SimpleConstraintManager.cpp revision 6bcf27bb9a4b5c3f79cb44c0e4654a6d7619ad89 
1//== SimpleConstraintManager.cpp --------------------------------*- 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 SimpleConstraintManager, a class that holds code shared
11//  between BasicConstraintManager and RangeConstraintManager.
12//
13//===----------------------------------------------------------------------===//
14
15#include "SimpleConstraintManager.h"
16#include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h"
17#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
19
20namespace clang {
21
22namespace ento {
23
24SimpleConstraintManager::~SimpleConstraintManager() {}
25
26bool SimpleConstraintManager::canReasonAbout(SVal X) const {
27  Optional<nonloc::SymbolVal> SymVal = X.getAs<nonloc::SymbolVal>();
28  if (SymVal && SymVal->isExpression()) {
29    const SymExpr *SE = SymVal->getSymbol();
30
31    if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(SE)) {
32      switch (SIE->getOpcode()) {
33          // We don't reason yet about bitwise-constraints on symbolic values.
34        case BO_And:
35        case BO_Or:
36        case BO_Xor:
37          return false;
38        // We don't reason yet about these arithmetic constraints on
39        // symbolic values.
40        case BO_Mul:
41        case BO_Div:
42        case BO_Rem:
43        case BO_Shl:
44        case BO_Shr:
45          return false;
46        // All other cases.
47        default:
48          return true;
49      }
50    }
51
52    if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(SE)) {
53      if (BinaryOperator::isComparisonOp(SSE->getOpcode())) {
54        // We handle Loc <> Loc comparisons, but not (yet) NonLoc <> NonLoc.
55        if (Loc::isLocType(SSE->getLHS()->getType())) {
56          assert(Loc::isLocType(SSE->getRHS()->getType()));
57          return true;
58        }
59      }
60    }
61
62    return false;
63  }
64
65  return true;
66}
67
68ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state,
69                                               DefinedSVal Cond,
70                                               bool Assumption) {
71  // If we have a Loc value, cast it to a bool NonLoc first.
72  if (Optional<Loc> LV = Cond.getAs<Loc>()) {
73    SValBuilder &SVB = state->getStateManager().getSValBuilder();
74    QualType T;
75    const MemRegion *MR = LV->getAsRegion();
76    if (const TypedRegion *TR = dyn_cast_or_null<TypedRegion>(MR))
77      T = TR->getLocationType();
78    else
79      T = SVB.getContext().VoidPtrTy;
80
81    Cond = SVB.evalCast(*LV, SVB.getContext().BoolTy, T).castAs<DefinedSVal>();
82  }
83
84  return assume(state, Cond.castAs<NonLoc>(), Assumption);
85}
86
87ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state,
88                                               NonLoc cond,
89                                               bool assumption) {
90  state = assumeAux(state, cond, assumption);
91  if (NotifyAssumeClients && SU)
92    return SU->processAssume(state, cond, assumption);
93  return state;
94}
95
96
97ProgramStateRef
98SimpleConstraintManager::assumeAuxForSymbol(ProgramStateRef State,
99                                            SymbolRef Sym, bool Assumption) {
100  BasicValueFactory &BVF = getBasicVals();
101  QualType T = Sym->getType();
102
103  // None of the constraint solvers currently support non-integer types.
104  if (!T->isIntegralOrEnumerationType())
105    return State;
106
107  const llvm::APSInt &zero = BVF.getValue(0, T);
108  if (Assumption)
109    return assumeSymNE(State, Sym, zero, zero);
110  else
111    return assumeSymEQ(State, Sym, zero, zero);
112}
113
114ProgramStateRef SimpleConstraintManager::assumeAux(ProgramStateRef state,
115                                                  NonLoc Cond,
116                                                  bool Assumption) {
117
118  // We cannot reason about SymSymExprs, and can only reason about some
119  // SymIntExprs.
120  if (!canReasonAbout(Cond)) {
121    // Just add the constraint to the expression without trying to simplify.
122    SymbolRef sym = Cond.getAsSymExpr();
123    return assumeAuxForSymbol(state, sym, Assumption);
124  }
125
126  switch (Cond.getSubKind()) {
127  default:
128    llvm_unreachable("'Assume' not implemented for this NonLoc");
129
130  case nonloc::SymbolValKind: {
131    nonloc::SymbolVal SV = Cond.castAs<nonloc::SymbolVal>();
132    SymbolRef sym = SV.getSymbol();
133    assert(sym);
134
135    // Handle SymbolData.
136    if (!SV.isExpression()) {
137      return assumeAuxForSymbol(state, sym, Assumption);
138
139    // Handle symbolic expression.
140    } else if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(sym)) {
141      // We can only simplify expressions whose RHS is an integer.
142
143      BinaryOperator::Opcode op = SE->getOpcode();
144      if (BinaryOperator::isComparisonOp(op)) {
145        if (!Assumption)
146          op = BinaryOperator::negateComparisonOp(op);
147
148        return assumeSymRel(state, SE->getLHS(), op, SE->getRHS());
149      }
150
151    } else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(sym)) {
152      // Translate "a != b" to "(b - a) != 0".
153      // We invert the order of the operands as a heuristic for how loop
154      // conditions are usually written ("begin != end") as compared to length
155      // calculations ("end - begin"). The more correct thing to do would be to
156      // canonicalize "a - b" and "b - a", which would allow us to treat
157      // "a != b" and "b != a" the same.
158      SymbolManager &SymMgr = getSymbolManager();
159      BinaryOperator::Opcode Op = SSE->getOpcode();
160      assert(BinaryOperator::isComparisonOp(Op));
161
162      // For now, we only support comparing pointers.
163      assert(Loc::isLocType(SSE->getLHS()->getType()));
164      assert(Loc::isLocType(SSE->getRHS()->getType()));
165      QualType DiffTy = SymMgr.getContext().getPointerDiffType();
166      SymbolRef Subtraction = SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub,
167                                                   SSE->getLHS(), DiffTy);
168
169      const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy);
170      Op = BinaryOperator::reverseComparisonOp(Op);
171      if (!Assumption)
172        Op = BinaryOperator::negateComparisonOp(Op);
173      return assumeSymRel(state, Subtraction, Op, Zero);
174    }
175
176    // If we get here, there's nothing else we can do but treat the symbol as
177    // opaque.
178    return assumeAuxForSymbol(state, sym, Assumption);
179  }
180
181  case nonloc::ConcreteIntKind: {
182    bool b = Cond.castAs<nonloc::ConcreteInt>().getValue() != 0;
183    bool isFeasible = b ? Assumption : !Assumption;
184    return isFeasible ? state : nullptr;
185  }
186
187  case nonloc::LocAsIntegerKind:
188    return assume(state, Cond.castAs<nonloc::LocAsInteger>().getLoc(),
189                  Assumption);
190  } // end switch
191}
192
193static void computeAdjustment(SymbolRef &Sym, llvm::APSInt &Adjustment) {
194  // Is it a "($sym+constant1)" expression?
195  if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
196    BinaryOperator::Opcode Op = SE->getOpcode();
197    if (Op == BO_Add || Op == BO_Sub) {
198      Sym = SE->getLHS();
199      Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
200
201      // Don't forget to negate the adjustment if it's being subtracted.
202      // This should happen /after/ promotion, in case the value being
203      // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
204      if (Op == BO_Sub)
205        Adjustment = -Adjustment;
206    }
207  }
208}
209
210ProgramStateRef SimpleConstraintManager::assumeSymRel(ProgramStateRef state,
211                                                     const SymExpr *LHS,
212                                                     BinaryOperator::Opcode op,
213                                                     const llvm::APSInt& Int) {
214  assert(BinaryOperator::isComparisonOp(op) &&
215         "Non-comparison ops should be rewritten as comparisons to zero.");
216
217  // Get the type used for calculating wraparound.
218  BasicValueFactory &BVF = getBasicVals();
219  APSIntType WraparoundType = BVF.getAPSIntType(LHS->getType());
220
221  // We only handle simple comparisons of the form "$sym == constant"
222  // or "($sym+constant1) == constant2".
223  // The adjustment is "constant1" in the above expression. It's used to
224  // "slide" the solution range around for modular arithmetic. For example,
225  // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
226  // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
227  // the subclasses of SimpleConstraintManager to handle the adjustment.
228  SymbolRef Sym = LHS;
229  llvm::APSInt Adjustment = WraparoundType.getZeroValue();
230  computeAdjustment(Sym, Adjustment);
231
232  // Convert the right-hand side integer as necessary.
233  APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
234  llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
235
236  // Prefer unsigned comparisons.
237  if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
238      ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
239    Adjustment.setIsSigned(false);
240
241  switch (op) {
242  default:
243    llvm_unreachable("invalid operation not caught by assertion above");
244
245  case BO_EQ:
246    return assumeSymEQ(state, Sym, ConvertedInt, Adjustment);
247
248  case BO_NE:
249    return assumeSymNE(state, Sym, ConvertedInt, Adjustment);
250
251  case BO_GT:
252    return assumeSymGT(state, Sym, ConvertedInt, Adjustment);
253
254  case BO_GE:
255    return assumeSymGE(state, Sym, ConvertedInt, Adjustment);
256
257  case BO_LT:
258    return assumeSymLT(state, Sym, ConvertedInt, Adjustment);
259
260  case BO_LE:
261    return assumeSymLE(state, Sym, ConvertedInt, Adjustment);
262  } // end switch
263}
264
265} // end of namespace ento
266
267} // end of namespace clang
268