clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp

   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   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
 101 ProgramStateRef 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
 132 ProgramStateRef
 133 RangedConstraintManager::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
 152 ProgramStateRef 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
 217 void 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
 235 SVal simplifyToSVal(ProgramStateRef State, SymbolRef Sym) {
 236   SValBuilder &SVB = State->getStateManager().getSValBuilder();
 237   return SVB.simplifySVal(State, SVB.makeSymbolVal(Sym));
 238 }
 239
 240 SymbolRef 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