2013-11-08 09:15:39 +08:00
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//== IdenticalExprChecker.cpp - Identical expression checker----------------==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// \brief This defines IdenticalExprChecker, a check that warns about
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/// unintended use of identical expressions.
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///
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/// It checks for use of identical expressions with comparison operators.
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///
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//===----------------------------------------------------------------------===//
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#include "ClangSACheckers.h"
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#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
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#include "clang/StaticAnalyzer/Core/Checker.h"
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#include "clang/StaticAnalyzer/Core/CheckerManager.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
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#include "clang/AST/RecursiveASTVisitor.h"
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using namespace clang;
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using namespace ento;
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static bool isIdenticalExpr(const ASTContext &Ctx, const Expr *Expr1,
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const Expr *Expr2);
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//===----------------------------------------------------------------------===//
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// FindIdenticalExprVisitor - Identify nodes using identical expressions.
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//===----------------------------------------------------------------------===//
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2013-11-14 23:46:10 +08:00
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namespace {
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2013-11-08 09:15:39 +08:00
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class FindIdenticalExprVisitor
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: public RecursiveASTVisitor<FindIdenticalExprVisitor> {
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public:
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explicit FindIdenticalExprVisitor(BugReporter &B, AnalysisDeclContext *A)
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: BR(B), AC(A) {}
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// FindIdenticalExprVisitor only visits nodes
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// that are binary operators.
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bool VisitBinaryOperator(const BinaryOperator *B);
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private:
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BugReporter &BR;
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AnalysisDeclContext *AC;
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};
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2013-11-14 23:46:10 +08:00
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} // end anonymous namespace
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2013-11-08 09:15:39 +08:00
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bool FindIdenticalExprVisitor::VisitBinaryOperator(const BinaryOperator *B) {
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BinaryOperator::Opcode Op = B->getOpcode();
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if (!BinaryOperator::isComparisonOp(Op))
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return true;
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//
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// Special case for floating-point representation.
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//
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// If expressions on both sides of comparison operator are of type float,
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// then for some comparison operators no warning shall be
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// reported even if the expressions are identical from a symbolic point of
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// view. Comparison between expressions, declared variables and literals
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// are treated differently.
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//
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// != and == between float literals that have the same value should NOT warn.
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// < > between float literals that have the same value SHOULD warn.
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//
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// != and == between the same float declaration should NOT warn.
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// < > between the same float declaration SHOULD warn.
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//
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// != and == between eq. expressions that evaluates into float
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// should NOT warn.
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// < > between eq. expressions that evaluates into float
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// should NOT warn.
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//
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const Expr *LHS = B->getLHS()->IgnoreParenImpCasts();
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const Expr *RHS = B->getRHS()->IgnoreParenImpCasts();
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const DeclRefExpr *DeclRef1 = dyn_cast<DeclRefExpr>(LHS);
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const DeclRefExpr *DeclRef2 = dyn_cast<DeclRefExpr>(RHS);
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const FloatingLiteral *FloatLit1 = dyn_cast<FloatingLiteral>(LHS);
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const FloatingLiteral *FloatLit2 = dyn_cast<FloatingLiteral>(RHS);
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if ((DeclRef1) && (DeclRef2)) {
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if ((DeclRef1->getType()->hasFloatingRepresentation()) &&
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(DeclRef2->getType()->hasFloatingRepresentation())) {
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if (DeclRef1->getDecl() == DeclRef2->getDecl()) {
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if ((Op == BO_EQ) || (Op == BO_NE)) {
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return true;
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}
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}
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}
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} else if ((FloatLit1) && (FloatLit2)) {
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if (FloatLit1->getValue().bitwiseIsEqual(FloatLit2->getValue())) {
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if ((Op == BO_EQ) || (Op == BO_NE)) {
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return true;
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}
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}
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} else if (LHS->getType()->hasFloatingRepresentation()) {
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// If any side of comparison operator still has floating-point
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// representation, then it's an expression. Don't warn.
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// Here only LHS is checked since RHS will be implicit casted to float.
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return true;
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} else {
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// No special case with floating-point representation, report as usual.
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}
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if (isIdenticalExpr(AC->getASTContext(), B->getLHS(), B->getRHS())) {
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PathDiagnosticLocation ELoc =
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PathDiagnosticLocation::createOperatorLoc(B, BR.getSourceManager());
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StringRef Message;
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if (((Op == BO_EQ) || (Op == BO_LE) || (Op == BO_GE)))
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Message = "comparison of identical expressions always evaluates to true";
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else
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Message = "comparison of identical expressions always evaluates to false";
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BR.EmitBasicReport(AC->getDecl(), "Compare of identical expressions",
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categories::LogicError, Message, ELoc);
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}
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// We want to visit ALL nodes (subexpressions of binary comparison
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// expressions too) that contains comparison operators.
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// True is always returned to traverse ALL nodes.
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return true;
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}
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/// \brief Determines whether two expression trees are identical regarding
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/// operators and symbols.
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///
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/// Exceptions: expressions containing macros or functions with possible side
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/// effects are never considered identical.
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/// Limitations: (t + u) and (u + t) are not considered identical.
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/// t*(u + t) and t*u + t*t are not considered identical.
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///
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static bool isIdenticalExpr(const ASTContext &Ctx, const Expr *Expr1,
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const Expr *Expr2) {
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// If Expr1 & Expr2 are of different class then they are not
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// identical expression.
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if (Expr1->getStmtClass() != Expr2->getStmtClass())
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return false;
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// If Expr1 has side effects then don't warn even if expressions
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// are identical.
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if (Expr1->HasSideEffects(Ctx))
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return false;
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// Is expression is based on macro then don't warn even if
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// the expressions are identical.
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if ((Expr1->getExprLoc().isMacroID()) || (Expr2->getExprLoc().isMacroID()))
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return false;
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// If all children of two expressions are identical, return true.
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Expr::const_child_iterator I1 = Expr1->child_begin();
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Expr::const_child_iterator I2 = Expr2->child_begin();
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while (I1 != Expr1->child_end() && I2 != Expr2->child_end()) {
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const Expr *Child1 = dyn_cast<Expr>(*I1);
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const Expr *Child2 = dyn_cast<Expr>(*I2);
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if (!Child1 || !Child2 || !isIdenticalExpr(Ctx, Child1, Child2))
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return false;
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++I1;
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++I2;
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}
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// If there are different number of children in the expressions, return false.
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// (TODO: check if this is a redundant condition.)
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if (I1 != Expr1->child_end())
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return false;
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if (I2 != Expr2->child_end())
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return false;
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switch (Expr1->getStmtClass()) {
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default:
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return false;
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case Stmt::ArraySubscriptExprClass:
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case Stmt::CStyleCastExprClass:
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case Stmt::ImplicitCastExprClass:
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case Stmt::ParenExprClass:
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return true;
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case Stmt::BinaryOperatorClass: {
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const BinaryOperator *BinOp1 = dyn_cast<BinaryOperator>(Expr1);
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const BinaryOperator *BinOp2 = dyn_cast<BinaryOperator>(Expr2);
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return BinOp1->getOpcode() == BinOp2->getOpcode();
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}
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case Stmt::CharacterLiteralClass: {
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const CharacterLiteral *CharLit1 = dyn_cast<CharacterLiteral>(Expr1);
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const CharacterLiteral *CharLit2 = dyn_cast<CharacterLiteral>(Expr2);
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return CharLit1->getValue() == CharLit2->getValue();
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}
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case Stmt::DeclRefExprClass: {
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const DeclRefExpr *DeclRef1 = dyn_cast<DeclRefExpr>(Expr1);
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const DeclRefExpr *DeclRef2 = dyn_cast<DeclRefExpr>(Expr2);
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return DeclRef1->getDecl() == DeclRef2->getDecl();
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}
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case Stmt::IntegerLiteralClass: {
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const IntegerLiteral *IntLit1 = dyn_cast<IntegerLiteral>(Expr1);
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const IntegerLiteral *IntLit2 = dyn_cast<IntegerLiteral>(Expr2);
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return IntLit1->getValue() == IntLit2->getValue();
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}
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case Stmt::FloatingLiteralClass: {
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const FloatingLiteral *FloatLit1 = dyn_cast<FloatingLiteral>(Expr1);
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const FloatingLiteral *FloatLit2 = dyn_cast<FloatingLiteral>(Expr2);
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return FloatLit1->getValue().bitwiseIsEqual(FloatLit2->getValue());
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}
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case Stmt::MemberExprClass: {
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const MemberExpr *MemberExpr1 = dyn_cast<MemberExpr>(Expr1);
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const MemberExpr *MemberExpr2 = dyn_cast<MemberExpr>(Expr2);
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return MemberExpr1->getMemberDecl() == MemberExpr2->getMemberDecl();
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}
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case Stmt::UnaryOperatorClass: {
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const UnaryOperator *UnaryOp1 = dyn_cast<UnaryOperator>(Expr1);
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const UnaryOperator *UnaryOp2 = dyn_cast<UnaryOperator>(Expr2);
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if (UnaryOp1->getOpcode() != UnaryOp2->getOpcode())
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return false;
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return !UnaryOp1->isIncrementDecrementOp();
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}
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}
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}
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//===----------------------------------------------------------------------===//
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// FindIdenticalExprChecker
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//===----------------------------------------------------------------------===//
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2013-11-14 23:46:10 +08:00
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namespace {
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2013-11-08 09:15:39 +08:00
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class FindIdenticalExprChecker : public Checker<check::ASTCodeBody> {
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public:
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void checkASTCodeBody(const Decl *D, AnalysisManager &Mgr,
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BugReporter &BR) const {
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FindIdenticalExprVisitor Visitor(BR, Mgr.getAnalysisDeclContext(D));
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Visitor.TraverseDecl(const_cast<Decl *>(D));
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}
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};
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2013-11-14 23:46:10 +08:00
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} // end anonymous namespace
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2013-11-08 09:15:39 +08:00
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void ento::registerIdenticalExprChecker(CheckerManager &Mgr) {
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Mgr.registerChecker<FindIdenticalExprChecker>();
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}
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