1 //== RangedConstraintManager.cpp --------------------------------*- C++ -*--==//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines RangedConstraintManager, a class that provides a
10 // range-based constraint manager interface.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
15 #include "clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h"
16
17 namespace clang {
18
19 namespace ento {
20
~RangedConstraintManager()21 RangedConstraintManager::~RangedConstraintManager() {}
22
assumeSym(ProgramStateRef State,SymbolRef Sym,bool Assumption)23 ProgramStateRef RangedConstraintManager::assumeSym(ProgramStateRef State,
24 SymbolRef Sym,
25 bool Assumption) {
26 Sym = simplify(State, Sym);
27
28 // Handle SymbolData.
29 if (isa<SymbolData>(Sym))
30 return assumeSymUnsupported(State, Sym, Assumption);
31
32 // Handle symbolic expression.
33 if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(Sym)) {
34 // We can only simplify expressions whose RHS is an integer.
35
36 BinaryOperator::Opcode op = SIE->getOpcode();
37 if (BinaryOperator::isComparisonOp(op) && op != BO_Cmp) {
38 if (!Assumption)
39 op = BinaryOperator::negateComparisonOp(op);
40
41 return assumeSymRel(State, SIE->getLHS(), op, SIE->getRHS());
42 }
43
44 } else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(Sym)) {
45 BinaryOperator::Opcode Op = SSE->getOpcode();
46 assert(BinaryOperator::isComparisonOp(Op));
47
48 // We convert equality operations for pointers only.
49 if (Loc::isLocType(SSE->getLHS()->getType()) &&
50 Loc::isLocType(SSE->getRHS()->getType())) {
51 // Translate "a != b" to "(b - a) != 0".
52 // We invert the order of the operands as a heuristic for how loop
53 // conditions are usually written ("begin != end") as compared to length
54 // calculations ("end - begin"). The more correct thing to do would be to
55 // canonicalize "a - b" and "b - a", which would allow us to treat
56 // "a != b" and "b != a" the same.
57
58 SymbolManager &SymMgr = getSymbolManager();
59 QualType DiffTy = SymMgr.getContext().getPointerDiffType();
60 SymbolRef Subtraction =
61 SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, SSE->getLHS(), DiffTy);
62
63 const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy);
64 Op = BinaryOperator::reverseComparisonOp(Op);
65 if (!Assumption)
66 Op = BinaryOperator::negateComparisonOp(Op);
67 return assumeSymRel(State, Subtraction, Op, Zero);
68 }
69
70 if (BinaryOperator::isEqualityOp(Op)) {
71 SymbolManager &SymMgr = getSymbolManager();
72
73 QualType ExprType = SSE->getType();
74 SymbolRef CanonicalEquality =
75 SymMgr.getSymSymExpr(SSE->getLHS(), BO_EQ, SSE->getRHS(), ExprType);
76
77 bool WasEqual = SSE->getOpcode() == BO_EQ;
78 bool IsExpectedEqual = WasEqual == Assumption;
79
80 const llvm::APSInt &Zero = getBasicVals().getValue(0, ExprType);
81
82 if (IsExpectedEqual) {
83 return assumeSymNE(State, CanonicalEquality, Zero, Zero);
84 }
85
86 return assumeSymEQ(State, CanonicalEquality, Zero, Zero);
87 }
88 }
89
90 // If we get here, there's nothing else we can do but treat the symbol as
91 // opaque.
92 return assumeSymUnsupported(State, Sym, Assumption);
93 }
94
assumeSymInclusiveRange(ProgramStateRef State,SymbolRef Sym,const llvm::APSInt & From,const llvm::APSInt & To,bool InRange)95 ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange(
96 ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From,
97 const llvm::APSInt &To, bool InRange) {
98
99 Sym = simplify(State, Sym);
100
101 // Get the type used for calculating wraparound.
102 BasicValueFactory &BVF = getBasicVals();
103 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
104
105 llvm::APSInt Adjustment = WraparoundType.getZeroValue();
106 SymbolRef AdjustedSym = Sym;
107 computeAdjustment(AdjustedSym, Adjustment);
108
109 // Convert the right-hand side integer as necessary.
110 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From));
111 llvm::APSInt ConvertedFrom = ComparisonType.convert(From);
112 llvm::APSInt ConvertedTo = ComparisonType.convert(To);
113
114 // Prefer unsigned comparisons.
115 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
116 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
117 Adjustment.setIsSigned(false);
118
119 if (InRange)
120 return assumeSymWithinInclusiveRange(State, AdjustedSym, ConvertedFrom,
121 ConvertedTo, Adjustment);
122 return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom,
123 ConvertedTo, Adjustment);
124 }
125
126 ProgramStateRef
assumeSymUnsupported(ProgramStateRef State,SymbolRef Sym,bool Assumption)127 RangedConstraintManager::assumeSymUnsupported(ProgramStateRef State,
128 SymbolRef Sym, bool Assumption) {
129 Sym = simplify(State, Sym);
130
131 BasicValueFactory &BVF = getBasicVals();
132 QualType T = Sym->getType();
133
134 // Non-integer types are not supported.
135 if (!T->isIntegralOrEnumerationType())
136 return State;
137
138 // Reverse the operation and add directly to state.
139 const llvm::APSInt &Zero = BVF.getValue(0, T);
140 if (Assumption)
141 return assumeSymNE(State, Sym, Zero, Zero);
142 else
143 return assumeSymEQ(State, Sym, Zero, Zero);
144 }
145
assumeSymRel(ProgramStateRef State,SymbolRef Sym,BinaryOperator::Opcode Op,const llvm::APSInt & Int)146 ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State,
147 SymbolRef Sym,
148 BinaryOperator::Opcode Op,
149 const llvm::APSInt &Int) {
150 assert(BinaryOperator::isComparisonOp(Op) &&
151 "Non-comparison ops should be rewritten as comparisons to zero.");
152
153 // Simplification: translate an assume of a constraint of the form
154 // "(exp comparison_op expr) != 0" to true into an assume of
155 // "exp comparison_op expr" to true. (And similarly, an assume of the form
156 // "(exp comparison_op expr) == 0" to true into an assume of
157 // "exp comparison_op expr" to false.)
158 if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) {
159 if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Sym))
160 if (BinaryOperator::isComparisonOp(SE->getOpcode()))
161 return assumeSym(State, Sym, (Op == BO_NE ? true : false));
162 }
163
164 // Get the type used for calculating wraparound.
165 BasicValueFactory &BVF = getBasicVals();
166 APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
167
168 // We only handle simple comparisons of the form "$sym == constant"
169 // or "($sym+constant1) == constant2".
170 // The adjustment is "constant1" in the above expression. It's used to
171 // "slide" the solution range around for modular arithmetic. For example,
172 // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
173 // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
174 // the subclasses of SimpleConstraintManager to handle the adjustment.
175 llvm::APSInt Adjustment = WraparoundType.getZeroValue();
176 computeAdjustment(Sym, Adjustment);
177
178 // Convert the right-hand side integer as necessary.
179 APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
180 llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
181
182 // Prefer unsigned comparisons.
183 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
184 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
185 Adjustment.setIsSigned(false);
186
187 switch (Op) {
188 default:
189 llvm_unreachable("invalid operation not caught by assertion above");
190
191 case BO_EQ:
192 return assumeSymEQ(State, Sym, ConvertedInt, Adjustment);
193
194 case BO_NE:
195 return assumeSymNE(State, Sym, ConvertedInt, Adjustment);
196
197 case BO_GT:
198 return assumeSymGT(State, Sym, ConvertedInt, Adjustment);
199
200 case BO_GE:
201 return assumeSymGE(State, Sym, ConvertedInt, Adjustment);
202
203 case BO_LT:
204 return assumeSymLT(State, Sym, ConvertedInt, Adjustment);
205
206 case BO_LE:
207 return assumeSymLE(State, Sym, ConvertedInt, Adjustment);
208 } // end switch
209 }
210
computeAdjustment(SymbolRef & Sym,llvm::APSInt & Adjustment)211 void RangedConstraintManager::computeAdjustment(SymbolRef &Sym,
212 llvm::APSInt &Adjustment) {
213 // Is it a "($sym+constant1)" expression?
214 if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
215 BinaryOperator::Opcode Op = SE->getOpcode();
216 if (Op == BO_Add || Op == BO_Sub) {
217 Sym = SE->getLHS();
218 Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
219
220 // Don't forget to negate the adjustment if it's being subtracted.
221 // This should happen /after/ promotion, in case the value being
222 // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
223 if (Op == BO_Sub)
224 Adjustment = -Adjustment;
225 }
226 }
227 }
228
simplify(ProgramStateRef State,SymbolRef Sym)229 SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) {
230 SValBuilder &SVB = State->getStateManager().getSValBuilder();
231 SVal SimplifiedVal = SVB.simplifySVal(State, SVB.makeSymbolVal(Sym));
232 if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol())
233 return SimplifiedSym;
234 return Sym;
235 }
236
237 } // end of namespace ento
238 } // end of namespace clang
239