gecko-dev/build/clang-plugin/NaNExprChecker.cpp

/* 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(hasIgnoringParenImpCasts(
                    declRefExpr(hasType(qualType((isFloat())))).bind("lhs"))),
                hasRHS(hasIgnoringParenImpCasts(
                    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) {
    // mozilla::IsNaN is not usable in C, so there is no point in issuing these
    // warnings.
    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->getLocStart(),
         "comparing a floating point value to itself for "
         "NaN checking can lead to incorrect results",
         DiagnosticIDs::Error);
    diag(Expression->getLocStart(), "consider using mozilla::IsNaN instead",
         DiagnosticIDs::Note);
  }
}