LLVM API Documentation
00001 //===- LowerAllocations.cpp - Reduce malloc & free insts to calls ---------===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // The LowerAllocations transformation is a target-dependent tranformation 00011 // because it depends on the size of data types and alignment constraints. 00012 // 00013 //===----------------------------------------------------------------------===// 00014 00015 #include "llvm/Transforms/Scalar.h" 00016 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h" 00017 #include "llvm/Module.h" 00018 #include "llvm/DerivedTypes.h" 00019 #include "llvm/Instructions.h" 00020 #include "llvm/Constants.h" 00021 #include "llvm/Pass.h" 00022 #include "llvm/ADT/Statistic.h" 00023 #include "llvm/Target/TargetData.h" 00024 #include "llvm/Support/Visibility.h" 00025 using namespace llvm; 00026 00027 namespace { 00028 Statistic<> NumLowered("lowerallocs", "Number of allocations lowered"); 00029 00030 /// LowerAllocations - Turn malloc and free instructions into %malloc and 00031 /// %free calls. 00032 /// 00033 class VISIBILITY_HIDDEN LowerAllocations : public BasicBlockPass { 00034 Function *MallocFunc; // Functions in the module we are processing 00035 Function *FreeFunc; // Initialized by doInitialization 00036 bool LowerMallocArgToInteger; 00037 public: 00038 LowerAllocations(bool LowerToInt = false) 00039 : MallocFunc(0), FreeFunc(0), LowerMallocArgToInteger(LowerToInt) {} 00040 00041 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 00042 AU.addRequired<TargetData>(); 00043 AU.setPreservesCFG(); 00044 00045 // This is a cluster of orthogonal Transforms: 00046 AU.addPreserved<UnifyFunctionExitNodes>(); 00047 AU.addPreservedID(PromoteMemoryToRegisterID); 00048 AU.addPreservedID(LowerSelectID); 00049 AU.addPreservedID(LowerSwitchID); 00050 AU.addPreservedID(LowerInvokePassID); 00051 } 00052 00053 /// doPassInitialization - For the lower allocations pass, this ensures that 00054 /// a module contains a declaration for a malloc and a free function. 00055 /// 00056 bool doInitialization(Module &M); 00057 00058 virtual bool doInitialization(Function &F) { 00059 return BasicBlockPass::doInitialization(F); 00060 } 00061 00062 /// runOnBasicBlock - This method does the actual work of converting 00063 /// instructions over, assuming that the pass has already been initialized. 00064 /// 00065 bool runOnBasicBlock(BasicBlock &BB); 00066 }; 00067 00068 RegisterOpt<LowerAllocations> 00069 X("lowerallocs", "Lower allocations from instructions to calls"); 00070 } 00071 00072 // Publically exposed interface to pass... 00073 const PassInfo *llvm::LowerAllocationsID = X.getPassInfo(); 00074 // createLowerAllocationsPass - Interface to this file... 00075 FunctionPass *llvm::createLowerAllocationsPass(bool LowerMallocArgToInteger) { 00076 return new LowerAllocations(LowerMallocArgToInteger); 00077 } 00078 00079 00080 // doInitialization - For the lower allocations pass, this ensures that a 00081 // module contains a declaration for a malloc and a free function. 00082 // 00083 // This function is always successful. 00084 // 00085 bool LowerAllocations::doInitialization(Module &M) { 00086 const Type *SBPTy = PointerType::get(Type::SByteTy); 00087 MallocFunc = M.getNamedFunction("malloc"); 00088 FreeFunc = M.getNamedFunction("free"); 00089 00090 if (MallocFunc == 0) { 00091 // Prototype malloc as "void* malloc(...)", because we don't know in 00092 // doInitialization whether size_t is int or long. 00093 FunctionType *FT = FunctionType::get(SBPTy,std::vector<const Type*>(),true); 00094 MallocFunc = M.getOrInsertFunction("malloc", FT); 00095 } 00096 if (FreeFunc == 0) 00097 FreeFunc = M.getOrInsertFunction("free" , Type::VoidTy, SBPTy, (Type *)0); 00098 00099 return true; 00100 } 00101 00102 // runOnBasicBlock - This method does the actual work of converting 00103 // instructions over, assuming that the pass has already been initialized. 00104 // 00105 bool LowerAllocations::runOnBasicBlock(BasicBlock &BB) { 00106 bool Changed = false; 00107 assert(MallocFunc && FreeFunc && "Pass not initialized!"); 00108 00109 BasicBlock::InstListType &BBIL = BB.getInstList(); 00110 00111 const TargetData &TD = getAnalysis<TargetData>(); 00112 const Type *IntPtrTy = TD.getIntPtrType(); 00113 00114 // Loop over all of the instructions, looking for malloc or free instructions 00115 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) { 00116 if (MallocInst *MI = dyn_cast<MallocInst>(I)) { 00117 const Type *AllocTy = MI->getType()->getElementType(); 00118 00119 // malloc(type) becomes sbyte *malloc(size) 00120 Value *MallocArg; 00121 if (LowerMallocArgToInteger) 00122 MallocArg = ConstantUInt::get(Type::ULongTy, TD.getTypeSize(AllocTy)); 00123 else 00124 MallocArg = ConstantExpr::getSizeOf(AllocTy); 00125 MallocArg = ConstantExpr::getCast(cast<Constant>(MallocArg), IntPtrTy); 00126 00127 if (MI->isArrayAllocation()) { 00128 if (isa<ConstantInt>(MallocArg) && 00129 cast<ConstantInt>(MallocArg)->getRawValue() == 1) { 00130 MallocArg = MI->getOperand(0); // Operand * 1 = Operand 00131 } else if (Constant *CO = dyn_cast<Constant>(MI->getOperand(0))) { 00132 CO = ConstantExpr::getCast(CO, IntPtrTy); 00133 MallocArg = ConstantExpr::getMul(CO, cast<Constant>(MallocArg)); 00134 } else { 00135 Value *Scale = MI->getOperand(0); 00136 if (Scale->getType() != IntPtrTy) 00137 Scale = new CastInst(Scale, IntPtrTy, "", I); 00138 00139 // Multiply it by the array size if necessary... 00140 MallocArg = BinaryOperator::create(Instruction::Mul, Scale, 00141 MallocArg, "", I); 00142 } 00143 } 00144 00145 const FunctionType *MallocFTy = MallocFunc->getFunctionType(); 00146 std::vector<Value*> MallocArgs; 00147 00148 if (MallocFTy->getNumParams() > 0 || MallocFTy->isVarArg()) { 00149 if (MallocFTy->isVarArg()) { 00150 if (MallocArg->getType() != IntPtrTy) 00151 MallocArg = new CastInst(MallocArg, IntPtrTy, "", I); 00152 } else if (MallocFTy->getNumParams() > 0 && 00153 MallocFTy->getParamType(0) != Type::UIntTy) 00154 MallocArg = new CastInst(MallocArg, MallocFTy->getParamType(0), "",I); 00155 MallocArgs.push_back(MallocArg); 00156 } 00157 00158 // If malloc is prototyped to take extra arguments, pass nulls. 00159 for (unsigned i = 1; i < MallocFTy->getNumParams(); ++i) 00160 MallocArgs.push_back(Constant::getNullValue(MallocFTy->getParamType(i))); 00161 00162 // Create the call to Malloc... 00163 CallInst *MCall = new CallInst(MallocFunc, MallocArgs, "", I); 00164 MCall->setTailCall(); 00165 00166 // Create a cast instruction to convert to the right type... 00167 Value *MCast; 00168 if (MCall->getType() != Type::VoidTy) 00169 MCast = new CastInst(MCall, MI->getType(), "", I); 00170 else 00171 MCast = Constant::getNullValue(MI->getType()); 00172 00173 // Replace all uses of the old malloc inst with the cast inst 00174 MI->replaceAllUsesWith(MCast); 00175 I = --BBIL.erase(I); // remove and delete the malloc instr... 00176 Changed = true; 00177 ++NumLowered; 00178 } else if (FreeInst *FI = dyn_cast<FreeInst>(I)) { 00179 const FunctionType *FreeFTy = FreeFunc->getFunctionType(); 00180 std::vector<Value*> FreeArgs; 00181 00182 if (FreeFTy->getNumParams() > 0 || FreeFTy->isVarArg()) { 00183 Value *MCast = FI->getOperand(0); 00184 if (FreeFTy->getNumParams() > 0 && 00185 FreeFTy->getParamType(0) != MCast->getType()) 00186 MCast = new CastInst(MCast, FreeFTy->getParamType(0), "", I); 00187 FreeArgs.push_back(MCast); 00188 } 00189 00190 // If malloc is prototyped to take extra arguments, pass nulls. 00191 for (unsigned i = 1; i < FreeFTy->getNumParams(); ++i) 00192 FreeArgs.push_back(Constant::getNullValue(FreeFTy->getParamType(i))); 00193 00194 // Insert a call to the free function... 00195 (new CallInst(FreeFunc, FreeArgs, "", I))->setTailCall(); 00196 00197 // Delete the old free instruction 00198 I = --BBIL.erase(I); 00199 Changed = true; 00200 ++NumLowered; 00201 } 00202 } 00203 00204 return Changed; 00205 } 00206