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//===- PointerTracking.h - 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.
// It knows that the libc functions "calloc" and "realloc" allocate memory, thus
// you should avoid using this pass if they mean something else for your
// language.
//
// All methods assume that the pointer is not NULL, if it is then the returned
// allocation size is wrong, and the result from checkLimits is wrong too.
// It also assumes that pointers are valid, and that it is not analyzing a
// use-after-free scenario.
// Due to these limitations the "size" returned by these methods should be
// considered as either 0 or the returned size.
//
// Another analysis pass should be used to find use-after-free/NULL dereference
// bugs.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_POINTERTRACKING_H
#define LLVM_ANALYSIS_POINTERTRACKING_H
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Support/PredIteratorCache.h"
namespace llvm {
class DominatorTree;
class ScalarEvolution;
class SCEV;
class Loop;
class LoopInfo;
class TargetData;
// Result from solver, assuming pointer is not NULL,
// and it is not a use-after-free situation.
enum SolverResult {
AlwaysFalse,// always false with above constraints
AlwaysTrue,// always true with above constraints
Unknown // it can sometimes be true, sometimes false, or it is undecided
};
class PointerTracking : public FunctionPass {
public:
typedef ICmpInst::Predicate Predicate;
static char ID;
PointerTracking();
virtual bool doInitialization(Module &M);
// If this pointer directly points to an allocation, return
// the number of elements of type Ty allocated.
// Otherwise return CouldNotCompute.
// Since allocations can fail by returning NULL, the real element count
// for every allocation is either 0 or the value returned by this function.
const SCEV *getAllocationElementCount(Value *P) const;
// Same as getAllocationSize() but returns size in bytes.
// We consider one byte as 8 bits.
const SCEV *getAllocationSizeInBytes(Value *V) const;
// Given a Pointer, determine a base pointer of known size, and an offset
// therefrom.
// When unable to determine, sets Base to NULL, and Limit/Offset to
// CouldNotCompute.
// BaseSize, and Offset are in bytes: Pointer == Base + Offset
void getPointerOffset(Value *Pointer, Value *&Base, const SCEV *& BaseSize,
const SCEV *&Offset) const;
// Compares the 2 scalar evolution expressions according to predicate,
// and if it can prove that the result is always true or always false
// return AlwaysTrue/AlwaysFalse. Otherwise it returns Unknown.
enum SolverResult compareSCEV(const SCEV *A, Predicate Pred, const SCEV *B,
const Loop *L);
// Determines whether the condition LHS <Pred> RHS is sufficient
// for the condition A <Pred> B to hold.
// Currently only ULT/ULE is supported.
// This errs on the side of returning false.
bool conditionSufficient(const SCEV *LHS, Predicate Pred1, const SCEV *RHS,
const SCEV *A, Predicate Pred2, const SCEV *B,
const Loop *L);
// Determines whether Offset is known to be always in [0, Limit) bounds.
// This errs on the side of returning Unknown.
enum SolverResult checkLimits(const SCEV *Offset, const SCEV *Limit,
BasicBlock *BB);
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
void print(raw_ostream &OS, const Module* = 0) const;
Value *computeAllocationCountValue(Value *P, const Type *&Ty) const;
private:
Function *FF;
TargetData *TD;
ScalarEvolution *SE;
LoopInfo *LI;
DominatorTree *DT;
Function *callocFunc;
Function *reallocFunc;
PredIteratorCache predCache;
SmallPtrSet<const SCEV*, 1> analyzing;
enum SolverResult isLoopGuardedBy(const Loop *L, Predicate Pred,
const SCEV *A, const SCEV *B) const;
static bool isMonotonic(const SCEV *S);
bool scevPositive(const SCEV *A, const Loop *L, bool strict=true) const;
bool conditionSufficient(Value *Cond, bool negated,
const SCEV *A, Predicate Pred, const SCEV *B);
Value *getConditionToReach(BasicBlock *A,
DomTreeNodeBase<BasicBlock> *B,
bool &negated);
Value *getConditionToReach(BasicBlock *A,
BasicBlock *B,
bool &negated);
const SCEV *computeAllocationCount(Value *P, const Type *&Ty) const;
const SCEV *computeAllocationCountForType(Value *P, const Type *Ty) const;
};
}
#endif
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