NaNExprChecker.cpp

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/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "NaNExprChecker.h"

#include "CustomMatchers.h"

void NaNExprChecker::registerMatchers(MatchFinder *AstMatcher) {

  AstMatcher->addMatcher(

      binaryOperator(

          allOf(binaryEqualityOperator(),

                hasLHS(has(ignoringParenImpCasts(

                    declRefExpr(hasType(qualType((isFloat())))).bind("lhs")))),

                hasRHS(has(ignoringParenImpCasts(

                    declRefExpr(hasType(qualType((isFloat())))).bind("rhs")))),

                unless(anyOf(isInSystemHeader(), isInWhitelistForNaNExpr()))))

          .bind("node"),

      this);

void NaNExprChecker::check(const MatchFinder::MatchResult &Result) {

  if (!Result.Context->getLangOpts().CPlusPlus) {

    return;

  const BinaryOperator *Expression =

      Result.Nodes.getNodeAs<BinaryOperator>("node");

  const DeclRefExpr *LHS = Result.Nodes.getNodeAs<DeclRefExpr>("lhs");

  const DeclRefExpr *RHS = Result.Nodes.getNodeAs<DeclRefExpr>("rhs");

  const ImplicitCastExpr *LHSExpr =

      dyn_cast<ImplicitCastExpr>(Expression->getLHS());

  const ImplicitCastExpr *RHSExpr =

      dyn_cast<ImplicitCastExpr>(Expression->getRHS());

  // The AST subtree that we are looking for will look like this:

  // -BinaryOperator ==/!=

  //  |-ImplicitCastExpr LValueToRValue

  //  | |-DeclRefExpr

  //  |-ImplicitCastExpr LValueToRValue

  //    |-DeclRefExpr

  // The check below ensures that we are dealing with the correct AST subtree

  // shape, and

  // also that both of the found DeclRefExpr's point to the same declaration.

  if (LHS->getFoundDecl() == RHS->getFoundDecl() && LHSExpr && RHSExpr &&

      std::distance(LHSExpr->child_begin(), LHSExpr->child_end()) == 1 &&

      std::distance(RHSExpr->child_begin(), RHSExpr->child_end()) == 1 &&

      *LHSExpr->child_begin() == LHS && *RHSExpr->child_begin() == RHS) {

    diag(Expression->getBeginLoc(),

         "comparing a floating point value to itself for "

         "NaN checking can lead to incorrect results",

         DiagnosticIDs::Error);

    diag(Expression->getBeginLoc(), "consider using std::isnan instead",

         DiagnosticIDs::Note);