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