1 //===- LowerAllocations.cpp - Reduce malloc & free insts to calls ---------===//
3 // The LowerAllocations transformation is a target dependant tranformation
4 // because it depends on the size of data types and alignment constraints.
6 //===----------------------------------------------------------------------===//
8 #include "llvm/Transforms/Scalar.h"
9 #include "llvm/Module.h"
10 #include "llvm/DerivedTypes.h"
11 #include "llvm/iMemory.h"
12 #include "llvm/iOther.h"
13 #include "llvm/Constants.h"
14 #include "llvm/Pass.h"
15 #include "llvm/Target/TargetData.h"
16 #include "Support/Statistic.h"
21 Statistic<> NumLowered("lowerallocs", "Number of allocations lowered");
23 /// LowerAllocations - Turn malloc and free instructions into %malloc and
26 class LowerAllocations : public BasicBlockPass {
27 Function *MallocFunc; // Functions in the module we are processing
28 Function *FreeFunc; // Initialized by doInitialization
30 LowerAllocations() : MallocFunc(0), FreeFunc(0) {}
32 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
33 AU.addRequired<TargetData>();
36 /// doPassInitialization - For the lower allocations pass, this ensures that
37 /// a module contains a declaration for a malloc and a free function.
39 bool doInitialization(Module &M);
41 /// runOnBasicBlock - This method does the actual work of converting
42 /// instructions over, assuming that the pass has already been initialized.
44 bool runOnBasicBlock(BasicBlock &BB);
47 RegisterOpt<LowerAllocations>
48 X("lowerallocs", "Lower allocations from instructions to calls");
51 // createLowerAllocationsPass - Interface to this file...
52 Pass *createLowerAllocationsPass() {
53 return new LowerAllocations();
57 // doInitialization - For the lower allocations pass, this ensures that a
58 // module contains a declaration for a malloc and a free function.
60 // This function is always successful.
62 bool LowerAllocations::doInitialization(Module &M) {
63 const FunctionType *MallocType =
64 FunctionType::get(PointerType::get(Type::SByteTy),
65 vector<const Type*>(1, Type::UIntTy), false);
66 const FunctionType *FreeType =
67 FunctionType::get(Type::VoidTy,
68 vector<const Type*>(1, PointerType::get(Type::SByteTy)),
71 MallocFunc = M.getOrInsertFunction("malloc", MallocType);
72 FreeFunc = M.getOrInsertFunction("free" , FreeType);
77 // runOnBasicBlock - This method does the actual work of converting
78 // instructions over, assuming that the pass has already been initialized.
80 bool LowerAllocations::runOnBasicBlock(BasicBlock &BB) {
82 assert(MallocFunc && FreeFunc && "Pass not initialized!");
84 BasicBlock::InstListType &BBIL = BB.getInstList();
85 TargetData &DataLayout = getAnalysis<TargetData>();
87 // Loop over all of the instructions, looking for malloc or free instructions
88 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) {
89 if (MallocInst *MI = dyn_cast<MallocInst>(&*I)) {
90 const Type *AllocTy = MI->getType()->getElementType();
92 // Get the number of bytes to be allocated for one element of the
94 unsigned Size = DataLayout.getTypeSize(AllocTy);
96 // malloc(type) becomes sbyte *malloc(constint)
97 Value *MallocArg = ConstantUInt::get(Type::UIntTy, Size);
98 if (MI->getNumOperands() && Size == 1) {
99 MallocArg = MI->getOperand(0); // Operand * 1 = Operand
100 } else if (MI->getNumOperands()) {
101 // Multiply it by the array size if neccesary...
102 MallocArg = BinaryOperator::create(Instruction::Mul, MI->getOperand(0),
106 // Create the call to Malloc...
107 CallInst *MCall = new CallInst(MallocFunc,
108 vector<Value*>(1, MallocArg), "", I);
110 // Create a cast instruction to convert to the right type...
111 CastInst *MCast = new CastInst(MCall, MI->getType(), "", I);
113 // Replace all uses of the old malloc inst with the cast inst
114 MI->replaceAllUsesWith(MCast);
115 I = --BBIL.erase(I); // remove and delete the malloc instr...
118 } else if (FreeInst *FI = dyn_cast<FreeInst>(&*I)) {
119 // Cast the argument to free into a ubyte*...
120 CastInst *MCast = new CastInst(FI->getOperand(0),
121 PointerType::get(Type::UByteTy), "", I);
123 // Insert a call to the free function...
124 CallInst *FCall = new CallInst(FreeFunc, vector<Value*>(1, MCast), "", I);
126 // Delete the old free instruction