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/Function.h"
11 #include "llvm/BasicBlock.h"
12 #include "llvm/DerivedTypes.h"
13 #include "llvm/iMemory.h"
14 #include "llvm/iOther.h"
15 #include "llvm/Constants.h"
16 #include "llvm/Pass.h"
17 #include "llvm/Target/TargetData.h"
18 #include "Support/StatisticReporter.h"
20 static Statistic<> NumLowered("lowerallocs\t- Number of allocations lowered");
25 // LowerAllocations - Turn malloc and free instructions into %malloc and %free
28 class LowerAllocations : public BasicBlockPass {
29 Function *MallocFunc; // Functions in the module we are processing
30 Function *FreeFunc; // Initialized by doInitialization
32 const TargetData &DataLayout;
34 LowerAllocations(const TargetData &TD) : DataLayout(TD) {
35 MallocFunc = FreeFunc = 0;
38 // doPassInitialization - For the lower allocations pass, this ensures that a
39 // module contains a declaration for a malloc and a free function.
41 bool doInitialization(Module &M);
43 // runOnBasicBlock - This method does the actual work of converting
44 // instructions over, assuming that the pass has already been initialized.
46 bool runOnBasicBlock(BasicBlock &BB);
50 // createLowerAllocationsPass - Interface to this file...
51 Pass *createLowerAllocationsPass(const TargetData &TD) {
52 return new LowerAllocations(TD);
55 static RegisterOpt<LowerAllocations>
56 X("lowerallocs", "Lower allocations from instructions to calls (TD)",
57 createLowerAllocationsPass);
60 // doInitialization - For the lower allocations pass, this ensures that a
61 // module contains a declaration for a malloc and a free function.
63 // This function is always successful.
65 bool LowerAllocations::doInitialization(Module &M) {
66 const FunctionType *MallocType =
67 FunctionType::get(PointerType::get(Type::SByteTy),
68 vector<const Type*>(1, Type::UIntTy), false);
69 const FunctionType *FreeType =
70 FunctionType::get(Type::VoidTy,
71 vector<const Type*>(1, PointerType::get(Type::SByteTy)),
74 MallocFunc = M.getOrInsertFunction("malloc", MallocType);
75 FreeFunc = M.getOrInsertFunction("free" , FreeType);
80 // runOnBasicBlock - This method does the actual work of converting
81 // instructions over, assuming that the pass has already been initialized.
83 bool LowerAllocations::runOnBasicBlock(BasicBlock &BB) {
85 assert(MallocFunc && FreeFunc && "Pass not initialized!");
87 BasicBlock::InstListType &BBIL = BB.getInstList();
89 // Loop over all of the instructions, looking for malloc or free instructions
90 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) {
91 if (MallocInst *MI = dyn_cast<MallocInst>(&*I)) {
92 BBIL.remove(I); // remove the malloc instr...
94 const Type *AllocTy = MI->getType()->getElementType();
96 // Get the number of bytes to be allocated for one element of the
98 unsigned Size = DataLayout.getTypeSize(AllocTy);
100 // malloc(type) becomes sbyte *malloc(constint)
101 Value *MallocArg = ConstantUInt::get(Type::UIntTy, Size);
102 if (MI->getNumOperands() && Size == 1) {
103 MallocArg = MI->getOperand(0); // Operand * 1 = Operand
104 } else if (MI->getNumOperands()) {
105 // Multiply it by the array size if neccesary...
106 MallocArg = BinaryOperator::create(Instruction::Mul,MI->getOperand(0),
108 I = ++BBIL.insert(I, cast<Instruction>(MallocArg));
111 // Create the call to Malloc...
112 CallInst *MCall = new CallInst(MallocFunc,
113 vector<Value*>(1, MallocArg));
114 I = BBIL.insert(I, MCall);
116 // Create a cast instruction to convert to the right type...
117 CastInst *MCast = new CastInst(MCall, MI->getType());
118 I = BBIL.insert(++I, MCast);
120 // Replace all uses of the old malloc inst with the cast inst
121 MI->replaceAllUsesWith(MCast);
122 delete MI; // Delete the malloc inst
125 } else if (FreeInst *FI = dyn_cast<FreeInst>(&*I)) {
128 // Cast the argument to free into a ubyte*...
129 CastInst *MCast = new CastInst(FI->getOperand(0),
130 PointerType::get(Type::UByteTy));
131 I = ++BBIL.insert(I, MCast);
133 // Insert a call to the free function...
134 CallInst *FCall = new CallInst(FreeFunc, vector<Value*>(1, MCast));
135 I = BBIL.insert(I, FCall);
137 // Delete the old free instruction