clang  3.7.0
RangeConstraintManager.cpp
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1 //== RangeConstraintManager.cpp - Manage range constraints.------*- C++ -*--==//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines RangeConstraintManager, a class that tracks simple
11 // equality and inequality constraints on symbolic values of ProgramState.
12 //
13 //===----------------------------------------------------------------------===//
14 
19 #include "llvm/ADT/FoldingSet.h"
20 #include "llvm/ADT/ImmutableSet.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Support/raw_ostream.h"
23 
24 using namespace clang;
25 using namespace ento;
26 
27 /// A Range represents the closed range [from, to]. The caller must
28 /// guarantee that from <= to. Note that Range is immutable, so as not
29 /// to subvert RangeSet's immutability.
30 namespace {
31 class Range : public std::pair<const llvm::APSInt*,
32  const llvm::APSInt*> {
33 public:
34  Range(const llvm::APSInt &from, const llvm::APSInt &to)
35  : std::pair<const llvm::APSInt*, const llvm::APSInt*>(&from, &to) {
36  assert(from <= to);
37  }
38  bool Includes(const llvm::APSInt &v) const {
39  return *first <= v && v <= *second;
40  }
41  const llvm::APSInt &From() const {
42  return *first;
43  }
44  const llvm::APSInt &To() const {
45  return *second;
46  }
47  const llvm::APSInt *getConcreteValue() const {
48  return &From() == &To() ? &From() : nullptr;
49  }
50 
51  void Profile(llvm::FoldingSetNodeID &ID) const {
52  ID.AddPointer(&From());
53  ID.AddPointer(&To());
54  }
55 };
56 
57 
58 class RangeTrait : public llvm::ImutContainerInfo<Range> {
59 public:
60  // When comparing if one Range is less than another, we should compare
61  // the actual APSInt values instead of their pointers. This keeps the order
62  // consistent (instead of comparing by pointer values) and can potentially
63  // be used to speed up some of the operations in RangeSet.
64  static inline bool isLess(key_type_ref lhs, key_type_ref rhs) {
65  return *lhs.first < *rhs.first || (!(*rhs.first < *lhs.first) &&
66  *lhs.second < *rhs.second);
67  }
68 };
69 
70 /// RangeSet contains a set of ranges. If the set is empty, then
71 /// there the value of a symbol is overly constrained and there are no
72 /// possible values for that symbol.
73 class RangeSet {
74  typedef llvm::ImmutableSet<Range, RangeTrait> PrimRangeSet;
75  PrimRangeSet ranges; // no need to make const, since it is an
76  // ImmutableSet - this allows default operator=
77  // to work.
78 public:
79  typedef PrimRangeSet::Factory Factory;
80  typedef PrimRangeSet::iterator iterator;
81 
82  RangeSet(PrimRangeSet RS) : ranges(RS) {}
83 
84  iterator begin() const { return ranges.begin(); }
85  iterator end() const { return ranges.end(); }
86 
87  bool isEmpty() const { return ranges.isEmpty(); }
88 
89  /// Construct a new RangeSet representing '{ [from, to] }'.
90  RangeSet(Factory &F, const llvm::APSInt &from, const llvm::APSInt &to)
91  : ranges(F.add(F.getEmptySet(), Range(from, to))) {}
92 
93  /// Profile - Generates a hash profile of this RangeSet for use
94  /// by FoldingSet.
95  void Profile(llvm::FoldingSetNodeID &ID) const { ranges.Profile(ID); }
96 
97  /// getConcreteValue - If a symbol is contrained to equal a specific integer
98  /// constant then this method returns that value. Otherwise, it returns
99  /// NULL.
100  const llvm::APSInt* getConcreteValue() const {
101  return ranges.isSingleton() ? ranges.begin()->getConcreteValue() : nullptr;
102  }
103 
104 private:
105  void IntersectInRange(BasicValueFactory &BV, Factory &F,
106  const llvm::APSInt &Lower,
107  const llvm::APSInt &Upper,
108  PrimRangeSet &newRanges,
109  PrimRangeSet::iterator &i,
110  PrimRangeSet::iterator &e) const {
111  // There are six cases for each range R in the set:
112  // 1. R is entirely before the intersection range.
113  // 2. R is entirely after the intersection range.
114  // 3. R contains the entire intersection range.
115  // 4. R starts before the intersection range and ends in the middle.
116  // 5. R starts in the middle of the intersection range and ends after it.
117  // 6. R is entirely contained in the intersection range.
118  // These correspond to each of the conditions below.
119  for (/* i = begin(), e = end() */; i != e; ++i) {
120  if (i->To() < Lower) {
121  continue;
122  }
123  if (i->From() > Upper) {
124  break;
125  }
126 
127  if (i->Includes(Lower)) {
128  if (i->Includes(Upper)) {
129  newRanges = F.add(newRanges, Range(BV.getValue(Lower),
130  BV.getValue(Upper)));
131  break;
132  } else
133  newRanges = F.add(newRanges, Range(BV.getValue(Lower), i->To()));
134  } else {
135  if (i->Includes(Upper)) {
136  newRanges = F.add(newRanges, Range(i->From(), BV.getValue(Upper)));
137  break;
138  } else
139  newRanges = F.add(newRanges, *i);
140  }
141  }
142  }
143 
144  const llvm::APSInt &getMinValue() const {
145  assert(!isEmpty());
146  return ranges.begin()->From();
147  }
148 
149  bool pin(llvm::APSInt &Lower, llvm::APSInt &Upper) const {
150  // This function has nine cases, the cartesian product of range-testing
151  // both the upper and lower bounds against the symbol's type.
152  // Each case requires a different pinning operation.
153  // The function returns false if the described range is entirely outside
154  // the range of values for the associated symbol.
155  APSIntType Type(getMinValue());
156  APSIntType::RangeTestResultKind LowerTest = Type.testInRange(Lower, true);
157  APSIntType::RangeTestResultKind UpperTest = Type.testInRange(Upper, true);
158 
159  switch (LowerTest) {
161  switch (UpperTest) {
163  // The entire range is outside the symbol's set of possible values.
164  // If this is a conventionally-ordered range, the state is infeasible.
165  if (Lower < Upper)
166  return false;
167 
168  // However, if the range wraps around, it spans all possible values.
169  Lower = Type.getMinValue();
170  Upper = Type.getMaxValue();
171  break;
173  // The range starts below what's possible but ends within it. Pin.
174  Lower = Type.getMinValue();
175  Type.apply(Upper);
176  break;
178  // The range spans all possible values for the symbol. Pin.
179  Lower = Type.getMinValue();
180  Upper = Type.getMaxValue();
181  break;
182  }
183  break;
185  switch (UpperTest) {
187  // The range wraps around, but all lower values are not possible.
188  Type.apply(Lower);
189  Upper = Type.getMaxValue();
190  break;
192  // The range may or may not wrap around, but both limits are valid.
193  Type.apply(Lower);
194  Type.apply(Upper);
195  break;
197  // The range starts within what's possible but ends above it. Pin.
198  Type.apply(Lower);
199  Upper = Type.getMaxValue();
200  break;
201  }
202  break;
204  switch (UpperTest) {
206  // The range wraps but is outside the symbol's set of possible values.
207  return false;
209  // The range starts above what's possible but ends within it (wrap).
210  Lower = Type.getMinValue();
211  Type.apply(Upper);
212  break;
214  // The entire range is outside the symbol's set of possible values.
215  // If this is a conventionally-ordered range, the state is infeasible.
216  if (Lower < Upper)
217  return false;
218 
219  // However, if the range wraps around, it spans all possible values.
220  Lower = Type.getMinValue();
221  Upper = Type.getMaxValue();
222  break;
223  }
224  break;
225  }
226 
227  return true;
228  }
229 
230 public:
231  // Returns a set containing the values in the receiving set, intersected with
232  // the closed range [Lower, Upper]. Unlike the Range type, this range uses
233  // modular arithmetic, corresponding to the common treatment of C integer
234  // overflow. Thus, if the Lower bound is greater than the Upper bound, the
235  // range is taken to wrap around. This is equivalent to taking the
236  // intersection with the two ranges [Min, Upper] and [Lower, Max],
237  // or, alternatively, /removing/ all integers between Upper and Lower.
238  RangeSet Intersect(BasicValueFactory &BV, Factory &F,
239  llvm::APSInt Lower, llvm::APSInt Upper) const {
240  if (!pin(Lower, Upper))
241  return F.getEmptySet();
242 
243  PrimRangeSet newRanges = F.getEmptySet();
244 
245  PrimRangeSet::iterator i = begin(), e = end();
246  if (Lower <= Upper)
247  IntersectInRange(BV, F, Lower, Upper, newRanges, i, e);
248  else {
249  // The order of the next two statements is important!
250  // IntersectInRange() does not reset the iteration state for i and e.
251  // Therefore, the lower range most be handled first.
252  IntersectInRange(BV, F, BV.getMinValue(Upper), Upper, newRanges, i, e);
253  IntersectInRange(BV, F, Lower, BV.getMaxValue(Lower), newRanges, i, e);
254  }
255 
256  return newRanges;
257  }
258 
259  void print(raw_ostream &os) const {
260  bool isFirst = true;
261  os << "{ ";
262  for (iterator i = begin(), e = end(); i != e; ++i) {
263  if (isFirst)
264  isFirst = false;
265  else
266  os << ", ";
267 
268  os << '[' << i->From().toString(10) << ", " << i->To().toString(10)
269  << ']';
270  }
271  os << " }";
272  }
273 
274  bool operator==(const RangeSet &other) const {
275  return ranges == other.ranges;
276  }
277 };
278 } // end anonymous namespace
279 
282  RangeSet))
283 
284 namespace {
285 class RangeConstraintManager : public SimpleConstraintManager{
286  RangeSet GetRange(ProgramStateRef state, SymbolRef sym);
287 public:
288  RangeConstraintManager(SubEngine *subengine, SValBuilder &SVB)
289  : SimpleConstraintManager(subengine, SVB) {}
290 
291  ProgramStateRef assumeSymNE(ProgramStateRef state, SymbolRef sym,
292  const llvm::APSInt& Int,
293  const llvm::APSInt& Adjustment) override;
294 
295  ProgramStateRef assumeSymEQ(ProgramStateRef state, SymbolRef sym,
296  const llvm::APSInt& Int,
297  const llvm::APSInt& Adjustment) override;
298 
299  ProgramStateRef assumeSymLT(ProgramStateRef state, SymbolRef sym,
300  const llvm::APSInt& Int,
301  const llvm::APSInt& Adjustment) override;
302 
303  ProgramStateRef assumeSymGT(ProgramStateRef state, SymbolRef sym,
304  const llvm::APSInt& Int,
305  const llvm::APSInt& Adjustment) override;
306 
307  ProgramStateRef assumeSymGE(ProgramStateRef state, SymbolRef sym,
308  const llvm::APSInt& Int,
309  const llvm::APSInt& Adjustment) override;
310 
311  ProgramStateRef assumeSymLE(ProgramStateRef state, SymbolRef sym,
312  const llvm::APSInt& Int,
313  const llvm::APSInt& Adjustment) override;
314 
315  const llvm::APSInt* getSymVal(ProgramStateRef St,
316  SymbolRef sym) const override;
317  ConditionTruthVal checkNull(ProgramStateRef State, SymbolRef Sym) override;
318 
319  ProgramStateRef removeDeadBindings(ProgramStateRef St,
320  SymbolReaper& SymReaper) override;
321 
322  void print(ProgramStateRef St, raw_ostream &Out,
323  const char* nl, const char *sep) override;
324 
325 private:
326  RangeSet::Factory F;
327 };
328 
329 } // end anonymous namespace
330 
331 std::unique_ptr<ConstraintManager>
333  return llvm::make_unique<RangeConstraintManager>(Eng, StMgr.getSValBuilder());
334 }
335 
336 const llvm::APSInt* RangeConstraintManager::getSymVal(ProgramStateRef St,
337  SymbolRef sym) const {
338  const ConstraintRangeTy::data_type *T = St->get<ConstraintRange>(sym);
339  return T ? T->getConcreteValue() : nullptr;
340 }
341 
342 ConditionTruthVal RangeConstraintManager::checkNull(ProgramStateRef State,
343  SymbolRef Sym) {
344  const RangeSet *Ranges = State->get<ConstraintRange>(Sym);
345 
346  // If we don't have any information about this symbol, it's underconstrained.
347  if (!Ranges)
348  return ConditionTruthVal();
349 
350  // If we have a concrete value, see if it's zero.
351  if (const llvm::APSInt *Value = Ranges->getConcreteValue())
352  return *Value == 0;
353 
354  BasicValueFactory &BV = getBasicVals();
355  APSIntType IntType = BV.getAPSIntType(Sym->getType());
356  llvm::APSInt Zero = IntType.getZeroValue();
357 
358  // Check if zero is in the set of possible values.
359  if (Ranges->Intersect(BV, F, Zero, Zero).isEmpty())
360  return false;
361 
362  // Zero is a possible value, but it is not the /only/ possible value.
363  return ConditionTruthVal();
364 }
365 
366 /// Scan all symbols referenced by the constraints. If the symbol is not alive
367 /// as marked in LSymbols, mark it as dead in DSymbols.
369 RangeConstraintManager::removeDeadBindings(ProgramStateRef state,
370  SymbolReaper& SymReaper) {
371 
372  ConstraintRangeTy CR = state->get<ConstraintRange>();
373  ConstraintRangeTy::Factory& CRFactory = state->get_context<ConstraintRange>();
374 
375  for (ConstraintRangeTy::iterator I = CR.begin(), E = CR.end(); I != E; ++I) {
376  SymbolRef sym = I.getKey();
377  if (SymReaper.maybeDead(sym))
378  CR = CRFactory.remove(CR, sym);
379  }
380 
381  return state->set<ConstraintRange>(CR);
382 }
383 
384 RangeSet
385 RangeConstraintManager::GetRange(ProgramStateRef state, SymbolRef sym) {
386  if (ConstraintRangeTy::data_type* V = state->get<ConstraintRange>(sym))
387  return *V;
388 
389  // Lazily generate a new RangeSet representing all possible values for the
390  // given symbol type.
391  BasicValueFactory &BV = getBasicVals();
392  QualType T = sym->getType();
393 
394  RangeSet Result(F, BV.getMinValue(T), BV.getMaxValue(T));
395 
396  // Special case: references are known to be non-zero.
397  if (T->isReferenceType()) {
398  APSIntType IntType = BV.getAPSIntType(T);
399  Result = Result.Intersect(BV, F, ++IntType.getZeroValue(),
400  --IntType.getZeroValue());
401  }
402 
403  return Result;
404 }
405 
406 //===------------------------------------------------------------------------===
407 // assumeSymX methods: public interface for RangeConstraintManager.
408 //===------------------------------------------------------------------------===/
409 
410 // The syntax for ranges below is mathematical, using [x, y] for closed ranges
411 // and (x, y) for open ranges. These ranges are modular, corresponding with
412 // a common treatment of C integer overflow. This means that these methods
413 // do not have to worry about overflow; RangeSet::Intersect can handle such a
414 // "wraparound" range.
415 // As an example, the range [UINT_MAX-1, 3) contains five values: UINT_MAX-1,
416 // UINT_MAX, 0, 1, and 2.
417 
419 RangeConstraintManager::assumeSymNE(ProgramStateRef St, SymbolRef Sym,
420  const llvm::APSInt &Int,
421  const llvm::APSInt &Adjustment) {
422  // Before we do any real work, see if the value can even show up.
423  APSIntType AdjustmentType(Adjustment);
424  if (AdjustmentType.testInRange(Int, true) != APSIntType::RTR_Within)
425  return St;
426 
427  llvm::APSInt Lower = AdjustmentType.convert(Int) - Adjustment;
428  llvm::APSInt Upper = Lower;
429  --Lower;
430  ++Upper;
431 
432  // [Int-Adjustment+1, Int-Adjustment-1]
433  // Notice that the lower bound is greater than the upper bound.
434  RangeSet New = GetRange(St, Sym).Intersect(getBasicVals(), F, Upper, Lower);
435  return New.isEmpty() ? nullptr : St->set<ConstraintRange>(Sym, New);
436 }
437 
439 RangeConstraintManager::assumeSymEQ(ProgramStateRef St, SymbolRef Sym,
440  const llvm::APSInt &Int,
441  const llvm::APSInt &Adjustment) {
442  // Before we do any real work, see if the value can even show up.
443  APSIntType AdjustmentType(Adjustment);
444  if (AdjustmentType.testInRange(Int, true) != APSIntType::RTR_Within)
445  return nullptr;
446 
447  // [Int-Adjustment, Int-Adjustment]
448  llvm::APSInt AdjInt = AdjustmentType.convert(Int) - Adjustment;
449  RangeSet New = GetRange(St, Sym).Intersect(getBasicVals(), F, AdjInt, AdjInt);
450  return New.isEmpty() ? nullptr : St->set<ConstraintRange>(Sym, New);
451 }
452 
454 RangeConstraintManager::assumeSymLT(ProgramStateRef St, SymbolRef Sym,
455  const llvm::APSInt &Int,
456  const llvm::APSInt &Adjustment) {
457  // Before we do any real work, see if the value can even show up.
458  APSIntType AdjustmentType(Adjustment);
459  switch (AdjustmentType.testInRange(Int, true)) {
461  return nullptr;
463  break;
465  return St;
466  }
467 
468  // Special case for Int == Min. This is always false.
469  llvm::APSInt ComparisonVal = AdjustmentType.convert(Int);
470  llvm::APSInt Min = AdjustmentType.getMinValue();
471  if (ComparisonVal == Min)
472  return nullptr;
473 
474  llvm::APSInt Lower = Min-Adjustment;
475  llvm::APSInt Upper = ComparisonVal-Adjustment;
476  --Upper;
477 
478  RangeSet New = GetRange(St, Sym).Intersect(getBasicVals(), F, Lower, Upper);
479  return New.isEmpty() ? nullptr : St->set<ConstraintRange>(Sym, New);
480 }
481 
483 RangeConstraintManager::assumeSymGT(ProgramStateRef St, SymbolRef Sym,
484  const llvm::APSInt &Int,
485  const llvm::APSInt &Adjustment) {
486  // Before we do any real work, see if the value can even show up.
487  APSIntType AdjustmentType(Adjustment);
488  switch (AdjustmentType.testInRange(Int, true)) {
490  return St;
492  break;
494  return nullptr;
495  }
496 
497  // Special case for Int == Max. This is always false.
498  llvm::APSInt ComparisonVal = AdjustmentType.convert(Int);
499  llvm::APSInt Max = AdjustmentType.getMaxValue();
500  if (ComparisonVal == Max)
501  return nullptr;
502 
503  llvm::APSInt Lower = ComparisonVal-Adjustment;
504  llvm::APSInt Upper = Max-Adjustment;
505  ++Lower;
506 
507  RangeSet New = GetRange(St, Sym).Intersect(getBasicVals(), F, Lower, Upper);
508  return New.isEmpty() ? nullptr : St->set<ConstraintRange>(Sym, New);
509 }
510 
512 RangeConstraintManager::assumeSymGE(ProgramStateRef St, SymbolRef Sym,
513  const llvm::APSInt &Int,
514  const llvm::APSInt &Adjustment) {
515  // Before we do any real work, see if the value can even show up.
516  APSIntType AdjustmentType(Adjustment);
517  switch (AdjustmentType.testInRange(Int, true)) {
519  return St;
521  break;
523  return nullptr;
524  }
525 
526  // Special case for Int == Min. This is always feasible.
527  llvm::APSInt ComparisonVal = AdjustmentType.convert(Int);
528  llvm::APSInt Min = AdjustmentType.getMinValue();
529  if (ComparisonVal == Min)
530  return St;
531 
532  llvm::APSInt Max = AdjustmentType.getMaxValue();
533  llvm::APSInt Lower = ComparisonVal-Adjustment;
534  llvm::APSInt Upper = Max-Adjustment;
535 
536  RangeSet New = GetRange(St, Sym).Intersect(getBasicVals(), F, Lower, Upper);
537  return New.isEmpty() ? nullptr : St->set<ConstraintRange>(Sym, New);
538 }
539 
541 RangeConstraintManager::assumeSymLE(ProgramStateRef St, SymbolRef Sym,
542  const llvm::APSInt &Int,
543  const llvm::APSInt &Adjustment) {
544  // Before we do any real work, see if the value can even show up.
545  APSIntType AdjustmentType(Adjustment);
546  switch (AdjustmentType.testInRange(Int, true)) {
548  return nullptr;
550  break;
552  return St;
553  }
554 
555  // Special case for Int == Max. This is always feasible.
556  llvm::APSInt ComparisonVal = AdjustmentType.convert(Int);
557  llvm::APSInt Max = AdjustmentType.getMaxValue();
558  if (ComparisonVal == Max)
559  return St;
560 
561  llvm::APSInt Min = AdjustmentType.getMinValue();
562  llvm::APSInt Lower = Min-Adjustment;
563  llvm::APSInt Upper = ComparisonVal-Adjustment;
564 
565  RangeSet New = GetRange(St, Sym).Intersect(getBasicVals(), F, Lower, Upper);
566  return New.isEmpty() ? nullptr : St->set<ConstraintRange>(Sym, New);
567 }
568 
569 //===------------------------------------------------------------------------===
570 // Pretty-printing.
571 //===------------------------------------------------------------------------===/
572 
573 void RangeConstraintManager::print(ProgramStateRef St, raw_ostream &Out,
574  const char* nl, const char *sep) {
575 
576  ConstraintRangeTy Ranges = St->get<ConstraintRange>();
577 
578  if (Ranges.isEmpty()) {
579  Out << nl << sep << "Ranges are empty." << nl;
580  return;
581  }
582 
583  Out << nl << sep << "Ranges of symbol values:";
584  for (ConstraintRangeTy::iterator I=Ranges.begin(), E=Ranges.end(); I!=E; ++I){
585  Out << nl << ' ' << I.getKey() << " : ";
586  I.getData().print(Out);
587  }
588  Out << nl;
589 }
Value is less than the minimum representable value.
Definition: APSIntType.h:78
bool operator==(CanQual< T > x, CanQual< U > y)
bool maybeDead(SymbolRef sym)
If a symbol is known to be live, marks the symbol as live.
std::unique_ptr< ConstraintManager > CreateRangeConstraintManager(ProgramStateManager &statemgr, SubEngine *subengine)
Symbolic value. These values used to capture symbolic execution of the program.
Definition: SymbolManager.h:42
LineState State
bool isReferenceType() const
Definition: Type.h:5241
SmallVector< CharSourceRange, 8 > Ranges
Definition: Format.cpp:1554
Value is representable using this type.
Definition: APSIntType.h:79
A record of the "type" of an APSInt, used for conversions.
Definition: APSIntType.h:20
llvm::APSInt getZeroValue() const LLVM_READONLY
Returns an all-zero value for this type.
Definition: APSIntType.h:56
virtual QualType getType() const =0
ID
Defines the set of possible language-specific address spaces.
Definition: AddressSpaces.h:27
REGISTER_TRAIT_WITH_PROGRAMSTATE(ConstraintRange, CLANG_ENTO_PROGRAMSTATE_MAP(SymbolRef, RangeSet)) namespace
The result type of a method or function.
do v
Definition: arm_acle.h:77
#define CLANG_ENTO_PROGRAMSTATE_MAP(Key, Value)
A class responsible for cleaning up unused symbols.
Value is greater than the maximum representable value.
Definition: APSIntType.h:80
const llvm::APSInt & getMinValue(const llvm::APSInt &v)
const llvm::APSInt & getMaxValue(const llvm::APSInt &v)
APSIntType getAPSIntType(QualType T) const
Returns the type of the APSInt used to store values of the given QualType.