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//===- LowerAllocations.cpp - Reduce malloc & free insts to calls ---------===//
//
// The LowerAllocations transformation is a target dependent tranformation
// because it depends on the size of data types and alignment constraints.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Module.h"
#include "llvm/DerivedTypes.h"
#include "llvm/iMemory.h"
#include "llvm/iOther.h"
#include "llvm/Constants.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetData.h"
#include "Support/Statistic.h"
namespace {
Statistic<> NumLowered("lowerallocs", "Number of allocations lowered");
/// LowerAllocations - Turn malloc and free instructions into %malloc and
/// %free calls.
///
class LowerAllocations : public BasicBlockPass {
Function *MallocFunc; // Functions in the module we are processing
Function *FreeFunc; // Initialized by doInitialization
public:
LowerAllocations() : MallocFunc(0), FreeFunc(0) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>();
}
/// doPassInitialization - For the lower allocations pass, this ensures that
/// a module contains a declaration for a malloc and a free function.
///
bool doInitialization(Module &M);
/// runOnBasicBlock - This method does the actual work of converting
/// instructions over, assuming that the pass has already been initialized.
///
bool runOnBasicBlock(BasicBlock &BB);
};
RegisterOpt<LowerAllocations>
X("lowerallocs", "Lower allocations from instructions to calls");
}
// createLowerAllocationsPass - Interface to this file...
FunctionPass *createLowerAllocationsPass() {
return new LowerAllocations();
}
// doInitialization - 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::doInitialization(Module &M) {
const Type *SBPTy = PointerType::get(Type::SByteTy);
MallocFunc = M.getOrInsertFunction("malloc", SBPTy, Type::UIntTy, 0);
FreeFunc = M.getOrInsertFunction("free" , Type::VoidTy, SBPTy, 0);
return true;
}
// runOnBasicBlock - This method does the actual work of converting
// instructions over, assuming that the pass has already been initialized.
//
bool LowerAllocations::runOnBasicBlock(BasicBlock &BB) {
bool Changed = false;
assert(MallocFunc && FreeFunc && "Pass not initialized!");
BasicBlock::InstListType &BBIL = BB.getInstList();
TargetData &DataLayout = getAnalysis<TargetData>();
// Loop over all of the instructions, looking for malloc or free instructions
for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) {
if (MallocInst *MI = dyn_cast<MallocInst>(I)) {
const Type *AllocTy = 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 necessary...
MallocArg = BinaryOperator::create(Instruction::Mul, MI->getOperand(0),
MallocArg, "", I);
}
// Create the call to Malloc...
CallInst *MCall = new CallInst(MallocFunc,
std::vector<Value*>(1, MallocArg), "", I);
// Create a cast instruction to convert to the right type...
CastInst *MCast = new CastInst(MCall, MI->getType(), "", I);
// Replace all uses of the old malloc inst with the cast inst
MI->replaceAllUsesWith(MCast);
I = --BBIL.erase(I); // remove and delete the malloc instr...
Changed = true;
++NumLowered;
} else if (FreeInst *FI = dyn_cast<FreeInst>(I)) {
// Cast the argument to free into a ubyte*...
CastInst *MCast = new CastInst(FI->getOperand(0),
PointerType::get(Type::SByteTy), "", I);
// Insert a call to the free function...
CallInst *FCall = new CallInst(FreeFunc, std::vector<Value*>(1, MCast),
"", I);
// Delete the old free instruction
I = --BBIL.erase(I);
Changed = true;
++NumLowered;
}
}
return Changed;
}
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