| //===- GlobalOpt.cpp - Optimize Global Variables --------------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and 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/Constants.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/Module.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/StringExtras.h" |
| #include <set> |
| #include <algorithm> |
| using namespace llvm; |
| |
| namespace { |
| Statistic<> NumMarked ("globalopt", "Number of globals marked constant"); |
| Statistic<> NumSRA ("globalopt", "Number of aggregate globals broken " |
| "into scalars"); |
| Statistic<> NumSubstitute("globalopt", |
| "Number of globals with initializers stored into them"); |
| Statistic<> NumDeleted ("globalopt", "Number of globals deleted"); |
| Statistic<> NumFnDeleted("globalopt", "Number of functions deleted"); |
| Statistic<> NumGlobUses ("globalopt", "Number of global uses devirtualized"); |
| Statistic<> NumLocalized("globalopt", "Number of globals localized"); |
| Statistic<> NumShrunkToBool("globalopt", |
| "Number of global vars shrunk to booleans"); |
| |
| struct GlobalOpt : public ModulePass { |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<TargetData>(); |
| } |
| |
| bool runOnModule(Module &M); |
| |
| private: |
| bool ProcessInternalGlobal(GlobalVariable *GV, Module::global_iterator &GVI); |
| }; |
| |
| RegisterOpt<GlobalOpt> X("globalopt", "Global Variable Optimizer"); |
| } |
| |
| ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); } |
| |
| /// 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 { |
| /// 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. |
| Function *AccessingFunction; |
| bool HasMultipleAccessingFunctions; |
| |
| /// isNotSuitableForSRA - Keep track of whether any SRA preventing users of |
| /// the global exist. Such users include GEP instruction with variable |
| /// indexes, and non-gep/load/store users like constant expr casts. |
| bool isNotSuitableForSRA; |
| |
| GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0), |
| AccessingFunction(0), HasMultipleAccessingFunctions(false), |
| isNotSuitableForSRA(false) {} |
| }; |
| |
| |
| |
| /// ConstantIsDead - Return true if the specified constant is (transitively) |
| /// dead. The constant may be used by other constants (e.g. constant arrays and |
| /// constant exprs) as long as they are dead, but it cannot be used by anything |
| /// else. |
| static bool ConstantIsDead(Constant *C) { |
| if (isa<GlobalValue>(C)) return false; |
| |
| for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI) |
| if (Constant *CU = dyn_cast<Constant>(*UI)) { |
| if (!ConstantIsDead(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(Value *V, GlobalStatus &GS, |
| std::set<PHINode*> &PHIUsers) { |
| for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) |
| if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) { |
| if (AnalyzeGlobal(CE, GS, PHIUsers)) return true; |
| if (CE->getOpcode() != Instruction::GetElementPtr) |
| GS.isNotSuitableForSRA = true; |
| else if (!GS.isNotSuitableForSRA) { |
| // 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. |
| if (CE->getNumOperands() < 3 || !CE->getOperand(1)->isNullValue()) |
| GS.isNotSuitableForSRA = true; |
| else { |
| for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) |
| if (!isa<ConstantInt>(CE->getOperand(i))) { |
| GS.isNotSuitableForSRA = true; |
| break; |
| } |
| } |
| } |
| |
| } else if (Instruction *I = dyn_cast<Instruction>(*UI)) { |
| if (!GS.HasMultipleAccessingFunctions) { |
| Function *F = I->getParent()->getParent(); |
| if (GS.AccessingFunction == 0) |
| GS.AccessingFunction = F; |
| else if (GS.AccessingFunction != F) |
| GS.HasMultipleAccessingFunctions = true; |
| } |
| if (isa<LoadInst>(I)) { |
| GS.isLoaded = true; |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { |
| // Don't allow a store OF the address, only stores TO the address. |
| if (SI->getOperand(0) == V) return true; |
| |
| // 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 (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))){ |
| Value *StoredVal = SI->getOperand(0); |
| if (StoredVal == GV->getInitializer()) { |
| if (GS.StoredType < GlobalStatus::isInitializerStored) |
| GS.StoredType = GlobalStatus::isInitializerStored; |
| } else if (isa<LoadInst>(StoredVal) && |
| cast<LoadInst>(StoredVal)->getOperand(0) == GV) { |
| // G = G |
| 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<GetElementPtrInst>(I)) { |
| if (AnalyzeGlobal(I, GS, PHIUsers)) return true; |
| |
| // If the first two indices are constants, this can be SRA'd. |
| if (isa<GlobalVariable>(I->getOperand(0))) { |
| if (I->getNumOperands() < 3 || !isa<Constant>(I->getOperand(1)) || |
| !cast<Constant>(I->getOperand(1))->isNullValue() || |
| !isa<ConstantInt>(I->getOperand(2))) |
| GS.isNotSuitableForSRA = true; |
| } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(I->getOperand(0))){ |
| if (CE->getOpcode() != Instruction::GetElementPtr || |
| CE->getNumOperands() < 3 || I->getNumOperands() < 2 || |
| !isa<Constant>(I->getOperand(0)) || |
| !cast<Constant>(I->getOperand(0))->isNullValue()) |
| GS.isNotSuitableForSRA = true; |
| } else { |
| GS.isNotSuitableForSRA = true; |
| } |
| } else if (isa<SelectInst>(I)) { |
| if (AnalyzeGlobal(I, GS, PHIUsers)) return true; |
| GS.isNotSuitableForSRA = true; |
| } else if (PHINode *PN = dyn_cast<PHINode>(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).second) // Not already visited. |
| if (AnalyzeGlobal(I, GS, PHIUsers)) return true; |
| GS.isNotSuitableForSRA = true; |
| } else if (isa<SetCondInst>(I)) { |
| GS.isNotSuitableForSRA = true; |
| } else if (isa<MemCpyInst>(I) || isa<MemMoveInst>(I)) { |
| if (I->getOperand(1) == V) |
| GS.StoredType = GlobalStatus::isStored; |
| if (I->getOperand(2) == V) |
| GS.isLoaded = true; |
| GS.isNotSuitableForSRA = true; |
| } else if (isa<MemSetInst>(I)) { |
| assert(I->getOperand(1) == V && "Memset only takes one pointer!"); |
| GS.StoredType = GlobalStatus::isStored; |
| GS.isNotSuitableForSRA = true; |
| } else { |
| return true; // Any other non-load instruction might take address! |
| } |
| } else if (Constant *C = dyn_cast<Constant>(*UI)) { |
| // We might have a dead and dangling constant hanging off of here. |
| if (!ConstantIsDead(C)) |
| return true; |
| } else { |
| // Otherwise must be a global or some other user. |
| return true; |
| } |
| |
| return false; |
| } |
| |
| static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) { |
| ConstantInt *CI = dyn_cast<ConstantInt>(Idx); |
| if (!CI) return 0; |
| unsigned IdxV = (unsigned)CI->getRawValue(); |
| |
| if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) { |
| if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV); |
| } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) { |
| if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV); |
| } else if (ConstantPacked *CP = dyn_cast<ConstantPacked>(Agg)) { |
| if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV); |
| } else if (isa<ConstantAggregateZero>(Agg)) { |
| if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) { |
| if (IdxV < STy->getNumElements()) |
| return Constant::getNullValue(STy->getElementType(IdxV)); |
| } else if (const SequentialType *STy = |
| dyn_cast<SequentialType>(Agg->getType())) { |
| return Constant::getNullValue(STy->getElementType()); |
| } |
| } else if (isa<UndefValue>(Agg)) { |
| if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) { |
| if (IdxV < STy->getNumElements()) |
| return UndefValue::get(STy->getElementType(IdxV)); |
| } else if (const SequentialType *STy = |
| dyn_cast<SequentialType>(Agg->getType())) { |
| return UndefValue::get(STy->getElementType()); |
| } |
| } |
| return 0; |
| } |
| |
| static Constant *TraverseGEPInitializer(User *GEP, Constant *Init) { |
| if (Init == 0) return 0; |
| if (GEP->getNumOperands() == 1 || |
| !isa<Constant>(GEP->getOperand(1)) || |
| !cast<Constant>(GEP->getOperand(1))->isNullValue()) |
| return 0; |
| |
| for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) { |
| ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i)); |
| if (!Idx) return 0; |
| Init = getAggregateConstantElement(Init, Idx); |
| if (Init == 0) return 0; |
| } |
| return Init; |
| } |
| |
| /// 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<LoadInst>(U)) { |
| if (Init) { |
| // Replace the load with the initializer. |
| LI->replaceAllUsesWith(Init); |
| LI->eraseFromParent(); |
| Changed = true; |
| } |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { |
| // Store must be unreachable or storing Init into the global. |
| SI->eraseFromParent(); |
| Changed = true; |
| } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { |
| if (CE->getOpcode() == Instruction::GetElementPtr) { |
| Constant *SubInit = TraverseGEPInitializer(CE, Init); |
| Changed |= CleanupConstantGlobalUsers(CE, SubInit); |
| } else if (CE->getOpcode() == Instruction::Cast && |
| isa<PointerType>(CE->getType())) { |
| // 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<GetElementPtrInst>(U)) { |
| Constant *SubInit = TraverseGEPInitializer(GEP, Init); |
| Changed |= CleanupConstantGlobalUsers(GEP, SubInit); |
| |
| if (GEP->use_empty()) { |
| GEP->eraseFromParent(); |
| Changed = true; |
| } |
| } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv |
| if (MI->getRawDest() == V) { |
| MI->eraseFromParent(); |
| Changed = true; |
| } |
| |
| } else if (Constant *C = dyn_cast<Constant>(U)) { |
| // If we have a chain of dead constantexprs or other things dangling from |
| // us, and if they are all dead, nuke them without remorse. |
| if (ConstantIsDead(C)) { |
| C->destroyConstant(); |
| // This could have invalidated UI, start over from scratch. |
| CleanupConstantGlobalUsers(V, Init); |
| return true; |
| } |
| } |
| } |
| return Changed; |
| } |
| |
| /// 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) { |
| assert(GV->hasInternalLinkage() && !GV->isConstant()); |
| Constant *Init = GV->getInitializer(); |
| const Type *Ty = Init->getType(); |
| |
| std::vector<GlobalVariable*> NewGlobals; |
| Module::GlobalListType &Globals = GV->getParent()->getGlobalList(); |
| |
| if (const StructType *STy = dyn_cast<StructType>(Ty)) { |
| NewGlobals.reserve(STy->getNumElements()); |
| for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { |
| Constant *In = getAggregateConstantElement(Init, |
| ConstantUInt::get(Type::UIntTy, i)); |
| assert(In && "Couldn't get element of initializer?"); |
| GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false, |
| GlobalVariable::InternalLinkage, |
| In, GV->getName()+"."+utostr(i)); |
| Globals.insert(GV, NGV); |
| NewGlobals.push_back(NGV); |
| } |
| } else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) { |
| unsigned NumElements = 0; |
| if (const ArrayType *ATy = dyn_cast<ArrayType>(STy)) |
| NumElements = ATy->getNumElements(); |
| else if (const PackedType *PTy = dyn_cast<PackedType>(STy)) |
| NumElements = PTy->getNumElements(); |
| else |
| assert(0 && "Unknown aggregate sequential type!"); |
| |
| if (NumElements > 16 && GV->hasNUsesOrMore(16)) |
| return 0; // It's not worth it. |
| NewGlobals.reserve(NumElements); |
| for (unsigned i = 0, e = NumElements; i != e; ++i) { |
| Constant *In = getAggregateConstantElement(Init, |
| ConstantUInt::get(Type::UIntTy, i)); |
| assert(In && "Couldn't get element of initializer?"); |
| |
| GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false, |
| GlobalVariable::InternalLinkage, |
| In, GV->getName()+"."+utostr(i)); |
| Globals.insert(GV, NGV); |
| NewGlobals.push_back(NGV); |
| } |
| } |
| |
| if (NewGlobals.empty()) |
| return 0; |
| |
| DEBUG(std::cerr << "PERFORMING GLOBAL SRA ON: " << *GV); |
| |
| Constant *NullInt = Constant::getNullValue(Type::IntTy); |
| |
| // 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<ConstantExpr>(GEP) && |
| cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| |
| isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); |
| |
| // Ignore the 1th operand, which has to be zero or else the program is quite |
| // broken (undefined). Get the 2nd operand, which is the structure or array |
| // index. |
| unsigned Val = |
| (unsigned)cast<ConstantInt>(GEP->getOperand(2))->getRawValue(); |
| if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. |
| |
| Value *NewPtr = NewGlobals[Val]; |
| |
| // Form a shorter GEP if needed. |
| if (GEP->getNumOperands() > 3) |
| if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { |
| std::vector<Constant*> Idxs; |
| Idxs.push_back(NullInt); |
| for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) |
| Idxs.push_back(CE->getOperand(i)); |
| NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs); |
| } else { |
| GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); |
| std::vector<Value*> Idxs; |
| Idxs.push_back(NullInt); |
| for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) |
| Idxs.push_back(GEPI->getOperand(i)); |
| NewPtr = new GetElementPtrInst(NewPtr, Idxs, |
| GEPI->getName()+"."+utostr(Val), GEPI); |
| } |
| GEP->replaceAllUsesWith(NewPtr); |
| |
| if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) |
| GEPI->eraseFromParent(); |
| else |
| cast<ConstantExpr>(GEP)->destroyConstant(); |
| } |
| |
| // Delete the old global, now that it is dead. |
| Globals.erase(GV); |
| ++NumSRA; |
| |
| // Loop over the new globals array deleting any globals that are obviously |
| // dead. This can arise due to scalarization of a structure or an array that |
| // has elements that are dead. |
| unsigned FirstGlobal = 0; |
| for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) |
| if (NewGlobals[i]->use_empty()) { |
| Globals.erase(NewGlobals[i]); |
| if (FirstGlobal == i) ++FirstGlobal; |
| } |
| |
| return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0; |
| } |
| |
| /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified |
| /// value will trap if the value is dynamically null. |
| static bool AllUsesOfValueWillTrapIfNull(Value *V) { |
| for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) |
| if (isa<LoadInst>(*UI)) { |
| // Will trap. |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { |
| if (SI->getOperand(0) == V) { |
| //std::cerr << "NONTRAPPING USE: " << **UI; |
| return false; // Storing the value. |
| } |
| } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { |
| if (CI->getOperand(0) != V) { |
| //std::cerr << "NONTRAPPING USE: " << **UI; |
| return false; // Not calling the ptr |
| } |
| } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { |
| if (II->getOperand(0) != V) { |
| //std::cerr << "NONTRAPPING USE: " << **UI; |
| return false; // Not calling the ptr |
| } |
| } else if (CastInst *CI = dyn_cast<CastInst>(*UI)) { |
| if (!AllUsesOfValueWillTrapIfNull(CI)) return false; |
| } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) { |
| if (!AllUsesOfValueWillTrapIfNull(GEPI)) return false; |
| } else if (isa<SetCondInst>(*UI) && |
| isa<ConstantPointerNull>(UI->getOperand(1))) { |
| // Ignore setcc X, null |
| } else { |
| //std::cerr << "NONTRAPPING USE: " << **UI; |
| 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(GlobalVariable *GV) { |
| for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI) |
| if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { |
| if (!AllUsesOfValueWillTrapIfNull(LI)) |
| return false; |
| } else if (isa<StoreInst>(*UI)) { |
| // Ignore stores to the global. |
| } else { |
| // We don't know or understand this user, bail out. |
| //std::cerr << "UNKNOWN USER OF GLOBAL!: " << **UI; |
| 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<Instruction>(*UI++); |
| if (LoadInst *LI = dyn_cast<LoadInst>(I)) { |
| LI->setOperand(0, NewV); |
| Changed = true; |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { |
| if (SI->getOperand(1) == V) { |
| SI->setOperand(1, NewV); |
| Changed = true; |
| } |
| } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { |
| if (I->getOperand(0) == V) { |
| // Calling through the pointer! Turn into a direct call, but be careful |
| // that the pointer is not also being passed as an argument. |
| I->setOperand(0, NewV); |
| Changed = true; |
| bool PassedAsArg = false; |
| for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i) |
| if (I->getOperand(i) == V) { |
| PassedAsArg = true; |
| I->setOperand(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<CastInst>(I)) { |
| Changed |= OptimizeAwayTrappingUsesOfValue(CI, |
| ConstantExpr::getCast(NewV, CI->getType())); |
| if (CI->use_empty()) { |
| Changed = true; |
| CI->eraseFromParent(); |
| } |
| } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { |
| // Should handle GEP here. |
| std::vector<Constant*> Indices; |
| Indices.reserve(GEPI->getNumOperands()-1); |
| for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i) |
| if (Constant *C = dyn_cast<Constant>(GEPI->getOperand(i))) |
| Indices.push_back(C); |
| else |
| break; |
| if (Indices.size() == GEPI->getNumOperands()-1) |
| Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, |
| ConstantExpr::getGetElementPtr(NewV, Indices)); |
| 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) { |
| std::vector<LoadInst*> Loads; |
| bool Changed = false; |
| |
| // 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; ++GUI) |
| if (LoadInst *LI = dyn_cast<LoadInst>(*GUI)) { |
| Loads.push_back(LI); |
| Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV); |
| } else { |
| assert(isa<StoreInst>(*GUI) && "Only expect load and stores!"); |
| } |
| |
| if (Changed) { |
| DEBUG(std::cerr << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV); |
| ++NumGlobUses; |
| } |
| |
| // Delete all of the loads we can, keeping track of whether we nuked them all! |
| bool AllLoadsGone = true; |
| while (!Loads.empty()) { |
| LoadInst *L = Loads.back(); |
| if (L->use_empty()) { |
| L->eraseFromParent(); |
| Changed = true; |
| } else { |
| AllLoadsGone = false; |
| } |
| Loads.pop_back(); |
| } |
| |
| // If we nuked all of the loads, then none of the stores are needed either, |
| // nor is the global. |
| if (AllLoadsGone) { |
| DEBUG(std::cerr << " *** 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<Instruction>(*UI++)) |
| 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 laods of GV as uses of the new global. |
| static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, |
| MallocInst *MI) { |
| DEBUG(std::cerr << "PROMOTING MALLOC GLOBAL: " << *GV << " MALLOC = " <<*MI); |
| ConstantInt *NElements = cast<ConstantInt>(MI->getArraySize()); |
| |
| if (NElements->getRawValue() != 1) { |
| // If we have an array allocation, transform it to a single element |
| // allocation to make the code below simpler. |
| Type *NewTy = ArrayType::get(MI->getAllocatedType(), |
| (unsigned)NElements->getRawValue()); |
| MallocInst *NewMI = |
| new MallocInst(NewTy, Constant::getNullValue(Type::UIntTy), |
| MI->getName(), MI); |
| std::vector<Value*> Indices; |
| Indices.push_back(Constant::getNullValue(Type::IntTy)); |
| Indices.push_back(Indices[0]); |
| Value *NewGEP = new GetElementPtrInst(NewMI, Indices, |
| NewMI->getName()+".el0", MI); |
| MI->replaceAllUsesWith(NewGEP); |
| MI->eraseFromParent(); |
| MI = NewMI; |
| } |
| |
| // Create the new global variable. The contents of the malloc'd memory is |
| // undefined, so initialize with an undef value. |
| Constant *Init = UndefValue::get(MI->getAllocatedType()); |
| GlobalVariable *NewGV = new GlobalVariable(MI->getAllocatedType(), false, |
| GlobalValue::InternalLinkage, Init, |
| GV->getName()+".body"); |
| GV->getParent()->getGlobalList().insert(GV, NewGV); |
| |
| // Anything that used the malloc now uses the global directly. |
| MI->replaceAllUsesWith(NewGV); |
| |
| Constant *RepValue = NewGV; |
| if (NewGV->getType() != GV->getType()->getElementType()) |
| RepValue = ConstantExpr::getCast(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::BoolTy, false, GlobalValue::InternalLinkage, |
| ConstantBool::False, GV->getName()+".init"); |
| bool InitBoolUsed = false; |
| |
| // Loop over all uses of GV, processing them in turn. |
| std::vector<StoreInst*> Stores; |
| while (!GV->use_empty()) |
| if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) { |
| while (!LI->use_empty()) { |
| Use &LoadUse = LI->use_begin().getUse(); |
| if (!isa<SetCondInst>(LoadUse.getUser())) |
| LoadUse = RepValue; |
| else { |
| // Replace the setcc X, 0 with a use of the bool value. |
| SetCondInst *SCI = cast<SetCondInst>(LoadUse.getUser()); |
| Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", SCI); |
| InitBoolUsed = true; |
| switch (SCI->getOpcode()) { |
| default: assert(0 && "Unknown opcode!"); |
| case Instruction::SetLT: |
| LV = ConstantBool::False; // X < null -> always false |
| break; |
| case Instruction::SetEQ: |
| case Instruction::SetLE: |
| LV = BinaryOperator::createNot(LV, "notinit", SCI); |
| break; |
| case Instruction::SetNE: |
| case Instruction::SetGE: |
| case Instruction::SetGT: |
| break; // no change. |
| } |
| SCI->replaceAllUsesWith(LV); |
| SCI->eraseFromParent(); |
| } |
| } |
| LI->eraseFromParent(); |
| } else { |
| StoreInst *SI = cast<StoreInst>(GV->use_back()); |
| // The global is initialized when the store to it occurs. |
| new StoreInst(ConstantBool::True, InitBool, SI); |
| SI->eraseFromParent(); |
| } |
| |
| // If the initialization boolean was used, insert it, otherwise delete it. |
| if (!InitBoolUsed) { |
| while (!InitBool->use_empty()) // Delete initializations |
| cast<Instruction>(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(); |
| MI->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(Instruction *V, |
| GlobalVariable *GV) { |
| for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI) |
| if (isa<LoadInst>(*UI) || isa<SetCondInst>(*UI)) { |
| // Fine, ignore. |
| } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { |
| if (SI->getOperand(0) == V && SI->getOperand(1) != GV) |
| return false; // Storing the pointer itself... bad. |
| // Otherwise, storing through it, or storing into GV... fine. |
| } else if (isa<GetElementPtrInst>(*UI) || isa<SelectInst>(*UI)) { |
| if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(cast<Instruction>(*UI),GV)) |
| return false; |
| } else { |
| return false; |
| } |
| return true; |
| |
| } |
| |
| // 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, |
| Module::global_iterator &GVI, TargetData &TD) { |
| if (CastInst *CI = dyn_cast<CastInst>(StoredOnceVal)) |
| StoredOnceVal = CI->getOperand(0); |
| else if (GetElementPtrInst *GEPI =dyn_cast<GetElementPtrInst>(StoredOnceVal)){ |
| // "getelementptr Ptr, 0, 0, 0" is really just a cast. |
| bool IsJustACast = true; |
| for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i) |
| if (!isa<Constant>(GEPI->getOperand(i)) || |
| !cast<Constant>(GEPI->getOperand(i))->isNullValue()) { |
| IsJustACast = false; |
| break; |
| } |
| if (IsJustACast) |
| StoredOnceVal = GEPI->getOperand(0); |
| } |
| |
| // 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 (isa<PointerType>(GV->getInitializer()->getType()) && |
| GV->getInitializer()->isNullValue()) { |
| if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { |
| if (GV->getInitializer()->getType() != SOVC->getType()) |
| SOVC = ConstantExpr::getCast(SOVC, GV->getInitializer()->getType()); |
| |
| // Optimize away any trapping uses of the loaded value. |
| if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC)) |
| return true; |
| } else if (MallocInst *MI = dyn_cast<MallocInst>(StoredOnceVal)) { |
| // If we have a global that is only initialized with a fixed size malloc, |
| // and if all users of the malloc trap, and if the malloc'd address is not |
| // put anywhere else, transform the program to use global memory instead |
| // of malloc'd memory. This eliminates dynamic allocation (good) and |
| // exposes the resultant global to further GlobalOpt (even better). Note |
| // that we 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 (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize())) |
| if (MI->getAllocatedType()->isSized() && |
| NElements->getRawValue()* |
| TD.getTypeSize(MI->getAllocatedType()) < 2048 && |
| AllUsesOfLoadedValueWillTrapIfNull(GV) && |
| ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV)) { |
| GVI = OptimizeGlobalAddressOfMalloc(GV, MI); |
| return true; |
| } |
| } |
| } |
| |
| return false; |
| } |
| |
| /// ShrinkGlobalToBoolean - At this point, we have learned that the only two |
| /// values ever stored into GV are its initializer and OtherVal. |
| static void ShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { |
| // Create the new global, initializing it to false. |
| GlobalVariable *NewGV = new GlobalVariable(Type::BoolTy, false, |
| GlobalValue::InternalLinkage, ConstantBool::False, GV->getName()+".b"); |
| GV->getParent()->getGlobalList().insert(GV, NewGV); |
| |
| Constant *InitVal = GV->getInitializer(); |
| assert(InitVal->getType() != Type::BoolTy && "No reason to shrink to bool!"); |
| |
| // If initialized to zero and storing one into the global, we can use a cast |
| // instead of a select to synthesize the desired value. |
| bool IsOneZero = false; |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) |
| IsOneZero = InitVal->isNullValue() && CI->equalsInt(1); |
| |
| while (!GV->use_empty()) { |
| Instruction *UI = cast<Instruction>(GV->use_back()); |
| if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { |
| // Change the store into a boolean store. |
| bool StoringOther = SI->getOperand(0) == OtherVal; |
| // Only do this if we weren't storing a loaded value. |
| Value *StoreVal; |
| if (StoringOther || SI->getOperand(0) == InitVal) |
| StoreVal = ConstantBool::get(StoringOther); |
| else { |
| // Otherwise, we are storing a previously loaded copy. To do this, |
| // change the copy from copying the original value to just copying the |
| // bool. |
| Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); |
| |
| // If we're already replaced the input, StoredVal will be a cast or |
| // select instruction. If not, it will be a load of the original |
| // global. |
| if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { |
| assert(LI->getOperand(0) == GV && "Not a copy!"); |
| // Insert a new load, to preserve the saved value. |
| StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI); |
| } else { |
| assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && |
| "This is not a form that we understand!"); |
| StoreVal = StoredVal->getOperand(0); |
| assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); |
| } |
| } |
| new StoreInst(StoreVal, NewGV, SI); |
| } else if (!UI->use_empty()) { |
| // Change the load into a load of bool then a select. |
| LoadInst *LI = cast<LoadInst>(UI); |
| |
| std::string Name = LI->getName(); LI->setName(""); |
| LoadInst *NLI = new LoadInst(NewGV, Name+".b", LI); |
| Value *NSI; |
| if (IsOneZero) |
| NSI = new CastInst(NLI, LI->getType(), Name, LI); |
| else |
| NSI = new SelectInst(NLI, OtherVal, InitVal, Name, LI); |
| LI->replaceAllUsesWith(NSI); |
| } |
| UI->eraseFromParent(); |
| } |
| |
| GV->eraseFromParent(); |
| } |
| |
| |
| /// 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) { |
| std::set<PHINode*> PHIUsers; |
| GlobalStatus GS; |
| PHIUsers.clear(); |
| GV->removeDeadConstantUsers(); |
| |
| if (GV->use_empty()) { |
| DEBUG(std::cerr << "GLOBAL DEAD: " << *GV); |
| GV->eraseFromParent(); |
| ++NumDeleted; |
| return true; |
| } |
| |
| if (!AnalyzeGlobal(GV, GS, PHIUsers)) { |
| // 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 first class types since we |
| // are just replacing static memory to stack memory. |
| if (!GS.HasMultipleAccessingFunctions && |
| GS.AccessingFunction && |
| GV->getType()->getElementType()->isFirstClassType() && |
| GS.AccessingFunction->getName() == "main" && |
| GS.AccessingFunction->hasExternalLinkage()) { |
| DEBUG(std::cerr << "LOCALIZING GLOBAL: " << *GV); |
| Instruction* FirstI = GS.AccessingFunction->getEntryBlock().begin(); |
| const Type* ElemTy = GV->getType()->getElementType(); |
| AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), FirstI); |
| if (!isa<UndefValue>(GV->getInitializer())) |
| new StoreInst(GV->getInitializer(), Alloca, FirstI); |
| |
| GV->replaceAllUsesWith(Alloca); |
| GV->eraseFromParent(); |
| ++NumLocalized; |
| return true; |
| } |
| // If the global is never loaded (but may be stored to), it is dead. |
| // Delete it now. |
| if (!GS.isLoaded) { |
| DEBUG(std::cerr << "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(std::cerr << "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(std::cerr << " *** Marking constant allowed us to simplify " |
| "all users and delete global!\n"); |
| GV->eraseFromParent(); |
| ++NumDeleted; |
| } |
| |
| ++NumMarked; |
| return true; |
| } else if (!GS.isNotSuitableForSRA && |
| !GV->getInitializer()->getType()->isFirstClassType()) { |
| if (GlobalVariable *FirstNewGV = SRAGlobal(GV)) { |
| 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 an undef value, then delete all stores to the |
| // global. This allows us to mark it constant. |
| if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) |
| if (isa<UndefValue>(GV->getInitializer())) { |
| // Change the initial value here. |
| GV->setInitializer(SOVConstant); |
| |
| // Clean up any obviously simplifiable users now. |
| CleanupConstantGlobalUsers(GV, GV->getInitializer()); |
| |
| if (GV->use_empty()) { |
| DEBUG(std::cerr << " *** 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, GVI, |
| getAnalysis<TargetData>())) |
| return true; |
| |
| // Otherwise, if the global was not a boolean, we can shrink it to be a |
| // boolean. |
| if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) |
| if (GV->getType()->getElementType() != Type::BoolTy && |
| !GV->getType()->getElementType()->isFloatingPoint()) { |
| DEBUG(std::cerr << " *** SHRINKING TO BOOL: " << *GV); |
| ShrinkGlobalToBoolean(GV, SOVConstant); |
| ++NumShrunkToBool; |
| return true; |
| } |
| } |
| } |
| return false; |
| } |
| |
| |
| bool GlobalOpt::runOnModule(Module &M) { |
| bool Changed = false; |
| |
| // As a prepass, delete functions that are trivially dead. |
| bool LocalChange = true; |
| while (LocalChange) { |
| LocalChange = false; |
| for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { |
| Function *F = FI++; |
| F->removeDeadConstantUsers(); |
| if (F->use_empty() && (F->hasInternalLinkage() || |
| F->hasLinkOnceLinkage())) { |
| M.getFunctionList().erase(F); |
| LocalChange = true; |
| ++NumFnDeleted; |
| } |
| } |
| Changed |= LocalChange; |
| } |
| |
| LocalChange = true; |
| while (LocalChange) { |
| LocalChange = false; |
| for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); GVI != E;) { |
| GlobalVariable *GV = GVI++; |
| if (!GV->isConstant() && GV->hasInternalLinkage() && |
| GV->hasInitializer()) |
| LocalChange |= ProcessInternalGlobal(GV, GVI); |
| } |
| Changed |= LocalChange; |
| } |
| return Changed; |
| } |