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267 lines
9.1 KiB
C++
267 lines
9.1 KiB
C++
//===- PointerTracking.cpp - Pointer Bounds Tracking ------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements tracking of pointer bounds.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/Analysis/PointerTracking.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Constants.h"
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#include "llvm/Module.h"
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#include "llvm/Value.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Support/InstIterator.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetData.h"
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using namespace llvm;
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char PointerTracking::ID = 0;
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PointerTracking::PointerTracking() : FunctionPass(&ID) {}
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bool PointerTracking::runOnFunction(Function &F) {
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predCache.clear();
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assert(analyzing.empty());
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FF = &F;
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TD = getAnalysisIfAvailable<TargetData>();
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SE = &getAnalysis<ScalarEvolution>();
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LI = &getAnalysis<LoopInfo>();
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DT = &getAnalysis<DominatorTree>();
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return false;
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}
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void PointerTracking::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredTransitive<DominatorTree>();
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AU.addRequiredTransitive<LoopInfo>();
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AU.addRequiredTransitive<ScalarEvolution>();
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AU.setPreservesAll();
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}
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bool PointerTracking::doInitialization(Module &M) {
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const Type *PTy = Type::getInt8PtrTy(M.getContext());
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// Find calloc(i64, i64) or calloc(i32, i32).
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callocFunc = M.getFunction("calloc");
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if (callocFunc) {
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const FunctionType *Ty = callocFunc->getFunctionType();
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std::vector<const Type*> args, args2;
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args.push_back(Type::getInt64Ty(M.getContext()));
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args.push_back(Type::getInt64Ty(M.getContext()));
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args2.push_back(Type::getInt32Ty(M.getContext()));
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args2.push_back(Type::getInt32Ty(M.getContext()));
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const FunctionType *Calloc1Type =
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FunctionType::get(PTy, args, false);
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const FunctionType *Calloc2Type =
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FunctionType::get(PTy, args2, false);
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if (Ty != Calloc1Type && Ty != Calloc2Type)
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callocFunc = 0; // Give up
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}
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// Find realloc(i8*, i64) or realloc(i8*, i32).
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reallocFunc = M.getFunction("realloc");
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if (reallocFunc) {
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const FunctionType *Ty = reallocFunc->getFunctionType();
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std::vector<const Type*> args, args2;
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args.push_back(PTy);
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args.push_back(Type::getInt64Ty(M.getContext()));
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args2.push_back(PTy);
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args2.push_back(Type::getInt32Ty(M.getContext()));
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const FunctionType *Realloc1Type =
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FunctionType::get(PTy, args, false);
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const FunctionType *Realloc2Type =
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FunctionType::get(PTy, args2, false);
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if (Ty != Realloc1Type && Ty != Realloc2Type)
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reallocFunc = 0; // Give up
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}
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return false;
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}
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// Calculates the number of elements allocated for pointer P,
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// the type of the element is stored in Ty.
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const SCEV *PointerTracking::computeAllocationCount(Value *P,
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const Type *&Ty) const {
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Value *V = P->stripPointerCasts();
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if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
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Value *arraySize = AI->getArraySize();
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Ty = AI->getAllocatedType();
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// arraySize elements of type Ty.
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return SE->getSCEV(arraySize);
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}
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if (CallInst *CI = extractMallocCall(V)) {
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Value *arraySize = getMallocArraySize(CI, P->getContext(), TD);
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const Type* AllocTy = getMallocAllocatedType(CI);
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if (!AllocTy || !arraySize) return SE->getCouldNotCompute();
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Ty = AllocTy;
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// arraySize elements of type Ty.
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return SE->getSCEV(arraySize);
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}
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
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if (GV->hasDefinitiveInitializer()) {
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Constant *C = GV->getInitializer();
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if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
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Ty = ATy->getElementType();
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return SE->getConstant(Type::getInt32Ty(P->getContext()),
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ATy->getNumElements());
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}
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}
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Ty = GV->getType();
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return SE->getConstant(Type::getInt32Ty(P->getContext()), 1);
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//TODO: implement more tracking for globals
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}
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if (CallInst *CI = dyn_cast<CallInst>(V)) {
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CallSite CS(CI);
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Function *F = dyn_cast<Function>(CS.getCalledValue()->stripPointerCasts());
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const Loop *L = LI->getLoopFor(CI->getParent());
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if (F == callocFunc) {
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Ty = Type::getInt8Ty(P->getContext());
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// calloc allocates arg0*arg1 bytes.
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return SE->getSCEVAtScope(SE->getMulExpr(SE->getSCEV(CS.getArgument(0)),
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SE->getSCEV(CS.getArgument(1))),
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L);
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} else if (F == reallocFunc) {
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Ty = Type::getInt8Ty(P->getContext());
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// realloc allocates arg1 bytes.
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return SE->getSCEVAtScope(CS.getArgument(1), L);
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}
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}
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return SE->getCouldNotCompute();
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}
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// Calculates the number of elements of type Ty allocated for P.
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const SCEV *PointerTracking::computeAllocationCountForType(Value *P,
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const Type *Ty)
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const {
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const Type *elementTy;
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const SCEV *Count = computeAllocationCount(P, elementTy);
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if (isa<SCEVCouldNotCompute>(Count))
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return Count;
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if (elementTy == Ty)
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return Count;
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if (!TD) // need TargetData from this point forward
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return SE->getCouldNotCompute();
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uint64_t elementSize = TD->getTypeAllocSize(elementTy);
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uint64_t wantSize = TD->getTypeAllocSize(Ty);
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if (elementSize == wantSize)
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return Count;
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if (elementSize % wantSize) //fractional counts not possible
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return SE->getCouldNotCompute();
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return SE->getMulExpr(Count, SE->getConstant(Count->getType(),
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elementSize/wantSize));
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}
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const SCEV *PointerTracking::getAllocationElementCount(Value *V) const {
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// We only deal with pointers.
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const PointerType *PTy = cast<PointerType>(V->getType());
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return computeAllocationCountForType(V, PTy->getElementType());
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}
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const SCEV *PointerTracking::getAllocationSizeInBytes(Value *V) const {
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return computeAllocationCountForType(V, Type::getInt8Ty(V->getContext()));
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}
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// Helper for isLoopGuardedBy that checks the swapped and inverted predicate too
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enum SolverResult PointerTracking::isLoopGuardedBy(const Loop *L,
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Predicate Pred,
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const SCEV *A,
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const SCEV *B) const {
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if (SE->isLoopGuardedByCond(L, Pred, A, B))
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return AlwaysTrue;
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Pred = ICmpInst::getSwappedPredicate(Pred);
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if (SE->isLoopGuardedByCond(L, Pred, B, A))
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return AlwaysTrue;
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Pred = ICmpInst::getInversePredicate(Pred);
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if (SE->isLoopGuardedByCond(L, Pred, B, A))
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return AlwaysFalse;
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Pred = ICmpInst::getSwappedPredicate(Pred);
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if (SE->isLoopGuardedByCond(L, Pred, A, B))
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return AlwaysTrue;
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return Unknown;
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}
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enum SolverResult PointerTracking::checkLimits(const SCEV *Offset,
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const SCEV *Limit,
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BasicBlock *BB)
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{
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//FIXME: merge implementation
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return Unknown;
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}
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void PointerTracking::getPointerOffset(Value *Pointer, Value *&Base,
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const SCEV *&Limit,
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const SCEV *&Offset) const
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{
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Pointer = Pointer->stripPointerCasts();
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Base = Pointer->getUnderlyingObject();
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Limit = getAllocationSizeInBytes(Base);
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if (isa<SCEVCouldNotCompute>(Limit)) {
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Base = 0;
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Offset = Limit;
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return;
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}
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Offset = SE->getMinusSCEV(SE->getSCEV(Pointer), SE->getSCEV(Base));
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if (isa<SCEVCouldNotCompute>(Offset)) {
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Base = 0;
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Limit = Offset;
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}
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}
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void PointerTracking::print(raw_ostream &OS, const Module* M) const {
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// Calling some PT methods may cause caches to be updated, however
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// this should be safe for the same reason its safe for SCEV.
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PointerTracking &PT = *const_cast<PointerTracking*>(this);
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for (inst_iterator I=inst_begin(*FF), E=inst_end(*FF); I != E; ++I) {
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if (!isa<PointerType>(I->getType()))
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continue;
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Value *Base;
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const SCEV *Limit, *Offset;
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getPointerOffset(&*I, Base, Limit, Offset);
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if (!Base)
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continue;
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if (Base == &*I) {
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const SCEV *S = getAllocationElementCount(Base);
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OS << *Base << " ==> " << *S << " elements, ";
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OS << *Limit << " bytes allocated\n";
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continue;
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}
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OS << &*I << " -- base: " << *Base;
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OS << " offset: " << *Offset;
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enum SolverResult res = PT.checkLimits(Offset, Limit, I->getParent());
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switch (res) {
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case AlwaysTrue:
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OS << " always safe\n";
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break;
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case AlwaysFalse:
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OS << " always unsafe\n";
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break;
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case Unknown:
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OS << " <<unknown>>\n";
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break;
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}
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}
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}
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static RegisterPass<PointerTracking> X("pointertracking",
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"Track pointer bounds", false, true);
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