1 files changed, 56 insertions, 0 deletions
diff --git a/build/clang-plugin/NaNExprChecker.cpp b/build/clang-plugin/NaNExprChecker.cpp
new file mode 100644
index 0000000000..6532443f23
--- /dev/null
+++ b/build/clang-plugin/NaNExprChecker.cpp
@@ -0,0 +1,56 @@
+/* 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) {
+    // 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->getBeginLoc(),
+         "comparing a floating point value to itself for "
+         "NaN checking can lead to incorrect results",
+         DiagnosticIDs::Error);
+    diag(Expression->getBeginLoc(), "consider using mozilla::IsNaN instead",
+         DiagnosticIDs::Note);
+  }
+}