SimpleConstraintManager.cpp revision b3b1ae85757a8722caccb742b73ca31b4b53bb0a 
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
141  // None of the constraint solvers currently support non-integer types.
142  if (!T->isIntegerType())
143    return State;
144
145  const llvm::APSInt &zero = BVF.getValue(0, T);
146  if (Assumption)
147    return assumeSymNE(State, Sym, zero, zero);
148  else
149    return assumeSymEQ(State, Sym, zero, zero);
150}
151
152ProgramStateRef SimpleConstraintManager::assumeAux(ProgramStateRef state,
153                                                  NonLoc Cond,
154                                                  bool Assumption) {
155
156  // We cannot reason about SymSymExprs, and can only reason about some
157  // SymIntExprs.
158  if (!canReasonAbout(Cond)) {
159    // Just add the constraint to the expression without trying to simplify.
160    SymbolRef sym = Cond.getAsSymExpr();
161    return assumeAuxForSymbol(state, sym, Assumption);
162  }
163
164  BasicValueFactory &BasicVals = getBasicVals();
165
166  switch (Cond.getSubKind()) {
167  default:
168    llvm_unreachable("'Assume' not implemented for this NonLoc");
169
170  case nonloc::SymbolValKind: {
171    nonloc::SymbolVal& SV = cast<nonloc::SymbolVal>(Cond);
172    SymbolRef sym = SV.getSymbol();
173    assert(sym);
174
175    // Handle SymbolData.
176    if (!SV.isExpression()) {
177      return assumeAuxForSymbol(state, sym, Assumption);
178
179    // Handle symbolic expression.
180    } else {
181      // We can only simplify expressions whose RHS is an integer.
182      const SymIntExpr *SE = dyn_cast<SymIntExpr>(sym);
183      if (!SE)
184        return assumeAuxForSymbol(state, sym, Assumption);
185
186      BinaryOperator::Opcode op = SE->getOpcode();
187      // Implicitly compare non-comparison expressions to 0.
188      if (!BinaryOperator::isComparisonOp(op)) {
189        QualType T = SE->getType(BasicVals.getContext());
190        const llvm::APSInt &zero = BasicVals.getValue(0, T);
191        op = (Assumption ? BO_NE : BO_EQ);
192        return assumeSymRel(state, SE, op, zero);
193      }
194      // From here on out, op is the real comparison we'll be testing.
195      if (!Assumption)
196        op = NegateComparison(op);
197
198      return assumeSymRel(state, SE->getLHS(), op, SE->getRHS());
199    }
200  }
201
202  case nonloc::ConcreteIntKind: {
203    bool b = cast<nonloc::ConcreteInt>(Cond).getValue() != 0;
204    bool isFeasible = b ? Assumption : !Assumption;
205    return isFeasible ? state : NULL;
206  }
207
208  case nonloc::LocAsIntegerKind:
209    return assumeAux(state, cast<nonloc::LocAsInteger>(Cond).getLoc(),
210                     Assumption);
211  } // end switch
212}
213
214static void computeAdjustment(SymbolRef &Sym, llvm::APSInt &Adjustment) {
215  // Is it a "($sym+constant1)" expression?
216  if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
217    BinaryOperator::Opcode Op = SE->getOpcode();
218    if (Op == BO_Add || Op == BO_Sub) {
219      Sym = SE->getLHS();
220      Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
221
222      // Don't forget to negate the adjustment if it's being subtracted.
223      // This should happen /after/ promotion, in case the value being
224      // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
225      if (Op == BO_Sub)
226        Adjustment = -Adjustment;
227    }
228  }
229}
230
231ProgramStateRef SimpleConstraintManager::assumeSymRel(ProgramStateRef state,
232                                                     const SymExpr *LHS,
233                                                     BinaryOperator::Opcode op,
234                                                     const llvm::APSInt& Int) {
235  assert(BinaryOperator::isComparisonOp(op) &&
236         "Non-comparison ops should be rewritten as comparisons to zero.");
237
238  BasicValueFactory &BVF = getBasicVals();
239  ASTContext &Ctx = BVF.getContext();
240
241  // Get the type used for calculating wraparound.
242  APSIntType WraparoundType = BVF.getAPSIntType(LHS->getType(Ctx));
243
244  // We only handle simple comparisons of the form "$sym == constant"
245  // or "($sym+constant1) == constant2".
246  // The adjustment is "constant1" in the above expression. It's used to
247  // "slide" the solution range around for modular arithmetic. For example,
248  // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
249  // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
250  // the subclasses of SimpleConstraintManager to handle the adjustment.
251  SymbolRef Sym = LHS;
252  llvm::APSInt Adjustment = WraparoundType.getZeroValue();
253  computeAdjustment(Sym, Adjustment);
254
255  // Convert the right-hand side integer as necessary.
256  APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
257  llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
258
259  switch (op) {
260  default:
261    // No logic yet for other operators.  assume the constraint is feasible.
262    return state;
263
264  case BO_EQ:
265    return assumeSymEQ(state, Sym, ConvertedInt, Adjustment);
266
267  case BO_NE:
268    return assumeSymNE(state, Sym, ConvertedInt, Adjustment);
269
270  case BO_GT:
271    return assumeSymGT(state, Sym, ConvertedInt, Adjustment);
272
273  case BO_GE:
274    return assumeSymGE(state, Sym, ConvertedInt, Adjustment);
275
276  case BO_LT:
277    return assumeSymLT(state, Sym, ConvertedInt, Adjustment);
278
279  case BO_LE:
280    return assumeSymLE(state, Sym, ConvertedInt, Adjustment);
281  } // end switch
282}
283
284} // end of namespace ento
285
286} // end of namespace clang
287