1 //===- LowerAllocations.cpp - Remove Malloc & Free Instructions -------------=//
3 // This file implements a pass that lowers malloc and free instructions to
4 // calls to %malloc & %free functions. This transformation is a target
5 // dependant tranformation because we depend on the size of data types and
6 // alignment constraints.
8 //===----------------------------------------------------------------------===//
10 #include "llvm/Transforms/LowerAllocations.h"
11 #include "llvm/Target/TargetData.h"
12 #include "llvm/DerivedTypes.h"
13 #include "llvm/iMemory.h"
14 #include "llvm/iOther.h"
15 #include "llvm/SymbolTable.h"
16 #include "llvm/ConstantVals.h"
20 // doInitialization - For the lower allocations pass, this ensures that a
21 // module contains a declaration for a malloc and a free function.
23 // This function is always successful.
25 bool LowerAllocations::doInitialization(Module *M) {
27 const MethodType *MallocType =
28 MethodType::get(PointerType::get(Type::SByteTy),
29 vector<const Type*>(1, Type::UIntTy), false);
31 SymbolTable *SymTab = M->getSymbolTableSure();
33 // Check for a definition of malloc
34 if (Value *V = SymTab->lookup(PointerType::get(MallocType), "malloc")) {
35 MallocMeth = cast<Method>(V); // Yup, got it
36 } else { // Nope, add one
37 M->getMethodList().push_back(MallocMeth = new Method(MallocType, false,
42 const MethodType *FreeType =
43 MethodType::get(Type::VoidTy,
44 vector<const Type*>(1, PointerType::get(Type::SByteTy)),
47 // Check for a definition of free
48 if (Value *V = SymTab->lookup(PointerType::get(FreeType), "free")) {
49 FreeMeth = cast<Method>(V); // Yup, got it
50 } else { // Nope, add one
51 M->getMethodList().push_back(FreeMeth = new Method(FreeType, false,"free"));
58 // runOnBasicBlock - This method does the actual work of converting
59 // instructions over, assuming that the pass has already been initialized.
61 bool LowerAllocations::runOnBasicBlock(BasicBlock *BB) {
63 assert(MallocMeth && FreeMeth && BB && "Pass not initialized!");
65 // Loop over all of the instructions, looking for malloc or free instructions
66 for (unsigned i = 0; i < BB->size(); ++i) {
67 BasicBlock::InstListType &BBIL = BB->getInstList();
68 if (MallocInst *MI = dyn_cast<MallocInst>(*(BBIL.begin()+i))) {
69 BBIL.remove(BBIL.begin()+i); // remove the malloc instr...
71 const Type *AllocTy =cast<PointerType>(MI->getType())->getElementType();
73 // Get the number of bytes to be allocated for one element of the
75 unsigned Size = DataLayout.getTypeSize(AllocTy);
77 // malloc(type) becomes sbyte *malloc(constint)
78 Value *MallocArg = ConstantUInt::get(Type::UIntTy, Size);
79 if (MI->getNumOperands() && Size == 1) {
80 MallocArg = MI->getOperand(0); // Operand * 1 = Operand
81 } else if (MI->getNumOperands()) {
82 // Multiply it by the array size if neccesary...
83 MallocArg = BinaryOperator::create(Instruction::Mul,MI->getOperand(0),
85 BBIL.insert(BBIL.begin()+i++, cast<Instruction>(MallocArg));
88 // Create the call to Malloc...
89 CallInst *MCall = new CallInst(MallocMeth,
90 vector<Value*>(1, MallocArg));
91 BBIL.insert(BBIL.begin()+i, MCall);
93 // Create a cast instruction to convert to the right type...
94 CastInst *MCast = new CastInst(MCall, MI->getType());
95 BBIL.insert(BBIL.begin()+i+1, MCast);
97 // Replace all uses of the old malloc inst with the cast inst
98 MI->replaceAllUsesWith(MCast);
99 delete MI; // Delete the malloc inst
101 } else if (FreeInst *FI = dyn_cast<FreeInst>(*(BBIL.begin()+i))) {
102 BBIL.remove(BB->getInstList().begin()+i);
104 // Cast the argument to free into a ubyte*...
105 CastInst *MCast = new CastInst(FI->getOperand(0),
106 PointerType::get(Type::UByteTy));
107 BBIL.insert(BBIL.begin()+i, MCast);
109 // Insert a call to the free function...
110 CallInst *FCall = new CallInst(FreeMeth,
111 vector<Value*>(1, MCast));
112 BBIL.insert(BBIL.begin()+i+1, FCall);
114 // Delete the old free instruction