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>(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    // Handle adjustment with non-comparison ops.
45    const llvm::APSInt &Zero = getBasicVals().getValue(0, SIE->getType());
46    return assumeSymRel(State, SIE, (Assumption ? BO_NE : BO_EQ), Zero);
47  }
48
49  if (const auto *SSE = dyn_cast<SymSymExpr>(Sym)) {
50    BinaryOperator::Opcode Op = SSE->getOpcode();
51    if (BinaryOperator::isComparisonOp(Op)) {
52
53      // We convert equality operations for pointers only.
54      if (Loc::isLocType(SSE->getLHS()->getType()) &&
55          Loc::isLocType(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 =
66            SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, SSE->getLHS(), DiffTy);
67
68        const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy);
69        Op = BinaryOperator::reverseComparisonOp(Op);
70        if (!Assumption)
71          Op = BinaryOperator::negateComparisonOp(Op);
72        return assumeSymRel(State, Subtraction, Op, Zero);
73      }
74
75      if (BinaryOperator::isEqualityOp(Op)) {
76        SymbolManager &SymMgr = getSymbolManager();
77
78        QualType ExprType = SSE->getType();
79        SymbolRef CanonicalEquality =
80            SymMgr.getSymSymExpr(SSE->getLHS(), BO_EQ, SSE->getRHS(), ExprType);
81
82        bool WasEqual = SSE->getOpcode() == BO_EQ;
83        bool IsExpectedEqual = WasEqual == Assumption;
84
85        const llvm::APSInt &Zero = getBasicVals().getValue(0, ExprType);
86
87        if (IsExpectedEqual) {
88          return assumeSymNE(State, CanonicalEquality, Zero, Zero);
89        }
90
91        return assumeSymEQ(State, CanonicalEquality, Zero, 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(Sym->getType());
110
111  llvm::APSInt Adjustment = WraparoundType.getZeroValue();
112  SymbolRef AdjustedSym = Sym;
113  computeAdjustment(AdjustedSym, Adjustment);
114
115  // Convert the right-hand side integer as necessary.
116  APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From));
117  llvm::APSInt ConvertedFrom = ComparisonType.convert(From);
118  llvm::APSInt ConvertedTo = ComparisonType.convert(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, AdjustedSym, ConvertedFrom,
127                                         ConvertedTo, Adjustment);
128  return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom,
129                                        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(0, T);
146  if (Assumption)
147    return assumeSymNE(State, Sym, Zero, Zero);
148  else
149    return assumeSymEQ(State, Sym, Zero, 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>(Sym))
166      if (BinaryOperator::isComparisonOp(SE->getOpcode()))
167        return assumeSym(State, Sym, (Op == BO_NE ? true : false));
168  }
169
170  // Get the type used for calculating wraparound.
171  BasicValueFactory &BVF = getBasicVals();
172  APSIntType WraparoundType = BVF.getAPSIntType(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(WraparoundType, APSIntType(Int));
186  llvm::APSInt ConvertedInt = ComparisonType.convert(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, ConvertedInt, Adjustment);
199
200  case BO_NE:
201    return assumeSymNE(State, Sym, ConvertedInt, Adjustment);
202
203  case BO_GT:
204    return assumeSymGT(State, Sym, ConvertedInt, Adjustment);
205
206  case BO_GE:
207    return assumeSymGE(State, Sym, ConvertedInt, Adjustment);
208
209  case BO_LT:
210    return assumeSymLT(State, Sym, ConvertedInt, Adjustment);
211
212  case BO_LE:
213    return assumeSymLE(State, Sym, 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>(Sym)) {
221    BinaryOperator::Opcode Op = SE->getOpcode();
222    if (Op == BO_Add || Op == BO_Sub) {
223      Sym = SE->getLHS();
224      Adjustment = APSIntType(Adjustment).convert(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, 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