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