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 
21 RangedConstraintManager::~RangedConstraintManager() {}
22 
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     // Translate "a != b" to "(b - a) != 0".
44     // We invert the order of the operands as a heuristic for how loop
45     // conditions are usually written ("begin != end") as compared to length
46     // calculations ("end - begin"). The more correct thing to do would be to
47     // canonicalize "a - b" and "b - a", which would allow us to treat
48     // "a != b" and "b != a" the same.
49     SymbolManager &SymMgr = getSymbolManager();
50     BinaryOperator::Opcode Op = SSE->getOpcode();
51     assert(BinaryOperator::isComparisonOp(Op));
52 
53     // For now, we only support comparing pointers.
54     if (Loc::isLocType(SSE->getLHS()->getType()) &&
55         Loc::isLocType(SSE->getRHS()->getType())) {
56       QualType DiffTy = SymMgr.getContext().getPointerDiffType();
57       SymbolRef Subtraction =
58           SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, SSE->getLHS(), DiffTy);
59 
60       const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy);
61       Op = BinaryOperator::reverseComparisonOp(Op);
62       if (!Assumption)
63         Op = BinaryOperator::negateComparisonOp(Op);
64       return assumeSymRel(State, Subtraction, Op, Zero);
65     }
66   }
67 
68   // If we get here, there's nothing else we can do but treat the symbol as
69   // opaque.
70   return assumeSymUnsupported(State, Sym, Assumption);
71 }
72 
73 ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange(
74     ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From,
75     const llvm::APSInt &To, bool InRange) {
76   // Get the type used for calculating wraparound.
77   BasicValueFactory &BVF = getBasicVals();
78   APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
79 
80   llvm::APSInt Adjustment = WraparoundType.getZeroValue();
81   SymbolRef AdjustedSym = Sym;
82   computeAdjustment(AdjustedSym, Adjustment);
83 
84   // Convert the right-hand side integer as necessary.
85   APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From));
86   llvm::APSInt ConvertedFrom = ComparisonType.convert(From);
87   llvm::APSInt ConvertedTo = ComparisonType.convert(To);
88 
89   // Prefer unsigned comparisons.
90   if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
91       ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
92     Adjustment.setIsSigned(false);
93 
94   if (InRange)
95     return assumeSymWithinInclusiveRange(State, AdjustedSym, ConvertedFrom,
96                                          ConvertedTo, Adjustment);
97   return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom,
98                                         ConvertedTo, Adjustment);
99 }
100 
101 ProgramStateRef
102 RangedConstraintManager::assumeSymUnsupported(ProgramStateRef State,
103                                               SymbolRef Sym, bool Assumption) {
104   BasicValueFactory &BVF = getBasicVals();
105   QualType T = Sym->getType();
106 
107   // Non-integer types are not supported.
108   if (!T->isIntegralOrEnumerationType())
109     return State;
110 
111   // Reverse the operation and add directly to state.
112   const llvm::APSInt &Zero = BVF.getValue(0, T);
113   if (Assumption)
114     return assumeSymNE(State, Sym, Zero, Zero);
115   else
116     return assumeSymEQ(State, Sym, Zero, Zero);
117 }
118 
119 ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State,
120                                                       SymbolRef Sym,
121                                                       BinaryOperator::Opcode Op,
122                                                       const llvm::APSInt &Int) {
123   assert(BinaryOperator::isComparisonOp(Op) &&
124          "Non-comparison ops should be rewritten as comparisons to zero.");
125 
126   // Simplification: translate an assume of a constraint of the form
127   // "(exp comparison_op expr) != 0" to true into an assume of
128   // "exp comparison_op expr" to true. (And similarly, an assume of the form
129   // "(exp comparison_op expr) == 0" to true into an assume of
130   // "exp comparison_op expr" to false.)
131   if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) {
132     if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Sym))
133       if (BinaryOperator::isComparisonOp(SE->getOpcode()))
134         return assumeSym(State, Sym, (Op == BO_NE ? true : false));
135   }
136 
137   // Get the type used for calculating wraparound.
138   BasicValueFactory &BVF = getBasicVals();
139   APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
140 
141   // We only handle simple comparisons of the form "$sym == constant"
142   // or "($sym+constant1) == constant2".
143   // The adjustment is "constant1" in the above expression. It's used to
144   // "slide" the solution range around for modular arithmetic. For example,
145   // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
146   // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
147   // the subclasses of SimpleConstraintManager to handle the adjustment.
148   llvm::APSInt Adjustment = WraparoundType.getZeroValue();
149   computeAdjustment(Sym, Adjustment);
150 
151   // Convert the right-hand side integer as necessary.
152   APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
153   llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
154 
155   // Prefer unsigned comparisons.
156   if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
157       ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
158     Adjustment.setIsSigned(false);
159 
160   switch (Op) {
161   default:
162     llvm_unreachable("invalid operation not caught by assertion above");
163 
164   case BO_EQ:
165     return assumeSymEQ(State, Sym, ConvertedInt, Adjustment);
166 
167   case BO_NE:
168     return assumeSymNE(State, Sym, ConvertedInt, Adjustment);
169 
170   case BO_GT:
171     return assumeSymGT(State, Sym, ConvertedInt, Adjustment);
172 
173   case BO_GE:
174     return assumeSymGE(State, Sym, ConvertedInt, Adjustment);
175 
176   case BO_LT:
177     return assumeSymLT(State, Sym, ConvertedInt, Adjustment);
178 
179   case BO_LE:
180     return assumeSymLE(State, Sym, ConvertedInt, Adjustment);
181   } // end switch
182 }
183 
184 void RangedConstraintManager::computeAdjustment(SymbolRef &Sym,
185                                                 llvm::APSInt &Adjustment) {
186   // Is it a "($sym+constant1)" expression?
187   if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
188     BinaryOperator::Opcode Op = SE->getOpcode();
189     if (Op == BO_Add || Op == BO_Sub) {
190       Sym = SE->getLHS();
191       Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
192 
193       // Don't forget to negate the adjustment if it's being subtracted.
194       // This should happen /after/ promotion, in case the value being
195       // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
196       if (Op == BO_Sub)
197         Adjustment = -Adjustment;
198     }
199   }
200 }
201 
202 void *ProgramStateTrait<ConstraintRange>::GDMIndex() {
203   static int Index;
204   return &Index;
205 }
206 
207 } // end of namespace ento
208 
209 } // end of namespace clang
210