DeadArgumentElimination.cpp [plain text]
#define DEBUG_TYPE "deadargelim"
#include "llvm/Transforms/IPO.h"
#include "llvm/CallingConv.h"
#include "llvm/Constant.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include <map>
#include <set>
using namespace llvm;
STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
STATISTIC(NumArgumentsReplacedWithUndef,
"Number of unread args replaced with undef");
namespace {
class DAE : public ModulePass {
public:
struct RetOrArg {
RetOrArg(const Function *F, unsigned Idx, bool IsArg) : F(F), Idx(Idx),
IsArg(IsArg) {}
const Function *F;
unsigned Idx;
bool IsArg;
bool operator<(const RetOrArg &O) const {
if (F != O.F)
return F < O.F;
else if (Idx != O.Idx)
return Idx < O.Idx;
else
return IsArg < O.IsArg;
}
bool operator==(const RetOrArg &O) const {
return F == O.F && Idx == O.Idx && IsArg == O.IsArg;
}
std::string getDescription() const {
return std::string((IsArg ? "Argument #" : "Return value #"))
+ utostr(Idx) + " of function " + F->getName().str();
}
};
enum Liveness { Live, MaybeLive };
RetOrArg CreateRet(const Function *F, unsigned Idx) {
return RetOrArg(F, Idx, false);
}
RetOrArg CreateArg(const Function *F, unsigned Idx) {
return RetOrArg(F, Idx, true);
}
typedef std::multimap<RetOrArg, RetOrArg> UseMap;
UseMap Uses;
typedef std::set<RetOrArg> LiveSet;
typedef std::set<const Function*> LiveFuncSet;
LiveSet LiveValues;
LiveFuncSet LiveFunctions;
typedef SmallVector<RetOrArg, 5> UseVector;
protected:
explicit DAE(char &ID) : ModulePass(ID) {}
public:
static char ID; DAE() : ModulePass(ID) {
initializeDAEPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M);
virtual bool ShouldHackArguments() const { return false; }
private:
Liveness MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses);
Liveness SurveyUse(Value::const_use_iterator U, UseVector &MaybeLiveUses,
unsigned RetValNum = 0);
Liveness SurveyUses(const Value *V, UseVector &MaybeLiveUses);
void SurveyFunction(const Function &F);
void MarkValue(const RetOrArg &RA, Liveness L,
const UseVector &MaybeLiveUses);
void MarkLive(const RetOrArg &RA);
void MarkLive(const Function &F);
void PropagateLiveness(const RetOrArg &RA);
bool RemoveDeadStuffFromFunction(Function *F);
bool DeleteDeadVarargs(Function &Fn);
bool RemoveDeadArgumentsFromCallers(Function &Fn);
};
}
char DAE::ID = 0;
INITIALIZE_PASS(DAE, "deadargelim", "Dead Argument Elimination", false, false)
namespace {
struct DAH : public DAE {
static char ID;
DAH() : DAE(ID) {}
virtual bool ShouldHackArguments() const { return true; }
};
}
char DAH::ID = 0;
INITIALIZE_PASS(DAH, "deadarghaX0r",
"Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)",
false, false)
ModulePass *llvm::createDeadArgEliminationPass() { return new DAE(); }
ModulePass *llvm::createDeadArgHackingPass() { return new DAH(); }
bool DAE::DeleteDeadVarargs(Function &Fn) {
assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
if (Fn.hasAddressTaken())
return false;
for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
if (II->getIntrinsicID() == Intrinsic::vastart)
return false;
}
}
}
FunctionType *FTy = Fn.getFunctionType();
std::vector<Type*> Params(FTy->param_begin(), FTy->param_end());
FunctionType *NFTy = FunctionType::get(FTy->getReturnType(),
Params, false);
unsigned NumArgs = Params.size();
Function *NF = Function::Create(NFTy, Fn.getLinkage());
NF->copyAttributesFrom(&Fn);
Fn.getParent()->getFunctionList().insert(&Fn, NF);
NF->takeName(&Fn);
std::vector<Value*> Args;
while (!Fn.use_empty()) {
CallSite CS(Fn.use_back());
Instruction *Call = CS.getInstruction();
Args.assign(CS.arg_begin(), CS.arg_begin() + NumArgs);
AttrListPtr PAL = CS.getAttributes();
if (!PAL.isEmpty() && PAL.getSlot(PAL.getNumSlots() - 1).Index > NumArgs) {
SmallVector<AttributeWithIndex, 8> AttributesVec;
for (unsigned i = 0; PAL.getSlot(i).Index <= NumArgs; ++i)
AttributesVec.push_back(PAL.getSlot(i));
if (Attributes FnAttrs = PAL.getFnAttributes())
AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
PAL = AttrListPtr::get(AttributesVec.begin(), AttributesVec.end());
}
Instruction *New;
if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
Args, "", Call);
cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
cast<InvokeInst>(New)->setAttributes(PAL);
} else {
New = CallInst::Create(NF, Args, "", Call);
cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
cast<CallInst>(New)->setAttributes(PAL);
if (cast<CallInst>(Call)->isTailCall())
cast<CallInst>(New)->setTailCall();
}
New->setDebugLoc(Call->getDebugLoc());
Args.clear();
if (!Call->use_empty())
Call->replaceAllUsesWith(New);
New->takeName(Call);
Call->eraseFromParent();
}
NF->getBasicBlockList().splice(NF->begin(), Fn.getBasicBlockList());
for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(),
I2 = NF->arg_begin(); I != E; ++I, ++I2) {
I->replaceAllUsesWith(I2);
I2->takeName(I);
}
Fn.eraseFromParent();
return true;
}
bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
{
if (Fn.isDeclaration() || Fn.mayBeOverridden())
return false;
if (Fn.hasLocalLinkage())
return false;
if (Fn.use_empty())
return false;
llvm::SmallVector<unsigned, 8> UnusedArgs;
for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end();
I != E; ++I) {
Argument *Arg = I;
if (Arg->use_empty() && !Arg->hasByValAttr())
UnusedArgs.push_back(Arg->getArgNo());
}
if (UnusedArgs.empty())
return false;
bool Changed = false;
for (Function::use_iterator I = Fn.use_begin(), E = Fn.use_end();
I != E; ++I) {
CallSite CS(*I);
if (!CS || !CS.isCallee(I))
continue;
for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
unsigned ArgNo = UnusedArgs[I];
Value *Arg = CS.getArgument(ArgNo);
CS.setArgument(ArgNo, UndefValue::get(Arg->getType()));
++NumArgumentsReplacedWithUndef;
Changed = true;
}
}
return Changed;
}
static unsigned NumRetVals(const Function *F) {
if (F->getReturnType()->isVoidTy())
return 0;
else if (StructType *STy = dyn_cast<StructType>(F->getReturnType()))
return STy->getNumElements();
else
return 1;
}
DAE::Liveness DAE::MarkIfNotLive(RetOrArg Use, UseVector &MaybeLiveUses) {
if (LiveFunctions.count(Use.F) || LiveValues.count(Use))
return Live;
MaybeLiveUses.push_back(Use);
return MaybeLive;
}
DAE::Liveness DAE::SurveyUse(Value::const_use_iterator U,
UseVector &MaybeLiveUses, unsigned RetValNum) {
const User *V = *U;
if (const ReturnInst *RI = dyn_cast<ReturnInst>(V)) {
RetOrArg Use = CreateRet(RI->getParent()->getParent(), RetValNum);
return MarkIfNotLive(Use, MaybeLiveUses);
}
if (const InsertValueInst *IV = dyn_cast<InsertValueInst>(V)) {
if (U.getOperandNo() != InsertValueInst::getAggregateOperandIndex()
&& IV->hasIndices())
RetValNum = *IV->idx_begin();
Liveness Result = MaybeLive;
for (Value::const_use_iterator I = IV->use_begin(),
E = V->use_end(); I != E; ++I) {
Result = SurveyUse(I, MaybeLiveUses, RetValNum);
if (Result == Live)
break;
}
return Result;
}
if (ImmutableCallSite CS = V) {
const Function *F = CS.getCalledFunction();
if (F) {
unsigned ArgNo = CS.getArgumentNo(U);
if (ArgNo >= F->getFunctionType()->getNumParams())
return Live;
assert(CS.getArgument(ArgNo)
== CS->getOperand(U.getOperandNo())
&& "Argument is not where we expected it");
RetOrArg Use = CreateArg(F, ArgNo);
return MarkIfNotLive(Use, MaybeLiveUses);
}
}
return Live;
}
DAE::Liveness DAE::SurveyUses(const Value *V, UseVector &MaybeLiveUses) {
Liveness Result = MaybeLive;
for (Value::const_use_iterator I = V->use_begin(),
E = V->use_end(); I != E; ++I) {
Result = SurveyUse(I, MaybeLiveUses);
if (Result == Live)
break;
}
return Result;
}
void DAE::SurveyFunction(const Function &F) {
unsigned RetCount = NumRetVals(&F);
typedef SmallVector<Liveness, 5> RetVals;
RetVals RetValLiveness(RetCount, MaybeLive);
typedef SmallVector<UseVector, 5> RetUses;
RetUses MaybeLiveRetUses(RetCount);
for (Function::const_iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (const ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
if (RI->getNumOperands() != 0 && RI->getOperand(0)->getType()
!= F.getFunctionType()->getReturnType()) {
MarkLive(F);
return;
}
if (!F.hasLocalLinkage() && (!ShouldHackArguments() || F.isIntrinsic())) {
MarkLive(F);
return;
}
DEBUG(dbgs() << "DAE - Inspecting callers for fn: " << F.getName() << "\n");
unsigned NumLiveRetVals = 0;
Type *STy = dyn_cast<StructType>(F.getReturnType());
for (Value::const_use_iterator I = F.use_begin(), E = F.use_end();
I != E; ++I) {
ImmutableCallSite CS(*I);
if (!CS || !CS.isCallee(I)) {
MarkLive(F);
return;
}
const Instruction *TheCall = CS.getInstruction();
if (!TheCall) { MarkLive(F);
return;
}
if (NumLiveRetVals != RetCount) {
if (STy) {
for (Value::const_use_iterator I = TheCall->use_begin(),
E = TheCall->use_end(); I != E; ++I) {
const ExtractValueInst *Ext = dyn_cast<ExtractValueInst>(*I);
if (Ext && Ext->hasIndices()) {
unsigned Idx = *Ext->idx_begin();
if (RetValLiveness[Idx] != Live) {
RetValLiveness[Idx] = SurveyUses(Ext, MaybeLiveRetUses[Idx]);
if (RetValLiveness[Idx] == Live)
NumLiveRetVals++;
}
} else {
for (unsigned i = 0; i != RetCount; ++i )
RetValLiveness[i] = Live;
NumLiveRetVals = RetCount;
break;
}
}
} else {
RetValLiveness[0] = SurveyUses(TheCall, MaybeLiveRetUses[0]);
if (RetValLiveness[0] == Live)
NumLiveRetVals = RetCount;
}
}
}
for (unsigned i = 0; i != RetCount; ++i)
MarkValue(CreateRet(&F, i), RetValLiveness[i], MaybeLiveRetUses[i]);
DEBUG(dbgs() << "DAE - Inspecting args for fn: " << F.getName() << "\n");
unsigned i = 0;
UseVector MaybeLiveArgUses;
for (Function::const_arg_iterator AI = F.arg_begin(),
E = F.arg_end(); AI != E; ++AI, ++i) {
Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
MaybeLiveArgUses.clear();
}
}
void DAE::MarkValue(const RetOrArg &RA, Liveness L,
const UseVector &MaybeLiveUses) {
switch (L) {
case Live: MarkLive(RA); break;
case MaybeLive:
{
for (UseVector::const_iterator UI = MaybeLiveUses.begin(),
UE = MaybeLiveUses.end(); UI != UE; ++UI)
Uses.insert(std::make_pair(*UI, RA));
break;
}
}
}
void DAE::MarkLive(const Function &F) {
DEBUG(dbgs() << "DAE - Intrinsically live fn: " << F.getName() << "\n");
LiveFunctions.insert(&F);
for (unsigned i = 0, e = F.arg_size(); i != e; ++i)
PropagateLiveness(CreateArg(&F, i));
for (unsigned i = 0, e = NumRetVals(&F); i != e; ++i)
PropagateLiveness(CreateRet(&F, i));
}
void DAE::MarkLive(const RetOrArg &RA) {
if (LiveFunctions.count(RA.F))
return;
if (!LiveValues.insert(RA).second)
return;
DEBUG(dbgs() << "DAE - Marking " << RA.getDescription() << " live\n");
PropagateLiveness(RA);
}
void DAE::PropagateLiveness(const RetOrArg &RA) {
UseMap::iterator Begin = Uses.lower_bound(RA);
UseMap::iterator E = Uses.end();
UseMap::iterator I;
for (I = Begin; I != E && I->first == RA; ++I)
MarkLive(I->second);
Uses.erase(Begin, I);
}
bool DAE::RemoveDeadStuffFromFunction(Function *F) {
if (LiveFunctions.count(F))
return false;
FunctionType *FTy = F->getFunctionType();
std::vector<Type*> Params;
SmallVector<AttributeWithIndex, 8> AttributesVec;
const AttrListPtr &PAL = F->getAttributes();
Attributes RAttrs = PAL.getRetAttributes();
Attributes FnAttrs = PAL.getFnAttributes();
Type *RetTy = FTy->getReturnType();
Type *NRetTy = NULL;
unsigned RetCount = NumRetVals(F);
SmallVector<int, 5> NewRetIdxs(RetCount, -1);
std::vector<Type*> RetTypes;
if (RetTy->isVoidTy()) {
NRetTy = RetTy;
} else {
StructType *STy = dyn_cast<StructType>(RetTy);
if (STy)
for (unsigned i = 0; i != RetCount; ++i) {
RetOrArg Ret = CreateRet(F, i);
if (LiveValues.erase(Ret)) {
RetTypes.push_back(STy->getElementType(i));
NewRetIdxs[i] = RetTypes.size() - 1;
} else {
++NumRetValsEliminated;
DEBUG(dbgs() << "DAE - Removing return value " << i << " from "
<< F->getName() << "\n");
}
}
else
if (LiveValues.erase(CreateRet(F, 0))) {
RetTypes.push_back(RetTy);
NewRetIdxs[0] = 0;
} else {
DEBUG(dbgs() << "DAE - Removing return value from " << F->getName()
<< "\n");
++NumRetValsEliminated;
}
if (RetTypes.size() > 1)
NRetTy = StructType::get(STy->getContext(), RetTypes, STy->isPacked());
else if (RetTypes.size() == 1)
NRetTy = RetTypes.front();
else if (RetTypes.size() == 0)
NRetTy = Type::getVoidTy(F->getContext());
}
assert(NRetTy && "No new return type found?");
if (NRetTy->isVoidTy())
RAttrs &= ~Attribute::typeIncompatible(NRetTy);
else
assert((RAttrs & Attribute::typeIncompatible(NRetTy)) == 0
&& "Return attributes no longer compatible?");
if (RAttrs)
AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
unsigned i = 0;
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
I != E; ++I, ++i) {
RetOrArg Arg = CreateArg(F, i);
if (LiveValues.erase(Arg)) {
Params.push_back(I->getType());
ArgAlive[i] = true;
if (Attributes Attrs = PAL.getParamAttributes(i + 1))
AttributesVec.push_back(AttributeWithIndex::get(Params.size(), Attrs));
} else {
++NumArgumentsEliminated;
DEBUG(dbgs() << "DAE - Removing argument " << i << " (" << I->getName()
<< ") from " << F->getName() << "\n");
}
}
if (FnAttrs != Attribute::None)
AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
AttrListPtr NewPAL = AttrListPtr::get(AttributesVec.begin(),
AttributesVec.end());
FunctionType *NFTy = FunctionType::get(NRetTy, Params, FTy->isVarArg());
if (NFTy == FTy)
return false;
Function *NF = Function::Create(NFTy, F->getLinkage());
NF->copyAttributesFrom(F);
NF->setAttributes(NewPAL);
F->getParent()->getFunctionList().insert(F, NF);
NF->takeName(F);
std::vector<Value*> Args;
while (!F->use_empty()) {
CallSite CS(F->use_back());
Instruction *Call = CS.getInstruction();
AttributesVec.clear();
const AttrListPtr &CallPAL = CS.getAttributes();
Attributes RAttrs = CallPAL.getRetAttributes();
Attributes FnAttrs = CallPAL.getFnAttributes();
RAttrs &= ~Attribute::typeIncompatible(NF->getReturnType());
if (RAttrs)
AttributesVec.push_back(AttributeWithIndex::get(0, RAttrs));
CallSite::arg_iterator I = CS.arg_begin();
unsigned i = 0;
for (unsigned e = FTy->getNumParams(); i != e; ++I, ++i)
if (ArgAlive[i]) {
Args.push_back(*I);
if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
}
for (CallSite::arg_iterator E = CS.arg_end(); I != E; ++I, ++i) {
Args.push_back(*I);
if (Attributes Attrs = CallPAL.getParamAttributes(i + 1))
AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs));
}
if (FnAttrs != Attribute::None)
AttributesVec.push_back(AttributeWithIndex::get(~0, FnAttrs));
AttrListPtr NewCallPAL = AttrListPtr::get(AttributesVec.begin(),
AttributesVec.end());
Instruction *New;
if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
Args, "", Call);
cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
cast<InvokeInst>(New)->setAttributes(NewCallPAL);
} else {
New = CallInst::Create(NF, Args, "", Call);
cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
cast<CallInst>(New)->setAttributes(NewCallPAL);
if (cast<CallInst>(Call)->isTailCall())
cast<CallInst>(New)->setTailCall();
}
New->setDebugLoc(Call->getDebugLoc());
Args.clear();
if (!Call->use_empty()) {
if (New->getType() == Call->getType()) {
Call->replaceAllUsesWith(New);
New->takeName(Call);
} else if (New->getType()->isVoidTy()) {
if (!Call->getType()->isX86_MMXTy())
Call->replaceAllUsesWith(Constant::getNullValue(Call->getType()));
} else {
assert(RetTy->isStructTy() &&
"Return type changed, but not into a void. The old return type"
" must have been a struct!");
Instruction *InsertPt = Call;
if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
BasicBlock::iterator IP = II->getNormalDest()->begin();
while (isa<PHINode>(IP)) ++IP;
InsertPt = IP;
}
Value *RetVal = UndefValue::get(RetTy);
for (unsigned i = 0; i != RetCount; ++i)
if (NewRetIdxs[i] != -1) {
Value *V;
if (RetTypes.size() > 1)
V = ExtractValueInst::Create(New, NewRetIdxs[i], "newret",
InsertPt);
else
V = New;
RetVal = InsertValueInst::Create(RetVal, V, i, "oldret", InsertPt);
}
Call->replaceAllUsesWith(RetVal);
New->takeName(Call);
}
}
Call->eraseFromParent();
}
NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
i = 0;
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
I2 = NF->arg_begin(); I != E; ++I, ++i)
if (ArgAlive[i]) {
I->replaceAllUsesWith(I2);
I2->takeName(I);
++I2;
} else {
if (!I->getType()->isX86_MMXTy())
I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
}
if (F->getReturnType() != NF->getReturnType())
for (Function::iterator BB = NF->begin(), E = NF->end(); BB != E; ++BB)
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
Value *RetVal;
if (NFTy->getReturnType()->isVoidTy()) {
RetVal = 0;
} else {
assert (RetTy->isStructTy());
Value *OldRet = RI->getOperand(0);
RetVal = UndefValue::get(NRetTy);
for (unsigned i = 0; i != RetCount; ++i)
if (NewRetIdxs[i] != -1) {
ExtractValueInst *EV = ExtractValueInst::Create(OldRet, i,
"oldret", RI);
if (RetTypes.size() > 1) {
RetVal = InsertValueInst::Create(RetVal, EV, NewRetIdxs[i],
"newret", RI);
} else {
RetVal = EV;
}
}
}
ReturnInst::Create(F->getContext(), RetVal, RI);
BB->getInstList().erase(RI);
}
F->eraseFromParent();
return true;
}
bool DAE::runOnModule(Module &M) {
bool Changed = false;
DEBUG(dbgs() << "DAE - Deleting dead varargs\n");
for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
Function &F = *I++;
if (F.getFunctionType()->isVarArg())
Changed |= DeleteDeadVarargs(F);
}
DEBUG(dbgs() << "DAE - Determining liveness\n");
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
SurveyFunction(*I);
for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
Function *F = I++;
Changed |= RemoveDeadStuffFromFunction(F);
}
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
Function& F = *I;
Changed |= RemoveDeadArgumentsFromCallers(F);
}
return Changed;
}