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
17namespace clang {
18
19namespace ento {
20
21RangedConstraintManager::~RangedConstraintManager() {}
22
23ProgramStateRef RangedConstraintManager::assumeSym(ProgramStateRef State,
24 SymbolRef Sym,
25 bool Assumption) {
26 Sym = simplify(State, Sym);
27
28 // Handle SymbolData.
29 if (isa<SymbolData>(Val: Sym))
30 return assumeSymUnsupported(State, Sym, Assumption);
31
32 // Handle symbolic expression.
33 if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(Val: Sym)) {
34 // We can only simplify expressions whose RHS is an integer.
35
36 BinaryOperator::Opcode op = SIE->getOpcode();
37 if (BinaryOperator::isComparisonOp(Opc: op) && op != BO_Cmp) {
38 if (!Assumption)
39 op = BinaryOperator::negateComparisonOp(Opc: op);
40
41 return assumeSymRel(State, Sym: SIE->getLHS(), op, Int: SIE->getRHS());
42 }
43
44 // Handle adjustment with non-comparison ops.
45 const llvm::APSInt &Zero = getBasicVals().getValue(X: 0, T: SIE->getType());
46 return assumeSymRel(State, Sym: SIE, op: (Assumption ? BO_NE : BO_EQ), Int: Zero);
47 }
48
49 if (const auto *SSE = dyn_cast<SymSymExpr>(Val: Sym)) {
50 BinaryOperator::Opcode Op = SSE->getOpcode();
51 if (BinaryOperator::isComparisonOp(Opc: Op)) {
52
53 // We convert equality operations for pointers only.
54 if (Loc::isLocType(T: SSE->getLHS()->getType()) &&
55 Loc::isLocType(T: SSE->getRHS()->getType())) {
56 // Translate "a != b" to "(b - a) != 0".
57 // We invert the order of the operands as a heuristic for how loop
58 // conditions are usually written ("begin != end") as compared to length
59 // calculations ("end - begin"). The more correct thing to do would be
60 // to canonicalize "a - b" and "b - a", which would allow us to treat
61 // "a != b" and "b != a" the same.
62
63 SymbolManager &SymMgr = getSymbolManager();
64 QualType DiffTy = SymMgr.getContext().getPointerDiffType();
65 SymbolRef Subtraction = SymMgr.acquire<SymSymExpr>(
66 args: SSE->getRHS(), args: BO_Sub, args: SSE->getLHS(), args&: DiffTy);
67
68 const llvm::APSInt &Zero = getBasicVals().getValue(X: 0, T: DiffTy);
69 Op = BinaryOperator::reverseComparisonOp(Opc: Op);
70 if (!Assumption)
71 Op = BinaryOperator::negateComparisonOp(Opc: Op);
72 return assumeSymRel(State, Sym: Subtraction, op: Op, Int: Zero);
73 }
74
75 if (BinaryOperator::isEqualityOp(Opc: Op)) {
76 SymbolManager &SymMgr = getSymbolManager();
77
78 QualType ExprType = SSE->getType();
79 SymbolRef CanonicalEquality = SymMgr.acquire<SymSymExpr>(
80 args: SSE->getLHS(), args: BO_EQ, args: SSE->getRHS(), args&: ExprType);
81
82 bool WasEqual = SSE->getOpcode() == BO_EQ;
83 bool IsExpectedEqual = WasEqual == Assumption;
84
85 const llvm::APSInt &Zero = getBasicVals().getValue(X: 0, T: ExprType);
86
87 if (IsExpectedEqual) {
88 return assumeSymNE(State, Sym: CanonicalEquality, V: Zero, Adjustment: Zero);
89 }
90
91 return assumeSymEQ(State, Sym: CanonicalEquality, V: Zero, Adjustment: Zero);
92 }
93 }
94 }
95
96 // If we get here, there's nothing else we can do but treat the symbol as
97 // opaque.
98 return assumeSymUnsupported(State, Sym, Assumption);
99}
100
101ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange(
102 ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From,
103 const llvm::APSInt &To, bool InRange) {
104
105 Sym = simplify(State, Sym);
106
107 // Get the type used for calculating wraparound.
108 BasicValueFactory &BVF = getBasicVals();
109 APSIntType WraparoundType = BVF.getAPSIntType(T: Sym->getType());
110
111 llvm::APSInt Adjustment = WraparoundType.getZeroValue();
112 SymbolRef AdjustedSym = Sym;
113 computeAdjustment(Sym&: AdjustedSym, Adjustment);
114
115 // Convert the right-hand side integer as necessary.
116 APSIntType ComparisonType = std::max(a: WraparoundType, b: APSIntType(From));
117 llvm::APSInt ConvertedFrom = ComparisonType.convert(Value: From);
118 llvm::APSInt ConvertedTo = ComparisonType.convert(Value: To);
119
120 // Prefer unsigned comparisons.
121 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
122 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
123 Adjustment.setIsSigned(false);
124
125 if (InRange)
126 return assumeSymWithinInclusiveRange(State, Sym: AdjustedSym, From: ConvertedFrom,
127 To: ConvertedTo, Adjustment);
128 return assumeSymOutsideInclusiveRange(State, Sym: AdjustedSym, From: ConvertedFrom,
129 To: ConvertedTo, Adjustment);
130}
131
132ProgramStateRef
133RangedConstraintManager::assumeSymUnsupported(ProgramStateRef State,
134 SymbolRef Sym, bool Assumption) {
135 Sym = simplify(State, Sym);
136
137 BasicValueFactory &BVF = getBasicVals();
138 QualType T = Sym->getType();
139
140 // Non-integer types are not supported.
141 if (!T->isIntegralOrEnumerationType())
142 return State;
143
144 // Reverse the operation and add directly to state.
145 const llvm::APSInt &Zero = BVF.getValue(X: 0, T);
146 if (Assumption)
147 return assumeSymNE(State, Sym, V: Zero, Adjustment: Zero);
148 else
149 return assumeSymEQ(State, Sym, V: Zero, Adjustment: Zero);
150}
151
152ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State,
153 SymbolRef Sym,
154 BinaryOperator::Opcode Op,
155 const llvm::APSInt &Int) {
156 assert(BinaryOperator::isComparisonOp(Op) &&
157 "Non-comparison ops should be rewritten as comparisons to zero.");
158
159 // Simplification: translate an assume of a constraint of the form
160 // "(exp comparison_op expr) != 0" to true into an assume of
161 // "exp comparison_op expr" to true. (And similarly, an assume of the form
162 // "(exp comparison_op expr) == 0" to true into an assume of
163 // "exp comparison_op expr" to false.)
164 if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) {
165 if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Val: Sym))
166 if (BinaryOperator::isComparisonOp(Opc: SE->getOpcode()))
167 return assumeSym(State, Sym, Assumption: (Op == BO_NE ? true : false));
168 }
169
170 // Get the type used for calculating wraparound.
171 BasicValueFactory &BVF = getBasicVals();
172 APSIntType WraparoundType = BVF.getAPSIntType(T: Sym->getType());
173
174 // We only handle simple comparisons of the form "$sym == constant"
175 // or "($sym+constant1) == constant2".
176 // The adjustment is "constant1" in the above expression. It's used to
177 // "slide" the solution range around for modular arithmetic. For example,
178 // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
179 // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
180 // the subclasses of SimpleConstraintManager to handle the adjustment.
181 llvm::APSInt Adjustment = WraparoundType.getZeroValue();
182 computeAdjustment(Sym, Adjustment);
183
184 // Convert the right-hand side integer as necessary.
185 APSIntType ComparisonType = std::max(a: WraparoundType, b: APSIntType(Int));
186 llvm::APSInt ConvertedInt = ComparisonType.convert(Value: Int);
187
188 // Prefer unsigned comparisons.
189 if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
190 ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
191 Adjustment.setIsSigned(false);
192
193 switch (Op) {
194 default:
195 llvm_unreachable("invalid operation not caught by assertion above");
196
197 case BO_EQ:
198 return assumeSymEQ(State, Sym, V: ConvertedInt, Adjustment);
199
200 case BO_NE:
201 return assumeSymNE(State, Sym, V: ConvertedInt, Adjustment);
202
203 case BO_GT:
204 return assumeSymGT(State, Sym, V: ConvertedInt, Adjustment);
205
206 case BO_GE:
207 return assumeSymGE(State, Sym, V: ConvertedInt, Adjustment);
208
209 case BO_LT:
210 return assumeSymLT(State, Sym, V: ConvertedInt, Adjustment);
211
212 case BO_LE:
213 return assumeSymLE(State, Sym, V: ConvertedInt, Adjustment);
214 } // end switch
215}
216
217void RangedConstraintManager::computeAdjustment(SymbolRef &Sym,
218 llvm::APSInt &Adjustment) {
219 // Is it a "($sym+constant1)" expression?
220 if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Val: Sym)) {
221 BinaryOperator::Opcode Op = SE->getOpcode();
222 if (Op == BO_Add || Op == BO_Sub) {
223 Sym = SE->getLHS();
224 Adjustment = APSIntType(Adjustment).convert(Value: SE->getRHS());
225
226 // Don't forget to negate the adjustment if it's being subtracted.
227 // This should happen /after/ promotion, in case the value being
228 // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
229 if (Op == BO_Sub)
230 Adjustment = -Adjustment;
231 }
232 }
233}
234
235SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym) {
236 SValBuilder &SVB = State->getStateManager().getSValBuilder();
237 return SVB.simplifySVal(State, Val: SVB.makeSymbolVal(Sym));
238}
239
240SymbolRef simplify(ProgramStateRef State, SymbolRef Sym) {
241 SVal SimplifiedVal = simplifyToSVal(State, Sym);
242 if (SymbolRef SimplifiedSym = SimplifiedVal.getAsSymbol())
243 return SimplifiedSym;
244 return Sym;
245}
246
247} // end of namespace ento
248} // end of namespace clang
249