // We succeeded at evaluating this block! return true; } else { // Did not know how to evaluate this! return false; } if (!CurInst->use_empty()) { if (ConstantExpr *CE = dyn_cast(InstResult)) InstResult = ConstantFoldConstantExpression(CE, TD, TLI); Values[CurInst] = InstResult; } // 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. static bool EvaluateFunction(Function *F, Constant *&RetVal, const SmallVectorImpl &ActualArgs, std::vector &CallStack, DenseMap &MutatedMemory, std::vector &AllocaTmps, SmallPtrSet &SimpleConstants, const TargetData *TD, const TargetLibraryInfo *TLI) { // 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); /// Values - As we compute SSA register values, we store their contents here. DenseMap Values; // 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) Values[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 ExecutedBlocks; // CurBB - The current basic block we're evaluating. BasicBlock *CurBB = F->begin(); while (1) { BasicBlock *NextBB; if (!EvaluateBlock(CurBB, NextBB, CallStack, Values, MutatedMemory, AllocaTmps, SimpleConstants, TD, TLI)) return false; if (NextBB == 0) { // 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(CurBB->getTerminator()); if (RI->getNumOperands()) RetVal = getVal(Values, 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 = 0; for (BasicBlock::iterator Inst = NextBB->begin(); (PN = dyn_cast(Inst)); ++Inst) Values[PN] = getVal(Values, 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 TargetData *TD, const TargetLibraryInfo *TLI) { /// 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 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. std::vector AllocaTmps; /// CallStack - This is used to detect recursion. In pathological situations /// we could hit exponential behavior, but at least there is nothing /// unbounded. std::vector CallStack; /// SimpleConstants - These are constants we have checked and know to be /// simple enough to live in a static initializer of a global. SmallPtrSet SimpleConstants; // Call the function. Constant *RetValDummy; bool EvalSuccess = EvaluateFunction(F, RetValDummy, SmallVector(), CallStack, MutatedMemory, AllocaTmps, SimpleConstants, TD, TLI); if (EvalSuccess) { // We succeeded at evaluation: commit the result. DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" << F->getName() << "' to " << MutatedMemory.size() << " stores.\n"); for (DenseMap::iterator I = MutatedMemory.begin(), E = MutatedMemory.end(); I != E; ++I) CommitValueTo(I->second, I->first); } // At this point, we are done interpreting. If we created any 'alloca' // temporaries, release them now. while (!AllocaTmps.empty()) { GlobalVariable *Tmp = AllocaTmps.back(); AllocaTmps.pop_back(); // 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())); delete Tmp; } return EvalSuccess; } /// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible. /// Return true if anything changed. bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) { std::vector Ctors = ParseGlobalCtors(GCL); bool MadeChange = false; if (Ctors.empty()) return false; const TargetData *TD = getAnalysisIfAvailable(); const TargetLibraryInfo *TLI = &getAnalysis(); // Loop over global ctors, optimizing them when we can. for (unsigned i = 0; i != Ctors.size(); ++i) { Function *F = Ctors[i]; // Found a null terminator in the middle of the list, prune off the rest of // the list. if (F == 0) { if (i != Ctors.size()-1) { Ctors.resize(i+1); MadeChange = true; } break; } // We cannot simplify external ctor functions. if (F->empty()) continue; // If we can evaluate the ctor at compile time, do. if (EvaluateStaticConstructor(F, TD, TLI)) { Ctors.erase(Ctors.begin()+i); MadeChange = true; --i; ++NumCtorsEvaluated; continue; } } if (!MadeChange) return false; GCL = InstallGlobalCtors(GCL, Ctors); return true; } bool GlobalOpt::OptimizeGlobalAliases(Module &M) { bool Changed = false; 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->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 = cast(Aliasee->stripPointerCasts()); Target->removeDeadConstantUsers(); bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse(); // Make all users of the alias use the aliasee instead. if (!J->use_empty()) { J->replaceAllUsesWith(Aliasee); ++NumAliasesResolved; Changed = true; } // If the alias is externally visible, we may still be able to simplify it. if (!J->hasLocalLinkage()) { // 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(...) if (!Target->hasLocalLinkage()) continue; // 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 (!hasOneUse) continue; // Give the aliasee the name, linkage and other attributes of the alias. Target->takeName(J); Target->setLinkage(J->getLinkage()); Target->GlobalValue::copyAttributesFrom(J); } // Delete the alias. M.getAliasList().erase(J); ++NumAliasesRemoved; Changed = true; } return Changed; } static Function *FindCXAAtExit(Module &M) { Function *Fn = M.getFunction("__cxa_atexit"); if (!Fn) return 0; 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 0; 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 side-effect free, 'ret' or 'call' to empty /// C++ dtor. static bool cxxDtorIsEmpty(const Function &Fn, SmallPtrSet &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(I)) { // Ignore debug intrinsics. if (isa(CI)) continue; const Function *CalledFn = CI->getCalledFunction(); if (!CalledFn) return false; SmallPtrSet NewCalledFunctions(CalledFunctions); // Don't treat recursive functions as empty. if (!NewCalledFunctions.insert(CalledFn)) return false; if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions)) return false; } else if (isa(*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 (Function::use_iterator I = CXAAtExitFn->use_begin(), E = CXAAtExitFn->use_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(*I++); if (!CI) continue; Function *DtorFn = dyn_cast(CI->getArgOperand(0)->stripPointerCasts()); if (!DtorFn) continue; SmallPtrSet 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; // Try to find the llvm.globalctors list. GlobalVariable *GlobalCtors = FindGlobalCtors(M); Function *CXAAtExitFn = FindCXAAtExit(M); bool LocalChange = true; while (LocalChange) { LocalChange = false; // Delete functions that are trivially dead, ccc -> fastcc LocalChange |= OptimizeFunctions(M); // Optimize global_ctors list. if (GlobalCtors) LocalChange |= OptimizeGlobalCtorsList(GlobalCtors); // Optimize non-address-taken globals. LocalChange |= OptimizeGlobalVars(M); // Resolve aliases, when possible. LocalChange |= OptimizeGlobalAliases(M); // Try to remove trivial global destructors. if (CXAAtExitFn) LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn); Changed |= LocalChange; } // TODO: Move all global ctors functions to the end of the module for code // layout. return Changed; }