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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 
20 namespace clang {
21 
22 namespace ento {
23 
~SimpleConstraintManager()24 SimpleConstraintManager::~SimpleConstraintManager() {}
25 
canReasonAbout(SVal X) const26 bool 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 
assume(ProgramStateRef state,DefinedSVal Cond,bool Assumption)68 ProgramStateRef 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 
assume(ProgramStateRef state,NonLoc cond,bool assumption)87 ProgramStateRef 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 
97 ProgramStateRef
assumeAuxForSymbol(ProgramStateRef State,SymbolRef Sym,bool Assumption)98 SimpleConstraintManager::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 
assumeAux(ProgramStateRef state,NonLoc Cond,bool Assumption)114 ProgramStateRef 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 
assumeWithinInclusiveRange(ProgramStateRef State,NonLoc Value,const llvm::APSInt & From,const llvm::APSInt & To,bool InRange)193 ProgramStateRef SimpleConstraintManager::assumeWithinInclusiveRange(
194     ProgramStateRef State, NonLoc Value, const llvm::APSInt &From,
195     const llvm::APSInt &To, bool InRange) {
196 
197   assert(From.isUnsigned() == To.isUnsigned() &&
198          From.getBitWidth() == To.getBitWidth() &&
199          "Values should have same types!");
200 
201   if (!canReasonAbout(Value)) {
202     // Just add the constraint to the expression without trying to simplify.
203     SymbolRef Sym = Value.getAsSymExpr();
204     assert(Sym);
205     return assumeSymWithinInclusiveRange(State, Sym, From, To, InRange);
206   }
207 
208   switch (Value.getSubKind()) {
209   default:
210     llvm_unreachable("'assumeWithinInclusiveRange' is not implemented"
211                      "for this NonLoc");
212 
213   case nonloc::LocAsIntegerKind:
214   case nonloc::SymbolValKind: {
215     if (SymbolRef Sym = Value.getAsSymbol())
216       return assumeSymWithinInclusiveRange(State, Sym, From, To, InRange);
217     return State;
218   } // end switch
219 
220   case nonloc::ConcreteIntKind: {
221     const llvm::APSInt &IntVal = Value.castAs<nonloc::ConcreteInt>().getValue();
222     bool IsInRange = IntVal >= From && IntVal <= To;
223     bool isFeasible = (IsInRange == InRange);
224     return isFeasible ? State : nullptr;
225   }
226   } // end switch
227 }
228 
computeAdjustment(SymbolRef & Sym,llvm::APSInt & Adjustment)229 static void computeAdjustment(SymbolRef &Sym, llvm::APSInt &Adjustment) {
230   // Is it a "($sym+constant1)" expression?
231   if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
232     BinaryOperator::Opcode Op = SE->getOpcode();
233     if (Op == BO_Add || Op == BO_Sub) {
234       Sym = SE->getLHS();
235       Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
236 
237       // Don't forget to negate the adjustment if it's being subtracted.
238       // This should happen /after/ promotion, in case the value being
239       // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
240       if (Op == BO_Sub)
241         Adjustment = -Adjustment;
242     }
243   }
244 }
245 
assumeSymRel(ProgramStateRef state,const SymExpr * LHS,BinaryOperator::Opcode op,const llvm::APSInt & Int)246 ProgramStateRef SimpleConstraintManager::assumeSymRel(ProgramStateRef state,
247                                                      const SymExpr *LHS,
248                                                      BinaryOperator::Opcode op,
249                                                      const llvm::APSInt& Int) {
250   assert(BinaryOperator::isComparisonOp(op) &&
251          "Non-comparison ops should be rewritten as comparisons to zero.");
252 
253   // Get the type used for calculating wraparound.
254   BasicValueFactory &BVF = getBasicVals();
255   APSIntType WraparoundType = BVF.getAPSIntType(LHS->getType());
256 
257   // We only handle simple comparisons of the form "$sym == constant"
258   // or "($sym+constant1) == constant2".
259   // The adjustment is "constant1" in the above expression. It's used to
260   // "slide" the solution range around for modular arithmetic. For example,
261   // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
262   // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
263   // the subclasses of SimpleConstraintManager to handle the adjustment.
264   SymbolRef Sym = LHS;
265   llvm::APSInt Adjustment = WraparoundType.getZeroValue();
266   computeAdjustment(Sym, Adjustment);
267 
268   // Convert the right-hand side integer as necessary.
269   APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
270   llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
271 
272   // Prefer unsigned comparisons.
273   if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
274       ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
275     Adjustment.setIsSigned(false);
276 
277   switch (op) {
278   default:
279     llvm_unreachable("invalid operation not caught by assertion above");
280 
281   case BO_EQ:
282     return assumeSymEQ(state, Sym, ConvertedInt, Adjustment);
283 
284   case BO_NE:
285     return assumeSymNE(state, Sym, ConvertedInt, Adjustment);
286 
287   case BO_GT:
288     return assumeSymGT(state, Sym, ConvertedInt, Adjustment);
289 
290   case BO_GE:
291     return assumeSymGE(state, Sym, ConvertedInt, Adjustment);
292 
293   case BO_LT:
294     return assumeSymLT(state, Sym, ConvertedInt, Adjustment);
295 
296   case BO_LE:
297     return assumeSymLE(state, Sym, ConvertedInt, Adjustment);
298   } // end switch
299 }
300 
301 ProgramStateRef
assumeSymWithinInclusiveRange(ProgramStateRef State,SymbolRef Sym,const llvm::APSInt & From,const llvm::APSInt & To,bool InRange)302 SimpleConstraintManager::assumeSymWithinInclusiveRange(ProgramStateRef State,
303                                                        SymbolRef Sym,
304                                                        const llvm::APSInt &From,
305                                                        const llvm::APSInt &To,
306                                                        bool InRange) {
307   // Get the type used for calculating wraparound.
308   BasicValueFactory &BVF = getBasicVals();
309   APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
310 
311   llvm::APSInt Adjustment = WraparoundType.getZeroValue();
312   SymbolRef AdjustedSym = Sym;
313   computeAdjustment(AdjustedSym, Adjustment);
314 
315   // Convert the right-hand side integer as necessary.
316   APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From));
317   llvm::APSInt ConvertedFrom = ComparisonType.convert(From);
318   llvm::APSInt ConvertedTo = ComparisonType.convert(To);
319 
320   // Prefer unsigned comparisons.
321   if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
322       ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
323     Adjustment.setIsSigned(false);
324 
325   if (InRange)
326     return assumeSymbolWithinInclusiveRange(State, AdjustedSym, ConvertedFrom,
327                                             ConvertedTo, Adjustment);
328   return assumeSymbolOutOfInclusiveRange(State, AdjustedSym, ConvertedFrom,
329                                          ConvertedTo, Adjustment);
330 }
331 
332 } // end of namespace ento
333 
334 } // end of namespace clang
335