SimpleConstraintManager.cpp revision 1d8db493f86761df9470254a2ad572fc6abf1bf6 
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  nonloc::SymbolVal *SymVal = dyn_cast<nonloc::SymbolVal>(&X);
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    return false;
53  }
54
55  return true;
56}
57
58ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state,
59                                               DefinedSVal Cond,
60                                               bool Assumption) {
61  if (isa<NonLoc>(Cond))
62    return assume(state, cast<NonLoc>(Cond), Assumption);
63  else
64    return assume(state, cast<Loc>(Cond), Assumption);
65}
66
67ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state, Loc cond,
68                                               bool assumption) {
69  state = assumeAux(state, cond, assumption);
70  return SU.processAssume(state, cond, assumption);
71}
72
73ProgramStateRef SimpleConstraintManager::assumeAux(ProgramStateRef state,
74                                                  Loc Cond, bool Assumption) {
75  switch (Cond.getSubKind()) {
76  default:
77    assert (false && "'Assume' not implemented for this Loc.");
78    return state;
79
80  case loc::MemRegionKind: {
81    // FIXME: Should this go into the storemanager?
82
83    const MemRegion *R = cast<loc::MemRegionVal>(Cond).getRegion();
84    const SubRegion *SubR = dyn_cast<SubRegion>(R);
85
86    while (SubR) {
87      // FIXME: now we only find the first symbolic region.
88      if (const SymbolicRegion *SymR = dyn_cast<SymbolicRegion>(SubR)) {
89        const llvm::APSInt &zero = getBasicVals().getZeroWithPtrWidth();
90        if (Assumption)
91          return assumeSymNE(state, SymR->getSymbol(), zero, zero);
92        else
93          return assumeSymEQ(state, SymR->getSymbol(), zero, zero);
94      }
95      SubR = dyn_cast<SubRegion>(SubR->getSuperRegion());
96    }
97
98    // FALL-THROUGH.
99  }
100
101  case loc::GotoLabelKind:
102    return Assumption ? state : NULL;
103
104  case loc::ConcreteIntKind: {
105    bool b = cast<loc::ConcreteInt>(Cond).getValue() != 0;
106    bool isFeasible = b ? Assumption : !Assumption;
107    return isFeasible ? state : NULL;
108  }
109  } // end switch
110}
111
112ProgramStateRef SimpleConstraintManager::assume(ProgramStateRef state,
113                                               NonLoc cond,
114                                               bool assumption) {
115  state = assumeAux(state, cond, assumption);
116  return SU.processAssume(state, cond, assumption);
117}
118
119static BinaryOperator::Opcode NegateComparison(BinaryOperator::Opcode op) {
120  // FIXME: This should probably be part of BinaryOperator, since this isn't
121  // the only place it's used. (This code was copied from SimpleSValBuilder.cpp.)
122  switch (op) {
123  default:
124    llvm_unreachable("Invalid opcode.");
125  case BO_LT: return BO_GE;
126  case BO_GT: return BO_LE;
127  case BO_LE: return BO_GT;
128  case BO_GE: return BO_LT;
129  case BO_EQ: return BO_NE;
130  case BO_NE: return BO_EQ;
131  }
132}
133
134
135ProgramStateRef
136SimpleConstraintManager::assumeAuxForSymbol(ProgramStateRef State,
137                                            SymbolRef Sym, bool Assumption) {
138  BasicValueFactory &BVF = getBasicVals();
139  QualType T = Sym->getType(BVF.getContext());
140  const llvm::APSInt &zero = BVF.getValue(0, T);
141  if (Assumption)
142    return assumeSymNE(State, Sym, zero, zero);
143  else
144    return assumeSymEQ(State, Sym, zero, zero);
145}
146
147ProgramStateRef SimpleConstraintManager::assumeAux(ProgramStateRef state,
148                                                  NonLoc Cond,
149                                                  bool Assumption) {
150
151  // We cannot reason about SymSymExprs, and can only reason about some
152  // SymIntExprs.
153  if (!canReasonAbout(Cond)) {
154    // Just add the constraint to the expression without trying to simplify.
155    SymbolRef sym = Cond.getAsSymExpr();
156    return assumeAuxForSymbol(state, sym, Assumption);
157  }
158
159  BasicValueFactory &BasicVals = getBasicVals();
160
161  switch (Cond.getSubKind()) {
162  default:
163    llvm_unreachable("'Assume' not implemented for this NonLoc");
164
165  case nonloc::SymbolValKind: {
166    nonloc::SymbolVal& SV = cast<nonloc::SymbolVal>(Cond);
167    SymbolRef sym = SV.getSymbol();
168    assert(sym);
169
170    // Handle SymbolData.
171    if (!SV.isExpression()) {
172      return assumeAuxForSymbol(state, sym, Assumption);
173
174    // Handle symbolic expression.
175    } else {
176      // We can only simplify expressions whose RHS is an integer.
177      const SymIntExpr *SE = dyn_cast<SymIntExpr>(sym);
178      if (!SE)
179        return assumeAuxForSymbol(state, sym, Assumption);
180
181      BinaryOperator::Opcode op = SE->getOpcode();
182      // Implicitly compare non-comparison expressions to 0.
183      if (!BinaryOperator::isComparisonOp(op)) {
184        QualType T = SE->getType(BasicVals.getContext());
185        const llvm::APSInt &zero = BasicVals.getValue(0, T);
186        op = (Assumption ? BO_NE : BO_EQ);
187        return assumeSymRel(state, SE, op, zero);
188      }
189      // From here on out, op is the real comparison we'll be testing.
190      if (!Assumption)
191        op = NegateComparison(op);
192
193      return assumeSymRel(state, SE->getLHS(), op, SE->getRHS());
194    }
195  }
196
197  case nonloc::ConcreteIntKind: {
198    bool b = cast<nonloc::ConcreteInt>(Cond).getValue() != 0;
199    bool isFeasible = b ? Assumption : !Assumption;
200    return isFeasible ? state : NULL;
201  }
202
203  case nonloc::LocAsIntegerKind:
204    return assumeAux(state, cast<nonloc::LocAsInteger>(Cond).getLoc(),
205                     Assumption);
206  } // end switch
207}
208
209static void computeAdjustment(SymbolRef &Sym, llvm::APSInt &Adjustment) {
210  // Is it a "($sym+constant1)" expression?
211  if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
212    BinaryOperator::Opcode Op = SE->getOpcode();
213    if (Op == BO_Add || Op == BO_Sub) {
214      Sym = SE->getLHS();
215      Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
216
217      // Don't forget to negate the adjustment if it's being subtracted.
218      // This should happen /after/ promotion, in case the value being
219      // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
220      if (Op == BO_Sub)
221        Adjustment = -Adjustment;
222    }
223  }
224}
225
226ProgramStateRef SimpleConstraintManager::assumeSymRel(ProgramStateRef state,
227                                                     const SymExpr *LHS,
228                                                     BinaryOperator::Opcode op,
229                                                     const llvm::APSInt& Int) {
230  assert(BinaryOperator::isComparisonOp(op) &&
231         "Non-comparison ops should be rewritten as comparisons to zero.");
232
233  BasicValueFactory &BVF = getBasicVals();
234  ASTContext &Ctx = BVF.getContext();
235
236  // Get the type used for calculating wraparound.
237  APSIntType WraparoundType = BVF.getAPSIntType(LHS->getType(Ctx));
238
239  // We only handle simple comparisons of the form "$sym == constant"
240  // or "($sym+constant1) == constant2".
241  // The adjustment is "constant1" in the above expression. It's used to
242  // "slide" the solution range around for modular arithmetic. For example,
243  // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
244  // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
245  // the subclasses of SimpleConstraintManager to handle the adjustment.
246  SymbolRef Sym = LHS;
247  llvm::APSInt Adjustment = WraparoundType.getZeroValue();
248  computeAdjustment(Sym, Adjustment);
249
250  // Convert the right-hand side integer as necessary.
251  APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
252  llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
253
254  switch (op) {
255  default:
256    // No logic yet for other operators.  assume the constraint is feasible.
257    return state;
258
259  case BO_EQ:
260    return assumeSymEQ(state, Sym, ConvertedInt, Adjustment);
261
262  case BO_NE:
263    return assumeSymNE(state, Sym, ConvertedInt, Adjustment);
264
265  case BO_GT:
266    return assumeSymGT(state, Sym, ConvertedInt, Adjustment);
267
268  case BO_GE:
269    return assumeSymGE(state, Sym, ConvertedInt, Adjustment);
270
271  case BO_LT:
272    return assumeSymLT(state, Sym, ConvertedInt, Adjustment);
273
274  case BO_LE:
275    return assumeSymLE(state, Sym, ConvertedInt, Adjustment);
276  } // end switch
277}
278
279} // end of namespace ento
280
281} // end of namespace clang
282