build/clang-plugin/NaNExprChecker.cpp

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #include "NaNExprChecker.h"
   6 #include "CustomMatchers.h"
   7
   8 void NaNExprChecker::registerMatchers(MatchFinder *AstMatcher) {
   9   AstMatcher->addMatcher(
  10       binaryOperator(
  11           allOf(binaryEqualityOperator(),
  12                 hasLHS(hasIgnoringParenImpCasts(
  13                     declRefExpr(hasType(qualType((isFloat())))).bind("lhs"))),
  14                 hasRHS(hasIgnoringParenImpCasts(
  15                     declRefExpr(hasType(qualType((isFloat())))).bind("rhs"))),
  16                 unless(anyOf(isInSystemHeader(), isInWhitelistForNaNExpr()))))
  17           .bind("node"),
  18       this);
  19 }
  20
  21 void NaNExprChecker::check(const MatchFinder::MatchResult &Result) {
  22   if (!Result.Context->getLangOpts().CPlusPlus) {
  23     // mozilla::IsNaN is not usable in C, so there is no point in issuing these
  24     // warnings.
  25     return;
  26   }
  27
  28   const BinaryOperator *Expression =
  29       Result.Nodes.getNodeAs<BinaryOperator>("node");
  30   const DeclRefExpr *LHS = Result.Nodes.getNodeAs<DeclRefExpr>("lhs");
  31   const DeclRefExpr *RHS = Result.Nodes.getNodeAs<DeclRefExpr>("rhs");
  32   const ImplicitCastExpr *LHSExpr =
  33       dyn_cast<ImplicitCastExpr>(Expression->getLHS());
  34   const ImplicitCastExpr *RHSExpr =
  35       dyn_cast<ImplicitCastExpr>(Expression->getRHS());
  36   // The AST subtree that we are looking for will look like this:
  37   // -BinaryOperator ==/!=
  38   //  |-ImplicitCastExpr LValueToRValue
  39   //  | |-DeclRefExpr
  40   //  |-ImplicitCastExpr LValueToRValue
  41   //    |-DeclRefExpr
  42   // The check below ensures that we are dealing with the correct AST subtree
  43   // shape, and
  44   // also that both of the found DeclRefExpr's point to the same declaration.
  45   if (LHS->getFoundDecl() == RHS->getFoundDecl() && LHSExpr && RHSExpr &&
  46       std::distance(LHSExpr->child_begin(), LHSExpr->child_end()) == 1 &&
  47       std::distance(RHSExpr->child_begin(), RHSExpr->child_end()) == 1 &&
  48       *LHSExpr->child_begin() == LHS && *RHSExpr->child_begin() == RHS) {
  49     diag(Expression->getBeginLoc(),
  50          "comparing a floating point value to itself for "
  51          "NaN checking can lead to incorrect results",
  52          DiagnosticIDs::Error);
  53     diag(Expression->getBeginLoc(), "consider using mozilla::IsNaN instead",
  54          DiagnosticIDs::Note);
  55   }
  56 }