224 lines
8.6 KiB
C++
224 lines
8.6 KiB
C++
//== RangedConstraintManager.cpp --------------------------------*- C++ -*--==//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines RangedConstraintManager, a class that provides a
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// range-based constraint manager interface.
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//
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//===----------------------------------------------------------------------===//
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#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/RangedConstraintManager.h"
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namespace clang {
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namespace ento {
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RangedConstraintManager::~RangedConstraintManager() {}
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ProgramStateRef RangedConstraintManager::assumeSym(ProgramStateRef State,
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SymbolRef Sym,
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bool Assumption) {
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// Handle SymbolData.
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if (isa<SymbolData>(Sym)) {
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return assumeSymUnsupported(State, Sym, Assumption);
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// Handle symbolic expression.
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} else if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(Sym)) {
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// We can only simplify expressions whose RHS is an integer.
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BinaryOperator::Opcode op = SIE->getOpcode();
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if (BinaryOperator::isComparisonOp(op) && op != BO_Cmp) {
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if (!Assumption)
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op = BinaryOperator::negateComparisonOp(op);
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return assumeSymRel(State, SIE->getLHS(), op, SIE->getRHS());
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}
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} else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(Sym)) {
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BinaryOperator::Opcode Op = SSE->getOpcode();
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assert(BinaryOperator::isComparisonOp(Op));
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// We convert equality operations for pointers only.
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if (Loc::isLocType(SSE->getLHS()->getType()) &&
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Loc::isLocType(SSE->getRHS()->getType())) {
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// Translate "a != b" to "(b - a) != 0".
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// We invert the order of the operands as a heuristic for how loop
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// conditions are usually written ("begin != end") as compared to length
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// calculations ("end - begin"). The more correct thing to do would be to
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// canonicalize "a - b" and "b - a", which would allow us to treat
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// "a != b" and "b != a" the same.
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SymbolManager &SymMgr = getSymbolManager();
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QualType DiffTy = SymMgr.getContext().getPointerDiffType();
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SymbolRef Subtraction =
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SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, SSE->getLHS(), DiffTy);
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const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy);
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Op = BinaryOperator::reverseComparisonOp(Op);
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if (!Assumption)
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Op = BinaryOperator::negateComparisonOp(Op);
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return assumeSymRel(State, Subtraction, Op, Zero);
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}
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if (BinaryOperator::isEqualityOp(Op)) {
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SymbolManager &SymMgr = getSymbolManager();
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QualType ExprType = SSE->getType();
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SymbolRef CanonicalEquality =
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SymMgr.getSymSymExpr(SSE->getLHS(), BO_EQ, SSE->getRHS(), ExprType);
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bool WasEqual = SSE->getOpcode() == BO_EQ;
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bool IsExpectedEqual = WasEqual == Assumption;
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const llvm::APSInt &Zero = getBasicVals().getValue(0, ExprType);
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if (IsExpectedEqual) {
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return assumeSymNE(State, CanonicalEquality, Zero, Zero);
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}
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return assumeSymEQ(State, CanonicalEquality, Zero, Zero);
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}
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}
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// If we get here, there's nothing else we can do but treat the symbol as
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// opaque.
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return assumeSymUnsupported(State, Sym, Assumption);
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}
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ProgramStateRef RangedConstraintManager::assumeSymInclusiveRange(
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ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From,
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const llvm::APSInt &To, bool InRange) {
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// Get the type used for calculating wraparound.
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BasicValueFactory &BVF = getBasicVals();
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APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
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llvm::APSInt Adjustment = WraparoundType.getZeroValue();
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SymbolRef AdjustedSym = Sym;
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computeAdjustment(AdjustedSym, Adjustment);
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// Convert the right-hand side integer as necessary.
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APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From));
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llvm::APSInt ConvertedFrom = ComparisonType.convert(From);
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llvm::APSInt ConvertedTo = ComparisonType.convert(To);
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// Prefer unsigned comparisons.
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if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
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ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
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Adjustment.setIsSigned(false);
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if (InRange)
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return assumeSymWithinInclusiveRange(State, AdjustedSym, ConvertedFrom,
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ConvertedTo, Adjustment);
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return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom,
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ConvertedTo, Adjustment);
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}
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ProgramStateRef
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RangedConstraintManager::assumeSymUnsupported(ProgramStateRef State,
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SymbolRef Sym, bool Assumption) {
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BasicValueFactory &BVF = getBasicVals();
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QualType T = Sym->getType();
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// Non-integer types are not supported.
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if (!T->isIntegralOrEnumerationType())
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return State;
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// Reverse the operation and add directly to state.
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const llvm::APSInt &Zero = BVF.getValue(0, T);
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if (Assumption)
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return assumeSymNE(State, Sym, Zero, Zero);
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else
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return assumeSymEQ(State, Sym, Zero, Zero);
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}
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ProgramStateRef RangedConstraintManager::assumeSymRel(ProgramStateRef State,
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SymbolRef Sym,
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BinaryOperator::Opcode Op,
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const llvm::APSInt &Int) {
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assert(BinaryOperator::isComparisonOp(Op) &&
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"Non-comparison ops should be rewritten as comparisons to zero.");
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// Simplification: translate an assume of a constraint of the form
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// "(exp comparison_op expr) != 0" to true into an assume of
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// "exp comparison_op expr" to true. (And similarly, an assume of the form
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// "(exp comparison_op expr) == 0" to true into an assume of
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// "exp comparison_op expr" to false.)
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if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) {
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if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Sym))
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if (BinaryOperator::isComparisonOp(SE->getOpcode()))
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return assumeSym(State, Sym, (Op == BO_NE ? true : false));
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}
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// Get the type used for calculating wraparound.
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BasicValueFactory &BVF = getBasicVals();
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APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
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// We only handle simple comparisons of the form "$sym == constant"
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// or "($sym+constant1) == constant2".
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// The adjustment is "constant1" in the above expression. It's used to
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// "slide" the solution range around for modular arithmetic. For example,
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// x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
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// in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
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// the subclasses of SimpleConstraintManager to handle the adjustment.
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llvm::APSInt Adjustment = WraparoundType.getZeroValue();
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computeAdjustment(Sym, Adjustment);
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// Convert the right-hand side integer as necessary.
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APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
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llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
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// Prefer unsigned comparisons.
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if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
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ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
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Adjustment.setIsSigned(false);
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switch (Op) {
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default:
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llvm_unreachable("invalid operation not caught by assertion above");
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case BO_EQ:
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return assumeSymEQ(State, Sym, ConvertedInt, Adjustment);
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case BO_NE:
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return assumeSymNE(State, Sym, ConvertedInt, Adjustment);
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case BO_GT:
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return assumeSymGT(State, Sym, ConvertedInt, Adjustment);
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case BO_GE:
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return assumeSymGE(State, Sym, ConvertedInt, Adjustment);
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case BO_LT:
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return assumeSymLT(State, Sym, ConvertedInt, Adjustment);
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case BO_LE:
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return assumeSymLE(State, Sym, ConvertedInt, Adjustment);
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} // end switch
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}
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void RangedConstraintManager::computeAdjustment(SymbolRef &Sym,
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llvm::APSInt &Adjustment) {
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// Is it a "($sym+constant1)" expression?
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if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
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BinaryOperator::Opcode Op = SE->getOpcode();
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if (Op == BO_Add || Op == BO_Sub) {
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Sym = SE->getLHS();
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Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
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// Don't forget to negate the adjustment if it's being subtracted.
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// This should happen /after/ promotion, in case the value being
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// subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
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if (Op == BO_Sub)
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Adjustment = -Adjustment;
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}
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}
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}
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} // end of namespace ento
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} // end of namespace clang
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