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//===- llvm/Transforms/LowerAllocations.h - Remove Malloc & Free Insts ------=//
//
// This file implements a pass that lowers malloc and free instructions to
// calls to %malloc & %free functions. This transformation is a target
// dependant tranformation because we depend on the size of data types and
// alignment constraints.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/LowerAllocations.h"
#include "llvm/Target/TargetData.h"
#include "llvm/DerivedTypes.h"
#include "llvm/iMemory.h"
#include "llvm/iOther.h"
#include "llvm/SymbolTable.h"
#include "llvm/ConstantVals.h"
using std::vector;
// doPassInitialization - For the lower allocations pass, this ensures that a
// module contains a declaration for a malloc and a free function.
//
// This function is always successful.
//
bool LowerAllocations::doPassInitialization(Module *M) {
bool Changed = false;
const MethodType *MallocType =
MethodType::get(PointerType::get(Type::SByteTy),
vector<const Type*>(1, Type::UIntTy), false);
SymbolTable *SymTab = M->getSymbolTableSure();
// Check for a definition of malloc
if (Value *V = SymTab->lookup(PointerType::get(MallocType), "malloc")) {
MallocMeth = cast<Method>(V); // Yup, got it
} else { // Nope, add one
M->getMethodList().push_back(MallocMeth = new Method(MallocType, false,
"malloc"));
Changed = true;
}
const MethodType *FreeType =
MethodType::get(Type::VoidTy,
vector<const Type*>(1, PointerType::get(Type::SByteTy)),
false);
// Check for a definition of free
if (Value *V = SymTab->lookup(PointerType::get(FreeType), "free")) {
FreeMeth = cast<Method>(V); // Yup, got it
} else { // Nope, add one
M->getMethodList().push_back(FreeMeth = new Method(FreeType, false,"free"));
Changed = true;
}
return Changed; // Always successful
}
// doPerMethodWork - This method does the actual work of converting
// instructions over, assuming that the pass has already been initialized.
//
bool LowerAllocations::doPerMethodWork(Method *M) {
bool Changed = false;
assert(MallocMeth && FreeMeth && M && "Pass not initialized!");
// Loop over all of the instructions, looking for malloc or free instructions
for (Method::iterator BBI = M->begin(), BBE = M->end(); BBI != BBE; ++BBI) {
BasicBlock *BB = *BBI;
for (unsigned i = 0; i < BB->size(); ++i) {
BasicBlock::InstListType &BBIL = BB->getInstList();
if (MallocInst *MI = dyn_cast<MallocInst>(*(BBIL.begin()+i))) {
BBIL.remove(BBIL.begin()+i); // remove the malloc instr...
const Type *AllocTy =cast<PointerType>(MI->getType())->getElementType();
// Get the number of bytes to be allocated for one element of the
// requested type...
unsigned Size = DataLayout.getTypeSize(AllocTy);
// malloc(type) becomes sbyte *malloc(constint)
Value *MallocArg = ConstantUInt::get(Type::UIntTy, Size);
if (MI->getNumOperands() && Size == 1) {
MallocArg = MI->getOperand(0); // Operand * 1 = Operand
} else if (MI->getNumOperands()) {
// Multiply it by the array size if neccesary...
MallocArg = BinaryOperator::create(Instruction::Mul,MI->getOperand(0),
MallocArg);
BBIL.insert(BBIL.begin()+i++, cast<Instruction>(MallocArg));
}
// Create the call to Malloc...
CallInst *MCall = new CallInst(MallocMeth,
vector<Value*>(1, MallocArg));
BBIL.insert(BBIL.begin()+i, MCall);
// Create a cast instruction to convert to the right type...
CastInst *MCast = new CastInst(MCall, MI->getType());
BBIL.insert(BBIL.begin()+i+1, MCast);
// Replace all uses of the old malloc inst with the cast inst
MI->replaceAllUsesWith(MCast);
delete MI; // Delete the malloc inst
Changed = true;
} else if (FreeInst *FI = dyn_cast<FreeInst>(*(BBIL.begin()+i))) {
BBIL.remove(BB->getInstList().begin()+i);
// Cast the argument to free into a ubyte*...
CastInst *MCast = new CastInst(FI->getOperand(0),
PointerType::get(Type::UByteTy));
BBIL.insert(BBIL.begin()+i, MCast);
// Insert a call to the free function...
CallInst *FCall = new CallInst(FreeMeth,
vector<Value*>(1, MCast));
BBIL.insert(BBIL.begin()+i+1, FCall);
// Delete the old free instruction
delete FI;
Changed = true;
}
}
}
return Changed;
}
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