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llvm-project/llvm/lib/Analysis/PointerTracking.cpp

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//===- PointerTracking.cpp - Pointer Bounds Tracking ------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements tracking of pointer bounds.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/PointerTracking.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Constants.h"
#include "llvm/Module.h"
#include "llvm/Value.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/InstIterator.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetData.h"
namespace llvm {
char PointerTracking::ID=0;
PointerTracking::PointerTracking() : FunctionPass(&ID) {}
bool PointerTracking::runOnFunction(Function &F) {
predCache.clear();
assert(analyzing.empty());
FF = &F;
TD = getAnalysisIfAvailable<TargetData>();
SE = &getAnalysis<ScalarEvolution>();
LI = &getAnalysis<LoopInfo>();
DT = &getAnalysis<DominatorTree>();
return false;
}
void PointerTracking::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredTransitive<DominatorTree>();
AU.addRequiredTransitive<LoopInfo>();
AU.addRequiredTransitive<ScalarEvolution>();
AU.setPreservesAll();
}
bool PointerTracking::doInitialization(Module &M) {
const Type *PTy = PointerType::getUnqual(Type::getInt8Ty(M.getContext()));
// Find calloc(i64, i64) or calloc(i32, i32).
callocFunc = M.getFunction("calloc");
if (callocFunc) {
const FunctionType *Ty = callocFunc->getFunctionType();
std::vector<const Type*> args, args2;
args.push_back(Type::getInt64Ty(M.getContext()));
args.push_back(Type::getInt64Ty(M.getContext()));
args2.push_back(Type::getInt32Ty(M.getContext()));
args2.push_back(Type::getInt32Ty(M.getContext()));
const FunctionType *Calloc1Type =
FunctionType::get(PTy, args, false);
const FunctionType *Calloc2Type =
FunctionType::get(PTy, args2, false);
if (Ty != Calloc1Type && Ty != Calloc2Type)
callocFunc = 0; // Give up
}
// Find realloc(i8*, i64) or realloc(i8*, i32).
reallocFunc = M.getFunction("realloc");
if (reallocFunc) {
const FunctionType *Ty = reallocFunc->getFunctionType();
std::vector<const Type*> args, args2;
args.push_back(PTy);
args.push_back(Type::getInt64Ty(M.getContext()));
args2.push_back(PTy);
args2.push_back(Type::getInt32Ty(M.getContext()));
const FunctionType *Realloc1Type =
FunctionType::get(PTy, args, false);
const FunctionType *Realloc2Type =
FunctionType::get(PTy, args2, false);
if (Ty != Realloc1Type && Ty != Realloc2Type)
reallocFunc = 0; // Give up
}
return false;
}
// Calculates the number of elements allocated for pointer P,
// the type of the element is stored in Ty.
const SCEV *PointerTracking::computeAllocationCount(Value *P,
const Type *&Ty) const {
Value *V = P->stripPointerCasts();
if (AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
Value *arraySize = AI->getArraySize();
Ty = AI->getAllocatedType();
// arraySize elements of type Ty.
return SE->getSCEV(arraySize);
}
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
if (GV->hasDefinitiveInitializer()) {
Constant *C = GV->getInitializer();
if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
Ty = ATy->getElementType();
return SE->getConstant(Type::getInt32Ty(P->getContext()),
ATy->getNumElements());
}
}
Ty = GV->getType();
return SE->getConstant(Type::getInt32Ty(P->getContext()), 1);
//TODO: implement more tracking for globals
}
if (CallInst *CI = dyn_cast<CallInst>(V)) {
CallSite CS(CI);
Function *F = dyn_cast<Function>(CS.getCalledValue()->stripPointerCasts());
const Loop *L = LI->getLoopFor(CI->getParent());
if (F == callocFunc) {
Ty = Type::getInt8Ty(P->getContext());
// calloc allocates arg0*arg1 bytes.
return SE->getSCEVAtScope(SE->getMulExpr(SE->getSCEV(CS.getArgument(0)),
SE->getSCEV(CS.getArgument(1))),
L);
} else if (F == reallocFunc) {
Ty = Type::getInt8Ty(P->getContext());
// realloc allocates arg1 bytes.
return SE->getSCEVAtScope(CS.getArgument(1), L);
}
}
return SE->getCouldNotCompute();
}
// Calculates the number of elements of type Ty allocated for P.
const SCEV *PointerTracking::computeAllocationCountForType(Value *P,
const Type *Ty)
const {
const Type *elementTy;
const SCEV *Count = computeAllocationCount(P, elementTy);
if (isa<SCEVCouldNotCompute>(Count))
return Count;
if (elementTy == Ty)
return Count;
if (!TD) // need TargetData from this point forward
return SE->getCouldNotCompute();
uint64_t elementSize = TD->getTypeAllocSize(elementTy);
uint64_t wantSize = TD->getTypeAllocSize(Ty);
if (elementSize == wantSize)
return Count;
if (elementSize % wantSize) //fractional counts not possible
return SE->getCouldNotCompute();
return SE->getMulExpr(Count, SE->getConstant(Count->getType(),
elementSize/wantSize));
}
const SCEV *PointerTracking::getAllocationElementCount(Value *V) const {
// We only deal with pointers.
const PointerType *PTy = cast<PointerType>(V->getType());
return computeAllocationCountForType(V, PTy->getElementType());
}
const SCEV *PointerTracking::getAllocationSizeInBytes(Value *V) const {
return computeAllocationCountForType(V, Type::getInt8Ty(V->getContext()));
}
// Helper for isLoopGuardedBy that checks the swapped and inverted predicate too
enum SolverResult PointerTracking::isLoopGuardedBy(const Loop *L,
Predicate Pred,
const SCEV *A,
const SCEV *B) const {
if (SE->isLoopGuardedByCond(L, Pred, A, B))
return AlwaysTrue;
Pred = ICmpInst::getSwappedPredicate(Pred);
if (SE->isLoopGuardedByCond(L, Pred, B, A))
return AlwaysTrue;
Pred = ICmpInst::getInversePredicate(Pred);
if (SE->isLoopGuardedByCond(L, Pred, B, A))
return AlwaysFalse;
Pred = ICmpInst::getSwappedPredicate(Pred);
if (SE->isLoopGuardedByCond(L, Pred, A, B))
return AlwaysTrue;
return Unknown;
}
enum SolverResult PointerTracking::checkLimits(const SCEV *Offset,
const SCEV *Limit,
BasicBlock *BB)
{
//FIXME: merge implementation
return Unknown;
}
void PointerTracking::getPointerOffset(Value *Pointer, Value *&Base,
const SCEV *&Limit,
const SCEV *&Offset) const
{
Pointer = Pointer->stripPointerCasts();
Base = Pointer->getUnderlyingObject();
Limit = getAllocationSizeInBytes(Base);
if (isa<SCEVCouldNotCompute>(Limit)) {
Base = 0;
Offset = Limit;
return;
}
Offset = SE->getMinusSCEV(SE->getSCEV(Pointer), SE->getSCEV(Base));
if (isa<SCEVCouldNotCompute>(Offset)) {
Base = 0;
Limit = Offset;
}
}
void PointerTracking::print(raw_ostream &OS, const Module* M) const {
// Calling some PT methods may cause caches to be updated, however
// this should be safe for the same reason its safe for SCEV.
PointerTracking &PT = *const_cast<PointerTracking*>(this);
for (inst_iterator I=inst_begin(*FF), E=inst_end(*FF); I != E; ++I) {
if (!isa<PointerType>(I->getType()))
continue;
Value *Base;
const SCEV *Limit, *Offset;
getPointerOffset(&*I, Base, Limit, Offset);
if (!Base)
continue;
if (Base == &*I) {
const SCEV *S = getAllocationElementCount(Base);
OS << *Base << " ==> " << *S << " elements, ";
OS << *Limit << " bytes allocated\n";
continue;
}
OS << &*I << " -- base: " << *Base;
OS << " offset: " << *Offset;
enum SolverResult res = PT.checkLimits(Offset, Limit, I->getParent());
switch (res) {
case AlwaysTrue:
OS << " always safe\n";
break;
case AlwaysFalse:
OS << " always unsafe\n";
break;
case Unknown:
OS << " <<unknown>>\n";
break;
}
}
}
void PointerTracking::print(std::ostream &o, const Module* M) const {
raw_os_ostream OS(o);
print(OS, M);
}
static RegisterPass<PointerTracking> X("pointertracking",
"Track pointer bounds", false, true);
}
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