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//===- LowerAllocations.cpp - Reduce malloc & free insts to calls ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The LowerAllocations transformation is a target-dependent tranformation
// because it depends on the size of data types and alignment constraints.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "lowerallocs"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
#include "llvm/Module.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Constants.h"
#include "llvm/LLVMContext.h"
#include "llvm/Pass.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Support/Compiler.h"
using namespace llvm;
STATISTIC(NumLowered, "Number of allocations lowered");
namespace {
/// LowerAllocations - Turn malloc and free instructions into %malloc and
/// %free calls.
///
class VISIBILITY_HIDDEN LowerAllocations : public BasicBlockPass {
Constant *MallocFunc; // Functions in the module we are processing
Constant *FreeFunc; // Initialized by doInitialization
bool LowerMallocArgToInteger;
public:
static char ID; // Pass ID, replacement for typeid
explicit LowerAllocations(bool LowerToInt = false)
: BasicBlockPass(&ID), MallocFunc(0), FreeFunc(0),
LowerMallocArgToInteger(LowerToInt) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>();
AU.setPreservesCFG();
// This is a cluster of orthogonal Transforms:
AU.addPreserved<UnifyFunctionExitNodes>();
AU.addPreservedID(PromoteMemoryToRegisterID);
AU.addPreservedID(LowerSwitchID);
AU.addPreservedID(LowerInvokePassID);
}
/// 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);
virtual bool doInitialization(Function &F) {
return doInitialization(*F.getParent());
}
/// runOnBasicBlock - This method does the actual work of converting
/// instructions over, assuming that the pass has already been initialized.
///
bool runOnBasicBlock(BasicBlock &BB);
};
}
char LowerAllocations::ID = 0;
static RegisterPass<LowerAllocations>
X("lowerallocs", "Lower allocations from instructions to calls");
// Publically exposed interface to pass...
const PassInfo *const llvm::LowerAllocationsID = &X;
// createLowerAllocationsPass - Interface to this file...
Pass *llvm::createLowerAllocationsPass(bool LowerMallocArgToInteger) {
return new LowerAllocations(LowerMallocArgToInteger);
}
// 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 *BPTy = M.getContext().getPointerTypeUnqual(Type::Int8Ty);
// Prototype malloc as "char* malloc(...)", because we don't know in
// doInitialization whether size_t is int or long.
FunctionType *FT = M.getContext().getFunctionType(BPTy, true);
MallocFunc = M.getOrInsertFunction("malloc", FT);
FreeFunc = M.getOrInsertFunction("free" , Type::VoidTy, BPTy, (Type *)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!");
LLVMContext &Context = BB.getContext();
BasicBlock::InstListType &BBIL = BB.getInstList();
const TargetData &TD = getAnalysis<TargetData>();
const Type *IntPtrTy = TD.getIntPtrType();
// 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();
// malloc(type) becomes i8 *malloc(size)
Value *MallocArg;
if (LowerMallocArgToInteger)
MallocArg = ConstantInt::get(Type::Int64Ty,
TD.getTypeAllocSize(AllocTy));
else
MallocArg = ConstantExpr::getSizeOf(AllocTy);
MallocArg =
ConstantExpr::getTruncOrBitCast(cast<Constant>(MallocArg),
IntPtrTy);
if (MI->isArrayAllocation()) {
if (isa<ConstantInt>(MallocArg) &&
cast<ConstantInt>(MallocArg)->isOne()) {
MallocArg = MI->getOperand(0); // Operand * 1 = Operand
} else if (Constant *CO = dyn_cast<Constant>(MI->getOperand(0))) {
CO =
ConstantExpr::getIntegerCast(CO, IntPtrTy, false /*ZExt*/);
MallocArg = ConstantExpr::getMul(CO,
cast<Constant>(MallocArg));
} else {
Value *Scale = MI->getOperand(0);
if (Scale->getType() != IntPtrTy)
Scale = CastInst::CreateIntegerCast(Scale, IntPtrTy, false /*ZExt*/,
"", I);
// Multiply it by the array size if necessary...
MallocArg = BinaryOperator::Create(Instruction::Mul, Scale,
MallocArg, "", I);
}
}
// Create the call to Malloc.
CallInst *MCall = CallInst::Create(MallocFunc, MallocArg, "", I);
MCall->setTailCall();
// Create a cast instruction to convert to the right type...
Value *MCast;
if (MCall->getType() != Type::VoidTy)
MCast = new BitCastInst(MCall, MI->getType(), "", I);
else
MCast = Context.getNullValue(MI->getType());
// 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)) {
Value *PtrCast =
new BitCastInst(FI->getOperand(0),
Context.getPointerTypeUnqual(Type::Int8Ty), "", I);
// Insert a call to the free function...
CallInst::Create(FreeFunc, PtrCast, "", I)->setTailCall();
// Delete the old free instruction
I = --BBIL.erase(I);
Changed = true;
++NumLowered;
}
}
return Changed;
}
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