#define DEBUG_TYPE "functionattrs"
#include "llvm/Transforms/IPO.h"
#include "llvm/CallGraphSCCPass.h"
#include "llvm/GlobalVariable.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/UniqueVector.h"
#include "llvm/Support/InstIterator.h"
using namespace llvm;
STATISTIC(NumReadNone, "Number of functions marked readnone");
STATISTIC(NumReadOnly, "Number of functions marked readonly");
STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
STATISTIC(NumNoAlias, "Number of function returns marked noalias");
namespace {
struct FunctionAttrs : public CallGraphSCCPass {
static char ID; FunctionAttrs() : CallGraphSCCPass(ID), AA(0) {
initializeFunctionAttrsPass(*PassRegistry::getPassRegistry());
}
bool runOnSCC(CallGraphSCC &SCC);
bool AddReadAttrs(const CallGraphSCC &SCC);
bool AddNoCaptureAttrs(const CallGraphSCC &SCC);
bool IsFunctionMallocLike(Function *F,
SmallPtrSet<Function*, 8> &) const;
bool AddNoAliasAttrs(const CallGraphSCC &SCC);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<AliasAnalysis>();
CallGraphSCCPass::getAnalysisUsage(AU);
}
private:
AliasAnalysis *AA;
};
}
char FunctionAttrs::ID = 0;
INITIALIZE_PASS_BEGIN(FunctionAttrs, "functionattrs",
"Deduce function attributes", false, false)
INITIALIZE_AG_DEPENDENCY(CallGraph)
INITIALIZE_PASS_END(FunctionAttrs, "functionattrs",
"Deduce function attributes", false, false)
Pass *llvm::createFunctionAttrsPass() { return new FunctionAttrs(); }
bool FunctionAttrs::AddReadAttrs(const CallGraphSCC &SCC) {
SmallPtrSet<Function*, 8> SCCNodes;
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
SCCNodes.insert((*I)->getFunction());
bool ReadsMemory = false;
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
Function *F = (*I)->getFunction();
if (F == 0)
return false;
AliasAnalysis::ModRefBehavior MRB = AA->getModRefBehavior(F);
if (MRB == AliasAnalysis::DoesNotAccessMemory)
continue;
if (F->isDeclaration() || F->mayBeOverridden()) {
if (!AliasAnalysis::onlyReadsMemory(MRB))
return false;
ReadsMemory = true;
continue;
}
for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
Instruction *I = &*II;
CallSite CS(cast<Value>(I));
if (CS) {
if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
continue;
AliasAnalysis::ModRefBehavior MRB = AA->getModRefBehavior(CS);
if (AliasAnalysis::onlyAccessesArgPointees(MRB)) {
if (AliasAnalysis::doesAccessArgPointees(MRB))
for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
CI != CE; ++CI) {
Value *Arg = *CI;
if (Arg->getType()->isPointerTy()) {
AliasAnalysis::Location Loc(Arg,
AliasAnalysis::UnknownSize,
I->getMetadata(LLVMContext::MD_tbaa));
if (!AA->pointsToConstantMemory(Loc, true)) {
if (MRB & AliasAnalysis::Mod)
return false;
if (MRB & AliasAnalysis::Ref)
ReadsMemory = true;
}
}
}
continue;
}
if (MRB & AliasAnalysis::Mod)
return false;
if (MRB & AliasAnalysis::Ref)
ReadsMemory = true;
continue;
} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
if (!LI->isVolatile()) {
AliasAnalysis::Location Loc = AA->getLocation(LI);
if (AA->pointsToConstantMemory(Loc, true))
continue;
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
if (!SI->isVolatile()) {
AliasAnalysis::Location Loc = AA->getLocation(SI);
if (AA->pointsToConstantMemory(Loc, true))
continue;
}
} else if (VAArgInst *VI = dyn_cast<VAArgInst>(I)) {
AliasAnalysis::Location Loc = AA->getLocation(VI);
if (AA->pointsToConstantMemory(Loc, true))
continue;
}
if (I->mayWriteToMemory())
return false;
ReadsMemory |= I->mayReadFromMemory();
}
}
bool MadeChange = false;
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
Function *F = (*I)->getFunction();
if (F->doesNotAccessMemory())
continue;
if (F->onlyReadsMemory() && ReadsMemory)
continue;
MadeChange = true;
F->removeAttribute(~0, Attribute::ReadOnly | Attribute::ReadNone);
F->addAttribute(~0, ReadsMemory? Attribute::ReadOnly : Attribute::ReadNone);
if (ReadsMemory)
++NumReadOnly;
else
++NumReadNone;
}
return MadeChange;
}
namespace {
struct ArgumentGraphNode {
Argument *Definition;
SmallVector<ArgumentGraphNode*, 4> Uses;
};
class ArgumentGraph {
typedef std::map<Argument*, ArgumentGraphNode> ArgumentMapTy;
ArgumentMapTy ArgumentMap;
ArgumentGraphNode SyntheticRoot;
public:
ArgumentGraph() { SyntheticRoot.Definition = 0; }
typedef SmallVectorImpl<ArgumentGraphNode*>::iterator iterator;
iterator begin() { return SyntheticRoot.Uses.begin(); }
iterator end() { return SyntheticRoot.Uses.end(); }
ArgumentGraphNode *getEntryNode() { return &SyntheticRoot; }
ArgumentGraphNode *operator[](Argument *A) {
ArgumentGraphNode &Node = ArgumentMap[A];
Node.Definition = A;
SyntheticRoot.Uses.push_back(&Node);
return &Node;
}
};
struct ArgumentUsesTracker : public CaptureTracker {
ArgumentUsesTracker(const SmallPtrSet<Function*, 8> &SCCNodes)
: Captured(false), SCCNodes(SCCNodes) {}
void tooManyUses() { Captured = true; }
bool shouldExplore(Use *U) { return true; }
bool captured(Use *U) {
CallSite CS(U->getUser());
if (!CS.getInstruction()) { Captured = true; return true; }
Function *F = CS.getCalledFunction();
if (!F || !SCCNodes.count(F)) { Captured = true; return true; }
Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
for (CallSite::arg_iterator PI = CS.arg_begin(), PE = CS.arg_end();
PI != PE; ++PI, ++AI) {
if (AI == AE) {
assert(F->isVarArg() && "More params than args in non-varargs call");
Captured = true;
return true;
}
if (PI == U) {
Uses.push_back(AI);
break;
}
}
assert(!Uses.empty() && "Capturing call-site captured nothing?");
return false;
}
bool Captured; SmallVector<Argument*, 4> Uses;
const SmallPtrSet<Function*, 8> &SCCNodes;
};
}
namespace llvm {
template<> struct GraphTraits<ArgumentGraphNode*> {
typedef ArgumentGraphNode NodeType;
typedef SmallVectorImpl<ArgumentGraphNode*>::iterator ChildIteratorType;
static inline NodeType *getEntryNode(NodeType *A) { return A; }
static inline ChildIteratorType child_begin(NodeType *N) {
return N->Uses.begin();
}
static inline ChildIteratorType child_end(NodeType *N) {
return N->Uses.end();
}
};
template<> struct GraphTraits<ArgumentGraph*>
: public GraphTraits<ArgumentGraphNode*> {
static NodeType *getEntryNode(ArgumentGraph *AG) {
return AG->getEntryNode();
}
static ChildIteratorType nodes_begin(ArgumentGraph *AG) {
return AG->begin();
}
static ChildIteratorType nodes_end(ArgumentGraph *AG) {
return AG->end();
}
};
}
bool FunctionAttrs::AddNoCaptureAttrs(const CallGraphSCC &SCC) {
bool Changed = false;
SmallPtrSet<Function*, 8> SCCNodes;
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
Function *F = (*I)->getFunction();
if (F && !F->isDeclaration() && !F->mayBeOverridden())
SCCNodes.insert(F);
}
ArgumentGraph AG;
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
Function *F = (*I)->getFunction();
if (F == 0)
continue;
if (F->isDeclaration() || F->mayBeOverridden())
continue;
if (F->onlyReadsMemory() && F->doesNotThrow() &&
F->getReturnType()->isVoidTy()) {
for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end();
A != E; ++A) {
if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
}
}
continue;
}
for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
ArgumentUsesTracker Tracker(SCCNodes);
PointerMayBeCaptured(A, &Tracker);
if (!Tracker.Captured) {
if (Tracker.Uses.empty()) {
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
} else {
ArgumentGraphNode *Node = AG[A];
for (SmallVectorImpl<Argument*>::iterator UI = Tracker.Uses.begin(),
UE = Tracker.Uses.end(); UI != UE; ++UI)
Node->Uses.push_back(AG[*UI]);
}
}
}
}
for (scc_iterator<ArgumentGraph*> I = scc_begin(&AG), E = scc_end(&AG);
I != E; ++I) {
std::vector<ArgumentGraphNode*> &ArgumentSCC = *I;
if (ArgumentSCC.size() == 1) {
if (!ArgumentSCC[0]->Definition) continue;
if (ArgumentSCC[0]->Uses.size() == 1 &&
ArgumentSCC[0]->Uses[0] == ArgumentSCC[0]) {
ArgumentSCC[0]->Definition->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
}
continue;
}
bool SCCCaptured = false;
for (std::vector<ArgumentGraphNode*>::iterator I = ArgumentSCC.begin(),
E = ArgumentSCC.end(); I != E && !SCCCaptured; ++I) {
ArgumentGraphNode *Node = *I;
if (Node->Uses.empty()) {
if (!Node->Definition->hasNoCaptureAttr())
SCCCaptured = true;
}
}
if (SCCCaptured) continue;
SmallPtrSet<Argument*, 8> ArgumentSCCNodes;
for (std::vector<ArgumentGraphNode*>::iterator I = ArgumentSCC.begin(),
E = ArgumentSCC.end(); I != E; ++I) {
ArgumentSCCNodes.insert((*I)->Definition);
}
for (std::vector<ArgumentGraphNode*>::iterator I = ArgumentSCC.begin(),
E = ArgumentSCC.end(); I != E && !SCCCaptured; ++I) {
ArgumentGraphNode *N = *I;
for (SmallVectorImpl<ArgumentGraphNode*>::iterator UI = N->Uses.begin(),
UE = N->Uses.end(); UI != UE; ++UI) {
Argument *A = (*UI)->Definition;
if (A->hasNoCaptureAttr() || ArgumentSCCNodes.count(A))
continue;
SCCCaptured = true;
break;
}
}
if (SCCCaptured) continue;
for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
Argument *A = ArgumentSCC[i]->Definition;
A->addAttr(Attribute::NoCapture);
++NumNoCapture;
Changed = true;
}
}
return Changed;
}
bool FunctionAttrs::IsFunctionMallocLike(Function *F,
SmallPtrSet<Function*, 8> &SCCNodes) const {
UniqueVector<Value *> FlowsToReturn;
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
if (ReturnInst *Ret = dyn_cast<ReturnInst>(I->getTerminator()))
FlowsToReturn.insert(Ret->getReturnValue());
for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
Value *RetVal = FlowsToReturn[i+1];
if (Constant *C = dyn_cast<Constant>(RetVal)) {
if (!C->isNullValue() && !isa<UndefValue>(C))
return false;
continue;
}
if (isa<Argument>(RetVal))
return false;
if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
switch (RVI->getOpcode()) {
case Instruction::BitCast:
case Instruction::GetElementPtr:
FlowsToReturn.insert(RVI->getOperand(0));
continue;
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(RVI);
FlowsToReturn.insert(SI->getTrueValue());
FlowsToReturn.insert(SI->getFalseValue());
continue;
}
case Instruction::PHI: {
PHINode *PN = cast<PHINode>(RVI);
for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
FlowsToReturn.insert(PN->getIncomingValue(i));
continue;
}
case Instruction::Alloca:
break;
case Instruction::Call:
case Instruction::Invoke: {
CallSite CS(RVI);
if (CS.paramHasAttr(0, Attribute::NoAlias))
break;
if (CS.getCalledFunction() &&
SCCNodes.count(CS.getCalledFunction()))
break;
} default:
return false; }
if (PointerMayBeCaptured(RetVal, false, false))
return false;
}
return true;
}
bool FunctionAttrs::AddNoAliasAttrs(const CallGraphSCC &SCC) {
SmallPtrSet<Function*, 8> SCCNodes;
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
SCCNodes.insert((*I)->getFunction());
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
Function *F = (*I)->getFunction();
if (F == 0)
return false;
if (F->doesNotAlias(0))
continue;
if (F->isDeclaration() || F->mayBeOverridden())
return false;
if (!F->getReturnType()->isPointerTy())
continue;
if (!IsFunctionMallocLike(F, SCCNodes))
return false;
}
bool MadeChange = false;
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
Function *F = (*I)->getFunction();
if (F->doesNotAlias(0) || !F->getReturnType()->isPointerTy())
continue;
F->setDoesNotAlias(0);
++NumNoAlias;
MadeChange = true;
}
return MadeChange;
}
bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
AA = &getAnalysis<AliasAnalysis>();
bool Changed = AddReadAttrs(SCC);
Changed |= AddNoCaptureAttrs(SCC);
Changed |= AddNoAliasAttrs(SCC);
return Changed;
}